Techniques to reduce P application rate and improve its efficiency in winter wheat-summer maize system on Eum-Orthic Anthrosols in Guanzhong area

Objectives We studied the possibility of decreasing phosphorus (P) fertilizer application rate and improving its efficiency.

Methods The treatments included no P application (CK), recommended P application rate (RP), 15% off RP (85%RP), straw-wrapped P fertilizer application at 85%RP (St85%RP), and 85%RP plus substituting urea with ammonium sulfate (Am85%RP). P fertilizer was broadcast in the RP treatment, and band application was adopted for the other treatments. The crop yield, P fertilizer efficiency, soil P pool, and crop mycorrhizal infection rate were investigated.

Results Compared with CK, all the other treatments except 85%RP significantly increased maize (17.1%−32.6%) and wheat (8.9%−12.8%) grain yields (P<0.05) , and the total yield of maize and wheat (13.1%−22.5%). Compared with RP, P reduction treatments occasionally decreased crop yields, e.g. the maize yield in 2018 and the wheat yield in 2020 under 85%RP. 85%RP, St85%RP, and Am85%RP had (P<0.05) higher P recovery rate, apparent use efficiency, and partial factor productivity than RP. Further, St85%RP recorded significantly higher P efficiencies than 85%RP. Compared with CK, P application (P<0.05) increased the soil available phosphorus (AP) and the microbial biomass phosphorus (MBP) contents. The soil AP and MBP under 85%RP were (P<0.05) lower than RP. St85%RP and Am85%RP did not decrease the soil AP. St85%RP (P<0.05) increased the MBP and the water-soluble phosphorus (WSP) contents. The apparent soil P balance under RP was slightly surplus and was closer to being balanced, while P reduction treatments recorded deficits. Compared with RP, St85%RP and Am85%RP improved the mycorrhizal infection rate of wheat roots.

Conclusions In the winter wheat-summer maize cropping system in Guanzhong, a reduction of 15% phosphate input under the recommended P application rate causes a deficit in the apparent soil phosphorus balance, increasing the risk of yield reduction. Reducing 15% of P fertilizer with straw-wrapped P fertilizer or replacing urea with ammonium sulfate could improve available soil P, microbial biomass P, and the mycorrhizal infection rates of wheat roots, thus improving P absorption and utilization in wheat. In addition to improving P fertilizer utilization efficiency, yield reduction risk caused by P reduction was minimized, which improved crop yield. This indicates that the two treatments are highly efficient regulation techniques for improving P fertilizer efficiency.