Bridging Systems Modeling and Engineering: Utilizing RZWQM for Water Stress-Based Irrigation Scheduling.

Crop water stress, a direct indicator of crop water deficit but difficult to measure, can be predicted using a well-calibrated RZWQM model. The objective of this study is to evaluate whether the RZWQM model can be used for crop water stress-based irrigation secluding. A water stress-based irrigation scheduling software (Irrigation Schedule) was developed using Java language to operate RZWQM for irrigation decision. This software package allowed customers to set crop water stress threshold and download online forecast weather data. The software therefore suggested irrigation amount when the water stress values is below this threshold and taking future crop water demand and rainfall into account. A case study was conducted using a full and deficit irrigation experiment for maize in 2010 near Greeley, Colorado. The water stress threshold in the RZWQM model was set at 0.7 and suggested irrigation amount was computed using calibrated soil information (field capacity and permanent wilting point), management allowable depletion (0.4 for maize with maximum ET of 10 mm), and RZWQM predicted rooting depth. This virtual experiment showed that the water-stress based irrigation approach resulted in slightly higher predicted yields compared to predicted yields based on actual irrigation record while using the same amount water for both full and deficit irrigation. For full irrigation, the predicted yield was 11.22 Mg/ha versus predicted yield of 10.52 Mg/ha based on actual irrigation record; for deficit irrigation the yields were 8.49 versus 8.42 Mg/ha. Besides, comparing to recorded irrigation events, the RZWQM water-stress based method reduced the number of irrigation events from 13 to 6 for full irrigation, and from 9 to 7 for deficit irrigation. In the future, the RZWQM water stress based irrigation scheduling will be applied in a field study and compared with other approaches such as soil moisture-based method.