水稲収量の成立原理とその応用に関する作物学的研究 : 第114報 分げつ期における硝酸態窒素利用率向上について

抄録

It is well known that the nitrogen loss of NO₃-N in paddy field is greater than that of NH₄-N, because NO₃-N is not adsorbed by the soil and is lost by denitrification. These properties of NO₃-N might conveniently be used to control the plant growth at any growth stage of the plant, if its utilization ratio were considerably raised up. Therefore, the authors examined the efficiency of NO₃-N absorption by the rice plant at the tillering stage with labelled nitrogen (¹5N), and obtained the following results: 1. It was estimated that the effective duration of NO₃-N applied in surface water of paddy field was less than 7 days. Judging from the results of ¹5N absorption by the rice plant, however, NO₃-N might be utilized at least for 2 weeks after top-dressing at the tillering stage. 2. The utilization ratio of NO₃-N in lowland soil was higher in the water-saturated paddy condition than in the flooded one, because of the high oxidation-reduction potentials of soil in the saturated condition. The utilization ratio of NO₃-N was about 70% comparing with that of NH₄-N. 3. In the upland soil, there was no difference in the utilization ratio regardless of water conditions and nitrogen sources, because of its high oxidation-reduction potentials. 4. When temperature was low at tillering period, the utilization ratio of NO₃-N in water-saturated paddy field was inferior to that of flooded paddy field, where a growth promotion by high water temperature was concerned, because flooded water was liable to be warmed by sunlight and water-temperature was higher than air-temperature. 5. Being applied at the given growth stage, NO₃-N showed higher efficiency in split application at the rate of half dose per week than that in the full dose (N 5 g/m²) application at a time. 6. The utilization ratio of NO₃-N applied by splitting method at the growth stage of 60-70 in the leaf number index can be raised up to about 70% comparing with that of NH₄-N.