Water deficits during reproductive growth of soybeans. II. Water use and water deficiency indicators

Abstract

&mdash; An experiment was carried out over 2 years with soybeans to study water use and performance of differ- ent indicators of water status under field controlled conditions, comparing an irrigated check with treatments with im- posed water deficiencies. Statistically significant differences were found between treatments in predawn water potential (PWP), noon water potential (NWP) and leaf resistance (LR). PWP best reflects soil water availability or percentage of available water (PAW). The determination coefficient (R 2 ) between PWP:PAW for both years was 0.77**. Water use was reduced when water deficiency was applied, and actual water use: potential evapotranspiration (WU:PET) relationship was drastically reduced for the dry treatments. (01, 10, 00) compared with the control (II), but it recovered almost completely when the deficiency was removed. Total water used efficiency (TWUE), as dry matter: water use (DM:WU) and water use efficiency (WUE); as seed yield: water use (SY:WU), were significantly higher for the second year. A time-integrated deficiency index (DI) was calculated as: for all PAW < AWT, where tb and te are the beginning and the end of the period, and AWT is the PAW threshold (62%). Below that value, WU and DM are reduced. Dry matter production and seed yield were related to DI as: * Correspondence and reprints pour toutes les situations PAW< SWT o tb et te sont l'initiation et la fin de la priode considre, et AWT est le seuil de PAW = 62%. En-dessous de ce seuil, WU et DM sont rduits. La production de matire sche et le rendement sont en relation avec DI selon les relations suivantes : Glycine max = soja / consommation d'eau / dficience en eau / efficience d'utilisation de l'eau / paramtre in- dicateur