Phosphorus balance and use efficiency on 21 intensive grass-based dairy farms in the South of Ireland

Abstract

SUMMARYGiven the finite nature of global phosphorus (P) resources, there is an increasing concern about balancing agronomic and environmental impacts from P usage on dairy farms. Data from a 3-year (2009–2011) survey were used to assess farm-gate P balances and P use efficiency (PUE) 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 P surplus was 5·09 kg/ha, or 0·004 kg P/kg milk solids (MS), and mean PUE was 0·70. Phosphorus imports were dominated by inorganic fertilizer (7·61 kg P/ha) and feeds (7·62 kg P/ha), while exports were dominated by milk (6·66 kg P/ha) and livestock (5·10 kg P/ha). Comparison to similar studies carried out before the introduction of the GAP regulations in 2006 indicated that P surplus, both per ha and per kg MS, has significantly decreased (by 74 and 81%, respectively) and PUE increased (by 48%), mostly due to decreased inorganic fertilizer P import and improvements in P management. There has been 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 suggested a positive impact of the GAP regulations on dairy farm P surplus and PUE, 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 dairy production. Results suggest that optimizing fertilizer and feed P imports combined with improved on-farm P recycling are the most effective way to increase PUE. Equally, continued monitoring of soil test P (STP) and P management will be necessary to ensure that adequate soil P fertility is maintained. Mean P surplus was lower and PUE was much higher than the overall mean surplus (15·92 kg P/ha) and PUE (0·47) from three studies of continental and English dairy farms, largely due to the low import system that is more typical in Ireland, with seasonal milk production (compact spring calving), low use of imported feeds and high use of grazed grass.

Estimation and determinants of phosphorus balance and use efficiency of dairy farms in Northern Ireland: A within and between farm random effects analysis

“…We are not aware of any previous econometric study on P balance and its determinants in Northern Ireland. While a few studies on P balance have been undertaken in the Republic of Ireland (Ruane et al, 2014;Buckley et al, 2015;Mihailescu, et al, 2015), these studies are based mainly on the farm gate approach. Northern Ireland presents an interesting case study for analysing P balance and P use efficiency (PUE) due to the significant expansion of the dairy sector in recent years.…”

Adsorption and desorption of phosphorus in subtropical soils as affected by management system and mineralogy

“…The efficient use and management of P in farming systems is fundamental to reach large agricultural productivity without threatening the environmental quality (MacDonald et al, 2011;Mihailescu et al, 2015).…”

Long‐term Changes in Grassland Soil Phosphorus with Fertilizer Application and Withdrawal

“…In Ireland, including both the Republic of Ireland and Northern Ireland, agricultural production is dominated by beef and dairy. These are both intensively managed to maximize grazing and silage from local grasslands (Mihailescu et al, 2015). In the 1960s to 1980s, fertilization was widely used to increase soil P fertility, with a 10‐fold increase in STP over 50 yr of fertilization (Tunney et al, 2000).…”

“…This, in turn, increased eutrophication (Bourke et al, 2008; Schulte et al, 2010; Buckley et al, 2016). There has been a decline in P fertilizer use in Ireland since the mid‐1990s, and more recent farm assessments suggest that more farms are relying on soil P reserves to support grass yields and are not fully replacing P removed in herbage (Daly et al, 2015; Kleinman et al, 2015; Mihailescu et al, 2015; Buckley et al, 2016). However, in Northern Ireland, the P concentrations of more than half of grassland soils remain above agronomic optima (Bailey, 2015).…”