Using the Kostiakov – Lewis Infiltration function to evaluate a furrow irrigated field at Mhlume, a region in the north-eastern Lowveld of Eswatini (Southern Africa)

Abstract

The Eswatini sugar industry grows fully irrigated sugarcane on 57 420 hectares of land producing 6 197 753 tonnes of cane and 871 301 tonnes of sucrose annually (ESA-Integrated Report, 2019). Poor and inefficient furrow irrigation is still practiced by many growers in particular the poor small holder farmers in the industry. The two treatments were; in-row irrigated furrows and interrow irrigated furrows. A total of ten advance-recession measures were conducted, five were conducted on each treatment. The furrows were of length of 240 m and gradient along the furrows was 1:250. Two Washington State flumes were used to measure flow. One was used to measure inlow at the beginning of the furrow, and another one was used to measure runoff (outflow) at the end of the fourrow. The time water was allowed into the furrow was recorded. Other measurements included the time water reached the furrow end, the time to the middle of the furrow, the wetted perimeter at each point, the depth of flow and the top width of the water level. These measurements were required for the calculation of the Kostiakov exponent “a” and the coefficient “k”. The results showed that the distribution uniformity (84%), application efficiency (88%) and deep percolation ratio (11%) were better in interrow irrigation than in in-row irrigation. However, runoff was higher with interrow irrigation at 6% compared to 2% with in-row irrigation.