Hardy catch crops such as oats are showing major promise for mopping up excess nitrogen after winter grazing and could
create a win-win for farmers in terms of their environmental footprint and profitability.
Dr Peter Carey, a Lincoln Agritech Field Researcher, is leading a three-year Ministry for Primary Industries (MPI)
Sustainable Farming Fund (SFF) research programme, in conjunction with Plant and Food Research, to apply the use of
catch crops more widely in winter forage rotations.
Dr Carey, who completed a PhD at Lincoln University on the use of catch crops, found that they can reduce nitrate
leaching by as much as 40%. This study looks to extend his research and apply it directly to commercial farms in
Canterbury and Southland. The project aims to adapt their use to the different soils and climatic conditions of each
region.
“Catch crop strategies are becoming more important, with the new Action for Healthy Waterways regulations coming into
effect in winter, 2021,” Dr Carey said. “These will prevent farmers from leaving paddocks bare for more than a month
after winter forage grazing. Fortunately, the research is showing that catch crop strategies can be a profitable avenue.
“Nitrate leaching, and nitrogen loss generally, is particularly problematic in winter as non-lactating dairy cows eat
large quantities of feed over a fairly short period of time to build up their body conditioning.
“Then they deposit large volumes of urine onto bare soil at a time when plant growth is minimal.
“Usually, catch crops are sown in autumn between the harvesting of the previous summer crop and a new crop in spring to
conserve soil nutrients over the winter but in winter forage rotations, they need to be sown at the end of the grazing
period, which is often mid-winter when soil and climate conditions are at their most difficult.
“But with the frequency of warmer and drier starts to winter increasing, hardy cereals like oats can be successfully
established in the cool conditions.”
Dr Carey said oats were tolerant to the cold and would germinate at 5 degrees and above, reducing water in the soil and
removing some of the nitrogen left when the cows had urinated on the ground.
“Once the soil warms, catch crops can rapidly mop-up the excess nitrogen, reducing the amount available for leaching.
“Even within a couple of months, we have seen catch crops take up as much as 40kg of nitrogen per hectare. By late
November, early-sown crops for green-chop silage in both Canterbury and Southland are often reaching 8-10 t DM/ha and
capturing 100-150 kg N/ha.”
The first year of the study has shown that the best results occur when the crops are sown as early as possible after
grazing has been completed and are established using direct drilling methods. In Southland, researchers used a
spader-drill, a relatively new piece of tillage technology, that enabled much earlier drilling than is usually possible.
“Although there is often substantial soil mineral-N available to the developing cereal crop, the second year of the
study showed that monitoring is advisable to ensure its N status remains sufficient to maintain quality and maximise
yield, so a modest spring nitrogen application may still be prudent,” Dr Carey said.
The SFF programme is primarily funded by MPI for three years (2018-21) and co-funded by Ballance Agrinutrients,
Ravensdown, Beef + Lamb New Zealand, Agricom, and Luisetti Seeds with a number of other farm and industry groups
providing in-kind co-funding as well.