Field study on nitrous oxide emissions from upland cropping systems in China

Nitrous oxide is an important greenhouse gas and it is considered that cropping systems may considerably affect N(2)O emissions. A field experiment was conducted to examine N(2)O emissions from three upland cropping systems, which included 0, 1, or 2 legumes cultivated in annual rotations in China. The three cropping systems were as follows: 1) winter fallow followed by summer upland rice, 2) winter rape followed by summer peanut, and 3) winter pea followed by summer soybean. Each cropping system, for both winter and summer crops, included two fertilization treatments 1) N, P, and K application at the local conventional rate, and 2) P and K application at the local conventional rate without N. A total of six treatments consisting of three replicates (5 X 5 m plots) were used according to a random block design in the sub-tropical region (Udic ferrisols) of China. N(2)O emissions were measured frequently from the planting day to harvest day along with the soil temperature and moisture. This experimental design was used to determine the differences in N(2)O emissions between the summer versus winter cropping, the effect of N fertilization, and the effect of legume versus non-legume cultivation. The cumulative N(2)O emissions were 0.86, 1.00, and 0.93 N(2)O-N kg ha(-1) from the winter fallow-upland rice, rape-peanut, and pea-soybean cropping systems, respectively without N application, while from the winter fallow-upland rice, rape-peanut, and pea-soybean cropping systems with N, the emissions were 0.99, 1.45, and 1.27 N(2)O-N kg ha(-1), respectively. The results indicated that both N fertilizer application and legume crop cultivation were one of the most important sources of N(2)O emissions. N(2)O emissions were significantly different among crop species and among cropping systems. This study showed that cropping systems considerably affected N(2)O emissions and that both N fertilization and legume crops contributed to N(2)O emissions.