CARBON-ISOTOPE DISCRIMINATION AND WATER-USE EFFICIENCY OF 6 CROPS GROWN UNDER WET AND DRYLAND CONDITIONS

Mustard (Sinapis alba L.), Argentine canola (Brassica napus L. cv. Wes tar), Polish canola (Brassica campestris L, cv. Tobin), pea (Pisum sat ivum L.), durum wheat (Triticum durum L. cv. Kyle) and soft wheat (Tri ticum aestivum L. cv. Fielder) were grown at Outlook, Saskatchewan, Ca nada, under irrigated and dryland conditions. Carbon isotope discrimin ation (Delta)and water-use efficiency (W), defined as grams of above g round dry matter produced per kilogram water used, were negatively cor related in the six field-grown crops. In irrigated plants Delta remain ed relatively constant (20-21 parts per thousand) throughout the growi ng season. However, in dryland plants, Delta declined in response to t he progressive depletion of stored soil water (Polish canola, 20.2-18. 8 parts per thousand; mustard, 19.9-18.5 parts per thousand; pea, 19.9 -17.2 parts per thousand; durum wheat, 19.7-16.4 parts per thousand; A rgentine canola, 19.4-17.6 parts per thousand; soft wheat, 19.0-17.4 p arts per thousand). Although there were genetic differences in Delta a mong the species, water availability was the major factor controlling Delta.