Improving phosphorus use efficiency of spring maize by reducing phosphate fertilizer rate and replacing urea with ammonium sulfate in dryland of Northwest China

Objectives Excessive application of P fertilizer in the planting area of Northwest China is common, which resulted low phosphorus (P) use efficiency in spring maize production. The present study aimed to explore the feasibility of reducing the application rate of P fertilizer, and setup an efficient fertilization regime for spring maize production in this area.

Methods A three-year of spring maize field trial was carried out in the rainfed area of Northwest China.The five treatments included no P fertilizer control (CK), farmers’ practice (FP, P₂O₅ rate of 120 kg/hm² and broadcasting), reduced P fertilization pattern (RP, P₂O₅ 70 kg/hm², in broadcasting method), banded P fertilization pattern (BF, P₂O₅ 70 kg/hm², in banding application method) and ammonium sulfate pattern (SA, P₂O₅ 70 kg/hm², in broadcasting method, and ammonium sulfate replaced urea). Plant roots and shoots, rhizosphere soil and bulk soil were sampled at the four- and five-leaf stage and the mature stage of the maize. The soil alkaline phosphatase activity, pH, Olsen-P content and arbuscular mycorrhizal (AM) infection rate were analyzed.The P concentration in grain, bract, spike-stalk, stem and leaf were measured. The length of roots, surface area of roots and root volume were determined by the WinRHIZO root scanning system.

Results Compared to the FP treatment, the maize grain yield and shoot biomass in the reduced P treatments of RP, BF and SA were not significantly different (P > 0.05), but the partial factor productivities (PFP) of P fertilizer were much higher, with an average increase of 68.0%. The maize grain P concentration and P accumulation of RP, BF and SA treatments were decreased by 7.1%‒12.9% and 8.8%‒17.0%, respectively, and the reduction of RP and BF reached a significant level. The recovery rate of P fertilizer was increased in the RP and SA treatments, and the increase in SA treatment was as high as 7.2 percent point (P < 0.05). Reducing P treatments increased the total length of roots, root surface area, fine root length (less than 0.50 mm in diameter) of maize, the SA treatment obtained significant increments of 13.9%‒37.9%, 8.6%‒46.1% and 12.2%‒43.0%, respectively. Compared to the FP treatment, RP and SA treatments increased the AM infection rate, with the significant increase rate of 16.2%‒21.7% at the four- and five-leaf stage of maize; the SA treatment increased the alkaline phosphatase activity significantly and the BF treatment increased the soil available P concentration significantly at the five-leaf stage of maize.

Conclusions In the dryland of northwest China, reducing the application rate of P₂O₅ from current 120 kg/hm² to 70–75 kg/hm² can still ensure the stable yield of spring maize. On basis of this, replacing urea with ammonium sulfate can promote the AM infection rate and the absorption of P, significantly stimulate the growth of maize roots.