Soil (aka dirt) is made up of sand, silt and clay particles of different sizes and ratios. Spring Ledge sits on top of clay soils, which are wet longer in the spring and much heavier than a river-valley soil or gravel soil. We take this into account when planting outside by using a bed-maker and by planting cover crops.
A basic tenet of organic and IPM methods is to feed the soil, not the plant. Soil is the most important part of smart farming and gardening. Besides providing nutrients and holding water, healthy soil is home to all sorts of organisms. Plants interact with good bugs, worms and microscopic fungi found in healthy soil to combat pests. Enriching the soil itself, not just adding fertilizer to the plant, is the basis of sustainable farming and gardening.
Along with the ecology of your soil, several other factors influence plant growth. Chief among these is pH. Soil pH affects which nutrients are available to the plant. To test your pH, contact the local extension office for a test kit. pH is easy to change using lime.
Another important soil state that we test at the farm is EC (electrical conductivity). We are most concerned with the EC level in our greenhouse crops as they are grown in pots without much buffering capacity. EC measures the amount of free anions and cations in soil. This translates into the salt levels. Too many salts can damage plant roots. Too few salts point to a lack of nutrition. EC levels can be adjusted upward by adding more fertilizer and can be lowered by leaching with clear water.
In our fields at Spring Ledge, we grow on a heavy clay soil which means it tends to be compacted and wet. Between the clay, sand and silt particles of soil are pores which can contain either air or water. Ideally, the pore space will contain half air (oxygen for the roots of plants) and water.
To improve our clay soils, we add as much organic matter as we can which “lightens” the soil, allowing better aeration. Think of the clay soil as a deck of cards. Once the cards are wet, it is very difficult to separate them from each other. By adding organic matter, we are helping push those cards apart and allowing roots to penetrate. The bulk of our organic matter comes from compost produce at Spring Ledge using leave, horse manure, and manure from our small collection of cows and sheep. After this mixture has cooked and digested for two years, it is spread on the fields and turned into the soil.
Another source of organic matter is cover cropping. After the vegetable crop is harvested, we plant the field to oats, winter rye and hairy vetch. These cover crops reduce soil erosion during the off-season and provide organic matter and nutrients when tilled back into the soil. In fact, a well grown crop of hairy vetch can add the equivalent of lbs of nitrogen per acre for use by the next crop.
Crop rotation is a very important part of IPM. Plants deplete different amounts and ratios of nutrients from the soil. Changing where we plant carrots each year, for example, balances out this depletion. Crop rotation also reduces buildup of diseases and insects. Many pests simply disappear if denied their favored host.
Building and maintaining a healthy soil is hard but essential work as Spring Ledge remains sustainable for the future.