Contrary Science; Cover Crop Mixtures, Monocultures, and Mechanisms

This post from Andrew McGuire of WSU is part of an ongoing scientific discussion about the relative effects of cover cropping and monoculture. This excellent summary of historic and ongoing research helps to bring us up to date on this complex, fascinating, and timely subject.

Excerpt from the article:

Soil diversity not linked to plant diversity

One last contrary finding. Another common belief is that a diverse mixture of plant species will drive greater diversity in the soil than a monoculture. This is often given as a reason to grow cover crop mixtures. Here again, we have a new analysis of the accumulated research investigating this mechanism. Zhou et al. (2020) analyzed 1235 experiments done around the world on the effects of what they call global change factors on soil microbial diversity. These change factors included land use change, such as occurs when a natural ecosystem is converted to agriculture, and nutrient fertilization. From this analysis they make several surprising conclusions.

First, most changes in the number of species (alpha diversity) can be explained by a change in pH. pH! It truly is the master variable in the soil. This is good news, as we can and often do manage soil pH.

Second, as they state it, “Conversion from highly diverse natural ecosystems to homogeneous agricultural monocultures has a positive effect on microbial alpha diversity.”

Read that again, a positive effect. The same goes for conversion to pasture.

What is more surprisingly contrary is that this implies, and the authors state this, that changes in soil microbial diversity (number of species) are NOT linked to changes in plant diversity. I know, heresy, but thus sayeth the science.

This does not mean that the conversion to agriculture is all positive. The microbial biomass is reduced, probably due to the change from perennial to annual plants and the associated decrease in carbon flow to the soil3. Agriculture also changes the structure of the microbial community. What these structural changes mean in the crazily complex soil is a difficult question to answer, but they may all not be beneficial with respect to the soil or the environment. This does, however, remove another purported reason of growing cover crop mixtures.

Read Andrew’s full article here:

Washington State High School Students Study Tardigrades

Last week, Lynn Bahrych delivered 30 living tardigrades to the science classes at the Friday Harbor High School on San Juan Island. The tardigrades will be studied and hopefully “cultured” in the classroom as part of a campaign to have the tardigrade designated as Washington State’s “Micro-Animal.”

On November 12, 2019, following the delivery of the tardigrades, Lynn and a volunteer marine biologist and videographer, Dr. Michael Noonan,  joined Sam Garson, the Friday Harbor High School science teacher, to introduce the project to his science class. Mr. Garson had prepared slides for the classroom microscopes, as well as a worksheet  (titled “Behold the Mighty Water Bear”) and video introductions of the tardigrade and the research being done on it now to study evolutionary development (”evo devo”).  

Not much is known for sure about tardigrades, so these students might be able to contribute something new to the field. Tardigrade ecology is in its “infancy,” according to experts. Exciting new ideas may come from the three classrooms across the state participating in this project. In addition to the Friday Harbor High School on San Juan Island, the Riverday School in Spokane, and the Roosevelt Middle School in Olympia are studying the enigmatic “moss piglet” or “water bear.”

For the state designation of the tardigrade, there are three state legislative sponsors at this time; Representative Jeff Morris of District 40, who is the primary sponsor,  Senator Debra Lekanoff also from District 40, and Representative Marcus Riccelli from Spokane.  Once the bill is filed in Olympia, other legislators will be invited to sign on.

This is the education and outreach project for the Soil Health Committee for 2019-2020. The goal is to raise awareness of soil health across the state by focusing on a charismatic animal that lives in soil and, in ways we are only beginning to understand, contributes to soil health.

A few fascinating facts about tardigrades:

  • In 2008, two “super-predator” Tardigrade species were discovered that suppress nematode communities despite being greatly outnumbered by the nematode populations. This may be very good news for producers with nematode issues. That is, unless the tardigrades also eat beneficial critters, which is why more research is needed.
  • In 2015, Japanese scientists found “high expressions of novel tardigrade-unique proteins,“ including one that suppresses radiation damage When inserted in human cultured cells, this unique tardigrade protein suppressed X-ray damage to human cells by 40%.
  • Tardigrades work as a “pioneer species” by inhabiting new developing environments and attracting other invertebrates, including predators looking for food.
  • Tardigrade species have been found in fossils 530 million years old and are often described as the champions of climate change, having survived the last five mass extinctions.