Nitrogen Fertilization in Relation to the Palatability and Nutritive Value of Orchardgrass

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Abstract
The effect of different levels and sources of nitrogen fertilizer on the composition, intake, digestibility and palatability of orchardgrass was determined in hay feeding trials with sheep and rabbits and in a fall grazing study with sheep. Levels of nitrogen from 0 to 448 kg. per hectare increased protein digestibility by sheep in the first- and second-cut hays, had no effect on dry matter or cellulose digestibility in the first cutting, but increased dry matter and cellulose digestibility in the regrowth hay. Nitrogen applied at 112 kg. per hectare in the form of sodium nitrate, ammonium nitrate, ammonium sulfate, diammonium phosphate or urea, had no effect on the digestibility of dry matter, cellulose or protein in the first-cut hay, but some differences in the aftermath forages were obtained. Neither level nor source of nitrogen affected ad libitum consumption of the first-cut hay. Levels of intake of hay fertilized with a high level of nitrogen (448 kg. N/ha.) or with ammonium sulfate were lower than those of other treatments in the aftermath orchardgrass. There was a significant tendency for a lower dry matter digestibility of the second-cut hays to be accompanied by higher intake values than were obtained with the first-cut forages. Cafeteria trials with sheep showed that both the level and form of nitrogen fertilizer markedly affected the palatability of the hays. Selection behavior was consistent among sheep and between cuttings. Acceptability of the orchardgrass declined with increasing levels of nitrogen fertilization, and there was evidence for a relationship between palatability and a soluble carbohydrate-nitrogen imbalance in the plant. In both hay cuttings preference rankings for orchardgrass fertilized with different forms of nitrogen were in the order: sodium nitrate, ammonium nitrate, ammonium sulfate, urea and diammonium phosphate. While palatability studies with rabbits showed consistency in feeding behavior between animals and among cuttings, there were definite animal species differences (sheep vs. rabbits). Rabbits consumed relatively more of the non-fertilized orchardgrass than of the fertilized hays and ranked the nitrogen source treatments in the order: ammonium sulfate, urea, sodium nitrate, diammonium phosphate and ammonium nitrate. A fall grazing trial, in which sheep were given free access to plots having all nitrogen treatments, showed highest intakes on herbage fertilized with higher levels of nitrogen. There were no significant differences in amount of herbage harvested from plots treated with different nitrogen sources. Intake of grass from individual treatments could be related to total herbage available and to plant composition. Analysis showed differences in composition of the fall harvested forage from that of the earlier hay cuttings. Under grazing conditions dry matter and lignin content of the herbage were correlated significantly with the feeding preferences of sheep. Copyright © 1966. American Society of Animal Science . Copyright 1966 by American Society of Animal Science