WET Sensor Technique to Evaluate Soil Moisture Distribution Patterns under Different Discharge Rates

doi:10.21608/ejss.2014.182

WET Sensor Technique to Evaluate Soil Moisture Distribution Patterns under Different Discharge Rates

Document Type : Original Article

10.21608/ejss.2014.182

Abstract

INSURANCE precise placement of water and fertilizer in active root …….zone is based on suitable moisture distribution pattern under point source emitter, consequently, is affected by some soil properties and emitter discharge rate. This investigation aims to evaluate the patterns of soil moisture distribution under different discharge rates for two different soils (sandy and loamy). The studied discharge rates were 1.8, 4.6 and 8 L h^-1, in addition to flooding application for comparison. The study also aims to detect the reliability of applying equivalent water depth equation, particularly when water is trickling. For all treatments, soil moisture was measured using a moisture meter called "WET sensor" which calibrated in Lab. for both soils before field work. Validation of Schwartzman and Zur’s model as a simplified semi-empirical method to determine the geometry of wetted soil volume was to detect both studied soils as an additional objective. The obtained results showed a high correlation between sensor reading and oven-dried value, introduced high R² values equaled 0.999 and 0.9804 for sandy and loamy soil, respectively. Based on the designed wetted soil volume, results showed that the best moisture distribution was recorded under 4.6 L h^-1 and flooding treatment for sandy soil while recorded under 1.8 and 4.6 L h^-1rates for loamy soil. Generally, the application rate of 4.6 L h^-1 could achieve the desired moisture distribution in both soils, therefore, this trickling rate should be selected in such soils than the other. Applying of equivalent water depth equation showed that desired progression of wettingfrontappeared to be closely achieved under flooding treatment in sandy soilthan in loamy. So, flooding irrigation could be successfully applied sandy soil with rationally water amounts. Therefore, from the view point of wastewater, nutrients loss and soil contamination, flooding could be more safety compared to the other treatments. On the other hand, applying the same equation for loamy soil could only be achieved by 87 % and 67 % of the desired moisture for a given depth under 8.0 L h^-1 and flooding treatments, respectively. So, 8.0 L h^-1 and flooding treatments are not recommended for such soil. Regarding both irrigation scheduling and design, the statistical analysis indicated that the most suitable wetted depth and width could be obtained under 4.6 L h^-1 for sandy soil and under 1.8 and 4.6 L h^-1 for loamy soil, therefore, an economic emitters distance and reduction of salt accumulation around the plant could be achieved. According to soil hydraulic conductivity, wetted width to witted depth ratio could be used as a decision support aid to determine the emitter distance and numbers, consequently, avoid wastewater and cost. Considering the difficult in measuring both laterally and vertically water movement, obtained results showed a good agreement between simulated of Schwartzman-Zur's model and field observations particularly for the loamy soil than sandy.

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