Catch crops a powerful tool for reducing nitrogen leaching
Looking for a way to reduce the risk of nitrogen (N) leaching and make the most of the valuable nutrients left behind after winter forage crop grazing? A catch crop could be the answer.
The role of a catch crop — a short-term crop sown between main crops or during pasture renewal — is to absorb residual soil N left after winter grazing, transforming it into valuable animal feed while significantly reducing the risk of nitrate leaching and nutrient runoff.
According to the recent Catch Crops for Cleaner Freshwater project, led by Dr Brendon Malcolm from Bioeconomy Science Institute (formerly Plant & Food Research), these crops can reduce N leaching by up to 60 per cent and sediment runoff by around 40 per cent.
Researchers have been particularly surprised at how well catch crops such as oats and Italian ryegrass can consistently perform when sown in winter, even in some of the toughest of years.
“Even during the coldest winter months, research indicates that delaying sowing by just a few weeks can greatly reduce yield and N uptake,” said Brendon.
“The key to success is to sow the crop as soon as possible after winter grazing, when soil temperatures are at 4°C or above.”
The research team checking the trial catch crops
Wet winter and spring conditions can limit sowing opportunities, making flexibility and planning for crops essential.
“Often some surface cultivation is necessary to achieve good soil-to-seed contact, but it is important to not over-cultivate as this can risk soil capping and further losses in wet years.”
Early sowing crucial for N utilisation
Even in the early stage, catch crops are playing an important environmental role.
While slow to establish in winter — often taking three-to-four weeks before they emerge — the root systems are developing three times faster than what is seen above-ground.
“Catch crops sown earlier develop their root systems sooner, allowing them to take advantage of rising soil temperatures. As a result, they can maintain a longer vegetative growth period, effectively capturing more nitrogen during the crucial leaching period,” Brendon said.
“Even when only 20 per cent of growth is achieved by the end of the leaching period around October, more than 50 per cent of the N is already captured.”
The benefits of catch crops go beyond nutrient capture
“Although more quantitative research is needed, the project has observed improvements in soil health, including enhanced soil structure, better aeration, improved water infiltration and storage, and a boost in soil life such as earthworms,” added Brendon.
Catch crops such as oats then pile on biomass in late spring, often growing at over 200 kg DM/ha/day, offering farmers a valuable return in livestock feed, like green-chop silage.
Backed by collaboration
Our principal farm systems advisor Shane Gilmer is excited to support a project that is showing tangible environmental outcomes when it comes to N leaching.
“From our perspective, catch crops are great tool for mopping up excess N when the leaching risk is high following winter grazing,” he said.
“It’s a win-win for farmers as catch crops not only help protect our groundwater, but they also improve soil structure and provide high-quality feed for livestock.”
The Catch Crops for Cleaner Freshwater project was supported by MPI’s Sustainable Land Management and Climate Change – Freshwater Mitigation programme, in partnership with Beef + Lamb New Zealand, Plant & Food Research, AgResearch, DairyNZ, the Foundation for Arable Research, Southern Dairy Hub, Environment Southland, and us.
For further information on catch crops and current projects, follow Catch Crops for Cleaner Water on Facebook or listen to the recent Country-Wide Podcast featuring Dr Brendon Malcom, Pushing the boundaries of catch crops.