ISHS Acta Horticulturae 119: III International Symposium on Water supply and Irrigation in the open and under Protected Cultivation
ROOT WATER UPTAKE MODEL DEPENDING ON SOIL WATER PRESSURE HEAD AND MAXIMUM EXTRACTION RATE |
| Authors: | J.C. Hoogland, R.A. Feddes, C. Belmans |
| Abstract:
Many present day models describing water uptake by root system are based on an analogy with Ohm's law. These models require rather detailed information about root distribution, root densities, conductivities of the soil-root system, soil and plant resistances, etc. Often these parameters vary with type of soil and, also, with depth and time. A rather simple approach has been proposed by Feddes, Kowalik and Zaradny (1978). They compute root water extraction at the various depth depending on potential transpiration rate, rooting depth and the local prevailing soil water pressure head. In this paper a modification is proposed in such a way that the maximum root water extraction is taken to be a decreasing function with depth. This function starts at the soil surface with a value derived from literature data. The modification offers the possibility that in the beginning of a drying period roots can extract water from the upper soil layers while still leaving the soil water in the deeper layers unused. On the other hand the modification also allows that in soil with dry soil layers at the top and a shallow groundwater table close to the root zone, most of the water can be taken from layers near the water table. A comparison between numerical and laboratory data is made and results of numerical experiments are shown. The model can be applied to evaluate the effect of root zone modifications such as changes in soil moisture, soil profile and groundwater table depth upon transpiration and crop production. | |
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