Deficit irrigation can help save water and increase productivity in field crops. When less water is used for irrigation, the productivity per unit of water applied goes up. However, when looking at the total water consumed by the crops, productivity decreases if deficit irrigation is more than 20%. This happens because crops need a certain amount of water to produce an initial yield, and they become more efficient at using water as they grow. So, in areas with limited water where water can be reused, deficit irrigation might not be the best choice for maximizing economic return.