Nitrogen flows and balances in four grassland‐based systems of dairy production on a clay‐loam soil in a moist temperate climate

Abstract

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 1AE75, 2AE10, 2AE50 and 2AE50 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. 106AE1), live weight or body condition score. Pre-grazing N concentrations in herbage increased (P < 0AE001) 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 0AE64, silage 0AE26 and concentrates 0AE10 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 0AE34 to 0AE24. More efficient N use was associated with lower N inputs and in particular lower N concentrations in grazed herbage.

Economic impacts of nitrogen and phosphorus use efficiency on nineteen intensive grass-based dairy farms in the South of Ireland

“…However, the N (Aarts, 2003;Goodlass et al, 2003;Humphreys et al, 2008;Jarvis, 1993) and P inputs (Van Keulen et al, 2000) from chemical fertilisers and feeds (concentrates, forages) typically exceed outputs in milk and livestock exported off the farms. These imbalances result in surplus N (Cherry et al, 2012;Gourley et al, 2010) or P (Arriaga et al, 2009;Gourley et al, 2010) that are either accumulated on, or lost from, dairy farms.…”

What Global and/or European Agriculture Will Need from Grasslands and Grassland Breeding over the Next 10–15 Years for a Sustainable Agriculture

“…Later publications (e.g. Humphreys et al 2008) use the same correction factor for much higher mineral N dressings, asssuming that the linear relationship holds beyond the originally tested low mineral N applications. Anyway, the formula quantifies common knowledge: to take maximum advantage of the biological fixation, external mineral N-input should be low.…”

N leaching to groundwater from dairy production involving grazing over the winter on a clay-loam soil

“…During 1999, most of the area of the farm (52 ha) was divided into 8 blocks (each an area approximately 6 ha) depending on soil type and drainage status as described by Humphreys et al (2008a). Six of these blocks were assigned into this experimental study (34 ha).…”

“…Cows were turned out (returned outside) to graze immediately after the calving date and remained outside until drying off the following winter, except when the ground was too wet and cows were occasionally retained indoors to avoid damaging the grassland. The length of the grazing season for each system was determined according to a number of days at pasture as described by Humphreys et al (2009).During 1999, most of the area of the farm (52 ha) was divided into 8 blocks (each an area approximately 6 ha) depending on soil type and drainage status as described by Humphreys et al (2008a). Six of these blocks were assigned into this experimental study (34 ha).…”