Sap testing technology game changer for growers


Nutrient testing by analysis of plant sap is a useful tool for crop nutrition management. Commonly used to monitor Australian crops such as wine grapes, apples and stone fruit, sap testing was introduced by Farmlands to the Marlborough viticulture sector in 2019. Farmlands works with Campbells Fertilisers to make this testing technology available to New Zealand growers.

How does plant sap testing differ from a dry matter test? Dry matter testing analyses the total amount of nutrients present in the dry matter of a plant leaf. These are fixed minerals present in the organic material of the plant. These nutrients are mainly complexed in cell walls and not totally available for plant development.

Plant sap tests provide the view of the total dissolved minerals in the sap directly available to the plant at that time, depending on temperature, light and soil conditions. Importantly sap testing is used to quickly identify and then manage deficiencies or excesses before they become visible.

There are key advantages to sap testing:

  1. fast and accurate feedback on nutrient status
  2. early and “real-time” detection of nutrient deficiencies, toxicities or imbalances
  3. identification of the most appropriate fertiliser applications
  4. determination of other factors that could limit nutrient uptake

Experience gathered from two seasons of Marlborough grape sap testing are:

  • useful for monitoring the nutrient status of blocks throughout the growing season. First testing is recommended pre-flower and then at subsequent significant growth stages (e.g. pre-bunch closure and veraison)
  • results demonstrate the effectiveness of fertiliser programmes and help determine specific nutrient requirements before nutrients become limiting
  • useful for comparing areas of variable performance to determine if nutrition is a factor
  • ideally suited to the use of fertigation or foliar products for timely remedial applications

Specific sampling protocols and results analysis are managed for a range of crops by AgVita, Australia (Quality Management System compliant with IS090001) using their nutrient database.

Standard sap testing provides nutrient uptake analysis of NH4, NO3, P, S, K, Ca, Mg, B, Cu, Fe, Mn, Zn, Na and Cl. Additional elements can be tested upon request.

Farmlands Technical Leader, Mart Verstappen has been working with Marlborough grape grower Ben McLauchlan at Rothay Vineyard.

“Sap sampling provides us with real time data so we can understand how and when the grapevine is using nutrients and how our foliar fert program can augment the plants nutrient uptake from the soil. Based on sap testing data we have altered and fine-tuned our foliar and solid fert program to maximise flowering and end of season vine performance. If you cannot measure it, how can you manage it,” Mart says.

For more information please contact your local Farmlands Technical Advisor.

Article supplied by Mart Verstappen,
Technical Leader – Viticulture, Farmlands