Appropriate Irrigation Reduction Increases  Soil Aggregate Stability of 20-80 Cm Soil Layer on Greenhouse Eggplant in Mollisols

Abstract

Excessive irrigation and fertilization over a long period of time can damage soil structure and increase the risk of soil degradation. In order to reveal the effects of  irrigation and fertilization reduction on soil water-stable aggregates and organic carbon (OC), a experiment was conducted in a facility vegetable field in Northeast China. Three different treatments were set up: conventional water and fertilizer treatment (WF), 80% conventional fertilizer and conventional water treatment (W80%F), and 80% conventional water and conventional fertilizer treatment (80%WF). The wet screening method was applied to analyse the changes on the OC content and stability of soil water-stable aggregates in different soil layers, as well as the distribution characteristics of OC in soil aggregates. The results demonstrated that the proportion and OC contents of macroaggregates (>0.25 mm) were both higher than that of microaggregates (<0.25 mm) under the three treatments. Compared with WF treatment, W80%F treatment reduced the proportion of large macroaggregates (>2 mm) in the 40-100 cm soil layer, lowered the values of mean weight diameter (MWD) and geometric mean diameter (GMD), and the proportion of >0.25 mm aggregates (R>0.25) values in the 40-100 cm layer, and significantly reduced OC content of aggregates across all sizes in the 0-100 cm soil layer. Whereas, compared with WF treatment, 80%WF treatment significantly increased the proportion of large macroaggregates (>2 mm), MWD, GMD, and R>0.25 values in the 20-80 cm soil layer, and significantly increased the OC content of aggregates in each size in 0-100 cm soil layer. In conclusion, appropriate irrigation reduction can increase the proportion and OC content of large macroaggregates (>2 mm), and thus enhance the stability of aggregates in 20-80 cm soil layer. However, appropriate fertilization reduction exhibited the opposite tendency.

Keywords: Irrigation reduction, Fertilization reduction, Facility vegetable fields, Soil aggregates, Soil organic carbon