Catch-crops such as Intimidator oats look set to play an increasingly important part in crop rotations, particularly as the regulatory spotlight falls on the environmental impact of winter feed crops.
Catch-crops are sown as early as possible after a winter feed crop has been grazed, with the aim of mopping up excess nutrients in the soil before they disappear over or down the soil profile and make their way into waterways.
Results from the first year of a Ministry for Primary Industries Sustainable Farming Fund (SFF) project, which is looking at using catch crops to mitigate nitrate (N) leaching during winter forage grazing have shown that the inclusion of a catch-crop (such as Intimidator green feed oats) can generate a gross profit of $2,500/ha. That is from a 12t dry matter (DM) per hectare crop harvested in November (range 8-12 t/ha). The DM is valued at 25c/kg.
In this particular example, where oats were sown into a grazed kale paddock in mid July, the oats pulled up 223kg N/ha, N that would have potentially been lost to the environment.
Peter Carey, a field research scientist with Lincoln Agritech, who is carrying out the three-year SFF project, says catch-crops increase the efficiency of the operation by retaining N in the system that farmers would otherwise have waved goodbye to.
He says forage crops (such as brassicas or fodder beet) can yield 15-25t DM and carry a lot of stock in a small area at a time where there is very little plant growth. This means there is a lot of urea sitting in the soil which will be turned into ammonium and then nitrified to nitrate, the most mobile form of N.
“While they are on relatively small areas these crops are potentially big sources of N loss and can have up to 300kg N/ha sitting there with nothing to take it up.”
Peter says oats are ideal as a catch-crop because they are more winter active, and, therefore, are growing when the bugs in the soil start turning the ammonium from the deposited urine into nitrate.
“Once the soil temperatures warm up enough to start the oats growing, it is exactly the same time as the nitrification process kicks into gear.”
Oats, with their larger seed, are also more cold tolerant, robust and have deep roots to capture the soil N.