Phosphorus Uptake by Soybeans as Influenced by Moisture Stress in the Fertilized Zone1

Abstract

AbstractReports on the effect of soil moisture stress on plant uptake of P have been conflicting. The effect of the dynamic variation in soil moisture on P uptake by soybeans (Glyfine max L. Merr.) was studied in vivo. A split‐root technique with plants grown in 3 liter containers in the greenhouse was used whereby moisture stress was localized in the zone having the only source of P for the roots, while water and P‐free nutrients were supplied through the other portion of the root system. The procedure minimized the effect of plant‐water deficit.Differences between moisture treatments accounted for 81.5% of plant P content when the effects of fertilizer treatments were removed, while variation in soil moisture content within each moisture treatment accounted for only 8%. The extent P uptake was impaired by high moisture stress was conditioned by the P status of the plant which in turn was determined by the previous soil moisture history of the zone supplying the P. After watering, plants exposed to a high moisture stress resumed P uptake at a rate exceeding that of plants absorbing P from the adequately watered compartment.The range of response to which increasing levels of fertilizer P was obtained increased as the period of moisture stress in the fertilized zone was prolonged. Temporary luxury consumption of P, induced by high levels of soil P and foliar application, benefited soybeans whose P supply was curtailed by high moisture stress.Moisture stress appeared to affect P uptake largely through its influence on diffusion rather than mass‐flow. It is suggested that the inconsistencies of field results reported in the literature studying the relationship of P uptake and moisture stress could be caused by the peculiar P uptake behavior found in these experiments.