Nitrogen balance and use efficiency on twenty-one intensive grass-based dairy farms in the South of Ireland

Abstract

SUMMARYThere is increasing concern about balancing agronomic and environmental gains from nitrogen (N) usage on dairy farms. Data from a 3-year (2009)(2010)(2011) survey were used to assess farm-gate N balances and N use efficiency (NUE) on 21 intensive grass-based dairy farms operating under the good agricultural practice (GAP) regulations in Ireland. Mean stocking rate (SR) was 2·06 livestock units (LU)/ha, mean N surplus was 175 kg/ha, or 0·28 kg N/kg milk solids (MS), and mean NUE was 0·23. Nitrogen inputs were dominated by inorganic fertilizer (186 kg N/ha) and concentrates (26·6 kg N/ha), whereas outputs were dominated by milk (40·2 kg N/ha) and livestock (12·8 kg N/ha). Comparison with similar studies carried out before the introduction of the GAP regulations in 2006 would suggest that N surplus, both per ha and per kg MS, have significantly decreased (by 40 and 32%, respectively) and NUE increased (by 27%), mostly due to decreased inorganic fertilizer N input and improvements in N management, with a notable shift towards spring application of organic manures, indicating improved awareness of the fertilizer value of organic manures and good compliance with the GAP regulations regarding fertilizer application timing. These results would suggest a positive impact of the GAP regulations on dairy farm N surplus and NUE, indicating an improvement in both environmental and economic sustainability of dairy production through improved resource-use efficiencies. Such improvements will be necessary to achieve national targets of improved water quality and increased efficiency/sustainability of the dairy industry. The weak impact of SR on N surplus found in the present study would suggest that, with good management, increased SR and milk output per ha may be achievable, while decreasing N surplus per ha. Mean N surplus was lower than the overall mean surplus (224 kg N/ha) from six studies of northern and continental European dairy farms, while mean NUE was similar, largely due to the low input/output system that is more typical in Ireland, with seasonal milk production (compact spring calving), low use of concentrates, imported feed and forages, high use of grazed grass and lower milk yields per ha.

Benchmarking the environmental performance of dairy farming systems

“…The farm N balances calculated in this study (mean: IR=217.3 kg N/ha, NL=196.5 kg N/ha) are within the range reported in literature (values range from 155 kg N/ha to 295 kg N/ha) Treacy et al, 2008;Beukes et al, 2012;Mihailescu et al, 2014). Mihailescu et al May in 2010 compared to the other two years, reducing grass growth rate and increasing the use of fertilizers.…”

“…When comparing farm area, stocking rate and milk yield per cow, the Irish farms used in this study scored close to, but slightly above the national average of dairy farms in Ireland (Mihailescu et al, 2014). The 13 Dutch farms we used in this study were included also in the study of Oenema et al (2012), which studied 16…”

“…The 19 Irish dairy farms used in this study were included also in the study of Mihailescu et al (2014), which studied 21 Irish dairy farms in total. When comparing farm area, stocking rate and milk yield per cow, the Irish farms used in this study scored close to, but slightly above the national average of dairy farms in Ireland (Mihailescu et al, 2014).…”

“…This assumption has been used previously with the objective of simplifying the calculation processes (e.g. Powell et al, 2010;Oenema et al,, 2012;Mihailescu et al,, 2014). Collecting data on changes in soil organic matter content is difficult and time consuming, or requires detailed modelling techniques.…”

Nitrogen flows on organic and conventional dairy farms: a comparison of three indicators

“…For example, one common indicator is the N surplus (N input -N output), which is often reported per unit cropland area (Nevens et al 2006;Oenema 2006;Dalgaard et al 2012), and sometimes per unit product (Dalgaard et al 1998;Schröder et al 2003;Mihailescu et al 2014;Mu et al 2016), or inversely, as product quantity per unit N surplus (''eco-efficiency'', Nevens et al 2006;Beukes et al 2012). Another indicator often constructed from farm-gate N budgets is the N use efficiency (NUE), defined as N output/N input (Schröder et al 2003;Godinot et al 2014;Gerber et al 2014).…”