CHAPTER 4 Prepared according to the guidelines of Agriculture, Ecosystems & Environment Comparative study on the influence of SLASH and its individual components on the production of maize (Zea mays) and heavy metal accumulation. W.F. Truter a * and N.F.G Rethman a a Department of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South Africa Abstract Utilizing a poor agricultural resource base to produce a staple commodity such as maize for a growing population, poses some significant challenges. A large percentage of South Africa's cropping soils are acidic and costs of fertilizers and lime for both subsistence and commercial farmers are becoming extremely difficult to meet. The need exists for alternative soil amendments and other forms of fertilizers to enhance plant productivity. In many countries technologies have been developed to use waste materials with agricultural benefits, and combine them to get a product, which serves as a soil ameliorant. In South Africa , the ameliorant produced is termed SLASH. SLASH is a mixture of sewage sludge, lime and class F fly ash. Sewage sludge's agricultural application is restricted because of its pathogenicity and possible heavy metal content whereas fly ash's restriction lies in its lack of macro nutrients such as N, P and K. However, sewage sludge is a good source of macronutrients and organic matter, and fly ash has liming qualities. Together a superior product is created. SLASH has proven to be a beneficial soil ameliorant and enhances plant growth substantially. Applications of between 7.5%-10% of the soil volume delivered the best results for maize Corresponding author.: Tel. +27-420-3224 Fax. +27-420-4120 Email address: [email protected] 140 production. Although heavy metal translocation and B phytotoxicity were a major concern, show that amounts of Ni, Cd and the micronutrient B were translocated, and that these were well below safety limits. Heavy metals are, therefore, not as mobile in SLASH as in sewage sludge. phytotoxicity, SLASH, soil Keywords: Acid <:Im,:>I,n'<:I 1. Introduction In South Africa increased food production is urgently required to improve both national and household food security. (Truter and Rethman, 2000). This is quite difficult especially on a poor agricultural resource base and with a population that is growing at an exponential rate. (Rethman et at, 1999b). Acid soils make up a large percentage of South Africa's arable land. sustainable soils are required to ensure in the nations staple commodity, maize. Soil acidification is, therefore, a serious socio-economic concem. Very few countries can afford the decline in food production, which often accompanies the changes, which are taking place in our soils. Nutrient management practices the viability of agricultural ecosystems. Soil acidity affects plant development by its influence on the availability of certain elements required for growth (Tisdale and Nelson, 1975). Maize (Zea mays is the third most important cereal grown in the world. In South and Central America, maize is grown mostly on acidic soils. On these soils, yields are limited by deficient levels of available P, Ca and Mg, and toxic of AI and Mn (Baligar et aI., 1997). Practices, which focus on reducing inputs, especially fertilizer inputs provide an important link between the needs of commercial farmers and those involved in subsistence agriculture. With commercial systems, the aim is to reduce inputs for economic/environmental reasons. Subsistence farmers have similar aims, but, in this it is because they have restricted access to inputs. Many countries including South Africa are experienCing waste material disposal problems. Two waste materials of major concern, are fly ash and sewage sludge. A growing population and increasing urbanization creates the need for more electricity, resulting in more fly ash being produced. In addition to 141 this is the higher production of sewage due to the increasing population. It is, therefore, desirable that one problem should be a solution for another. Reynolds et aI., (1999) determined the feasibility of converting waste disposal problems in South Africa into a soil beneficiation strategy. The alkaline stabilization of sludge with fly ash and lime, delivered a product termed SLASH (that contains 60 % class F fly ash, 30 % sewage sludge and 10% unslaked lime on a dry matter basis), which has beneficial soil ameliorant effects. This study entails the comparison fly ash, sewage sludge and lime with SLASH in maize production. 1.1 Fly ash The potential limitation of fly ash's agronomic use includes its low levels of N, and excessive levels of B (Aitken et aI., 1984). Selenium and boron, which can be the rate-limiting elements for maximum permissible loading rates of fly ash for soil amendments, did not, however, accumulate in plants in quantities that would be of concern for plant health or animal and human consumption (Cline et aI., 2000). Boron in fly ash is also readily available to plants. In fact numerous investigators (Holliday et aI., 1958; Cope, 1962; Hodgson and Townsend, 1973; Townsend and e t , 1978; Ciravolo and Adriano, 1979; Adriano et aI., Gillham, 1975; 1980) considered B to be a major limiting factor for successful cropland utilization of ashes, especially when such ash is not fully weathered. Crops also exhibit varying degrees of tolerance to B in soils (Bingham, 1973; Adriano et ai., 1980). Fly ash application may also decrease plant uptake of elements such as Cd, Cu, Cr, Petruzzelli Mn, and Zn (Schnappinger et aI., 1975; Adriano et aI., 1 et aI., 1986; Schumann and Sumner, 2000). Phosphorus concentrations in plant foliage were often reduced by fly ash applications (Elseewi et aI., 1980; Moliner and Street, 1982; Schumann and Sumner, 2000). Corn (Zea mays L) plant emergence, grain yield, percent moisture, and harvest index were not significantly influenced by fly ash applications either. 142 1.2 Biosolids Local authorities, both overseas and in South Africa, are continually searching for environmentally acceptable as well as beneficial and economical means of disposal of sewage sludge. Biosolids that have not undergone pathogen destruction cannot be land applied. Land application of sludge is not common in many countries since very little research has been carried out under local conditions. While extensive overseas studies can provide some guidance to the potential for sludge utilization, ultimately sludge management practices should be developed on local soils under local conditions. Existing regulations set limits for the content of heavy metals in sewage sludge as well as the maximum annual and cumulative loadings to land. These loadings are primarily based on health risk (pathogenic micro-organisms) and soil contamination aspects (heavy metals) (Barry aI., 1995). Dowdy et aI., (1983) found that the Ni and Zn content of corn (Zea mays L.) silage increased linearly with biosolid application rate (Sloan aI., 1997). In a study conducted in Australia on estimating sludge application to land, they concluded that elements Cd, Ni and Cu were all retained to a greater extent in the surface horizon, most likely due to their affinity for organic matter (Barry aI., 1995). Liming acidic soils that have received biosolids application reduces plant uptake of Cd, and to lesser extent Cu and Pb (Braillier et aI., 1996; Logan and Chaney, 1983; Mahler et 1987; Basta and Sloan, 1999). Alkaline biosolids, produced when biosolids is treated with alkaline materials to kill pathogens, have a relatively high CaC03 and may serve as a liming material (Little et aI., 1991; Basta and Sloan, 1999). Because alkaline biosolids are effective liming materials, application of alkaline biosolids resulted in less plant uptake of Cd (Brown and Brush, 1992; and Sloan, 1999) and Cu, Ni, and Zn (Mulchi et , 1987; Basta and Sloan, 1999). Cadmium and Zn are usually the most bio-available heavy metals of sludge origin (Alloway 1995; Berti and Jacobs, 1996; Sloan et aI., 1997; McGrath aI., 2000). Cadmium is of major concern in terms of the transfer into the food chain (Sanders et aL, 1987; Lubben aI., 1991 ;Chandri et 143 aI., 1993; McGrath et aI., 1995; McGrath et at, 2000), but plant species differed markedly in the transfer efficiency of and Cd from soil to plants (McGrath et aI., 2000), 1.3 Alkaline- biosolids Application of alkaline biosolids to acidic soil to achieve final soil pH > 5 will minimize risk from soil solution Cd and and plant uptake of heavy metals (Basta and Sloan, 1999). Metal movement is <;.;a.:><;.;y to increase with soil pH. It is possible that the same mechanism that facilitates Ca movement may permit the movement of trace metals through the soil profile (Brown et aI., 1997). A leaching potential test of the ameliorant SLASH was conducted by Reynolds al., (2000) and shown to within the (Toxicity Characteristics Leaching Procedure) guidelines. The TCLP leaching of the SLASH product showed that the heavy metals of sewage sludge are immobilized within the fly ash component and do not leach out in either of the simulated conditions. Although the two methods gave similar results, it was noted that Mn, Mo, Ni, and Zn leached more in the TCLP leachate than in the acid rain leachate, while Cu leached less. This may as a result of the differing pHs of the leachates (Reynolds et ai, 2002). Fly ash alone is a poor source of the macronutrients such as Nand P (Carlson and Adriano, 1993; Jackson et aL, 1999). Nitrogen is volatilized during the process of coal combustion, while most fly ash P is relatively unavailable (Bradshaw and Chadwick, 1980; Jackson at, 1999). Sewage sludge on the other hand can be a valuable source of plant nutrients such as N, P, and S, and the organic matter contained in the sludge also can help improve soil conditions (McGrath, 2000) and enhance plant growth. The high Nand P content of sewage sludge complements the higher levels of micronutrients in the fly ash and will thus reduce the need for inorganic fertilizers. Therefore, fly ash mixed with other organic waste will be an attractive and economical option that should be considered (Wong and Wong, 1990). 144 2. Material and Methods A study of maize (Zea mays) in a raised bed trial was undertaken and was based on the work which Rethman et aI., (1999a,b) conducted. Rethman et aI., (1999a,b) and (Truter, 2002c) concluded that the best plant growth responses had been achieved on the 5 and 10% SLASH treated soils. Essentially it was because of those results that this study on SLASH was initiated. A randomized layout of constructed raised beds (net plot: 1m x 0.30m = 0.3m 2) as illustrated in (Fig.1) was conducted at the Hatfield Experimental Farm, Pretoria, South Africa (25°45'S 28°16'E), 1327m above sea level. A uniform sandy loam soil was ameliorated with sewage sludge, fly ash and reactive lime (CaO) in combination (SLASH) at four different levels and individually. The treatments were: T1 (Control - 0% SLASH), T2 - [2.5% SLASH (8kg)], T3 - [5.0% SLASH (16kg)], T4 - [7 .5% SLASH (24kg)], T5 - [10% SLASH (32kg)], T6 - Sewage Sludge (4.32kg), T7 - Fly ash (10.24 kg) and T8 - Lime (1.44kg) and were . replicated five times. Initially these raised beds were planted to cabbages, carrots, stocks, sweet peas and statice. These vegetable and flower crops represented the 1st cropping cycle of the raised bed trial (Ramagadza, 2002). The 2nd cropping cycle was maize (Zea mays). Ten seeds were planted, and the seeds that did not germinate were blanked in. After the 2nd cropping cycle of maize (Zea mays) the soils were planted to Triticale (Triticale hexaploide), sorghum (Sorghum sp.) and rye (Secale sp.) as successive 3rd , 4th , and 5th cropping cycles (Truter, 2002c). The objective of the study was to compare the SLASH at different levels to the separate components of SLASH. These raised beds were used to evaluate the relative effects of SLASH, sewage sludge, lime and fly ash in soil on the dry matter production of maize (Zea mays) at different stages of the growth cycle. Three plants were harvested when the best treatment reached a height of 20 cm (1 st harvest); 40 cm (2 nd harvest) and the other 4 plants were harvested when they were fully grown. (3 rd harvest). This observation was to determine at what stage the various treatments started to have an effect on plant growth . 145 Ramagadza (2002) reported that the plants of the 1st cropping cycle were showing signs of K deficiency. Due to this, K had been applied to the treatments at the beginning of the 2nd cropping cycle of maize to eliminate K deficiency as a limiting growth factor. The treated soils received regular watering, to eliminate moisture as an additional limiting growth factor. 1 Statistical analyses All dry matter-, grain production data and elemental analyses was statistically analyzed using PROC GLM (1996/1997 and 199711998) and PROC ANOVA (1997/1998). Statistical analysis was performed using SAS (SAS Institute, 1996) software. were taken at 0.05. Results and Discussion Previous studies reported on the growth of various crop species to SLASH and the ingredients on which it is based (Rethman 1999a,b; Rethman 2000a,b; Rethman and Truter, 2001 Truter and Rethman 2000; Truter, 2002a,b, c). The findings of those studies have been confirmed in this study. From all the work conducted on SLASH the conclusion has been drawn that levels of SLASH at 0% of the soil volume enhanced plant growth remarkably. Table 1 clearly indicates that even at an early stage of the maize growth cycle SLASH had an effect on growth rate. Sewage sludge had the most substantial influence on the growth of the maize plants. results emphasize the importance of organic matter, which is evidently supplied by sewage sludge. Despite the good results obtained from the sewage sludge (T6) treatment, it can not be recommended because of the variability of the sludge sources which can possibly contain a wide range of heavy metals and can often be pathogenic. Similar results had been observed for the harvest taken at 40 cm with sewage sludge maintaining an exceptionally higher yield than the of treatments. SLASH treatments were performing Slightly better than the control, fly ash and lime treatments, but not significantly. Nevertheless, treatment effects could be seen throughout the cropping cycle. 147 Table 1 Dry matter production (g/plant) of maize (Zea mays) at different stages on soils treated with SLASH (T2-T5), sewage sludge (T6), fly ash (T7) and lime (T8). T1- Control b 14. 94b b 16.18 T2- 2.5% SLASH 1.36 T3- 5% SLASH 1.42 T4-7.5% SLASH 1.62b T5- 10% SLASH T6- Sewage sludge T7- Fly ash b 486. 94 b b 526. 96 14.74 14.06 11 52.94 b 13.00 Bb b 8 15.34 1.26 445.10bC b 629.92 320.28 11 cd T8- Lime " abc Column means with common alphabetical superscripts do not differ significantly (P> 0.05) (Tukey's Studentized Range Test) Individual plants harvested at maturity illustrate how SLASH treatments had benefited plant growth by as much as 100% on average. The sludge treatment yielded 140% more on average than the control (Table 1). Although it seems that when combining sewage sludge with fly ash, the effect of sewage sludge on plant growth is reduced. It has been shown that even though this comment true, the compromise is reached evidently in the conclusion drawn from the work done by Truter, (2002a,b, c), that SLASH has a longer residual effect than sewage sludge. SLASH therefore, prolongs significantly higher yields than the sewage sludge treatment relative to the control. Sewage sludge eventually becomes depleted, while SLASH maintains it's "slow release" of nutrients over a longer period of time (Truter, .....,...'......,/ As for grain production, similar trends, as for the plant material, are noted in 2. SLASH treatments gave up to 225% better yields than the control while the sludge treatment gave 385% better yields. Once more, the 7.5% (T4) and 10% (TS) SLASH treatments delivered the best results for the SLASH treatments for both dry matter yields and grain yields. 148 The risk of heavy metal translocation from sludge will depend on the source of sludge. In contrast, SLASH ensures the immobilization of heavy metals and a safer product to handle and apply in of possible disease organisms. With respect to the micronutrient B and heavy metals analyses of 11'>:;;1',/1'>";: (Table 2) the results obtained were compared to the limits set by law (Kabata Pendias and Pendias, 1984). In Table 2 the Cd and Ni analyses indicate that all treatments had insignificant levels and that they were well below these limits (Kabata- Pendias and Pendlas, 1984). However, the SLASH treatments tended to have a higher B concentration, and this can possibly be ascribed the contribution of B, which is usually found in fly ash. Table 2 The mean elemental concentration and (±MSE) in maize leaves (mg kgT5), sewage T1-Control T4- 7.5% SLASH (mg kg-i) (mg kg-i) 2.90£1 (±0.45) 2.59 (±1.06) (±0.54) (±13.03) 1 a 5.64 (±4.07) TS- 10% SLASH 3.93 T6- 3.30 T7- Fly ash TS- Lime grown on SLASH (T2- fly ash (17) and lime (T8) treated soils T2- 2.5% SLASH T3- 5% SLASH 1 ) 8 .30) a 8 a 3.18 (±1 (mg kg-i) 8 27.96 (±0.45) 8 23.93 (±0.45) (±1.76) 45.71£1 (±0.45) 5.64£1 (±3.75) 34.41 a (±O.45) 6.19£1 (±S.22) 3S.66 (±0.45) a (±2.40) (±1.1S) 8 24.30 (±O.4S) 26.40£1 (±O.45) *a Column means with common alphabetical superscripts do not differ significantly (P> 0.05) (Tukey's Studentized The concern about heavy metals (Ni and Cd) translocation was not supported by the results obtained for the leaf analysis, although the concern about translocation to the most important plant component, grain, prevailed. Although Rethman et aI., (1999a) found no significant translocation of heavy metals to the 151 grain at 1% SLASH applications, grain produced on soils treated with higher SLASH applications was of concern. Table 3 provides the results obtained for heavy metal content of selected treatments. The analysis of grain indicated that there was heavy metals present in all the treatments including the control. The B concentration differed from what was found in the leaf material, this demonstrates that B is not concentrated more in the grain than in the leaf material, and is still well below the limits set by law. To support the fact that the heavy metal content of sewage sludge varies, depending on the source, the sludge's Ni and Cd content was similar to that of the SLASH treatments and the control. However, Ni was more concentrated in the grain than in the leaves of the plant. It was, nevertheless, still well below the safety limits. Table 3 The mean elemental concentration and (±MSE) in maize grain (mg kg· 1 ) grown on SLASH (T2- T5), sewage sludge (T6), fly ash (T7) and lime (T8) treated soils B Cd Ni (mg kg"') (mg kg"') (mg kg"') Treatments 8 B B T1 - Control 26.28 (±3.42) 9.89 (±0.32) T3 - 5% SLASH 9.36 (±0.53) 102.79 (±4.43) 9.81a (±0.38) T6 - Sewage sludge 27.278 (±5.76) 8 29.26 (±5.24) 8 25.61 (±5.64) 8.81c (±0.29) 104.45 (±2.17) c 99.13 (±3.59) Safety limit 80 15.7 400 T5 -10% SLASH b 106.99 (±3.33) b b *abc Column means with common alphabetical superscripts do not differ Significantly (P> 0.05) (Bonferroni Test) 4. Conclusion Maize can be produced on acidic or nutrient depleted soils, by using an alternative method rather than the conventional liming and inorganic fertilization of soils. At the same time the environmental problem of waste disposal can be alleviated. With the exception of sewage sludge, SLASH offered greater benefits than any individual ingredients. Plant growth responded exceptionally well to sewage sludge. It cannot, however, be recommended due to the pathogenicity of the sludge ,and the possible heavy metal content, depending on the source of sewage 152 sludge, and the fact that heavy metals are not immobilized in the sludge, as they are in the SLASH. This ameliorant SLASH has promising liming qualities and is a good source of nutrients, which improves soil condition making it more suitable for plant growth. Although SLASH is seen as a good source of nutrients required for plant growth, it does not necessarily contain a full range of nutrients. The batch of SLASH that was used in this study was devoid of K, for example, and the need to supplement it with an inorganic fertilizer or possibly another organic will material, which has high concentrations of K, such as animal manures. Since waste material composition, nutrient balance and nutrient bioavailability is extremely variable, it is important to characterize waste materials before mixing them and using them to the benefits of plant growth. Various problems can experienced with the application of such wastes, such as possible phytotoxicity from trace element excesses or possible a fixation of other nutrients such as Most of these problems can be overcome by combining two or more waste materials together, thereby utilizing the combined complementary qualities of each waste for crop production. The rationale behind such mixed wastes is that the mixture itself is a superior soil amendment to either component alone. use of an organic waste addresses the defiCiency of macronutrients in fly ash, while fly ash can act as a bulking agent for the organic wastes, substantially reduces odor, and can offset soil acidity problems that may through continued land application of organic wastes. It is concluded that the 0% SLASH application rates ultimately deliver the best results compared to the other SLASH treatments. Regarding the uptake of potentially toxic elements, no significant uptake was noted or even translocated to the grain under regulated experimental conditions. The two potential problem heavy metals, Ni and Cd, and the micronutrient which can be toxic at very high levels, were within the current safety specifications, but these may be open for review. economic reasons, in South use of SLASH at high levels is limited due to high transport costs, and the ameliorant's use will restricted to 153 sites in relative close proximity to the waste raw materials used in it's manufacture. Nevertheless, the ameliorant SLASH has definite agricultural potential!' References Adriano, D.C., Page, A.L., Elseewi, AA., Chang, AC., Straughan, I., 1980. Utilization and disposal fly and other coal residues in terrestrial ecosystems: A review. J Environ. Qual. 9, 333-344. 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Soil Science of America Jou mal Iss 1 64,41 Sloan, J.J., Dowdy, H., Dolan, Linden, DR., 1997. Long-Term Effects of Biosolids applications on heavy metal bioavailability in agricultural soils. J. Environ. Qual. 26,966-974 L., Nelson, W.L., 1 Tisdale, Soil fertility and fertilizers. Macmillan, New York. Townsend, W.N., Gillham, E.W.F., 1 Pulverized fuel ash as a medium for plant growth. In: M.J. Chadwick and G.T. Goodman (Editors), Resource Degradation , Rothmans, N. Truer, amended soils. Ecology of Renewal. Blackwell, Oxford, pp. 287-304. 2000. Crop productivity in fly ash/sewage sludge Joint. Cont. Pretoria, South Africa. Truter, W.F., Rethman, N.F.G. , Reynolds, K.A., Kruger, RA., 2001. use of a soil ameliorant based on fly ash and se\JV2CIA sludge. Proc. 2001 Internat. Ash Sympos. Lexington, Kentucky, U Truter, W.F., 2002a. Multiple cropping of soils sludge, and fly ash (SLASH). MSc with a mixture of sewage Use of products to enhance plant productivity on acidic and infertile substrates. University of Pretoria. Chapter 2.pp 107-121. W.F., 2002 The influence of a mixture of sewage sludge, fly and lime (SLASH) on biomass production of two grasses and two legumes. MSc (Agric) Thesis. Use of waste products to enhance plant productivity on acidic and infertile substrates. University of Pretoria. Chapter pp 122-139 158 Truter, W.F., 2002c. Forage production from cereal and grain crops on fly ash biosolid amended soils. MSc (Agric) Thesis. of waste products to enhance plant productivity on acidic and infertile substrates. University of Pretoria. Chapter 5 pp160-173. Truter, W.F., 2002d. The influence of a fly ash-biosolid mixture on chemical soil properties. MSc (Thesis) Use waste products to plant productivity on acidic and infertile substrates. University of Pretoria. Chapter 6 pp.174-197 Wong, M.H., Wong, J.W.C., 1989. Germination and seedling growth of vegetable crops in fly ash-amended soils. Agric., Ecosys. and Environ. 26,23-25 159 CHAPTER 5 Prepared according to the guidelines of the Journal of Plant Science Forage production from cereal and grain crops on fly ash biosolid amended soils W.F.Trute,.a· and N.F.G. Rethman a • Oepartment of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South Africa Abstract The non-agricultural activities of man compete with agriculture for land. The demands on land made by increasing urban, industrial, mining, recreation and other developments, and the attendant infrastructure - largely the result of a fast growing population - leave an ever-shrinking area for producing food and fibre. Utilization of natural resources is of importance for the survival of people as long as it is not at the expense of environmental degradation i.e. it must be sustainable. Many waste materials, which are the end products of processes that ensure life on earth, have to be used beneficially. The combination of waste materials such as sewage sludge and fly ash is not unknown to the scientific world as a beneficial technology to stabilize sewage sludge by adding an alkaline material. The use of such a mixture of waste products for agricultural purposes, still, however, needs to be refined. Previous research, both internationally and in South Africa, has developed effective waste product mixtures, which can be used for agricultural purposes. SLASH (60% class F fly ash, 30% sewage sludge and 10% reactive lime (CaO)) is such a waste product mixture, which can be used as a soil ameliorant to address the problems of soil acidity and infertility. The utilization of SLASH as such in crop production has already been researched but what is relevant in this study is how the SLASH compares to its individual components in terms of forage production and long-term residual effects. It was evident from this study that the effect of 5-10% SLASH treatments still persisted and gave up to 30% better yields Corresponding author.: Tel. +27-420-3224 Fax. +27-420-4120 Email address: [email protected] 160 36 months after the initial application of treatments. Sewage sludge on the other hand. although giving the best production for almost the entire study. can not be recommended because of its pathogenicity and possible heavy metal translocation. Furthermore, the sewage sludge treatment showed signs of becoming depleted by the end of the study, indicating that it did not compare favourably with the "slow release" capability (slow release of essential nutrients required for plant growth) of SLASH. Keywords: Acid and infertile soils, fly ash, sewage sludge, SLASH, soil ameliorant, waste materials. 1. Introduction South Africa is characterized by a poor resource base [1 Socio-economic problems in this resource poor sub-continent have been compounded by a large population, a rapid population growth rate of 2.5% per annum, growing urbanization and a high of unemployment. There is, therefore, a desperate need for strategies, which will improve both national and household food security. at the same time create more job opportunities. In a country where natural resources have already been seriously impacted by agricultural, industrial mining industries, and where the disposal of waste products is often a problem, the possibility of using waste products to improve the natural resources (especially soil) deserves more intensive investigation. Previous work conducted to determine the feasibility of converting waste disposal problems in South Africa into a soil beneficiation strategy has been positive [3]. Two problems experienced in the sludge were, firstly, that contains heavy metals and pathogens. As a result restricted for agricultural land application. Secondly, fly use is production in countries, which rely on coal for energy, such as South Africa, presents a major problem to those responsible for the consequences and implications of disposing of such "waste" products [4], co-utilization of fly ash and sewage sludge with added lime delivered a product termed SLASH (containing % class F fly ash, 30 % sewage sludge and 10% unslaked lime on a dry matter basis), which has beneficial soil 161 ameliorant effects [3]. use of fly ash (FA) as a soil amendment is hindered by a lack of macronutrients in Mixing and concerns about trace element availability. with an organic waste can increase macronutrients while reducing odor and improving material handling, but the element solubility requires investigation. As with fly ash, only a fraction of total nutrients (especially Nand P) supplied by organic wastes are available to crops in a particular season, since they must be mineralized from organic to inorganic forms. sewage sludge and animal manures may be these limitations, most cost effective supplement for co-utilization with fly ash in crop fertilization. Mixtures of fly with organic wastes already have a proven track record [5,6,7,8,9,10,11,12,13], but the preparation of mixtures has usually proceeded by trial and error. Prediction of plant nutrient supply from fly and bio-solids (sewage sludge and poultry manure) may enhance their agricultural use as a crop fertilizer. The resin method was useful for major nutrient (N, P, K, Mg, S) extraction from fly and organic materials, particularly where mineralizable fractions of Nand P under aerobic conditions are required {13]. Extraction of fly ash using a dilute buffered nutrient solution was more successful because micronutrient recovery was improved; macronutrients were correlated to the resin method. nutrient supply from extremely variable fly ashes was: Cu = B, Mo > overall >S> >Mn > N > Mg > P > K (high micronutrient, low macro nutrient supply). bio-solids, the macronutrients ranked: P> N, Ca > S> Mg > K (sewage sludges), and N > Ca, K > P > Mg > S (poultry manures). In mixtures of fly ash with 26% sewage sludge the order was: Ca > S > N > Mg > P > K, while in mixtures of fly and 1 poultry manure, the nutrients ranked: > K, N, S > Mg > P. Optimal plant nutrition (especially N-P-K balancing) should be possible by mixing these three materials [13]. initial cropping cycle of this programme was to determine how sewage sludge, fly ash and lime both in combination (SLASH) individually, would affect the growth of various flower and vegetable crops [14]. Subsequently, another study, prior to the one being reported on, had also been undertaken which represented the cropping cycle of the programme [1 It focused on the 162 production of mays) on the soils, which were used in this study. objective of that study was to determine if two specific heavy metals (Ni, Cd) and micronutrient B would translocated to the leaves and grain of maize. Translocation would possibly place from soils treated with SLASH and it was compared to the individual components of which SLASH is made In addition this, dry matter (OM) and grain production were also recorded. This investigation followed on that work. objective of this study was to further evaluate the long-term residual effect, which different levels of SLASH might have (in terms of forage production), in comparison to the individual components of SLASH. It is hypothesized that while the individual components have their own beneficial characteristics, these do not compare with the complementary effect of the mixture in sustaining optimal plant growth. The soils treated with different amendments were utilized intenSively the cropping cycle of maize, with consecutive crops such as Triticale (Triticale sp.), sorghum (Sorghum sp.) and rye (Secale sp.) as successive 3rd , 4th and 5th cropping cycles over a period 24 months. 2. Material and Methods When using SLASH for flower and crop production, the best performance was achieved with the 5% and 10% SLASH levels [16,1 It was because of this conclusion that this raised bed study was undertaken to compare SLASH treatments to the individual components of SLASH. Constructed plot: 1.2m x 0.50m ::: 0.6m Experimental 2 ) (net as illustrated in (Fig.1) were used at the Hatfield , Pretoria, South Africa (25°45'S 28°1 1327m above sea level. 163 growing grain crop. These crops are generally used for animal crops were sown These a rate of 150kg/ha in three evenly spaced rows of 12.5cm for each treatment in the beds (Fig 1). Forage production was regular harvests within each growing season. by Once the best treatment had reached flowering stage, the harvest was taken. harvests were recorded for Triticale hexaploid and Sorghum sp. and two harvests Secale cerea/a .AII treatments received regular watering to eliminate moisture as a limiting growth factor. No additional fertilizer had been applied to the soil during the period of this study, since the cropping with maize. 1 Statistical analyses All dry matter production and root study data was statistically using PROC GLM (1996/1997 and 199711998). Statistical analysis was performed using SAS software [20]. were taken 0.05. 3. Results and Discussion response of Triticale (Triticale hexaploide), a hybrid between wheat (Triticum) and Rye (Seca/e) , in the third cropping cycle on these (a) different levels of and (b) beds to different components which make up SLASH, was assessed in the winter and spring of 2000. The relative mass (g) of uniform sample taken from each treatment for consecutive harvests is shown in Table 1. Despite this being the cropping cycle on beds, response pattem of the Triticale (in terms of forage production) was still essentially the same as that of maize in the second cropping cycle [1 The growth response of Triticale to the SLASH and sewage sludge treatments was markedly beUer than the control, fly and lime treatments. Nevertheless, fly and lime treatments had a marginal beneficial effect on plant yield above the control, (12 and 11% respectively). SLASH, in contrast, improved plant yields by 240%. However, sludge on its own improved plant yields by 368% over the control. 165 Table 1 Influence of sewage lime and fly ash individually and in combination (SLASH) on the mean dry matter production (Triticale hexaploid) - 350 T2- 2.5% SLASH after the treatment T5- 10% SLASH T6- Sewage sludge T7 ash and by Mass Mass Mass Relative mass (g) Relative mass (g) Relative mass (g) 25.06 f1 b (±7.70) 22.28 as (±3.1 0) (±3.85) 27.70s a (±5.12) T3- 5% SLASH T4- 7.5% SLASH plot) and the ±MSE of the cereal crop f1 32.54 b (±4.81) B 45.76 b (±16.27) 44.92f1b (±9.84) 17} 4.57) 31.08"a (±3.58) " (±5.84) a 35.00 a a 46.46 b a (±7.11) (±5.48) a 53.10 B (±8.03) b (±8.33) 31.00B" *abc Column means with common alphabetical subscripts do not differ significantly (P> 0.05) (Boflferroni Test) Due to sludge's limitations it is not, however, safe and practical to use. It should noted, that the higher the SLASH application, 0-10%, the higher the growth response was in terms of yield. This substantiates the results obtained from other studies [16,17J, that the best results were obtained from the 5-10% SLASH levels. It is evident from Table 1 that the third harvest gave a much higher yield that the other two harvests. This can ascribed to the longer interval between harvests because seasons were changing and Triticale was becoming reproductive. The total dry matter production (all three harvests) of aU harvests Triticale (Triticale hexaploid) for the growing season is illustrated in 2). It is shown that the total dry matter production of Triticale (Triticale hexaploide) as illustrated in the histogram (Fig 2) for the entire growing season, was most definitely the highest on the sewage sludge treatment (T6). Sewage sludge improved the yield of Triticale by 268%. Due to the limitations on the use of sewage sludge, as previously mentioned, the next best treatment to sewage 166 Table 2 Influence of sewage sludge, lime and fly ash individually and in combination (SLASH) on the mean dry matter production (g/net plot) and (±MSE) of sorghum (Sorghum sp.cv. Hypergraze) - 470days after the treatment application and preceded by three cropping cycles Treatments st 1 Harvest Dry 2 nd Harvest Dry Mass T2- 2.5% SLASH Tl-5%SLASH T4- 7.5% SLASH TS- 10% SLASH TS- Sewage sludge T7 ash TS- Lime Mass 8 87.24 a (±14.36) 90.42 8 b (±16.61) 102.48\ (±15.11) 71.24 73.0B 47.46 8 (±i6.B6) 8 7.30) a 8 8 65.44 8 ab 69.78 82.34 (±1S.49) 81 (±10.38) 8 8 60.20 a (±7.35) 65.72 abc (±8.8S) 78.1 (±19.24) abc a 45.64 mass ab 8 91 130.40\ 8 lrd Harvest Dry 8 a 82.26 8 8 (±9.12) a (±9.74) 8 11 5.73) (±11.74) (±3B.68) (±S.43) (±7.B7) 5.02) 11 (±6.37) a (±5.34) 8 46.74 "abc Column means with common alphabetical subscripts do not differ significantly (P> 0.05) (Bonferroni Test) Fig. 3 clearly shows that, on average, the 10% SLASH treatment forage production. The the best treatment gave approximately 120% beUer yield than the control, 80% better yield than the sewage sludge treatment (T6) and 60% better yield than the fly ash treatment (T7). Reasons for this sudden change in production on the sewage sludge treatment may be ascribed to the depletion of the organic and nutrient source. In other studies it is noted that after 36 months of multiple cropping, the soils treated with sewage sludge had markedly high phosphate levels [19]. These nutrient inbalances could impact negatively on plant growth, which may explain the reduction in plant growth response to the sewage sludge treatment. On the other hand SLASH treatments maintained a relatively good performance. 168 4. Conclusion The addition of SLASH to infertile or acidic soils as a soil ameliorant holds definite agricultural potential. 7.5%-10% SLASH delivers the best results compared to the rest of the good source treatments. Although nutrients required for plant growth, it of nutrients. Depending on the source of example, adequate K, creating is seen as a not contain a full range sludge it may lack, for need for supplementary fertilization. Quality control of waste products used in such mixtures, is therefore, essential to be able to calculate the required levels for speCific soils and crops. Focusing on the performance of the individual waste products (sewage sludge and fly ash), it is clear from the results that sewage sludge (T6) gave the best overall yields. Although sewage sludge is a good source of organic material with high amounts of essential macronutrients, it must be taken into consideration that the use of sludge is limited because of its potential disease risk and possible heavy metal pollution. The fly ash treatment (T7) did not give significantly higher yields than the control. This supports the importance organic material for optimum plant growth. Fly ash is a good source of micronutrients, which may beneficial to certain plant growth processes, but on contribute to the enhancement of plant growth. own it does not necessarily ash characteristically has a larger influence on the soil properties and hence indirectly enhances plant growth, by ensuring a good medium for plant growth, especially in acidic soils. Sustainable crop productivity depends on the use of non-acidic soils and ameliorated acid soils. From this study the conclusion can be drawn that U L /.... ~I has marked beneficial effects on plant productivity. This is ascribed to the ameliorating effects, which this product has on soil pH and nutrient status. These effects, unlike many inorganic fertilization programmes, have long-term residual effects. 171 5. References [1] D.M. Scotney, J.E. Volschenk, P.S. van Heerden, The potential and utilization of the natural agricultural resources of South Africa. Dept. Agric. Devpt. Pretoria, South Africa. (1990) 11 p. [2] N.F.G. Rethman, E. du Toit, E.J. Ramagadza, W.F. Truter, The use of fly ash and biosolids to ameliorate soils, revegetate disturbed areas and improve plant productivity. (2000a) Proc. 25th Conf. Canadian Land Recio Assoc. Edmonton, Canada. [3] K.A Reynolds, R.A Kruger, N.F.G. Rethman, The manufacture and evaluation of an artificial soil prepared from fly ash and sewage sludge. (1999). Proc. Internat. Ash Utiliz. Sympos. Lexington Kentucky, U.S.A pp. 378- 385. [4] W.F. Truter, N.F.G. Rethman, K.A Reynolds, R.A Kruger, The use of a soil ameliorant based on fly ash and sewage sludge. Proc. 2001 Internat. Ash Uti liz. Sympos. Lexington, Kentucky, U.S.A (2001) [5] B.P. Jackson, W.P. Miller AW. Schumann, M.E Sumner, Trace element solubility from land application of fly ash/organic waste mixtures . J. Environ. Qual. Iss. 2 28 (1999) 639-647 [6] J.R. Pichtel, J.M. Hayes, Influence of fly ash on soil microbial activity and populations. J. Environ. Qual. 19 (1990) 593-597. [7] L. Belau, Laboratory investigations into the microbial decomposition and nitrogen supply of mixtures of poultry excrement and power plant ash in soils. Zentralblattfur Mikrobiologie.146 (1991) 117-123. [8] AP. Schwab, M.B. Tomecek, P.O. Ohlenbusch, Plant availability of lead, cadmium, and boron in amended coal ash. Water Air Soil Pollut. 57-58 (1991) 297-306. [9] J.T. Sims, B.L. Vasilas, M. Gbodrati. Effect of coal fly ash and co composted sewage sludge on emergence and early growth of cover crops. Comm. Soil Sci. Plant Anal. 24 (1993) 503-512 . [10] M. Vincini, F. Cairini, S. Silva, Use of alkaline fly ash as an amendment for swine manure. Biores. Techno!. 49 (1994) 213-222. 172 [11] K.S. Sajwan, W. Youngblood, The Omes, of fly ash/sewage sludge mixtures and application rates on biomass production. J. Environ. Health (1995) 1 337. [12] J.W.C. Wong, The production of artificial soil mix from fly ash and sewage sludge. Environ. Technol. 16 (1995) 741 [13] AW. Schumann, M.E. Sumner. Chemical evaluation of nutrient supply from fly ash-biosolids mixtures. Soil Am. J. 1 64 (2000) 419-426 [14] E.J. Ramagadza, Utilization of "SLASH" for flower and vegetable production in the informal sec:tor in South Africa. Mlnst.Agrar (Thesis). University of (2002) [15] W.F. Truter. Comparative study on the influence of SLASH and its individual components on the production of Zea mays and heavy metal accumulation. of waste products to enhance plant productivity on acidic MSc (Thesis) and infertile substrates. University of Chapter 4 (2002) pp.140-1 [16] N.F.G. Rethman, K.A Reynolds, R.A Kruger, Crop responses to SLASH (Mixture of Sewage Sludge, and Fly Ash) as Influenced by Soil Texture, Acidity and Fertility. Proc. 1999 Internal. Ash Utiliz. Sympos. Lexington, Kentucky, (1999) pp. 387-397. [17] N.F.G. Rethman, K.A Reynolds, R.A Kruger, E.J. Ramagadza, , du for flower and vegetable production in the informal sector in Toit, South Africa. Proc. Internal. Ash Utiliz. (1999) [18] W.F. Truter, influence of a fly ash-biosolid mixture on chemical soil properties. MSc (Thesis) Use of waste products to enhance plant productivity on and infertile substrates. University of Pretoria. Chapter 6 (2002) pp. 174-1 [19] Institute Inc., The SAS system for Windows. SAS Institute Inc. SAS Campus drive, Cary, North Carolina, USA (1 173 CHAPTER 6 Prepared according to the guidelines of Journal of Waste Management The influence of a fly ash-biosolid mixture on soil chemical properties W.F. Truter a a Department and N.F.G Rethman a of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South Africa Abstract Agricultural and industrial activities have greatly accelerated the pace of soil acidification. Soil acidification and nutrient depletion is, therefore, a serious socio-economic concern. Very few countries can afford the decline in food production, which often accompany the changes, which are taking place in our soils. Nutrient management practices affect the viability of agricultural ecosystems. External sources of plant nutrients will, therefore, continue to be an essential part of agriculture as we strive to replace the nutrients lost in successive crop harvests. Many countries experience waste product disposal problems. Many of these waste materials are excellent sources of plant nutrients and also have potential soil ameliorating qualities, which can be utilized for crop production if rendered innocuous. One of the more recent methods of sewage sludge treatments, which are being more widely used, is the alkaline stabilization of biosolids. This process involves the mixing of partially dewatered sewage sludge with an alkaline material such as fly ash or a blend of materials. This advanced technology, which has also been used in South Africa, has provided a product termed SLASH. Not only has SLASH become a possible solution to various problems experienced in South Africa such as ash and sewage sludge disposal, but is also an alternative measure for ameliorating our acid and nutrient depleted soils. Where fertility was limiting, SLASH had a beneficial effect. 5-10% SLASH levels improved the soil pH and have thereby made essential plant growth elements more readily available over a longer period. SLASH does have beneficial soil ameliorating qualities, and can be used as an Corresponding author. : Tel. +27-420-3224 Fax. +27-420-4120 Email address: [email protected] 174 alternative amendment. SLASH's effectiveness has been recorded over at least 36 months, maintaining an improved pH of one pH unit on average relative to the even during intensive cropping of soils. Long-term residual effects of sewage sludge are also prolonged by combining it with fly ash. SLASH and similar products definitely have agricultural potential. Keywords: Alkaline stabilization, nutrient dep,letlcm soil acidification 1. Introduction Nutrient poor and acidic soils in South Africa are becoming more prevalent and many farmers require alternatives to the high priced conventional methods of soil amelioration currently in use [1]. Previous work has indicated that the application of limestone and CCS's (coal combustion by-products) P availability efficiency (the amount of plant yield produced per unit of extractable P and P utilization (amount of plant yield produced per unit of P in the plant) [2,3,4,5]. Either limestone or CCS application increased the availability of soil P to plants. probably due to a better developed root system resulting from the alleviation of AI toxicity and increased availability of [6, 9). It can, therefore, be said that the application of CCS's and limestone to acidic soils results in healthier plants with a better developed root system due to higher soil pH and increased Ca and Mg supply. The better developed root systems result in an enhanced P availability and P utilization efficiency and thus improved plant-soil relationship of P in acid soils [5]. Coal combustion by products (CCS's) have widely as cost effective amendments for acid soils. It holds true that ashes have several advantages, and their application is often recommended [6]. Although information is needed on the proper combination of CCS's with chemical fertilizers or other organic and inorganic amendments to improve the productivity of acid soils. [7] 1.1 Fly In South Africa approximately 28 million tons the energy generation industry to ash is produced annually, by the energy reqUirements of a population of 175 45 million people and growing. This largely untapped resource, together with power utilities, is generally situated in areas with high agricultural potential, which are being acidified because of effect of "acid rain" and agronomic practices. Only a small percentage of this untapped resource of fly ash is currently used in the plastics, rubber and paint industries [8]. The alkaline nature of fly ash led to an examination of its use as a liming grade CaC03 on acidic agricultural soils and coal mine to replace spoils [9,10,11]. Furthermore, the enriched macro- and micronutrients which fly ash contains, may enhance plant growth in nutrient-deficient soils [12,13,11]. fly ash is relatively rich in trace elements, it has also been successfully used to alleviate micronutrient deficiencies [14,15]. Fly ash amendments have been used to correct deficiencies of B [9,16,17], Mg [1 Mo [17,19,20,], S [17,18,20,21], and [9,17,22,]. Fly ash alone, as previously mentioned, is usually a poor source of the macronutrients such as Nand P [15]. Nitrogen coal combustion, while most fly volatilized during the process of P is relatively unavailable [1 Notwithstanding these facts, land application of fly ash is still viewed as an attractive alternative means of disposal [1 Coal fly ash physical chemical characteristics that make it useful as a soil amendment. One of the more important of these being the potential to permanently improve Changes in the infiltration soil water relations of sandy, drought-prone soils. and water holding capacity of a sandy soil after application of high rates (up to 950 ha- 1) of a Class F fly ash were examined. Fly ash amendment not only increased water-holding capacity but also increased plant available water. [24]. 1.2 Biosolids Sewage sludge is classified as a toxic waste and produced at a of 800 tons/day dry mass in South Africa [25]. This problem, in addition to the large volumes of fly ash produced, emphasizes the need for co-utilization of wastes 176 and thereby identifies possible strategies for the safe disposal (use) of such waste products. Regarding amendment of infertile soils, many studies have demonstrated the ability of sewage sludge to restore degraded lands [26]. Sewage sludge can be a valuable source of plant nutrients such as N, P, and S, and organic matter contained in the sludge can also help improve soil physical conditions thereby reducing runoff and increasing infiltration, which in turn results in increased biomass growth and quality. Of the major environmental problems associated with the land use of sewage sludge is the addition of potentially toxic heavy metals in soils and possible pathogenicity. Repeated applications of contaminated sewage sludge can result in an accumulation metal such toxic metals in the soil. Once accumulated, heavy metals are highly persistent in the topsoil, and can cause potential problems such as phytotoxicity, injury to soil microorganisms and elevated transfer to food chain [27J especially under acidic conditions. Local authorities, both overseas and in South Africa, are continually searching for environmentally acceptable, as well as beneficial and economical, means of disposal of sewage sludge [28]. Land application of biosolids is still not completely accepted in the scientific community as a beneficial disposal option, with concern persisting over the fate and phyto-availability of biosolids-applied trace metals over time [29,30]. 1.3 Biosolid-fly ash mixtures The addition of organic wastes such as sewage sludge, chicken manure or compost will increase the organic carbon content in soil receiving ash amendment. This will initiate soil microbial activities for the cycling of nutrients [31, 32J. The high Nand P contents in these wastes may also reduce the need for inorganic fertilizer. Fly ash mixed with other organic waste will be an attractive and economical option that should be considered [32]. If the pathogen reduction process in sewage sludge treatment involves the addition of hydrated lime and/or an alkaline substance, resulting in a pH of 12, a 177 built in source of alkalinity is realized [33], and can be regarded as a possible amendment for acidic and infertile The extreme variability measured in fly ash and organic wastes in terms total nutrient concentrations, extractable nutrients, and relative nutrient balance is common in many studies, reinforcing the urgent need to characterize waste materials before mixing and use in crop fertilization. potential pitfalls of indiscriminate waste application to soil include (I) potential phytotoxicity from micronutrient excesses (especially B); (ii) shortages of essential macro nutrients such as N, P, and K due to low supply; (iii) nutrient deficiencies caused by unfavorable fly ash pH, slow nutrient release, and fixation of other nutrients such as P already present in the soil solution; and (iv) induced nutrient deficiencies from the supply of elements in incorrect proportions. Most of these problems can be overcome by exploiting the complementary nature of fly ash, sewage sludge, and poultry manure, and additional nutritional (especially N-P-K balancing) should be possible by mixing these three waste materials together [17]. Previous work by Reynolds et al [34] to determine the feasibility of converting waste disposal problems in South Africa into a soil beneficiation strategy has proven viable. The co-utilization of fly ash and sewage sludge with added lime delivered a product termed SLASH (that contains 60 % fly ash, 30 % sewage sludge and 10% unslaked lime on a dry matter basis), which has beneficial soil ameliorant effects. Reynolds et a/., [341, Rethman et aI., [35,36] have reported on the use of SLASH for a variety of flower crop such as including corn, beans, potatoes, spinach and a These reports highlighted eliminate the potential problems with use of SLASH to organisms or heavy metal pollutants, while improving soil pH, Ca, Mg and P. The growth and productivity of such crops was improved markedly under conditions of low fertility type, rate of SLASH application and plant species were identified as being important in this regard. It was concluded that wherever fertility was limiting, SLASH had a beneficial effect [1,35]. At pot low application it was found that no heavy metals had used in these translocated. Subsequent 178 trials with higher application rates (up 30 of soil volume) were conducted and it was concluded that rates at 30 % were too high, compared to the 0 % treatments [1,38, 39]. The rationale behind such mixed wastes, are that the mixtures are superior soil amendments to either fly addresses or sewage sludge. The use of an organic waste deficiency of macronutrients in fly ash, while fly ash can act as a bulking agent for organic wastes, substantially reduces odor, and can offset soil acidity problems that may through continued land application of organic wastes. [40,15] . .........,,,....... on the conclusions made by Rethman et 36, 39,] and Truter, [1] this study concentrated on the effects SLASH had on soils at levels that did not exceeded 10%. The SLASH treatments were compared to sewage sludge, fly and lime in this study. 2. Experimental procedures A randomized trial was conducted in constructed O.SOm ::: 0.6m 2 ) (net plot: 1 x on the Hatfield Experimental Farm, Pretoria, South Africa o (2S 4S'S 28°16'E), 1327m above sea level, to determine whether a mixture of waste materials could improve infertile acidic soils, thereby creating better soil conditions for crop production. A uniform sandy loam soil was ameliorated with sewage sludge, fly ash and reactive lime (CaD), in combination (SLASH) at four different levels and separately. These treated soils were placed into these constructed raised treatments [T1 (Control - 0% SLASH), T2 - [2.5% SLASH (8kg)], - [5.0% SLASH (16kg)], T4 - [7.5% SLASH (24kg)], TS - [10% SLASH (32kg)], T6 Sewage Sludge (4.32kg), - Fly ash (10.24 kg) and - Lime (1.44kg)] were replicated five times. These raised beds were used to evaluate the effects of SLASH, sewage sludge, lime and fly ash in soil on the dry matter production of various crops and soil chemical properties. Initially raised beds were planted to 179 cabbages, carrots, stocks, sweet peas and statice. These vegetable and flower crops represented the 1st cropping cycle of the raised bed trial [42]. Maize (Zea mays) [38], Triticale (Triticale hexaploide), sorghum (Sorghum sp.) and rye (Secale cerea/a) represented the 2nd , 3rd, 4th and 5th cropping cycles [43]. The treatments were applied to the soil in the raised beds at the start of the trial and were monitored over a period of 36 months. initial analyses for this work was after the 1st cropping cycle done by Ramagadza [42]. The study. also aimed to evaluate the effect treatments on crop production and the soils condition. The soils were sampled and analyzed once each cropping cycle had been completed. The chemical properties that were analyzed by the Soil Science Department, University of Pretoria, were the pH (H 20) and the content of macronutrients (Bray 1 P), K, Ca and Mg. The %C was also occasionally determined. The soils received regular watering to eliminate moisture as a limiting growth factor. Due to the variability of the raw materials used in these waste material mixtures, a relatively low concentration of a macronutrient was expected. Plants in the 1st cropping cycle showed symptoms of K deficiency and to determine if this was true for the batch of used for that study, K was applied to 2nd cropping cycle (maize) only. This was necessary to eliminate K from being a possible growth-limiting factor for the 2nd cropping cycle. Thereafter, no additional inorganic fertilizer or additional applications of or other components were applied. When using SLASH for flower and crop production, the best performances were achieved with the 5% and 10% SLASH levels (35,36,43]. It was because of this conclusion that this raised bed study was undertaken to compare treatments to the individual components of SLASH to notice the benefits of combining the waste materials. Forage production for the various test crops was assessed by regular harvests within each growing season. These soils had been intensively cropped to get maximum production. 180 which is relatively low in P, it can reduce the availability of P in sludge and make it slowly available over time (Fig. 6). These effects can be attributed to an increase in soil pH by formation of insoluble complexes [53, 54]. SLASH treatments, can be related ash and the lower soil P levels seen on the the conclusion made by Schumann and Sumner, [54] that the soil P deficiencies were exacerbated by fly ash applications, due to precipitation of P and cation imbalances caused from excess Ca compounds. The P level obtained in the analysis at 360 days is not valid. This may ascribed to a non-representative sample, which did not contain significant sewage sludge, which influenced the mean value for that period. This observation emphasizes the difficulty of handling, applying and incorporating a waste material such as sewage sludge. SLASH and similar waste product mixtures, based on same principles, deliver a more granular soil like texture facilitating it's even incorporation into the soils. 3.3 Calcium (Ca) Calcium is absorbed by plants in relatively large amounts and regarded as a macro nutrient. function of in the plant is the formation of Ca pectates in the middel lamella of the cell wall and membranes therefore, stabilization of Thus, damage of the root could result from a disturbance of cell wall formation in the root meristem or through disturbance of the integrity and function of membrane, especially the plasmalemma. The chemical barrier to root development existing in the sub-soils of acid is a subject of increasing interest. In order to better understand the factors involved in the amelioration of subsoil acidity, phosphogypsum and calcium carbonate on phases of subsoil samples and on mays L.) were evaluated effects of calcium sulphate, properties of solid and liquid growth and nutrient uptake by maize Calcium carbonate reduced activity of A1 3+ IIJ'V'"Q"H:O'V of the increase in pH. The subsoil samples presented severe restrictions for maize root growth and all treatments were equally effective in increasing root development, which could be attributed to the supply of calcium and a 186 360 days the KCL application, the K levels had returned to the original level after being depleted by the two crops that utilized this K. as seen from 540 remaining K levels onwards, are not sufficient for optimum crop production and quality plant material. The need, therefore, exists supplemental inorganic fertilization, or the addition of an organic material, which is relatively high in K as are animal manures. 3.5 Magnesium (Mg) Magnesium forms the core of the complex chlorophyll molecule, which is important in the photosynthetic process. Shortages can occur in low CEC or sandy soils. Mg is also present in seeds and is involved in the translocation of P. Once an adequate amount of exchangeable Mg2+ is present, it has been shown that the ratio of Ca/Mg can anywhere in the range of 1:1 to 49:1 without affecting crop yields [60]. Sewage sludge can supply Mg and other essential nutrients, but it depends greatly on the source from where sewage sludge comes from. Fly produced from South African coals, can be relatively low in Mg. Nevertheless, 180 days after the application of treatments the Mg levels weren't Significantly different to each other. In the following months, it is obvious from Fig. 9 that the lime, the lowest SLASH treatment, sewage sludge, fly and control's Mg dropped. While the other SLASH treatments maintained relatively constant Mg levels for at least days longer than the other treatments. These results re'nect variation in the of various interactions between elements themselves, but can also be ascribed to the different nutrient requirements crop species. Overall, the 0% SLASH treatments gave the results, which can thus emphasize the benefits of combining two waste products that have unique characteristics in of improving specific soil conditions or enhancing plant growth processes. 189 levels were not considerable. Therefore, the optimum level of SLASH can 5-10% of the soil volume depending on the specific soil condition. range Sewage sludge is an excellent source of N and of can result Unfortunately; P fixation excessively high levels P supplied by sewage By mixing sewage sludge with fly ash (SLASH) the P were lowered to more acceptable levels, and made available over time. Potassium is a very essential nutrient for plant growth. Very low levels of K are found in both sewage sludge and fly It is, therefore, critical that K is supplemented by adding K in an inorganic form, or possibly combining with an additional organic material, which is high in K, such as animal manures. improvement physical properties were observed but not measured. This requires further investigation to substantiate the hypotheSiS that SLASH does improve physical properties. Combining waste materials produces mixtures, which are superior soil amendments than individual components. these mixtures can resolve the deficiency use of organic wastes used in macronutrients in the fly ash, as can fly ash address the deficiency of micronutrients in the organic wastes. In addition to this, the fly ash acts as a bulking agent for organic wastes, reducing odour, and can offsetting soil acidity problems as well. References [1] Truter WF Rethman Reynolds KA, Kruger RA. The use of a soil ameliorant based on fly and I sludge. Proc. 2001 Internal. Ash Utiliz. Sympos. Lexington, Kentucky, U.S.A. 2001. [2] Baligar VC , He Martens DC, Ritchey KD. Effect of phosphate rock, lime and cellulose on plant growth in acidic Plant Soil 1997;1 129 136. [3} He Zelazny LW, Baligar Ritchey Martens Ionic strength effects on sulfate and phosphate adsorption on gamma-alumina and kaolinite: triple-layer model. Sci. Am. J. 1997;61:784-793. 191 Ritchey KD, He ZL, Baligar VC, Martens ryegrass growth to labile P in materials, of AM. amended with phosphate rock, liming cellulose. Agronomy Abstracts 1 1997 Annual Meetings, Anaheim CA. [5] He ZL, Baligar VC, Martens Ritchey KD, Elrashidi MA. Relationship of Ryegrass Growth to Extractable Phosphorus in Acidic Soil with Phosphate rock, Coal Combustion By-Product, Limestone, and cellulose. Commun. Soil Plant Anal. 1999;30(3&4):457-470. [6] Katzur J, Haubold-Rosar M. Amelioration and reforestation of sulfurous mine soils in Lasatia (eastern Germany). Water, Air He ZL, 17- Ritchey KD, Elrashidi AM. Effect of VC, Martens byproduct, nitrogen fertilizer, and extractable phosphorus in acid [8] Pollut., 1996;91(1 on phosphate rock dissolution Plant and Soil 1999;208:199-207. Reynolds KA, Kruger RA, Rethman NFG, Truter artificial soil from sewage sludge ash and production an subsequent evaluation of growth enhancement, heavy metal translocation and leaching potential. Proc. WISA Conf. Durban, South Africa (In Press) 2002. Martens DC. Availability of plant nutrients in fly Compost. 1971;12:1 [10] Moliner AM, of corn JJ. Effect fly L.) on acid and lime on growth and composition soils. Proc. Soil Crop Sci. Soc. 1982;41 [11] Wong MH, Wong JWC. Germination and seedling growth of vegetable in fly ash-amended soils. Agric., [12] Plank CO, fly ash to soil. and Environ. 1 DC. Boron availability as influenced by an application of Soc. Am. 1974;38:974-977. [13] Martens DC, Beahm BR. Chemical effects on plant growth of fly incorporation into soil. In: Adriano and I Environmental Chemistry and Cycling Processes, 760429, Brisin (Editors), Symp. Ser. CONF Commerce, Springfield, VA. 1978. 192 [14] EI-Mogazi D, lisk DJ, Weinstein LH. A review of physical, chemical, and biological properties of fly ash and on agricultural ecosystems. Total Environ. 1988;74:1-37. [1 Jackson BP, Miller WP, Schumann AW, Sumner Trace element solubility from land application of fly ash/organic waste mixtures . J. Environ. Qual 1999;28(2):639-647. [16] Ransome LS, Dowdy Soybean growth and boron distribution in sandy soil amended with scrubber sludge. J. Environ. Qual. 1 [17] Schumann AW, Sumner Chemical evaluation of nutrient supply from fly ash-biosolids mixtures. Soil Sci. [18] Hill MF, Lamp CA 16:171-1 Am. J. 2000;64 (1):419-426 of pulverized fuel ash from Victorian brown source of nutrients for a pasture speCies. Aust. J. as a Agric. Anim. Husb.1980;20:377-84. [19] Doran JW, Martens Molybdenum availability as influenced by application of fly ash to soil. J. Environ. Qual., 1972;1:186-189. ''''.......,1\1, AA, Straughan IR, Page AL. [20] Sequential cropping of fly ash amended soils: effects on soil chemical properties and yield and elemental composition of plants. Total. Environ., 1980;1 1] Elseewi AA, Bingham RT, Page J. Availability of sulfur in fly ash to plants. Qual. 1 [22] Schnappinger MG Jr, Martens DC, Planks CO. Zinc availability as in11uenced by application of fly ash to soil. [23] Bradshaw AD, Chadwick MJ. Sci. 1 restoration of land. Univ. of California Berkeley. 1980. [24] Gangloff WJ, Ghodrati M, Sims JT, Vasilas BL Study: Influence of fly ash on leachate composition in an excessively drained J. Environ. Qual. 1997;26:714-723. [25] Reynolds, K.A 1996. Ash utilization -- Evaluation of ash soil. Eskom Research Report. TRRlS96/158. Eskom Technology Services. [26] Sopper WE. Reclamation of mine land using municipal sludge. Adv. Soil 1 17:351-432. 193 [27] McGrath SP, Zhao FJ, Dunham SJ, Crosland Coleman K. Long term changes in the extractability and bioavailability zinc and cadmium after sludge application. J. Environ. Qual. 2000;29:875-883. [28] Barry GA, Chudek PJ, EK, Moody PW. Estimating sludge application to land based on heavy metal and phosphorus sorption characteristics of soil. Wat. Res. 1995;29(9):2031-L............ [29] McBride MB. Toxic metal accumulation from agricultural use sludge: Are regulations protective? J. Environ. Qual. 1995;24:5-18. [30] Brown Chaney Angle Subsurface liming and metal movement in soils amended with lime stabilized biosolids. Environ. Qual 1997;26: 724 732. [31] Wong MH, Wong JWC. Effects of fly ash on soil microbial activity. Environ. Pollut. (Ser.A) 1986;40:127-144. [32] Wong JWC, Wong MH. Effects of fly ash on and elemental composition of two vegetables, Brassica parachinensis and B. chinensis. Ag and Environ. 1 -264. [33] Abbott DE, Essington ME, Mullen MD, Ammons ..IT. Fly Ash and Lime Stabilized Biosolid Mixtures in Mine Spoil Reclamation : Simulated Weathering. J. Environ. Qual. 2001 ;30:608-616. (34] Reynolds KA, Kruger RA, Rethman NFG. The manufacture and evaluation of an artificial soil prepared from fly and sewage sludge. Proc. 1999 Internat. Ash Utiliz. Sympos. Lexington Kentucky, U.S.A. 1999:378- 385. Rethman NFG, Reynolds KA, Kruger Crop responses to (mixture of sewage sludge, lime and fly ash) as influenced by soil texture, acidity and fertility. Proc. 1 InternaU Ash Utiliz. Sympos. Lexington, Kentucky, U.S.A. 1999:387-397. Rethman NFG, Reynolds KA, Kruger EJ, Ramagadza du SLASH for flower and vegetable production in the informal Africa. ES. in South Internat. Ash Utiliz. Sympos. Lexington, Kentucky, USA. 1999:83-86. 194 [37] Rethman NFG, Truter WF. responses on soils ameliorated with waste products. 18 th National Meeting of ASSMR. Albuquerque, New Mexico. U.S.A. 2001 [38] Truter WF. Comparative study on the influence of SLASH and it's individual components on production MSc(Agric) Use of waste products to Zea mays and heavy metal accumulation. plant productivity on acidic and infertile substrates. 2002. pp 140-1 [39] Rethman NFG, E, Ramagadza E, WF. use of fly and biosolids to ameliorate soils, revegetate disturbed areas and improve plant productivity. Proc. 25 th Conf. Canadian Land Edmonton, Canada. 2000. Kirk WW. Lester IN. Fractionation, characterization, and speciation [40] Lake of heavy metals in sewage sludge and sludge-amended soils. J. Environ. Qual. 1984;1 175-183. [41] Ramagadza EJ. Utilisation of in the informal Pr.::.tnri<:l for flower and vegetable production in South Africa. Mlnst.Agrar. (Thesis). University of 2002. [42] Truter WF. Forage production from cereal and grain crops on fly ash-biosolid amended soils. MSc{Agric) Use of waste products to enhance plant productivity on acidic and infertile substrates. 2002. pp160-173 [43] Cavallaro N, Padilla N, Villarrubia J. Sewage sludge effects on chemical properties of acid soils. Sci. 1 56:63-70. [44] Heil OM, Barbarick KA. Water treatment sludge influence on the growth of sorghum-sudangrass. J.Environ. Qual. 1989;1 [45] Hue NV. Correcting soil acidity of a highly weathered Ultisol with chicken manure sewage sludge. Commun. Soil Plant Anal. 1992;23:241 264. OA, [46] ",.o,.,.o<:l Jr Martens Limestabilized and chemically fixed sewage sludges as lime amendments. Bioresource Technol. 1991 ;37:93 102. [47] Sloan JJ, Basta NT. Remediation of acid Environ. Qual. 1995;24:1 by using alkaline biosolids. J. 103. 195 AC, Straughan L Utilization and [48J Adriano DC, Page AL, in terrestrial ecosystems: A disposal of fly ash and other review. J. Environ. Qual. 1980;9: KF, Sabey BR. as a coal mine spoil amendment for revegetation in Colorado. J. Environ. Qual. 1986;15:44-49. [50] Thorne ME, Zamora BA, Kennedy AC. Sewage sludge and mycorrhizal on mine spoil. J. Environ. Qual. effects on secar bluebunch 1998;27: 1228-1233. [51] Seaker EM, Sopper WE. Municipal sludge for minespoil reclamation: I. Effects on microbial populations and activity. J. Environ. Qual. 1998;1 597. ability of high pH, high calcium, Gray CA, Schwab AP. coal combustion waste Air Soil Pollut. 1993;69:309-320. Schumann AW, Sumner Plant Nutrient Availability from Mixtu res of Fly and Biosolids. J. Environ. Qual. 1 Legge Thompson JE, Baker 1651 657. M . The effect of Ca on the fluidity and phase properties of microsomal membranes isolated from postclimacteric Golden Delicious Plant Cell Physiol 1982;23:161 169. Hanson JB . The functions of calcium A (eds) Advances in plant nutrition 1. Runge M, Rode MW. Ulrich and plant nutrition. In: Tinker PB, Lauchli r~QinQrSci, of M.E Sumner NY, pp 149-208. 1984. on plant associations. In Acidity.Springer-Verlag Berlin Heidelberg. p. 183-202. 1991. [57] Carvalho MCS, Raij B. Calcium sulphate, phosphogypsum and calcium carbonate in the amelioration of acid subsoil's for root growth. Plant and Soil. 1997;192(1 ):37-48. Sumner ME, Fey MV, Noble AD. Nutrient soils. In B. Ulrich and M and toxicity problems in acid Sumner (eds.) Sorl Acidity.Springer-Verlag Berlin Heidelberg. p. 149-182. 1991. 196 [59] McLean EO , Brown JR. Crop responses to lime in the Midwestern United States. Agronomy Monograph no. 12 ( 2nd eds.) Soil Acidity and Liming. ASA, CSSA, SSSA, Madison, WI 53711. p. 267-303. 1984. 197 CHAPTER 7 General conclusions and recommendations The land application of by-products from municipal, industrial or agricultural sources is certainly not a new phenomena. In many cases, a coal combustion by product (CCB) or an organic waste may not be ideal by itself for land application as a soil amendment. The coal combustion by-product fly ash, has shown potential as a soil amendment and is a source of trace elements beneficial to plants. However, agricultural utilization of fly ash has been restricted because it is a poor source of macronutrients such as Nand P, which is evident from the results obtained in the raised bed trials. Another assumption that can be made, but needs to be researched properly, is that P can become more available, because of the Si present in the fly ash, which can physically compete with the P on the clay minerals, thus making P more available for uptake by plants. The alkaline nature of fly ash, however, has made some significant contributions to the neutralization of acid soils. It can also be hypothesized that fly ash is more mobile in the soil than lime, which is not. This is important in neutralizing subsoil acidity, and this can possibly be ascribed to the presence of Ca silicates in the fly ash, but this requires further investigation. Another conclusion drawn from these studies, is that initially the fly ash application rates were calculated on a neutralizing value of 20% of agricultural lime, but from these studies, it can be concluded that fly ash has a higher neutralizing capacity than 20%. This, however, needs to be researched in more detail. Significantly high B levels in fly ash, which can be detrimental to crop production, were of no concern in these studies, and this may be due to the source, quality and age of the fly ash used in this programme. The application of sewage sludge, more recently known as biosolids, is not very common in many countries because very little research has been carried out under local conditions, because of the high variability of biosolid compositions. It is clear from the high yields obtained in this study that sewage sludge is a good 198 source of organic material with high amounts of macronutrients (especially Nand P). Unfortunately, P fixation can because of these high levels of P present in sewage sludge. Sewage sludge the ability to improve physical soil properties. Improvements in water holding capacity were noted during the cultivation of the treated with Despite the statistically different yields obtained with the sewage sludge, legislation ""u:.. use of this by-product '-''''''.............''' of associated problems, pathogenic micro-organisms, which can become a ,J"'..... restrictions on the as the high levels of the possible contamination aspects, as a result of excessive heavy metal contents, the associated odour problems and the acidifying effect it on agricultural soils. In addition to sewage sludge's limitations, practical restrictions such as transport, handling and application makes sewage a difficult by-product to use for agricultural It was, therefore, very important to develop tec:nnOIOlalEIS that can be used to produce soil ameliorants from these waste products with can be beneficially used to address problems properties that with conventional sludge and fly ash disposal practices, while simultaneously creating a beneficial use waste products to the benefit of interested parties. Co-utilization is simply the production of new products by combining two or more by-products. of two or more value added product. South Africa has successfully materials results in a other countries in developing a technology to convert waste beneficiation strategy. By combining sewage sludge, fly into a soil and CaO, a ameliorant SLASH is produced locally. SLASH is a superior soil amendment, which combines the amending qualities of two materials, which can overcome soil acidity and infertility problems by exploiting the complementary of fly ash and sludge. SLASH programme has been concentrated on the agricultural use of To extrapolate conclusions, biomass species, long term residual effects, heavy metal of a wide range of and 199 chemical properties were examined. During these studies, suprising results were "nl~onJon which emphasizes the need to investigate further possible v"~Anv Concerning the rate of SLASH application, it is clear from the in these that the optimal level of SLASH is between sandy loam volume. One may require different application and type of soil that is being dealt with and on the acidity long term obtained 10% of the ncr,cTI from the of SLASH. The reason one would apply lower more frequent time. hor,otl't~ would LlG"~'lG"I"" ex(~ee,amla may to have a slow response over a longer period of 10% will still deliver substantial in of inhibiting germination of seeds or in of but growth growth stages. The visual observations germination indicate that the 30% SLASH treatment for of an inhibiting and on seed germination and subsequently establishment. once seedlings had established themselves, exponential growth These were, however, not necessarily better than treatments. It is, therefore, concluded that the the 5-10% between 0% level and the 30% SLASH level in did not justify the higher level of SLASH . ........ ,""'''''''' of all the different species in Crop production were conSistently good. prolonged growth enhancement over a minimum period of 36 months the SLASH and other treatments showed signs depletion. Ne'verme,less. the contributed significantly to the immediate growth yields. and produced high yields from the germination enhancement SLASH treatment still maintained the better improved and high yielding production of leguminous plants. For a healthy to establish itself, a legume needs to develop healthy nodules (usually by inoculating with Rhizobia) on it's roots to be able to fix N. This aspect is important in inputs of inorganic nitrogen in any crop production system, which is reliant on nitrogen for production. Legumes produced on treated soils had Th is may be ascribed to yield improvements and consistently high production. reasons, firstly, the organic contribution from 200 SLASH with the essential macronutrients and microorganisms suppJied by the sewage sludge component the supply of micronutrients from the fly component of SLASH. Secondly, the amendment of soil pH creating a beUer thirdly the development and presence of a vast medium for root development amount of nodules, which were observed visually. This was an interesting researched more intensively to obtain clarity on observation, but would need to this aspect, although the literature has indicated that fly encourages or stimulates microbial populations. studies conducted in the From programme, many answers have been provided. Nevertheless, gaps in our knowledge obtained to many other questions. applications of SLASH whether response to, and from crop to crop and often and the results effect of, high especially on test crop was planted with fine seed, vegetative material or seedlings. findings find application in strategies using SLASH other than purely agricultura!. These ameliorating unlike many inorganic fertilization programmes, have long residual effects, which is clear from the studies conducted. The length of effects is approximately condition of the soil involved and the crops etc.). This finding, months depending on the type and nTOnC:H'I'\/ of cropping (irrigation, multiple important implications for and frequency application of SLASH. In this context the following questions should also addressed: Should heavy applications of SLASH be applied infrequently or lighter applications each year crops? Although, the lifespan of SLASH been 36 months with one heavy application (30% of soil volume), compared to lighter applications (5-10% of the soil volume), no significant differences in were noted. Should applications be incorporated or may top dressings also used? Consistently good results have been obtained when the SLASH applications were incorporated, so that the treatments were able to react with the medium. The use of as a top-dressing, however, remains to investigated. creates favourable conditions for improved root development, which is essential to ensure aboveground plant growth. can provide a 201 good balance of essential nutrients, which are slowly released. Although SLASH is a good source of a wide of nutrients, it often low levels of K, because sludge and fly ash are often K deficient. This aspect emphasizes the need to supplement SLASH with a potassium source. This limitation has the need for further incorporating other material, to as animal manures, which are a good source of K. SLASH also definite potential to improve soil physical properties, but research must be conducted to able to substantiate the visual observations made during this study. An important consideration, which should be kept in mind, is that eliminating water as a limiting growth factor plays an important role in the rate at which soil chemical reactions place. Mine rehabilitation studies, using the ameliorant SLASH to improve degraded mine (soils impacted by acid mine drainage and acidic cover soil used in the rehabilitation process) after open operations can mrnrng important for future application. Results from dry-land crop production studies and mine rehabilitation studies using SLASH as an amendment, to improve poor agricultural soils and degraded mine soils (soils impacted by acid mine drainage and acidic cover soil used in the rehabilitation process), should for large provide valuable information in terms of recommendations application. Sewage sludge, which comes from a source which contains high levels of heavy metals, the concern of translocation to plant material. If sewage sludge with a high heavy metal content is used in the manufacturing SLASH, authorities During the process of of concern about possible heavy metal contamination. manufacture, heavy have been immobilized, and this programme has substantiated this. No significant translocation two hazardous heavy metals (Ni and Cd) or the micronutrient B was measured in maize plant material. The levels measured were within current speCifications but these may be open for review. Uptake by different crop species is important factor to consider. It is recommended that heavy metal and other toxic element analyses be continued on other crop species. 202 Despite the good results obtained with SLASH, guidelines for the effective use of SLASH need to as a compiled, for specific situations or conditions. Nevertheless, of the high amounts of SLASH required for ameliorating soils in an extremely poor condition, such a product should only be used in close proximity to source of individual waste products. Many by-products low intrinsic value, but co-utilization strategies are aimed at producing value added products. Any activity performed on a by product, e.g. loading on trucks, transporting adds an additional cost. economics of utilizing these by products are further complicated by the fact that for many industrial, agricultural or muniCipal wastes, the money spent on dealing with generated is relatively low. However, the fact remains that this money is used to dispose of, or manage the waste, not necessarily waste. Co-utilization products can change the natural resource base, provide value-added products, create new industries and associated employment, and in handling wastes produced by sectors of the population, and being both economically and sociably viable. Thus, production of waste product mixtures can be one of the many tools for achieving sustainability. Future research needs to include: the evaluation of by-products mixtures ensuring an optimal nutrient balance for large scale land application; development of accurate, calibrated analyses of organic and nutrient content; environmental impact of land spreading; economic value of by-products and improved storage and handling of by-products to reduce nutrient loss. Most importantly, logistical difficulties, such as transportation and application and social acceptance issues (which require education of the public, government officials, and the agricultural community) need to be addressed. If the agronomic community can realize the full benefits of co-utilization high quality by-products, these may viewed as the great resources they can be, rather than the difficult disposal problems they are. 203
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