Cover Crops

Introduction to Cover Crops

Cover crops can improve soil health and water quality while meeting a variety of other needs on the farm. During the growing season, the cover will keep the nutrient cycle in place. Any nutrients that are highly mobile in the soil will be absorbed by the cover will work to keep those nutrients in place. Additionally, some plants can create (legumes) or mine the soil (brassicas) for nutrients with their diverse root systems. After the cover crop is terminated, the dying plant material builds organic matter and provides a habitat for microorganisms which, in return, help to cycle those nutrients. This all translates to greater resilience in the face of many risks, including drought and flooding. If soil is covered year-round it is also less vulnerable to erosion and runoff. Anchoring and shielding the soil with cover crops is a simple step to preserve topsoil. Select cover crops that accomplish the goals of the farm - whether it be building up nitrogen or organic matter, breaking the hard pan, suppressing weeds, or interrupting a disease cycle.

Understanding Soil Health

Soil productivity, usually measured in terms of crop yield, is influenced by physical, biological, and chemical components that all interact. Visual indicators include exposure of the subsoil, change in soil color, gullies, ponding, runoff, plant condition, blowing soil and deposition. Physical indicators involve the arrangement of the soil particles and pores; we can understand these factors by observing topsoil depth, bulk density, porosity, aggregate stability, texture, crusting and compaction. Physical indicators affect root growth, seedling emergence, water infiltration and movement within the soil profile.

Soil productivity, usually measured in terms of crop yield, is influenced by physical, biological, and chemical components that all interact. Visual indicators include exposure of the subsoil, change in soil color, gullies, ponding, runoff, plant condition, blowing soil and deposition. Physical indicators involve the arrangement of the soil particles and pores; we can understand these factors by observing topsoil depth, bulk density, porosity, aggregate stability, texture, crusting and compaction. Physical indicators affect root growth, seedling emergence, water infiltration and movement within the soil profile.

Chemical Indicators

A soil test will be needed to give you a chemical profile of your soil. Critical chemical soil characteristics to look for are pH, major nutrients (nitrogen, phosphorus, potassium), secondary nutrients (sulfur, calcium, magnesium), and micronutrients (especially boron, copper, manganese, zinc; but also iron, molybdenum, chlorine, selenium, and cobalt). pH is important to know because it influences the availability of most nutrients. Biological indicators of soil health include the effects of the micro and macro-organisms, their activity and/or their byproducts, which contribute to the formation and stability of the organic matter portion of the soil. Many are also critical to supplying nutrients to the living plants, as their population is greatly concentrated in the rhizosphere (or growing root zone of the living plants). Several important soil indicators include:

• Aggregate Stability - The ability of soil aggregates to resist disruption when outside forces (usually associated with water) are applied.
• Infiltration - Water movement in the soil as a result of soil texture, crusts, compaction, aggregation and structure, water content, frozen surfaces, organic matter, and pores.
• Bulk Density - The ratio of dry soil mass to bulk soil volume (including pore spaces). This can be measured and expressed in grams per cubic centimeter and is largely a function of relative pore space and organic matter content. Bulk density influences water infiltration and plant root health and reflects the degree of soil compaction.
• pH - Negative logarithmic scale that measures the “Potential of Hydrogen” concentrations in aqueous solutions.

Soil pH influences the solubility, and therefore the availability, of several plant nutrients. It also affects the activity of microorganisms responsible for breaking down organic matter, as well as chemical transformations in the soil. The type and population densities of soil microorganisms change with pH. A pH of 6.6 to 7.3 is favorable for microbial activities that contribute to the availability of nitrogen, sulfur, and phosphorus in soils.

• Soil Crusts - Created by the breakdown of soil structural units by flowing water or raindrops, or through freeze-thaw action. Crusts reduce water infiltration and increase runoff, restrict seedling emergence, reduce surface water evaporation, and increase wind erosion in sandy soils. Heavier clay soils and surface-applied manure are particularly prone to crusting.
• Organic Matter - Soil organic matter is the fraction of the soil composed of anything that once lived. Organic matter gives soil a sponge-like quality that allows it to soak up about twelve times its weight in moisture, which helps prevent nutrients from leaching out and makes your system less “leaky.” Soil food web organisms derive their energy from feeding off of organic matter inputs.
• Available Water Capacity- Available water near the surface is especially important at the seedling and transplant stage when the roots are very shallow and not yet fully developed.
• Soil Biodiversity - The mix of living organisms in the soil that comprise the “soil food web,” such as insects, worms, and microorganisms, whose interaction and biological activity influence many soil processes, such as nutrient cycling, residue decomposition, and the entry and storage of water into the soil and resistance to erosion.

These charts should help you better understand soil sample results:

Mehlich I Soil Extraction Parameters

Mehlich III Soil Extraction Parameters