Effects of flow depth on distribution uniformity of water and bromide in a sandy loam soil in furrow irrigation

In this study, the effect of flow depth on water content and solute distribution was assessed in furrow irrigation. Two series of field experiments including small and large scale furrow experiments were conducted. In large scale, four experiments were carried out. One experiment was conducted under free-draining (FD) conditions in which bromide was applied during the entire irrigation event and three experiments were carried out in blocked-end furrows in which bromide was injected either during the entire irrigation event (100%), the first half of the irrigation (FH), and the second half of the irrigation (SH) event. In small scale, five field experiments were conducted on short blocked-end furrows. Three experiments were carried out, each with the same duration but with different amounts of water and solutes resulting from 6, 10, and 14 cm furrow water depths. Two more experiments were performed with the same amounts of applied water and solute and, consequently, different durations, on furrows with depths of 6 and 10 cm of water. Soil water contents at different times and locations in furrow cross-section were measured with neutron probe tubes and TDR. Soil samples for bromide analysis and gravimetric soil water contents from all the experiments were collected at different depths up to 1.80 m, 5 days after the irrigation at three locations near the inlet, in the middle, and close to the outlet of the experimental furrows. Results in large scale experiments showed substantial non-uniformity in solute distribution along the monitored furrows, with the degree of non-uniformity depending upon flow depth and solute application time. The effects of flow depth and irrigation/bromide application time on soil water contents were more pronounced in the soil surface layers and were found to be relatively minor at deeper depths. Water and solute deep percolation rates also showed dependency to flow depth and solute application/opportunity time and gradually decreased along the furrows. In small scale experiments, results showed that both the water level and the duration played an important role in distributing water and solutes in the soil profile. A positive correlation was found between water level and infiltrated amount of water or solute. Irrigation with the 14 cm water level and short application time improved the distribution of water and solutes within the soil profiles, while also causing relatively less deep percolation of water and solutes as compared to low and moderate water levels and relatively long duration times.