WATER CONTROL IN AGRICULTURE

Press, Volume XCVII, Issue 28701, 26 September 1958, Page 11 (Supplement)

WATER CONTROL IN AGRICULTURE

By

A. W. RIDDOLLS,

Senior Lecturer in Engineering, Canterbury Agricultural College, Lincoln.

A simple calculation based on past meteorological data and the known water needs of crops shows clearly that the Canterbury Plains suffer regularly from a soil moisture deficiency during the growing season.

For example, the average growing season rainfall at Lincoln College is about 10 inches less than is required for maximum growth of pastures. In drier seasons the deficiency is much greater than this and only very rarely is seasonal rainfall sufficient for plant growth.

If this deficiency in water for plant growth is made good by irrigation, large increases in production are obtained. Measurements made under flood irrigation at Winchmore and spray irrigation at Lincoln College show that production can be doubled in many seasons under irrigation. Irrigation offers great possibilities for substantial increases in production in Canterbury from pastures, forage, vegetable, and fruit crops. Fortunately, Canterbury is well situated for irrigation water, with large rivers flowing at high levels in summer and good supplies of ground water at shallow depths in many areas. In many other parts of New Zealand irrigation shows a similar response to that obtained in Canterbury. On the other hand, many lowlying areas suffer from excess soil moisture in winter and spring. In these areas water tables are too high, resulting in poor growth, difficulty and delay in working the soil and pugging of pastures. On the foothills and downlands, tight clay soils lie cold and wet through winter and spring. All of these areas will give a response to drainage, whether by open drains, tiles, mole or simple surface drainage systems. The great open and tile drainage works installed last century by John Grigg, of Longbeach, and many other pioneer farmers, and in more recent years spectacular increases in production obtained on the Lincoln College farm from tile and mole drainage, show what drainage can do to increase farm production. Erosion On the lower mountain slopes, foothills and downlands uncontrolled runoff from rainfall, accentuated by the destruction of plant cover by rabbits, overgrazing by sheep, and burning has played havoc with z the land. The most casual inspection will show deep gullies, rilling and

sheet erosion, and shingle and silt washed down to spread an infertile layer over large areas of once fertile flat land. Stream channels blocked with debris eroded from the hills overflow and damage valuable farm land. Many farmers on valley floors are afraid to cultivate for fear that their topsoil will be washed away by floods. Uncontrolled runoff and seepage from the steeper slopes keeps the flatter, ploughable land excessively wet. In spite of the good work done in recent years by many farmers aided by catchment boards and the Soil Conservation Council, much remains to be done in water control and conservation on our hill country. The catchment control scheme at Glenmark, near Waipara, provides an excellent example of what can be done to control runoff.

By a co-operative effort between the farmers in this catchment area, assisted by the Soil Conservation Council and the Soil Conservation Service of the Department of Agriculture, a comprehensive scheme involving fencing for grazing control, tree planting, dams, contour pasture furrows, graded banks and grassed waterways, promises to end the flooding and shingle debouchment on the flatter areas and by holding water on the hills to increase summer production.

This kind of scheme could be duplicated over and over again in the valleys of the hills bordering the Canterbury plains and river valleys, and in many other parts of New Zealand. Proper control of water, so that plants have enough but not too much at the right time, and so that valuable soil is not washed away or covered by debris, can bring immense benefits, on an economical basis, to Canterbury and to most parts' of New Zealand. So far, we have only touched the fringes of the probI lem of water control. z