Effects of Tillage Systems on Labile Fractions of Soil Organic Nitrogen of a Freeze-Thaw Agricultural Area in Northeast China

Abstract

The impact of tillage systems is obvious in the nitrogen mineralization. Few studies have focused on the relationship between labile fraction of soil organic nitrogen (SON) and crop nitrogen absorption under different tillage systems in freeze-thaw agricultural area. In this study, the effects of conventional tillage (CT) and no-tillage (NT) on the labile fractions of soil organic nitrogen and the relationships with the potentially mineralizable nitrogen (N0) at different soil depths in seeding, jointing, filling and maturity seasons over four years (2010, 2011, 2015 and 2016) were explored. It has been demonstrated that the labile fractions of SON and N0 in NT were higher than in CT at 0-5, 0-10 and 0-20cm. N0 was positively and highly related to the medium particulate organic carbon (mPOM-C) (P<0.01) under CT and NT, whereas highly significant and negative correlations (P<0.01) between N0 and medium particulate organic nitrogen (mPOM-N) were detected under both tillage systems at 0-5 and 0-10cm. The difference in these correlations between tillage systems had been found to be the most notable at the 0-5cm depth. The higher SON fractions content would contribute to the nitrogen mineralization potential because of freeze-thaw conditions during the crop growing season.