Soil-plant nutrition studies on tropical rice VI. The effect of different levels of nitrogenous fertilizer application on plant growth, grain yield, and nitrogen utilization by rice plants

The effect of different levels of nitrogenous fertilizer application on plant growth, grain yield, and both the amount of soil nitrogen and applied fertilizer nitrogen utilized by plants was investigated in the Bangkhen paddy field. The results furnished clear evidence that the recoveries of added fertilizer nitrogen by plants were increased along with an advance in plant growth, and that the plant uptake of soil nitrogen was independent of the nitrogen level applied. A linear relation was found between total nitrogen absorbed by plants and the levels of nitrogen applied indicating that the extrapolated yield of the nitrogen value could be used for the evaluation of the soil nitrogen supply. The present study demonstrated also the importance of examining the proportion of two kinds of nitrogen in plants, one derived from fertilizer and the other from soil nitrogen, in the evaluation of the fertilizer effect, and made it clear that the evaluation of fertilizer effect based only on the quantity of fertilizers absorbed by plants represents only a part of the whole picture.