Effects of conservational tillage measures on distributions of organic carbon and nitrogen in soil microaggregates

A seven year location experiment in the condition of wheat-corn rotation of Lou soil in Guanzhong plain was conducted. The effects of the subsoiling, rotary tillage and no-tillage on the distributions of micro-aggregates and the contents of organic carbon and nitrogen in soil micro-aggregates were studied. The results show that the compositional proportions of soil characteristic micro-aggregates are increased under the rotary tillage with straw pulverizing and the subsoiling with straw mulching, while there are little effects on the proportion under the conventional tillage (plow and rotary tillage) with straw incorporated and no-tillage. Compared with the conventional tillage, the subsoiling and rotary tillage could increase the contents of organic carbon and nitrogen in 0.05-0.25 mm and 0.01-0.05 mm micro-aggregates, and the no-tillage could decrease the contents of organic carbon and nitrogeni in 0.01-0.05 mm micro-aggregates. The rotary tillage, subsoiling and no-tillage have little effects on the contents of organic carbon and nitrogen in <0.01 mm micro-aggregates. The correlation analysis demonstrates that the total soil organic carbon is related to the contents of organic carbon and nitrogen in 0.05-0.25 mm and 0.01-0.05 mm micro-aggregates and is not related to the contents of organic carbon and nitrogen in <0.01 mm micro-aggregates. Total nitrogen in soil is significantly correlated to the contents of organic carbon and nitrogen in 0.05-0.25 mm micro-aggregates. The contents of organic carbon and nitrogen in 0.01-0.05 mm micro-aggregates are significantly correlated to soil total nitrogen. The contents of organic carbon and nitrogen in <0.01 mm micro-aggregate are not correlated to those of the other sized micro-aggregates. Considering the distributions of organic carbon and nitrogen in soil micro-aggregates, the rotary tillage and subsoiling are the recommended tillage measures in Guanzhong plain.