Root and shoot development of wheat (Triticum aestivum L.) grown with limiting water

Abstract

Two-year studies (1979-1980, 1980-1981) designed to measure the relation of plant development to yield of spring wheats were undertaken at the University of Arizona Mesa Experiment Station and at the Casa Grande Overpass Farm, Tucson. Low density seeding rates (15 to 20 kg/ha) were used in both studies. The soil at Mesa and in Tucson were clay and sandy barns, respectively. All plants grown under limiting water conditions received 150 kg/m² pre-plant irrigation. Supplemental water as rainfall in the 1979-1980, 1980-1981 seasons were 153 and 79 kg/m² atMesa respectively, and 134 and 116 kg/m2 in Tucson for the respective seasons. Experiments were also conducted in Tucson during the two seasons to evaluate yield performance of wheats under well-watered conditions (525 kg 1m2 and 400 kg/m² irrigation water in the 1979-1980, 1980-1981 seasons, respectively) and on plants which received a single added irrigation approximately 2 to 3 weeks prior to the estimated time of anthesis. Yields in Mesa ranged from 2400 to 3700 kg/ha in 1980 and from 1800 to 3600 kg/ha in 1981. When grown under limiting water conditions in Tucson yields ranged from 1100 to 3000 kg/ha in 1980 and from 2000 to 4100 kg/ha in 1981. Productivities of plants grown with a single added irrigation ranged from 2000 to 4200 kg/ha. Under minimal water conditions yield was correlated with head weight of the main culm, average head weight, grain weight per spike, number of grains per unit land area, Leaf area and Flag leaf area indices at later stages of development, total plant dry weights, root depths and dry weights. Differences were found in tissue water status and leaf growth of selected entries. Tissue water potential was higher in a higher yielding than in a low yielding entry. Additionally, tissues at the basal region tended to be more "sensitive" to changes in soil moisture than those at the mid-section of the expanding leaf. Difficulty in sample selection and variability with plants militated against using leaf growth as an index for determining the degree of stress in field grown wheat cultivars. Neutron probe analysis of soil profile water depletion of a high yielding, long rooted cultivar was greater at the lower depths (60 to 120 cm) after anthesis than for an intermediate or low yielder.