Vineyard Nutrient Management
Diagnosing Grapevine Nutrient Deficiencies
The correct diagnosis of nutritional deficiencies is important in maintaining optimum plant growth. The recognition of these symptoms allows growers to fine tune nutritional regimes as well as minimize stress conditions. A lot of the uncertainty in identifying nutritional problems can be reduced by keeping accurate, up-to-date records on the day-to-day events in the production process and, specifically, the details about application dates of water, fertilizer, and pesticides; and other factors affecting growth. Despite these efforts, nutritional problems arise even in the most carefully thought-out fertility programs. In most cases, symptoms of nutritional disorders occur in defined patterns and are specific for each nutrient. For instance, elements that are mobile within the plant generally induce deficiencies on the older (lower) leaves first, while immobile elements induce deficiencies on the younger (upper) leaves. In some cases, pesticide toxicity or disease symptoms may resemble nutrient deficiencies or toxicities. In addition, symptoms of nutritional disorders are often species or cultivar dependent. Therefore, growers should become familiar with nutritional deficiencies on a crop-by-crop basis.
Common Deficiency Symptoms
A first step in diagnosing nutrient deficiencies is to describe the symptoms. Each deficiency symptom is related to some function of the nutrient in the plant. Symptoms caused by nutrient deficiencies are generally grouped into five categories: (1) stunted growth, (2) chlorosis, (3) interveinal chlorosis, (4) purplish-red coloring, and (5) necrosis. Stunting is a common symptom for many deficient nutrients due to their varied roles in the plant. For example, when nutrients involved in plant functions such as stem elongation, photosynthesis, and protein production are deficient, plant growth is typically slow, and plants are small in stature.
Nutrient Mobility within the Plant
All nutrients move relatively easily from the root to the growing portion of the plant through the xylem. Interestingly, some nutrients can also move from older leaves (the source) into developing flowers or leaves (the sink) if there is a deficiency of that nutrient. Knowing which nutrients are mobile (i.e., able to move) is very useful in diagnosing plant nutrient deficiencies because if only the lower leaves are affected, then a mobile nutrient is most likely causing the deficiency.
Monitoring Nutrient Status
There are three basic tools available for monitoring nutrient status: (1) visual symptoms, (2) soil analyses, and (3)plant tissue analysis. It is not possible to rely on visual symptoms of nutrient deficiency as a single element since symptoms can often be confused with each other or with disease or other stresses. Also, once the deficiency has manifested itself by way of a symptom, the yield penalty may have already occurred. In many cases, plants will not show obvious signs of a deficiency even though crop growth may be restricted. This reinforces the need to undertake plant tissue and soil testing as a regular means of monitoring crop growth and performance. The analysis of plant tissues is an extremely useful tool for growers.
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