In the mid-1970s, Dr. Robert Westerman banded 18-46-0 with wheat at planting in a low-pH soil near Haskell, Oklahoma. The impact was immediately evident. Soon after, Oklahoma State University published an extension brochure titled “Banding Phosphate in Wheat: A Temporary Alternative to Liming” (Figure 1). This method was a temporary solution for the significant amount of Oklahoma winter wheat that was either too far from a reliable lime source or under a short-term-lease contract.
- Soil acidification is a natural process in high rainfall environments where leaching slowly acidifies soil over time.
- Intensive agriculture can speed up soil acidification through many processes – increasing leaching, addition of fertilizers, removal of produce and build-up of soil organic matter.
- Of all the major fertilizer nutrients, nitrogen is the main nutrient affecting soil pH, and soils can become more acidic or more alkaline depending on the type of nitrogen fertilizer used.
- Nitrate-based products are the least acidifying of the nitrogen fertilizers, while ammonium-based products have the greatest potential to acidify soil.
- Soil acidification due to use of phosphorus fertilizers is small compared to that attributed to nitrogen, due to the lower amounts of this nutrient used and the lower acidification per kg phosphorus. Phosphoric acid is the most acidifying phosphorus fertilizer.
- Potassium fertilizers have little or no effect on soil pH.
Applying nitrogen (N) again this year? Chances are you applied N on the same field last year — that is, you’re one of the many farmers planting more corn after corn. In the Midwest, much of the additional corn acres are coming from ground that farmers previously rotated to soybean production every other year. So now, instead of applying N once every two years, many are applying N every year.
Despite record corn yields in some parts of the country, low commodity prices may increase soybean acres in 2015. Rotating crops from corn to soybeans is a common practice; however, with the record yields comes record nutrient removal.