Modelling options to increase milk production while reducing N leaching for an irrigated dairy farm in Canterbury

Abstract

Abstract The Forages for Reduced Nitrate Leaching programme (FRNL) aims to address the challenge of presenting farmers with alternatives for forage production that will sustain milk production and farm profit, but simultaneously reduce nitrogen leaching by 20% from current levels. This paper describes the improvements made to a dairy model comprising three software packages, and how this model was used to evaluate proposed farm system changes on a Canterbury dairy farm (Canlac Holdings) associated with the FRNL programme. After a baseline scenario was sensechecked against actual farm physical and financial data for the 2014-2015 season, alternative options were modelled in an additive way by expanding the effluent area, growing fodder beet on the platform, replacing some pasture with maize silage, growing diverse pastures on 7% of the milking platform, and including a feed pad. The cumulative effect of these changes was an increase of 3 and 13% in production and profit respectively, but only a 5% decrease in nitrogen leaching as estimated for the combined platform and support block areas over 3 climate years. A hypothetical scenario, of a third of the platform in diverse pastures, less nitrogen fertiliser, all fodder beet grown on the milking platform, lifted and fed on the feed pad, and with an oats catch crop following fodder beet, increased production and profit by 2 and 10%, respectively, with a reduction in N leaching of 19%. This result indicates that high-performing farmers have scope to reduce N leaching by ~20% and still increase profit by implementing some of the options emanating from the FRNL programme. Keywords: diverse pastures, dairy farm system, fodder beet, effluent block, feed pad, catch crop