Catch crops should be sown as soon as possible after winter grazing has finished, as long as soil temperatures are two degrees and above.
This is one of the recommendations that has come out of the four-year ‘Catch crops for cleaner freshwater’ trials.
Funded by the Ministry for Primary Industries Sustainable Land Management and Climate Change – Freshwater Mitigation programme, the trials are being run by Plant & Food Research and AgResearch.
Over a year into the programme, Soil Scientist Dr Brendon Malcolm from Plant & Food Research is encouraging farmers to grab small windows of opportunity to get catch crops in the ground as early as possible.
On-farm trial work is suggesting that this could be as early as June and while this is obviously more difficult to do in Southland than in Canterbury, half of the winter block could potentially be sown in early July (roughly the mid-point of winter grazing) then the other half in early August.
Timing is critical with catch crops, and Brendon explains that crops need to be sown well before mid-October when drainage stops.
Dr Malcolm says even if the early-sown plants appear to be dormant after establishment, they will be building underground root systems and capturing nitrogen (N), so when soil temperatures rise, they will be so much further ahead.
He recommends, where possible, using minimum or no-till techniques to establish the crops and ensure good soil to seed contact at drilling. Remedial cultivation might be required where soils have been damaged through pugging.
Targeting plant populations of 300 plants per square metre (a seeding rate of 110-120kg/ha for oats) will help optimise the uptake of N left in the soil in the wake of intensive grazing. Trial results have shown there is no yield penalty in grain crops established with higher plant densities, the only downside is the additional seed cost.
While ryecorn, triticale, wheat and Italian ryegrass and mixes of these are all good options as catch crops, Dr Malcolm says oats are the go-to crop as they are the most consistent performers.
Ultimately, the decision about what to grow depends upon the intended end use of the crop and how it fits with the farm’s crop rotation.
Typically, catch crops are cut for green-chop or whole-crop cereal silage, although Dr Malcolm says trial work is being done on wheat, sown as a catch crop and grown out for grain.
Irrespective of the crop, weed management is important to maximise yields and quality.
While N will not be needed in the early stages of the crop (as the plants mop up the soil N) it may require small dressings (40-50 kg N/ha) in late October or November to help maximise yield.
Dr Malcolm says the Catch Crops for Cleaner Freshwater programme is also focusing on the role of catch crops in reducing run-off from paddocks that had been used for intensive winter grazing. Previous work on catch crops has concentrated on their role in reducing leaching.
Trial sites have been established on farms in Southland, Canterbury and on the West Coast and a lysimeter has been installed at the Southern Dairy Hub in southland.
A Facebook page @catchcrops is allowing farmers and anyone interested to follow the trial work, see the scientists and technicians working in the field and be updated on the initial findings and key messages.
Another tranche of this project uses a modelling tool to extrapolate the results of the trials onto different soils types, climatic conditions and seasonal variations amongst other variables. This will give farmers an indication of how catch crops might perform in a range of environments and climates.