Context: Overall, our results indicate that an electric motor running at a constant 1770 rpm will use excess energy for much of the center pivot revolution. VFD operation includes the installation of a pressure sensor somewhere on the system. The controller part of the VFD adjusts the motor speed to maintain a set pipeline pressure wherever the sensor is positioned. Some sensors are placed at the pump outlet, but if the irrigated area has a lot of topography, that position is often the worst location for the sensor.

Question: what does the controller part of the VFD do?

Answer: adjusts the motor speed to maintain a set pipeline pressure wherever the sensor is positioned

Melvin, S. (2017). Predicting Late-Season Irrigation Needs. UNL Water. https://water.unl.edu/article/agricultural-irrigation/predicting-late-season-irrigation-needs


Context: Determine the average rainfall per week for the remaining weeks of crop growth and add it into the prediction of how much water may be needed from irrigation. This number should be recalculated each week until the crop is mature. Use Figures 2 and 3 to determine the average rainfall per week in August and in September for central Buffalo County. The chart shows that, on average, central Buffalo County gets 0.60 inch of rain per week in August and 0.55 inch per week in September. The crop is expected to continue growing for three weeks in August and two weeks in September. Remaining available water at maturity is 5.25 inches. The you subtract the average august rain for three weeks which is 1.80 inches. Then you subtract the average September rain for 2 weeks which is 1.10 inches. This gives us that the water we need after accounting for average rain is 2.35 inches. The chart predicts that if average rainfall is received over the next five weeks, only 2.35 inches of irrigation would be needed to mature the crop.

Question: how many inches of irrigation would be needed to mature the crop using the average average rainfall per week for august and September for the crop and the remaining available water at maturity?

Answer: 2.35 inches

Barker, J. B. (2017). Considerations in Adopting Variable Rate Irrigation for Center Pivots and Lateral Systems. http://extensionpublications.unl.edu/assets/pdf/ec2000.pdf.


Context: The description of a dynamic VRI irrigation prescription is that it changes frequently during the season, possible for each irrigation event. Considerations include that it may be complicated and increase management efforts and that it may provide maximum gross benefit. Example uses include varying irrigation to each part of the field as needed and adjusting areas as needs change over the season as well as variable rate chemigation.

Question: what are example uses for dynamic VRI irrigation prescriptions?

Answer: varying irrigation to each part of the field as needed and adjusting areas as needs change over the season as well as variable rate chemigation

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years


Context: However, the winter and spring of 2022-23 has been an exception for most of Nebraska, with off-season precipitation well below normal. This has highlighted the only downside to leaving the soil dry at the end of the irrigation season: In years when we have a very dry off-season, we will need to pump some water in June to refill the profile before the high water demand days of July arrive. The data showed that some fields were at field capacity at the end of the irrigation season in 2022, but many of the silt loam soil fields would require four to five inches of water to refill the profile. The problem is, without soil water monitoring equipment, one will not know if their field is already refilled to field capacity or not. Other lighter soil texture fields will take less water to refill them.

Question: how much water did the data indicate silt loam fields would require in Nebraska in 2022?

Answer: four to five inches of water to refill the profile

Melvin, S. (2023). Study Reviews Farmer Irrigation Scheduling Tendencies in Dry Years. UNL CropWatch. https://cropwatch.unl.edu/2023/study-reviews-farmer-irrigation-scheduling-tendencies-dry-years