Physiology of Cotton under Irrigated and Dryland Conditions in Spain

The main cotton-producing area in Spain is Andalucia, where it is grown mainly under irrigation (about 100,000 ha). Efforts are being made to increase the efficiency of irrigation water use. This investigation compares responses of five cultivars of upland cotton to growth under irrigated (Las Torres field station at Alcalá del Rio) or rainfed conditions (Tomejil, both managed by Dpto. del Algodón, CIFA). Plants at Tomejil were much smaller than those at Las Torres and gave lower yields of seed cotton. Stomatal conductance (gs), measured either with a porometer or infra-red gas analysers, was lower at Tomejil than at Las Torres. Gas exchange parameters (net photosynthesis, transpiration and instantaneous water use efficiency) were also lower, while leaf temperatures (measured with an infra-red thermometer) were higher. Some variation in the ratio of adaxial to abaxial stomatal conductance was observed, especially at the dryland site at Tomejil. Carbon isotope discrimination () values were related to the development of water deficits but did not correlate with instantaneous gas measurements at Tomejil. Concentrations of Na+, K+, Mg++, Ca++, Cl-, SO4-and malate in leaf sap were very much higher at Tomejil than at Las Torres. Glycinebetaine, a quaternary ammonium osmoprotectant, increased in concentration to about 90 mol m-3 in leaf sap under severe water deficit at Tomejil compared to 30 mol m-3 at Las Torres. Physiological differences only partly accounted for varietal differences in yield at Tomejil. Introduction The most important cotton-producing area in Spain is in Andalucia (in the South West), where about 100,000 ha is grown mainly under irrigation with a small percentage under dryland conditions. Efforts are being made to increase the efficiency of irrigation water use in view of the potentially conflicting requirements of industry, agriculture and the domestic sector for the finite water resources of the region. This investigation compares the physiological responses of five varieties of upland cotton in 1996 to growth at two sites under irrigated (Las Torres field station at Alcalá del Rio) or rainfed conditions (Tomejil). Previous work (Lopez et al., 1993) demonstrated genotypic variation for photosynthetic rate, stomatal conductance, water use efficiency and leaf temperature among 70 cotton cultivars grown under water deficit stress in this region. Material and Methods Twenty six cotton cultivars were sown in 1996 at an irrigated field site (Las Torres, Province of Seville, S.W. Spain, Typic Xerofluvent sandy loam soil) and at a nearby dryland site (Tomejil, Typic Chromoxerert clay soil). Both sites are managed by Dpto. del Algodón, CIFA. A randomised complete block design was used with 6 replicates of 15 m rows at 5-7 plants m-1. Row spacing was 0.75 m at Tomejil and 0.95 m at Las Torres. Physiological measurements on five varieties were made at both sites during August. Gas exchange measurements were made on young expanded leaves in the late morning with a CIRAS-1 infra-red gas analyser (PP Systems Ltd.) and a broadleaf chamber at saturating photosynthetic (400-700 nm) photon flux densities (>1,500 mol m-2 s-1). Dry air was fed to the leaf chamber at 350 mol mol-1 CO2. Measurements were also made on the same day with an LCA2 infra-red gas analyser (ADC Ltd.). Further stomatal conductance measurements were made with an AP4 porometer (Delta-T Devices Ltd.). The instrument was carefully calibrated each morning, and used with the limits specified for this porometer. Both abaxial and adaxial surfaces were measured. Leaf temperatures were measured with a Raytec infra-red thermometer. Osmotic potentials were measured in frozen-thawed samples using a Wescor HR33 microvoltmeter and C52 thermocouple psychrometer chambers. Dry leaves were powdered and analysed for C isotope composition by mass spectrometry in the laboratory of Prof. G. Farquhar in Canberra, Australia. Fresh leaf samples were frozen in microcentrifuge tubes and taken to Bangor, Wales, for chemical analysis. Sap was extracted by centrifugation after thawing the samples, and inorganic ions measured by ion chromatography. Quaternary ammonium compounds (mainly glycinebetaine) were measured using a modified Proceedings of the World Cotton Research Conference -2. Athens, Greece, September 6 -12, 1998. pp.591-594. J. Gorham et al.