The interest in sustainability in this review is due to recent dairy system development and research in Canterbury has focused on balancing profitability with environmental
responsibility (DairyNZ, 2013). In an international context, mixed systems have been associated with sustainable systems (Devendra, 1999; Russelle et al., 2007; Stokes, McAllister, & Ash, 2006). The integration of crop and livestock offers synergies (between crop, livestock and soil) that farmers can build into their operations (Villano et al., 2010). These synergies of mixed faming can increase efficiency in the system (van Keulen & Schiere, 2004) and therefore build toward a more sustainable system. Russelle et al. (2007) noted integration can reduce risk because it diversifies production and that reducing risk could be a form of economic sustainability. In Europe integrated farming is advocated as a sustainable approach to agricultural production which can maintain farmer income and safeguard the environment (Morris & Winter, 1999).
Agricultural sustainability is a broad term used to encompass both the economics and environmental aspects of agriculture internationally. The concept of sustainability in agriculture has emerged as an important factor in both conventional plant and animal systems of production (Hendrickson et al., 2008). It is therefore a major component when analysing animal and plant systems in agricultural production. Sustainability can be defined as:
“An approach to producing food and fibre which is profitable, uses on-farm resources
efficiently to minimize adverse effects on the environment and people, preserves the natural productivity and quality of land and water, and sustains vibrant rural communities”
(UCSUSA, 2005 cited in Hendrickson et al., 2008, p. 268).
Lyson (2002) breaks sustainable agriculture down into three clear dimensions; 1) ecological 2) economic and 3) social – community. The economic aspects of sustainability have been regarded as relevant in the agricultural industry for decades. The social aspect of
sustainability as a concept is far newer (Thiesse, 2010). Furthermore, it is the social aspect which is becoming a driver for change in developed countries (Thiesse, 2010). There is, however, difficulty around the definition of the social aspect. This arises because it is not based on economic research or science, rather on concepts, business strategies, opinions
33 and preferences of a personal nature (Thiesse, 2010). Weil (1990) defined the social
sustainability concept and public welfare concerns as food safety, human exposure to toxic chemicals and environmental concerns based on human preference for landscape
aesthetics. Thiesse (2010) suggests that the farmers’ view of risk could also be part of the social concept as it is based on the personal nature and the application of strategy by the farmer.
Certain crops grown on milking platforms can increase the sustainability of the dairy system (Johnstone et al., 2010). First, crop production can be used to increase supplementary feed made on farm and reduce the use of imported feeds. However, it must be noted that imported feeds are often chosen because they are a lower cost alternative.
Nutrient loading can be high in dairy farm soils that are regularly irrigated with shed effluent. There are negative effects on the environment and on animal health which can occur as a consequence (Houlbrooke, Horne, Hedley, Snow, & Hanly, 2008; Wang, Magesan, & Bolan, 2004). Maize (unlike some crops) is ideal for mining nutrients on dairy farms because it commonly produces a biomass above 20 tonne per hectare (Li et al., 2009). At average P, N and K concentrations in the maize plants tissue, crop removal can easily exceed 250kg N, 40kg P and 250kg K per/ha/season (Johnstone et al., 2010). In 2007, a three year project to monitor nutrient loading impacts through the strategic use of maize commenced (Johnstone et al., 2010). Nine on-farm trials showed that nitrogen fertiliser is not needed to maximise maize silage yield for a first season crop which was planted in nutrient-rich, effluent treated soils. Using maize on effluent soils not only reduced the fertiliser requirement, it was also shown to reduce residual soil mineral N levels at harvest (Johnstone et al., 2010).
Integration of crops on dairy farms has also been recognized as a method of using dairy shed effluent (Selvarajah, 1999) to improve soil properties and plant nutrient availability with less fertiliser. It is estimated that six to ten percent of daily dairy excreta is deposited in the milking shed or yards and when the shed is cleaned by high pressure hoses an estimated 50 litres of water-effluent is generated per cow (Mason, 1997; Selvarajah, 1999). Correctly applied, agricultural effluents can improve soil properties such as plant nutrient availability, soil pH, organic matter, cation exchange capacity, water holding capacity and soil tilth which can lead to an increase in the yield of pastures and crops (Eck & Stewart, 1995). From the
34 point of view of benefiting a crop farm, pasture can enhance soil quality when integrated into cropping systems due to the deep and abundant roots systems of pasture plant species and the ecological functions of pasture plants such as nitrogen fixers (A. Clark, 2004).
Crop production on dairy farms can also increase pasture renewal (MacLeod & Moller, 2006; Pyke, 2011). There is a low rate of pasture renewal on dairy farms which is perceived to be reducing the potential for improved genetics to increase pasture productivity (D. Clark et al., 2007).Thus increasing crop production may create the need for crop rotation plans and allow greater annual pasture renewal and therefore increase the efficiency of the farm system (Pyke, 2011)
When applying Lyson’s (2002) social issue, it has to be noted that social issues include not just the farmers, but the whole of societies view from farm employees to urban onlookers. According to Clark et al., (2007) it is well publicised that society is becoming less tolerant of the negative impacts of dairy farming even though agriculture makes both economic and social contributions to society.