Catch crop trials show promise for reducing soil nitrogen

Catch crop trials in the Upper Waitaki show strong potential to reduce nitrogen (N) losses and protect water quality in the Ahuriri catchment. The trials offer farmers a practical way to boost winter feed while supporting sustainable land management. Find out how these practices could work on your farm.

Catch crops thriving this winter

Catch crops planted this winter in a trial on three Upper Waitaki farms are thriving, particularly forage oats.

Catch crops are sown between main crops or during pasture renewal and absorb residual soil mineral nitrogen (N) during the coolest months of the year when soils are draining, reducing the risk of nitrate leaching and contaminant runoff. They also produce valuable animal feed.

We’re supporting a two-year study on the potential for catch crops in the Ahuriri catchment as part of a wider focus to protect the health and water quality of Lake Benmore.

Lead researcher Dr Brendon Malcolm of the Bioeconomy Science Institute has already found that catch crops can reduce N leaching by up to 60 per cent and sediment runoff by around 40 per cent after winter forage crop grazing.

Trialling catch crops in high-country grazing systems

In winter 2025, the team planted winter-active species of oats, ryecorn, Italian ryegrass and tetraploid hybrid ryegrass under different densities and combinations on a sheep and beef farm, a dairy farm, and a sheep and beef farm at a higher altitude in the Ahuriri catchment area.

The goal is understanding how N moves through winter grazing systems, and how catch crops and improvements in fertiliser management might help reduce the risk of N loss to the environment, while also being economically viable for farmers.

Over two seasons, the researchers will monitor soil N levels before winter grazing of kale or fodder beet, through winter, and into spring, while also measuring how well the different catch crops grow and pick up N.

Frost-hardy forage oats thriving

The trials seem to be a success so far. With crops being harvested in late November or early December, all species are thriving.

“Straight up, we have been very pleasantly surprised by how the crops have worked in these cold high-country environments, especially the oats,” said Lead researcher Dr Brendon Malcolm.

In another study of catch crops in the Ashburton Lakes and Rakaia Gorge, Brendon found oats sown in August consistently outperformed other species tested, with yields ranging from 6.8 to 10.5 t DM/ha. For instance, oats often outyielded ryecorn by more than 2 t DM/ha, which Brendon attributes to improved genetics of forage oats.

More about this trial: Catch crops a powerful tool for reducing nitrogen leaching