Archive for the ‘Dr. Jill Clapperton’ Category

Acids and Exudates: Plant Diversity Improves Soil

The more I learn about farming, the more I realize that plants are truly wondrous living things.  It’s easy to think plants are boring and passive.  After all, they just sit there.  But here’s some news!  Plants are powerful chemists and VERY active participators in their environment.  For our farm, we now see plant properties and behaviors as a tool for rejuvenating our dead soil.  This post explains what we’ve learned so far and how we plan to implement our new plant knowledge.

 Plants Leak Yummy Exudates

At the 2011 Acres USA conference, we learned a lot about what plants do below ground.  We learned that plants make a lot of sugars and other compounds from photosynthesis, and instead of using them all for energy, they leak a lot of them from their roots to attract and stimulate soil microbes.  These compounds are called “root exudates”.  

Plant root exudates. "Signaling molucules" that stimulate beneficial bacteria and fungi. From Marschner, 1995. http://edu.griggbrothers.com/TechnicalBulletins/TB2008b_printer.shtml

We learned even more about root exudates from Jill Clapperton.  She said that every plant variety leaks its own signature of chemicals in the form of amino acids, carbon, and organic acids to attract the beneficial soil microbes it needs to live and thrive.  She said that plants modify their environment and build their own microbial community in the soil.  Plants MODIFY their environment and build their own community?  This was news to us, and we thought it was really cool! 

She went on to say that plants leak a LOT of chemicals.  These chemical compounds are signs of welcome and warning.  Most of the compounds are welcome chemicals that attract a very beneficial and helpful bacteria and fungi community that like the plant and promote its growth.  Plants also leak warning compounds to keep themselves safe from soil herbivores and other threats. 

Exudates Can Improve Soil

Then Clapperton started talking about how farmers and gardeners can take advantage of plant properties to improve soil and grow food that’s very nutritious.  She encouraged the audience to fill the soil profile with different plants that have shallow, medium, and deep roots.  Filling the soil with many diverse plant roots will take advantage of the fact that all plants leak different compounds that will stimulate different segments of soil’s beneficial biology. 

Our soil has a long way to go before it is truly fertile with a fully restored biology.  We need a diverse soil biology community, so we were very interested in what she said about advantages of different plant categories:

  • Cowpeas (black-eyed peas), one of the best legumes for building soil.

    LEGUMES such as peas, beans, clover, and alfalfa leak exudates that attract both Rhizobium bacteria and mycorrhizae fungi.  Both of these are huge plant growth promoters.  Rhizobium fixes nitrogen from the air in return for sugary exudates.  Mycorrhizae are amazing symbiotic fungi that work wonders for the soil.  They go for maximum carbon exudates from the plant.  To get what they want, they boost the plant’s photosynthesis by conferring drought resistance and bringing phosphorus, copper, zinc, manganese and other ions and amino acids to the plant.  By making the plant healthier, they get even more carbonaceous exudates from their host.  Mycorrhizae turn a lot of it into glomalin, a significant carbon component in the soil that helps glue soil particles together and form wonderful aggregates that let more air and water percolate through the soil.  Legumes are clearly a win-win-win for soil.

    Sorghum, a warm season grass

  • CORN and WARM-SEASON GRASSES and Broadleaves such as SUNFLOWERS leak massive amounts of exudates.  They are trying to attract a large, diverse microbe community for protection and growth promotion, including lots of mycorrhizae (myco).  So this plant category can also stimulate lots of soil biology and sequester quite a bit of carbon via myco.
  • BRASSICAS such as mustards, radishes, broccoli, kale, etc. are different.  They do not associate with

    Mustard, a great brassica for improving soil.

    myco.  Instead, they leak some rather harsh acids.  They don’t need myco to go get soil minerals because they can use acids to get it for themselves.  Brassicas’ acid exudates can cleave off calcium that is tightly bound to phosphorus in the soil.  The brassica plant then soaks the phosphorus right up.  That’s why planting brassicas is a good method for “mineralizing” tightly bound phosphorus and making it available for the next plants that grow as the brassica decomposes.  Brassicas also stimulate the middle of the soil food web, arguably the most important part – the mites, earthworms, and other recyclers that prey on bacteria and fungi to keep them in a healthy balance.  Clapperton said she found through multiple studies that for some reason, brassicas make earthworms and other soil animals go really nuts in a good way.  So brassicas are key for mineralizing hard to get soil minerals and for stimulating the very important soil animals.

    Alfalfa

  • DEEP ROOTERS such as ALFALFA and SWEET CLOVER can bring up fertilizers from long ago that have leached deep into the soil profile.  The long roots also make channels for earthworms and other beneficial biology to travel.  The channels provide for better air and water percolation which fights compaction and improves soil structure.
  • POLLINATORS like PHACELIA and other FLOWERS have nice, fine roots with lots of fungi.  As pollinators, they can attract more above-ground diversity to our farm.

Our Plan

We probably won’t get livestock this year, so we’re going to take advantage of our prolonged delay to improve the soil by growing a big cover crop cocktail.  We’ve ordered the seed mix that includes several varieties from each category mentioned above. 

 

Phacelia tanacetifolia, a native pollinator that also helps rejuvenate soil. And it's pretty!

Our neighbor’s 20 acres has a rye and vetch cover crop growing like crazy right now.  We’ll mow when it flowers to kill it, then drill (plant) the cover crop seed.  Our own 20 acres are in perennial grasses (planted fall 2008).  We’ll lightly rotovate them to kill, then drill in the cover crop. 

We’re really excited to see how the cocktail grows.  With the big diversity of plants and flowers, I’m hoping it will be super pretty.  As late summer nears, we hope to see more wildlife and insects and good water retention.  And as all the different plants stimulate all parts of soil life, we should see our subsequent crops growing much better.  Thanks for reading!

Save the Microarthropods! Rethinking Tillage and Rotovating

We’ve gone from tillage-happy to tillage-doubtful.  We learned some things about tillage at the December 2011 Acres USA conference that really resonated with us, so we’re reconsidering our plowing down cover crop strategy in order to nurture a key part of the soil food web…

Rotovating in late August 2011

Up to now, our strategy for improving our sandy soil’s fertility involved growing massive cover crops to maturity and then plowing them down every spring and fall.  The “plowing down” involved using our rotovator (a very wide garden tiller) to incorporate most of the plant tissue into the topsoil so it could stimulate soil biology and eventually break down into organic matter.  At the Acres conference, we got confirmation from several speakers that this was the best method for improving soil’s biological fertility, especially if the plants are mature and lignified (more brown than green).  It felt great to hear this because it fit exactly with our plan!  Then we heard Jill Clapperton speak.  She was the rhizosphere ecologist for Canada’s agriculture department, and her research really compelled us to reconsider tilling so often.  Here’s why:

Lots of Tillage Hurts the Soil Animals in Middle of Food Web

Soil Food Web

The bottom of a very simplified version of the soil food web starts with bacteria and fungi, which are the primary digesters.  The middle group is the small animals, and they eat everything!  They prey on each other, bacteria and fungi, and plant residue.  This group consists of microarthropods (mites), earthworms, nematodes, enchytraeids, and some protozoa.  The top of the simplified food web is the larger animals that live on the soil surface like springtails, beetles, and even mammals like field mice.

Clapperton talked about long-term research results that showed some of the small animals in the middle of the food web disappearing after five years of tillage.  She said most of the small animals, especially the microarthropods, make their homes in the top few inches of the soil, and when tillage repeatedly destroys their infrastructure, the animals just leave.  The microarthropods cannot live in such an unstable environment.

Plants pick up and assimilate nutrients that have gone through soil’s biological system much better than nutrients from fertilizer.  For this reason, it behooves us as farmers with the goal of growing top quality grass to nurture the soil’s biology as much as we can.  We’d love to have the microarthropods on our farm just because they’re pretty amazing animals, but more than that, they are a very essential part of a vibrant soil food web.

Microarthropods are Voracious Predators

Macromite's Blog selection of soil mites, springtails, and Parajapyx. http://macromite.wordpress.com/2009/04/29/a-menagerie-of-microarthropods/

The animals in the middle of the food web are soil’s predators and recyclers.  This video shows two soil mites battling over a juicy springtail.  If we saw large, familiar animals trying to rip apart another animal like this on a regular basis, we’d probably have a whole different view of nature!  But violent predation like this happens all the time in the soil, and the soil’s health, and therefore the nutritious quality of our food, depends on it.  Here’s how:

The microarthropods chew up bacteria and fungi, poop them out, and regenerate the whole food web cycle in a very positive way around plant roots.  Without the good, natural predation check, the bacteria and fungi proliferate too much and start competing with plants for nutrients that plants need to grow and thrive.  Soil bacteria and fungi will beat out plants every time for nutrients if they’re allowed to do so.  Therefore, predators like microarthropods are essential for healthy, vibrant plants.

Microarthropods Stimulate the Soil Food Web

The microarthropods also help out bacterial and fungi.  They eat everything, including each other and larger pieces of plant residue.  Everything they eat is pooped out in new, much smaller particle sizes that are now accessible to bacteria and fungi for food.  This stimulates the bacteria and fungi to multiply at a good rate, in turn feeding the whole system.

Tiny Oribatid mite: Synchthonius crenulatus (Jacot) on a Times-Roman 12 pt Period. At http://macromite.wordpress.com/2009/07/01/full-stop-on-canada-day/

So, the middle of the food web is essential to healthy soil and therefore, high quality grass.  If repeated tillage makes them go away, we’re going to stop.

Our New Plan

Instead of rotovating our cover crops into the soil every spring and fall, we’re going to instead mow at the right time to kill them.  Clapperton advocates mowing because the clippings act as a good armor for the soil, and they insulate the soil from temperature extremes.  This helps the soil food web stay active during the hottest, driest times of the year.  She also said plant roots are soil’s most available form of organic matter.  Roots leak carbon and nitrogen compounds constantly to stimulate beneficial bacteria and fungi.  When the plant dies, the roots decompose into organic matter, and the tunnels left behind are great for air/water infiltration and for providing movement channels for earthworms and other animals.  Another disadvantage of tillage is that it collapses a lot of these tunnels.

We’re not going to sell our rotovator.  We’ll use it this spring to rough up our 20 acres of perennial pasture so we can give our new cover crop cocktail a good chance to grow.  We’ll rotovate very lightly and probably leave a lot of the grass standing.  We’ll then plant successions of cover crops, and then plant our final perennial pasture mix for grazing.  We might not ever need to rotovate our fields again, unless we want to kill the perennials again to do some crop rotation, or we detect soil compaction problems (unlikely in our very sandy soil, with the help of cover crops).

We hope that our new plan will help our soil thrive.  Giving up repeated tillage will hopefully give our farm a very healthy, complete soil ecology that includes the very necessary predators and recyclers and will also help maintain good soil structure with intact earthworm channels.

Most of the info in this post came from Jill Clapperton’s two presentations at Acres.  Audios of her presentations are available here.

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