A glance at today’s headlines quickly reminds farmers managing nutrients isn’t only about crop production; it’s also about safeguarding the water we all drink.
After all, protecting water is something farmers want to do anyway, points out Farm Journal Field Agronomist Ken Ferrie. Not only do they want to keep water clean, but they want to avoid their fertilizer washing away.
To be mindful of water quality, you must understand the risk of nutrient loss, particularly nitrogen and phosphorus, from each of your fields and what you can do to help nutrients stay put.
In one watershed, water quality improvements might focus on cleaning up a stream to improve habitat for rainbow trout. “That involves controlling sediment,” Ferrie says.
But another watershed might be different. “In contrast, aquatic life is abundant in the Mississippi River, despite a large volume of sediment, which it contained even before the area was intensively farmed,” he adds. “So the water quality issues are different.
“Other areas, such as the Des Moines River watershed, have drinking water issues involving nitrates. The Chesapeake Bay and Gulf of Mexico have hypoxia problems resulting from excess nitrogen and phosphorus. There are different ways to clean up each of these problems,” Ferrie says.
For farmers, sedimentation is the easiest challenge to address (although there always will be some natural sedimentation from streambank erosion). “It involves controlling soil erosion using conservation tillage, contour farming and grass buffer strips to slow runoff water and filter out sediment,” Ferrie says.
Keeping tabs on nitrogen and phosphorus and how they effect water quality is tougher. “It’s impossible to have no nitrogen or phosphorus in water because they get there naturally,” Ferrie says. “They come from soil, which constantly cycles nitrogen and phosphorus, whether it’s growing corn, grass or forests. Nitrogen can be lost while it’s in the nitrate form. Nutrients also enter water from natural processes such as streambank erosion.”
Problems arise when nitrogen and phosphorus reach certain amounts in water. With nitrogen, the Environmental Protection Agency has set the allowable limit for drinking water at 10 ppm. “Above that amount, you can swim and bathe in the water, but it is considered dangerous for pregnant women and small children to drink,” Ferrie explains. “So nitrogen becomes a concern in drinking water supplies.”
Phosphorus isn’t a hazard in drinking water until it unites with nitrogen.
“Nitrogen and phosphorus are important building blocks in the life cycle of phytoplankton, or algae,” Ferrie says. “They cause the algae to reproduce explosively. Some algae blooms, such as one on a Canadian lake I’m familiar with, happen naturally. But human activities no doubt are a factor in areas such as the Gulf, the Chesapeake Bay and Lake Erie.”
You probably have seen algae blooms in farm ponds. “Algae may release toxins that irritate skin and impart an unpleasant odor to water,” Ferrie says. “The odor can become a concern for municipal water supplies. All these issues make it difficult to use the water for recreation—fishing, swimming and water skiing.
“Even worse, when algae blooms die, the process of decomposition uses up oxygen in the water, which is called hypoxia. In small ponds, oxygen depletion might cause fish to die. When hypoxia occurs in larger bodies of water, such as the Gulf of Mexico, Chesapeake Bay and Lake Erie, fish can swim away from the hypoxic zone, but less mobile creatures might die.”
Algae isn’t intrinsically bad in normal amounts. “We’d be in a sorry state if there were no algae because 90% of the world’s photosynthesis, a process basic to life, occurs in phytoplankton, compared to only 10% from plants on land,” Ferrie says. “Excessive algae causes problems, triggered by a combination of nitrogen and phosphorus.”
There are two types of phosphorus involved in algae production. They require different control measures.
“Particulate phosphorus is tied to soil particles or other organic material,” Ferrie explains. “When soil or other material washes into streams, it carries particulate phosphorus along with it. The eroded soil comes not just from farms, but from many sources, including streambank erosion and municipal runoff.”
The other form is ortho phosphorus, in solution or suspension in the water. Ortho phosphorus comes from microbial activity. In some waters, especially streams, particulate phosphorus makes up the highest volume of phosphorus. But particulate phosphorus tends to settle to the bottom, so it doesn’t travel as far from its source. Also, it is less bioactive and likely to react to the environment. Particulate phosphorus is only 30% bioactive, compared with 95% bioactive for the ortho, or dissolved, form. “Phosphorus enters water from many sources,” Ferrie says. “Even under optimum conditions, municipal sewage plants release some dissolved phosphorus in their discharge water. When the plants are overrun with rainfall, they discharge
a lot more.
“Even so, the farm community must acknowledge we have a leaky system—nutrients can wash away and leave fields through waterways or tile. It’s on everyone’s shoulders to do everything they can to reduce nutrients in water systems,” Ferrie says.
For agriculture, measures taken to reduce nitrogen and phosphorus loss must be tailored not only to the specific problem but also to the farming practices in each area. “If water from farms drains into a river that provides drinking water, the greatest issue might be nitrates,” Ferrie says. “Elsewhere, the biggest concern might be preventing nitrogen and phosphorus from reaching the Gulf of Mexico.”
Wherever you farm, whatever the water quality issues, your first step should be to inventory the risk of nutrient loss from your fields. That starts with soil testing to find out what levels of nutrients are present.
Your soil test probably won’t show ortho phosphorus because that value changes constantly based on microbial activity, which is driven by temperature and soil moisture levels. But the P2O5 reading correlates with the amount of dissolved phosphorus that will be released by microbes during the growing season.
“Just because a soil has a higher P2O5 value doesn’t necessarily mean it will have more loss,” Ferrie says. “For nutrients to reach water, there must be a transport system, such as soil erosion or a drainage system. That’s where risk assessment comes in.”
As part of risk assessment, some farmers collect runoff samples during storms to find how many nutrients are actually leaving their fields during rain events. (Consult with a laboratory before you do this because there are procedures that must be followed.)
If you find fields at risk of loss, there is an abundance of resources to help you develop a nutrient reduction plan. They range from the Natural Resources Conservation Service and land-grant universities to certified crop advisers and technical service providers “Most states have developed nutrient reduction strategies, which are important to study,” Ferrie says.
Nutrient reduction practices include filter strips at the edges of fields to filter sediment out of runoff water. Gated tile systems control when water leaves a field. Wetlands and bioreactors might help, especially with nitrogen. Some practices might qualify for federal or state cost assistance.
“Some risky fields may have to be switched from cash grain production to permanent pasture or timber,” Ferrie says. “Or they could be enrolled in the Conservation Reserve Program. Renting ground to the government is an excellent way to remove high-risk fields from production, especially when grain prices are low.” If you’re willing to devote hard-to-farm areas to wildlife habitat, organizations such as Pheasants Forever and Quail Forever might be willing to provide seed and planting equipment.
Of the two nutrients, nitrogen offers the most opportunities for management. “Implementing the 4Rs will go a long way toward preventing nitrogen loss,” Ferrie says. “Apply the right product at the right rate, at the right time [close to plant uptake, using multiple applications] and in the right place [such as banding near the row].
“Use soil tests for mineralizable nitrogen and nitrate-N, and computer programs to dial in various factors to determine timing and rate.”
Some practices apply to both nitrogen and phosphorus management. “Cover crops capture nutrients and provide a bridge to the next cash crop,” Ferrie says. “But remember, cover crops require management, too. Be sure to choose one that releases nutrients while the cash crop is growing, rather than too early or too late, when the nutrients can still be lost.”