Nitrate leaching from
winter forage crops and
SDH farm systems

Measured differenced in nitrate leaching under
winter crops - Kale vs Beet



Key person
Ross Monaghan

Project objectives

  • Measure N leaching losses from autumn and winter grazed fodder beet, winter grazed kale and selected pasture paddocks to determine and compare the farm system comparison losses of N.

Project description

Traditionally, non-lactating in-calf dairy cows have been wintered off pasture on brassica crops. For this reason, autumn- and winter-grazed fodder beet (FB) crops are key to the FB farmlets at the Southern Dairy Hub (SDH), while kale is the winter feed in the other two farmlets. To increase knowledge of the environmental impacts of these grazed forage crops, N leaching losses were measured in selected treatments to provide:

  • quantitative N leaching data for the crops, soils and climate of SDH

  • N leaching comparisons (autumn-grazed v lifted FB, winter-grazed kale v winter-grazed FB, and selected pastures on the milking platform).

Project outcomes/learnings

  • Average N leaching losses for the 3 years of measurements are presented in Figure 1. N leaching under the winter-grazed fodder beet crops was on average only 50% of that under the winter-grazed kale crops, while the autumn harvested FB leached a similar amount to the winter grazed kale.

  • Using losses calculated by Overseer for the pasture areas of the milking platform combined with the measured N losses from the winter crop areas, we have estimated that the change in fertiliser N inputs resulted in about 22% less N leached. Similarly changing from kale to fodder beet as the winter crop lowered N leaching losses by about 16%. The lower impact FB (LI FB) treatment leached 34% less than the standard kale farmlet. Overall, measured losses of N from the pasture paddocks were relatively low, and similar to Overseer predicted losses.

  • If lifting fodder beet in autumn to feed elsewhere or grazing in paddock, aim to replant the paddock as soon as possible to reduce N loss from drainage during the winter period

  • Fodder beet offers potential to decrease winter nitrate leaching losses, despite the increase in stocking density required with the higher dry matter yield.

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