Effects of rotational tillage on soil physical properties and winter wheat root growth on annual double cropping area

Rotary tillage is a very common practice in the Guanzhong area. However,many problems occur for winter wheat fields with long-term rotary tillage,including poor soil water vapor transmission and low soil fertility,which are not favorable to winter wheat growth. To solve these problems,a 4-year field experiment was carried out from 2009 to 2012 in Yangling,Shaanxi Province of China,which is an annual double cropping area. The experiment compared three tillage patterns: RT( rotary tillage for 4 years),PNT( a deep plowing followed by a non-tillage year alternation) and SNT( a subsoiling year followed by a non-tillage year alternation). This study evaluated the impacts of the three tillage patterns on soil bulk density,soil compaction across the 0-40 cm soil profile,and winter wheat root growth. Results showed that after the summer maize harvest( October,2013),the soil bulk density under the SNT and PNT treatments significantly( P 0.05) decreased at 0-10 and 10-20 cm compared with the previous treatment,but the soil bulk density significantly increased under the RT treatment at 10-20 cm,with no significant difference at 0-10 cm. The dynamic changes of soil bulk density at 0-10 and 10-20 cm at different times were a measure of the ability of the soil to maintain structural stability. During the whole growth period of the fourth season winter wheat,the variation coefficient of soil bulk densityunder the SNT and PNT treatments at 0-10 and 10-20 cm was lower than that under the RT treatment. The soil compaction under the SNT and PNT treatments at 0-10 and 10-20 cm was also lower than that under the RT treatment.The improved efficiency of the SNT and PNT treatments on soil physics was more evident at 10-20 cm during the late growth period of winter wheat. There was a significant negative correlation between the soil compaction and soil water content under the RT treatment at 0-10 and 10-20 cm,with correlation coefficients of-0.89 and-0.85,respectively,but there was no significant correlation at these depths between the SNT and PNT treatments. This indicated that the soil structure in the RT treatment was more sensitive to the change in environment than in the SNT and PNT treatments. Soil aggregates were decomposed into smaller aggregates and particles during the frequent tillage,and this would be the main factor causing the reduced porosity and poor soil structure performance. The SNT and PNT treatments were more effective in increasing root weight density and root