Response of Plant Water Potential to the Irrigated Environment of Southern Idaho¹

Abstract

Laboratory studies have shown that plant water potential affects a number of key processes involved in growth, but there has been almost no information on what levels of water potential occur under irrigated conditions in the field. Before assessing the practical implication of laboratory results on soil and crop management, this type of information must be available. Consequently, plant water potential in irrigated crops of Zea mays, Triticum aestivum, Hordeum vulgaris, PhaseoIns vulgaris, Pisum sativum, Solanum tuberosum, Beta vulgaris, and Medicago sativa, L. was measured throughout the growing season in southern Idaho. Soil moisture conditions and potential evapotranspiration were monitored. Daily changes in plant water potential varied from Iess than 5 bars to more than 20 bars, while random sampling of supposedly homogeneous sets of plants showed an average variation of about 2 bars. Changes due to differences in soil moisture were also detected, even though the soil moisture potential was kept high enough for near-optimum crop production. Though the crops differed widely in their response to changes in environment, the plant water potential was strongly affected by microarnatic conditions. Day-to-day changes in plant water potential generally correlated more closely with changes in potential evapotranspiration than with changes in soil moisture content. Many of the daily changes observed in the plants remain unexplained, however. In general, the average water potential levels of all the field-grown plants were lower than levels reported from growth chamber studies. Potentials seldom rose above -8 bars and were never observed above -5 bars.Additional index words: Soil water, Soil temperature, Microclimate.

The relationship between solar radiation, soil water, and water potential of ears of wheat

“…Thus on a day receiving insolation at near maximal rates for this location, computed water potentials are of the same order as those measured by Millar et aZ. (1971) and Cary & Wright (1971). Presumably ear water potentials would fall below these values when water uptake is severely limited by soil water or when transpiration is accelerated by inputs of advected energy.…”

“…J n wheat tillers with rolled leaves water potentials of ears and flag leaves were generally below -25 bars between 0900 and 1000 h. In other ears of wheat, water potentials below -25 bars were recorded, even though there were no signs of leaf rolling. Cary & Wright (1971) found that the daily range of water potential of irrigated wheat was between -10 and -35 bars with maxima ranging between -10 and -25 bars and minima as high as -15 bars and as low as -35 bars. The levels of plant water potential recorded in this 'Kopara' wheat and in Cary & Wright's were frequently lower than the water potentials at which net photosynthesis, leaf enlargement, and other growth processes slow to low rates in controlled environments (Boyer 1970;Frank et al 1973).…”

Plant Abiotic Stress: Water

“…As the soils dried down during water stress (Figure 1), soil water potential decreased from approximately À 0.01 to À 0.6 MPa (moderate drought stress) and root and leaf water potentials further decreased from approximately À 0.4 to À 1.2 and approximately À 1.0 to À 1.6 MPa, respectively, in maize seedlings (Adeoye and Rawlins, 1981). Under field conditions, leaf water potentials in the range of À 0.5 to À 2.5 MPa are commonly seen for crop species (Cary and Wright, 1971). Leaf water potential can change significantly during the day, with maximum values in the morning and minimum values during the afternoon (Cary and Wright, 1971;Acevedo et al, 1979).…”

Leaf water potential and leaf extension in a sudax crop

“…In the dryland plots, differences of up to 4 bars were recorded in the upper canopy, but variations were less in the irrigated plots. Differences were probably associated with plant-toplant variability which Cary & Wright (1971) reported to be as high as 2-3 bars for field-grown wheat and barley. Short-term changes in radiation intensity, especially in mid canopy positions between successive measurements, would also increase measurement variability.…”