Effect of different nitrogen application on rice yield and N uptake of white soil under wheat straw turnover

【Objectives】 Effects of different nitrogen (N) ratios of basal and topdressing application on rice growth and N uptake in the condition of wheat straw direct turnover were studied to provide a scientific base for rice applying N rationally in low-yield white paddy soil of middle region of China.【Methods】Two levels of wheat straw turnover (0 and 3000 kg/hm2) and three N application ratios of basal and topdressing (80-0-20, 60-20-20, and 40-30-30), and N omitted treatment were designed, which were reordered as N80-0-20, N60-20-20, N40-30-30, N80-0-20+S, N60-20-20+S, N40-30-30+S and CK, respectively. The representative samples were collected to investigate rice yield components at the harvest period, and the yields and N concentrations in grain and straw were also measured to determine N uptake and nitrogen use efficiency. 【Results】 The treatment of N60-20-20 obtains the highest rice grain yields which are increased by 9.4%-12.9% in 2011 and 7.4%-8.9% in 2012, respectively, compared with the control N80-0-20. In the condition of wheat straw direct turnover, rice grain yields are increased by 10.2%-23.4% and 0.8%-5.5%, respectively, compared with the no straw turnover treatments. The N content in rice grains of the N60-20-20 treatment reaches the highest, which is 11.3% higher than that in the CK treatment, while the N contents in straw are increased with the increase of N topdressing application ratio at the mid-late period. Increasing N application rate of topdressing can promote the N contents in grains and straw in the condition of wheat straw turnover. The total N uptakes in rice grains reach the highest for the N60-20-20 treatment, and are significantly increased by 13.7% and 24.8% in 2011 and 14.5% and 9.2% in 2012, respectively, compared with the N80-0-20 treatment. The N uptakes in rice straw are increased with the increase of N topdressing application in mid-late period, and the uptake of the treatment N40-30-30 reaches the highest. The dry matter production efficiency, grain production efficiency and harvest index of nitrogen reach their peaks in the N60-20-20 treatment with no wheat straw turnover, in which the amount of N absorption per 100 kg grains drops to the lowest, while a contrary result shows when wheat straw turnover. The agronomy efficiency, apparent recovery efficiency and partial productivity of nitrogen are also significantly promoted in the N60-20-20 treatment by 4.90 and 2.44 kg grain per kg N, and 7.82 and 21.29, and 4.90 and 2.44 percentage points, respectively, compared with the N80-0-20 treatment.【Conclusions】 Considering rice grain yield, N uptake and nitrogen use efficiency, the 60-20-20 N application ratio of base-jointing-panicle development stages is suitable for single-reason rice in Jianghuai hilly land region with low-yield white soils, Anhui province under the condition of wheat straw direct turnover.