Objectives We investigated the effects of nitrogen and potassium partition ratios on the dry matter accumulation and translocation, nutrient uptake and utilization, and yield formation in mechanically direct-seeded rice.

Methods A two-factor split-plot experiment was carried out in the experimental field of Rice Research Institute of Sichuan Agricultural University in Chongzhou City in 2018 and 2019, respectively. F You 498, a mechanical direct seeding rice cultivar, was used as the test materials. The main plots were two K fertilizer application ways at base to spike fertilizer ratio of 10∶0 (K1) and 5∶5 (K2); and the split plots were three nitrogen fertilization modes at base : tiller : spike ratio of 7∶3∶0 (N1), 5∶3∶2 (N2) and 3∶3∶4 (N3). Both the total amount of nitrogen and potassium fertilizer were 150 kg/hm². At full tillering, jointing, spike flushing, and maturing stage, rice plant samples were collected for analysis of dry matter accumulation, N and K absorption, and the transportaion rate of dry matter and nutrients were then calculated. At the maturity stage, rice yield and the yield components were investigated.

Results Compared with K1 on the two-year average, K2 treatment increased rice yield by 4.44%, enhanced the total dry matter accumulation by 4.91% and 2.61% at the full heading and maturing stages, respectively, increased the apparent export rate of dry matter from stems and leaves, stem sheaths, leaves, and the harvest index by 8.61%, 7.44%, 12.91%, and 4.12%, respectively. K2 treatment promoted the absorption and utilization of N and K by rice. The spike N and K contents under K2 treatments were increased by 8.01% and 16.04%, compared with K1 on two-years of average. Among the three N rates tested under K2 treatment, the N2 rate stood out with a two-year averaged grain yield that was 10.56% and 6.42% higher than that of N1 and N3, respectively. Notably, N2 also exhibited the highest 1 m² effective panicle number, grain number per panicle, and total spikelet number. At the full heading stage, the dry matter accumulation and translocation ratio in N2 were 21.37% and 10.28% higher than in N1, and 15.76% and 7.05% higher than in N3. N2 treatment increased the total N and K accumulation and their harvest indices, with an enhancement of the apparent N transport amount by 17.59% and the spike N accumulation by 29.23% when compared to N1, and an enhancement by 9.06% and 18.89% when compared with N3 treatment. The apparent K transport amount and transport rate in N2 were 18.46% and 6.60% higher than in N1 treatment, and 27.80% and 24.57% higher than in N3 treatment.

Conclusions When applying the same amount of nitrogen and potassium fertilizer to mechanically direct-seeded rice, using a fertilizer ratio of 5∶5 for potassium (base fertilizer to panicle fertilizer) and a ratio of 5∶3∶2 for nitrogen (base fertilizer to tillering fertilizer to panicle fertilizer) can significantly increase the total nutrient uptake. This ratio also facilitates the translocation of nutrients and dry matter to the panicles during the later growth stages of rice, thereby improving the utilization efficiency of nitrogen and potassium and ultimately increasing rice yield.