In conclusion, PFM with spring wheat significantly increased grain yield and straw biomass in two growing seasons. However, rainfall and its distribution affected growth and grain yield of spring wheat and crop harvest index. Due to increased P uptake
by spring wheat, PFM significantly reduced the amount of P left in soil. In semi-arid areas, the balance of soil available phosphorus was affected by crop biomass in different growing seasons. We suggest that there are different limiting factors in different situations for soil available phosphorus. Serious competition for soil Olsen-P
existed between crop and soil microbes in the PFM treatment. We also found that PFM on soil significantly promotes the availability of phosphorus to crops in semi-arid areas, especially Ca2-P and Al- P in Pi fractions. Therefore, we suggest that plastic film mulching is more beneficial for reducing P remaining in soil and promoting inorganic P fraction availability to crops in semi-arid areas. We suggest that future research focuses on the mechanism for the effect of PFM on soil P availability and the inorganic P fractions with wheat and other crops. The information from such studies will be useful
for fertilizer decision support system required for improved input use efficiency and crop production in semi-arid areas.