Impact of incorporating wheat straw together with basal nitrogen ratio on panicle formation and grain yield in rice

Increasing spikelets differentiation, reducing their degradation and promoting big panicle formation are crucial approaches to increasing grain yield in rice. Straw incorporation and nitrogen (N) application have vital effects on rice yield, but the influence of incorporating wheat straw with N fertilizer ratio on spikelet differentiation, degeneration, and grain yield in rice is not clear. In this experiment, hybrid rice Fengyouxiangzhan (FY) and Yongyou 2640 (YY) were used as materials. Under the condition of total nitrogen application rate of 270 kg ha^{- 2}, the effects of local farmers' fertilizer practice (FP, basal fertilizer: tillering fertilizer: panicle fertilizer = 5: 1: 4) and improving basal fertilizer proportion (IP, basal fertilizer: tillering fertilizer: panicle fertilizer = 7: 1: 2) on the grain yield, branch and spikelet differentiation and degeneration of the above rice varieties were studied under the conditions of non-wheat straw returning (NR) and wheat straw full returning (WR). The 2-year (2020-2021) results in field trials showed that: (1) under NR, compared with FP, although the panicles per unit area were increased, the spikelet number per panicle, filled grains, and grain weight decreased to varying degrees, and finally the grain yield decreased significantly in IP. Under WR, although the filled grains and grain weight were decreased in IP treatment, the total spikelets (panicles per unit area × spikelet number per panicle) was increased significantly, and the grain yield was finally increased significantly compared with FP, with an increase of 6.85 ~ 7.08%. (2) There was a strong positive link between the total spikelets and grain yield, but a substantial negative relationship between the total spikelets and the number of filled grains and grain weight. (3) Straw treatment and nitrogen treatment mainly affected the spikelet number per panicle by affecting the differentiation and degeneration of secondary branches and spikelets. Under WR, IP increased the differentiation number of secondary spikelet in the middle and basal parts of FY by 22.0% and 30.9% with FP, respectively, but also increased the number and rate of secondary spikelet degeneration in the middle and basal parts. Under IP, compared with NR treatment, the differentiated number, degenerated number, surviving number, and degradation rate of the middle and basal parts of the secondary spikelets in the two varieties were increased in WR treatment. Overall, these results demonstrated that under WR, IP was beneficial to increase effective panicle numbers and the spikelet number per panicle. More secondary spikelet differentiation in the middle and basal parts per panicle was a main reason for increasing the spikelet number per panicle to increase grain yield under IP treatment.