Pecan Leaf Sampling: Effective Nutrient Management for Improved Yields

Pecan leaf sampling as a tool

By Dr Chris Schmidt, Kynoch

Leaf sampling and analysis offer good value as a management tool, such as information on the nutritional needs of the tree and the levels of nutrition. In order to avoid variation in results, a standard methodology is followed when sampling.

Usually only leaves from bearing trees are collected during mid-summer, approximately 120 days after flowering (beginning of January). The various nutritional elements follow different-level behaviour during a season. According to a study by Walworth et al. (2005), nitrogen, phosphorus, and potassium tend to be relatively high in the beginning of a season and then decline sharply over the remainder of the season (RotS). Sulphur tends to be lower in the beginning and declines very slowly over the RotS. Zinc declines very little over the RotS and tends to be almost stable. Magnesium, iron, and copper tend to increase slowly over the RotS, while calcium, manganese, and boron seem to increase more steeply over the RotS.

In most cases, the correlations between the elements and behaviour were rather poor. Although a need exists among producers to collect leaf samples regularly during a season, norms for this do not exist. For this reason, the focus is still on mid-summer sampling, since values are stable and correlate with yield, while others during the season do not.

Sampling Leaves

Ideally, leaves should be collected from the middle height of a tree, needing specialised machinery. However, such machinery is not always available, putting the sample collector in a position to opt for the more practical approach, namely to sample a tree at shoulder height. Leaves to be sampled are those situated in the middle of the new growth for the current season. Two leaves are chosen from the compiled leaf in the middle of the growth (depicted in Figure 1).

Leaves to be sampled are those situated in the middle of the new growth for the current season.

Depending on the size of the trees, a combined sample across numerous trees should at least contain 100 leaves. If soil types and management zones in orchards differ, it is best to sample the groups separately.

The following need to be avoided:

• sampling of dead branches, as well as affected leaves (diseases), except if it is the purpose of sampling.
• sampling on the outside of orchards.
• placing and sending samples in sealed-off plastic bags.
• use of galvanised containers and instruments coming into contact with leaves.
• sampling of mechanically or insect-damaged trees.
• mixing of leaves from trees of different ages.
• sampling from trees under drought stress.
• inclusion of roots, soil, and branches along with leaves.

References

1. Flynn, 1999. Sampling for Plant Tissue Analysis – Guide A-123. Extension Agronomy Specialist Shane T. Ball, Extension Agronomy Specialist R.D. Baker, Extension Agronomist.
2. Hammar, 1955. Effect of spray residues and other contaminants on leaf analysis. Horticultural Crops Research Branch, Agricultural Research Service, US Department of Agriculture, Shreveport, Louisiana.
3. Hannan, 2015. Instruction for collecting leaf sample. Iowa State University, Extension and Outreach. http://www.iowaproduce.org/instructionscollecting- leaf-samples. Visited 26 March 2017.
4. Diagnosing Nutrient Disorders of New Mexico Pecan Trees. Guide H-658. College of Agricultural, Consumer and Environmental Sciences, New Mexico State University
5. Spectrum Analytic Inc., 2009. Illustrated Guide to Sampling for Plant Analysis.
6. Labanauskas, 1968. Washing Citrus Leaves Leaf Analysis. California Agriculture.
7. Storey, 2012. Pecan leaf sampling. In Texas Pecan Handbook, (Stein, McEachern & Nesbitt, eds.). AgriLIFE Extension. Texas, USA.
8. Walworth & Kilby, 2002. Pecan Leaf Tissue Nutrient Concentrations: Temporal Relationships and Preliminary Standards. 2002 Citrus and Deciduous Fruit and Nut Research Report. University of Arizona, Tucson, AZ.
9. Walworth, Sower, Pond, Kilby, Gibson, Call & Lewis, 2005. Pecan leaf nutrition status. Western Nutrient Management Conference. Vol 6. Salt Lake, USA.

For more information visit www.kynoch.co.za.