Climatic and Water Availability Effects on Water-Use Efficiency in Wheat P. E. Abbate,* J. L. Dardanelli, M. G. Cantarero, M. Maturano, R. J. M. Melchiori, and E. E. Suero ABSTRACT purposes and to adopt management practices that allow WUE to be maximized. In Argentina, wheat (Triticum aestivum L.) is cropped over a wide In Argentina, wheat is mainly cropped from 32 to range of climatic conditions. Considerable variability in the ratio of 39S and 57 to 63W (Hall et al., 1992). Considerable dry weight produced per unit of transpired water, usually referred to variability in climatic conditions and WUE is expected as water-use efficiency (WUE), is expected as variation in climatic factors affects photosynthesis and transpiration in different ways. throughout this zone. Several authors have proposed Also, previous studies have shown that water supply limitations may the use of environmental indexes to explain changes in affect WUE in wheat. The objective of this study was to quantify the WUE across environments. Some of the most frequently effects of climatic environment and water availability on WUE in used indexes were mean pan evaporation (de Wit, 1958), wheat crops. Six experiments were conducted at different locations mean relative humidity (Arkley, 1963), mean vapor of the Argentine wheat belt and crop dry weight and water use were pressure deficit (VPD) (Bierhuizen and Slatyer, 1965), measured in periods when water use was dominated by transpiration. and mean potential water use (Doorenbos and Kassam, Three of the experiments included both irrigated and rainfed treat- 1979). Vapor pressure deficit is a widely used and con- ments. Mean daily values of (i) pan evaporation, (ii) relative humidity, cise index that explains changes in the ratio yield/water (iii) potential water use, and (iv) vapor pressure deficit, were used use (Angus and van Herwaarden, 2001). The effect of to find a general relationship that explained effects of the climatic VPD on WUE has been reported for corn (Zea mays environment on WUE. For experiments with high water availability, L.), sorghum [Sorghum bicolor (L.) Moench], potato daytime vapor pressure deficit was better related to WUE than the (Solanum tuberosum L.), alfalfa (Medicago sativa L.), other climatic factors. WUE was greater for experiments with water soybean [Glycine max (L.) Merr.] (Tanner and Sinclair, limitation, probably because stomatal closure to restrict transpiration rate occurred around midday when vapor pressure deficit was highest. 1983), and barley (Hordeum vulgare L.) (Monteith, As a consequence, relative dry weight under water limitation was not 1986). Comparisons of the abilities of different meteoro- linearly related to relative water use as proposed in previous studies. logical indexes to explain environmental effects on A quadratic relationship that better represented this response was WUE (under well watered or water deficit conditions) derived. are scarce. To our knowledge, no relationship between WUE and VPD has been reported for wheat. On the other hand, several reports have shown that W ater supply is often the most critical factor lim- water-supply limitations create other additional source iting crop growth and yield in rainfed areas and of WUE variation besides the climatic conditions. When the most expensive input of irrigated crops. Therefore, WUE in wheat under water limitation was compared crop production usually requires maximizing yields on with well-watered checks, the results showed that WUE limited available water resources. In absence of nutrient either increased (Barraclough et al., 1989; Fischer, 1980; limitations, the most critical period for yield determina- Mohamed and Abdel Monem, 1994; Zhang et al., 1998), tion in wheat (Fischer, 1979; Abbate et al., 1997) gener- did not change (van den Boogaard et al., 1996b), or ally takes place while water use (WU) is dominated decreased (El Hafid et al., 1998). The aim of this study by transpiration. One of the key components of crop was to quantify, under field conditions across the Argen- production is to achieve the greatest ratio of dry weight tine wheat belt (i) the ability of different meteorological to transpiration, usually known as water-use efficiency indexes to explain environmental effects on WUE in (WUE). Water-use efficiency is strongly influenced by well-watered crops and (ii) to assess the effects of water weather conditions affecting transpiration and assimila- supply limitations on WUE. tion by leaves, plants, and crop differently (de Wit, 1958; Fischer and Turner, 1979; Fischer, 1980; Tanner and MATERIALS AND METHODS Sinclair, 1983). The effect of climate on WUE based on transpiration, is to be assessed both for modeling Six experiments (Table 1) were conducted in Argentina: two at Co ´ rdoba (3130 S, 6400 W, altitude 360 m), one at Parana ´ (3147 S, 6029 W, altitude 79 m), one at Pergamino P.E. Abbate and E.E. Suero, Unidad Integrada Balcarce, Estacio ´n (3356 S, 6033 W, altitude 65 m), and two at Balcarce (3745 Experimental Agropecuaria (EEA) Balcarce of INTA (Instituto Nacio- S, 5818 W, altitude 130 m). The soil at Co ´ rdoba was a silty nal de Tecnologı ´a Agropecuaria) and Facultad de Ciencias Agrarias loam Enthic Haplustoll (USDA Soil Taxonomy) with 23 g of Univ. Nacional de Mar del Plata, CC 276 (7620), Balcarce, Bs.As., kg 1 organic matter in the top 20 cm of soil; at Pergamino, it Argentina; J.L. Dardanelli, EEA Manfredi, INTA, Ruta 9, Km 636 was a silty loam Typic Argiudol with 30 g kg 1 organic matter; (5988), Manfredi, Co ´ rdoba, Argentina; M.G. Cantarero, Facultad de Ciencias Agropecuarias, Univ. Nacional de Co ´ rdoba, Av. Valparaı ´so and at Parana ´, it was a silty loam Aquic Argiudol with 33 g s/n, Ciudad Universitaria (5000), Co ´ rdoba, Argentina. M. Maturano, EEA Pergamino, INTA, CC 31 (2700), Pergamino, Bs.As., Argentina; Abbreviations: DW, dry weight; GAI, green area index; GAR, green R.J.M. Melchiori, EEA Parana ´ , INTA, CC 128 (3100), Parana ´ , Entre area ratio; H, high water availability treatments (irrigated); L, low Rı ´os, Argentina. Received 22 Dec. 2001. *Corresponding author water availability treatments (rainfed); LAI, leaf area index; PAN, pan (menegot@mdp.edu.ar). evaporation; PAR, photosynthetically active radiation; PEN, Penman- FAO potential water use; RH, percentage relative humidity; SE, stan- Published in Crop Sci. 44:474–483 (2004).  Crop Science Society of America dard error of mean; SEE, standard error of estimate; VPD, vapor pressure deficit; WU, water use; WUE, water-use efficiency. 677 S. Segoe Rd., Madison, WI 53711 USA 474