Sometimes the public perception of agriculture is that all growers use too much fertilizer. One way we can show the public that growers are using phosphorus fertilizer properly is by monitoring soil test level trends over time. Phosphorus is one nutrient that is thought to be contributing to environmental problems in the Gulf of Mexico. Some environmentalists presume that excessive application of phosphorus fertilizer is getting into streams in the Midwest and ending up in the Gulf of Mexico where the “P” would contribute to environmental problems. If this was the case, soil test levels of phosphorus in the Midwest would have been increasing for the past 15 years.
To learn more about the rates of phosphorus fertilizer that growers have been applying, we summarized the soil test data for a specific area in Southern Minnesota. We looked at the average phosphorus soil test level for the past ten years, following sugarbeets and corn (two high value, high input crops). The soil test data is based on thousands of soil samples in each year from the same geographic area, represented by the 562 zip code (see figure). As you can see in the figure, the average soil test value for phosphorus has been stable for many years with no significant changes. This means that growers have not been applying phosphorus fertilizer in excess of crop needs. If they had, the phosphorus soil test trends would have been increasing. This doesn’t mean that phosphorus that is reaching water ways through soil erosion and mismanaged manure application is not a problem. We need to do all the right things to control soil erosion and manage manure better. This soil test summary information shows that growers are good stewards of the land, past and present, and are managing phosphorus properly. We need to keep on top of what the public thinks concerning practices in agriculture. We need to do our part by keeping the facts and good science on the “Front Page” for the public to see.