Globally there is increasing interest and research in cover crops within cropping systems. The questions New Zealand growers are asking are, ‘what benefits can they bring to our systems and how can they be practically managed’?’

Allister Holmes, FAR’s Waikato based Research and Extension Manager, says weed suppression, improved soil health and reduced erosion, nitrogen fixation, improved biodiversity and the ability to provide in situ or cut and carry animal feed are just some of the reported benefits associated with the use of cover crops. However, he says, more work is required in order to understand how any effects, either positive or negative, can be managed in individual farm systems.

“Recently FAR have increased their research into cover crops, focussing on their integration with maize systems. Much of this research has been based at FAR’s Northern Crop Research Site (NCRS) at Tamahere in Waikato, where currently six cover crop trials are underway. These trials are investigating issues such weed suppression, growth and development patterns, growing cover crops under maize, intercropping, establishment techniques and the impact of cover crops on following crops.”

Cover crops and weed suppression
Assessing different cover crops and their weed suppressive abilities. The trial, which is looking at faba beans, gland clover, oats and annual ryegrass, builds on a trial from last season, investigating a range of pre- and post-emergent herbicides and whether the weed control provided by cover crops could be used to reduce herbicide applications. The cover crops were sown in early winter and maize will be over sown in spring, before harvest assessments are carried out in autumn. Trevor James and Mike Trolove from AgResearch’s Farm Systems are undertaking this work.

Growth and development patterns
Observing growth and development patterns of a range of cover crop species were sown with two sowing dates, and 11 cover crop species (faba bean, oats, annual ryegrass, six annual clovers, red clover and lupin) sown in monoculture and one mix species plot (faba beans, oats and red clover). This is a small plot trial and will be concluding shortly.
A similar trial is being undertaken near Pukekawa, observing five monocultures (faba beans, alsike clover, subterranean clover, triticale and annual ryegrass) and four bi-cultures, containing triticale and either faba beans, alsike clover, subterranean clover or red clover. Assessments of accumulated dry matter will be made before spring.

Cover crops under maize
Two trials have been established researching methods of growing cover crops concurrently underneath maize crops. This approach reduces weed establishment and maximises solar radiation utilisation around the maize crop, however the challenge is to find crops and methods which don’t compete with the maize crop and therefore reduce yields.

Intercropping
An intercropping trial was established in October 2015, with a range of six cover crop species being sown into standing maize at three different timings. The plantings occurred at V4, V7 and the start of dry-down. Preliminary results suggest chicory and red clover performed well when sown into V4 maize. This coming season, further research into managing the effects of herbicides on cover crop establishment and trialling of suitable species is planned.

Cover crop establishment
In late autumn, a new trial was established looking at a new approach to establishing cover crops, with four clover species and annual ryegrass. Two herbicides will be used to ‘knock back’ the cover crops at the time of maize planting, with the ultimate aim being to allow the maize to establish above the cover crops and managing the cover crop growth until the silage harvesting or the start of grain dry down.

Impact of cover crops on following crops
Investigating the effects of crop rotation on the yields of the subsequent crop. Often maize is the sole crop grown long term on the same ground, despite research showing crop rotation can provide yield benefits. This trial will assess the yield and financial effects of growing maize after maize compared with adding faba beans or gland clover in rotation.

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