Nitrogen fertilizer management for high yield and high efficiency of rice in the Songnen Plain

Objectives The effects of controlled-release nitrogen fertilizer (CRU) management on rice yield, nitrogen (N) use efficiency and soil N supply in the Songnen Plain were investigated, in order to provide a basis for scientific and efficient CRU management of rice in this region.

Methods Field experiments were conducted in 2021 and 2022 in Songyuan City of Jilin Province, using rice cultivar Dongdao 3 as the test materials. Under the total N rate of 200 kg/hm², no N application (N0), multiple urea topdressing (OPT), and conventional urea fertilization (FP) were taken as controls, CRU basal application plus common urea (CU) topdressing in N ratio of 4:6, 6:4, 8:2 and 10:0 were setup (denoted as CRU40%, CRU60%, CRU80% and CRU100%, in turn). Plant biomass, N content and soil inorganic N content were analyzed during the main growth period of rice. The yield and yield components were investigated at harvest. And N uptake, N use efficiency and N balance in soil-crop system were calculated.

Results Compared with FP treatment, all the fertilizer treatments increased plant N accumulation from full heading to mature stage, plant N accumulation and allocation ratio after full heading stage, and the contribution rate of N accumulation to grain after full heading stage of rice (P<0.05), and CRU80% and OPT were recorded similar but higher values than the other treatments. All the CRU and OPT treatments stabilized seed-setting rate and 1000-grain weight, and increased effective panicle number, grain number per panicle than FP, thereby significantly increased rice yields and net incomes (P<0.05), and CRU80% and OPT increased significantly yield and net incomes than the other treatments as well. The two year average yield of CRU80% was 8.0%, 2.9%, and 4.8% higher than CRU40%, CRU60% and CRU100%, and the average net income was 13.7%, 4.8%, and 7.9% higher, respectively. CRU80% and OPT were also recorded the highest N recovery efficiency, agronomic efficiency and partial factor productivity. N balance in soil-crop system showed that the apparent N loss in CRU80% was similar to that in OPT, but was 16.6%, 8.8% and 8.0% lower than those in CRU40%, CRU60% and CRU100% treatments, respectively. The path analysis results showed that plant N accumulation before and after full heading stage significantly affected on rice yield through affecting effective panicle number, grain number per panicle, and seed-setting rate of rice, the effects of N accumulation after the full heading stage were higher than those before the full heading stage.

Conclusions In the rice production region of Songnen Plain, basal application of 80% CRU combined with 20% CU topdressing as tillering fertilizer, or optimized application of common urea (multiple application) could significantly increase rice yield, net income and N use efficiency, and reduce N loss. Considering the high labor input by common urea, controlled release fertilizer is recommended.