Phosphorous is a key element in our everyday lives. High amounts can also present issues when it comes to soil and water. Although the amount of phosphorous that is produced in agriculture isn’t the only contributor to algae growth in water, it is often the most looked at. Easy-to-view farm fields and manure application make algal growths on surface water easy to point out and agriculture an easy culprit. To shield ourselves from blame, University of Wisconsin-Madison extension specialist Francisco Arriaga explained some management practices farmers can implement that will help reduce phosphorous losses from soil and surface water when utilizing manure at a recent Agronomy and Soils Field Day.
Torrential amounts of rain on cropland can lead to runoff, resulting in phosphorous losses. To reduce the amount of runoff losses, consider manure and tillage management strategies. Beginning with a nutrient management plan, determine nutrient availability and appropriate manure application rates that are field specific. How the waste is applied also plays a role. Is it injected? Is it land applied? “Injecting liquid dairy manure is the best approach to reduce losses in runoff versus surface application. A cover crop with at least 1,500 pounds per acre of dry biomass can be beneficial in situations when other crop residues are lacking,” said Arriaga. When doing so, be sure to consider the timing of application. Avoid times of the year where the risk of runoff is high, such as during snowmelt.
Tilling practices can also contribute to phosphorous losses if not managed correctly. “Excessive tillage disrupts soil aggregates, increasing the chance for sediment transport and particulate phosphorous losses. Crop residues need to be considered when thinking about tillage since the lack of surface residues can lead to phosphorous losses in runoff with reduced or no tillage,” noted the extension specialist. It may be worth considering implementing a cover crop to add surface residue that will uptake phosphorous.
Minimizing the amount of phosphorous inputs that we incorporate into the soil will ultimately help better our soil and crops. We also need to be mindful of phosphorous levels in our dairy rations, aiming for 0.35% to 0.38%. Additional phosphorous outside this range can result in up to 31 pounds of phosphorous lost per cow per acre. “The recommended phosphorous application rate for corn silage ranges between 20 pounds and 60 pounds per acre for soil in the optimum range. Thus, one cow that is overfed phosphorous units in its ration can supply almost all the phosphorous needs for a following corn silage crop on an acre basis,” cited Arriaga.
Other tips to reduce the amount of phosphorous lost from manure were to consider grazing, support conservation management practices, and properly manage drain tile.
