Importance of soil structure, carbon translocation and crop residue quality for carbon storage in cropland soils

农田土壤可能是大气中二氧化碳的汇或源。一般认为土壤碳输入量与土壤有机碳（SOC）水平呈线性相关。这就引起了有关清除作物残留物的环境问题。近年来的研究表明，残留物的掺入对土壤有机碳水平的提高作用很小。在德国Puch精心设计和记录的长期实验中，观察到的二次关系与预测（Rothamsted Carbon模型26-3）碳输入（1-5 Mg C ha-1年-1）与SOC变化的关系相矛盾。该项目的目的是通过考虑土壤结构、氮有效性和碳饱和度效应来寻找观察到的关系的解释。可控的短期培养实验、物理、生物和化学分馏方法以及土壤结构特性的发展将与田间试验的控制较少但长期的结果有关。在本案例研究中，解释预测与观测之间的偏差将是设计气候友好型和经济上合理的农业，同时保持物理、生物和化学土壤肥力的重要一步。

Cropland soils may be a sink or source for atmospheric CO2. In general, it is assumed that C-input into soil and soil organic carbon (SOC) levels are linearly related. This gives rise to environmental concerns regarding the removal of crop residue. In recent years it has been shown that residue incorporation increases SOC levels only to small extents. In the well designed and documented long-term experiment of Puch, Germany, an observed quadratic relationship contradicted the predicted (Rothamsted Carbon model 26-3) relationship of C-input (range of 1-5 Mg C ha-1 year-1) and SOC changes. The purpose of the proposed project is to find explanations for the observed relationships by considering soil structure, nitrogen availability, and carbon saturation effects. Controlled short-term incubation experiments, physical, biological and chemical fractionation methods and development of soil structural properties will be related to the less controlled, but long-term, findings of the field experiment. Explaining the deviations between prediction and observation in this case study will be an important step in designing a climate friendly and economically sound agriculture while sustaining physical, biological and chemical soil fertility.