Growth of winged bean in three soil types in Okinawa and the effect of phosphorus nutrition
2016
Kitou, M. (University of the Ryukyus, Okinawa (Japan). Faculty of Agriculture) | Nakama, T. | Nagumo, F.
Acidic soil (red soil: RS), neutral soil (dark red soil: DRS), and alkaline soil (gray soil: GS) are main soils in Okinawa islands. We examined the growth and yield of winged bean (Psophocarpus tetragonolobus) cultivated in these soils in the field in 2007 and 2008. In RS, the contents of total phosphorus (P), Ca-bound P (available P), and Al-bounded P (unavailable) were lowest. Growth and yield of winged bean were significantly lower in RS than in DRS or GS. We also grew winged bean and velvet bean (Mucuna pruriens) in pots with RS with or without liming and P application. The growth of both species was promoted by P application but not by liming. Without P application, the growth of winged bean was lower than that of velvet bean. Tolerance of these species to low P was investigated in akadama soil, in which P was mainly bound to Al; the phosphate absorption coefficient of this soil was 23.9 g /kg. P-deficient (DP) and P-sufficient (SP) conditions were achieved by adding P at rates of 1% and 10% of the phosphate absorption coefficient, respectively. Growth and N-fixing activity of winged bean were significantly lower than those of velvet bean. We conclude that the decrease of winged bean growth and yield in RS is caused by P deficiency rather than its sensitivity to soil acidity.
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