Why is leaf sap analysis important?

Balanced nutrient uptake is essential for plant health and also affects fruit quality and yield. Key macronutrients and micronutrients play different roles in plant growth and development: some are integral to photosynthesis, while others help convert the sugars produced during photosynthesis into other compounds.

A deficiency or excess of any nutrient can negatively affect plant growth and development. Understanding whether a plant is taking up and assimilating macronutrients and micronutrients in a balanced way is essential, but not always straightforward. For example, a soil analysis tells us which elements are present in the soil at a particular moment, but not necessarily which are available to the plant. Plant tissue analysis, based on dry matter, is another way to assess nutrition. It shows all the mineral nutrients in the sampled leaf and is particularly useful at the end of the season for evaluating the effects of the fertilisers used. This analysis looks at the plant’s nutritional history. What matters most, however, is understanding what is available to the plant at the time of sampling and analysis.

To address this need, the Dutch company NovaCropControl introduced leaf sap analysis in 2009. The laboratory uses modern, rapid and effective technologies and methods to deliver results within a short time.

IOTO Agro works closely with NovaCropControl. The results of leaf sap analysis are used to develop nutrition programmes for different crops.

Leaf sap analysis is the most accurate way to measure the nutrients available to a plant at the time of sampling. It measures the active fluids in the vascular tissues, including the xylem and phloem, and can reveal details that may not appear in a conventional leaf analysis. Its main advantage is that it detects potential deficiencies earlier than tissue analysis, sometimes by one or two weeks. Taking boron as an example, leaf sap analysis shows the amount of this micronutrient in the plant in ppm. By comparing sap from young and older leaves, farmers can assess nutrient mobility and detect an emerging deficiency before visible symptoms appear. Tissue analysis cannot provide all this information.

Tissue analysis assesses what has happened in the past, whereas sap analysis provides a real-time picture of nutrient availability. Sap analysis also allows farmers to see when antagonistic nutrients are competing with one another. This helps ensure that plants receive the right nutrients at each phenological stage.

In general, mobile nutrients include:

Nitrogen (N)
Potassium (K)
Magnesium (Mg)
Phosphorus (P)

Deficiencies of these elements first appear in older leaves.

Moderately mobile nutrients include:

Sulphur (S)
Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Copper (Cu)
Molybdenum (Mo)

Immobile nutrients include:

Calcium (Ca)
Boron (B)

Deficiencies of these elements first appear in young leaves.

Nutrient antagonism includes the following relationships:

When potassium (K) increases, calcium (Ca), magnesium (Mg) and sodium (Na) decrease.
When phosphorus (P) increases, chlorine (Cl), nitrates and sulphur (S) decrease.
When sodium (Na) increases, calcium (Ca), magnesium (Mg) and potassium (K) decrease.
When phosphorus (P) increases, iron (Fe), magnesium (Mg) and zinc (Zn) decrease.

The effect of pH on nutrient uptake is also important. A high pH reduces the uptake of phosphorus and micronutrients such as iron, zinc, manganese and copper, while improving molybdenum uptake. A low pH reduces the uptake of phosphorus, molybdenum, potassium, calcium, magnesium, nitrogen, sulphur and boron. Under these conditions, aluminium is taken up more readily.

NovaCropControl offers sap analysis for more than 200 crops. The analysis measures 16 different nutrients, including nitrogen in 3 different forms, as well as total sugars, EC and pH.

Calcium (Ca)
Potassium (K)
Magnesium (Mg)
Sodium (Na)
Nitrogen (nitrate, ammoniacal and total nitrogen)
Chlorine (Cl)
Sulphur (S)
Phosphorus (P)
Silicon (Si)
Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Boron (B)
Copper (Cu)
Molybdenum (Mo)
Aluminium (Al)

The main benefits of leaf sap analysis are:

Understanding nutrient availability and uptake within the plant.
Improving fertiliser efficiency.
Preventing nutrient deficiencies or excesses before visible symptoms appear.
Improving plant health and, in turn, reducing pesticide use.
Improving plant and fruit quality.

This analysis allows us to make timely, accurate decisions throughout the growing season to support plant growth and development and achieve a productive harvest.