Plant sap analysis as an alternative to chart crop's fertilizer uptake

Adjustments in fertilization usually depend on the results of soil, substrate or drain water samples. To an increasing extent however, a chemical analysis of the crop itself is used, which has the added advantage of charting the plant’s uptake as well as its yield. In their newsletter, Relab den Haan explains the plant sap analysis.

Leaf is usually only analysed in case of excess symptoms. By comparing the leaf’s chemical composition to the objectives, it becomes clear whether the crop has taken in the right quantities of nutrients. But even without outward symptoms it can be useful to subject a plant to analysis. By taking regular leaf samples one can determine which elements a particular crop needs, and what the proper composition should be. 

The life cycle of a leaf has several stages. After the leaf is developed, it will start contributing to respiration and photosynthesis. At a later stage, the leaf is being used as a storage device until it has served its purpose and is disposed of. When taking leaf samples it is important to take this cycle into account, as these stages influence the chemical composition. The last fully grown leaf is therefore the most illustrative in charting the plant’s overall condition. 

Of most crops, the target values are known. These targets generally differ per species and sometimes race or cultivation. The table below lists a number of main crops targets of the main elements.

The target value of a crop monster not only revolves around the absolute amount, but also around the relationships between the elements. A high nitrogen / potassium ratio may lead to a weak growth, while both of these elements are within the target range. And a sufficiently high iron content can, in case of too much zinc, still lead to a lack of iron. 

Above issues can make sap analysis a complex procedure. In case of doubt, our experts are ready to receive your questions.