Abstract:

To deeply understand the effect of straw returning on soil improvement of low hill citrus orchards, a two-year micro-area field experiment was carried out. Five treatments were set up, including control (no straw), mulch returning, shallow returning, deep plough returning and full layer returning. The effects of different ways of straw returning on soil carbon pool and water content were studied. The results showed that all the straw returning patterns improved soil physical properties, organic carbon content, fertility index and enzyme activity in varying degrees, but their effects on different soil layers were different. Straw mulch returning could only improve the physical and chemical properties of the uppermost part of topsoil, and its improvement on surface moisture condition was better than that of other patterns of returning, but its effect on deep soil was not obvious. Straw deep plough returning could loosen the soil and increase the organic matter input. It could improve the physical properties of soil layers at different depths and the accumulation of organic matter and nutrients at the same time. The effects on soil were stronger than that of straw mulch returning. In general, the effects of straw deep plough returning and full layer returning on soil improvement were greater than that of straw shallow returning, and straw deep plough returning had especially significant effect on increasing the storage of organic carbon and water in deep soil layer. It is concluded that the combination of straw deep plough returning and surface mulch returning could improve the soil properties of citrus orchards in an all-round way. In the early stage of new orchards, straw deep plough returning should be considered, and in the later stage, the straw returning could be gradually changed to shallow returning or mulch returning.

Key words: straw returning pattern, surface coverage, deep plough returning, organic carbon component, water storage capacity