Mineralization and volatile loss of nitrogen from soils treated with coal combustion byproducts

There is an increasing need to find a suitable means for disposal of coal combustion byproducts because of the increasing world-wide production of these byproducts. This need has prompted interest in the use of land disposal, but there are concerns that this use may degrade the quality of soil. To determine the influence of coal combustion byproducts on the transformation and fate of soil N and assess the potential impact of land disposal on soil quality, we studied the effects of two combustion byproducts (fly ash and bed ash) applied at rates of 22.5, 45, 90, and 180 Mg ha^-1 on mineralization and volatile loss of N from soil. Studies comparing the influence of the byproducts on these processes showed that whereas fly ash had little influence on the fate of soil N, bed ash caused substantial mineralization of organic soil N and volatile loss of this N as NH₃. Studies monitoring the pH of soils treated with bed ash showed that soil pH increased immediately after this treatment, with values reaching as high as 12.8. These studies indicated that such extreme alkaline conditions caused chemical degradation and volatile loss of as much as 10% of the organic N in soil, and they provide strong evidence that the improper disposal of bed ash on land can have a substantial negative impact on soil quality.     

Effects of liming,fertilization and acidification on pH,soil moisture,and ATP content of soil from a spruce forest in Southern Germany

Short-term and medíum-term effects of liming (CaCO₃), fertilization [5Ca(NO)₃)₂·NH₄NO₃], and acidification on soil bioactivity were measured in a spruce stand in Southern Germany. The experiment was set up in a randomized block design. Acid precipitation lowered the pH, liming increased the pH, while fertilization caused only small alterations in pH values. Significant differences in soil moisture occurred only in the mineral horizons. The soil ATP content of the humus layers decreased in all plots (control included) up to day 100. On all sampling dates, a pronounced decrease in ATP content followed the acidification. Minor decreases in ATP were observed after fertilization, while liming produced no defined effects. Similar trends, but less pronounced, were observed in the mineral horizons. Only a few significant correlations were found between pH values and ATP or between moisture and ATP within a treatment and sampling date. Present address: Institut für Biologie II (Zoologie), RWTH Aachen, Kopernikusstrasse 16, D-52056 Aachen, Germany     

Effects of artificial acidification and liming on the activity of digestive enzymes in Cognettia sphagnetorum (Vejdovsky´, 1878) (Annelida, Enchytraeidae)

The effects of simulated acid rain and acidification, combined with liming, on amylolytic, laminarinolytic and xylanolytic activity in whole body homogenates of enchytraeids Cognettia sphagnetorum were studied under field conditions. Simulated acid rain (pH 2.5) and simulated acid rain with subsequent liming (CaCO₃) were applied to experimental plots in a mixed forest soil. The pH of the soil was lowered by acid treatment (4.3), while the pH increased after liming (6.3) in comparison with the control (4.5). Acidification of soil caused a decrease in enchytraeid body mass and amylolytic activity. In acidified plots after liming, amylolytic activity and laminarinolytic activity increased, while live body mass decreased. The enzymatic activity of enchytraeids depended on season and also indirectly on individual mean mass. Received: 12 February 1996     

Liming effects on soil pH and crop yield depend on lime material type,application method and rate,and crop species: a global meta-analysis

Purpose

The aim of this meta-analysis was to investigate the interactive effects of environmental and managerial factors on soil pH and crop yield related to liming across different cropping systems on a global scale.

Materials and methods

This study examined the effects of liming rate, lime application method, and liming material type on various soil chemical properties and crop yield based on data collected from 175 published studies worldwide since 1980.

Results and discussion

The most important variables that drive changes in soil pH and crop yield were liming rate and crop species, respectively. Soil conditions, such as initial soil organic matter and soil pH, were more important for increasing soil pH in field-based experiments, while lime material type and application method were more important for improving crop yield. To effectively neutralize soil acidity, the optimum liming duration, rate, and material type were?<?3 years, 3–6 Mg ha^?1, and Ca (OH)₂, respectively. Averaged across different crop species, the application of CaO, CaCO₃, Ca (OH)₂, and CaMg (CO₃)₂ increased yield by 13.2, 34.3, 29.2, and 66.5%, respectively.

Conclusions

This meta-analysis will help design liming management strategies to ameliorate soil acidity and thus improve crop yield in agroecosystems.

     

Phosphorus availability to corn from wood ash-amended soils

Wood ash is a residual material produced during biomass burning. In the northeastern United States up to 80 % of the ash is spread on agricultural lands as a liming amendment with the remainder being disposed of in landfills. As well as raising soil pH, wood ash also adds plant nutrients to soil. This study is an examination of the plant availability of the P in 8 different soils amended with one wood ash. Plant availability was assessed by measuring the biomass and P concentration of corn (Zea mays) L.) plants grown in the greenhouse for 28 d in soil amended with either CaCO₃ (control), wood ash to supply 200 mg kg^?1 total P, or monocalcium phosphate (MCP) to supply 200 mg kg^?1 total P and CaCO₃. Both corn growth and P uptake were highest in the MCP treatments, intermediate in the wood ash treatments, and lowest in the controls for all soil types. The soil property which seemed to have the greatest influence on P availability was pH buffer capacity. The soils with the greatest capacity to buffer OH additions also tended to exhibit the greatest absolute P uptake from wood ash-amended soils and the greatest P uptake relative to that from MCP-amended soils. The ability of soil test extractants to predict uptake of P in the three soil treatments was examined. A buffered ammonium acetate extradant overestimated P availability in the ash-amended soils relative to the MCP-amended soils. An unbuffered, acid, fluoride-containing extract provided a measure of P levels that was consistent with P uptake from all soil treatments. In this study the predictive relationship was as follows: P uptake = 0.017× (Bray P, mg kg^?1) + 1.19; r = 0.81.     

Liming Potential of Composts Applied To an Acid Oxisol in Burundi

The adverse effect of soil acidity on plant growth and yield, and the scarcity of commercial agricultural lime (CaCO₃) in Burundi necessitated a search for alternative liming materials. Thus, the liming potential of locally made composts was evaluated in a greenhouse experiment, using an acid Oxisol with sorghum (Sorghum vulgaris) as a test plant. Application rates were 10 g/kg (approximately 20 ton/ha) for the composts and 0, 0.85 and 1.70 g/kg for Verrundi lime. Results showed that the application of lime increased plant growth by reducing exchangeable Al, and by increasing soil pH and available P. So did the composts, which were more effective in correcting soil acidity when they were fresh and enriched with some nutrients during the composting process. Apparently, organic molecules produced by the composts helped to chelate and/or precipitate Al, making the soil more suitable for plant growth. Specifically, an application of 20 ton/ha of composts was equivalent to 0.6 - 1.7 ton CaCO₃/ha, depending on the compost quality.     

Liming effects on some chemical and biological parameters of soil (spodosols and histosols) in a hardwood forest watershed

Acidic lakes and streams can be restored with base application (usually limestone) provided that the base does not wash out before the benefits of alkalization can be realized; liming soils of the adjoining watershed may be an alternative approach. This study was conducted to provide a scientific basis for soil liming. Plots (50 m²) with different limestone dosages (e.g. 0, 5, 10 or 15 Mg CaCO₃ ha^?1) were established on each of two different soils (a Spodosol and a Histosol) in the Woods Lake watershed of the Adirondack Park Region of New York, USA. Six months after soil liming much of the added limestone was still present in both the Spodosol and in the Histosol. Ten months after soil liming results indicated that: (1) soil pH increased (>1 unit) but mostly in the top 1 cm; (2) net N mineralization increased from 9.6 to ca. 15 µg N g^?1 d^?1 and nitrification increased from 2.8 to ca. 8 µg N g^?1 d^?1; (3) denitrification was not affected (98 µg N g^?1 d^?1); (4) CO₂ production potential decreased in the surface soil and as a function of limestone dosage (60 to 6 µmol g^?1 d^?1); and (5) soluble SO ₄ ^2? concentrations in the Histosol were not affected (105 µmol L^?1). Liming acidic forest soils with >5 Mg CaCO₃ ha^?1 may increase the soil's acid neutralizing capacity, which could provide long-term benefits for surface water acidification.     

种植苹果树对渭北果园土壤胶结物质分布的影响

本研究通过系统研究种植果树对土壤胶结性物质的演化规律及其与土壤团聚体稳定性之间关系的影响,探索影响果园土壤团聚体状态的因素,以期为果园科学管理提供理论依据。在渭北旱塬苹果主产区分别选取10 a、20 a的苹果园和农田(冬小麦-夏玉米轮作,对照)各4个,在果树冠层投影范围内距树干2/3处逐层采集0~100 cm土层土壤样品和0~50 cm土层原状土壤样品,研究不同植果年限果园及农田土壤剖面黏粒、有机质、CaCO_3等团聚体胶结物质的分布及其与团聚体稳定性之间的关系。结果发现:在0~100 cm土层范围内,各果园土壤黏粒含量基本随土层深度的增加而递增,且在0~40 cm土层表现为农田10 a果园20 a果园,40 cm以下土层则呈现相反的态势;种植果树相比农田可显著增加0~100 cm土层土壤有机质总储量,但随着种植果树年限的增加,土壤有机质总储量呈递减趋势;在0~100 cm土层土壤CaCO_3总储量表现为10 a果园农田20a果园,但在0~40 cm土层CaCO_3含量及储量表现为10 a果园农田20 a果园,而40~100 cm土层则为20 a果园10 a农田。皮尔森相关分析发现(29)0.25 mm土壤团聚体的数量和平均重量直径(MWD)与土壤黏粒、有机质和CaCO_3含量密切相关,其中机械稳定性团聚体的数量和稳定性主要受土壤中CaCO_3、有机质含量的影响,水稳性团聚体的数量和稳定性主要受土壤中黏粒和CaCO_3的影响。总之,植果显著改变了土壤中黏粒、有机质、CaCO_3的演化过程和趋势,随植果年限增加,果园土壤黏粒和CaCO_3在土壤较深土层淋溶淀积明显;各果园土壤有机质总储量虽然高于农田,但随植果年限增加,有逐渐减少的趋势。可见植果明显加速了渭北黄土塬地土壤的残积黏化和钙化过程,影响着表层土壤团聚作用和底层土壤的紧实化和坚硬化程度。     

Use of crop residues with alkaline slag to ameliorate soil acidity in an Ultisol

Information regarding the interaction between liming agents and crop residues on soil acidity amelioration is limited. A laboratory incubation study was undertaken to investigate the combined application of alkaline slag (AS, the major component is CaO) and crop residues with different C/N ratios and ash alkalinity content. Incorporation of amendments was effective in reducing soil exchangeable acidity and Al saturation and increasing exchangeable base cations (P < 0.05), but the effect of AS on soil pH adjustment was reduced when added with a high amount of residue with a low C/N ratio. Initial increases in soil pH were attributed to the release of alkalinity from the combined amendments and the mineralization of organic nitrogen (N). During subsequent incubation, the soil pH decreased because of nitrification. Crop residues with a high C/N ratio increased N immobilization and reduced net nitrification, resulting in a slight pH decrease. Crop residues with a low C/N ratio resulted in a sharp decrease in soil pH when applied with low levels of AS because of stimulated soil nitrification, whereas high AS had no consistent effect on net nitrification. Hence, compared to the control (pH = 4.21), a large increase in soil pH occurred, especially when peanut straw was applied at 10 g/kg (pH = 5.16). It is suggested that crop residues with high C/N ratio and also combined with a liming agent such as AS are preferred to ameliorate soil acidity. The liming effect of AS is likely to be negated if added in combination with residues with high N contents.     

Effect of pH and calcium content of soil on earthworm cast production in the laboratory

The relative importance of pH and Ca content of soil in determining cast production by Allolobophora caliginosa (Savigny) was evaluated by a mini-frame technique using soil to which increasing amounts of four inorganic Ca salts were added. Whereas soil pH increased with the addition of increasing amounts of CaCO₃ and Ca(OH)₂, it remained constant with increasing amounts of CaSO₄ and Ca(NO₃)₂. Over the range of values studied, cast production increased with increasing pH and Ca level but did not increase with increasing Ca when soil pH was constant. Decreases in cast production were obtained above pH 7.3 with CaCO₃ and above 6.7 with Ca(OH)₂. Separate studies suggested that a high osmotic pressure of the soil solution resulting from the addition of high levels of soluble Ca(NO₃)₂ was responsible for the dramatic decrease in cast production obtained with this salt. The present study has provided useful methods for related studies of the effect of a range of fertilizer materials on earthworm activity.     

Effects of acidification and liming on carbon and nitrogen mineralization and soil organisms in mor humus

The aim was to determine if changes in C and N mineralization after acidification and liming could be explained by changes in the soil organism biomass. Intact soil cores from F/H layers in a Norway spruce (C:N=31) and a Scots pine (C:N=44) stand in central Sweden were treated in the laboratory for 55 days with deionized water (control), weak H₂SO₄ (successively applied as 72 mm of acid rain of pH 3.1), strong H₂SO₄ (applied as a single high dose of pH 1), and lime CaCO₃. Strong acidification reduced C mineralization and increased net N mineralization in both soils. Weak acidification resulted in similar but less pronounced effects. Liming initially stimulated C mineralization rate, but the rates declined, indicating that an easily available C source was successively used up by the microorganisms. Liming also increased net N mineralization in the C:N=31 humus, but not significantly in the C:N--44 humus. Strong acidification generally affected the amounts of FDA-active fungal hyphae, nematodes and enchytraeids more than the other treatments did. The increases in net N mineralization after acidification and liming could only partly be explained by the decreases in biomass N in soil organisms. Mineralization of biomass N from killed soil organisms could at the most explain up to about 30% of the increase in net N mineralization after strong acidification. Most of the effects on N mineralization seemed to depend on the fact that acidification reduced and liming increased the availability of C and N to the microorganisms. Furthermore, acidification seemed to reduce the incorporation of N from dead organisms into the soil organic matter and, thereby, make the N compounds more readily available to microbial decomposition and mineralization.     

Acid soil tolerance of leucaena species in greenhouse trials

Abstract

Lines of Leucaena leucocephala (Lam.) de Wit were grown in greenhouse pots of an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic typic Hapludult) treated with 0 or 3000 ppm CaCO₃ to give final soil pH values of 4.1 and 5.3, respectively. Lines of L. leucocephala, plus those of other Leucaena species, were also tested on an acid, Monmouth soil (clayey, mixed, mesic, typic Hapludult) treated with 0 or 1500 ppm CaCO₃ to give final soil pH values of 4.8 and 6.6, respectively. The major index of acid soil tolerance used was relative root yield (unlimed/limed %).

Relative root yields of 117 L. leucocephala lines on Tatum soil ranged from 34 to 246%. Hence, liming the soil from pH 4.1 to 5.3 was highly beneficial to some lines and highly detrimental to others. Because Tatum subsoil is 89% Al saturated at pH 4.1, line tolerance to unlimed soil indicates tolerance to Al. Causes of yield depression at pH 5.3 were not determined.

On Monmouth soil, in a test involving 148 lines of 6 Leucaena species, relative root yields (unlimed/limed %) ranged from 23 to 386%. The line showing highest tolerance to the acid soil (P.I. 279578) and that showing lowest tolerance (P.I? 281636) are both L,. leucocephala. The majority of lines used on Monmouth soil (124 of a total of 148) were from this species. Average performances of the 6 species indicated that L. diversifolia Benth. (5 lines) was most tolerant to the acid Monmouth soil and liming the soil from pH 4.8 to 6.6 actually decreased root yields. The species L.. leucocephala (124 entries) and L. pulverulenta Benth. (4 lines) were intermediate, and L. lanceolata S. Wats. (3 lines) and I., retusa Benth. (1 line) appeared more sensitive to acid Monmouth soil. The Al saturation of Monmouth soil at pH 4.8 was only 23% (compared with 89% for Tatum at pH 4.1). The major growth limiting factor in acid Monmouth soil is believed to be Al toxicity, but this soil has not been as throughly characterized as has Tatum, and other factors may well be involved in explaining differential tolerances of Leucaena lines on the unlimed versus limed soil.

Results of these studies indicate that Leucaena species and lines within species differ significantly in tolerance to acid soils having high levels of exchangeable Al. Acid soil tolerant lines of Leucaena may be useful in expanding the acreage of this crop on oxisols and ultisols of the tropics and subtropics.     

Effect of soil pH and nitrogen source on nutrient status in peach: I. Macronutrients

Following 13‐year treatments of soil pH and nitrogen (N) source in a peach orchard of North Carolina, the concentration of calcium (Ca), magnesium (Mg), N, phosphorus (P), and potassium (K) in leaves, shoots, trunks and roots, as well as soil pH, soil exchangeable Ca, Mg, and K content, were determined. Through liming, higher soil pH treatment enhanced soil Ca and tissue Ca level. Among six N sources examined, the highest values of soil pH and soil Ca, Mg, and K were detected following poultry manure application. Compared to ammonium sulfate [(NH₄)₂SO₄], calcium nitrate [Ca(NO₃)₂] increased soil pH and soil Ca and K content, but reduced soil Mg. For most of macronutrients examined in peach tissues, the highest levels were found in manure treatment. Mineral N sources containing Ca(NO₃)₂ resulted in high tissue Ca and low tissue N. In the above‐ground tissues, Mg concentration was relatively low following application of mineral N materials containing Ca, K, or sodium (Na). Acid‐ forming N, especially (NH₄)₂SO₄, reduced tissue Ca and P. The magnitude of impact of liming and N source on macronutrients was tissue‐type dependent, with leaves and other new growth the most sensitive ones while trunks seldom responded to the treatments.     

Effects of artificial acidification and liming on biomass and on the activity of digestive enzymes in Enchytraeidae (Oligochaeta): Results of an ongoing study

Summary The effects of simulated acid rain and acidification combined with liming on enzymatic activities in the gut of the enchytraied Fridericia sp. were studied under laboratory conditions. Simulated mild (pH 4.4) and strong (pH 3.1) acid rain was applied throughout a 52-day experiment. Liming, at rates of 1500 and 4000 kg CaCO₃ powder ha^-1, was applied once on the 27th day of acid rain. After 52 days, the treatment effects were determined by analysing changes in the fresh body weight of enchytraeids and the activities of amylase (EC 3.2.1.1), xylanase (EC 3.2.1.8), trehalase (EC 3.2.1.28) and C₁-cellulase (EC 3.2.1.91) in the gut. The effects were significant in only a few instances. After acidification, xylanase and trehalase activities decreased. The changes in fresh body biomass were not significant. Amylase and cellulase activities increased slightly, possibly because the acidification had a stimulatory effect on soil amylolytic and cellulolytic microorganisms. After liming, both xylanase activity and the enchytraeid body biomass decreased. This was the only marked evidence of a negative effect on the enchytraeids. The high amylase, trehalase and cellulase activities that were observed might have been caused by intensive digestion of dead acidophilous microflora.     

Evaluation of two coal-derived organic products in ameliorating surface and subsurface soil acidity

Acidity in the soil surface and subsurface is of major concern in horticulture, cropping and pasture production systems in southern Australia. Broadcast applications of lime to the surface have proved to be ineffective in ameliorating subsurface acidity in the short term. Two calcium-saturated coal-derived organic products, an ‘oxi-product’ (OXPR) and an ‘oxi-fulvate’ (OXFU), were evaluated for use as liming materials with specific consideration given to amelioration of subsurface acidity. The effects of these two organic products and of lime on the chemical composition of the A₁ and A₂ horizons of an acid red podzol were investigated in leaching columns, 20 cm long. OXPR and OXFU supplying 80 or 160 g Ca m^?2 were compared to 160 g Ca m^?2 applied as CaCO₃ and a control receiving no amendments. The effects of CaCO₃ on exchangeable Al and pH were limited to the surface 2 cm. In contrast, the two organic amendments were effective in decreasing exchangeable Al and increasing pH and exchangeable Ca to depth, the extent being a function of amendment and rate applied. The formation of inorganic and organic complexes were assumed to be responsible for the movement of Al out of the column in the leachate, although significant quantities of Al were precipitated in the column. Significant linear regressions were observed between the ionic strength and Al in the leachate. Significant quantities of Mg and K were displaced by Ca and leached from the column; consequently, this loss must be considered against the benefits of decreased exchangeable Al when assessing fertility for plant production.     

Liming effects on some chemical and biological parameters of soil (spodosols and histosols) in a hardwood forest watershed

Acidic lakes and streams can be restored with base application (usually limestone) provided that the base does not wash out before the benefits of alkalization can be realized; liming soils of the adjoining watershed may be an alternative approach. This study was conducted to provide a scientific basis for soil liming. Plots (50 m²) with different limestone dosages (e.g. 0, 5, 10 or 15 Mg CaCO₃ ha^–1) were established on each of two different soils (a Spodosol and a Histosol) in the Woods Lake watershed of the Adirondack Park Region of New York, USA. Six months after soil liming much of the added limestone was still present in both the Spodosol and in the Histosol. Ten months after soil liming results indicated that: (1) soil pH increased (> 1 unit) but mostly in the top 1 cm; (2) net N mineralization increased from 9.6 to ca. 15 µg N g^–1 d ^–1 and nitrification increased from 2.8 to ca. 8 µg N g^–1 d^–1; (3) denitrification was not affected (98 µg N g^–1 d^–1);(4) CO₂ production potential decreased in the surface soil and as a function of limestone dosage (60 to 6 µmol g^–1 d^–1); and (5) soluble SO _inf4 ^sup2– concentrations in the Histosol were not affected (105 µmol L^–1). Liming acidic forest soils with > 5 Mg CaCO₃ ha^–1 may increase the soil's acid neutralizing capacity, which could provide long-term benefits for surface water acidification.     

Spatial heterogeneity in the relocation of added C within the structure of an upland grassland soil

A pulse of ¹³CO₂ was added to the above ground vegetation in an upland grassland to determine the effects of faunal diversity on the flux of carbon to the surface horizons of the soil. Faunal diversity was manipulated by liming and biocide treatments for three years prior to the pulse addition. The relocation of ¹³C within roots and rhizosphere soil was determined by analysis of samples of bulk soil and of specific features identified on soil thin sections on four dates after the addition of the ¹³CO₂ pulse. Analysis of bulk soils showed only a small enrichment in ¹³C and no significant effects of the treatments. Analysis by isotope ratio mass spectrometry of the products of in situ laser combustion of root material and aggregates formed from faunal excrement showed that the distribution of the newly photosynthesised ¹³C is very localised, with large spatial variability in soil and root δ¹³C at scales of less than 1 mm. δ¹³C values ranged from the natural abundance level of around −28‰ to −4.9‰ in roots and to −8.4‰ in aggregates. The small pulse and large spatial variability masked any effects of the liming and biocide treatments in these soils. However, the variability in the relocation of newly photosynthesised carbon may help to explain the large spatial variability found in bacterial numbers at the sub-mm scale within soils and emphasises the importance of the accessibility of substrates to decomposers in undisturbed structured soils.     

Changes in the chemical properties of acid soil and aggregate stability in the whole profile under long-term management history

ABSTRACT

The effects of long-term (1959–2005) liming in combination with cattle manure application on the chemical properties and aggregate stability of acid soil were investigated in the whole soil profile to a 100 cm depth. Investigations were performed in a long-term liming and fertilizing field trial at Vezaiciai Branch of Lithuanian Research Centre for Agriculture and Forestry situated in West Lithuania. The soil of the study site is Bathygleyic Distric Glossic Retisol (WRB 2014) with a texture of moraine loam. Acid soil had been periodically limed and manured at different intensity for 47 years. The experiment involved the following treatments: (1) unlimed and unfertilized (control); (2) unlimed and 60 t ha^?1 manure; (3) limed and unfertilized; and (4) limed and 60 t ha^?1 manure. During the 47-year period, liming was performed using pulverized limestone at a rate 1.0 (by hydrolytic soil acidity) every 7 years. During the whole study period, the soil received 38.7–36.5 t ha^?1 CaCO₃; 840 t ha^?1 cattle manure, 2740 kg ha^?1 mineral nitrogen; 3030 kg ha^?1 phosphorus and 3810?kg?ha^?1 potassium. The data showed that long-term (47 years) periodic liming of different intensities in combination with cattle manure application significantly changed the chemical properties of the whole soil profile. The soil acidification was neutralized in the topsoil and subsoil to the 60?cm depth when the soil had been systematically limed with 1.0 rate every 7 years in combination with 60?t?ha^?1 manure application every 3–4 years. Periodic long-term liming in combination with manuring had a positive effect on the improvement of chemical properties of acid soil profile in the ElB₁ and ElB₂ horizons. The data of the soil structure in the topsoil and subsoil showed that such liming practice together with manuring had a positive effect on soil aggregate stability.     

Changes in soil acidity and the size and activity of the microbial biomass in response to the addition of sugar mill wastes

The effects of additions of three wastes from sugar mills on the properties of two acid soils were investigated. The wastes used were boiler ash and filter cake from a conventional mill and fly ash from a new mill, where filter cake is burnt. Additions of each of the wastes raised soil pH, reduced concentrations of exchangeable Al and total and monomeric Al in soil solution and increased maize yields in a pot experiment. Microbial biomass C and the percentage of organic C present as microbial biomass were decreased by additions of wastes but the effect was less marked at the higher rate of addition. Although basal respiration was decreased or unaffected by the lower rate of addition of wastes it was increased by the higher rate. The metabolic quotient increased in the order: control4⁺ and NO₃^- accumulated during incubation and arginine ammonification rate were all less at the higher rate of addition of each of the wastes. This was attributed to microbial immobilization of mineral N and arginine due to the wide C/N ratio of light fraction organic matter present in the study soil. It was concluded that all three waste materials were effective liming materials but their effect on soil microbial activity was complex.     

Formulation of Environmentally Sound Waste Mixtures for Land Application

Major impediments to the land application of coal combustion byproducts (fly ash) for crop fertilization have been the presence of heavy metals and their relatively low and imbalanced essential nutrient concentration. Although nutrient deficiencies, in particular N, P, and K, may be readily augmented by adding organic wastes such as sewage sludge and animal manure, the indiscriminate application of mixtures to crops can cause excessive soil alkalinity, imbalanced nutrition (P, Mg), phytotoxicities (B, Mn, ammonia, nitrite), and unspecified contamination of the food chain by elements such as As. In this study, nutrient availability data and linear programming (LP) were used to solve these problems by formulating fly ash-biosolid triple mixtures which complied with both plant and soil fertilization requirements, and met existing U.S.A. environmental regulations for total As application in sewage sludge (EPA-503). Thirteen different fly ash samples were LP-formulated with sewage sludge, poultry manure, CaCO₃, and KCl to yield 13 unique mixtures, which were then evaluated in greenhouse pot experiments. Results indicated that normal growth and balanced nutrition of sorghum (Sorghumbicolor L.) and soybean (Glycine max (L.) Merr.) crops were achieved in all mixtures, comparable to a balanced fertilizer reference treatment, and significantly better than the untreated control. Phytotoxic levels of B, NH₃, NO₂ ^-, overliming problems, and excessive As levels which were previously encountered from indiscriminate use of these waste materials, were all well controlled by LP-formulated mixtures. Most fly ash quantities in mixtures were limited by either available B (< 4 kg ha^-1) or total As (< 2 kg ha^-1) restrictions during formulation, while the most alkaline fly ash was limited by its high calcium carbonate equivalence (CCE = 53.9%). These results confirmed that fly ash land application should not be at arbitrary fixed rates, but should be variable, depending on the soil, crop, and particularly the fly ash chemistry.