The many benefits of crop rotation

by Michael Smith (Veshengro)

crop-rotationCrop rotation is a common farming practice where different series of crops are planted in the same area each sequential season. Planting different crops on the same piece of land has been used since Roman times and has been proven to improve plant nutrition, benefit soil health, and control the spread of disease.

A new study, and yes they indeed needed a study again to tell farmers what our ancestors have known all along, to be published in Nature's 'The ISME Journal' reveals just how profound crop rotation's effect is on enriching soil with bacteria, fungi and protozoa.

"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 Professor Philip Poole from the John Innes Centre.

Researchers collected soil from a field 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 soil around the roots was similar before and after growing wheat, but peas and oats re-set of the diversity of microbes," said Professor Poole.

After only four weeks of growth, the soil surrounding wheat contained about 3% eukaryotes. This went up to 12-15% for oat and pea.

Every gram of soil contains over 50,000 species of bacteria so the task is enormous when analyzing DNA samples, so researchers sequenced RNA so a full snapshot can be taken of the active bacteria, fungi, protozoa and other microbes in the soil.

"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 Professor Poole.

The findings of the study could be used to develop plant varieties that encourage beneficial microbes in the soil. John Innes Centre scientists are already investigating the possibility of engineering cereal crops able to associate with the nitrogen-fixing bacteria normally associated with peas.

Professor Poole comments, "Scientists, breeders and farmers can make the most of these effects not only with what they grow but how they grow it."

The fact that crop rotation works has been known for millenniums probably and it was for that reason that there always was a rotation cycle in vegetable gardens and on fields before the agro-chemical industry tried to make us believe that we could just throw chemicals at the plants and that would be all that would be needed. It is not.

Soil leaches its nutrients when plant food, aka fertilizer, more often then not nowadays in the form of some petroleum derivative, is thrown at the plants. The structure of the soil gets destroyed by planting the same crop each and every season on the same plot of land and then bombarding the area with chemicals and the nutrients are getting more and more depleated.

It is for this very reason that yields, per acre, are larger on Amish farms than they are on the big "commercial" farms, those that are worked with heavy machines and where the plants get bombarded with chemical fertilizers.

Where manure is being used, such as on organic farms, and those of the Amish people, the soil is what is enriched and in that way the plants are. Another well-known fact required a million dollar study to discover the truth already known.

Sometimes one can all but wonder where all the ancient knowledge has gone. It would appear that there are far too many people about who have been educated well beyond their capacity. The gods help us!

© 2013