In the hills behind Byron Bay at Newrybar, the coffee pioneering Zentvelds family, are in their third year of planting cover crops in select sites across the coffee farm.

With another wet spring-summer predicted, a mix of radish, buckwheat, woolly vetch, millet, clover and ryecorn (cereal rye) is being planted in between the 30-year-old established coffee rows.

Whilst not yet established practice across the Australian coffee growing industry, Zentvelds are keen on cover crops. Rebecca Zentveld, founder of Zentvelds Coffee is the chief enthusiast for planting cover crops for a number of reasons:

“They add nutrition, feed the microbial life, and add biological diversity above and below the soil. We don’t need cover crops (as other farms do) to add cover to the soil or reduce erosion. We haven’t had that problem, as we have initiated plenty of cover of our rich red soil for over 30 years now.

“We plant cover crops to add biodiversity, add nutrition naturally, and enhance soil life for the good of our coffee trees without the use of synthetic fertilisers.”

The more vigorous climbers of cow pea and lab lab will be planted together in a clear block, bringing enhanced nitrogen and biomass before new arabica coffee varietals will be ready for a trial planting in the spring of 2023.

Table 1: Summary of species planted on each site, highlighted species germinated and
grew successfully as indicated by their presence in plant biomass sampling at
cover crop termination. Peters and Koonorigan sites were abandoned due to low germination. 

Mrs Zentveld said having planted these same legumes last summer in between the coffee rows, their overactive climbing tendencies were not appreciated as they wound themselves up into the coffee trees causing some concern of the photosynthesis of the coffee leaves being reduced, such was their vigour.

Working closely with Southern Cross University School of Organics and Regenerative Agriculture Alliance, Zentvelds coffee farm is an active participant in SCU’s current study of cover crops in subtropical tree crop plantations.

The Soil Extension Program Research Project 2 – Multispecies cover crops in subtropical horticultural plantations is a three-year program funded by the Department of Agriculture, Fisheries and Forestry (DAFF).

A field day was held at Zentvelds coffee farm and roastery on 13 Sep 2022 to discuss some of the key learnings from the research project to date.

Reaching the halfway point in these crop trials, researchers were ready to share some preliminary findings with local growers attending the field day morning at Zentveld’s coffee farm – and at a macadamia farm in the afternoon.

Attendees learnt about tracking soil health, the selection of cover crop species with site-specific and regional constraints and learnings of planting amongst perennial horticultural crops in the cooler subtropical climate.

The researchers also discussed the benefits of creating a natural insectary, through allowing the cover crop to go to flower, attracting beneficial predatory insects and pollinators.

Director of the Centre for Organics Research at Southern Cross University, Professor Terry Rose said it had become evident that planting cover crops in the subtropics through the cooler months bring the most benefits, rather than in summer.

“When cover crops are grown over summer, they may start outcompeting and shading out the permanent perennial groundcovers that provide permanent soil protection. Our research to date has shown that the cover crops in the cooler growing seasons of the subtropics bring biodiversity and contribute carbon to feed soil microbes whilst the perennial summer-growing grasses are dormant.”

With consecutive plantings, late winter cover crops planted at Zentvelds are now in flower, becoming a lively insectary, welcoming predatory insects and beneficial pollinators such as native and honey bees, hoverflies, lady bugs and more.

"The cover crops are so evidently a rich source of nutrition from the ground up. Or rather, below,” Mrs Zentveld said. “From the microbial life below, to feeding the pollinators and predatory insects above, that then become food for the spiders, food for birds – we are creating homes and food for wildlife – above and below the soil.”

Mrs Zentveld delights in the wildlife that is attracted to the flowers. And enthuses of the flowers that bring her joy as well. “What is not to like about cover crops, if you welcome biodiversity and the life it brings both above and below the soil?

“As long as you are willing to have self-seeders come up randomly over the years to come, allowing the cover crops to go right through to flower and seed stage, are a welcome asset.

“You could of course terminate the cover crops before they go to flower, by just ‘chop and drop’ method, mowing them in. There is always that option if you don’t want the added benefits of becoming an insectary and natural seed stock. But we reckon you should. Even just to bring a smile, and some joy in this farming life.”

Summary: 

- Not all species sown germinated, this may be due to climatic conditions being unsuitable for growth or competition i.e. too many different plant types. Buckwheat, sunflower andchicory were unsuccessful at all sites. Canola was only successful on the Wyrallah site

- Rye corn, field pea and tillage radish were the most consistent, growing on all sites, vetch was also highly successful. Rye corn and mixed unsown grass made up the majority of the total biomass at each site. At the Silver site, there was a high DM contribution of tillage radish to the total biomass

- All controls had a high proportion of mixed grass compared to broadleaf weeds

- Difference in total biomass between the un-mown controls and cover cropped inter-rows varied from site to site. Silver and Zentveld had significantly higher biomass in cover crop areas than the controls, whereas Grellman had equivalent biomass between cover crop and the control.