Many types of chemical, microbiological and physical soil testing is available to winegrowers, which can be employed in order make more informed soil management decisions. What viticulturists commonly call "soil analysis" is chemical analysis for the type and amount of available minerals in the soil. By 1950 exhaustive land grant university work had developed technology able to predict the productivity of a given soil by the mineral balance in the top seven inches. The base saturation percentages of calcium, magnesium, potassium and sodium and the available pounds of sulfate, phosphate, boron, copper, iron, manganese and zinc are critical to the health of the living microbial biomass and to the grape vine health...and therefore wine quality.
Chemical extraction procedures were developed in order to predict the roots ability to uptake mineral salts in the rhizosphere where young active roots encounter minerals in available forms. The assumption is that the root comes in contact with the minerals. For a plant root to uptake minerals a young root tip must come into contact with the mineral salts or the minerals must leach onto the root in a dissolved state. Additionally, roots that are colonized by certain soil dwelling fungi can access minerals due to the extensive foraging activity of hyphae. A soil analysis identifies what minerals are present in the soil zone sampled and predicts the quantity of a given mineral that is estimated to be available in the event of the root and mineral making contact.
The laboratory that conducts the chemical extractions of your soil is an important source of information regarding both field collection of samples and interpretation of the data generated. Get to know the lab that does your soil analysis and follow their directions for collection of soil and interpretation of the lab data.
Critical information for interpreting a laboratory soil analysis would include
- Depth at which the soil was collected and the density of active roots at the selected soil depth
- The structure of the soil where the samples were collected, and structure of the A horizon
- Past fertilizer and soil amendment applications. Know your soil and the lab work will mean more.
Soils are dynamic systems with no clearly defined boundaries between the scientifically described biological, chemical physical parameters. Soil analysis for mineral balance is most valuable when interpreted with consideration of the living microbial biomass health, the structure of the soil, health of the vine and character of the wine. Soil analysis for mineral balance is most effective when employed to feed the soil in order to increase the healthy and productive functioning of the soil food web and thereby feeding the vine.
Tips and typical problems encountered during soil analysis interpretation:
- Use soil analysis to understand better how to feed the soil.
- Apply fertilizer or soil amendments to the soil based on soil analysis, not on leaf or petiole analysis.
- If the soil pH is high, determine which mineral(s) is excessive. High pH usually means excess.
- If the soil pH is low, determine which mineral(s) is deficient. Low pH usually means deficient.
- Do not confuse pH with calcium levels in the soil. High pH soils very often require calcium.
- Excess mineral levels can limit vine growth, as much a deficient mineral levels-balance is the key.
- Due to the interaction between minerals and due to soil physical conditions, a mineral that is found by testing to be "sufficient" or in a "desirable range" still may not be available to the vine in great enough quantity or available at the time when the vine needs it most.
- Organic matter (carbon) is required in large amounts to maintain a healthy soil and the best conditions for mineral uptake by the vines. Compost and cover crops can be high quality sources of organic matter. Often, the most limiting element in our soils in Northern California is carbon.
- For healthy soil balance the minerals, balance air and water and increase the soil organic matter.
Bob Shaffer
Native Cultures
1497 Hill Road, Glen Ellen, CA 95442
phone 707.938.8665
fax 938.8667
nativecultures@aol.com