Effect of nitrogen management and cultivation method on grain-filling characteristics and grain yield of indica hybrid rice

The effects of nitrogen managementratios of transplant-tiller to panicle of N-fertilizer were 9:1 (N₁), 7:3 (N₂) and 5:5 (N₃) and cultivation method (C₁, wide and narrow row cultivation; C₂, triangular cultivation; C₃, wide row and narrow space cultivation; and C₄, seedling-throwing cultivation) on sink potential, grain-filling properties and grain yield were studied in two widely variable ecological conditions (Wenjiang and Hanyuan in Sichuan Province) using indica hybrid rice 'Ⅱ-you-498'. The aim of the study was to clarify the correlation among ecological conditions, nitrogen management and cultivation method with grain-filling properties and grain yield formation. The results were as follows:1) Grain sink potential, grain plumpness, seed setting rate and 1000-grain weight in Hanyuan were better than those in Wenjiang. Furthermore, it was easy to have high yield with low initial growth vigor due to delayed date for peak grain-filling rate, high grain-filling rate and long grain-filling duration at early and middle stages and long active grain-filling period in Hanyuan. 2) With increasing nitrogen application ratio at the late stage, the maximum sink potential decreased while grain-filling indexes, seed setting rate and 1000-grain weight increased. The initial growth vigor reduced at grain-filling, and the maximum and mean grain-filling rates (G_max and G_mean) increased. Also, the time to reach peak grain-filling delayed with higher proportion of growth while the duration of grain-filling shortened. The highest yield was under N₂. 3) There were little differences in seed-setting rate and 1000-grain weight but significant differences in biomass yield, sink potential and grain-filling characteristics among different cultivation methods. For the highest yield performance under different cultivation methods, there were similar grain-filling characteristics, such as larger sink potential, lower initial growth vigor at grain-filling, delayed time to reach maximum grain-filling and higher G_max and G_mean. The wide and narrow row cultivation, triangule cultivation, wide row and narrow space cultivation and seedling-throwing cultivation had the highest yield when the ratio of transplant-tiller and panicle N-fertilizer was 9:1, 9:1, 7:3 and 5:5, respectively. Triangular cultivation had the highest yield among the four cultivation methods. 4) Correlation analysis showed that with increasing maximum sink potential, initial growth vigor at grain-filling and delayed time to reach maximum grain-filling rate decrease. The high grain yield obtained was attributed to increasing duration of grain-filling, grain-filling rate and growth increment, especially in the early and middle stages. Thus any further improvement in rice yield depended on local ecological conditions and cultivation methods, combined with optimized nitrogen management.