Drainage water recycling shows promise in Iowa09/16/2019 | Crop Production Research, Soil Health, Water Quality
By Chris Hay, ISA senior environmental scientist
Recycling drainage water captured from crop fields for use during periods of insufficient rainfall is a promising new practice for farmers, a recent study concluded.
Research conducted with Iowa State University (ISU), Purdue University and Iowa Soybean Association found that the practice could help manage water-related production risks while also reducing downstream nutrient loss. Results of the study were recently published in the journal “Agricultural Water Management.”
Titled “Simulated water quality and irrigation benefits from drainage water recycling at two tile-drained sites in the U.S. Midwest,” the study used a model that combined a water balance for the field and the storage reservoir to evaluate potential benefits of the practice.
Data used in the study were from the ISU Southeast Research Farm near Crawfordsville and the Davis Purdue Agricultural Center in Indiana. The study covered the 10-year period from 2007 to 2016.
There was a need for supplemental irrigation in all 10 years at the Indiana site, but only in three of the years at the Iowa research farm. However, the irrigation needs in those three dry years at the ISU site were greater than those at Purdue. In the years when irrigation was needed at the Purdue farm, annual irrigation requirements ranged from 4 inches to 8 inches.
Using an assumed reservoir depth of 10 feet, a reservoir area of 6 percent of the irrigated area was sufficient to meet the irrigation needs at the Purdue site. Because of the greater irrigation needs in dry years at the ISU site, a reservoir area of 8 percent of the irrigated area was needed to fully meet the irrigation needs.
The same reservoir sizes (6 percent at Purdue; 8 percent at ISU) could capture and store on average 5 inches of drainage water per year at the Purdue site and 3 inches per year at the ISU site. Capturing and reusing this drainage water could reduce downstream nutrient loss (nitrogen and phosphorus) by about 20 percent at Crawfordsville and 40 percent at the Indiana site, according to the research.
This study helps establish the potential for drainage water recycling as both a crop production and water quality practice, but some questions remain. A key question is economics and how much of the investment in a drainage water recycling system can be offset by increased production and higher yields, particularly when irrigation is needed only some of the years. For more information about the project, read the Agricultural Water Management journal article.
Two new projects are underway in Iowa — in cooperation with Iowa State University, the Iowa Department of Agriculture and Land Stewardship and Iowa Soybean Association — to evaluate drainage water recycling to better understand the economic and agronomic feasibility.
For more information about drainage water recycling, visit the Transforming Drainage website.
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