Irrigation investigations in Otago, New Zealand

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Abstract
Physical analyses, including texture, available moisture, and porosity, support the grouping of these soils into brown-grey and yellow-grey earths. The brown-grey earths were denser than the yellow-grey on virgin sites. They also had lower field capacities, lower moisture storage, and less organic matter. Under irrigation the densities of both soil groups increased, especially in the surface 4 in. The field capacities and organic matter of the brown-grey earths increased, but those of the yellow-grey earths did not. Both soil groups increased their available moisture, but the gain was greater for the brown-grey earths. The most important physical property is field capacity, and the derived available moisture. Neither the 1/3-bar retention value nor the moisture equivalent is a reliable estimate of top-soil field capacity, which should be determined in the field. It is recommended that the amount of water applied at an irrigation should not exceed 1 in. for each 4 in. of soil depth.

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