LEAF AREA DEVELOPMENT IN SOYBEAN AS AFFECTED BY PHOSPHORUS NUTRITION AND WATER DEFICIT

Abstract

Leaf area development is an important factor in crop production because it affects the amount of radiation intercepted and, therefore, plant growth. Even though phosphorus (P) deficit and water stress have been studied as isolated factors limiting leaf area development in soybean (Glycine max (L.) Merr.), little has been done on their possible interactions. A pot experiment was conducted to determine the effects of P supply and water deficit on leaf-area development in soybean, and whether P nutrition affects soybean response to water stress. Plants were grown in pots for 49 days. The soil used was a Sadler silt loam (fine-silty, mixed, mesic Glossic Fragiudalf), which contained 5.3 mg P kg−1 (Mehlich III). Additional P was added at 0, 20, and 80 mg P kg−1 soil. Water treatments consisted of keeping the soil-water content at 85% (well watered), 60% (mild water stress) and 35% (severe water stress) of the 10 kPa soil-water content. Phosphorus nutrition did not affect the response of soybean to water stress in most of the measured variables. Relative reductions due to water stress were similar at every P level for individual leaf area, whole-plant leaf area, aboveground biomass, stomatal conductance, and transpiration. Only plant development was slowed to a greater extent by water stress in P-deficient plants. Water stress had no effect on P nutrition, since it did not affect P concentration in plant tissue.