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Effect of N Fertilization on Dry Matter Yield, Total-N, N Recovery, and Nitrate-N Concentration of Three Cool-Season Forage Grass Species¹

This study was undertaken because of continued interest in replacement of legume N with commercial N for perennial grasses. More information is needed on the time and level of applied N to maximize total yield, seasonal distribution of forage, and efficient use of N fertilizer, while minimizing nitrate-N accumulations in the forage. Timothy (Phleum pratense L.), smooth bromegrass (Bromus inermis Leyss.), and orchardgrass (Dactylis glomerata L.) were evaluated during the 1st (1964) and 2nd (1965) years after seeding. Nitrogen levels employed were O, 21, 42, 84, 168, and 336 kg/ha applied each harvest, providing maximum annual rates of 1,008 kg/ha for timothy and 1,344 kg/ha each for bromegrass and orchardgrass.

Highest dry matter yields were obtained with orchardgrass, followed by bromegrass and then timothy. Yields were limited by drought in 1964, with timothy the most sensitive. Dry matter yields of orchardgrass and bromegrass exceeded 11,000 kg/ha in 1965, whereas timothy produced a maximum of 6,770 kg/ha. Production of orchardgrass was generally superior in midsummer. A low priority is suggested for timothy in the central and southern Corn Belt region due to its poor drought tolerance and low yield. Higher rates of N depressed forage yields, especially in 1965 due to a reduction in stand, with timothy affected most.

Total-N concentrations were similar in bromegrass and orchardgrass and generally lower in timothy. Recovery of applied N in the harvested forage was highest when 2 kg/ha of N was topdressed per harvest. Nitrogen recoveries were higher in 1965 with maximums of 48.5, 71.8, and 66.6% for timothy, bromegrass, and orchardgrass, respectively. These data suggest that established sod-forming species may utilize applied N more efficiently than bunchgrasses, with timothy being quite inefficient presumably due to limited root volume and poor drought tolerance.

Potentially toxic concentrations of nitrate-N (.15%) were not found when N rates did not exceed levels required to maximize forage yield. The major exception occurred for July harvests of bromegrass and orchardgrass in 1965. These data suggest that bromegrass should be added to the list of species that could accumulate "unsafe" levels of nitrate-N under certain conditions of N fertilization.

Key Words: Timothy • Smooth bromegrass • Orchardgrass • Forage quality • Nitrate toxicity

² Graduate Research Assistant in Agronomy (presently Associate Professor of Agronomy, Iowa State University), Professor of Agronomy, Professor of Animal Sciences, Graduate Research Assistant in Agronomy (presently Graduate Assistant, University of Illinois), and Instructor of Agronomy (presently Plant Physiologist, Plant Science Research Division, ARS, USDA, Raleigh, N. C.), respectively, Purdue Agricultural Experiment Station, Lafayette, Ind. 47907.

Received for publication February 17, 1972.