Effect of organic-inorganic fertilizer application ratio on rice grain weight and seed-setting rate at different positions of rice spike

【Objectives】The effects of long-term organic-inorganic fertilization on rice grain weight and seed-setting rate at different positions of rice spike were evaluated through the analysis of the samples from a long-term field experiment.【Methods】A field experiment with indica rice cultivar 926 as test material was conducted in Jiangxi Province, and the spike samples were collected from different parts after harvest. Four treatments i.e. mineral N, P and K (NPK), 70% chemical fertilizers plus 30% organic manure (70F＋30M), 50% chemical fertilizers plus 50% organic manure (50F＋50M), and 30% chemical fertilizers plus 70% organic manure (30F＋70M) were selected for the investigation from the 30-year long-term field experiment. All 4 treatments had the same rates of N, P, and K nutrients. The organic fertilizers were milk vetch and composted pig manure for early and late rice respectively, while the chemical fertilizers sources of N, P and K were urea, super-phosphate and potassium chloride respectively.【Results】1) The seed-setting rates in the three combination ratios of organic and chemical fertilizer treatments were increased, especially those in the middle and lower parts of an spike. Although the increments were not statistically significant, the coefficient of variation in the seed-setting rates was far lower than that in NPK treatment. 2) Different ratios of organic manure and the chemical fertilizers had different effects on the grain weight. The 50F+50M treatment significantly increased rice grain weight by 3.1% compared with NPK treatment, but the 70F+30M treatment and 30F+70M treatment did not. 3) Dividing a spike into upper, middle and lower parts, the grain weights in the three parts of spike were not significantly increased in treatments of 70F+30M and 30F+70M, but was increased by 4.7% and 3.8% in the primary and secondary branch of rice spike in the treatment of 50F+50M, although not significant due to the high coefficient of variation. 4) Compared with treatment NPK, 50F+50M increased the rice grain weight by 4.8% and 4.7% in the primary and secondary branch of the upper parts, respectively, for the middle parts of spike by 3.0% and 4.6% respectively. However, treatments 70F+30M and 30F+70M had no significant difference with treatment NPK in rice grain weight in any branches of upper and middle parts of spike. 5)Organic-inorganic combined fertilization had no difference with NPK in seed-setting rate of different branches from upper parts of rice spike, but increased the set-setting rate in primary and secondary branches from middle and basal parts of rice spike, especially secondary branch of middle and basal parts of rice spike, but the use of organic fertilizer can't improve the stability of the seed-setting rate in secondary branch of middle and basal parts of rice spike.【Conclusions】The ratio of organic and inorganic fertilizer has different effect on the seed weight and seed-setting rate in different parts and branches of a spike. In this experimental condition, 50% chemical fertilizer and 50% organic fertilizer shows significant increase in the seed weight in the primary and secondary branches of the middle and upper parts of a spike, which could be the main reason for the high yield. The 50% chemical fertilizer plus 50% organic fertilizer treatment is also good for the seed setting rate in the middle and basal parts of the secondary branches. So, 50 to 50 in organic and chemical nutrients should be recommended as a reasonable ratio.