Mixed species fallow crops improve soil health

April 30, 2019

Mixed-species fallow crops are on the rise in the Wet Tropics – and the results are encouraging farmers.

As fallow crops become a more mainstream practice, the Wet Tropics Sugar Industry Partnership’s Laurent Verpeaux says farmers are taking it a step further and planting up to five species at a time to improve soil health.

Mossman district cane grower Clint Reynolds was pleased to find earthworms in his sandy soils recently, and good levels of organic carbon matter.

The fourth-generation cane farmer has been planting mixed species cover crops for three years, building on more than 15 years of results from standard cover-cropping on Daintree and Mowbray Valley properties.

“The biggest difference has been in our sandy soils,’’ he said. “Recent soil tests have confirmed organic carbon levels of 1.8 per cent following one mixed species fallow crop, and we’ve found earthworms in and around the (cane) stools.

“That’s something we’ve never seen in our sandy soils. It makes you think you must be doing something right.”

The Reynolds trialled a five-seed mix of tillage radishes, ebony and meringa cowpeas, soy beans, sunflowers and centrosema last year on their 526-hectare Daintree farm in trials through Project Catalyst. They will also be using sorghum and lab lab this year.

“Up until three years ago we planted fallow crops of legumes or soya beans. While that is better than leaving the ground bare, we were replacing a monoculture with a different monoculture,” Clint said.

“I’ve been to conferences, forums and workshops since and spoken to other growers who are using mixed species and it just makes sense. The different species bring different benefits. We’re planning on cutting back from 140 to 120kg of bagged nitrogen per hectare this year on the back of our results.”

Mossman cane growers Gerard Padovan and Brett Coulthard are also planting multiple species.

Brett is using meringa, black stallion and ebony cowpeas, and different varieties of sunflower seeds, after decades of planting either one variety of cowpeas or soya beans.

“This is our second year – the main goal is to try and get more carbon back into our clay soils,’’ he said. “Another benefit is increasing the strike rate in severe (weather) conditions.”

Gerard’s family moved from single varieties to seed mixes after going to Wet Tropics Sugar Industry Partnership (WTSIP) workshops, working with a WTSIP extension officer on a nutrient management plan and hearing from other growers at a Regenerative Cane Farming Forum.

They are trialling a mix of sunflowers and ebony cowpeas on 20 hectares of the farm and are in the process of adding a bean planter to their bed former to reduce the number of passes required once fallow cropping is added to the mix.

“Our mixed fallow was planted four months ago and it is doing its job,’’ Gerard said. “The sunflowers have come through and died off, the beans are still in the ground and we’ll be leaving them in as long as possible so the plant cane can feed off the nitrogen.

“Next year we’ll be looking at four or five species.”

WTSIP’s Laurent Verpeaux said it was great to see the Mossman Agricultural Services bean planter booked out for the season, and a larger number of growers ordering fallow seeds.

“Many have been to soil health workshops and they are trying different things, seeing the benefits and talking about them,’’ he said.

“Growers only have four to five months in cane crop cycles that can span five to 10 years in this district, but in a short time you can achieve a lot.

“Mixed fallow cropping creates habitat and niches for an incredible diversity of soil micro-organisms and bugs that help with nutrient cycling and improve soil structure.”

The uptake in the northern Wet Tropics coincides with promising Project Catalyst trials at the southern end of the region, which began three years ago on Ingham cane grower Lawrence Di Bella’s farm.

Soil tests at the site have shown mixed plots have a low ratio of bad nematodes and a high ratio of good nematodes. Higher nitrogen, potassium and phosphorous counts have also been recorded when crops are mixed, bringing different benefits from each species and in some cases balancing out less favourable traits.

Laurent said recent organic carbon results on the Reynolds’ farm were also encouraging.

“It is hard to get above two or three percent for organic carbon in the Wet Tropics because of the climate and disturbances created by tillage and compaction,’’ he said. “Organic matter tends to break down more quickly and the key is trying to keep as much as you can as humus.

“Funding programs have been encouraging reduced, zonal or even zero tillage techniques for many years which, when combined with mixed fallow crops, will improve your soil health.

For more information about soil health, visit the Wet Tropics Sugar Industry Partnership website for a series of short videos with agroecologist David Hardwick and WTSIP extension officer contact details. To find out more about Project Catalyst, ring Terrain NRM’s Michael Waring on 0428 771 361.