The Fate of Fertilizer Nitrogen Applied to the Paddy Field and Its Absorption by Rice Plant : II. The fate of basal nitrogen in the paddy field

Abstract

The fate of basal nitrogen (ammonium sulfate) enriched with 15N was investigated in the paddy field in 1969 and 1970. The paddy soil was relatively poor in organic matter, fine-textured and poorly drained. Rice plant was transplanted at two different times and was grown with two rates of basal nitrogen addition as previouly reported. The soil ammonium nitrogen derived from the basal fertilizer was more in the plots with the high rate of basal nitrogen than in those with the low rate. It decreased gradually and almost disappeared in every experimental, plot at the end of June. The fact above-mentioned was coincident with the results of a previous paper indicating that the absorption of basal nitrogen was finished in all the experimental plots at the end of June. The quantities of fertilizer nitrogen left in the soil after harvest ranged from 18 to 21 per cent. On the other hand, 22 to 27 per cent of the nitrogen was absorbed by rice plant. Therefore, the recovery of basal nitrogen was less than 50 per cent. According to the frequent determinations of the amounts of nitrogen absorbed by rice plant and soil ammonium nitrogen, it was assumed that ammonium formation in the soil had two maxima during the growing season -one, from the early to middle June and another, from the end of July to early in August.