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Abstract: The effect of three land use types on decomposition of 14C-labelled maize (Zea mays L.) residues and soil organic matter were investigated under laboratory conditions. Samples of three Dystric Cambisols under plow tillage (PT), reduced tillage (RT) and grassland (GL) collected from the upper 5cm of the soil profile were incubated for 159days at 20°C with or without 14C-labelled maize residue. After 7days cumulative CO2 production was highest in GL and lowest in PT, reflecting differences in soil organic C (SOC) concentration among the three land use types and indicating that mineralized C is a sensitive indicator of the effects of land use regime on SOC. 14CO2 efflux from maize residue decomposition was higher in GL than in PT, possibly due to higher SOC and microbial biomass C (MBC) in GL than in PT. 14CO2 efflux dynamics from RT soil were different from those of PT and GL. RT had the lowest 14CO2 efflux from days 2 to 14 and the highest from days 28 to 159. The lowest MBC in RT explained the delayed decomposition of residues at the beginning. A double exponential model gave a good fit to the mineralization of SOC and residue-14C (R 2 >0.99) and allowed estimation of decomposition rates as dependent on land use. Land use affected the decomposition of labile fractions of SOC and of maize residue, but had no effect on the decomposition of recalcitrant fractions. We conclude that land use affected the decomposition dynamics within the first 1.5months mainly because of differences in soil microbial biomass but had low effect on cumulative decomposition of maize residues within 5months. [Copyright &y& Elsevier]

Abstract: Labile soil organic matter (SOM) fractions are especially important because they are more vulnerable to disturbance and play a crucial role for nutrient and carbon cycling. Although water conservation has become increasingly important in rice–wheat rotation, the effects of non-flooded mulching cultivation on labile SOM fractions remain unknown. Based on a long-term field experiment (10 years), we analyzed the impact of non-flooded mulching cultivation and cropping season on labile SOM fractions in a rice–wheat rotation in Chengdu Plain, southwest China. Compared with traditional flooding (TF), the plastic film mulching (PM) and wheat straw mulching (SM) treatments increased dissolved organic carbon (DOC) (42% after rice season and 41% after wheat season), but decreased microbial biomass carbon (MBC) (19% after rice season and 28% after wheat season) and nitrogen (MBN) (17% after rice season and 24% after wheat season) in the 0–5 cm depth. SM increased particulate organic carbon (POC) and KMnO4-oxidizable C (KMnO4-C) contents after both the rice and wheat seasons. Microbial biomass and DOC concentrations were higher for all three cultivations after the rice season than after the wheat season. In contrast, POC contents under PM and SM were higher after the wheat season than after the rice season. In general, results in this study indicate that non-flooded mulching and cropping season significantly influenced labile SOM fractions. The DOC fraction was the most sensitive fraction affected by non-flooded mulching, while POC and PON fractions respond fast within the two cropping seasons. [Copyright &y& Elsevier]

• Maize-based organic amendments were examined after seven years of annual application. • All organic amendments increased SOM in bulk soil and all physical fractions. • Biochar exerted the strongest positive effect on SOC contents and thermal stability. • The majority of the accumulated C and N occurred in the silt + clay fractions. Application of organic amendments and N fertilizer can affect C and N sequestration, however, the degree to which diverse organic amendments and optimal N fertilization for matching demand for high crop productivity contributes to soil organic matter (SOM) of Cambisol in the North China Plain is not fully known. The objective was to evaluate the combined effects of annual maize straw-derived organic amendments (straw, manure, compost, biogas residue, or biochar) and in-season mineral N fertilizer amendment on soil organic carbon (SOC) and total N (TN) accumulation and thermal stability in bulk soils and physically isolated soil aggregate fractions in a long-term field experiment on the North China Plain. Application of organic amendments either alone or with N increased the proportion of macroaggregates (+62 to 137 %), aggregate mean weight diameter (+50 to 106 %), SOC (+38 to 206 %) and TN (+13 to 52 %) contents in bulk soil. The organic amendments and N fertilizer additions also increased SOC and TN contents in each of the isolated fractions: macroaggregates (+119 to 851 % for SOC, +109 to 237 % for TN) and microaggregates (+42 to 192 % for SOC and +30 to 145 % for TN), total fine particulate organic matter (T fPOM, +143 to 891 % for T fPOM-SOC, +129 to 549 % for T fPOM-TN) and total silt + clay within aggregates (53–139 % for SOC and 20–106 % for TN). Biochar resulted in the largest increase in SOC contents and improved soil aggregation without N fertilization, but fertilization greatly decreased these responses. The majority of the accumulated C and N occurred in the total silt + clay fractions, making up 50–90 % of total SOC and 79–96 % of total TN. Total fine POM and total silt + clay within aggregates contributed to 40–78 % and 10–56 % of SOC, 28–60 % and 37–71 % of TN increase between soil with and without organic amendments. Our results suggested that C and N retained in T fPOM and silt + clay fractions within aggregates were important mechanisms for C and N stabilization. Substitution of annual above-ground litter with biochar with or without mineral N fertilizer was the most effective way for SOM build up and stabilization under a wheat/maize system in the North China Plain, while manure, compost and biogas residue resulted in little to no increases of SOM in bulk soils and physically isolated aggregate fractions compared to straw amendment. Besides the effects of each amendment type on SOC, the different recovery rates of the various amendments, which determines the total quantity of each amendment that can be produced, should be taken into consideration in decisions about maize residue management at the regional scale in the North China Plain. [ABSTRACT FROM AUTHOR]

A comprehensive synthesis of 32 long-term experiments in China is performed by comparing yields and SOM contents and their time by nutrient management responses (TNMR) to determine whether and to what extent combined application of organics amendments and fertilizers (organics + fertilizers) can increase productivity and soil organic matter (SOM) content and enhance the sustainability of diverse cropping systems. TNMR is defined as percentage changes over time in yields and SOM contents in external nutrient input treatments relative to initial and control plots and represents the net effects of nutrient management strategies on yields and SOM contents. Organics + fertilizers significantly increased yields over three crops (wheat, maize and rice) on average by 29% relative to sole organics and 8% to fertilizer only. Higher TNMR values in yields were found with organics + fertilizers in the sequence wheat (53%) > maize (40%) > rice (8%). Significant and positive time trends in TNMR of organics + fertilizers in wheat and maize yield may imply enhanced sustainability of cropping systems. Addition of organics (alone or combined with fertilizers) increased SOM contents and their TNMR over fertilizers applied alone. However, benefits varied between organics and organics + fertilizers by land use type. The latter led to higher SOM contents than (for dry land) and similar to the former (for dry-flooded and flooded systems). 2.3 and 1.4 times higher TNMR of organics + fertilizers in SOM content in dry land than dry-flooded and flooded systems implies that dry land was more responsive in SOM content increase upon adoption of organics + fertilizers than the latter. Overall, despite variation in the quantitative magnitude in crop or land use type, compared with application of organics or fertilizers only, a combination of both represents the most effective way to produce more food, build up SOM and enhance sustainability, especially in dry land cropping systems. [ABSTRACT FROM AUTHOR]