Energy flow in natural systems as a model for sustainable agriculture

Spring Valley Ecofarms is a non-profit organization focusing on education, research and outreach to promote more ecologically sustainable agriculture.  The seat is 100 acres in the Georgia Piedmont. The vision is to reduce reliance on external subsidies in agricultural systems through utilization of the free services of nature.  The goal is to define agricultural sustainability and to develop techniques to maintain and manage it.

Changes in the soil profile during 200 years in the Piedmont region of Georgia


A. Soil under old-growth oak hickory stand, never cultivated.
B. Soil after 100 years of cotton farming.
C. Soil after 60 years of pine growth in abandoned cotton field
D. Soil after 20 years of vegetable cropping with manure, cover cropping, and no-till cultivation
 

 

When the first settlers arrived in the Georgia Piedmont in the early 1800s, they encountered soil that looked like that in pit A under old-growth stands of oak and hickory. The top 10-12 inches (the “A” horizon) has a high content of blackish soil organic matter, rich in essential nutrients. Ecologists call this “natural capital” because of its economic potential. At the bottom of the A horizon, there is a sharp transition to the underlying clay minerals, the B horizon.  After 100 years of cotton farming, all the soil organic matter was depleted due to erosion and oxidation caused by plowing. It is represented by pit B, in a field where the soil was abandoned from cotton farming in about 1940, but was kept in row crops till about 2016, and then allowed to fallow. There are a few brown traces of organic matter originating from decomposed roots of grasses and annual herbs, but mostly it is red clay. Production was maintained by heavy inorganic fertilization. Because the clay hardens when dry, it was used as cement by early settlers.  After abandonment from cotton, some areas of the farm were no longer cultivated, and loblolly pine invaded. Soil pit C represents what the soil looks like after 80 years of pine growth. Organic acids leached from the pine needle litter decomposed all the remaining organic matter in the A horizon. Nutrients that were released either were leached away or taken up by the pines.  Pit D is in an area of the farm used for experimental restoration of soil organic matter. In 1995, it looked very much like pit B. For 20 years it was used for vegetable production, using no-till techniques, cover cropping, and occasional compost application.  Natural capital was restored, but it took 20 years. Transition to organic agriculture often is feasible if the farmer transitions only a small portion of the farm every year, because for the first few years under organic management, production can be low, or if compost or manure is added, it can be expensive. 

 

 
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