Long term impact of different soil management on nitrogen supplying potential in rice based cropping system

A long term experiment was conducted to investigate the impact of different tillage and fertilization on the N mineralization potential of soils in rice based cropping system. The results showed that the nitrogen release potential in both of tilled and no tilled soils at the depth of 0 to 5cm was relatively lasting. The nitrogen release potential of tilled soils at the depth of 5 to 15cm revealed greater than no tilled soils. Fallowed soils at the depth of 0 to 5cm had remarkable higher No and N mineralized in short period (Nm) in no tilled soils (NT) than tilled soils (CT). But no evident differences of No and N m in soils at the depth of 5 to 15cm and 15 to 30cm between these two tillage methods were found . There was a trend that No and Nm in soils of treatments CF (only chemical fertilizer),PM (pig manure +chemical fertilizer) and CS (crop straw+chemical fertilizer) were higher under NT than under CT. No and Nm in no tilled soils at the depth of 15 to 30cm were greater than tilled soils. While the No and Nm between no tilled and tilled soils at the depth of 15 to 30cm did not differ significantly. N uptake by 25 crops in PM and CS treatments under NT was almost the same as that under CT, but in CK (no fertilizer) and CF treatments N uptake for NT was less than for CT. Under no tillage system, No and Nm in soils with combined fertilization (PM and CS) kept higher than CF and CK treatments while CK treatment was the lowest one, however, under fallow condition, No and Nm in soils normally showed very high;under tilled system , No and Nm for PM and CS were the highest among the all fertilization treatments. These differences mainly existed in the soils of the depth of 0 to 5cm.