Biological activity and organic matter mineralization of soils amended with biowaste composts

This study aims to elucidate the significance of compost and soil characteristics for the biological activity of compost‐amended soils. Two agricultural soils (Ap horizon, loamy arable Orthic Luvisol and Ah horizon, sandy meadow Dystric Cambisol) and a humus‐free sandy mineral substrate were amended with two biowaste composts of different maturity in a controlled microcosm system for 18 months at 5 °C and 14 °C, respectively. Compost application increased the organic matter mineralization, the C_mic : C_org ratio, and the metabolic quotients significantly in all treatments. The total amount of C_org mineralized ranged from < 1 % (control plots) to 20 % (compost amended Dystric Cambisol). Incubation at 14 °C resulted in 2.7‐ to 4‐fold higher cumulative C_org mineralization compared to 5 °C. The C_mic : C_org ratios of the compost‐amended plots declined rapidly during the first 6 months and reached a similar range as the control plots at the end of the experiment. This effect may identify the compost‐derived microbial biomass as an easily degradable C source. Decreasing mineralization rates and metabolic quotients indicated a shift from a compost‐derived to a soil‐adapted microbial community. The C_org mineralization of the compost amended soils was mainly regulated by the compost maturity and the soil texture (higher activity in the sandy textured soils). The pattern of biological activity in the compost‐amended mineral substrate did not differ markedly from that of the compost‐amended agricultural soils, showing that the turnover of compost‐derived organic matter dominated the overall decay process in each soil. However, a priming effect occurring for the Dystric Cambisol indicated, that the effect of compost application may be soil specific.     

The effect of earthworms on carbon storage and soil organic matter composition in tropical soil amended with compost and vermicompost

The use of organic matter (OM) amendments is widespread in tropical countries and may be beneficial for soil carbon storage. Interactions between earthworms and OM amendments in tropical soils are largely unknown. The aim of this study was to investigate the effect of bioturbation on the quantity and chemical composition of OM in soil amended with compost and vermicompost. Our approach included comparison of soil samples amended with compost, vermicompost or chemical fertilizers in the presence or absence of earthworms during a one-year greenhouse experiment. The soils were submitted to a regular cultivation cycle. After one year, we analysed bulk samples for soil OM elemental composition and characterised its lignin and non-cellulosic carbohydrate components.Our results showed a decrease of the carbon and nitrogen content in soil amended with chemical fertilizers. Vermicompost amendment led to unchanged OC content, whereas the compost amendment increased the soils OC content compared to initial soil. The addition of earthworms reduced OC and N content in soils with organic amendments. This is in contrast to soil amended with mineral fertilizer only, where the presence of earthworms did not have any effect. Bioturbation influenced the lignin signature of the soils, and to a lesser extent the non-cellulosic carbohydrate signature. In conclusion, compost amendment combined with bioturbation influenced the quality and quantity of SOM and as result carbon storage and its biogeochemical cycling in tropical soils. Implications for soil fertility remain to be elucidated.     

Modelling long‐term carbon dynamics in soils reconstituted with large quantities of organic matter

In urban conditions, the widescale availability of organic matter to be recycled and the necessity for soil reconstitution (Technosol) has led to the input of very large quantities of organic matter (up to 50% v/v). The long‐term degradation of these large quantities of organic matter in the soil is not well known. We monitored, over a 60‐month period, the total carbon (C) content and the particulate and biochemical fractions of reconstituted soils placed in 600‐litre boxes under natural conditions. The top layer was a sandy loam amended with 20 or 40% of sphagnum peat or organic compost (sewage sludge, wood chip compost or green waste compost) lying on a layer of sandy loam. We measured C mineralization over time under controlled conditions and built a long‐term model to simulate carbon dynamics where exogenous organic carbon (EOC) was divided into two biodegradable compartments. The model yielded the proportions of EOC that either resisted degradation or contributed to soil organic C storage by mineralization and/or humification. Organic matter degradation was linked to its maturity and to its contents in certain particulate and biochemical fractions but was independent of how much of a given organic matter was introduced. We found a good correlation between the degradable organic compartment and the lignin and cutin‐like, hemicellulose and cellulose‐like fractions larger than 1 mm. The model showed that a large part of initial EOC was still present in the soil after 5 years in a potentially biodegradable but resistant compartment. The degradation of that compartment by mineralization or humification is therefore expected to take longer.     

Artificial soils to assess temperature sensitivity of the decomposition of model organic compounds: effects of chemical recalcitrance and clay‐mineral composition

Understanding the temperature sensitivity of soil organic matter (SOM) decomposition is important to predict the response of soil carbon (C) dynamics to projected global warming. There is no consensus, however, as to whether or not the decomposition of recalcitrant soil C is as sensitive to temperature as is that of labile soil C. Soil C is stabilized by three mechanisms: chemical recalcitrance, mineral interaction and physical accessibility. We used artificial soils with controlled compositions to assess the effects of chemical recalcitrance (cellulose compared with lignin) and clay‐mineral composition with montmorillonite (M) or kaolinite (K) on the decomposition of model organic compounds at 2, 12, 22 and 32°C. When only substrate composition was varied, the presence of cellulose enhanced the decomposition rate of lignin. Treatments with relatively large amounts of cellulose were very sensitive to temperature only at low temperatures (2–12°C), whereas treatments with relatively large amounts of lignin had similar temperature sensitivities at all temperatures. When only clay‐mineral composition was varied, CO₂ production rates were greatest in soils containing kaolinite‐montmorillonite mixtures (10% K:20% M) and least in soils containing kaolinite only at temperatures ≥12°C. Clay mixtures and pure montmorillonite treatments had their greatest temperature sensitivities at 2–12°C, whereas pure kaolinite treatments had the greatest temperature sensitivities at 12–22°C. Temperature sensitivities at the highest temperatures (22–32°C) were all small (Q₁₀ < 1.1 on days 30 and 140). Artificial soils with controlled but flexible compositions may serve as simple and useful models for evaluating SOM dynamics with a minimum of confounding factors.     

Effects of activated charcoal and tannin added to compost and to soil on carbon dioxide,nitrous oxide and ammonia volatilization

Given high mineralization rates of soil organic matter addition of organic fertilizers such as compost and manure is a particularly important component of soil fertility management under irrigated subtropical conditions as in Oman. However, such applications are often accompanied by high leaching and volatilization losses of N. Two experiments were therefore conducted to quantify the effects of additions of activated charcoal and tannin either to compost in the field or directly to the soil. In the compost experiment, activated charcoal and tannins were added to compost made from goat manure and plant material at a rate of either 0.5 t activated charcoal ha^?1, 0.8 t tannin extract ha^?1, or 0.6 t activated charcoal and tannin ha^?1 in a mixed application. Subsequently, emissions of CO₂, N₂O, and NH₃ volatilization were determined for 69 d of composting. The results were verified in a 20‐d soil incubation experiment in which C and N emissions from a soil amended with goat manure (equivalent to 135 kg N ha^?1) and additional amendments of either 3 t activated charcoal ha^?1, or 2 t tannin extract ha^?1, or the sum of both additives were determined. While activated charcoal failed to affect the measured parameters, both experiments showed that peaks of gaseous CO₂ and N emission were reduced and/or occurred at different times when tannin was applied to compost and soil. Application of tannins to compost reduced cumulative gaseous C emissions by 40% and of N by 36% compared with the non‐amended compost. Tannins applied directly to the soil reduced emission of N₂O by 17% and volatilization of NH₃ by 51% compared to the control. However, emissions of all gases increased in compost amended with activated charcoal, and the organic C concentration of the activated charcoal amended soil increased significantly compared to the control. Based on these results, tannins appear to be a promising amendment to reduce gaseous emissions from composts, particularly under subtropical conditions.     

Size Characterization by Laser Granulometry of Colloids Extracted from Compost at Different Temperatures

The objective of this work was to characterize colloids extracted from composts and their potential retention in soils. Compost made of sludge and green wastes was sampled (i) during the fermentation phase and (ii) after maturation. The same kind of compost was used in a long-term field experiment at Feucherolles (France), near Paris where amended and nonamended soils were sampled. The colloidal fraction was extracted from composts in water at room temperature (20°C) and compared to the colloidal fraction extracted from the soil. Composts were also extracted by pressurized hot liquid water at 50, 125 and 175°C. The total organic carbon of the extracts was measured and the particle size distribution (PSD) of colloidal extracts was analyzed by laser granulometry. The diameters of the colloids extracted from the soil ranged between 0.040 and 0.300 μm, independently of the temperature. For composts, it varied from 0.040 to 3.200 μm when extraction was done at 20°C, while at higher temperatures, much more organic matter was extracted, and colloid diameters ranged from 0.040 μm to 0.200 μm. The water-soluble C decreased and the size of colloids recovered in water at temperatures below 50°C increased when compost maturity increased. The adsorption on soils of colloidal particles extracted from composts was characterized. The largest adsorption (up to 30% of the initial soluble C) occurred with the extracts recovered at high temperature, in relation to the more hydrophobic properties of the colloids extracted with hot water maintained in subcritical conditions. After adsorption, the particle size distribution in the colloidal fraction extracted at 20°C moved towards finer fractions; by contrast, the colloidal fraction extracted at 175°C moved towards coarser fractions. The coarsest colloids coming from the soil disappeared during the adsorption experiment, probably because of the coprecipitation with the finest colloids coming from compost.     

Sorption of s-Triazine Herbicides in Organic Matter Amended Soils: Fresh and Incubated Systems

Fresh amendment of soil with sewage sludge and composted sewage sludge resulted in increased sorption of three s-triazine herbicides: atrazine, ametryn and terbuthylazine. The extent of increased sorption (as evaluated by sorption coefficients K_d or K_f) was a function of soil type, such that sorption in amended organic carbon-poor soil (0.4% OC) was more enhanced than in amended organic carbon-rich soil (1.55% OC). Despite significant differences between the organic amendments in terms of humic and fulvic acid content, humin content, soluble organic matter content, total organic matter content, and H/C and O/C atomic ratios, organic matter composition had no discernible effect on either sorption distribution coefficients or on isotherm linearity in amended soils. Soils amended with composted sludge had the same sorption potential as did soils amended with the analogous uncomposted sludge. After incubating soil-sludge mixtures for a year at room temperature, organic matter content decreased to original pre-amendment levels. Sorption coefficients for the three compounds similarly decreased to initial pre-amendment values. Organic carbon normalized sorption coefficients (K_oc) were essentially identical in the soils, amended soils, and incubated amended soils, indicating that sludge and compost derived organic matter does not have a significantly different sorption capacity as compared with the original soils, despite compositional differences.     

13C solid-state NMR assessment of decomposition pattern during co-composting of sewage sludge and green wastes

The fate of organic matter during composting is poorly understood. Therefore, we analysed composts of sewage sludges and green wastes (44 samples representative of 11 stages of biodegradation) by conventional chemical methods: pH, humic (HA) and fulvic acid (FA) content, C, N and organic matter (OM) content, and by ¹³C CPMAS NMR to assess the decomposition process of the organic matter. Chemical changes clearly occurred in two phases: first, decomposition of OM during the first 2 months was characterized by decreased C/N ratios, OM content and increased pH; and second, a humification process with increased HA/FA ratios. NMR spectrum changes confirmed this pattern, with an increase in aromaticity and a decrease in alkyl C. A decrease of syringyl to guaiacyl ratio (S/G), a sign of lignin transformation, also indicated humification during composting. NMR spectroscopic properties of composts were also studied by means of principal components analysis (PCA) and revealed changes according to the degree of compost maturation. The factorial map presents a chronological distribution of composts on the two first principal components. The influences of eight chemical factors on the PCA ordination of composts as monitored by their evolution by NMR were also studied by multivariate analyses. PCA clearly indicated two phases: the rapid decomposition of organic matter followed by the formation of humic‐like substances. The first phase, that is ‘new’ composts, was strongly correlated with OM contents, pH and C/N ratios whereas the second phase, corresponding to ‘old’ compost, was correlated with pH, HA content and HA/FA ratio. These results confirm that knowledge of the formation of humic substances is indispensable to suitable monitoring of the composting process.     

Growth of Date Palm (Phoenix dactylifera L.) in Composts of Olive Oil Mill Waste with Organic Household Refuse

This study highlights the effects of composts of olive mill wastes and organic household refuse with a pH range of 7 to 7.98 and a C/N ratio between 14.9 and 22, to improve the growth and the mineral nutrition of the date palm (Phoenix dactylifera L.). After 7 months of cultivation, plants amended with composts showed higher biomass production than the controls. Compost C1, i.e., the basic compost with no additives phosphate, at 100% and 45% doubled the production of dry matter in comparison with control plants. The rise of root biomass was considerably greater for plants grown with compost C1 without phosphate. In contrast, the shoot biomass was highly significant for composts C2 and C3 enriched with phosphate. The control plants, grown without amendment, showed significantly higher specific root length (SRL) and specific leaf length (SLL). The efficiency of compost application was reflected by the biomass rise, the number of emerged leaves (2.6–4), and the rise in leaf area (3.3 to 6.7 cm²) by improving the mineral nutrition of the date palm. The composts of olive mill waste and organic household refuse supplemented with natural rock phosphate, or not, generated a notable agronomic added value.     

Rice yield nutrient uptake as affected by cyanobacteria soil amendments—a pot experiment

Rice production and cyanobacterial N in acid soil can be improved by liming. There is evidence that the organic amendments can increase the soil pH. The aim of this study was to find appropriate combination of soil amendments and cyanobacteria capable for enhancing nutrient uptake and improving rice yield in acidic paddy soil. Three soil amendments (rice straw, sewage‐sludge composts, NPK) with and without inoculation of cyanobacteria were studied for rice plants (Oryza sativa L.) in a pot experiment. The sludge compost had significantly reduced soil acidity from 5.44 to 6.67. The plant N and K uptake increased significantly with sludge and cyanobacteria application. The yield components increased significantly with sludge, but decreased thereafter, an exception was the number of panicles, with straw compost. These characters were also significantly affected by inoculation with cyanobacteria except 100‐grain weight, filled‐grain percentage, and harvest index. The combination of sludge compost and cyanobacteria improved the yield components and consequently grain yield (138 g pot^–1) compared with sludge treatment only (132 g pot^–1). The amount of cyanobacterial N absorbed (N‐difference method) by rice plant under sludge compost was higher than that of soils amended with either rice straw or NPK treatments. Therefore, the addition of sewage sludge to acid paddy soil not only amended the soil properties but also activated the cyanobacteria and consequently improved rice plant nutrition and grain yield.     

Chemistry of soil organic matter as related to C : N in Norway spruce forest (Picea abies(L.) Karst.) floors and mineral soils

Due to high nitrogen deposition in central Europe, the C : N ratio of litter and the forest floor has narrowed in the past. This may cause changes in the chemical composition of the soil organic matter. Here we investigate the composition of organic matter in Oh and A horizons of 15 Norway spruce soils with a wide range of C : N ratios. Samples are analyzed with solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy, along with chemolytic analyses of lignin, polysaccharides, and amino acid‐N. The data are investigated for functional relationships between C, N contents and C : N ratios by structural analysis. With increasing N content, the concentration of lignin decreases in the Oh horizons, but increases in the A horizons. A negative effect of N on lignin degradation is observed in the mineral soil, but not in the humus layer. In the A horizons non‐phenolic aromatic C compounds accumulate, especially at low N values. At high N levels, N is preferentially incorporated into the amino acid fraction and only to a smaller extent into the non‐hydrolyzable N fraction. High total N concentrations are associated with a higher relative contribution of organic matter of microbial origin.     

Organic Amendment Effects on the Transformation and Fractionation of Aluminum in Acidic Sandy Soil

Addition of organic amendments can alleviate the level of aluminum (Al) phytotoxicity in acid soils by affecting the nature and quantity of Al species. This study evaluated the transformation of Al in an acidic sandy Alaquod soil amended with composts (10 and 50 g kg^?1 soil of yard waste, yard + municipal waste, GreenEdge^®, and synthetic humic acid) based on soil Al fractionation by single and sequential extractions. Though the organic compost amendments increased total Al in soil, they alleviated Al potential toxicity in acidic soil by increasing soil pH and converting exchangeable Al to organically bound and other noncrystalline fractions, stressing the benefits of amending composts to improve acid soil fertility. The single‐extraction method appears to be more reliable for exchangeable Al than sequential extraction because of the use of nonbuffered pH extract solution.     

Carbon and nitrogen isotope composition of bulk soils, particle-size fractions and organic material after treatment with hydrofluoric acid

Soils and sediments contain only small amounts of organic matter, and large concentrations of paramagnetic metals can give poor solid‐state nuclear magnetic resonance (NMR) spectra of organic matter. Pretreatment of samples with hydrofluoric acid (HF) dissolves significant proportions of the mineral matrix and extracts paramagnetic elements. We investigated the effects of 10% HF treatment on the stable isotope content of carbon (C) and nitrogen (N) of organic matter from soils, composts and shales. Additionally we inferred molecular and isotopic characteristics of lost materials from calculations of isotope mass balances. Treatment with HF enriched C and N in mineral samples substantially (factors 2.5–42.4), except for Podzol B horizons (1.1–1.7) and organic material (1.0–1.3). After treatment most of the C (59.7–91.7%) and N (53.7–86.6%) was recovered, although changing C/N ratios often indicated a preferential loss of N‐rich material. Isotope ratios of C and N in the remaining material became more negative when net alterations exceeded 0.3‰. The isotope ratios of the lost material contained more ¹³C (1–2‰) and ¹⁵N (1–4‰) than the initial organic matter. Acid hydrolysis typically removes proteins, amino acids and polysaccharides, all of which are enriched in ¹³C, and in the case of proteins and amino acids, enriched in ¹⁵N as well. We conclude that HF treatment released fresh, soluble, probably microbial, biomass in addition to carbohydrates. Net changes of the bulk chemical composition of organic matter were small for most soils, size fractions and plant material, but not for samples containing little organic matter, or those rich in easily soluble organic matter associated with iron oxides, such as Podzol B horizons.     

Distribution of polycyclic aromatic hydrocarbons in particle‐size separates and density fractions of typical agricultural soils in the Yangtze River Delta,east China

Soil organic matter can be divided into different organic carbon (C) pools with different turnover rates. The organic pollutants in soils associated with these organic C pools may have different bioavailability and environmental risks during the decomposition of soil organic matter. We studied the distribution patterns of 15 USEPA priority polycyclic aromatic hydrocarbons (PAHs) in different particle‐size separates (clay, fine silt, coarse silt, fine sand and coarse sand) and density fractions (light and heavy fractions) of nine agricultural topsoils (0–20 cm depth) from a contaminated area in the Yangtze River Delta region of east China. There was a decreasing trend in PAH concentration in particle‐size separates with decreasing particle size. However, the different particle‐size separates had similar PAH composition. The concentration of PAHs in the light fraction ranged from 13 037 to 107 299 μg kg^?1, far higher than in the heavy fraction, which ranged from 222 to 298 μg kg^?1. Although the light fraction accounted for only 0.4–2.3% of the soils, it was associated with 31.5–69.5% of soil PAHs. The organic matter in coarse silt had the strongest capacity for enrichment with PAHs. Combining the distributions of PAHs and the turnover rates of organic matter in different soil fractions, the environmental risks of PAH‐polluted soils may be due mainly to the PAHs associated with sand and the light fraction.     

Long-term effects of compost amendment of soil on functional and structural diversity and microbial activity

We studied the effects of applying different composts (urban organic waste, green waste, manure and sewage sludge), mineral fertilizer and compost plus mineral fertilizer on chemical, biological and soil microbiological parameters over a 12‐year period. The organic C and total N levels in soils were increased by all compost and compost + N treatments. Microbial biomass C was significantly (P ≤ 0.05) increased for some compost treatments. In addition, basal respiration and the metabolic quotient (qCO₂) were significantly higher in all soils that had received sewage sludge compost. The Shannon diversity index (H), based on community level physiological profiling, showed a higher consumption of carbon sources in soils treated with compost and compost + N compared with the control. The utilization of different guilds of carbon sources varied amongst the treatments (compost, compost + N or mineral fertilizer). Cluster analysis of polymerase chain reaction‐denaturing gradient gel electrophoresis patterns showed two major clusters, the first containing the mineral fertilization and compost treatments, and the second, the composts + N treatments. No differences in bacterial community structure could be determined between the different types of compost. However, the results suggest that long‐term compost treatments do have effects on the soil biota. The results indicate that the effects on the qCO₂ may be due to shifts in community composition. In this study, it was not possible to distinguish with certainty between the effects of different composts except for compost derived from sewage sludge.     

Paddy management on different soil types does not promote lignin accumulation

Paddy soil management is generally thought to promote the accumulation of soil organic matter (SOM) and specifically lignin. Lignin is considered particularly susceptible to accumulation under these circumstances because of the recalcitrance of its aromatic structure to biodegradation under anaerobic conditions (i.e ., during inundation of paddy fields). The present study investigates the effect of paddy soil management on SOM composition in comparison to nearby agricultural soils that are not used for rice production (non‐paddy soils). Soil types typically used for rice cultivation were selected, including Alisol, Andosol and Vertisol sites in Indonesia (humid tropical climate of Java) and an Alisol site in China (humid subtropical climate, Jiangxi province). These soil types represent a range of soil properties to be expected in Asian paddy fields. All upper‐most A horizons were analysed for their SOM composition by solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy and for lignin‐derived phenols by the CuO oxidation method. The SOM composition was similar for all of the above named parent soil types (non‐paddy soils) and was also not affected by paddy soil management. A substantial proportion (up to 23%) of the total aryl‐carbon in some paddy and non‐paddy soils was found to originate from condensed aromatic‐carbon (e.g ., charcoal). This may be attributed to the burning of crop residues. On average, the proportion of lignin was low and made up 20% of the total SOM, and showed no differences between straw, particulate organic matter (POM), and the bulk soil material. The results from CuO oxidation are consistent with the data obtained from solid‐state ¹³C NMR spectroscopy. The extraction of lignin‐derived phenols revealed low VSC (vanillyl, syringyl, cinnamyl) values for all investigated soils in a range (4 to 12 g kg⁻¹ OC) that was typical for agricultural soils. In comparison to adjacent non‐paddy soils, the data do not provide evidence for a substantial accumulation of phenolic lignin‐derived structures in the paddy soils, even for those characterized by higher organic carbon (OC) contents (e.g ., Andosol‐ and Alisol (China)‐derived paddy soils). We conclude that the properties of the parent soil types are more important for the lignin content of the soils than the effect of paddy management itself.     

Changes in organic matter and enzymatic activity of an agricultural soil amended with metal‐contaminated sewage sludge compost

Abstract

The effect of organic amendment with sewage sludge composts of varying heavy metal content on the organic matter content and enzymatic activity of an agricultural soil supporting barley (Hordeum vulgare L.) or lettuce (Lactuca sativa L.) crops was studied. The organic amendments did not improved lettuce growth, the contaminated composts having a negative effect on yield. However, all organic amendments improved barley straw yields although they did not affect grain yields. The addition of the organic materials increased the total carbohydrate content of the soil although this content decreased with cultivation. There was a clearly observed effect of crop type and the degree of heavy metal contamination of the amendment on the most labile carbon (C) fractions (water‐soluble C, carbohydrates, and polyphenolics). In general, soil enzymatic activities were stimulated by addition of sewage sludge compost with low heavy metal content. The compost containing high level of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) inhibited protease‐BAA activity with respect to the other composts. After cultivation, urease activity increased in soil amended with the high dose of composts, regardless their degree of metallic contamination. Both crop type and metallic contamination contained in the organic materials added influenced phosphatase and ß‐glucosidase activity.     

Short‐term effect of biochar and compost on soil fertility and water status of a Dystric Cambisol in NE Germany under field conditions

Crop growth in sandy soils is usually limited by plant‐available nutrients and water contents. This study was conducted to determine whether these limiting factors could be improved through applications of compost and biochar. For this purpose, a maize (Zea mays L.) field trial was established at 1 ha area of a Dystric Cambisol in Brandenburg, NE Germany. Five treatments (control, compost, and three biochar‐compost mixtures with constant compost amount (32.5 Mg ha^–1) and increasing biochar amount, ranging from 5–20 Mg ha^–1) were compared. Analyses comprised total organic C (TOC), total N (TN), plant‐available nutrients, and volumetric soil water content for 4 months under field conditions during the growing season 2009. In addition, soil water‐retention characteristics were analyzed on undisturbed soil columns in the laboratory. Total organic‐C content could be increased by a factor of 2.5 from 0.8 to 2% (p < 0.01) at the highest biochar‐compost level compared with control while TN content only slightly increased. Plant‐available Ca, K, P, and Na contents increased by a factor of 2.2, 2.5, 1.2, and 2.8, respectively. With compost addition, the soil pH value significantly increased by up to 0.6 (p < 0.05) and plant‐available soil water retention increased by a factor of 2. Our results clearly demonstrated a synergistic positive effect of compost and biochar mixtures on soil organic‐matter content, nutrients levels, and water‐storage capacity of a sandy soil under field conditions.     

Retention of Metals in Agricultural Soils After Amending with MSW and MSW-Biosolids Compost

The goal of this study was to measure the As, Cu, Fe, Pb and Zn contents of soils amended with municipal solid waste (MSW) and MSW-biosolids compost and to determine the long-term transport of these metals to lower soil horizons. Lead, Cu, Cd and Zn contents in the composts were 3–20 times more concentrated in the compost compared to the soil at the Calverton, NY, U.S.A. farm. As a result, Pb, Cd, Cu and Zn were elevated in the upper 5 cm soil layer following compost application and the metal enrichment was proportional to the amount of compost applied (21–62 Mg ha^-1). In addition, Pb, As and Cu contents of the non-compost amended Calverton soils were enriched above the tillage depth (20–25 cm). Cu, Pb and As enrichment was attributed to the historical use of sodium arsenite, lead arsenate and copper sulfate insecticides and fungicides. Results of the metal analyses of soil cores collected 16 and 52 months following compost application showed that Cu, Zn and Pb remained confined to the upper 5 cm soil layer. The low water extractable fraction of these metals in MSW and MSW-biosolids compost was a major factor limiting the transport of these metals to lower soil horizons. In contrast, Cd leaching from the upper 0–5 and 5–10 cm soil layers was continuous over the 52 month study period and was attributed primarily to the presence of soluble Cd in phosphate fertilizer initially applied to the Calverton farm soil.