Soil water measurements on four alluvial soils in Canterbury 2. Soil wetting patterns under pasture

Abstract

Changes in water content of four soils from alluvium were monitored with a neutron probe during wetting up phases in two seasons. The soil types varied in texture and depth to sandy gravels and are representative of a large area of the Canterbury and North Otago Plains. Soil wetting from rainfall did not occur as a wetting front progressively restoring deeper layers to field capacity. Rather, initial rainfalls only partially restored the deficit of the upper 40–60 cm of soil material. Subsequent rainfalls progressively recharged these horizons, and, at the same time, water penetrated more deeply into the soil, partially wetting successively deeper horizons. In some cases, water penetrated to 120 cm before the uppermost horizons were fully recharged. A wet front formed by heavy rain when the soil was dry showed the marked spatial variability of wetting possible under heavy rainfall in these soils.

Keywords:

• wetting
• infiltration
• recharge
• macropores
• Canterbury
• soil types
• soil water