The Effects of Spatial Variability of Infiltration Rate Along a Furrow on Furrow Irrigation Efficiencies

Variability on soil properties along a furrow and through a growth season causes the variability in infiltration rate and eventually leads to the variability on irrigation efficiencies. The aim of this study is to find if infiltration rate variability along a furrow affects irrigation efficiencies, i.e., Distribution Uniformity (DU), Application efficiency (Ea), Deep Percolation Ratio (DPR) and Tail Water Ratio (TWR), and how does the infiltration change spatially and temporally through a growth season. Soil had sandy clay loam texture. To achieve the goal of this study, two furrows with 140 m length and 1.83 m width were selected in Amir Kabir unit by Product Company in spring and summer Evaluation measurements were made in six furrows with 140 m length and 1.83 m width, grouped in two sets of three furrows each. The middle furrow in each set was used to conduct measurements and the other used as buffers. In the first group (uniform assumption) irrigation performances were calculated assuming uniform soil infiltration properties along the furrow, but the middle furrow of the second group (variable assumption) was divided to four sections each of which was 35 m and infiltration was calculated for each section separately, to calculate irrigation performances accounting for infiltration variability along the furrow. Also irrigation performances were simulated by both above mentioned assumptions. Then calculated irrigation performances were compared with performances simulated by the model, through growth season. Results indicated that if (CVf0) along a furrow is considered in estimating irrigation performances, DU will change significantly in compare to other performances. In which applying (CVf0=0.28), Du decreased 33% from uniform to variable assumption. But, the reduction of Ea was %6. DPR increased 26% from uniform to variable assumption, and TWR showed no changes by the change of the coefficient of variation of final infiltration.