Inhibition of seedling establishment by nitrogen application in direct sowing culture of paddy rice in old region

Abstract

The effects of the nitrogen application rate and type of nitrogen fertilizer on rice seedling establishment for seeds without or with calcium peroxide coating under drained paddy field conditions were investigated. The seedling establishment rate for the seeds without coating decreased with the application of ammonium sulfate (AS) at the rates of 4 and 8 g m−2. The pH in the soil solution was in the appropriate range for rice growth, and the ferrous ion concentration and EC in the soil solution were lower than the threshold for rice growth in all the plots. The ammonium nitrogen concentrations in the soil solution in the AS application plots were exceeded 2 mg kg−1, which is the threshold for seed emergence. Seedling establishment for the seeds with calcium peroxide coating was not inhibited by the AS application even at the rate of 8 g m−2. The application of ammonium phosphate (AP), urea (U), and polyolefin-coated urea (PCU) at the rate of 4 g m−2 did not inhibit the seedling establishment in the case of both calcium peroxide-coated seeds and non-coated seeds. The ammonium nitrogen concentration in the soil solution at the time of sowing was less than 2 mg kg−1 in all the treatments except for the AS treatment. These results showed that nitrogen application, which increases the ammonium nitrogen concentration in the soil solution at sowing, inhibits seedling establishment for non-coated seeds and does not inhibit seedling establishment for coated seeds.