Tools To Keep Nitrate Available For Crops

Ken Ferrie thinks new edge-of-field tools, such as gated tile systems, saturated buffer strips and bioreactors, will help farmers slash nutrient losses further and faster. ( Darrell Smith )

Some good news has Farm Journal Field Agronomist Ken Ferrie feeling optimistic and proud of farmers in the battle to prevent crop nutrients from being lost to streams and water bodies.

A report from the Illinois Environmental Protection Agency shows between 2011 and 2015, nitrate-nitrogen loads in the state’s waters were 10% less than during the baseline years of 1980 to 1996. The report also notes state fertilizer sales have changed little since 1980, yet yields have increased. That suggests farmers have become significantly more efficient with their nitrogen fertilizer.

An important aspect, Ferrie notes, is no one is asking farmers to apply fewer nutrients. “The goal is to prevent loss, which is something every farm operator can support,” he says.

According to the Illinois report, “farmers are increasingly adopting 4R [right source, right rate, right time, right place] nutrient stewardship, which offers a possible explanation for why fertilizer sales have been static as crop yields continue to increase.” The 4Rs, says Ferrie, are in-field practices, which farmers can adopt just by tweaking management and technology. Cover crops are another in-field practice.

Ferrie thinks new edge-of-field tools, such as gated tile systems, saturated buffer strips and bioreactors, will help farmers slash nutrient losses further and faster.

The use of gated tile systems, which can hold water in the tile when desired rather than letting it quickly leave fields, is often called drainage water management. It involves regulating the depth of the water table—lowering it when necessary to prevent saturated soil and raising it by holding water in the lines for dry spells.

From an environmental perspective, holding water in tile lines lets plants use nutrients rather than allowing them to escape into drainage ditches and streams—ultimately all the way to water bodies such as the Gulf of Mexico or Chesapeake Bay where nitrate and phosphorus cause algal blooms.

Ferrie has first-hand experience with gated tile systems, from a field-scale trial underway since 2015. “In 2016, we saw a 16% to 40% reduction in tile nitrate loss, depending on the depth and width of tile,” he says.

The study also is providing insights into how nutrients are lost. “We found peak nitrate loss correlates with peak water flow,” Ferrie says. “During rain events, both the volume of water and the amount of nitrate spike at the same time. This is contrary to what I expected, based on the old saying that ‘the solution to pollution is dilution.’”

Despite Expectations. Ferrie says in a dry spell and then a rain, the highest nitrate levels occured during peak water flow. With multiple rains and peak flow each time, the concentration of nitrate fell with successive rains.

“That shows the first rain event in a series is the one that flushes the most nitrate out of a field,” he says. “So if we can hold water back following the rain event and prevent the flow from spiking, which usually happens in 24 to 48 hours, we can prevent a lot of nitrates from leaving the field. Holding that water in the tile line provides an opportunity for water to be pulled into plants, carrying nutrients with it, or evaporated from the surface.”

That’s what happens during normal rainfall patterns. During wet spells, some water is allowed to flow over the gates to prevent the soil from becoming saturated and damaging crops. “But if you can use the gates to hold back water for just three or four rain events, it will make quite a difference in nitrate loss,” Ferrie says.

Following a 1" rain on June 21, 2016, Ferrie compared the nitrate loss over nine days in ungated tile and gated tile in 30', 60' and 120' spacings. Compared with the non-gated systems, the gated system retained 2.4 lb. more nitrate per acre in 30' spacings, 6.1 lb. per acre in 60' spacings and 7.3 lb. per acre in 120' spacings.

The difference among the gated systems resulted from the depth of the tile lines. “The wider the spacing, the deeper the tile must be placed,” Ferrie says. “We pull the water table to the depth of the tile line, so the 120' spacing moves more water (and nitrate).”

A 2 lb. to 7 lb. saving per rain event might not sound impressive, Ferrie notes, but it’s a significant reduction from the 15 lb. to 25 lb. of nitrate lost by a typical Midwestern acre (in either corn or soybeans) during the course of a growing season.

Where they fit the topography, gated tile systems let you actively manage rain, with benefits to crop yield and the environment. During a dry spell in July and August 2017, Ferrie discovered what a gated system could do.

“When the soil cracks, it sets the stage for peripheral flow, in which water reaches tile lines within minutes, carrying nutrients along with it,” Ferrie says. “When we saw the forecast for substantial rain, we closed the gates to stop peripheral flow and give the soil time to soak up the water and expand and close the cracks. It was impressive how quickly that happened. We were able to rehydrate the soil, saving that water for the crop while we prevented a surge of nutrients from leaving the field.” 

After harvest and fall field work, gated systems can be used to retain water until spring, Ferrie adds. “We’re not concerned about saturated soil during that period,” he says. “In fact, it creates good conditions for freezing and thawing of the soil. And it protects nitrogen from loss until a few weeks before planting. Of course, if the soil becomes saturated, there’s a risk of surface runoff, which may require other protective measures to prevent nutrient loss.”

Like everything, gated tile systems require management, Ferrie says. Raise the gates too late, and you can lose yield from saturated soil. Raise them too soon and you lose nutrients.

“In our study, we have seen higher yield from managing the depth of the water table. It’s not a huge increase, but if you can raise yield while protecting water quality, that’s a win.”

Additional Methods. Saturated buffer strips and bioreactors hold great potential to reduce nutrient loss as well. Typically, saturated buffers involve placing a water control structure in the main tile outlet. The structure diverts the flow to a lateral, perforated distribution line running parallel to the drainage ditch or stream, which discharges into a grass buffer strip.

“Holding water in the saturated buffer lets nitrates be consumed by denitrifying microbes and are available for plant growth,” Ferrie says.

Bioreactors, placed between the field and a water course and filled with wood chips, provide an environment for bacteria to remove nitrate from drainage water. They involve structures that route water into the reactor and allow excess water to bypass it during periods of high flow. An outflow control structure holds water inside the reactor long enough for the microbes to do their work.

“Saturated buffers and bioreactors are new,” Ferrie says, “and research is underway to find the best ways to use them. The practices will improve over time.”

Traditional buffer strips filter surface runoff and should be in place along every stream and drainage ditch, Ferrie says. Like traditional buffer strips, wetlands can filter nitrates but take land of out production.

“We don’t know exactly what led to the nitrate reduction shown in the Illinois EPA report,” Ferrie says. “I suspect it resulted from a combination of things—adoption of the 4Rs, cover crops, edge-of-field measures and, in some instances, converting cropland to wetlands or permanent pasture. But it’s exciting news because many of these practices are just taking off and because farmers are embracing the concept of nutrient loss reduction.” 




Survey Shows Less Fall-Applied Nitrogen

A 10% reduction in nitrate losses achieved by Illinois farmers (see story) was accomplished by using numerous tools, says Farm Journal Field Agronomist Ken Ferrie. One of those tools appears to be shifting away from fall nitrogen fertilizer application and applying it in the spring or summer, closer to the time plants need it. That allows less time for nitrate to be lost by leaching or denitrification.

A survey by USDA–National Agricultural Statistics Service asked how many farmers were applying less than 50% of their nitrogen fertilizer in the fall, with the rest split between preplant and sidedress applications. “Between 2011 and 2015, the acres in this category increased by 28%,” Ferrie says. “There also was a 7% increase in the acres on which all nitrogen fertilizer was applied in the spring and none in the fall.”

Fertilizer Application Strategies



Gulf Of Mexico Dead ZonePhosphorus Tougher To Control

Unfortunately, preventing phosphorus losses from fields is proving harder than preventing nitrate losses. A recent Illinois survey indicated the state’s average nitrate loss declined 10% from 2011 and 2015, but total phosphorus loss increased by 17%.

That’s key because phosphorus is usually the limiting agent in algae blooms, which cause hypoxia, or depleted oxygen conditions, in water bodies such as the Gulf of Mexico and Chesapeake Bay.

Phosphorus losses include particulate phosphorus, which is attached to soil particles, and dissolved phosphorus, which is carried off in water, just like nitrate-nitrogen. Dissolved phosphorus also comes from water treatment facilities; so some of the increased loss might be due to population growth. But farmers still need to do all they can to prevent losses from their fields.

“We can manage particulate phosphorus by controlling soil erosion,” says Farm Journal Field Agronomist Ken Ferrie. “Consider the erosion potential resulting from slope and contour, and address it with conservation tillage and cover crops. Place buffer strips at the edge of the field to filter sediment out of runoff water. Wetlands also can trap some particulate phosphorus.”

Dissolved phosphorus, which can escape from fields in surface runoff and tile drainage water, is the toughest form to tackle. Besides being difficult to keep in place, dissolved phosphorus is more bioreactive than the particulate form, once it gets into water supplies. “Dissolved phosphorus could be much of the reason that the 2017 Dead Zone in the Gulf of Mexico was the largest ever,” Ferrie says.

Dissolved phosphorus passes through wetlands, saturated buffers and bioreactors unless plants manage to take it up, Ferrie points out. So those measures are only partially effective.

For now, the best way to reduce phosphorus losses is to follow the 4Rs. “Don’t apply phosphorus fertilizer on frozen ground,” Ferrie advises. “Test soil frequently, and use the results to determine application rates. Keep soil phosphorus levels at optimum rather than high, and forget the old adage that fertilizer in the soil is like money in the bank.”




A Soil Health Dilemma Rears Its Head

Farm Journal Field Agronomist Ken Ferrie spends a lot of time thinking about soil health. This question has him concerned: Does improved soil health lead to improved water quality?

“So far, the answer is not always,” Ferrie says.

Nutrients reach water two ways: in sediment carried by surface runoff and as dissolved nutrients in surface runoff and subsurface water. “Reduced tillage and cover crops, if done right, can definitely reduce sediment loading,” Ferrie says. But dissolved nutrients are another matter.

Nitrate is a source of concern in drinking water, and the combination of nitrate and phosphorus causes algae blooms in water bodies.

“The dilemma that’s coming to light is healthy soil releases more nutrients into the soil solution,” Ferrie says. “That’s good for plant growth, but nitrate and dissolved (ortho) phosphorus are highly leachable. In our studies, it’s more difficult to keep nitrate and dissolved phosphorus out of surface runoff and tile water under no-till and no-till with cover crops than under tilled soil.”

The first two years of a four-year study at Kansas State University echoed Ferrie’s observations that no-till with a cover crop increased the loss of dissolved phosphorus versus no-till without a cover.

Dissolved phosphorus is a bigger threat to water than particulate phosphorus, which is attached to soil particles and can be controlled by reducing soil erosion. Dissolved phosphorus is much more bioreactive (80% to 90%) than particulate phosphorus (30% to 35%).

“There also are indications nitrate and dissolved phosphorus are stronger in surface runoff under no-till and cover crops because of the decomposing residue,” Ferrie says.

“While cover crops can pick up nutrients, reducing their loss through drainage water, that residue decomposes. Decomposition releases nutrients at the soil surface, where they can be carried off in runoff water,” he adds.

Protecting water quality seems to depend more on balanced fertility and the 4Rs than on no-till or cover crops, Ferrie says. “As we strive to improve soil health, we must look at all these practices, as well as edge-of-field practices such as tile gates and bioreactors,” he says. “It would be a mistake to promote only a couple soil health practices, which might fail to improve water quality.”