Reducing environmental risk by improving N management in intensive Chinese agricultural systems.
Excessive N fertilization in intensive agricultural areas of China has resulted in serious environmental problems because of atmospheric, soil, and water enrichment with reactive N of agricultural origin. This study examines grain yields and N loss pathways using a synthetic approach in 2 of the most intensive double-cropping systems in China: waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain. When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields but do lead to about 2 times larger N losses to the environment. The higher N loss rates and lower N retention rates indicate little utilization of residual N by the succeeding crop in rice/wheat systems in comparison with wheat/maize systems. Periodic waterlogging of upland systems caused large N losses by denitrification in the Taihu region. Calcareous soils and concentrated summer rainfall resulted in ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems. More than 2-fold increases in atmospheric deposition and irrigation water N reflect heavy air and water pollution and these have become important N sources to agricultural ecosystems. A better N balance can be achieved without sacrificing crop yields but significantly reducing environmental risk by adopting optimum N fertilization techniques, controlling the primary N loss pathways, and improving the performance of the agricultural Extension Service.
Ju
Xiao-Tang
XT
Key Laboratory of Plant and Soil Interactions, Ministry of Education, China, and College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China. juxt@cau.edu.cn
Xing
Guang-Xi
GX
Chen
Xin-Ping
XP
Zhang
Shao-Lin
SL
Zhang
Li-Juan
LJ
Liu
Xue-Jun
XJ
Cui
Zhen-Ling
ZL
Yin
Bin
B
Christie
Peter
P
Zhu
Zhao-Liang
ZL
Zhang
Fu-Suo
FS
D000383:Agriculture / Q000379:methods*; D002681:China; D018556:Crops, Agricultural; D004777:Environment; D009584:Nitrogen / Q000737:chemistry*; D012306:Risk
D009584:Nitrogen