Vineyard Nutrient Management
Plant tissue analysis for grapevines, which involves testing the petioles or leaf blades, is the preferred method of monitoring the nutritional health of vineyards. Tissue analysis may be done for two reasons: the first is troubleshooting to confirm or deny a suspected nutrient problem within the grapevines, and the second is to monitor nutrient levels within the vines to detect a nutritional problem before it negatively impacts yield and fruit quality. When samples are systematically collected during a period of years, tissue test results can be a valuable tool to manage the nutritional status of vines, especially when combined with other information from the vineyard such as previous and current season’s growth, weather conditions, and recent inputs to the vines (e.g., fertilizer, irrigation, and tillage).
Time of Sampling
Tissues can be sampled at two different times during the growing season—bloom-time (when ⅔ of the flowering caps have been shed) and véraison (mid-July to mid-August). Bloom time is important because insufficient levels of micronutrients at bloom can have a season-long effect on fruit quality.
Leaf Blade versus Petiole Sampling
Analysis of either petiole or leaf blade will give a reasonable estimation of nutrient status. However, petiole analysis best indicates the current movement of nutrients towards the leaf blade, and is sensitive to the status of “mobile” nutrients such as nitrogen, phosphorous, potassium, and magnesium. Mobile nutrients are redistributed from older leaves to the growing points so that deficiency will be apparent in the older leaves first.
Samples should be taken from a single block or management area and should represent a single variety and rootstock and represent a block that is maintained under the same cultural practices (i.e., fertilization, irrigation, and vigor control practices).
In the case, when “troubleshooting” nutrient deficiencies, collect petioles/leaf blades from symptomatic leaves regardless of their shoot position.
At bloom, collect petioles from leaves located opposite the first or second flower cluster from the bottom of the shoot (See Figure 16.2).
Petiole sampling at véraison is similar in procedure, but rather than sampling petioles opposite of the first grape cluster, petioles should come from the youngest fully expanded (mature) leaves on the shoot, usually located from five to seven leaves back from the shoot tip (See Figure 16.3).
Tissue samples should be placed in a clean paper bag and labeled with the location, row number, growth stage, and date. The samples should be sent to the laboratory immediately.
Interpreting the Analyses
A complete tissue analysis will assess levels of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), manganese (Mn), boron (B), iron (Fe), and sometimes sulfur (S) and sodium (Na), all expressed either as percent or as parts per million (ppm).
In order to assess the effectiveness of your vine nutrition program, you must maintain a set of records of all tissue analyses and fertilizer applications (including compost and manure). Tissue analysis continued over a number of years in a given vineyard will help establish a base line for general nutritional status.
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