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Winter forage crops such as fodder beet and kale play an important role in many New Zealand farming systems. However, these crops also present a potential risk of nitrogen (N) leaching during and after grazing due to extended periods of bare soil, wet winter conditions, and high rainfall. Nitrogen that could be potentially lost from grazed winter forage paddocks via leaching has negative environmental implications and represents an opportunity to produce additional drymatter (DM). Catch cropping is an important tool that helps reduce nutrient losses while maintaining productivity.
Establishing a catch crop as soon as practical after winter forage grazing provides the greatest opportunity to reduce nitrate leaching while maximising harvestable DM production. Because grazing is typically completed during winter species options are relatively limited. Crowa forage oats establish well under cool conditions and begin taking up soil nitrogen soon after emergence. Research from the Forages for Reduced Nitrate Leaching (FRNL) and Pastoral 21 (P21) projects (Horrocks et al., 2021) demonstrated that forage oats can produce substantial amounts of DM, at a relatively low cost per kilogram of DM, while reducing nitrate leaching by up to 40%. Traditionally, perennial or short-rotation pasture is established after harvesting the oats.
Other trials have evaluated a range of species and species mixtures for their suitability as catch crops and their ability to continue producing forage following the initial harvest or grazing. Revel annual ryegrass or Manta Italian ryegrass are good options in this situation, due to their establishment vigour and cool season growth. Although they cannot produce the large bulk of feed for a single harvest like Crowa, they offer great regrowth following grazing or harvesting.
One of the most successful combinations has been Crowa forage oats (sown at 80 kg/ha) and Manta Italian ryegrass (sown at 20 kg/ha). Crowa can produce large volumes of high-quality forage over a short period of time, while Manta continues to produce dry matter after the oats have been harvested and can remain productive for up to 12 months following the initial harvest. These findings align closely with the FRNL project, which concluded that sowing oats (80 kg/ha) together with Italian ryegrass (20 kg/ha) is an effective option for farmers wishing to minimise production losses following the oat crop. Although the oats and Italian ryegrass mixture produced slightly less DM than oats alone (refer to the figure below), the Italian ryegrass continued producing valuable forage throughout summer after the oats were harvested, resulting in greater total annual feed production.
The success of any catch crop depends on several factors, including sowing timing, sowing depth, soil conditions, and climate. One of the major advantages of Crowa forage oats, and cereals generally, is their ability to germinate at soil temperatures as low as 5°C, allowing for establishment as soon as paddock conditions permit. Correct sowing depth is a critical factor that is often overlooked but is easily managed. A drilling depth of 30 to 40 mm is recommended to ensure good seed-to-soil contact and complete seed coverage, reducing losses from birds and other pests. However, it is important that the sowing depth of Manta Italian ryegrass does not exceed 10-20 mm to ensure germination. Where possible, direct drilling is recommended to preserve soil structure and minimise disturbance. If cultivation is required to improve seedbed conditions, it should be kept to a minimum, as excessive cultivation can damage soil structure and stimulate additional nitrogen mineralisation. Rolling with a Cambridge roller after sowing is also beneficial, particularly where the crop will be harvested as silage or baleage.
Sowing Crowa forage oats, either alone or in combination with Manta Italian ryegrass, into grazed winter forage paddocks provides an excellent opportunity to produce significant quantities of high-quality forage from land that would otherwise remain largely unproductive until spring. At the same time, catch cropping is an effective strategy for capturing residual soil nitrogen, reducing nitrate leaching, and improving the overall productivity and sustainability of New Zealand pastoral farming systems.
For further information, please contact your local Agricom representative.
References
Horrocks, A., Beare, M., Malcolm, B., Teixeira, E., Carey, P., Clement, A., Maley, S., McMillan, N., Scobie, D., Pinxterhuis, I., & Edwards, P. (2021). Catch crops for reduced nitrate leaching: Lessons from the “Forages for Reduced Nitrate Leaching” programme and Sustainable Food and Fibre Futures project “Catch Crops to Reduce Nitrate Leaching” (Guidelines). DairyNZ. https://www.dairynz.co.nz/media/x0xhwwtc/catch-crop-guidelines_august2021.pdf