Science and Ecology

Many of the organic farming practices that exist today have their roots in very traditional practices. These tried and true practices were carried out by farmers well before the advent of industrial agriculture. These agricultural methods were developed inherently through trial and error and today are considered “sustainable”. While the pre-industrial farmers understood that their practices were beneficial to their crops and farms, the underlying scientific principles for why the methods worked were not understood; farming was intuitive.

At Spring Valley EcoFarms we investigate the ecological mechanisms that are the underpinnings to sustainable agriculture. In essence, we attempt to scientifically understand, quantify and explain traditional methods of organic agriculture which until recently have been largely ignored or misunderstood. An example is as follows: For more than a century, agricultural scientists have known that the benefits of manure come about because manure replaces the nutrients that are lost when a crop is harvested from a field. They also know that mixing manure with wood chips, straw, or rice hulls results in compost that has the right balance of carbon to nitrogen to optimize delivery of nutrients to a crop. But why is compost so efficient in optimizing nutrient supply to plants? Why is there less loss of nutrients to leaching and volatilization compared to nutrients supplied through conventional inorganic fertilizers? The answer lies in the way nutrients are held in the soil. Most inorganic nutrients are held on clay particles by relatively weak electrostatic charges. As a result, the nutrients are easily leached. In contrast, nutrients in soils rich in organic matter are incorporated within the diverse and vigorous community of microorganisms living in the organic matter, a community that is largely absent in soils that are plowed and fertilized conventionally. This community forms a complex food web, through which nutrients are continually passed. (Fig. 1). Bacteria, fungi and herbivorous nematodes are the primary feeders, and they obtain their food (energy) from the complex carbohydrates that constitute manure, compost, or other sources of organic matter that they decompose. At the same time that they are ingesting the carbohydrates, they also are ingesting the nutrients such as nitrogen, potassium, and phosphorus that are bound by other molecules that comprise the organic matter. The primary consumers are eaten by protozoans, microarthropods and fungal/bacterial feeding nematodes at the second trophic level. These are connected in the food web to larger arthropods and nematodes, and finally to higher level predators such as birds and small mammals. At each level of the food web, nutrients are held within the bodies of the organisms. This is the key to nutrient conservation. As long as nutrients are part of the living soil community, there is little chance that they can leach or volatilize. Thus they are conserved.

So how do the nutrients become available to plants? Each organism in the food web excretes or egests a small portion of the food it consumes, and it is through these processes that nutrients are released and therefore become available for uptake by plants. This slow release is often in synchrony with the need for nutrients by the plant. But as long as the remainder of the nutrients are bound up in the bodies of the soil microorganisms, they cannot be leached. This is in contrast to how nutrients are held in in soils that are regularly plowed and tilled. In these systems, the continual turning over of the soil provides oxygen to the microbes buried beneath the surface, and their increased respiration rapidly burns up the organic matter they encounter. The soil community disappears due to lack of energy, and the fertilizers that are applied to the soil are held only by weak electrostatic exchange on the surface of clay minerals. If these nutrients are not taken up quickly by roots, they are leached away by rain.

While there also are other ways in which nutrients are conserved in organic systems, our research at Spring Valley EcoFarms has helped develop an understanding of a relatively little known mechanism regarding why organic farming systems are so much more efficient at recycling and conserving nutrients that farming systems using conventional tillage and inorganic fertilizers. It is the community of soil microorganisms that keeps the nutrients from being leached, and allows a slow release of nutrients at a rate need by growing plants. And it is the organic matter itself that provides the food (energy) to keep the soil community alive.