Increased Soil Aggregate Stability by Altering Contents and Chemical Composition of Organic Carbon Fractions via Seven Years of Manure Addition in Mollisols

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Abstract

Mollisols include an abundance of soil organic carbon (SOC) which is easily influenced by fertilization management. Manure addition could enhance soil aggregate stability; however, the dominating factor affecting its stabilization remains controversial. The fertilization practices were initiated in 2012 to investigate the influences of different fertilization managements on the contents and molecular characterization of organic carbon (OC) fractions, and to clarify the underlying mechanism of soil aggregate stability change. NoF (non-fertilizer), CF (only chemical fertilizer), CF + DM (chemical fertilizer plus single dairy manure at 15 t ha−1), and CF + 2DM (chemical fertilizer plus double dairy manure at 30 t ha−1) treatments were established. This research was aimed at exploring the potential mechanism that affects aggregate stability in Mollisols through the variation of contents and chemical composition of OC fractions, and screening out the appropriate fertilization practice on promoting SOC stabilization and crop yield under 7-year manure addition. Compared to CF, 7-year manure addition significantly enhanced SOC content by 17.4–35.9% at 0–10 cm depth, which was evidenced from the contribution of increased aromatic compounds with 4.3–19.9%. Simultaneously, compared with CF, CF + DM and CF + 2DM both significantly enhanced dissolved organic carbon and easily oxidizable organic carbon contents by 12.5–37.7% at a 0–30 cm soil layer. In regard to soil aggregates, the increased OC content and mass percentage of macroaggregates, and the decreased mass percentage of free microaggregates both improved aggregate stability under manure addition at 0-30 cm soil layer, which was proven to be the increment in mean weight diameter (MWD) and geometric mean diameter (GMD) values by 17.6–22.1%. Moreover, CF + DM and CF + 2DM raised aromatic compound amounts of POM fractions within macroaggregates [M(c)POM] by 5.6–11.6% and within free microaggregates (Fm-POM) by 4.3–10%. Furthermore, CF + DM and CF + 2DM both significantly increased maize yield by 5.7% and 4.2% compared to CF, but no significant difference was observed between CF + DM and CF + 2DM treatments. Collectively, physical protection through the occlusion within aggregates of POM might be the central mechanism for soil aggregate stability of manure addition in Mollisols. The manure addition of 15 t ha−1 was the effective management method to enhance SOC stabilization and crop yield in Mollisols.

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Xuejun Liu, Ying. Zhang, Wenxuan Han … (2013)

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4(+)) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3(-)), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.