Leaf Analysis - What's the Story?

During July and August when many leaf samples are being collected for analysis, the weather can be unforgiving - hot, dry, no rain and often very high humidity. Under these weather conditions, if irrigation was not provided, there was reduced plant growth, low transpiration rates and dry soils. All these factors combined will have an effect on the nutrient concentrations in the leaves and will affect your interpretation of the results.

General points to remember when reviewing leaf analysis results:

1. The sunlight, rainfall and temperature that occurred over the past 30 days prior to collecting the samples will affect nutrient levels.
2. In addition to being affected by low soil moisture, tissue concentrations are influenced by light, soil and air temperature, relative humidity, cultivar, and age of leaf selected for analysis. All these factors interact, affecting leaf nutrient levels - not just the drier weather.
3. Nitrate, sulphate, boron, calcium and magnesium move through the soil primarily by mass flow. Low soil moisture, reduced transpiration caused by low temperature or high humidity may be reflected in lower leaf concentrations of these nutrients.
4. Potassium and phosphorus move primarily by diffusion. Dry soils restrict the flow of these nutrients to the root.
5. Maintaining soil moisture levels between wilting and field capacity tends to lower the nutrient concentrations in the plant. This is because plant growth is stimulated. As a result dry matter increases and dilutes the nutrient content. Reduced plant growth is often reflected in increased nutrient levels.

The table below lists a few observations you may notice when comparing leaf analysis with previous years for non-irrigated crops. Without a historical record from past seasons, it will be difficult to interpret leaf analysis without a reference baseline for that location.

Management options: The tissue results do not necessarily mean that you need to adjust soil fertility rates. Make sure a soil sample is completed in the fall, if a sample was not recently done within the past 2-3 years. Consider soil management practices, such as mulches or improving irrigation to ensure even soil moisture.

Weather effects on interpreting leaf nutrient concentrations are important considerations for perennial crops where the leaf analysis from this season will be used to adjust the next year's program.

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