DROUGHT RESISTANCE IN RANGE AND PASTURE GRASSES

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Abstract
Several grasses were studied under field and greenhouse conditions to investigate temp. injury and the use of resistance to high temp. as an index of drought resistance. Grasses grown under different moisture and clipping treatments to represent 4 different carbohydrate supply levels were tested for heat resistance. Heat resistance varied significantly. Buchloe dactyloides and Cynodon dactylon were very resistant, Agropyron smithii was intermediate and A. pauciflorum, Bromus inermis, and Poa pratensis were low in resistance. Heat resistance of, the species tested corresponds closely with the aridity of their natural habitat and is apparently a measure of drought resistance. Accumulation of food reserves was essential to heat resistance. Hardening by drought increased heat resistance although spp. which stooled out near the ground were less affected than taller, upright spp. Protected and moderately grazed grasses accumulated excess food reserves as they entered drought. Large accumulation of colloidal carbohydrates was associated with drought resistance. Overgrazed and closely clipped plants did not accumulate food reserves during drought. Soil temps. were found to be much higher (to 15oC) on overgrazed range than on areas supporting a good vegetative cover. Establishment of proper utilization standards is recommended on arid ranges to provide for: (a) hardened plants capable of withstanding drought; (b) adequate food reserves for respiration and vigorous recovery after drought; and (c) reduction in drought conditions by a protective vegetative cover which guards against high soil temps. and water loss.