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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.
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 models, 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 maize straw (MinP + StrP), MinP plus low rate of farmyard swine manure (MinP + L.Man) and MinP plus high rate of manure .Based on the two models, the mean agronomic critical levels of soil Olsen-P for optimal maize and wheat yield 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.