B+LNZ is encouraging farmers to consider planting catch crops this spring to capture and utilise residual soil nitrogen left in the wake of winter grazing.
Key takeaways
- Planting catch crops as early as possible after grazing increases their effectiveness in reducing nitrate leaching and sediment loss and can boost the annual yield of a paddock.
- Cereals (e.g. oats, ryecorn, triticale, wheat or barley) are more effective than grass species (e.g. Italian ryegrass) as catch crops following a winter crop grazing.
Beef + Lamb New Zealand is encouraging farmers to consider planting catch-crops this spring to capture and utilise residual soil nitrogen left in the wake of winter grazing.
Planted as soon soil conditions allow, catch crops give farmers the ability to turn residual nitrogen (N) into valuable drymatter while reducing the risk of nitrate leaching.
According to the findings of the B+LNZ-supported Catch Crops for Cleaner Freshwater project, catch crops are typically sown at the coldest time of the year and the best sowing options are winter active crops such as oats, ryecorn, triticale and Italian ryegrasses – which can be sown with a cereal such as oats.
Research has shown that it is important to get catch crops into the ground as soon as possible after the paddock has been grazed, when soil temperatures are four degrees and above.
Timing is critical with catch crops, and research has shown that sowing oats immediately after grazing has the greatest impact on reducing N losses. With every month that sowing is delayed, there is a notable reduction in effectiveness.
While July-sown oats can be very slow to come away, they are still capturing a significant amount of N through their root system during the high-risk period, despite the small amount of above ground foliage.
Ideally the paddock should only be minimally cultivated, just enough to ensure good soil-to-seed contact, but pugged soils may require more cultivation.
Trial work has shown that a high plant population is best to capture the N and maximise dry matter production. A sowing rate of 110-120 kg seeds/ha for oats is recommended to target an optimal plant population of 300 plants per square metre.
Weed control is also important.
For catch crops grown for green-chop silage, the timing of harvest is important. Ideally, the crop should be harvested when the oats just start to go reproductive. Quality can quickly decline after this stage.
A typical yield of a green chop silage crop sown after winter grazing is 6-10 t DM/ha with a feed value of around 11 MJME/kg DM.
While catch crops offer significant benefits, they are not suitable for every farm system. Taking an oat catch crop through to green-chop silage can delay the sowing of subsequent winter forage crops.
This is particularly the case with two-year fodder beet rotations as the optimum harvest time of the catch crop is past the essential sowing window for fodder beet.
However, research how shown that when balanced out over a 12-month period, a paddock will grow more feed in total when a catch crop grown for green chop silage follows a winter forage crop such as kale.
A particularly wet spring may also make it difficult to establish catch crops in time to fully capture their benefits.
The Catch Crops for Cleaner Freshwater project was funded through MPI’s Sustainable Land Management and Climate Change – Freshwater Mitigation programme in partnership with Beef + lamb New Zealand, Plant & Food Research, AgResearch, DairyNZ, Foundation for Arable Research, Southern Dairy Hub, Environment Canterbury and Environment Southland.
To hear more go to Catch crops: a way to reduce N leaching after winter crops, with Dr Brendon Malcolm, Plant & Food Research | Beef + Lamb New Zealand (beeflambnz.com)
Read more about catch crops here catch-crop-guidelines_august2021.pdf (dairynz.co.nz)