ISHS Acta Horticulturae 278: Symposium on Scheduling of Irrigation for Vegetable Crops under Field Condition
FIELD EVALUATION OF PLANT EXTRACTABLE SOIL WATER FOR IRRIGATION SCHEDULING |
| Authors: | J.T. Ritchie, M. Amato |
| Abstract:
The concept of soil water available for plant growth and the methods for its measurement are discussed in relation to problems and limitations of the traditional approaches. The biophysical explanation of plant extractable soil water (PESW) is, given an established crop on a soil at field capacity, with no further water supply, the total soil water that is extracted by roots up to a time when the plants have prematurely died or gone into dormancy resulting from a lack of water supply. A definition of the upper and lower limit of PESW is suggested, that takes into account both soil profile and rooting characteristics of the crop; methods for the field determination of such limits are also discussed. A field study is presented that illustrates how spatial variation in water availability can affect crop performance. Simulation with the CERES model is used to show how the relationships between soil and crop variability change with weather patterns. The knowledge of PESW spatial variation is then used as a basis for comparing irrigation strategies: uniform irrigation is compared with differential water application over a heterogeneous field. Water savings and crop performance for each strategy are evaluated through a 30-year simulation with the CERES model. Uniform application of water results in yield losses and/or excessive water application, due to under-treating of some areas and over-treating of others. Other applications of the concept of PESW are discussed for fine-tuning of irrigation, in view of more efficient use of precipitation and reduction of leaching. The concept of 'soil deficit irrigation' is introduced as an alternative to water supply to full capacity, for geographic areas where the rainfall probability during the growing season is high. | |
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