The long-term (9 years) effect of pig slurry applications vs mineral fertilization on denitrifying activity, N2O production and soil organic carbon (C) (extractable C, microbial biomass C and total organic C) was compared at three soil depths of adjacent plots. The denitrifying activities were measured on undisturbed soil cores and on sieved soil samples with acetylene method to estimate denitrification rates under field or potential conditions. Pig slurry applications had a moderate impact on the C pools. Total organic C was increased by +6.5% and microbial biomass C by ≥25%. The potential denitrifying activity on soil suspension was stimulated (×1.8, P<0.05) 12 days after the last slurry application. This stimulation was still apparent, but not significant, 10 months later and, according to both methods of denitrifying activity measurement (r2=0.916, P<0.01 on sieved soil; r2=0.845, P<0.001 on soil cores), was associated with an increase in microbial biomass C above a threshold of about 105 mg kg−1. The effect of pig slurry on denitrification and N2O reduction rates was detected on the surface layer (0–20 cm) only. However, no pig slurry effect could be detected on soil cores at field conditions or after NO3− enrichments at 20°C. Although the potential denitrifying activity in sieved soil samples was stimulated, the N2O production was lower (P<0.03) in the plot fertilized with pig slurry, indicating a lower N2O/(N2O + N2) ratio of the released gases. The pig-slurry-fertilized plot also showed a higher N2O reduction activity, which is coherent with the lower N2O production in anaerobiosis. 相似文献
Residue retention and reduced tillage are both conservation agricultural management options that may enhance soil organic carbon (SOC) stabilization in tropical soils. Therefore, we evaluated the effects of long-term tillage and residue management on SOC dynamics in a Chromic Luvisol (red clay soil) and Areni-Gleyic Luvisol (sandy soil) in Zimbabwe. At the time of sampling the soils had been under conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR) for 9 years. Soil was fully dispersed and separated into 212–2000 μm (coarse sand), 53–212 μm (fine sand), 20–53 μm (coarse silt), 5–20 μm (fine silt) and 0–5 μm (clay) size fractions. The whole soil and size fractions were analyzed for C content. Conventional tillage treatments had the least amount of SOC, with 14.9 mg C g−1 soil and 4.2 mg C g−1 soil for the red clay and sandy soils, respectively. The highest SOC content was 6.8 mg C g−1 soil in the sandy soil under MR, whereas for the red clay soil, TR had the highest SOC content of 20.4 mg C g−1 soil. Organic C in the size fractions increased with decreasing size of the fractions. In both soils, the smallest response to management was observed in the clay size fractions, confirming that this size fraction is the most stable. The coarse sand-size fraction was most responsive to management in the sandy soil where MR had 42% more organic C than CR, suggesting that SOC contents of this fraction are predominantly controlled by amounts of C input. In contrast, the fine sand fraction was the most responsive fraction in the red clay soil with a 66% greater C content in the TR than CT. This result suggests that tillage disturbance is the dominant factor reducing C stabilization in a clayey soil, probably by reducing C stabilization within microaggregates. In conclusion, developing viable conservation agriculture practices to optimize SOC contents and long-term agroecosystem sustainability should prioritize the maintenance of C inputs (e.g. residue retention) to coarse textured soils, but should focus on the reduction of SOC decomposition (e.g. through reduced tillage) in fine textured soils. 相似文献
This study investigated the effects of mineral-N addition and intensive mixing (analogous to disturbance by plowing) on decomposition of 14C-labelled maize (Zea mays L.) residue and soil organic matter (SOM). Soils were collected from the upper 5 cm of three land use types at Edelweiler, Germany: plow tillage (PT), reduced tillage (RT), and grassland (GL). Soils were incubated for 112 days at 20 °C, with or without 14C-labelled maize residue (4 g DM kg−1 soil), with or without nitrogen (100 mg N kg−1 soil as NH4NO3) and with or without intensive mixing.
The effect of mineral-N on maize residue decomposition differed depending on the stage of decomposition and land use type. Nitrogen accelerated residue decomposition rates in the first 5 days in RT and GL soils, but not in PT soil, and decreased residue decomposition rate in all three land use types after 11 days. At the end of the incubation, N suppressed 14CO2 efflux in RT and PT soils, but not in GL soil. Mineral-N did not increase SOM decomposition independently on the land use types.
Intensive mixing stimulated decomposition of both plant residue and SOM in all three land use types. However, effects were smaller in GL soil than in RT or PT soil, presumably because stronger soil aggregates in GL would have been less affected by mixing and allowed greater protection of SOM and plant residue against decomposition. 相似文献
Forty-seven different animal wastes were characterized using chemical and organic matter fractionation methods (water extraction and Van Soest method) and 224-day incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis were performed to establish relationships between the composition of these wastes and C and N mineralization. Carbon and N contents ranged from 101 to 469 mg C kg−1 dry matter (d.m.) and from 4 to 39 mg N kg−1 d.m. Soluble C and N represented less than 9% of organic C and 1.5% of total N at 20°C, respectively. The C fractions soluble at 100°C or in neutral detergent were larger and represented 14 and 32% of the organic C, respectively. The hemicellulose-like (HEM) and cellulose-like (CEL) fractions contained about 16.5 and 6% of the organic N, respectively. The C distribution in the lignin-like (LIG) and CEL fractions was comparable, but the former contained more N. Carbon mineralization varied from 5 to 62% of the organic C added during the 224-day incubation; 70% of the wastes induced net N mineralization at the end of incubation (from 3 to 51% of organic N). Other wastes induced net soil inorganic N immobilization, from −1 to −31% of the organic N added. Most highly significant correlations were established between the C mineralization and the C present in the water-soluble fraction at 20°C, and the HEM and LIG fractions. Relationships between N mineralization and biochemical characteristics were weak, except with the soluble Van Soest fraction, and highly significant correlations were observed between N mineralization rates calculated at 224 days of incubation and the organic N content or C/N ratio of wastes. Finally, an objective hierarchical classification based on composition criteria and C and N mineralization led to the definition of six different classes of wastes. It permitted differentiation between four composted wastes and intrinsically different wastes (i.e., cattle manures, pig manures, and poultry manures) which could not be objectively regrouped. It also placed some very different types of waste (solid phase from pig slurry separation, pig manures, and composted pig mixtures) in the same class. 相似文献
Dissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water‐soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water‐soluble organic C, WSOC) from seven mineral horizons of three forest soils from North‐Rhine Westphalia, Germany, with demineralized H2O, 0.01 M CaCl2, and 0.5 M K2SO4. We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K2SO4 extracted the largest amounts of WSOC (up to 126 mg C kg–1) followed by H2O followed by CaCl2. The H2O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol–1 cm–1) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water‐soluble organic matter extracted by K2SO4 bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate‐limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous. 相似文献
ABSTRACTCrop wastes or by-products can have the potential to be used as effective amendments to improve agricultural soil quality and/or crop yields subject to appropriate screening and testing. Sugarcane (Saccharum officinarum L.) waste by-products from an ethanol production plant, including boiler ash, filter cake, and vinasse, were applied as soil amendments at 5%, 10%, 20%, and 40% (w/w) to study the relationship between pH and organic matter (OM) on cadmium (Cd) bioavailability and adsorption via organic matter using the Cd sequential extraction procedure. Soil pH was significantly affected by aging of the treatment with boiler ash, filter cake, and vinasse. At the end of the experiment, the Cd concentrations with all treatments were mainly released in the first two extraction steps of the sequential procedure, i.e., most mobile and easily mobilized fractions. Pearson correlation analyses revealed a negative relationship between pH and bioavailable Cd and between OM and oxidizable Cd. The pH reduction induced by the amendments was a major factor affecting soil Cd bioavailability. The effect of OM on Cd fractionation could not be clearly observed and interpreted in this study. 相似文献
Summary This study aimed to establish the effects of Millsonia anomala, a tropical geophagous earthworm common in the humid savannas of Lamto (Ivory Coast), on soil organic matter dynamics over different time scales under laboratory conditions. The texture of casts produced by the worms fed on a shrub savanna soil was not significantly different from that of the soil, which showed that M. anomala ingested soil particles without selection. Physical fractionation of soil organic matter showed that the coarse organic fraction (250–2000 m) was depleted by 25–30% in fresh casts compared to the control noningested soil; this was mainly due to a fragmentation of coarse organic debris. Incubation of casts and a 2-mm sieved control soil under laboratory conditions for more than 1 year showed that the C mineralisation rate was almost four times lower in the casts (3% year-1) than in the control soil (11% year-1). We therefore concluded that on a long time scale M. anomala populations may significantly reduce the decomposition rate of soil organic matter in Lamto savannas. 相似文献
Summary Loss-on-ignition (LOI) and the organic C content have been used to estimate soil organic matter. Organic matter is often estimated from organic C by applying a factor of 1.724. Several authors have examined the relationship between LOI, used as an estimate of organic matter, and C by simple linear regressions. In the present study, this approach was examined in relation to two sets of data. LOI overestimates organic matter in soils with significant proportions of clay minerals because of bound water, and correcting for bound water gives some LOI: C ratios of less than 1. It is concluded that differences in the nature of the organic matter in different soils and horizons make the simple regression approach unsuitable. More attention needs to be paid to studies of the nature of the organic matter. 相似文献