Humates for Agriculture

Humates are organic acids derived from the outer layers of some coal seams. They are used to condition soils and increase plant growth. Mixed with conventional fertilisers they help retain P and N nutrients in the soil and act synergistically to make nutrients more available to plants. In NZ, humates are extracted at the New Vale coal mine near Gore, crushed and shipped around the country. An increasing number of pastoral farmers are using humates to enhance soil fertility and plant production. 

Humates are complex organic chemicals formed by the microbial breakdown of dead plant material. The main constituents are humic acids, fulvic acids, and humin. They have many actions in the soil including stimulating biological activity, and enhancing water holding capacity and making nutrients more available to plants. The more humates in soil, the more productive the soil is with studies showing relatively large increases in plant growth at low application rates.

One way of increasing humates in soil is to add compost, which generally has a moderately high humate content. Another way, which has been used for at least 70 years in NZ and much longer elsewhere, is application of ground-up soft weathered coal that has a very high humate content – around 15 to 20 times as much as compost.

At the New Vale coal mine in Southland, humate-rich material is extracted from the rider seam, the thin outer layer above the main seam, which is usually discarded. Prolonged weathering has probably caused the freeing up of humic and fulvic acids in this material.

Mine manager Antony Stodart says that the material is dug out and put through two crushing processes to form a coarse powder that is stockpiled prior to trucking to a bagging plant. Samples are taken regularly for testing to ensure that the humate is up to specification. About 1,000 tonnes are processed annually, which makes it a minor product compared with the 320,000 tonnes of lignite coal the mine produces.

Since 2006 David Whitteker, managing director of Humates NZ Ltd, has been distributing humates to fertiliser companies and other wholesalers. He says that the New Vale product is around 65% carbon and a good source of humic and fulvic acids.

“When humates are mixed in with fertilisers like lime, urea and phosphate they act as a food source for fungi and bacteria and assist in breaking down the fertiliser into soluble forms so nutrients are more easily taken up by plants.”

“The carbon is in the form of carbohydrate and some farmers feed it to their cows at a rate of 50 g per day and it is said to improve ammonia retention in the rumen and absorb toxins.”

David believes that farms can maximise the value of conventional fertilisers by mixing in humates to reduce leaching of nutrients. Microbial activity is also stimulated and this has the effect of unlocking nutrients and making them more available.

“There is a lot of phosphate in the ground already that farmers have applied over the years but it is bound up and unavailable. Using humates results in the release of this phosphate making it available to plants. A year after putting humates on, you can usually detect an increase in available phosphate,” he says.

“It is also very good for locking up heavy metals – superphosphate contains cadmium that is accumulating in soil, and we have done trials with Solid Energy mixing 2 – 3% of humates in with phosphate and it actually locks up the cadmium so that it doesn’t appear in plants or waterways.”

David’s company sells most humates in crushed form but also extracts and dries the humic and fulvic acids and sells them separately. The dried humic acid can be mixed with urea, says David, and this reduces nitrogen losses to the environment dramatically.

“We have also done trials mixing 3% humic acid with urea and it can reduce the nitrate in the pasture from very high toxic levels down to safe levels and can reduce leaching by about 75%,” he says.

“The extracted fulvic acid enhances leaf absorption, so if you mix it with glyphosate you can reduce the amount needed to kill weeds by about 50%.”

The company currently sells about 1500 tonnes of humate product annually and demand is increasing every year.

“It is BioGro certified which makes it suitable for organic and biological farming, but more than 80% of the farmers using it are conventional. It’s not that they are necessarily going ‘green’ – they just see the biological benefits of using humates mixed with their conventional fertilisers,” says David.

Humate products from Southland are now available throughout the South Island and are shipped to Taranaki and Tauranga. David says that some farmers put humates directly onto pasture at 100 to 150kg per hectare while others get 5 – 10% mixed in with their fertilisers by their bulk suppliers.

“Sure, there is a cost involved but if farmers look at the bigger picture, they can see the value of it in terms of better pasture and crop growth and better nutritional value in the forage,” says David.

“Many farmers find that they can reduce the amount of conventional fertiliser they use and see the benefits in better soil, plant and animal production.”

One farmer who has recently tried humates is very happy with the result. David Kennedy, who owns a 176ha dairy farm in Southland, heard about humates from a neighbour.

“He had good results and he said that now he wouldn’t use urea without mixing in humates, in so I thought we would give it a trial,” says David.

“This season we’ve grown a lot more grass and baled a lot more baleage than we have ever done before.”

Farm manager Luke Stewart agrees. “We wanted to try something different, something that is organic and not chemically based and is good for the soil. When you mix it with urea it reduces losses of nitrogen to the environment, and for me it made life a lot easier because you can put it on at almost any time and in any weather,” says Luke.

“We put in 10% of humates with urea, so we get 9 tonnes of urea and 1 tonne of humates mixed by the trucking company. We put the first lot on about 30 ha and it went well, so we carried on using it. Since then every lot of urea that I have put on has humates in it.”

“Throughout the season the grass has looked healthier. I think we are getting a longer response from the urea because it is being taken up by plants rather than being lost, and I’m sure we have had increased growth. We will certainly continue to use it and we are looking at putting it in with the main fertiliser too.”