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Assessment of spatial variation in nutrient status

High spatial variability of nutrient status of grapevines within vineyard blocks suggests that combining samples from across a block provides a poor indication of nutrition requirements. Intensive sampling and analysis of nutrient status of individual vines is more appropriate than the traditional practice of bulking uniform samples in vineyards with:

  • variable plant health or vigour,
  • known nutrient problems, or
  • highly controlled management of inputs.

Practical implementation of zonal management requires that zones, in which vines have similar nutrient status, can be identified and that these zones remain relatively stable over time (to avoid a need for frequent, intensive sampling).

 

Method

Traditional sampling procedures provide a single analysis result for a block of vines, with no indication of the variation in nutrient status within the block. To assess spatial variation in grapevine nutrition, the method of sample collection remains essentially unchanged, only intensity of sampling is altered, such that:

  • Samples are taken from, and analysed for, individual vines (reference vines) across a block, and
  • Twenty petioles (or blades, as appropriate for the nutrition standards to be used for analysis interpretation) are collected per vine.

 

Reference vines

Figure 1 - Cattle ear-tags (with vine identification umbers) attached to trunks with zip-ties allow quick identification for future sampling.
Figure 1. Cattle ear-tags (with vine identification numbers) attached to trunks with zip-ties allow quick identification for future sampling.

 

The number of reference vines will depend on block size and analysis cost. The ability to accurately define appropriate management zones increases as the sampling intensity increases and is influenced by the degree of variability across the block.

  • Select reference vines in a standard grid pattern of 40 m x 40 m. Modify grid size until an acceptable balance is reached between sample intensity and analysis cost. Grid pattern may be modified based on grower knowledge of vine health or changes in soil type across the block.
  • Clear areas of symptomatic vines (vines with visual symptoms of a nutrient deficiency or toxicity) can be sampled as a single unit (i.e. a combined sample from a number of symptomatic vines) to reduce costs. Intensive sampling of non-symptomatic vines will then assist delineation of areas of vines with marginal nutrient status that may not be showing visual symptoms.
  • Reference vines are identified by location (e.g. row and panel number or GPS co-ordinates) and tagged to ensure future sampling of the same vines. This is particularly important when zonal management is adopted to enable assessment of impacts of variable rate application of fertilisers or to confirm that spatial patterns are stable.

 

Sampling

  • Detailed guides outlining sample collection, handling and preparation for analysis are provided by various sources including the Cooperative Research Centre for Viticulture Vitinotes series (Grapevine nutrition 3: Petiole analysis, www.crcv.com.au/viticare/vitinotes/Viti-Notes). Alternatively, analysis laboratories or consultants can provide detailed sampling guidelines with regard to the type of sample to be collected (petiole or blade and location on shoot), growth stage, and handling procedures.
  • Samples are taken along the cordon on both sides of the reference vine from both inner and outer canopy layers. Samples are placed in paper bags clearly marked with the vine location number.
  • Samples are prepared and analysed ensuring that material from individual vines is kept separate.

graph showing Nitrogen concentration in petioles at flowering

Figure 2. Nitrogen (N) concentration in petioles at flowering. Horizontal lines indicate the upper and lower thresholds of the ‘adequate’ range defined by Robinson et. al. (1997)

Interpretation of results

  • Test results are compared to industry standards (e.g. Robinson et al. 1997), with particular attention paid to the range of nutrient concentrations. Plotting data (Figure 2) provides a good visual representation of results.
  • Results for nutrients of interest (e.g. those that are commonly applied or that are of concern with regard to deficient, marginal, high or toxic status) and with a large range in concentrations are mapped. Mapping can be performed using GIS software, but simple maps can be created on paper using the following procedure:
  1. Rank vines in order of lowest to highest concentrations of the nutrient to be mapped.
  2. Divide vines into four or five groups with similar nutrient concentrations.
  3. Map the block indicating reference vine locations, each reference vine is assigned a symbol according to its group (see step 2, Figure 3).
  • Examine the map, considering whether nutrient status appears to have a spatial pattern or a random distribution. If appropriate, define zones of low/moderate/high nutrient status (Figure 4).
  • Discuss appropriate management options with your consultant, taking into consideration site conditions and potential causes of spatial variation in nutrient status.

Figure 3. map showing spatial variation in nitrogen concentrations in petioles at flowering

Figure 3. Map of spatial variation in nitrogen concentration in petioles at flowering (N). ‘Adequate’ is as defined by Robinson et al. (1997).

Figure 4. Map showing possible mapping zones

Figure 4. Possible N management zones.

Temporal stability

Stability of spatial patterns between years varies between nutrients. Zonal nutrition management plans should take into account the temporal stability of relative nutrient concentrations. Nutrient tests from one year cannot be relied upon to determine nutrient zones in the following year if temporal stability is poor for that nutrient.

Intensive nutrient monitoring at five Shiraz vineyards over three seasons indicated that, while nutrient concentrations fluctuated between years, the rank order of vine nutrient status would be similar between years for nitrogen (N), magnesium (Mg), sodium (Na) and manganese (Mn). The probability that relative nutrient concentrations would be similar between years was more moderate, but still significant, for phosphorus (P), calcium (Ca) and sulphur (S). Relative concentrations of potassium (K) and boron (B) were moderately stable at four of the five sites but the rank order was unlikely to be similar between years at the fifth site.

Spatial patterns are likely to change if variable rate fertiliser application is adopted. Intensive sampling should be repeated after a number of years to examine impacts on spatial patterns.

 

Further references

Corporate Research Centre for Viticulture , 2006, Vitinotes – Grapevine nutrition 3: Petiole analysis.

Robinson, J.B., Treeby, M.T., and Stephenson, R.A. (1997). Fruits, vines and nuts. In: Plant Analysis An Interpretation Manual. D.J. Reuter and J.B. Robinson (Eds). (CSIRO Publishing: Melbourne) pp 347-389.

 

 

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