Integrated nitrogen management based on leaf diagnosis increases yield and fertilizer efficiency of direct-seeding rice

Objectives Direct-seeding rice production has attracted great attentions because of its social and economical benefits. The effects of nitrogen management practice on grain yield and N, P, K absorption and utilization and nitrogen use efficiency of rice under direct-seeding condition were studied with expectation for providing theoretical basis for optimum nitrogen fertilizer management in direct-seeding rice.

Methods A field experiment with super-high-yield hybrid rice (SHYR), ordinary hybrid and inbred rice cultivars were conducted in Chengdu Plain in 2016 and 2017. Both conventional N management (N1) and integrated N management relying on nutrition diagnosis of leaves and without basal fertilizer (N2) were applied on all the four rice cultivars. Grain yield, nutrient uptake, nitrogen use efficiency and NPK requirement for producing 1000 kg grains were measured at maturing stage of rice.

Results In treatment N2, the total N application rate was 33.3%–40.0% lower than that in treatment N1, but there was not significant difference in grain yield between them. The agronomic efficiency, partial factor productivity and recovery efficiency of N fertilizer in treatment N2 were 48.9%, 56.7% and 11.9% higher than those in treatment N1, respectively. The N and K uptake in direct-seeding rice in treatment N2 were 10.8% and 5.8% lower, and the N and K requirements for producing 1000 kg grains were 9.4% and 4.0% lower than those in treatment N1, which were mainly due to the higher N and K harvest index of direct-seeding rice in treatment N2; the P uptake and P requirement for producing 1000 kg grains were similar in treatment N2 and N1. Compared with ordinary hybrid and inbred rice cultivars, SHYR had higher grain yield and NPK uptake. On average, the N, P and K requirement for producing 1000 kg grains of SHYR were 8.9%, 24.3% and 6.5% higher than those of ordinary hybrid, and inbred rice cultivars.

Conclusions Direct-seeding rice shows positive response to the integrated N management relying on nutrition diagnostics at mid- and late stage. The technology could reduce total N input by 1/3 while sustain yield, decrease N and K requirement for production 1000 kg grains, and increase the fertilizer efficiencies significantly. Therefore, the integrated N management technology should be promoted in Chengdu Plain, especially in super-high-yield hybrid rice under direct seeding.