Archive for February, 2012

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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