Want Good Soil? Feed the Microbes

In June of 2014, Grist reporter Nathanael Johnson reported on a battle between two men in New South Wales Australia. Clive Kirkby and John Kirkegaard were having it out over the proper handling of crop residues after harvest. Kirkby was trying to get farmers to stop torching wheat stubble. Rather than letting fire release all that carbon into the atmosphere, he told them that they could increase soil organic matter and build healthier, carbon-rich soils by leaving the stubble in the field.  John Kirkegaard, an agronomist, told Kirkby he was wrong. The practice of burning and cultivating was what was growing the best crops. As most folks will tell you nowadays, cultivating, or plowing, disrupts soil microbes and releases even more carbon into the air. That's why no-till is becoming increasingly popular. But the practice that Kirkby was promoting didn’t seem to be making a difference either. After six years of leaving stubble in the field, Kirkegaard’s data showed that soil organic matter and the carbon it holds wasn’t increasing, and in some cases, it was even decreasing. Farmers have been encouraged to leave stubble in the field for the same reason that management-intensive grazing proponents leave plenty of forage behind in pasture: It’s food for the soil. Put more precisely, it’s fuel for a comp

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8 thoughts on “Want Good Soil? Feed the Microbes

  1. David –

    I can’t point you to a specific study, but I’d refer you to a few books that have extensive references. Marschner’s Mineral Nutrition of Higher Plants, Healthy Crops: A New Agricultural Revolution by Chaboussou, Mineral Nutrition and Plant Disease by Datnoff, Elmer, Huber, and of course, Sir Albert Howard’s An Agricultural Testament. Since you are in Australia you should check out Graeme Sait and his company, Nutritech Solutions – they have a lot of info on their website. You can also read some good information from another Australian at amazingcarbon.com. It seems like you are on the right track and you are blessed to be in an area with great climate and rainfall(for the time being).

    1. I want to see recent case studies and/or peer-reviewed studies to back up the claims made by these folks. Sait’s company WWW site has diddly squat in this regard. And I can’t find the hundreds of articles he claims to have authored beyond his blog posts.

      Here’s some material that might be of interest:

      http://onpasture.com/2014/06/23/soil-balancing-does-it-work/

      and these:

      http://www.moffittsfarm.com.au/2013/09/27/woady-yaloak-alternative-fertiliser-trial-review/

      http://www.woadyyaloak.com.au/resources/Evaluating%20alternative%20fertilisers%20and%20biological%20products%20for%20pastures%20and%20crops%20(final%20report).pdf

      http://www.wgcma.vic.gov.au/for-landholders/gippsland-soil-trials/parks-dairy-foliar-nutrient-and-seaweed-demonstration

      and I couldn’t find any peer reviewed or well conducted case studies showing benefits from using Sait’s nutri-tech products.

      I’m not going to spend money on compost teas/expensive supplements and courses/foliar sprays etc until a/ I see some objective, third-party evidence that they work and b/ if they do work that they are cost-effective compared to other approaches giving similar results.

  2. Hi Don,

    Can you point me at some science/well-run trials to backup these statements? Or perhaps the site hosts could comment?

    “Better plant nutrition through organic methods leads to better photosynthetic capacity which means more sugars exuded through the roots to feed the microbiology”

    “Aggressive soil biology produces enzymes and acids that make even more nutrients available to the plant”

    “a foliar application of trace elements can improve your photosynthetic rate, increasing the quality of your crop and the amount of exudates that feed your soil biology, while being more cost effective than applying compost.”

    Thanks

    David

  3. Don’t clip your grass short, unless it is dead/dormant, otherwise you slow or stop photosythesis, which is what is feeding the soil biology. Learn about “tall grazing” and see how that applies to mowing/clipping grasses.

  4. What happens with soil carbon when you mow/slash pasture as against graze it? We have some land in Sth Gippsland which we’re developing as an agroforestry site. We exclude stock for some years after planting as they will eat young trees. We manage the pasture – ungrazed grass can grow to 1.5m in spring – in these fields by slashing it. The area averages rainfall over 1000mm/annum and has a mild climate by northern hemisphere standards although it can reach over 35C in summer. So the soil microbes will generally have reasonably comfy climate conditions to do their thang.

    I’ve been assuming that this will build up soil carbon but would be interested if anyone has any comments, pointers to related research etc.

    We should get some soil tests but because the grass growth is so strong I’ve not worried about it to date. And I could look into cheap onfarm carbon tests if such a thing exists. My first degree was in chemistry so I’m not afraid to wield a testtube.

    Thanks

    David

    1. I think the trick to getting the quickest results without livestock or soil amendments while clipping is to manage for earthworms. The ground should be continuously covered with litter in various stages of decomposition and a generous stubble height after clipping to provide shade. It will be a balancing act to be able to let the grass grow to sufficient maturity before clipping so that it doesn’t decompose too quickly and clipping it often enough to provide the earthworms with a fairly constant source of green clippings.

  5. It might be appropriate to mention how those wheat fields were farmed(conventionally, organically, biodynamically). Many pesticides, fungicides, herbicides used to grow wheat conventionally are also detrimental to soil biology and it isn’t surprising that wheat stubble wouldn’t break down. Better plant nutrition through organic methods leads to better photosynthetic capacity which means more sugars exuded through the roots to feed the microbiology. Aggressive soil biology produces enzymes and acids that make even more nutrients available to the plant, which creates even more photosynthetic capacity, etc. It’s imperative to feed your soil biology and photosynthesis trumps compost. A lot of times a foliar application of trace elements can improve your photosynthetic rate, increasing the quality of your crop and the amount of exudates that feed your soil biology, while being more cost effective than applying compost. Either way – feed your soil biology and you’ll increase water holding capacity, have healthier crops, and sequester carbon in your soil.

  6. Burning wheat stubble or grass residue is not 100% combusted, a small fraction remains as a biochar which has been addressed previous. This is an extremely stable form of carbon and becomes a home for soil microbes.

    There is also evidence from ISU and elsewhere that patch burned pasture is preferred by grazing livestock, (Ryan Harr) in his trials they were able to establish a semi-rotational impact by have a three year burning regimen.

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