Increasing Yield of Soybeans by Rhizobium Japonicum and Nitrogen Fertilizer

Abstract

The application of nitrogen fertilizer and Rhizobium japonicum to increase yield of soybean was conducted in the northeastern part of Thailand where the fertility of soil is usually poor and devoid of soybean rhizobia. Experiments were undertaken in 1973 at Roi-et, Khon Kaen and Nakornrajasrima and again in 1974 at Roit-et, Khon Kaen and Mahasarakam, Rates of N fertilizer used in 1973 were 0, 3, 6 and 12 kg N/rai and in 1974 were 0, 3, 6, 12 and 24 kg N/rai. Each arate of N fertilizer was applied with and without rhizobial inoculuant. All treatments were supplemented with 9 kg of P2O5 and 6 kg of K2O/rai. Results of 1973 for three locations agreed that the application of N fertilizer at any rate together with rhizobial inoculant could not increase soybean yield over inoculation alone. Moreover, inoculation alone could increase soybean yield significantly higher than the highest rate of 12 kg N/rai applied ithout inoculant. It was also found in 1974 that the results for all locations were confirmed the 1973 experiments. eventhough the higher rate of 24 kg N/rai was used in 1974 is still could not be comparable to rhizobial inoculant. From two consecutive years of study comprise 6 experiments it could therefore be concluded that nitrogen fertilizer should not be recomended for soybean.