Thursday, April 25, 2024

Timing of catch crop sowing key to efficacy

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While catch crops can alleviate nitrate leaching, research has shown delayed sowing reduces its effectiveness. Annette Scott spoke to Food Research Lincoln scientist Brendon Malcolm about best practices.
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Computer simulation modelling has shown that catch crops can reduce nitrate leaching in wet and dry years, but with every month that sowing is delayed, the effectiveness drops about 10%.

Plant & Food Research trials show short rotation (catch) crops grown between two main crops can mop up residual soil nitrogen and reduce nitrate leaching, significantly improving environmental outcomes from winter grazed forage crops.

Catch crops can be implemented after any winter-grazed forage crop, such as kale, fodder beet, swedes and turnips, but depending on the next main crop, this can dictate what catch crop is best to use, and when it should be harvested or terminated, Plant & Food Research Lincoln scientist Brendon Malcolm says.

“The main drivers for farmers in terms of what catch crop is best to use will depend on nitrate leaching reduction targets, the intended use for the catch crop and the overall crop rotation,” Malcolm said.

He says sowing them in winter, after forage crop grazing, means there is a typically short window of opportunity in which catch crops can effectively mop up nitrogen and reduce leaching, therefore, it is particularly important to choose the right crop and to sow as early as possible after grazing.

“Timing of catch crop sowing is important and generally if sowings are delayed too far into September, the benefits are negligible and at that point it is more sensible to focus on establishing the next main crop,” he said.

Winter active cereals such as oats, triticale and ryecorn make good catch crops.

Other cereals such as wheat and barley can also be used as a catch crop, however, barley is the least tolerant of cold, wet soils of all the cereals.

Grown for green-chop silage, booting – the point at which bulk feed and quality is at an optimum – oats has tended to be the most consistent performing crop overall.

Ryecorn is a crop that can offer the greatest environmental performance during the coldest parts of the year, particularly in cold climates like Southland.

Ryecorn emerges several days earlier than other cereals and takes up more nitrogen early on.

“It does, however, mature quickly and its quality can decline rapidly, making it less suitable for green-chop silage,” he said.

“If the purpose is to use as a green manure or as a short-term grazing option, then ryecorn is a good option to consider.”

Although forage cropping over consecutive years is not recommended, catch crops can be used in between winter forage crops.

As an example, oats can be sown after kale or other winter forage crop, taken through to green-chop silage in late November and then kale replanted.

While the second kale crop is sown later than in conventional kale-fallow-kale rotations, oat yields will generally more than compensate for any yield losses from the kale.

The exception is fodder beet after a catch crop.

Fodder beet needs to be sown on time to capture its high yield potential, given the high cost of establishment.

To meet target sowing time for fodder beet means the yield potential of the previous catch crop is not likely to be met.

However, environmentally the catch crop has done most of its job when terminated or harvested early in late September/early October, in time for sowing fodder beet.

Sowing Italian ryegrass with a cereal like oats is a popular option.

Malcolm says research work suggests the Italian does not compromise performance too much and offers subsequent grazing or cuts from Italian regrowth after the oats have been taken off for green-chop silage.

As an alternative to green-chop silage, other cereals like triticale and barley can be taken through to a later maturity stage and make good whole-crop silage at the milky-dough stage of grain-fill, while wheat and barley also have the option to be taken through for grain. 

This winter the Plant & Food Research Lincoln project team is trialing the production and environmental trade-offs associated with different cereal species and end-uses such as green-chop, whole-crop or grain.

Catch crops can also be grazed or incorporated as a green manure. 

By mid-spring, the main drainage leaching period has generally stopped and therefore, there is likely no adverse environmental effects of incorporating the catch crops or returning nitrogen to the soil through grazing events.

For further information on the catch crop trials, contact Brendon Malcolm at Plant & Food Research: Brendon.Malcolm@plantandfood.co.nz or https://twitter.com/malcolm_brendon

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