中文摘要：

Sufficient soil phosphorus（P） content is essential for achieving optimal crop yields,but accumulation of P in the soil due to excessive P applications can cause a risk of P loss and contribute to eutrophication of surface waters.Determination of a critical soil P value is fundamental for making appropriate P fertilization recommendations to ensure safety of both environment and crop production.In this study,agronomic and environmental critical P levels were determined by using linear-linear and linear-plateau models,and two segment linear model,for a maize（Zea mays L.）-winter wheat（Triticum aestivum L.） rotation system based on a 22-yr field experiment on a Haplic Luvisol soil in northern China.This study included six treatments:control（unfertilized）,no P（NoP）,application of mineral P fertilizer（MinP）,MinP plus return of maize straw（MinP+StrP）,MinP plus low rate of farmyard swine manure（MinP+L.Man） and MinP plus high rate of manure（MinP+H.Man）.Based on the two models,the mean agronomic critical levels of soil Olsen-P for optimal maize and wheat yields were 12.3 and 12.8 mg kg-1,respectively.The environmental critical P value as an indicator for P leaching was 30.6 mg Olsen-P kg-1,which was 2.4 times higher than the agronomic critical P value(on average 12.5 mg P kg-1).It was calculated that soil Olsen-P content would reach the environmental critical P value in 41 years in the MinP treatment,but in only 5-6years in the two manure treatments.Application of manure could significantly raise soil Olsen-P content and cause an obvious risk of P leaching.In conclusion,the threshold range of soil Olsen-P is from 12.5 to 30.6 mg P kg-1 to optimize crop yields and meanwhile maintain relatively low risk of P leaching in Haplic Luvisol soil,northern China.

英文摘要：

Sufficient soil phosphorus （P） content is essential for achieving optimal crop yields, but accumulation of P in the soil due to excessive P applications can cause a risk of P loss and contribute to eutrophication of surface waters. Determination of a critical soil P value is fundamental for making appropriate P fertilization recommendations to ensure safety of both environment and crop production. In this study, agronomic and environmental critical P levels were determined by using linear-linear and linear-plateau models, and two segment linear model, for a maize （Zea mays L.）-winter wheat （Triticum aestivum L.） rotation system based on a 22-yr field experiment on a Haplic Luvisol soil in northern China. This study included six treatments： control （unfertilized）, no P （NoP）, application of mineral P fertilizer （MinP）, MinP plus return of maize straw （MinP＋StrP）, MinP plus low rate of farmyard swine manure （MinP＋L.Man） and MinP plus high rate of manure （MinP＋ H.Man）. Based on the two models, the mean agronomic critical levels of soil Olsen-P for optimal maize and wheat yields were 12.3 and 12.8 mg kg-1, respectively. The environmental critical P value as an indicator for P leaching was 30.6 mg Olsen-P kg-1, which was 2.4 times higher than the agronomic critical P value （on average 12.5 mg P kg-1）. It was calculated that soil OIsen-P content would reach the environmental critical P value in 41 years in the MinP treatment, but in only 5-6 years in the two manure treatments. Application of manure could significantly raise soil Olsen-P content and cause an obvious risk of P leaching. In conclusion, the threshold range of soil Olsen-P is from 12.5 to 30.6 mg P kg-1 to optimize crop yields and meanwhile maintain relatively low risk of P leaching in Haplic Luvisol soil, northern China.