Phosphorus (P) loss from farms can cause harmful algal blooms in water bodies like Lake Erie and Saginaw Bay. Here are four strategies for reducing P loss from subsurface-drained farms:
1. Reduce surface runoff by improving soil health: This can be done by implementing minimum or no soil disturbance, permanent cover crop, and diverse crop rotation. These practices help build soil organic matter, which improves soil structure and increases infiltration, thereby reducing surface runoff and particulate P loss.
2. Reduce soil test P: Reduce the soil test P and apply fertilizer as needed with 4R nutrient management. This means applying the right source, right rate, right time, and right place of fertilizer. Reduce the excess soil test P by performing soil testing and only applying as needed to maintain a soil test P as low as possible. Go with subsurface placement (subsurface banding, injection) of fertilizer instead of surface broadcasting to reduce P loss. If subsurface placement is unfeasible, incorporate the fertilizer after surface broadcast. Check the weather forecast to put as much time as possible between the time of fertilizer application and rainfall.
3. Manage water: Reduce the amount of water leaving the field with water management. Implement water management practices to reduce the drainage discharge leaving the field, thereby reducing the soluble P loss. Examples of these practices are controlled drainage, saturated buffer, and drainage water recycling. Even with those conservation drainage practices, some of the water reaches the ditch. That’s where two-stage ditches are useful because they have potential to reduce P loss from the stream flow.
4. Capture phosphorus: Capture phosphorus with a phosphorus removal structure. Even with nutrient and water management practices, some fields can have high P loss. In that case, a P removal structure can be used to capture the excess P in drainage discharge using a P sorption material. Because event flows dominate P loss (89% in a study at Michigan State University Extension), P structures should be designed to capture as much P as possible from event flows.
When a P removal structure is coupled with controlled drainage, the control structure dampens the peak flow and temporarily stores water in the field, thereby treating more water and capturing more P from the large event flows. Like in a controlled drainage system, dampening the peak flow can be achieved during most of the year except for when the system needs to be under free drainage for spring planting and fall harvest.
By implementing a combination of these strategies, farmers can significantly reduce phosphorus loss from their fields and help to protect water quality.
Photo Credit: gettyimages-gabrielabertolini
Categories: Michigan, Crops