Effects of Tillage Practices and Straw Management on Physical Properties of Mollisols, Root Architecture and Maize Yield in Northeast China

Tillage practices and organic amendment are strategies used worldwide to preserve the properties and fertility of soils.This study aimed to elucidate effects of 3-year field treatments of tillage practice and straw management on physical properties of Mollisols, root architecture and maize yield in northeast China. The experiment was conducted from 2015 to 2018 following a splitplot design of a randomized complete block with tillage practices rotary tillage（R） and deep tillage（D） as main plots and straw managements straw returning（S）, straw returning and organic fertilizer（M）, straw removal（T） as subplots. Soil samples at 0-15,15-30, 30-50 cm depths and root samples at the seedling stage were collected. The results showed that DM treatment significantly improved soil moisture content at 10-50 cm soil depth and decreased soil compaction（P＜0.05）, which led to a better root architecture.Rotary tillage had a slower thermal conductivity but better thermal insulation performance, while deep tillage showed a higher daily temperature difference. Bulk density of topsoil was significantly lower in DS(1.16 g·cm^-3) than in other treatments, but the soil permeability in DS(1.40 mm·min^-1 in 0-15 soil depth and 1.45 mm·min^-1 in 15-30 cm soil depth) was the highest. At the maize seedling stage, DM had the highest root dry weight, root-shoot ratio and root length, while RM had the highest root volume, root furcation number and root tip number. The maize yield of three years in DM was 6.19%, 5.21% and 15.72% higher than that in DS,DT and RM（P＜0.01）, respectively. Relative to RT and DT, a slight decrease（2.72% and 0.93%, respectively） in maize yield under RS and DS was observed, which could be alleviated by the addition of organic fertilizer. The correlation matrix indicated that kernel per ear number and 100-kernel weight were the dominant factors that affected maize yield. Redundancy analysis suggested that straw managements and tillage practices were significantly positively correlated with root-shoot ratio, root dry weight, maximum root length, the total root length and maize yield, but significantly negatively correlated with soil compaction, bulk density, soil moisture content and soil temperature. Among all the treatments, deep tillage with straw returning and the addition of organic fertilizer was recommended as a promising strategy in restoring soil productivity, promoting maize growth and increasing maize yield in Mollisols of northeast China and similar regions around the world.