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Efficiency of Recovery of Applied Nitrate Nitrogen by Perennial Ryegrass from Different Soils¹

ABSTRACT

The objectives of this study were to determine efficiency of recovery of applied nitrate nitrogen on 7 pairs of soils fertilized at 4 rates of nitrogen and to relate these results to intrinsic soil properties. Soils were sampled so that texture and organic matter content were the main soil variables. Ryegrass was grown on the soils until added nitrogen was exhausted.

Nitrogen fertilizer was generally more efficient at the higher rates of application, but not on all soils. Efficiency decreased with rate on a few soils and remained constant on others. Two of the soil pairs showed significantly lower nitrogen efficiency than the other five. Low efficiency on one soil appeared to be caused by relatively lower dry matter production for each unit of applied nitrogen. Efficiency was much higher in this experiment than on the same soils in situ.

Regression analyses indicated that efficiency was not related to ability of the unfertilized soils to yield nitrogen; i.e., increases in yield of nitrogen due to nitrogen applications controlled efficiency rather than the absolute yield of nitrogen. Some 53 and 70% of the variation in average nitrogen efficiency for the 14 soils was associated with percent clay and surface area, respectively. Because efficiency was lower on finer-textured soils, it was proposed that lower efficiency may have been caused by denitrification losses brought about by slower oxygen diffusion.

¹ Research performed under Colorado Project 147, a joint project of the Colorado Agr. Exp. Sta. and Soil and Water Conservation Research Division, ARS, USDA, Ft. Collins, Colo. Colorado Agr. Exp. Sta. Scientific Journal Series No. 623.

² Soil Scientist, Soil and Water Conservation Research Division, ARS, USDA, and Associate Agronomist (Soils), Colorado State University, Fort Collins, respectively.

Received for publication March 17, 1960. Accepted for publication June 9, 1960.