Clay Mineral Changes with Different Farming Practices In Europe and America.

The intimate relation between plants and soil clays is beginning to be investigated and will perhaps one day be understood.  One aspect, which is of immediate importance today, is the impact of agricultural practice on the clays and their capacity to generate fertility useful for successive generations of crops.

Since the 1950’s agricultural practice has changed radically where plant – soil interactions were largely dictated by the chemistry generated by factory processes.  This method replaced the age-old practices of alternating crops and plant regimes (prairies and cropping) in order to maintain a natural equilibrium.  Today certain parts of society wish to return to less chemical methods of farming and thus are in need of more information on the relations of plant – soil clay mineral interactions.

We outline several examples of soil use which affect the clays and hence the overall fertility of the soil.  Clays hold chemical elements released upon need which engender plant growth and they also form aggregates in combination with organic matter to form reservoirs for moisture in periods of low abundance.  The key clays are of the 2:1 structural type.

Illustrations of cropping effects are given where a natural prairie regime on sediments poldered over several centuries time stabilizes soil fertility (potassic 2:1 clay minerals) at the surface but below the zone of plant activity, the potassic clays are lost.  A similar situation of poldering but under traditional agriculture (crop rotation, use of animal manure) indicates that the 2:1 clays are stabilized and in fact enriched in potassium potential.  Another example shows that heavy grazing can also affect the clay mineralogy.  On the contrary, when monoculture is practiced (maize, University of Illinois Morrow plots) strong loss of potassic minerals is observed, but the same minerals are maintained in parallel plots under crop rotation.  However intensive use of fertilizer can maintain and even increase the potassium mineral content of clays as seen in a experiment at the Grignion experimental station near Paris.

Other experiments comparing potassium and manure fertilizer in un-cultured and cultured plots indicates that manure can be very effective in increasing the potassium mineral content of the soils.

These examples indicate that there are several ways to maintain or loose soil fertility with different farming practices, which will depend upon the initial clay mineralogy and that engendered by the plant regime affecting the soil substrate.