Objectives The purpose of the study was investigating the effects of wheat and faba bean intercropping on the available phosphorus (P) contents in rhizospheric soil and P uptake by crops, in order to increase utilization rates of P fertilizers.

Methods Field trials were conducted on arable red soil in Pilot Base of Yunnan Agricultural University in 2016 and 2017. The tested wheat cultivar was Triticum aestivum L. cv. Yunmai-52 and fafa bean cultivar was Vicia faba L. cv. Yuxidalidou. The three P application rates were: P₂O₅ 0 (P₀), P₂O₅ 45 kg/hm² (P₄₅) and 90 kg/hm² (P₉₀). The planting patterns included mono-cropped wheat (M_W), mono-cropped faba bean (M_F), and wheat-faba bean intercropping (I). The rhizosphere soil samples were taken at tillering, joining, heading, filling and maturity stages of wheat, and at branching, flowering, podding, seed filling and harvesting stages of faba bean every year for determining available P contents in rhizosphere.The grain yields of wheat and faba bean were weighed, and the P contents in aboveground parts of crops were measured. The land equivalent ratios (LER) and phosphorous agronomy efficiencies were calculated.

Results Compared to monocropping, the grain yields of intercropped wheat in P₀, P₄₅ and P₉₀ treatments were increased by 12.5%, 21.7%, and 17.3%, respectively in 2016, while the seed yields of intercropped faba bean were decreased by 16.8%, 11.7%, and 8.2% respectively in 2017. The land equivalent ratio (LER) ranged from 0.95 to 1.18, showing land use advantages of intercropping over monocropping. The yields of intercropped wheat and faba bean were not declined in the P₄₅ treatment, compared to corresponding monocropping in P₉₀ treatment. Intercropping had no significant effect on available P contents in wheat rhizosphere (except at the mature stage in 2016), but decreased those in the faba bean rhizosphere by 20.8%, 44.5% and 18% in 2017 at the branching, flowering and podding stages of faba bean, as compared to those of M_F. Meanwhile, the available P contents in the rhizosphere of intercropped wheat and faba bean under P₄₅ rate were not reduced as compared to those of monocropping wheat and faba bean under P₉₀ rate. The total P uptake by wheat and faba bean were mainly regulated by P rates, not by the planting patterns, and there was no difference in the agronomy efficiency of P fertilizers between mono-cropped and intercropped wheat.

Conclusions Under the tested conditions, intercropping could increase wheat grain yield but decrease faba bean yield, and increase the general land use efficiencies. The intercropping has impact on the available P contents in the rhizosphere mainly at early growth stages of faba bean, so has no effect on the P uptake by crops. Wheat and faba bean intercropping shows potential to reduce P application rate while sustain crop yields and rhizosphere available P.