Soil Solutions for Nutrient Runoff

October 24, 2015 03:23 AM

Research analyzes how no-till, reduced tillage and cover crops keep nutrients in place

The drumbeat signaling regulatory change over nutrient runoff from  production agriculture has grown increasingly strong in the past decade. Runoff concerns, combined with “Waters of the United States” expansion are raising new questions regarding soil conservation. Whether related to Lake Erie, Des Moines Water Works or the Gulf of Mexico, mandated federal nutrient regulations are creeping closer to farmland.

The No. 1 contaminant in U.S. waterways is sediment. Stemming sediment loss doesn’t prevent the escape of soluble nitrogen and phosphorus via water, but preventative measures help manage runoff. Jason Krutz, irrigation specialist with Mississippi State University, and Martin Locke, soil scientist with the USDA–Agricultural Research Service, are making major research strides with a cover crop system reducing sediment runoff. 

In the heart of the Delta, on a series of test plots in Stoneville, Miss., Krutz and Locke are searching for runoff answers translating to actionable, economical practices for farmers. The research acreage—labeled the 21-gun plots—features 21 400'-long plots drained with separate pipes fitted through a berm and into a tail-water ditch. The 8-row plots are set up on 40" spacing and twin-row soybeans, backed by 21 sample houses equipped to capture sediment and nutrient runoff. Krutz and Locke are in the process of analyzing data from 12 years of no-till and reduced tillage with cover crops, which includes eight years of dryland cotton, three years of irrigated corn and the first of four years of soybeans, funded by the Mississippi Soybean Board.

Nutrient runoff revolves around a host of layered, moving parts: soil quality, sediment runoff, erosion, water and wind. The 21-gun plots have to account for the cost of planting cover crops, killing cover crops and tillage. Krutz and Locke are keenly aware of the necessity to tie their research to profitability. 

“[Keeping] the EPA off our backs is a no-brainer,” Krutz says. “Is the system going to cost growers more money? That remains to be seen. We’re going to look at costs, yield, water savings and much more on a big scale.”

Anything on the soil surface, particularly a cover crop, reduces the movement of soil particles.

Reduced tillage with a rye cover crop has shown a bounty of benefits in other studies by Krutz and Locke. With a rain simulator (2" in 60 minutes), reduced tillage with a rye cover decreased runoff by 50%. 

“Reduced tillage with a rye cover is as good as a no-till system to reduce the total amount of water leaving the field,” Locke describes. “By reducing the carrier, you’re reducing the amount of nitrogen and phosphorus lost.” 

In the 21-gun study, Krutz and Locke found an irrigation application of 3 acre-inches onto traditional tillage resulted in 1.5" acre-inches of runoff. However, no-till and reduced tillage  fields with a rye cover allowed only 0.5 acre-inches of escape. The data demonstrates the soil profile is storing significantly larger amounts of water.

The 21-gun plots in Stoneville, Miss., focus on improving infiltration rates, reducing erosion and lowering nutrient transport. The 8-row, 400'-long plots drain via pipes fitted through a berm and into a tail-water ditch. Sample houses capture sediment and nutrient runoff. 

Krutz is amazed by how effectively a reduced tillage/rye cover crop combo, as well as a no-till system, decreases surface crusting to prevent water from entering the profile. “No other tools we’ve seen are comparable. Both systems have drastically improved infiltration rates,” he notes.

However, a rye cover crop can interfere with planting cash crops. The textbook answer for killing and rolling rye is at milk stage. Rye’s allelopathic potential means a two-week wait before planting into the mat. The wait could bump soybean planting to mid-May, an unacceptable date for many farmers in the South. 

“By April 20, we start losing about a quarter bushel of yield per day, and that’s my primary concern,” Krutz says. 

However, Krutz and Locke realize other cover crops can winter-kill, build organic carbon, offer surface protection and still allow planting by March. They plan to plant tillage radishes in 2016 since they die off from frost in the winter, and the remaining tuber might create macropores for irrigation infiltration. 

Coupled with tillage radishes, the duo plans to gather data on deep tillage, eager to find systems to improve infiltration rates, reduce erosion and lower nutrient transport. They’re focusing on an agronomic triple: maintenance of producer profit and soil health enhancement while addressing concerns in the legal pipeline related to regulating nutrients in water. “Going forward, producers need systems that make financial sense but still reduce nutrient transport to address those concerns,” Krutz says. “It’s our responsibility and duty to help prepare producers.”

Conservation Practices that Address EPA Concerns

Martin Locke, research leader at the USDA–Agricultural Research Service National Sedimentation Laboratory in Oxford, Miss., began the 21-gun project in 2004. He has worked with no-till, reduced tillage and cover crops throughout his career. 

“I started the 21-gun plots at Stoneville to improve soil and environmental and water quality,” he says. “Certainly, EPA regulations are a factor, but if farmers follow conservation practices, they’ll preemptively address EPA concerns.”

When sediment is lost, nutrients are lost in tandem. Nitrogen and phosphorus are saved in sediment, but the story isn’t clear with soluble nitrogen and phosphorus, Locke notes. Conservation practices reduce sediment loss and attached nutrients, but dissolved nitrogen and phosphorus are still lost in water. 

“These are workable, manageable systems,” Locke says. “If everyone does this, it will be a tremendous help, but I won’t say the problem of nutrients will be solved. Why? Dissolved nutrients escape in water.”

Locke advocates a multifaceted conservation approach and firmly believes edge-of-field management is crucial to an integrated farming system. Buffer zones, ditch weirs and vegetation traps impede water flow and process nutrients. 

“Slow down the water and throw things in front of the flow—essentially trap the nutrients or hold them long enough for microbes to process,” he advises.

On a given operation, how many acres should involve conservation management? In theory, the entire farm, according to Locke, but he says small steps should match management knowledge since conservation requires more attention to detail. 

“Conservation practices get a bad name when someone tries them, finds trouble or poor yields and quits. Yield and conservation are not opposing forces but if farmers are apprehensive about adopting conservation practices, changes should be implemented in baby steps and acreage increased as they work through the learning curve,” he says.


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