EXTRACTION METHODS FOR THE DETERMINATION OF MAJOR ELEMENTS IN GREENHOUSE SOILS AND POTTING - AND CULTURE MEDIA

For many crops grown in greenhouses, the levels of nutrients in the soil should be rather high. The nutrients, however, must not be overdosed as otherwise the growth of the crops is reduced by a too high salt concentration of the soil solution. For these reasons, it is important to analyse greenhouse soils regular. In some areas, regular soil testing is also necessary because of saline irrigation water.

Practically all laboratories engaged in routine testing of greenhouse soils employ one or another water-extraction technique. The equeous extracts are primarily used to determine the salinity level of the soils by means of measuring the electrical conductivity. Some laboratories use aqueous extracts also for the determination of nutrient levels. Most laboratories, however, extract the nutrients with other extractants, like diluted acids and buffer solutions. As compared with water, such extractants generally extract larger amounts of nutrients.

From research work at Naaldwijk, the conclusion can be drawn that aqueous extracts are most suited for the determination of the nutrient levels of greenhouse soils. I want to give some resukts of this work.

The analytical results of these extracts were closely correlated. For potting - and culture media, there are problems in the interpretation of the analytical results of aqueous