title: Reducing environmental risk by improving N management in intensive Chinese agricultural systems.
abstract: 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.
authors.affiliation: 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
authors.forename: Xiao-Tang
authors.initials: XT
authors.lastname: Ju
authors.forename: Guang-Xi
authors.initials: GX
authors.lastname: Xing
authors.forename: Xin-Ping
authors.initials: XP
authors.lastname: Chen
authors.forename: Shao-Lin
authors.initials: SL
authors.lastname: Zhang
authors.forename: Li-Juan
authors.initials: LJ
authors.lastname: Zhang
authors.forename: Xue-Jun
authors.initials: XJ
authors.lastname: Liu
authors.forename: Zhen-Ling
authors.initials: ZL
authors.lastname: Cui
authors.forename: Bin
authors.initials: B
authors.lastname: Yin
authors.forename: Peter
authors.initials: P
authors.lastname: Christie
authors.forename: Zhao-Liang
authors.initials: ZL
authors.lastname: Zhu
authors.forename: Fu-Suo
authors.initials: FS
authors.lastname: Zhang
mesh_terms: D000383:Agriculture / Q000379:methods*; D002681:China; D018556:Crops, Agricultural; D004777:Environment; D009584:Nitrogen / Q000737:chemistry*; D012306:Risk
chemical_list: D009584:Nitrogen