| Agriculture accounts for the most consuming water. Since the available freshwater is decreasing because of pollution, global warming and accelerating industry water use, we have to develop water saving agriculture (WSA) through more intensive research and technology.After experiencing soil water deficit under the threshold time, the crop's stomata conductance, photosynthesis (Pn), growth rate and water use efficiency (WUE) rebound to or even surpass those of the control's which have never been under water stress. This is called compensatory effect or over-compensatory effect. This compensatory mechanism could be applied to develop regulated deficit irrigation (RDI) and partial rootzone drying (PRD) irrigation methods.We designed an automatic irrigation scheduling system which was based on the water deficit threshold studies of our group in rice. (1) The scheduling was based on sensing the leaf turgor pressure (water potential) changes of the rice leaves. (2) When the plants are under good soil water status, the switch of the scheduling is off, no water irrigation switch off. (3) When the plants are under critical water stress, the turgor pressure decreases and irrigation starts. (4) When the water stress relieves after enough irrigation, sensing of the rebound leaf water potential and turgor-pressure would make the controlling system switch off the irrigation water.We also studied the water deficit compensatory effect after re-water and the deficit threshold time on broad bean (Vicia faba) which separately experienced 3, 6, 9 and 12 days water deficit treatment before re-water. The Pn and WUE of 3 days, 6 days treatments showed satisfactory compensatory effects and symbolized promising water saving irrigation method. But the Pn and WUE of 9 days and 12 days treatment didn't present compensatory effects after re-water compared to the control. These results suggest that the deficit threshold time of blooming broad bean is 6 days.
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