Realising the potential of soil with cover cropping and other practices

This article is an update of an article published in October 2017

NICK KELLY is busy building a huge workforce at his Newdegate farm. But unlike most labour sources, this one just works for food and shelter.

The workforce is the millions of soil micro-organisms and other soil life that live below ground.

Typically an unrecognised farm resource, soil biology can do some heavy lifting, such as improving soil structure and suppressing disease.

One of the key tools that Nick uses to support this workforce is cover cropping. Cover crop residues provide an energy source for soil biology, and also serve other purposes, such as nutrient capture and controlling weeds.

Nick first got involved with cover crops to control wild radish and ryegrass on his 3,000 hectares of cropping country. The weeds had become a major issue, and his rigorous spray program only seemed to result in herbicide resistance. With the weed-seed bank appearing to be unbreakable, Nick started to look at an integrated approach that included increasing competition for weeds with cover crops.

The search for more information on cover cropping introduced him to American growers like Dwayne Beck, and more recently Rick Bieber, who argues that cover cropping is a key tool for improving soil, leading to better use of rainfall and lower cost of production. It’s an argument that attracted Nick, who was soon adhering to the principles of zero tillage, maintaining total soil cover, growing plants all year round and maximising plant diversity to build soil carbon and support soil biology.

One of the keys to increasing soil carbon is having plants growing for more months of the year. Summer cover crops could be a vital link to achieve this, so one of Nick’s first goals was to find out which species could best survive a Mediterranean summer.

The first crop recommended to Nick was White French Millet due to its water use efficiency and root bulb. After using it as a monoculture, Nick trialled the millet in a mix with other summer crops and found that survival seemed to improve. He is currently combining the millet with sunflowers, lablab and cowpeas. Results can vary with soil type, with Nick’s soils varying from clays to sandy gravels.

The summer crops can either be cash crops or cover crops. Nick sows cash crops around late August to early September and harvests in late February to early March. Summer cover crops are sown at harvest time after a winter cash crop and allowed to senesce naturally.

Nick has also established some areas to warm season perennials such as Gatton Panic, Setaria, Rhodes grass and summer active Lucerne, and is starting to trial cropping into this pasture when the perennials go dormant with cooler temperatures. So far he has successfully cropped lupins and vetch into the pastures, but is still developing the system.

One concern with cropping in summer is the potential water deficit for winter crops. While this can occur, Rick Bieber believes that the use of a bit more water is worth it, given the benefits that cover crops and associated biological activity provide to soil. Improvements in soil structure, increased infiltration and moisture retention should help the winter crop make the best use of rain during the traditional growing season.

Nick says he doesn’t experience a moisture penalty in his winter cash crops. Instead, he just sees the benefits of healthier soils, and now thinks that soil with poor structure and biology could be a bigger limitation to production than rainfall.

But Nick does point out that improving soil health and soil moisture is  a bit of a “chicken and egg” scenario, because the crop growth required to build soil health and moisture retention is dependent on there being sufficient soil moisture in the first place. Nick says that he just kept putting seeds into the ground, and with each year the crop came up more easily.

The economic relationship between soil moisture and soil health may deserve more attention from research organisations. But it isn’t an easy topic to consider, given the complex relationships with other factors such as disease and weed suppression.

Reducing the need for summer weed control, and in Nick’s case an estimated 60% reduction in herbicide use, is a major benefit of the cover crop system. The cover crops reduce weed growth by competing for leftover nitrogen, space and light. Nick now says he’s replacing the boom spray with an air-seeder. Instead of killing something, he is growing something in its place.

In terms of disease control, the key goal is to increase the activity and diversity of soil biology so it can compete with and suppress pathogens. Providing a diverse mix of crop residues to fuel this biological community is a key strategy. Nick also uses compost extracts to help stimulate activity.

The compost extraction process takes place on farm and involves washing the compost in an agitator, filtering it and then spraying the liquid into furrows at 70-80 litres per hectare. Typically, only one kg of compost is required per hectare. Mature compost is essential, with Nick stockpiling compost brought off-farm for 12 months before extraction.

With this system up and running, Nick is now looking to make his own compost using farm wastes.  While livestock hasn’t traditionally been a part of his enterprise, Nick recently introduced cattle onto the property.

Biological activity can be suppressed by tillage and over-use of fertilisers.  While no-till has been practiced for some time, Nick has recently phased out synthetic fertilisers. He says that growing legumes, combined with the breakdown of crop residues, now makes up an essential part of his nutrition strategy.

Nick is also using winter cover crop mixes like wheat, barley, oats, cereal rye, lupins, canola, peas, vetch and clover. And some of these like lupins can even be grown in summer beneath a canopy of millet.

Nick says there are no silver bullets, and learning what you can and can’t get away with can be risky and expensive.  But now, the reduction in input costs means that farm risk is easier to manage. And it appears there are other forms of risk mitigation occurring. Compared to his neighbours, Nick says he may have less impact from frost in spring and erosion during summer storms.

Nick warns against going “cold turkey” or trying to change everything in one year, but also says that you will never know unless you push your boundaries. He admits that the transition saw a decline in yield and some pretty tough times that needed a fair bit of resolve to get through. But now the system is more profitable, primarily off the back of reduced input costs and a lower cost of production.

Thanks to Nick and WIG (www.WIG.farm) for helping with this article.

Monthly rainfall at nearby Newdegate Research Station since Nick began summer cropping

Comparison of monthly spring and summer rainfall between Newdegate and sites in the Blackwood catchment. Data from September 2006 to February 2018 accessed from http://bom.gov.au/climate/data/

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