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Response of Semiarid Grassland Sites to Nitrogen Fertilization: II. Fertilizer Recovery¹

ABSTRACT

The fate of N fertilizer applied annually for 5 or 6 years at rates up to 200 kg N ha^–1 year^–1 was determined on eight perennial grassland sites in western North Dakota. The amount of fertilizer N found in plant tops, roots, and as residual soil inorganic N, and the sum of these three fractions were determined for each site. The amount of fertilizer N recovered in each of these fractions was linearly correlated with the amount of fertilizer N applied to each site in almost all instances. Fertilizer N recovered in top growth was highest for smooth bromegrass (Bromus inermis) (about 80% of that applied), and least for the native prairie grasses (about 15% of applied), with intermediate values for crested wheatgrass (Agropyron desertorum). Likewise fertilizer N recovered in roots was greatest for bromegrass (near 15%), whereas soil inorganic N content was usually greatest under native range. Total fertilizer N recovered in these three fractions was usually near 50% for bromegrass sites, but only about 30% for native range sites. There was no evidence of appreciable runoff or deep percolation of nitrates. Fertilizer N not recovered was either immobilized in other forms of soil organic matter or lost to the atmosphere in gaseous forms. Available evidence indicates that only small quantities of fertilizer N would be expected to be immobilized in organic forms other than in plant roots, thereby suggesting that gaseous loss of applied N may have been significant at these dryland perennial grass sites.

¹ Contribution from North Central Region, Science & Education Administration-Agricultural Research, USDA.

² Research Soil Scientist, SEA-AR, USDA, Univ. of Nebraska, Lincoln, NE 68583 (formerly Northern Great Plains Research Center, Mandan, N.Dak.).

Received for publication May 29, 1979. Accepted for publication February 15, 1980.