Moisture regimes of a cracking clay soil under furrow irrigated cotton

Abstract

The moisture regimes of a self-mulching cracking grey clay under furrow irrigation in the Namoi Valley, New South Wales, were measured during the 1979-80 cotton season. A moisture profile of 0.1 9 g/g down to at least 150 cm depth was observed at permanent wilting point of the cotton plants. Five weeks later, further drying of the profile to 0.14 g/g (- 80 bars) at 150 cm had occurred, probably by evaporation through the cracks. The maximum storage capacity of the soil for available water to 1 50 cm depth was 19.5 cm of water. However, only 10.9 cm of this was replenished by furrow irrigation after 48 h of redistribution. The discrepancy was explained in terms of the rapid sealing of cracks due to slaking and swelling of the soil, which limited the wetting front to about 80 cm depth. Poor aeration prevailed in the soil after every furrow irrigation because a region of very low air-filled porosity (<5%) was created in the wetted subsoil.