PLANT GROWTH AFFECTED BY WATER-TABLE

Gisborne Herald, Volume LXXVI, Issue 23023, 13 August 1949, Page 8

PLANT GROWTH AFFECTED BY WATER-TABLE

Although excess water in the soil "is available to plants—in the sense that there is an abundance of it—it is not utilised bv the most desirable plants because of the lack of air. which has been expelled from the soil, and the absence of desirable micro organic activity. Such excess water is definitely harmful when occurring within the root' 7one of plants for more than a day or two. Excess or gravitational, water is that which mav be present in the soil in excess of hygroscopic and capillary water, and which, if not prevented by Ihc presence of impervious layers, is free to drain away. If it does not drain away it fills the pore spaces in (he soil, and in doing so it exc’udes air and sets up what is termed water-logged conditions. When a dry. or comparatively dry. soil is wetted from above, the top layers of the soil retain as much water as its capillary capacity will allow, and anything in excess of that passes downward as gravitational water, but becomes capillary water of the soil at lower depths. If a layer impervious to water is met with, excess water from above tends to accumulate, and a ground water level or water-table results' in cases where such water is supplied to the layer more rapidly than it can be removed by plants, upward caod'arv movement or by drainage. If the impervious layer is within a few feet of the surface. the excess water mav accumulate to such an extent as to cause the water-table to reach the surface for prolonged periods in the wetter seasons of the year. In low-lying areas receiving natural drainage from higher-surrounding country. excess water may accumulate and rise to the surface even though the impervious laver which prevents its downward movement is far below the surface. Such conditions give rise to many of the New Zealand swamps.