Nitrous oxide emissions from an intensively cultivated maize-wheat rotation soil in the North China Plain.

N2O emissions from a maize-wheat rotation field were monitored in the Fengqiu State Key Agro-Ecological Experimental Station (Fengqiu County, Henan Province, China) from June 2004 to June 2005. The experiment included four treatments: a bare (crop-absent) soil treated with 150 kg N ha-1 (WN150) and soils fertilized with 0 (N0), 150 (N150), and 250 (N250) kg N ha-1 and cropped with maize or wheat. The bulk of the N2O emissions occurred in pulses following the application of fertilizer N at soil temperatures of 15 degrees C or more. The application of fertilizer N significantly increased the N2O emission, from 636 g N2O-N ha-1 year-1 in the N0 treatment to 4480 g N2O-N ha-1 year-1 in the N250 treatment. However, this increase primarily occurred during the maize growing season. The emission factor of applied fertilizer N as N2O was 1.05-1.34% and 0.24-0.26% during the 105-day maize and 241-day wheat growing seasons, respectively, and was on average 0.61-0.77%. Increasing the rate of fertilizer application increased the emission factor during the maize growing season. The presence of maize appears to increase N2O emission by 45% versus bare soil during the maize growing season. And, N2O emission during the maize season were significantly related to CO2 production (R=0.43-0.81, n=30, P<0.05). N2O emission was greatly affected by soil moisture during the maize growing season and by soil temperature during the wheat growing season. The maximum rates of nitrification occurred when soil moisture was in the range of 45-60% WFPS, with the optimum value being approximately 50%. However, soil moisture influenced N2O emission only when the soil temperature was at the optimum level. It is suggested that reducing the application rate of basal fertilizer N during the maize growing season could decrease N2O emission.