Estimating recession times in furrows with small longitudinal slope on a clay soil

Advance and recession characteristics are the two main parameters for determining the performance of furrow irrigation. Field estimation of recession times can be a difficult task on a clay soil. There is no suitable technique available for estimating the recession times in furrow irrigation on fields with a high clay content and small longitudinal slope. Two methods, viz., zero-depth and waterlevel drop rate methods are investigated for estimation of recession times in furrow irrigation. The methods were applied to 13 irrigation events on furrows monitored on a farm in northern New South Wales, Australia. The soil type at the experimental site has a high clay content (up to 67%) and develops cracks when dry. The accuracy of the proposed methods was evaluated by comparing the calculated total volume of water infiltrated in furrow with that observed in the field. The water-level drop rate method was more accurate than the zero-depth method for estimating recession times. The zero-depth method resulted in overestimation of recession times for all the irrigation events considered in this study. A possible explanation for poor performance of the zero-depth method is related to stagnation of water in furrows due to low final infiltration rate and small bed slope.