SOIL MOISTURE CONTROLLED SUBSURFACE DRIP IRRIGATION ON SANDY SOILS

Abstract

Subsurface drip irrigation (SDI) is being adopted in areas to conserve water while maintaining economicalproduction of crops. These systems have not been evaluated on sandy soils common to Florida. An SDI system was installedon a well-drained sandy soil for sweet corn production in Florida. SDI tubing was buried under each row (76-cm spacing)at either two depths of 23 or 33 cm below the ground surface to result in two experimental treatments. Additionally, twomethods of irrigation scheduling were imposed on the SDI treatments. One scheduling treatment was the initiation andtermination of irrigation based on soil moisture measured by time domain reflectometry (TDR) probes installed 5 cm abovethe drip line. The other scheduling treatment was a daily irrigation event at rates consistent with typical practice in the region.Sprinkler irrigation scheduled similar to farmer practices in the region and non-irrigated control treatments were alsoestablished. The soil moisture based irrigation scheduling regime resulted in high frequency short duration (30-min)irrigation events to meet crop water needs. The 23-cm deep soil moisture-based treatment resulted in similar yields andsimilar water use in 2002 and reduced water use 11% with similar yields compared to sprinkler irrigation in 2003. Thisindicates that 23-cm deep SDI is feasible for sweet corn production under these conditions. The combination of optimum yieldand minimum water use was achieved with soil moisture based set points of 10% to 12% by volume (on-off). The 33-cm depthSDI treatment was found to be too deep for optimal yield results on sweet corn under the type of sandy soil in the study.Time-based SDI treatments were under-irrigated but showed evidence of considerable drainage based on soil moisturemeasurements due to single daily irrigation events that promoted movement of irrigation water below the root zone.Comparison of drainage calculations beneath the SDI treatments and sprinkler treatments indicated that up to 24% lessdrainage may have occurred on SDI plots compared to sprinkler plots largely because SDI applied water to the root zone andnot the furrows.