Crops draw nutrients from the soil in order to thrive. We then "draw" the nutrients from the crops into our bodies in order to thrive. "We are what we eat" is still the cry of organic advocates. We eat produce to get the nutrients. It is important, therefore, that the crops be full of the nutrients we need. This seems obvious. What might not be so obvious to the non-farmer is that a crop can completely deplete the soil of those very nutrients. Potatoes, for instance, are very heavy feeders of nitrogen, and if potatoes are continually planted in the same fields without restoring this nutrient, then ensuing potato crops will fail. There are other reasons for a crop failure, such as pests, disease or weather, but right now we’re addressing cover crops.
When a crop has been harvested, the organic farmer does not leave the soil inactive or "fallow." He plants a cover crop, also known as "green manure." This is a crop that is grown for a season, returning nutrients such as nitrogen to the soil as it grows and finally adding all that it is back to the soil when tilled in at the end of the season. These crops also help to aerate the soil with their long roots which open up the soil, thus encouraging air flow and water absorption. When the crop is tilled in, it creates a huge infusion of organic material back into the soil.
Among some of the crops typically grown as green manure you'll find alfalfa, clover and vetch.
Fields left unused will almost instantly become home to thousands of weeds. If the field is actively used in growing a crop, then the weeds do not have an opportunity to get established. The cover crops act as a preventive, keeping the fields weed-free. Similarly, fields left unused are at risk of eroding or even washing away. The planting of a cover crop holds the soil in place, thus preventing soil loss.
Cover crops are almost always used in fields that contain annual crops such as beans or tomatoes because the field is left empty at the end of the season. Perennial crops, such as asparagus, remain in the soil for many years and so the soil cannot be easily turned. Green manure is also used sometimes in vineyards and orchards between rows to enrich the soil and prevent weeds.
The planting of cover crops is a truly organic act and encourages the cycling of nutrients from soil to crop to the consumer.
|