Submitted to: International Water and Irrigation Review
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2001
Publication Date: N/A
Interpretive Summary: Drip and sprinkler irrigation control systems are now common and have reduced farm labor requirements. However, these systems still require that the farmer decide when and how much to irrigate. The decision process is error prone and time consuming, often leading to lower than expected yields and wasted water. We tested an automatic irrigation scheduling and control system for three seasons of soybean and two seasons of field corn. The system senses crop leaf temperature, which typically rises as the crop runs out of water and becomes stressed. Results were compared with traditional weekly manual irrigation based on measurements of soil water content. For corn under the automatic system, yield and the efficiency with which water was used were both stable and high across years, with yield approaching the maximum yield potential for corn in the southern High Plains. The manual method resulted in lower yields and less efficient water use when the season was relatively dry and hot. For soybean, yields were stable at approximately 70 bushels per acre for all irrigation depths greater than 24 inches, and the manual and automatic systems performed equally well. The lack of success with soybean was linked to its lower yield potential, which is about one third that of corn, and its lower susceptibility to water stress during critical crop growth stages.
Technical Abstract: An automatic irrigation system that allowed control of yields and water use efficiency would improve the economic use of water in agriculture. We tested a system that uses crop canopy temperature to automatically schedule and apply irrigations by surface and subsurface drip irrigation. Corn (Zea mays L., hybrid Pioneer 3162) was grown in 1997 and 1999; and soybean (Glycine Max (L.), var. Pioneer 9481) was grown in 1996, 1998, and 2000. Four automatic treatments were compared with a manual weekly irrigation regime that was 100% replenishment of water to field capacity as measured by neutron probe. Treatments of 67% and 33% of the 100% amount were also applied manually to provide data for curves of yield vs. water use. Treatments were triply replicated. Most or all of the automatic treatments out yielded the 100% treatment in each year. Corn yield, total water use (mm) and water use efficiency, WUE, were stable across years for the automatic irrigation treatments. Corn yield, water use and WUE varied widely over the two years for the manual treatments. The automatic system was able to respond to low stress levels resulting from good rainfall, and thus delivered larger irrigation WUE values when rainfall was more plentiful. For soybean, yields and WUE were not more stable for all automatic treatments. It appears that manipulation of irrigation control parameters will allow a choice between larger yields and larger water use efficiencies to be achieved for corn, but not for soybean.