Effect of mixed basal application of controlled release urea and common urea on the nitrogen uptake, utilization and yield of winter wheat

Objectives We investigated the effect of the mixed application of controlled release urea (CRU) with common urea (CU) on the yield, relocation of accumulated N to grains, and soil nitrate contents at different stage of winter wheat, to serve the efficient production of winter wheat in Guanzhong Plain, Shaanxi Province.

Methods A winter wheat field experiment was conducted in Xianyang, Shanxi Province from 2020 to 2022, the tested CRU is resin coated urea with N release period of 90 days. Two N application amounts 192 and 240 kg/hm² were set up, and five mix ratio treatments were included under each N rate, as: CU control (as basal and topdressing fertilizer, F1), and basal application of CRU and CU in mix ratio of 30%+70% (F2), 50% +50% (F3), 70%+30% (F4), and 100%CRU (F5). At the main growth stages of winter wheat, 0−40 cm deep soil samples were collected with one sample every 10 cm, and at maturity stage, 0−200 cm soil samples were collected with one sample every 20 cm for the determination of nitrate concentration. At the overwintering, regreening, jointing, flowering, and maturing stages of wheat, wheat plants were sampled for the above ground biomass and N content analysis. The plant samples at flowering stage were divided into three parts (ear, stem and sheath, and leaves), and at maturing stage were divided into four parts (grains, glume + rachis, stem + sheath, leaves) for the measurement of N content. And the yield and yield components were investigated at maturing stage.

Results F2 treatment was recorded the highest NO₃⁻-N in 0−20 cm soil layer before regreening stage; F4 and F5 treatment were recorded the lowest NO₃⁻-N at regreening stage, and that in the 80−200 cm soil layer at maturing stage, while achieved significantly higher yield than the other treatments due to the higher number of spikes. F2 and F3 treatments achieved similar yields on average under both N2 and N1 rate. F4 and F5 treatments had higher yields under N2 rate than under N1 rate, thereby their net benefits under N2 increased by 10.08% and 6.41% than under N1 rate, and the N internal utilization efficiency were not changed significantly. Compared with F1, the relocation amount of pre-anthesis N accumulation to grain was averagely increased by 18.63%, and the grain N accumulation increased by16.96% in F4 treatment. The 0−20 cm soil NO₃⁻-N at jointing stage was positively correlated with the relocation amount of pre-anthesis N accumulation to grain. There was a positive (P<0.05) correlation between 0−20 cm soil NO₃⁻-N at anthesis stage and the N transport at pre-anthesis stage and N accumulation at post-anthesis stage.

Conclusions Properly high N accumulation during anthesis stage is beneficial to the relocation of N from vegetative organs to grains, and the increase of winter wheat yield and N utilization efficiency as result. Complete basal application of N 240 kg/hm² in ratio of 70% resin coated urea with 30% ordinary urea could maintain high nitrate concentration in 0−20 cm soil from regreening to anthesis stage of winter wheat, so promoting the total number of stems and spikelet, increasing the plant N accumulation during anthesis period, and leave low NO₃⁻-N in 80−200 cm soil layer at harvest.