No-tillage winter wheat (Triticum aestivum L.) grown in a wheat-fallow cropping system has consistently produced lower grain yields than conventionally tilled soils in the semiarid Pacific Northwest. A 2-year study was conducted in a long-term tillage trial at Moro, OR to determine factors responsible for differences in wheat growth and yield as affected by moldboard plow, stubble mulch, and no-tillage fallow method. Soil water, soil mineral N, plant N uptake, soil temperature, above-ground dry matter accumulation, and yield components were measured. The highest fallow efficiency during both years was achieved by stubble mulch tillage, followed by the plow and no-tillage systems. Accelerated water loss from no-tillage fallow occurred during the hot, dry summer due to uninterrupted capillary flow. The main yield limitations to no-tillage technology in this study were: (1) diminished seedzone water at planting time in the fall which resulted in reduced germination and stand establishment; (2) cooler spring soil temperatures which slowed crop development and dry matter accumulation, and; (3) production of fewer spikes per unit area. The second objective of this study was to determine if late season seedzone water loss from fallow could be reduced by altering the physical characteristics of the dust mulch. Loss of seedzone water appears to accelerate in late August and September because of increased diurnal heat flux. Compacting the soil surface with a roller in mid-August increased surface bulk density and volumetric water content to depths as great as 10 cm. Evaporative water loss from compacted plots, however, occurred at a faster rate than from control plots and, by mid-September, there were no differences in seedzone water content among treatments. Increased soil thermal conductivity appeared to be the reason for accelerated water loss in compacted treatments. Although water loss occurred at a faster rate in compacted treatments, compacting fallow soils with a roller immediately prior to fall seeding may increase winter wheat germination, emergence, and stand establishment during years of marginal seedzone water. / Graduation date: 1992

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.

This thesis examines the response to P fertiliser by wheat crops growing in the vertosol soils of the low rainfall areas of the northern grain zone of eastern Australia. Farmers in this region depend on water accumulated from rainfall over a fallow period and stored in the subsoil to increase wheat grain yield beyond that normally achievable from in-crop rainfall and to decrease the production risks due to rainfall variability. The large variability in stored water, seasonal rainfall and subsoil properties result in extremely varied yield and yield responses to P fertiliser between seasons and between sites. Finally, as a practical guide to predicting wheat response to P fertilizer: 1/. current sampling strategies of determining P only in the surface 10 cm appear to be adequate for soils with bicarbonate P concentrations greater than 15 mg/kg. 2/. For soils with lower concentrations in the surface, sampling of 80 cm is recommended. Crops with a mean concentration of bicarbonate P greater than 7 mg/kg between 10 - 80 cm are unlikely to respond to P fertiliser. 3/. No increase in profitable grain yield response was found for fertiliser applications greater than 10 kg P/ha. / Doctor of Philosophy (PhD)

Graduation date: 1995

No description available.

Differential adaptations of barley (Hordeum vulgare L.) and wheat (Triticum spp.) genotypes suggest that they be evaluated under multi-environmental conditions. The objectives of this study were to determine if small grain genotypes, bred for various moisture conditions, respond differently in terms of yield, water use, and rooting pattern to contrasting moisture conditions. Eight small grain genotypes were compared under a gradient of water from 89 to 404 mm (plus 254 mm of stored water) in a field study at Marana, AZ. A barley bred for low input conditions had greater root density in the subsoil and used moisture earlier in the season when compared to a high input barley (WestBred Gustoe). The cultivars bred for high input conditions required more water for optimum yield compared to those bred for low input conditions.

Bibliography: leaves 223-247. Effects of water availability during grain filling is examined in wheat (Triticum aestivum L.) and barley (Hordum vulgare L.) genotypes. The study tests the accumulation of dry matter (DM) and nitrogen (N) in the grain and also their remobilization from the shoot to the grain. Water stress during grain filling was found to reduce DM and N accumulation and also to increase N concentration in both wheat and barley grain.

Graduation date: 1994

Bibliography: leaves 223-247. / xiii, 247 p. : ill, maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Effects of water availability during grain filling is examined in wheat (Triticum aestivum L.) and barley (Hordum vulgare L.) genotypes. The study tests the accumulation of dry matter (DM) and nitrogen (N) in the grain and also their remobilization from the shoot to the grain. Water stress during grain filling was found to reduce DM and N accumulation and also to increase N concentration in both wheat and barley grain. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996

The actual evapotranspiration rate for wheat at the Campus Agriculture Center (CAC) and alfalfa at the Maricopa Agricultural Center (MAC) were measured using the Bowen ratio technique for near real-time irrigation scheduling. The Bowen ratio method underestimated evapotranspiration when compared with AZMET and Penman data. There were problems with the hygrometer and the net radiometer which might have caused this underestimation. The height-fetch ratio requirement was not met, and this may have affected the data. Irrigation scheduling programs and the technique to schedule irrigation in a near real-time were developed. Irrigation programs were not field tested because of the problem with field data. Simulated data was successfully used to demonstrate its application. It was found that irrigation could be scheduled in a near real-time with the programs provided reliable data and proper data acquisition systems are used.