Foliage temperatures of cotton obtained by means of infrared thermometry, along with air wet and dry bulb temperature measurements, were used to investigate certain relationships existing between the water contents of soil and air and the ability of the crop to maintain transpiration at the potential rate. It was found that as soil water content is progressively depleted fo!lowing an irrigation, departure from potential transpiration begins to occur at smaller and smaller values of air vapor pressure deficit in a regularly predictable fashion. It was also demonstrated that the plant water potential of cotton transpiring at the potential rate is a function of the air vapor pressure deficit and that the difference between this base value and the tension that develops under nonpotential conditions is a unique function of a newly developed plant water stress index. Finally, an example of the application of this foliage temperature-based index to evaluating the effects of an irrigation event is presented.
SUMMARYThe mineral content of N, P and K in leaves, stems, roots and seed of field beans, subjected to four watering regimes were compared in 1976 and 1977, and of a foliar nutrient spray in the latter year.N, P and K content increased in all treatments with the increase in plant size and then declined at about the time of podding and death of the leaves.Water shortage reduced the amounts of N, P and K throughout the growth period and for the seed at final harvest; the decrease was more pronounced in 1976 than in 1977. The plants under stress conditions benefited from the foliar nutrient spray more than the unstressed plants.
Field beans (Viciafaba L.) were given three irrigation treatments in the field during two seasons to examine reduction in leaf area by water shortage, through effects on number of cells, cell volume and cell arrangement.The two crops behaved differently in the two seasons, presumably because of differences in environmental conditions. Season 1976 was brighter, warmer and drier than 1977. Water shortage reduced leaf area, dry matter and economic yield. The rate of leaf appearance and leaf longevity were also decreased by water shortage. The greatest biological and economic yields were produced by the wet treatment, followed by the medium and dry treatments. The treatment open to natural rainfall yielded least in 1976, but the second most in 1977. The yields of 1976 were considerably less than those of 1977.
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