Response of Apios americana to Nitrogen and Inoculation

Abstract

Apios americana Medikus (apios) is a wild tuberous legume with potential as a crop plant. Five apios accessions were grown in sand culture in two greenhouse experiments to examine the effect of N fertilization and inoculation with Bradyrhizobium japonicum on yield and plant characteristics. A common soybean B. japonicum strain (USDA76) was applied to plants watered with 0, 50, 100, 200, or 300 ppm N solutions (NH 4 NO 3 ), plus a complete nutrient solution. At 0 N, total dry matter yield of noninoculated plants was only ≈ 30% of inoculated plants. However, total dry-matter yields of inoculated plants at 0 N were only ≈77% of plants supplemented with 50 or 100 ppm, indicating that inoculation alone was insufficient to meet the N needs of the plant. Tuber weight was increased by both N and inoculation, but tuber weight decreased at N concentrations >100 ppm. Differences among plant accessions with regard to tuber fresh weight, harvest index, and modulation were found. These studies indicated that N fertilization maybe required to maximize tuber yields of apios.