Post harvest fertility management has a major impact on next year’s growth
Preparing your vines for winter begins between harvest and the first frost. This stage of development is critically important to the success of next season. Once the grapes are harvested, vines divert their energy to storing essential nutrients in the roots and cordon. The fall and winter months are an excellent time to focus on the real heroes of the vineyard - soil microbes. After all, soil biology is responsible for nutrient uptake in the vines and the taste of the wine.
Start by identifying nutrient deficiencies and correct imbalancesSoil testing
Soil analysis is used to identify soil chemistry imbalances. There are two areas I focus on first. 1. pH. 2. Sodium Adsorption Ratio. Southern California soils are known to have high alkalinity (high pH) and sodicity (high sodium concentration). Organic matter is usually very low as a result of dry climates and no cover crops. Amending soil in the fall with sulfur, or gypsum has a positive effect on soil structure and reducing sodium and chloride levels. Soil amendments take several months to take effect as nutrient availability relies on microbial action.Plant sap analysis
Useful for identifying nutrient deficiencies in the vine. Plant sap analysis indicates nutrient concentration levels in the leaf sap. These concentrations can be quickly adjusted with foliar applications of amino acid chelated nutrients. Positive results are seen in days, not months.
Proper identification and correction of nutrient deficiencies ultimately results in disease suppressive soils.
When grape vines have adequate nutrient concentrations (present in the leaves), they form complex carbohydrates called polysaccharides during photosynthesis. Photosynthates are then converted to a microbial food source called mucilage or root exudates.
The quality of root exudation plays a role in determining what the soil ecology of the rhizosphere will be. The mucilage secreted by the growing root tips will attract the types of soil microbes needed to improve nutrient uptake. A special type of microbe, mycorrhizae, are attracted to polysaccharides. They will infect the root sheath and form a mutualistic relationship that benefits both the plant and the fungi.
Deciduous vines and trees rely on a colonies of endomycorrhizal fungi to scavenge the soil for nutrients. Fungal hyphae secrete enzymes with specialized proteins used to make nutrients available for microbial and plant uptake. Fungi convert free floating soil minerals into plant available forms in exchange for the carbon in root exudates. This plants exchange carbohydrates for an on-demand supply of soil nutrients that may be unavailable otherwise.
Root exudates containing mostly polysaccharides tend to produce a disease suppressive microbiome, while root exudates primarily composed of monosaccharides can enhance soil borne diseases. Monosaccharides are formed when plant are nutrients deficient, and photosynthesis is not efficient.
Disease suppressive soils were originally defined by Baker and Cook (1974) as “soils in which the pathogen does not establish or persist, establishes but causes little or no damage, or establishes and causes disease for a while but thereafter the disease is less important, although the pathogen may persist in the soil.
Through proper nutrient management, vine stress can be minimized - ensuring optimal accumulation and storage of non-structural carbohydrates in buds and woody tissues.