Farmers finishing their winter forage crops are being encouraged to consider planting a catch crop this spring to capture soil nitrogen and turn it into valuable drymatter.
Findings from the Beef + Lamb New Zealand supported Catch Crops for Cleaner Freshwater project, Forages for Reduced Nitrate Leaching and Pastoral 21 projects have all demonstrated that forage oats in particular, can reduce nitrate leaching by up to 40 percent while producing substantial amounts of drymatter at a relatively low cost.
Greg Dunshea, a forage systems agronomist from Agricom, says growing oats for green chop cereal silage could be a way to bank a large volume of quality supplementary feed in spring. This feed could be particularly valuable if the forecast Super El Nino was to bring hot, dry conditions along the east coast of both Islands.
He says oats, such as Crowa forage oats, have the ability to germinate in soil temperatures as low as five degrees celsius, making them a great option to plant into ex winter feed paddocks when soil and weather conditions allow.
“Depending on planting date and environmental conditions, oats are capable of producing greenchop cereal silage yields of up to 10t DM/ha with harvest timings ranging from 70 to 110 days after establishment,”
He says early sown crops will be in the ground for longer and will have a higher yield potential while later sown crops will race through their lifecycle and be lower yielding.
“With a harvest timing of around late October to mid-November, it is still possible for the timely establishment of pasture or another crop post-harvest.”
Catch crop establishment
When sowing catch crops, if cultivation is required to improve seed-soil contact, Dunshea recommends a light surface work rather than full cultivation if possible, as this will help minimise additional nitrogen losses from the soil.
He says drilling depths of 30-50mm are ideal, with good seed to soil contact being critical. A sowing rate of 100-120kg/ha sowing rate is recommended for a target plant population of 300 plants per square metre.
Full coverage of the seed is crucial, so a Cambridge roll post-sowing could be used to improve soil consolidation if required. This pass with a roller will also help bury stones which is important if the crop is to be mown for silage.
Post-establishment, herbicides should be used to control problem weeds as weeds will compete with the crop for resources and reduce the quality of the silage.
“Catch crops can also be a useful tool within a farm’s rotation to tidy up problem weeds before establishing the following crop.”
Harvest timing
To ensure the right balance of energy and crude protein is present in the resulting supplementary feed, (important for driving animal performance) it is important that oats are harvested at the right time.
To get the best balance of yield and feed quality, Dunshea say the crop should be harvested at the ‘booting’ stage, which is when the seed head nears the top of the stem but before awns/seedhead emerge. Forage oats harvested at this stage can have an ME value of 10.5-11.5 MJME/kgDM, whereas oats with seedhead emergence will often have an ME value of less than 9 MJME/kgDM.
He urges farmers to monitor crops closely as harvest time approaches to ensure the harvest window is not missed.
“It is better to harvest too early rather than too late, you really don’t want to see any seedhead emergence from a feed quality perspective.”
Dunshea also encourages farmers to think about total DM yields from the paddock over time, rather than just individual crops.
“Don’t let the catch crop effect the timing of sowing the following crop. Work backwards from the planned planting date of the next crop and harvest the oats when required so you can get the next crop in on time.”
“Don’t chase additional silage yields and reduce the yield potential of the following crop by delaying sowing.”
Sowing in combination
Forage oats can be sown alone as a single harvest crop, or in combination with an Italian ryegrass to produce a productive short term pasture. Dunshea recommends a combination of Manta Italian ryegrass sown at 20kg/ha and Crowa forage oats sown at 80kg/ha for a robust short term pasture.
Although the Crowa and Manta mix could produce slightly less dry matter in the initial harvest compared to straight Crowa, the Manta will bounce back and continue to produce valuable forage throughout summer and into the autumn/winter.