Economic performance of 3 farm systems differing in sward species diversity and nitrogen fertilization level across a range of future economic scenarios.

Globally pasture-based dairy systems (depending on milk production levels) are usually more competitive in temperate climates because they offer consistent profit margins at lower costs than systems that rely more on external supplements. In such systems, perennial ryegrass has been the predominant grass species used because of its capability to produce consistently high-quality forage over a long growing season and ease of management. However, perennial ryegrass swards are heavily reliant on chemical nitrogen (N) fertilizer applications and rising N fertilizer and energy costs have substantially increased the costs of milk production in such systems. Also, the continued use of high levels of chemical N fertilizer raises questions due to the impacts of N fertilizer production and application on both GHG emissions and nutrient losses. Alternatives are legumes such as white clover sown into perennial ryegrass pastures which requires less N, or even a greater variety of grass, legume and herb species which may additionally have ecosystem, environmental and biodiversity above and below ground benefits. However, the management of diverse swards can be more challenging because minimum clover contributions (20%) are required for optimal sward and animal performances, and the persistency and botanical stability of swards can vary within and between years. Consequently, the potential economic benefits of both perennial ryegrass-white clover and multispecies swards arising from increased animal performance and N fertilization saving may be diminished by increased costs associated with more frequent reseeding, or over-sowing, to maintain botanical contributions within the sward. To study the economic performance of the three systems, the objective of the authors cited was to compare their present and possible future economic performance as it applies to Ireland.

The three systems were, respectively: a perennial ryegrass (Lolium perenne L.; PRG) receiving 250 kg N/ha (PRG-250N); a PRG-white clover (Trifolium repens L.; WC) receiving 125 kg N/ha (PRGWC-125N); and a multispecies (MSS) sward composed of grasses, legumes, and herbs receiving 125 kg N/ha (MSS-125N) [meadow fescue (Festucapratensis L), Timothy (Phleum pratense L), WC, red clover (Trifolium pratense L), hybrid clover (Trifolium hybridum L), plantain and chicory]. Sward and animal performances were measured over three years in a system-scale study involving three farmlets. Based on the physical data collected, an economic performance of each sward system was evaluated using current output prices and input costs in the Ireland Moorepark Dairy Systems Model.

The economic results show similar net farm profitability for both PRG-250N and PRGWC-125N. The PRGWC-125N system had lower costs linked to fertilizer; however, more grass silage was purchased due to reduced grass production. The MSS-125N system outperformed both PRG-250N and PRGWC-125N in net farm profitability (+€167/ha and +€148/ha, respectively) due to increased milk output coupled with reduced N fertilizer use. Sensitivity analyses indicated that MSS-125N was the most profitable system under varying milk and fertilizer prices. Given the variability of clover and herb establishment between paddocks for PRGWC-125N and MSS-125N, an increase in the reseeding frequency and over-sowing frequency was simulated and resulted in reductions in farm profitability for both systems (€-14.25/ha per year and €-28.25/ha per year, respectively).

In summary: The PRGWC-125N system (10% over-sown) achieved net farm profitability comparable to the traditional PRG-250N system, with similar milk production and reduced fertilizer costs offsetting lower herbage yields. The MSS-125N system increased net farm profitability, driven mainly by higher milk production. Overall, the results show that increasing sward species diversity (including legumes and herbs) can enhance the economic performance of grazing systems through improved animal productivity and lower fertilizer inputs. However, they also highlight the financial risk of poor white clover establishment, which can limit the economic benefits of such based systems.