Inoculation methods and nitrogen fertilizer effects on soybeans in the tropics; dry matter and seed yields

Abstract

The effects of N fertilizer and Rhizobium japonicum inoculation on soybean growth and grain yield were determined on Philippine paddy differing in off-season soybean cropping history. Nitrogen fertilizer treatments were: 0, 20 or 25, and 80 or 50 kg ha-1 applied at planting. Inoculation treatments were: no inoculation, seed-inoculation, seed-and-furrow inoculation. Regardless of past cropping history, N fertilizer increased dry matter yield, leaf area and grain yield. On a field never previously cropped with soybeans in the post-rice seasons, seed inoculation and seed-and-furrow inoculation increased grain yield by 65% over uninoculated treatments. Despite responses to both factors, the best treatments at the respective locations produced grain yields of only 1.2-1.3 t ha-1. Fertilizer and inoculation management practices which will increase N assimilation more dramatically than those tested in this study are a prerequisite for substantial yield increases of soybeans of soybeans cultivated during the post-paddy rice season.