Effects of Amount and Interval of Chemical Fertilizer Application on the Nitrogen Absorption and Nitrate-nitrogen Content in Tillers of Napiergrass (Pennisetum purpureum Schumach)

摘要

Nitrogen absorption and nitrate-N content in napiergrass were investigated together with their variations among tillers by applying chemical fertilizer under more frequent and heavier amount of applications than the ordinarily normal applications. Plants were grown by transplanting the overwintered rooted tillers under the density of four plants/m2 in early May. The fertilizer application was the combination of two levels of amount (900kgN/ha/year, H-plot and 600kgN/ha/year, M-plot) and three regimesof interval (every 4 weeks, 2 weeks and 1 week). The variations in dry matter weight, total nitrogen (TN) content and nitrate N concentration among tillers tended to decrease with time. In the whole plant, TN concentration, TN yield and nitrate N concentration were higher in H plot than in M plot in the most cases, if compared at the same application interval, and they tended to be higher with shortening the application interval before late August. It was also suggested as the prompt application methodfor suppressing the deterioration in forage quality that the amount of fertilizer applied in chemicals should be increased after late August, due to the lesser increase in the nitrate N concentration compared with the case applied before August. These findings for the chemical fertilizer application were discussed with the case of cattle manure application for the slow-released effect.