Crop establishment using subsurface drip irrigation: a comparison of point and area sources

One of the greatest challenges faced by irrigators using subsurface drip irrigation (SDI) is crop establishment. Establishment with SDI relies on unsaturated water movement from the buried source to the seed or seedling. Establishment is therefore affected by distance to source, soil texture, structure, and antecedent water content. Two products were compared (drip tape and CRZI – Capillary Root Zone Irrigation) in a field trial designed to address the establishment issue. To measure the widest establishment extent, a crop was sown perpendicular to the drip laterals. The CRZI system comprises a combination of both impermeable and highly conductive materials designed to produce a wider lateral wetting pattern, while reducing drainage and surface tunnelling. The hypothesis being tested was that the CRZI concept would offer some advantage over drip tape for addressing the establishment issue. Results showed that for the soil at the experimental site (Hanwood loam), installation depth of either product should be no greater than 0.2 m. If attempting to establish a broadsown crop such as lucerne or pasture, lateral spacing should be no greater than 1.0 m. With this configuration, an application depth of 120 mm should still be expected for total surface coverage. CRZI did not produce any establishment advantage over drip tape. Two explanations are given for this result. Firstly, the soil in which the trial was performed has excellent capillary properties and has a natural clay pan which would serve to even out results. Secondly, the two products exploited very different wetting methods to produce similar surface wetting efficiency (ratio of surface wetted width to applied irrigation volume). The drip tape quickly saturated the surface and wet outwards through surface flow. As CRZI did not utilise the surface to aid with distribution, it produced a slower, more even, wetting pattern.Communicated by P. Thorburn