Key discussion included current results, issues and benefits around the establishment of catch crops, including crop type, cultivation and soil management methods.
In opening the workshop, Plant & Food Research scientist Brendon Malcolm encouraged farmers to “get ahead of the curve” and put some catch crops in.
“It’s about being the ambulance at the top of the hill,” Malcolm said.
A catch crop is any crop that is sown with the primary objective of utilising excess nitrogen in soils that otherwise may be lost to the environment through leaching.
Trials completed in Canterbury, Waikato and Southland have found cereals were more effective than grass species following winter grazing.
The earlier the crop is planted, the greater the opportunity to reduce leaching, with catch crops also able to increase the total annual yield of a paddock.
The three-year Ministry for Primary Industries (MPI) Sustainable Farming Fund (SFF) project contract is widely supported by industries looking to reduce environmental impacts from winter forage crop grazing.
Malcolm says the main driver of the catch crop research is mopping up nitrogen.
One Canterbury trial of kale grazed over winter, then sown in oats late-July, captured 65 kilograms of nitrogen.
“The oat crop is taking up more nitrogen than it requires, so the result is a luxury uptake – high nitrogen percentage,” he said.
“It is a tool not a silver bullet and there is no one size fits all.”
Key agronomic recommendations are to sow the catch crop as soon as possible after grazing, select winter active species such as oats, target minimum or no tillage and targeting high plant populations, ideally 110-120kg of seed per hectare for oats, using certified high vigour seed.
Aim for good soil-to-seed contact, this may require some surface tillage, minimum weed competition and applying nitrogen fertiliser in October if required, then harvest at green-chop silage for maximum yield and quality.
Trial results to date show cereals perform better than ryegrass and Italian grass that struggle in the colder temperatures.
An oat-Italian mix is a popular choice, but dry matter yield performance lagged a straight oat crop in both Canterbury and Southland trials.
“More seed (means) more cost, but (also) more crop – it is really important to target high plant populations,” Plant & Food Research science team leader for field operations Shane Maley said.
“It’s all about sourcing appropriate seed and getting enough seed in the ground to get a result; lower plant population resulted in 30-40% less nitrogen update.
“I can’t stress enough the need to get really good seed for high vigour at this time of the year as you want to catch crops off by mid-November at the very latest, or it becomes too hard to look at the next crop.
“Catch crops are low input, there’s no need to put nitrogen on at planting at all.
“Ideally 300 plants per square metre, and that smothers weeds out quite nicely too.”
Harvest at green-crop not only maximises yield and quality, but also opens other windows for follow-on plantings.
Catch crops do not work with fodder beet rotation.
While trials have been conducted on the West Coast, in Canterbury and Southland this year, with some work also being done in Hawke’s Bay, the trial work is not yet programmed into Overseer.
“But we do expect it will improve the number,” he said.
“We are working with Overseer now and applying to MPI to get some more funding to get into Overseer.”
