Growth of Winged Bean in Three Soil Types in Okinawa and the Effect of Phosphorus Nutrition

摘要

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~(-1). 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.%和文要約沖繩 に分布する酸性の赤色土、中性の暗赤色土、アルカリ 性の灰色低地土の圃場で栽培したシカクマメ （Psophocarpus tetragonolobus)の生育量と収量を2007年と2008年の2年 間調査した。全リンおよびCa型リン酸、A1型リン酸の最も 少ない赤色土でシカクマメ生育量と収量はたの土壌に比べて 有意に低下した。赤色土に石灰施用とリン施肥の有無による 処理区を設けて栽培したシカクマメとハツショゥマメ (Mucuna pruriens)の生育量は石灰施用の有無にかかわらず リン施肥で低下し、低下度合はシカクマメで強く示された。 リン酸をA1型で固定する赤玉土にリン酸吸収係数の1%と 10%のリン酸施肥をして準備したリン欠乏区とリン適量区で シカクマメとハツショゥマメを栽培した結果、欠乏区におけ る生育量と窒素固定活性はシカクマメで著しく低下した。こ れらのことから赤色土でのシカクマメの生育量と収量の低下 は土壌酸性による影響よりもリン欠乏の可能性が明らかにな つた。