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Nitrogen flows and balances in four grassland‐based systems of dairy production on a clay‐loam soil in a moist temperate climate
Author(s) -
Humphreys J.,
O’Connell K.,
Casey I. A.
Publication year - 2008
Publication title -
grass and forage science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.716
H-Index - 56
eISSN - 1365-2494
pISSN - 0142-5242
DOI - 10.1111/j.1365-2494.2008.00660.x
Subject(s) - silage , grazing , stocking , zoology , dry matter , agronomy , temperate climate , loam , grassland , productivity , lactation , ice calving , environmental science , biology , soil water , ecology , pregnancy , genetics , macroeconomics , economics
This study examined productivity, nitrogen (N) flows and N balances in grassland‐based systems of dairy production in Ireland. There were four stocking densities of dairy cows on grass/white clover pastures and four inputs of N as fertilizers, concentrates and biological fixation over 2 years; 2001 and 2002. Annual stocking densities were 1·75, 2·10, 2·50 and 2·50 cows ha −1 . Associated N inputs were 205, 230, 300 and 400 kg ha −1 respectively. There were eighteen cows per system. Cows calved within a 12‐week interval in spring with a mean calving date of 28 February and lactation extended until mid‐December in each year. There were no differences in annual milk yield (6337 kg cow −1 ; s.e.m. 106·1), live weight or body condition score. Pre‐grazing N concentrations in herbage increased ( P < 0·001) with increasing N input, whereas there were no differences in N concentrations in silage reflecting optimum N inputs for silage production. Grazed herbage accounted for 0·64, silage 0·26 and concentrates 0·10 of annual dry matter consumed by the cows. Annual intakes of N ranged from 144 to 158 kg cow −1 and were mostly influenced by N concentration in grazed herbage. Annual output of N in milk and liveweight change was 38 kg cow −1 and was not different between systems. Annual N surpluses increased with increasing N inputs from 137 to 307 kg ha −1 , whereas the proportion of N inputs recovered in products declined from 0·34 to 0·24. More efficient N use was associated with lower N inputs and in particular lower N concentrations in grazed herbage.