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Abstract
Two studies of the distribution of the levels of the nutrients phosphate, sulphate, potassium, magnesium, sodium, calcium, and of pH levels, were carried out in sheep pastures that were flood‐irrigated by the border strip method in mid Canterbury, New Zealand. The border strips had been formed by grading the land to a gently sloping plane surface, then creating c. 12 m‐wide, 200–300 m long strips by raising “borders” c. 1.8 m wide and c. 12 m apart, with strips aligned with the direction of maximum fall. The first study involved four 30‐year‐old border‐strip pastures at Winch‐more Research Station, whereas the second study involved 20 border‐strip pastures of varying age on nine commercial farms in Ashburton County. In both instances 75 nun‐deep soil samples were taken from the tops of the irrigation borders and from the border crutches and strips, at varying positions up and down the length of the border‐strip systems. In both studies nutrient levels were in general lowest in the strips, highest in the crutches, and intermediate on the borders. These differences are presumed to have been caused by stock camping on the borders and in the crutches, and the movement of faeces by irrigation water. A practical outcome of the study is the conclusion that fertiliser and lime applications can be restricted to the strips.
