2.2 Experimental design
The long-term experiment was set up in 2003 using a randomized complete block design with three replicates. Each plot size was 5 m × 5 m, the crop was continuous spring maize and there was a fallow period from November to March.
Three N fertilizer rates were applied under two tillage treatments in this study and the two tillage practices were CT (conventional tillage with maize stalk removed after harvesting, plowed twice to about 25 cm depth using moldboard plow after harvesting and before seeding, and fertilized before plow in April) and NT (no-tillage with the maize stalk mulched after harvesting, then seeded with a no-till planter and N fertilizer were applied in small holes between two maize in each row in April). The three N fertilizer rates were N1 (105 kg N ha-1), N2 (180 kg N ha-1), and N3 (210 kg N ha-1) using urea. The row and plant spacings were 60 and 30 cm, respectively.