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NITROGEN MANAGEMENT

The Ecologically Optimum Application of Nitrogen in Wheat Season of Rice–Wheat Cropping System

^a Dep. of Environmental Engineering, College of Natural Resources and Environmental Science, Zhejiang Univ., Hangzhou, 310029, PR China
^b Dep. of Resource and Environment, Huangshan Univ., Huangshan, 245000, PR China

^* Corresponding author (liang410{at}zju.edu.cn).

Because excessive application of N fertilizer for crop production leads to environmental pollution and low N utility efficiency, a better understanding of the effects of N application rates on crop yields and NO₃–N leaching is required for developing optimum ecological N management that reduces NO₃–N leaching while keeping crop yield. Field experiments at two sites in the Taihu region of China were conducted to study the ecologically optimum application of N in wheat (Triticum aestivum L.) season of rice (Oryza sativa L.)–wheat cropping system. The experiment at either site had five N rates on wheat (0–360 kg N ha^–1 in 90-kg increments) and NO₃–N in leachate were collected by wedge-shaped fiberglass wick lysimeters. At either site, the N-wheat yield quadratic response curve was fitted quite well and a significantly linear relationship between N rates and seasonal NO₃–N masses in leachate was also found. The calculated economically optimum N rate for wheat was more site related than depending on changing growing conditions from year to year, while the ecologically optimum N rate was significantly different both at sites and growing conditions (P = 0.01). The results suggest that applying the ecologically optimum N rates of 120–180 kg N ha^–1 to wheat is beneficial for maximally reducing NO₃–N leaching loss but minimally decreasing yield.

Abbreviations: CVR, cost:value ratio • R-W, rice and wheat