Residual effects of nitrogen fertilization on foliar chlorophyll and yield of the succeeding rice crop

The residual effects of nitrogen fertilization during the dry season on four rice cultivars were investigated on the succeeding wet season N-unfertilized 'IR72' crop. Significant differences in the chlorophyll content (SPAD values) of the leaves were found among the different growth stages and between plots in previously N-fertilized plots but only at 42 and 56 DAT. Grain yield of 'IR72' during the dry season was the lowest among the cultivars. However, during the wet season when 'IR72' was planted in all plots previously planted to other cultivars, the grain yield from plots where 'IR72' was planted was the highest. Grain yield increased with an increase in nitrogen fertilization in both dry season (4 cultivars) and wet season (IR72) crops. These results were obtained in spite of the nonsignificant differences in the amount of total N and organic carbon of the soil before transplanting and after harvest of the wet season crop. There was no interactive effect between N and cultivar on the grain yield of the succeeding crop of 'IR72'. The results indicated, however, that N and cultivar had a significant separate effect on the succeeding crop. It also showed that maximum mineralization of N in the paddy fields occurs about 42 to 56 DAT and suggests that the non-symbiotic N-fixing bacteria in rice field may have different effects on residues of various cultivars.