[permaculture] Fwd: Crop Rotation Works - Here's Why

John D'hondt dhondt at eircom.net
Mon Jul 22 20:23:49 EDT 2013

And there I have been moving away from crop rotation for exactly the same 
You don't avoid potato blight here by moving a potato field a hundred or a 
few hundred meters for blight is everywhere. Only in the fields that grew 
potatoes before there are the supporting organisms that keep the plants 
healthy without any chemical intervention.
I first got a notion of this a long time ago when I saw how healthy 
volunteer potatoes were. And without deadly toxic sprays there will always 
be volunteers. You will never get the last little tuber out of the ground.
I found this (not rotating) working for almost all other crops as well.

> Crop Rotation Works - Here's Why
> By News Staff | July 21st 2013 10:18 AM
> The ancient Romans were the first to officially discovered that rotating
> crops improves plant nutrition and inhibits the spread of disease.
> While it's common wisdom today, science is often about confirming why
> nature works the way it does. A new paper details profound effect crop
> rotation has on enriching soil with bacteria, fungi and protozoa.
> Soil was collected from a field near Norwich and planted with wheat, oats
> and peas. After growing wheat, it remained largely unchanged and the
> microbes in it were mostly bacteria. However, growing oat and pea in the
> same sample caused a huge shift towards protozoa and nematode worms. Soil
> grown with peas was highly enriched for fungi.
> The scientists also grew an oat variety unable to produce normal levels of
> avenacin, a compound that protects roots from fungal pathogens. They
> expected the soil to contain higher levels of fungi as a result, but
> instead found it contained a greater diversity of other eukaryotes such as
> protozoa. All organisms on our planet can be divided between prokaryotes
> (which include bacteria) and eukaryotes (which include humans, plants and
> animals as well as fungi). After only four weeks of growth, the soil
> surrounding wheat contained about 3% eukaryotes. This went up to 12-15% 
> for
> oat and pea. The change of balance is likely to be even more marked in the
> field where crops are grown for months rather than weeks.
> The findings of the study could be used to develop plant varieties that
> encourage beneficial microbes in the soil. The scientists are already
> investigating the possibility of engineering cereal crops able to 
> associate
> with the nitrogen-fixing bacteria normally associated with peas.
> "Changing the crop species massively changes the content of microbes in 
> the
> soil, which in turn helps the plant to acquire nutrients, regulate growth
> and protect itself against pests and diseases, boosting yield," said
> co-author Professor Philip Poole from the John Innes Centre.
> "The soil around the roots was similar before and after growing wheat, but
> peas and oats re-set of the diversity of microbes."
> Analysis has previously relied on amplifying DNA samples. This limits
> scientists to analyzing one taxonomic group at a time such as bacteria. It
> also means that everything present in that group is analyzed rather than
> what is playing an active role. Every gram of soil contains over 50,000
> species of bacteria so the task is enormous.
> There are relatively fewer actively expressed genes - RNA. It is now
> possible to sequence RNA across kingdoms so a full snapshot can be taken 
> of
> the active bacteria, fungi, protozoa and other microbes in the soil. The
> research was carried out in collaboration with the University of East
> Anglia and The Genome Analysis Centre on Norwich Research Park.
> "By sequencing RNA, we can look at the big picture of active microbes in
> the soil," said PhD student Tom Turner from the John Innes Centre.  "This
> also allows us to work out what they are doing there, including how they
> might be helping the plants out."
> "Our work helps explain the experience of farmers in the field," said
> Poole. "The best seed needs to be combined with the best agronomic
> practices to get the full potential benefits. While continued planting of
> one species in monoculture pulls the soil in one direction, rotating to a
> different one benefits soil health."
> Seeds can be inoculated with bacteria before planting out, just like 
> humans
> taking a dose of friendly bacteria. But this does not achieve the 
> diversity
> or quantity of microbes found in this study.
> "Small changes in plant genotype can have complex and unexpected effects 
> on
> soil microbes surrounding the roots," said Poole. "Scientists, breeders 
> and
> farmers can make the most of these effects not only with what they grow 
> but
> how they grow it."
> The research was made possible with funding from the Earth and Life 
> Systems
> Alliance at the University of East Anglia and from the core strategic 
> grant
> to the John Innes Centre from the Biotechnology and Biological Sciences
> Research Council (BBSRC).
> Reference: 'Comparative metatranscriptomics reveals Kingdom level changes
> in the rhizosphere microbiome of plants' by Thomas Turner et al., ISME
> Journal.
> http://www.science20.com/news_articles/crop_rotation_works_heres_why-116804
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