CSA news this month has an article that talks about phosphorous losses from subsoil. The article goes on to say that there is good evidence that soil drainage is a culprit. We can prevent or reduce phosphorous losses with tillage, but then we risk erosion losses. We solve one problem and create another. This study does not look at soil phosphorous test levels, but other information I have seen says that dissolved phosphorous in surface water increases as soil test phosphorous levels increase. Nutrient stratification is also an issue. We apply phosphorous over the top, even in no-till situations, but the surface applied phosphorous then concentrates at the surface and dissolves into otherwise fairly clean runoff.
In many ways the idea of over applying nutrients to store them for later is past.
- We need to reduce soil phosphorous levels where concentrations are high.
- Tillage may be a good management tool where erosion is low risk.
- Manure needs to be applied to fields where the nutrients are need. We can't just use the same field over and over as a disposal site.
- Applying nutrients on frozen or show covered ground can increase the risk of nutrient runoff, even though it won't happen every time.
- Keep soil test levels below 40 ppm Meilich 3 P.