Friday, October 2, 2009

Needed: Winter Cover Crop

The northwest corner of the Indian Valley Organic Farm (pictured above) lies fallow and compacted. Now, we need to get the soil ready for spring planting.  The main concern about the area is erosion.  It is not clear how much water will run across this ground in the upcoming winter, but, based on the lay of the land, a natural southwestern slope, chances are, it will host a fair amount of water in what is predicted to be a heavy rain year.  Steve Quirt has asked us to come up with a plan for cover cropping this area, and to share our reasoning.

Our priority will be erosion control for this terraced area, but there are so many additional reasons to plant a cover crop.  I often turn to The Rodale Institute  for detailed and reliable farming and gardening information.  Here is a list of why they suggest cover crops (this list can be found on the website link above):
  • They produce a lot of biomass, at least 3 tons above-ground dry matter per acre.
  • They are readily killed by mowing, rolling or other mechanical means, forming a mulch or
  • they are reliably winter-killed, leaving a mulch for spring no-till planting, or
  • they die down naturally in time to plant summer vegetables.
  • Their residues are sufficient to provide effective weed control in the subsequent vegetable crop.
  • They provide habitat for natural enemies of vegetable crop pests.
  • They have favorable (or at least neutral) effect on levels of available soil N, P and K.
  • They do not suppress the vegetable through chemical (allelopathic) or microbial effects.
  • They do not present serious weed, pest, disease or other management problems.

Based on some results tables on the Rodale and UC Davis websites, I determined that Oats would be a great winter cover crop for fast erosion control, weed control and loosening topsoil.  Oats also fare well in low-fertility soil, which probably describes this un-amended area, and they are able to tolerate drought and flood.  They establish quickly and provide large amounts of biomass to the soil when cut.  That means lots of "green manure." The drawback is that Oats contain allelopathic compounds in their roots which can hinder weed growth for a few weeks.  Sounds great...right?  Only problem is that there are a few other crops, such as lettuce, watercress, wheat, and peas that are are susceptible, so it is recommended we wait three weeks after incorporating the oats if we will seed any of those crops.  With all of the hardy traits, and their rapid growth, I felt Oats might be a good start.


Next I looked at complimentary crops and found that Purple Vetch looks good.  It also grows rapidly, which means we can get our crop going early in the spring if we so desire.  Purple Vetch establishes deep roots, so it will be good for erosion control and loosening soil, and it grows happily up around the oats.  It also attracts beneficials and fixes Nitrogen in the soil.  Finally, I have seen a fair amount of Purple vetch growing in the garden and thriving, so i feel confident it will do well.

Purple Vetch (otherwise known as Cow Pea)

Crops from the pea family (legumes) which are especially good at fixing Nitrogen in the soil (translation:  gathering and holding Nitrogen in the soil so future crops may use it).  A  Rhizobia Bacteria lives in the roots of legumes.  This bacteria gets nitrogen gas from the air in the soil and change it into a nitrate form which the plants can use. We pulled up some bell beans today in a row at the Farm and found a healthy colony of little white root nodules that indicate the gathering of Nitrogen.

Nitrogen fixation on Bell Bean roots

The way to find out if the bacteria are doing their job and Nitrogen fixation is happening is to cut or break open the nodules and look for a pink interior.  A pink shade indicates Nitrogen fixation.

Finally, I thought, why don't we add Bush Peas to our Oats and Vetch cover crop experiment. More Nitrogen fixation and it's always nice to have something  good to munch on in the mix.

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