OPPORTUNITIES FOR REDUCING THE ENVIRONMENTAL-IMPACT OF DAIRY FARMING MANAGEMENTS - A SYSTEMS-APPROACH

Dairy farming systems are important sources for the emission of a numb er of materials that include various forms of nitrogen (NO3-, N2O and NH3) with potential environmental impact. The present paper is a syste ms synthesis study and assesses the likely impact of changes in manage ment on N flows and losses, These include tactical fertilizer adjustme nt, slurry injection, maize silage production and the use of white clo ver as an alternative to fertilizer N. Implications for greenhouse gas es (N2O and CH4) and support energy have also been considered. Substan tial reductions in inputs and total and proportional losses by all the options considered were predicted by this study, Thus, using a tactic al approach to fertilizer application and injecting slurry or using 50 % maize silage reduced overall N losses from 160 (under conventional m anagement) to 86 and 109 kg N ha(-1) respectively. Combining both poss ibilities reduced losses further to 69 kg ha(-1). Although use of whit e clover, especially at low contents in the sward, was the most effect ive regime to reduce losses, this was at some cost to production so th at losses per livestock unit (LU) did not always differ from those und er other managements, Changing the N management had consequences for g reenhouse gas emission with an estimated maximum 70% reduction in N2O release. The effects on CH4 emissions were relatively small. Substanti al reductions in support energy costs were also obtained: these arose mainly from the reduction in fertilizer N use, which represented 66% o f the total support energy in the original system.