Last year, Van der Knaap conducted a trial to see what symptoms crops show when lacking certain nutrients.

The test

The formation of defects means that the plant cannot absorb one or more nutrient elements sufficiently. The lack of a particular element manifests itself in deviant growth, production or color of the crop. During the test, the defects of two crops, hydrangea and pepper were observed while lacking certain nutritional elements.

The hydrangea was put on 100% fine coco substrate (Knaap Elite), the pepper was grown in Forteco Power Grow pots. In order to influence the test as little as possible, no basic fertilization was given to the substrate.

Both crops received a nutritional solution with an EC value of 2.5. In each treatment one element was omitted. The reference plants did not miss main or trace elements. The elements whose effects on the crops were tested were: phosphorus, nitrogen, potassium, calcium, magnesium, iron, boron, sulfate, zinc, copper, molybdenum and manganese.

Of both crops, soil and leaf samples were taken to determine whether the missing element could not be recovered in the leaf or in the substrate. In addition, it became visible whether the plant had absorbed the other elements sufficiently. In all cases it was found that the element in question was not really present and that there were no disturbances in the absorption of the remaining nutritional elements.

Above ground
Over the entire test it can be concluded that the lack of certain elements, such as nitrogen, phosphorus, potassium, calcium, magnesium and iron, was readily visible. A shortage of phosphorus, for example, led to a stop in growth and development after one week; with the absence of nitrogen, this was even from the start. Necrosis was noticeable in the absence of potassium, boron and calcium. The latter also caused tip rot in the pepper. A shortage of iron led to yellow discoloration of the leafs.

In general, it can be said that in the case of abnormal growth above ground, the root development also was poor. The limited growth above ground resulted in a wetter pot clod, which is detrimental to root development. In addition, due to the absence of certain nutrients, the plant also lacked the enzymes that enhance root development.

Harvest (pepper)
The effect of zinc and copper deficiency was a high fruit weight, but a very low number of fruits. The crop with the potassium deficit, on the other hand, had a lot of fruits, but of a lower average weight. The reference plant performed the best with a good average fruit weight and number of fruits.

For more information: 
Van der Knaap Groep
Raymond van Ispelen
Bovendijk 50 
2295 RZ Kwintsheul 
T: +31(0)174 296606