Studies on the nutrition of rice plant (Oryza sativa L.)

Summary

Comparative efficiency of a short durationindica variety (Ptb 10) and ajaponica variety (Aikoku) has been tested under increasing nitrogen levels in water culture trials. Theindica variety does well at 20 p.p.m. of nitrogen, but at higher nitrogen levels the grain yield is pulled down. Thejaponica variety on the other hand grows well at nitrogen levels of 60 p.p.m. and there is no appreciable decrease in grain yield even at 150 p.p.m. nitrogen. Thejaponica variety however fares very badly at nitrogen levels of 20 p.p.m. and less and the grain yield at these levels is even poorer than that of theindica variety.

Efficiency of nitrogen utilization by two varieties has been measured by the ratio of soluble to protein nitrogen in the plant both at vegetative and reproductive stages. There is no difference in this ratio of the two varieties at the vegetative stage. At the reproductive stage however, theindica variety has a higher ratio of soluble to protein nitrogen both at 60 and 150 p.p.m. nitrogen than that of thejaponica variety, showing a disturbed nitrogen metabolism ofindica under high manuring condition. The depression of the grain yield ofindica at higher nitrogen levels is also seen to be due to decrease both in the number of filled grains per panicle and weight of 1,000 grains, factors which are mainly decided at the reproductive stage. It is therefore concluded that the nitrogen metabolism ofindica gets disturbed at the reproductive stage due to excess nitrogen level and the variety is not able to utilise nitrogen efficiently for formation of grain. Thejaponica variety however, utilises nitrogen efficiently under high manuring conditions and gives greater yield.