Effects of Long-Term Mulched Drip Irrigation on Soil Quality in the Northwest China

Abstract

Mulched drip irrigation (MDI) is an efficient irrigation technique that greatly enhanced the availability of soil moisture. Despite it has been widely practiced in many regions, soil quality changes after its long-term application remains largely unknown. In this study, we determined the evolved characteristics of main soil-quality indicators after converting natural saline-alkali ecosystems to cultivated land via MDI, and identified the most sensitive indicators fully reflecting soil quality. Soil samples were collected from 5 independent cotton fields with various MDI starting year (7–22 years), which were both converted from natural saline-alkali soil of Northwest China. And a natural uncultivated land was selected as control. Through total/minimum data set methods and regressive analysis we found that after conversion, soil quality yearly increased until 14 years, due to the improvement of soil structure including bulk density, aggregates stability, and the accumulation of soil nutrients concentration including total carbon, organic carbon, total nitrogen, available phosphorus. As results, during this period soil microbial community was restructured and the microbial activity obviously increased. Besides, soil salinity greatly decreased especially in the first few years, and desalination rate was gradually decreased. Soil quality reached steady-state profile, or even fall after 16–22 years of application of MDI as the accumulation of residual plastic fragments, increasing bulk density, and decline in microbial diversity. We identified microbial activity was the most informative soil-quality indictor form 23 parameters through path analysis, following by bacterial high-quality sequence, fungal Simpson index, and water stability of aggregate. Crop yield increased after conversion closely resulted from the declines of soil salinity and enhancement of seedling survival rate, although the improvement of soil quality lags behind that of yield. Overall, long-term application of MDI promotes soil quality and crop yield, but the accumulated residual plastic fragments and secondary salinization risk the its sustainability.

Keywords: Mulching drip irrigation, Soil Quality, field cotton, salt-affected soil, soil ecology