Reducing Nutrient and Sediment Loss: Part 4

Research being done at the Blanchard River Demonstration Farms and other related sites around the state is helping researchers determine what practices work best for reducing nutrient and sediment loss. Over the last five years, on-farm research has shown that three practices in particular help reduce nutrient and sediment loss:

  • Following the 4R approach
  • Reducing soil erosion
  • Developing a water management plan

Research shows that phosphorus is leaving the farm via water, through both surface and subsurface runoff. Implementing practices that slow, stop and/or treat water before it exits the farm can greatly reduce phosphorus discharge downstream. However, the unpredictability of the weather can make this difficult. In fact, the frequency of rainfall events totaling 1 inch or more has almost doubled in most northwest Ohio towns. These intense rainfall events drive a majority of nutrients downstream each year.

By developing a water management plan, you can begin to identify where nutrients are potentially escaping your farm and determine appropriate solutions, such as drainage water management structures, phosphorus removal beds, two-stage ditches, reconstructed wetlands and filter strips.

Saturated Buffer

What is it: Saturated buffers are a new practice that redirects a portion of field tile drainage water into riparian zones rather than into surface waters like traditional tile outlets. Riparian zones are areas adjacent to streams. Diverted waters then filter through the soil in the riparian zone before entering surface water/streams. Research on saturated buffers is ongoing.

How it helps: The goal of the saturated buffer is to use the riparian zone as a sponge to treat the tile water leaving the field. Once the riparian zone is full of water, or saturated, the water is slowly released through the soil and the nutrients are removed. This process is most effective at reducing nitrogen by causing it to turn into a gas, or denitrify. Phosphorus removal is still highly variable and needs to be studied further.

Drainage Water Management

What is it: Drainage Water Management (DWM) is an NRCS-approved conservation engineering practice that manages water discharge from surface and/or subsurface agricultural drainage systems. A DWM structure holds water in root zones when crops need it and drains it when there’s too much.

How it helps: By adjusting the tile outlet elevation, a DWM structure manages the timing and amount of water discharged from agricultural drainage systems. From a water quality standpoint, DWM provides the most benefit by raising the tile outlet elevation immediately after harvest until early spring. A DWM structure can impact nutrient movement, primarily reducing nitrogen loss.

“If we can get by with free-flowing drainage only three or four months a year we can show that constant drip from the tile going into the steams. We will spend about $4,000 for 50 more acres of controlled drainage structures. If we would get a 5% yield increase in a couple of dry years, it pays for itself.” – Duane Stateler

Sites should be evaluated by SWCD and NRCS professionals to determine if this practice can address the resource concern of the producer. If reduction of phosphorus is the primary resource concern, then the producer should look to other practices that are more efficient at removing phosphorus.

 

This article was featured in the September/October 2021 edition of Our Ohio Magazine

After fall field work is complete, the structures are closed until mid-March. Then the structures are opened, allowing drainage water to flow freely to the outlet. After spring field work is completed (planting and sidedressing corn), the structures are closed again until two weeks prior to harvest. This allows the soil to once again drain freely so harvest equipment can enter the field. Once fall field work is complete, the structures are closed.

Drainage Water Management Structures

Drainage Water Management (DWM) is an NRCS-approved conservation engineering practice that manages water discharges from subsurface agricultural drainage systems. A DWM structure holds water in root zones when crops need it while also allowing it to drain when there’s too much. It manages the timing and amount of water discharged from agricultural drainage systems and may also retain water needed for late-season crop production.

Drainage Water Management Effects on Tile Discharge and Water Quality

Drainage water management (DWM) has received considerable attention as a potential best management practice (BMP) for improving water quality in tile-drained landscapes. The objective of this study was to evaluate the effects of DWM on subsurface drain discharge as well as on nitrogen (N) and phosphorus (P) loads in drainage water. Tile discharge and nutrient concentrations were measured from two adjacent tile drainage outlets in an Ohio, USA headwater watershed for 7 years (2006–2012). A control structure was installed in 2009 to allow DWM at one of the outlets from 2009 to 2012. A before-after control–impact (BACI) study design was used to assess the impact of DWM on tile discharge and nutrient loads. Results showed that DWM significantly decreased annual tile discharge between 11 and 178 mm, which was equivalent to an 8 to 34% reduction inflow. DWM significantly decreased annual NO3 N loads by −1.3 to 26.8 kg ha−1 (−8 to 44%) and annual dissolved P loads by 0.04 to 0.51 kg ha−1 (40 to 68%). Nutrient concentrations were not significantly affected by DWM indicating that decreases in nutrient loads were primarily due to reductions in tile discharge rather than changes in concentration. Results from the current study support the use of DWM as a BMP to decrease N and P loads in subsurface drain discharge throughout the U.S. Midwest. Future research should focus on quantifying the effect of DWM on nutrient transport in other flow paths (e.g., lateral seepage, surface runoff) to further evaluate its use as a BMP in tile-drained landscapes.

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