CROP REQUIREMENTS FOR WATER: SOME VIEWS ON THE NEEDS FOR FUTURE RESEARCH

T. McBurney
The central theme of this 4th International Symposium on Water Supply and Irrigation has been the problem of how to determine the timing and amount of irrigation to be applied to a crop in order to achieve maximum economic production. More land is being irrigated as demands increase for greater production and increased levels of crop quality and continuity of supply. There is an increasing need for a better basis of rationalising this use of water.

Plants consist largely of water and lose considerable quantities by evaporation from the leaves (process of transpiration). If transpiration exceeds the rate at which water can flow through the roots and soil the plant becomes dehydrated and water stressed. The consequences of water stress have been widely studied and include yield reduction and effects on crop quality.

Crop demand for water depends on the evaporative conditions which vary from site to site. Attempts at estimating water demand are often based on meteorological measurements with account taken of soil and crop factors. Measurements are sometimes made of evaporation from an open water tank with a correction intended to take into account differences in plant size and species. There is uncertainty about what proportion of the water demand measured by these means needs to be applied as irrigation for a range of conditions. The methods measure or estimate the water potential of the soil (rather than of the platn) and may be checked against measurements made with a tensiometer, neutron probe or gravimetric technique. They cannot take into account the differing abilities of plant roots to penetrate the soil and extract water from it nor predict the influence of temporary rapid increases in evaporative demand occurring during the course of each day.

The ideal way of overcoming these difficulties would be to monitor water stress directly by measuring plant water potentials. The only means available for measuring plant water potentials in the field is the pressure chamber technique (Scholander et al., 1965). This requires considerable operator skill and the use of high pressure equipment and furthermore each measurement requires a leaf to be removed from the plant. At best this technique can only give spot

McBurney, T. (1988). CROP REQUIREMENTS FOR WATER: SOME VIEWS ON THE NEEDS FOR FUTURE RESEARCH. Acta Hortic. 228, 335-337
DOI: 10.17660/ActaHortic.1988.228.38
https://doi.org/10.17660/ActaHortic.1988.228.38

Acta Horticulturae