Sap analyses
Sap analysis allows monitoring of plant nutrition during its growth cycle. Used alongside soil analyses, it is a decision support tool and for agronomic and economic performance.
Why this analysis?
Analyses show deficiencies and excesses. This is very important because it is often realized that excesses can create shortages. This may be due to an imbalance already present in the soil or to an application that blocked another element and created nutritional stress afterwards. It is important to consider the interactions between elements, whether synergistic like K and Mn, or antagonistic like K and Ca. For example, if there is an excess of potassium blocking magnesium or calcium, manganese can be applied to regulate potassium absorption in the plant.
- While tissue analyses take on average 3 to 4 weeks between sampling and recommendation. During this period, the plant has had time to evolve so we cannot respond at the right time to the plant’s nutritional needs.
- With the sap analyses we use, there is about one week between sending and interpretation. This is therefore 3 times faster than tissue analysis. This allows anticipation of future blockages that could occur during the plant’s vegetative cycle and grain filling. Deficiencies can thus be anticipated 3 weeks before their potentially visible effects.
- Photosynthesis is the process of biomass production. The idea is to maximize it. Sap analyses will allow regulating deficits and/or excesses, especially concerning essential nutrients (N, P, Mg, Fe, Mn, S, etc.).
- Proper nutrition has a positive impact on disease resistance. A balanced nutritional profile will stimulate the plant’s active and passive defenses, making it less sensitive to pests. It also affects grain filling: quality, sizing, etc.
How does it work?
There are ready-to-use kits. Leaf sampling is done in the morning. They must be placed in the bag and sent by mail. There are often 2 bags (except for wheat at early tillering for example): one bag for young leaves and another for old leaves. It is the comparison of the two that will allow understanding. The idea is to monitor the crop at 3 stages during the season. For example, for wheat: tillering, 1 cm ear, and end of stem elongation.
It should be noted that some elements are:
- mobile in the phloem - the sap-conducting tissue: N, P, K, Mg. Nitrogen, phosphorus, potassium, and magnesium move quickly in the phloem. The plant can redirect them from old leaves to young leaves.
- other elements are not (Ca, B, Mn).
For example, if potassium is in excess, a lower value in young leaves than in old leaves is observed. This means the leaf does not need this K so it stores it in the old leaves. Conversely, if more K is observed in young leaves, it indicates a deficiency: the plant begins to mobilize K and redirect it to young leaves.
Actionable levers?
Recommendations following sap analysis results generally involve foliar applications of trace elements. Except for some elements like calcium, which is difficult to absorb through the leaf and where correction is mainly done via the soil, almost all other elements can be applied foliarly, always in small doses.
The composition may change depending on the plant’s condition. We try to keep it at a maximum of €7-15/ha, always mixed with a chelating agent and a reducing agent to improve absorption, especially for iron and manganese. It is essential that they are absorbed in reduced form. They can be reduced with citric acid and chelated with humic/fulvic acid. Amino acids can also be added to complex the spray mixture.
Results
The goal is not strictly to increase plant yield, but to avoid losing it. With sap analyses, nutritional stresses that impact yield can be managed.
Sources
Sap analyses: an effective decision support tool - with Anthony Frison and Lennart Claassen - AgroLeague
