黏质红壤团聚体稳定性的季节性变化及驱动机制

Red soil has high amounts of aggregate in South of China, and the aggregate stability index (Ka) is better to predict the amount of soil erosion than soil erodibility index (K). But the red soil aggregate stability is a dynamic soil property with seasonal time, which is influenced by soil properties (soil organic matter and fertility levels), management practices (fertilization and cultivation), and climate factors (precipitation and temperature). And the seasonal soil aggregate variation and the driving mechanisms are still not clear. Field study will be conducted to investigate the dynamics of soil water, temperature, and concentration of clayey red soil under different land use and fertilizer treatments. Through field study, aggregate stability seasonal variation and short term dynamics after a rain event will be investigated to explore regulation of aggregate stability variation and the major factors. Besides, a laboratory study will be conducted to simulate the abrupt change of concentration due to fertilizer treatments and rainfall by preparing solution with chemical amendment and other salts at different concentration levels. Through laboratory study, the red soil aggregate swelling, slaking, surface potential, and charge repulsion of particles will be explored to investigate the driving mechanisms of both aggregate water stability and chemical stability variation. The results will be helpful to investigate the red soil aggregate stability seasonal dynamics under different land use and fertilization and to demonstrate the influencing factors and driving mechanisms. The research will also provide theory for soil and water resources use and erosion prediction.

我国南方红壤团聚体含量高，红壤团聚体特征参数Ka较可蚀性K值能更好地预测侵蚀量。但红壤团聚体受自身性质（有机质含量和肥力水平）、管理措施（施肥和耕作）和自然条件（降水和气温）多种因素影响，稳定性随季节动态变化，对其变化规律和驱动机制认识还不充分。本项目通过野外定位试验，监测不同利用方式以及不同施肥制度下的一种黏质红壤的水分、温度、浓度动态，监测团聚体稳定性的季节波动和降雨前后短期变化，探明团聚体稳定性的变化规律与主要影响因素；另一方面通过室内添加结构改良剂，配制盐溶液和设置浓度梯度，模拟田间施肥水平和降雨引起的浓度的瞬时变化，研究该红壤团聚体的膨胀、消散、表面电位、电荷斥力等，从水稳定性和电化学稳定性角度，揭示团聚体稳定性变化的驱动机理。研究结果可探明不同利用方式和施肥制度下的红壤团聚体季节性变化模式，并可望揭示其动态变化的影响因素和驱动机制，为该地区水土资源利用和侵蚀预报提供理论依据。

该项目通过土壤室内培养和田间长期定位监测试验，研究在不同长期施肥和不同植被条件的自然降雨条件下黏质红壤团聚体结构的季节性动态变化规律，并分析影响团聚体季节性动态的内在因素和机理。项目1）明确了不同长期施肥措施和植被类型对红壤含水量的长期季节性动态影响。2）探明了红壤水分动态（含水量和波动幅度）对团聚体稳定性的影响。体现为长期施加有机粪肥增加了团聚体在剧烈水分动态下的稳定性(抑制消散作用)，且土壤大团聚体百分含量（0.25-2mm）显著高于NPK+秸秆、NPK和对照处理；红壤水分动态对不同植被下的团聚体稳定性动态影响规律与在施肥条件下类似，但受植被类型影响。3）初步揭示了土壤水分动态对团聚体的影响是通过间接改变土壤铁氧化物类型、含量及土壤zeta电位进行的。在剧烈水分波动下（粪肥，NPK+秸秆处理），土壤铁氧化物向络合态和非晶态转变，这种形态的氧化物有助于团聚体的形成和稳定；由于土壤水分的波动，土壤溶液的浓度(EC)发生波动并改变土壤的zeta电位，当含水量较低的干旱期EC升高，负zeta电位值降低从而导致< 40 μm的颗粒体积含量很高从团聚体表面脱落，团聚体稳定性降低。项目发表研究论文5篇，其中SCI收录3篇，中文核心期刊1篇，还有1篇暂不属于SCI,具体为：Soil & Tillage Research，Journal of Soil and Water Conservation, Catena, SN Applied Science, 水土保持学报。项目明确了红壤水分波动对团聚体季节性稳定性影响的主要机理，证实了植被和施肥措施都可以通过调控土壤水分调控红壤团聚体性质，丰富了团聚体稳定性变化的驱动机理。