Nitrogen and Phosphorus Availability in a Fertilized Rangeland Ecosystem of the Northern Great Plains

Factorial combinations of ammonium nitrate at rates of 0, 100, 300, and 900 lb. N/acre and concentrated superphosphate at rates of 0, 100, and 200 lb. P/acre were broadcast on a native range site (a Bouteloua-Carex-[Stipa] faciation of a mixed prairie association) near Sidney, Montana. In 2 years, the addition of a high rate of N and P fertilizer increased total forage production 3.3-fold, total crude protein 6.7-fold, and plant N and P percentages about 2.0-fold. High rates of N applied alone had no marked effect on plant P percentage the year of application, but plant P percentage was reduced nearly 2.0-fold the second year by all rates of N. Nitrate-nitrogen was concentrated in the upper 3 feet of soil in 1969 and in the upper 5 feet of soil in 1970. Nearly all of the P fertilizer applied was concentrated in the upper 3 inches of soil in 1969 and in the upper 6 inches of soil in 1970. The high rate of N applied alone decreased soil pH from about 6.9 to 6.1 in the 0- to 6-inch soil depth in 1969 and from 6.9 to 6.5 in 1970 even though the soil was strongly calcareous.