Irrigation investigations in Otago, New Zealand

Abstract

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.