Less water, similar yield

Appropriate irrigation is key to managing both the quality and quantity of Nebraska’s precious groundwater reserves as well as maximizing agricultural productivity, but what is the best way to determine when and how much to irrigate? Helping producers to evaluate precision irrigation sensing equipment was the goal of a recent study at the South Central Agricultural Laboratory (SCAL), commissioned by the Upper Big Blue and Little Blue Natural Resources Districts. 

The NRDs partnered with SCAL researchers in Clay Center on a study to evaluate different irrigation sensor technologies as well as deficit irrigation strategies. The result of the 2024 growing season study showed that even in a dry year, it is possible to grow a healthy crop while using less water with precision irrigation tools. 

The study utilized two types of technology, Watermark soil tension sensors (which are inserted in the soil at 1-, 2-, and 3-foot depths) and Aluvio Precision Irrigation Scheduling (which uses satellite imagery in addition to soil sensors and real-time weather data). Using these tools in different plots, they irrigated some plots at 100 percent of the rate recommended by the technology, and other plots at 70 percent of the recommended rate. This meant that the total irrigation ranged from 4.38 to 8.15 inches throughout the growing season, based on the different recommendations from the two technologies and the different rates utilized. Irrigation was applied with a pivot equipped with variable rate.

The Aluvio system suggested irrigating starting two weeks earlier than the Watermark sensors. Overall, the study organizers felt that the Aluvio system was more effective than the Watermark sensors, though it does come at a higher cost. Watermark sensors are a low-cost way to improve data driven decision making about irrigation. The Upper Big Blue NRD offers district producers discounts on Watermark sensors as well as other irrigation equipment to encourage their use. Scheduling based on Watermark sensors was included in the study because this is the most common method of irrigation scheduling in the region after traditional scheduling based on condition of crop and feel of soil. 

Saleh Taghvaeian oversaw the irrigation study at SCAL, from design to final analysis of results. Taghvaeian is an associate professor and irrigation engineer at the University of Nebraska Lincoln as well as a Daugherty Water for Food Global Institute faculty fellow. His area of specialty is precision irrigation technology.  

The average yield for the study was 249.6 bu/ac. Fields in a 25-mile radius that were not a part of the study that were using the same hybrid ranged between 230 and 280 bu/ac according to Bayer Crop Science, so the irrigation study yields were very close to the average. Drilling down further on the yields, the two Aluvio-managed fields that received full irrigation and the one that received only 70 percent irrigation (5.65 inches) had very similar yields (about 251 bu/ac). 

If yield is the only measure of success, then the field managed by Watermark sensors at 100 percent of the recommended rate was the winner, with 254.4 bu/ac. However, that was also the field that received the greatest amount of irrigation (8.75 inches). The average yield of the Watermark sensor managed field at a deficit (4.38 inches applied for the season) yielded 239.5 bu/ac. This is a statistically significant decrease; however, it is worth noting that this is only a 6 percent yield drop with about 50 percent less irrigation applied.

The average yield of dryland (non-irrigated) corn at SCAL for the same hybrid and same row spacing was 180 bu/ac in 2024. “Based on this, we can estimate the Irrigation Water Productivity (IWP) as the yield increase that was achieved compared to the dryland yield because of irrigation application,” Taghvaeian stated in his report on the project. He estimated that for every inch applied there was a 14 bu/ac yield increase. There is a balance to be reached to maximize yield potential as well as return on investment for irrigation cost.

The main take away was that reducing irrigation during a dry growing season can still yield a healthy crop if appropriate technology is utilized to maximize timing of the irrigation.

Organizers anticipate that this study will be continued in the 2025 growing season and may evaluate additional irrigation scheduling technologies including FieldNET or Soil Scout. 

This project was conducted at the South-Central Agricultural Laboratory (SCAL) located in Clay County in south-central Nebraska. With over 100 field research trials per year, SCAL is dedicated to developing and refining irrigated crop production practices. The total area of irrigated research fields at SCAL is about 600 acres. Approximately 80 percent of the registered irrigation wells in Nebraska are within a 75-mile radius of SCAL. As a result, research findings of projects conducted at SCAL receive a great deal of attention from local irrigators. The soils at SCAL are mostly Crete and Hastings silt loam. Normal precipitation at SCAL is 30 inches, however in 2024 just 25.1 inches of rain fell January 1-December 31; 16.7 inches of precipitation was measured during the growing season.