Automated Subsurface Drip Irrigation Based on Soil Moisture

Abstract

A subsurface drip irrigation (SDI) system was installed on a well-drained sandy soil for sweet corn and peanut 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, two methods of irrigation scheduling were imposed on the SDI treatments. One scheduling treatment was the initiation and termination of irrigation based on soil moisture measured by time domain reflectometry (TDR) probes installed 5 cm above the 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 also established. The soil moisture-based irrigation scheduling regime resulted in high frequency short duration irrigation events to meet crop water needs. The 23 cm deep soil moisture based treatment resulted in similar yields and similar water use in 2002 and reduced water use 11% (23% when adjusted for excessive irrigation due to equipment problems) with similar yields compared sprinkler irrigation in 2003. The soil moisture based set points for these results were 10-12% by volume (on-off). The 33 cm depth SDI 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 moisture measurements. Comparison of drainage calculations beneath the SDI treatments and sprinkler treatments indicated that up to 24% less drainage (50% for adjusted data) may have occurred on SDI plots compared to sprinkler plots. Irrigation was not necessary for peanut planted in rotation with sweet corn in the rainy Florida summer climate.