旱地轮作周期经济合理施肥技术研究朱润身高世铭兰晓泉（甘肃省农科院旱农所兰州７３００７０）农业生产是一个动态开放系统，随着田间作物产品的收获和外运，其农业生态系统的平衡便遭到破坏。为了恢复这种平衡，就必须设法将每年收获物从土壤中携出的大量营养物质归还给... Study on Economic and Rational Fertilization Techniques in Crop Rotation Cycle Zhu Run-sheng Gao Shi-ming Lan Xiao-quan (Institute of Dryland Farming, Gansu Academy of Agricultural Sciences, Lanzhou 730070) Agricultural production is a dynamic and open system. With the harvesting and unloading of field crop products, The balance of the system is destroyed. In order to regain this balance, it is necessary to try to return a large amount of nutrients carried from the soil to the ...