Efficacy of perforating the soil to capture and store rain during fallow in dry regions
1999
Cattle, S. R.
Perforating topsoil of poor conductivity with artificial macropores can often improve the capture and storage of rain in dryland cropping. However, several features can render it of little merit. These include the inability of artificial macropores effectively to harvest coalescing water on the soil surface, and the increased evaporation caused by the greater surface area of subsoil exposed to the atmosphere in such pores. To ascertain the extent of these effects I used a sprinkling infiltrometer to determine the timeâtoâponding of small areas of perforated and unperforated soil subjected to different intensities of ‘rain’, and determined the rate of evaporation on perforated and unperforated microlysimeters. On average the perforated plots tended to take longer to pond than the unperforated ones, but the waterâharvesting efficacy of individual artificial macropores was highly variable, depending on their position in the microlandscape, the degree of connectivity with subsoil pores, the rate at which the water was applied, and the antecedent water content of the topsoil. The microlysimeter experiments revealed consistently greater evaporation from the perforated samples, with average daily differences between the treatments ranging from 2 to 26%. Antecedent soil water content and air temperature and windspeed affected the amounts of evaporation from both treatments. The ultimate efficacy of perforation for capturing water will vary spatially and temporally according to the extent to which the properties of the soil and environment impact on the behaviour of the penetrating water.
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