The movement of water in soils is of great importance to all of us but especially to agriculturalists. If it were not for this movement plants would not be able to survive in soil. If the moisture moves too freely in the soil insufficient water can be stored to supply plants during dry periods. The movement of water through soil may remove plant nutrients or accumulate salts in soil horizons.

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Soil moisture information can be used accurately in determining the timing and amount of irrigation applied to plants. Pan and Pan et al. proposed a robust and simple daily diagnostic equation for estimating daily soil moisture. The diagnostic equation evaluates the relationship between the soil moisture loss function and the summation weighted average of precipitation. The loss function uses the sinusoidal wave function which employs day of the year (DOY) to evaluate the seasonal variation in soil moisture loss for a given year. This was incorporated into the daily diagnostic equation to estimate the daily soil moisture for a location. Solar radiation is an energy source that drives the energy and water exchanges between vegetation and the atmosphere (i.e., evapotranspiration), and thus impacts the soil moisture dry-down. In this paper, two parameters (the actual solar radiation and the clear sky solar radiation) are introduced into loss function coefficient to improve the estimation of soil moisture. After the Introduction of the solar radiation data into soil moisture loss function, a slight improvement was observed in the estimated daily soil moisture. Pan observed that generally the correlation coefficient between the estimated and the observed soil moisture is above 0.75 and the root mean square error is below 5.0 (%v/v). The introduction solar radiation data (i.e. clear sky solar radiation and actual solar) improve the correlation coefficient average for all the sites evaluated by 0.03 when the root mean square error is generally below 4.5(%v/v) for the entire root zone.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1946 B8 / Master of Science

The recent development of the peltier-type thermocouple psychrometer has made possible the measurement of soil moisture potentials to values as low as -80 bars. The applicability of this type of psychrometer to "in situ" measurements of moisture potential at a Sonoran desert field site is investigated. An evaluation is made of the effect of variations in soil temperature, moisture content, and solute concentrations on the psychrometric measurements. Moisture potential measurements with the psychrometer are shown to be limited to a moisture content range composing approximately 50 per cent of the total variation in soil moisture observed during the study. A significant quantity of moisture is transferred across the soilatmosphere interface at moisture contents both above and below the measurement range of the psychrometer. Psychrometric measurements cannot be used to determine the total moisture flux into or out of the soil horizon. The temperature component of the total soil moisture potential is not measurable with the thermocouple psychrometer. Under conditions occurring frequently within the study period, this component is shown to be of equivalent or greater magnitude than the components measured with psychrometric techniques. Laboratory measurements of the sorption-desorption isotherms for the field soils were made using thermocouple psychrometers. The isotherms vary significantly among samples, as a function of soil composition. This variation prevents the determination of absolute values of soil moisture content from measurements of soil moisture potential. However, for the soils at the field site, the slope of the moisture isotherms at a given potential does not vary significantly among samples. Psychrometric measurements can be used to determine moisture content changes at the study site, within the measurement range of the psychrometers. The variation in moisture isotherms, the significance of temperature induced moisture flux, and the limited moisture range of psychrometric measurements prevents the construction of a quantitative model of soil moisture movement from potential measurements made with thermocouple psychrometers. The effect of Celtis pallida (desert hackberry), a native plant species, on the soil moisture regime is described. Moisture uptake by the plant, and precipitation input to the soil near the plant are described in terms of the potential variations they produce. The particular hackberry plant studied is shown to be removing moisture from the soil at potential values as low as -30 atmospheres. Moisture potentials in the root zone were within the measurement range of the psychrometers throughout most of the year. The measurement of soil moisture potentials with the thermocouple psychrometer is shown to be an effective means of studying moisture content variations in the root zone of desert plant species.

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The experiment was conducted at the University of Arizona Campus Agricultural Center to evaluate the effect of soil moisture stress on photosynthesis, transpiration, diffusive resistance, temperature differential, leaf temperature, and specific leaf weight of seven sorghum Sorghum bicolor (L.) Moench cytoplasms represented by nine lines. As soil moisture stress increased, diffusive resistance and leaf temperature increased whereas photosynthesis and transpiration decreased. Temperature differential was highest under high soil moisture stress and lowest under medium soil moisture stress. Specific leaf weight was highest under medium soil moisture stress. Three lines, AKS37, AKS38, and A2Tx398, representing two different germplasms under high soil moisture stress exhibited high photosynthesis and transpiration rates, high specific leaf weights, and low diffusive resistance. Differences in photosynthesis rates under non-soil moisture stress between A1 and A2 cytoplasmic sterility systems were significant.

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No description available.