Effects of N rate and planting density on nutrient uptake and utilization of hybrid rice under different ecological conditions

Objectives The objective of this study is to explore the suitable N fertilizer rate and planting density of one cultivar under different ecological conditions.

Methods Two-factor split-plot design field experiments with hybrid rice cultivar Jingyou 127 as tested crop were conducted in Deyang City and Luzhou City, Sichuan Province. The main plots were two N rates: medium (N 120 kg/hm²) and high (N 180 kg /hm²). The subplots were three planting densities: low density (12.0 hills/m²), medium density (16.5 hills/m²) and high density (22.5 hills/m²). The grain yield, the uptakes and use efficiency of N, P and K by hybrid rice were analyzed.

Results The soil total N and available N contents in Deyang City is higher than in Luzhou City. Deyang City also has higher average solar radiation, maximum and minimum temperature, larger diurnal temperature difference and higher accumulated temperature during the whole rice growing season. With the same hybrid cultivar, the averaged rice yield, N, P and K uptakes in Deyang site were 19.2%, 24.0%, 3.3% and 9.5% higher than those in Luzhou site (P<0.05), the requirements for P and K nutrients to produce 1000 kg grain yield in Deyang was 15.2% and 8.0% lower than those in Luzhou, and that for N was similar. The consequent N, P and K harvest indices in Deyang were 9.2%, 9.4% and 5.6% higher than in Luzhou. In Deyang. the rice yields were higher with medium N rate treatments, while the N, P and K uptakes were higher with the high N rate treatments. The rice yields, N, P and K uptakes were increased with the increase of the planting density, and the highest grain yield (10.87–11.72 t/hm²) was recorded in the treatment of medium N with high density, but the highest N, P and K uptake were in treatment of high N treatments. The relatively high N, P and K harvest indies in the medium N with high density treatment resulted in lower for N, P and K requirements for producing 1000 kg grain yield. In Luzhou. the rice yields and N, P and K uptakes were increased with the high N rate and increased planting density. The high N and high density combination produced the highest grain yield (9.25–9.85 t/hm²) and relatively high N, P and K uptakes, but similar N, P and K requirements for producing 1000 kg of grain among the six combinations.

Conclusions There were significant differences in the characteristic of N, P and K uptakes and its use efficiency between the two different ecological conditions. The optimum light and temperature is helpful for N, P and K uptake and usage in grain formation, leading to high N, P and K harvest indices. For rice production in Deyang, the optimum combination is N 120 kg/hm² plus density of 22.5 hills/m², and N 180 kg/ hm² plus density of 22.5 hills/m² in Luzhou.