Using microsprinkler irrigation to reduce leaching in a shrink/swell clay soil

Preferential flow allows agricultural chemicals to rapidly move past crop root zone to subsoil, potentially contaminating groundwater. Deep shrinkage cracks in a shrink/swell soil may serve as preferential flow channels. Design and operation of an irrigation system is critical in shrink/swell soils in order to reduce or eliminate preferential flow while providing sufficient water for plant growth. The objective of this study was to compare microsprinkler irrigation (MI) and surface flood irrigation (FI) systems for their ability to reduce preferential flow and chemical leaching through a shrink/swell soil in a pear orchard. The MI system applied water at a rate of 2.8 mm h(-1), and the FI followed the traditional orchard irrigation method. Bromide tracer was applied to the pear orchard, Soil cores and percolate samples from passive capillary samplers (PCAPS) installed at 1.2 m depth were collected to test for the presence of Br tracer in the soil and percolate. The MI system greatly decreased water and Br leaching from soil to the PCAPS in comparison to FI. The percolate in MI was nearly zero. Most of the loss of Br occurred in the first one or two FI events. MI systems, such as that used in this study should be considered as an alternative to FI in such shrink/swell soils to reduce macropore flow. (C) 2002 Elsevier Science B.V. All rights reserved.