Recycling drainage water may be another tool for better soybean yields  - Indiana Corn and Soy

Recycling drainage water may be another tool for better soybean yields 

By Carol Brown 
Soybean Research Information Network 

Growing crops requires healthy soil, sunlight and water. Crops grow well when they receive water at key times, which isn’t always possible with natural rainfall. Scientists have developed irrigation methods to water the crop when rain is in short supply, which improves growth and ultimately yield. 

Irrigation control structures like this one help crops receive water when needed. 
(Photo courtesy United Soybean Board) 

Drainage water management can be another tool to help crops use water at the right time. It can reduce excess water coming from tile lines in the spring and also hold water in the soil for crop use later in the season. Laura Bowling, a Purdue University hydrologist, is part of a team of Midwest agronomists and water drainage experts looking for efficient ways to supply water to crops when needed. 

“Over the last 100 years, our annual precipitation has increased and most of the increase is coming in the winter and spring. This is when we have the greatest need for drainage to get water out of the field for timely planting,” Bowling said. “But more installed tile lines puts additional stress on the drainage infrastructure — too much water leaves the fields too quickly. Then come the warm summers with greater risk of drying soil later in the season when crops can use more water. It makes sense to hold this water and then apply it as supplemental irrigation later in the growing season.” 

Larger volumes of water leaving fields in the spring can carry excess amounts of nutrients, which can negatively impact water quality for those downstream. 

Drainage water management practices can help with these issues. Controlled drainage, saturated buffers and drainage water recycling are similar in their goals for managing water and reducing nitrate loss, but each of these practices work better in certain areas depending on the slope of the land or access to a stream. 

Better yields and water quality 

Bowling leads a project that explores whether drainage water recycling can improve soybean yields and water quality. A recycled drainage system consists of a pond, drainage ditch, or reservoir adjacent to an agricultural field with an irrigation system connected to the waterbody. 

The waterbody captures rainwater and excess water drained from fields and holds it until the crop is in need. And in some cases, the stored water may naturally denitrify thanks to bacteria, which lowers nitrogen levels before the water is released to the field or downstream. 

The research project began in 2021 and was supported by the Indiana Soybean Alliance. She and her team regulated when and how much water the crops in the adjacent field received through an installed water control structure and irrigation system. In 2022, the team earned a USDA National Institute of Food and Agriculture grant to expand the experiment during four years. 

“This is a prototype project,” Bowling explained. “Instead of digging a pond, we modified a jurisdictional wetland area at the Agronomy Center for Research and Education (ACRE) near West Lafayette. The wetland receives subsurface drainage from about 175 acres of the farm.” 

They added a control structure to drain or hold water, as needed, trying to be as efficient as possible with water use. They installed surface drip irrigation lines. 

The study is a comparison of irrigated plots with standard management, irrigated plots with fungicide and insecticide applications, and a third plot with fertigation, which includes extra nitrogen, sulfur and potassium added to the irrigation water. 

The team then compares soybean yields from the irrigated plots to rain-fed plots with standard management and rain-fed plots with intensive management of applied sulfur, fungicide and insecticide. 

A corn/soybean rotation study 

In 2021, the team planted soybeans on the experimental field, Bowling said, and they irrigated the field a few times late in the growing season. But they didn’t gather as much data as intended, due to unexpected issues including a leaking control structure. In 2022, the team expanded the experiment and grew soybeans and corn in the field. Through the USDA-NIFA grant, they will be able to study the corn/soybean rotation for four years. 

Bowling is part of the team on the Transforming Drainage project, also funded by USDA-NIFA and led by colleague Jane Frankenburger, an agricultural engineer at Purdue. The eight-state project concluded recently and studied controlled drainage, saturated buffers and recycled drainage. 

The data collected from the Indiana recycled drainage structure will be included in the project’s database, available on the Transforming Drainage website. The website contains webinars, videos, and publications on how each drainage structure functions as well as tools to help evaluate and plan for drainage system installations. 

Bowling intends for the Purdue University recycled drainage site to be an educational venue where farmers can learn more about drainage management and see if a system could benefit their land. Bowling has hosted field days and hopes to schedule more during the duration of the NIFA project. 

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