Submitted to: International Irrigation Show
Publication Type: Proceedings
Publication Acceptance Date: November 4, 2001
Publication Date: November 4, 2001
Interpretive Summary: Irrigation of crops should be done at times and with quantities of water that avoid waste of water and that maximize the use of rainfall while maintaining high yields. This is difficult to do with current manual irrigation scheduling methods. An automatic irrigation scheduling and control system was investigated for drip irrigation of corn and soybean. The system relies on measurements of crop leaf temperature. It assessed crop water stress levels by comparing the leaf temperature to a threshold temperature that was determined for a well-watered, unstressed crop. The automatic system was compared against a manual method that used soil water measurements to assess the amount of water used by the crop each week, so that the next irrigation could apply that amount of water to replenish the soil water reservoir. Over two years with quite different rainfall amounts, corn yield, total water use and water use efficiency (WUE, the amount of yield per inch of water used) were stable for the automatic irrigation treatments. But, corn water use and WUE varied widely over the two years of corn production 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 the automatic irrigation system will allow a choice between larger yields or larger water use efficiencies to be achieved for corn, but not for soybean. However for both crops, the automatic system delivered yields as large or larger than those obtained with the manual system in all years, with less management time and effort.
Technical Abstract: An automatic irrigation system that allowed either high yields or high water use efficiency to be chosen would be a useful farming tool. We tested a system that uses crop canopy temperature to automatically schedule and apply irrigations. 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, all with surface and subsurface drip irrigation. Each year, the 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 for the automatic cirrigation treatments. Corn 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 or larger water use efficiencies to be achieved for corn, but not for soybean.