Influence of fertiliser nitrogen on higher fatty acids and on Mg, Ca, K, and P in grazed grass-clover herbage

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Abstract
Total and individual higher fatty acid contents, and Mg, Ca, K, and P contents were measured throughout a year in a grass-clover pasture fertilised with lime-ammonium nitrate at 0, 112, and 448 kg N/ha. Higher fatty acid content of the herbage was highest for all treatments during late winter-early spring. Total higher fatty acid was significantly correlated with herbage total N and “protein” N contents. The rate of fertiliser N application had no significant effect on levels of total or individual higher fatty acids. The proportions of individual higher fatty acids remained constant throughout the year, linolenic (c. 65%), palmitic (c. 14%), and linoleic (c. 10%) acids being the major components. Concentrations of Mg, Ca, K, and P in the herbage varied markedly throughout the year with Mg and Ca at a maximum during summer and early autumn. Nitrogen fertiliser application had no overall significant effect on the concentrations of these elements in the herbage; however, from May to January the total yield of each element was significantly increased by fertiliser application because of the increase in dry matter production. Results are discussed in relation to the role of pasture chemical composition in the hypomagnesaemic tetany syndrome.

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