The second in this two-part series looks at sowing rates, nitrogen use, harvest timings and some of the challenges with catch crops.
Along with several other organisations, B+LNZ helped fund the catch crops for reduced nitrate leaching project. The outcomes highlighted the value of catch crops as a tool to capture and use nitrogen left in the wake of winter forage crops, provided the correct management principles were followed.
Making the best use of catch crops
- Sow as early as possible after grazing.
- Select winter-active species.
- Target minimum or no-tillage.
- Target high plant populations and use seed with good vigour.
- Minimise weed competition.
- Apply nitrogen fertiliser from October if required.
- Harvest at green-chop silage (booting) for maximum yield and quality.
High sowing rates
Shane Maley from Plant and Food says high sowing rates of 110-120kg/ha are needed to get good nitrogen uptake, fast canopy closure and to produce a high yielding crop.
In an oat- Italian ryegrass mix, rates of 70-80kg/ha of oats and 20kg/ha of Italian ryegrass are recommended.
Shane says in an oat crop, the aim is to get 300 plants/m2 to achieve canopy closure as quickly as possible.
“If you don’t get high plant populations you will struggle to get canopy closure”
High plant populations will also out-compete weeds.
Some crops may require a dressing of N in October just to finish the crop off, but Shane says 60% of catch crops won’t need any. It depends on the season and the soil type.
DO NOT APPLY N AT SOWING! He says this is important as it defeats the purpose of the crop. Even if the crops are slow to establish, they will still be capturing N.
Trials have shown that for maximum yield and quality (ME) the crop should be harvested at the green-chop silage (booting) stage.
Harvest as the panicles begin to emerge, if not before. Once the panicle emerges, quality declines quickly. Crude protein levels peak at 13-15 ( % of DM) at Growth Stage 39-45 before dropping off.
“At the end of the day it depends on what the crops is being used for, quality feed versus bulk feed,” says Shane.
Not a silver bullet
Taking an oat crop to green-chop silage will delay the sowing of the subsequent winter forage crop, but overall, the paddock will be growing more total feed over a 12-month period.
“They are not a silver bullet and they are not going to work in all years, but they are a tool and no one size fits all.”
If it is too wet to get on a paddock before the end of August/beginning of September, then planting a catch crop is probably less attractive.
“It’s not really viable for the crops to do what you need them to do.”
Catch crops can be difficult to fit into a milking platform rotation, but an oat and Italian ryegrass mix can help by growing feed into summer.
Catch crops are probably also not going to fit well into a fodder beet-to-fodder beet rotation (which is not recommended anyway) as the harvest of the catch crop is past the optimum sowing window for fodder beet. The focus needs to be on getting the fodder beet planted at the optimal time.
In seasons where water is limited, catch crops can deplete soil moisture that would be otherwise available for subsequent main crops.
Catch crops also provide feed at a time of the year when feed is often not required. Conserving feed adds costs and logistical challenges.
Due to the popularity of catch crops, sourcing the appropriate seed can be difficult, but it is really important to get good seed as vigour is important when sowing in winter.