Determination of the control point position for the estimation of the optimal cutoff time of closed-end furrow irrigation systems

Furrow irrigation systems are one of the dominant methods for growing cotton in the North China Plain and in other parts of the word. Many attempts have been made to improve furrow irrigation performance by selecting an optimal cut off time. The objective of this study is to determine the appropriate control point position for the estimation of the optimal cutoff time in a field situation with a closed-end furrow irrigation system. The experiments were conducted in a cotton field at the EcoAgricultural Experimental Station in Wuqiao, Hebei Province, North China Plain. Simulations employing two optimization strategies were used for determining the optimal cutoff time. These strategies were selected based on the irrigation system properties (total water applied depth and field characteristics), aiming to maximize application efficiency or requirement efficiency. The results show that the optimal cutoff time could be selected based on the relationship between the cutoff time and the advance time to a particular control point downstream. The position of this control point depends on the range of the inflow rate. The recommended control point position for estimating the optimal cutoff time was set at 0.9 of a furrow length for inflow rates less than 1.6 l/s and at 0.8 and 0.7 for inflow rates ranging between 1.6 and 2.0 l/s and 2.0 and 2.6 l/s, respectively. The results also show that to achieve a high irrigation performance when the inflow rate is high, it is better to reduce the requirements of irrigation and increase the number of irrigations. Determining the appropriate position of the control point helps to select the optimal cutoff time without requiring knowledge of the other irrigation system properties (i.e., soil water content, etc.). Keywords: Closed-end