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Regression of Nitrogen Uptake on Nitrogen Added from Four Sources Applied to Grass¹

Research was conducted to evaluate efficiencies of N fertilizers by comparing slopes of N uptake on N applied regression equations. Ammonium nitrate (33.5-0-0), diammonium phosphate (21-23-0), urea (45-0-0), and ureaammonium phosphate (33-9-0) were surface applied at four rates of N to Coastal bermudagrass on Norfolk sandy loam and to Pensacola bahiagrass on Boswell fine sandy loam. Relative efficiencies for N recovery were determined by comparison of the slopes (b) of the equations. The highest average efficiency (b = 0.80) was obtained with ammonium nitrate on bermudagrass. Values of b were similar for all sources of N on bahiagrass. There was a straight line relationship when dry forage produced (y) was plotted against N uptake (x). The equations were y = 1,500 -f 48x and y = 3,000 -j- 34x for bahiagrass and bermudagrass, respectively. These differences in slopes of the equations reflect the differences both in N contents and yields of the forage.

Key Words: Efficiency of nitrogen recovery

² Contribution from Auburn University Agricultural Experiment Station. Research supported in part by Tennessee Valley Authority Contract, TV 13436A.

Received for publication February 13, 1970.