Decreasing hill density combined with increasing nitrogen rate led to yield decline in hybrid rice under low-light conditions

Abstract

Low light is a common environmental factor that adversely affects rice yields. This study was conducted to evaluate the combined effect of hill density and nitrogen (N) fertilizer rate on yield attributes in hybrid rice under low-light conditions. Field experiments were conducted in 2014 and 2015. Two hybrid rice cultivars (Y-liangyou 1 and Luoyou 9348) were grown under combinations of three hill density levels (high, 40 × 10⁴ hills ha^-1; moderate, 27 × 10⁴ hills ha^-1; low, 14 × 10⁴ hills ha^-1) and two N rate levels (high, 240 kg ha^-1; moderate, 143-148 kg ha^-1), and shaded from heading to maturity. Grain yield was highest in the combination of high hill density and moderate N rate and significantly declined with decreasing hill density combined with increasing N rate for both cultivars in both years. Averaged across two cultivars and two years, grain yield declined by about 4% for each 10% decrease in hill density combined with each 10% increase in N rate. A significant reduction in spikelet filling percentage was observed with decreasing hill density combined with increasing N rate in Y-liangyou 1 in 2015 and Luoyou 9348 in 2014. The same trend was observed for grain weight in Y-liangyou 1 in 2014 and Luoyou 9348 in 2015. These results indicate that adopting the practice of decreasing hill density combined with increasing N rate can result in poor grain filling and consequently yield decline in hybrid rice under low-light conditions.

Figure 1

Grain yield in two hybrid rice cultivars, Y-liangyou 1 (A,B) and Luoyou 9348 (C,D), as affected by combinations of hill density and N rate under low-light conditions in 2014 (A,C) and 2015 (B,D). Data describing grain yield (ordinate) are separated by the LSD (0.05) value (the least significant difference at the 0.05 probability level) and color coded. * and ** denote significant relationships between grain yield (y) with hill density (x) and N rate (z) at the 0.05 and 0.01 probability levels, respectively.

Figure 2

Spikelet number (A–D), spikelet filling percentage (E–H), and grain weight (I–L) in two hybrid rice cultivars, Y-liangyou 1 (A,B,E,F,I,J) and Luoyou 9348 (C,D,G,H,K,L), as affected by combinations of hill density and N rate under low-light conditions in 2014 (A,C,E,G,I,K) and 2015 (B,D,F,H,J,L). Data describing yield attributes (ordinate) are separated by the LSD (0.05) value (the least significant difference at the 0.05 probability level) and color coded. * and ** denote significant relationships between yield attributes (y) with hill density (x) and N rate (z) at the 0.05 and 0.01 probability levels, respectively.