| Popis: |
Field evaluations of on-farm surface irrigation systems provide information to assess and improve irrigation system performance, design new irrigation systems, and compare irrigation methods and practices. Among the most important field data needed for evaluating on-farm surface irrigation systems are accurate measurements of the water advance and recession times at multiple stations along the irrigation length of run. However, manual data collection is labor and time intensive and is often inaccurate due to lack of visibility of surface water at remote locations in large fields. To overcome these obstacles, an inexpensive field probe was developed to measure and record the water advance and recession times. The objectives of this article are to present information on the design, construction, and validation of the probe. The battery-operated probe consists of a programmable microcontroller chip, designed to be a real-time clock and calendar, a 16 character × 1 line LCD display module writer, and fiber optics sensors at the probe base to detect the presence and absence of water. Component cost to construct the probe is about $50 US. Field evaluation of probe performance was conducted in irrigated-furrows utilizing 40 and 28 probes in two separate field tests. Mean probe times for advance were 1.1 min longer than mean observed advance times for both tests and mean probe times for recession were 1.0 min longer, and 2.6 min shorter than mean observed recession for the first and second test, respectively. The mean differences were significantly different from zero according to paired T-tests, indicating a general bias towards slightly longer probe times than observed. However, mean absolute errors for probe times were less than 8% for advance and less than 3% for recession, suggesting that the probes will provide acceptable advance and recession information for most surface-irrigation evaluation applications. The Nash-Sutcliffe model efficiency coefficients for assessing goodness of fit were above 0.94 for advance and above 0.57 for recession, which also indicated that probe times achieved good agreement with observed times. |
