Efficacy of perforating the soil to capture and store rain during fallow in dry regions

Perforating topsoil of poor conductivity with artificial macropores can oft en improve the capture and storage of rain in dryland cropping. However, se veral features can render it of little merit. These include the inability o f 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 time-t o-ponding of small areas of perforated and unperforated soil subjected to d ifferent intensities of 'rain', and determined the rate of evaporation on p erforated and unperforated microlysimeters. On average the perforated plots tended to take longer to pond than the unperforated ones, but the water-ha rvesting efficacy of individual artificial macropores was highly variable, depending on their position in the microlandscape, the degree of connectivi ty with subsoil pores, the rate at which the water was applied, and the ant ecedent water content of the topsoil. The microlysimeter experiments reveal ed consistently greater evaporation from the perforated samples, with avera ge daily differences between the treatments ranging from 2 to 26%. Antecede nt soil water content and air temperature and windspeed affected the amount s of evaporation from both treatments. The ultimate efficacy of perforation for capturing water will vary spatially and temporally according to the ex tent to which the properties of the soil and environment impact on the beha viour of the penetrating water.