What is drainage water recycling?

By Greg LaBarge, Ohio State University Extension

Ohio’s farmers know the value of managing water through surface and subsurface (tile) drainage. The economic return from increased yield and timely planting has been proven repeatedly. Yet, each year around corn pollination and soybean flowering, we often look for rain because it has gotten dry. Could we store the water we send to Lake Erie or the Ohio River for those dry July and August periods? That describes the thought behind drainage water recycling.

What is drainage water recycling? The practice involves capturing water drained from fields for storage in a pond, a reservoir, or a drainage ditch, for use later in the season to irrigate crops. Additionally, the practice creates a closed system that reduces field nutrient loss by reducing drainage water released from a site. Reducing nutrient loss helps to improve downstream water quality. However, we will still release some water downstream when drainage water exceeds storage capacity.

Irrigation methods are overhead irrigation or subsurface irrigation. Overhead irrigation design is flexible and able to fit different field layouts. With subsurface irrigation, we pump water back into the tile system to raise the water table to the crop rooting zone. Sub-irrigation sounds simple but recognize not every tile system can be retrofitted for irrigation. Several factors, such as subsoil permeability, slope, and tile depth, influence a site’s suitability.

Drainage water recycling is not a new concept in Ohio. For example, an 11-year project looked at yield and water quality results from drainage water recycling in Defiance, Fulton, and Van Wert Counties. In this project, drainage water was directed to a wetland and stored in a reservoir. Then, the stored water was sub-irrigated back into a corn and soybean crop when needed. The USDA-ARS Soil Drainage Unit, Ohio State University Extension, and Maumee Valley RC&D coordinated the work.

Figure 1 shows the yield results for corn and soybeans from one project site in Fulton County. This site was a 40-acre split into two 20-acre zones with one zone sub-irrigated (tiled at 15 foot spacing) and the second zone free drained (tiled at 45-foot spacing). Corn yields were higher in the sub-irrigated plot in 10 of 11 years. The yield increase ranged from 17 to 119 bushels. The only year corn yield was not higher was in 2003, when timely rains occurred throughout the growing season, and both treatments yielded 230 bushels per acre. 

It is essential when reviewing Figure 1 to note there are both wet and dry years included. The sub-irrigated area has a closer tile spacing of 15 feet. Therefore in some of the wet years, the sub-irrigated area benefitted from increased yield due to improved drainage. The project three-site average yield increase for corn and soybeans, respectively, were 30.8 % and 26.0 % during drier growing seasons, 13.3 % and 6.9 % during near average to wetter growing seasons, and 18.1 % and 13.0 % overall. For more information on this Ohio project, see https://go.osu.edu/ohiodwrreport.

Anticipating how much yield response you might see with irrigation is essential to determine the economic return of drainage water recycling. The potential yield increase is needed to pay for the practice. Primary practice costs are the water holding structure, pumps, irrigation system, and any land taken out of production. Costs from drainage water recycling are site-specific. For example, reservoir development costs would be lower at a site with an existing reservoir or natural depression than where a new upland reservoir is needed. 

The “Transforming Drainage Project” works with drainage water recycling, saturated buffers, and drainage water management practices. The group consists of Midwest drainage researchers and extension specialists looking at better water management practices for subsurface drainage. The “Transforming Drainage Project” released three videos in January to spotlight drainage water recycling projects in Missouri, Minnesota, and Michigan. View these videos at https://go.osu.edu/dwrvideo. While at the site, be sure to search through other resources they have on improved drainage water management practices. They have plenty of helpful information.

Fall manure and nitrogen retention

With current fertilizer N prices, we want to take advantage of every unit of N we apply when determining N application rates for the 2023 corn crop. One place to look for N is from fall manure applications. We can make loss predictions based on application timing and placement, but doing a Pre-sidedress Nitrogen Test will increase our confidence in knowing how much N is there.

One guide to understanding N loss potential is soil temperature after application. For example, the soil temperature recommendation for anhydrous ammonia is to wait for applications until 4-inch soil temperatures are less than 50 degrees F and continue to go down. Retaining the ammonium in fall-applied manure would follow the same principle. By waiting to apply ammonium until the soil temperature is less than 50 degrees, the bacteria that convert ammonium (soil stable N) to nitrate (leachable N lost through tile) are less active. So, one question to ask is what soil temperatures you had after the fall manure application.

The other important factor in retaining manure N is placement. Surface applied versus incorporated manure will result in higher N losses. Data from Minnesota show the amount of applied N available in the year after application. For example, dairy manure, with broadcast/incorporated more than 8 days — 25% available, broadcast/incorporated in 0.5 to 8 days — 45% available, broadcast/incorporated in 0 to 12 hours — 55% available. Shorter periods between application and incorporation result in more crop available N in the following year.

A Pre-Sidedress Nitrogen Test (PSNT) before sidedress is the best tool to evaluate available N from fall-applied manure for 2023 corn. In 2021 and 2022, Glen Arnold and I used the PSNT on incorporated fall-applied manure plots at Northwest Ag Research Station. A 185 pounds of N comparison rate was applied as 28% UAN. Based on the PSNT test result, we reduced the sidedress N rate from 185 pounds. With a PSNT of 10-14 PPM Nitrate-N, the N rate was reduced by 50 pounds. With a 15-18 PPM Nitrate-N, we reduced the sidedress N rate by 95 pounds. Corn yields were higher with fall manure and a 50-pound reduced rate (135 pounds N applied as UAN) or 95-pound (90 pounds N applied as UAN) sidedress reduced rate compared to 185 pounds of N applied as 28% UAN rate. Figure 2 shows corn yields.

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