LAUSR

Phosphorus (P) fertilizer application and increasing soil total P can cause environmental issues. Therefore, in the present study an experiment was carried out with optimal P-fertilizer recommendation based on the environmental aspects for two years (2015 & 2016). In 2015, 90 soil samples were collected from agricultural lands of Iran and their environmental P index (EPI) was estimated. Also, through maize greenhouse cultivation, the available P critical level was determined. Then, P requirement for 90 fields was assessed based on EPI and soil available P. In 2016, through an onsite field experiment, the effects of P fertilizer levels on yield were estimated. The results revealed that the farmers are permitted to apply P fertilizer only at 8 fields out of 90 according to EPI. While based on the soil available P, 36 farms of 90 need to receive P-fertilizer, and the farmers can apply P fertilizer only at 4 fields out of 36 according to EPI. Considering EPI with no P application farmers faced a 23% yield reduction. If the farmers are not satisfied with this reduction, increasing EPI with P application should reduce soil erosion. Using a 50 kg ha P2O5 application should reduce soil erosion from 7 to 2 ton ha.