Effect of the Nitrification Inhibitor on Nitrification of Ammonium Fertilizer and Yield of Rice Sown Directly on Unflooded Paddy Field. : Part 3. Relation between the Effect of 2-Mercaptobenzothiazole (MBT) and the Fertilizer Particle Size.

This experiment was carried out to make clear the relation between the effect of 2 Mercaptobenzothiazole (MBT) on the nitrification of ammonium nitrogen applied to rice culture by direct sowing on unflooded field and the yielding effects on the plant growth and grain yield therby and the fertilizer particle size. The results obtained were as follows: 1 . The inhibitory effect of MBT on the nitrification of applied nitrogen was clearly recognized in every plots. I n the plot of large particles, the effect was not so large by the reason which the soluble rate of large particle fertilizer was rather slow. It was suggested that, however, the large particle fertilizer exhibited the slowly available nature. The effect of MBT on nitrification terminated within about 40 days. 2 MBT showed superior effects on the rice plant growth in every plots. And it was indicated that the effect in the initial growth increased with a decrease of fertilizer particle size. The total nitrogen absorption and the nitrogen utilization coefficient in rice plant were higher in +MBT plots of every fertilizer particle size than in-MBT plots of every fertilizer particle size than in -MBT plots, respectively. 3. The yielding effect of MBT on the rice grain yield was clearly recognized in every plots. The grain yields showed the following order: Small (0. 71-1. 70mm) + MBT Large (5.00-25.00mm) +MBT>Large -MBT-Small -MBT -Powder (0. 06-0.25mm) +MBT > Medium (2.40-4. 00mm) +MBT > Medium-MBT > Powder-MBT. 4. From the results mentioned above, it was showed that the MBT added to the ferti. lizer for basal application exhidited a considerable effect on an increase of the rice grain yield. However, it was suggested that, even if the MBT was not added to the fertilizer for basal application, the corresponding yield to or the higher yield than + MBT plot of ”Medium” (namely, this particle size is the same fertilizer particle size with MBT on the market) was able to get by the application of fertilizer with suitable particle size. 5. Almost no physiological obstacle of MBT on rice plant was observed throughout all the growing stages. (Received Jane 30, 1974)