Irrigation investigations in Otago, New Zealand

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Abstract
Physical properties, including the percentage of fine particles, organic carbon, 15-bar retention, held capacity, and available moisture. show consistent increases between virgin soil groups formed under semiarid (brown-grey earths), sub-humid (yellow-grey earths), and humid (yellow-brown earths) climates. Bulk density values decrease throughout the same sequence. There is a tendency for similar changes to occur with soils of increasing ground surface age within the brown-grey earths. There is an insufficient range of ground surface ages to establish this tendency for the other groups. Irrigation, and associated management, have tended to alter the properties of a particular soil group in the direction of those of the group formed under a higher rainfall. This tendency is not true for the bulk density, which is in most cases higher under irrigation. The available moisture held in the top 12 in. of the soils studied ranged from 1.58 in. to 4.30 in. If irrigation was applied at wilting point, the soils in the three zonal groups would retain the following approximate amounts: brown-grey earths, 2 in. to 2 1/2 in.; yellow-grey earths, 2 1/2 in. to 3 1/2 in.; yellow-brown earths, 3 in. to 4 in.

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