Effect of irrigation and Rhizobium japonicum strain 110 upon yield and nitrogen accumulation and distribution of determinate soybeans

Abstract

Abstract In the southeastern Coastal Plains determinate soybean [Clycine max (L.) Merr.] is grown on soils with low water‐holding capacities and N contents. Therefore, N fixation and management of water are important in soybean production. Several studies were conducted to increase the understanding of the interaction of these two factors on soybean growth and yield. Experiments were conducted in 1976, 1978, and 1979 on a ‘ Norfolk loamy sand (Typic Paleudult) with soybean of maturity groups VI, VII, and VIII grown under irrigated and nonirrigated conditions each year with soil water monitored to 60‐cm depths. In 1979 the plots were split by inoculating with Rhizobium japonicum strain 110 at a rate of 108 organisms/cm of row. Serological analyses indicated that strain 110 infection of nodules was near 0% in the noninoculated plots and 7 to 21% in the inoculated plots. Irrigation water increased leaf‐N concentration and seed yield during the severe droughts of 1976 and 1978; yields were >3 and <1.5 t/ha for irrigated and nonirrigated soybean, respectively. In 1979 there was only a short‐term drought which did not affect the total N accumulation, nor leaf‐N content for the noninoculated soybean. However, the drought was associated with a significant reduction in leaf‐N content of the inoculated soybean, 4.74 and 4.36%, irrigated and nonirrigated, respectively. Additionally, there was a significantly more negative leaf xylem potential for inoculated than for noninoculated soybean plants under drought. These differences, coupled with varying maturities, contributed to a significant variety x irrigation x R. japonicum strain 110 interaction for yield. These results show that water management affects soybean N accumulation, distribution, and yield and that R. japonicum strain 110 may intensify or diminish the impact of water regimes on determinate soybean growth and yield.