The problems probably stem from the recent use of a certain fertilizer. In the period 2010-2012 the fertilizer Ecofeed was allowed for organic growing by SKAL, being a natural N-fertilizer. Because this fertilizer is based on the resource chilisalpeter, this fertilizer contains a natural amount of perchlorate.
Perchlorate is hardly broken down and is persistent in the soil and is relatively easy to absorb for crops. A limited part of this ends up in the fruits, because the most goes to the vaporizing parts. The fertilizer can be flushed from the soil, research showed, but even after flushing the amount of perchlorate remained relatively high, and only just low enough to meet the norm of 0.2 ppm.
Recommendations
The researchers make the following recommendations:
• Flushing will have to be spread over a longer period to keep the soil in high moisturized condition for lengthened periods of time, to stimulate diffusion from micro pores. This also closes tears (macro pores) by swelling, and prevents accelerated drainage without contact with macro and micro pores.
• Flushing has to be done by a cyclic irrigation program, with sizes of max 2-3 mm each time, and no more than 15-20 mm per day.
• The crop residue and herbage has to be removed from the company as much as possible.
• Finally "dry growing", in which periods of capillary supply from the underground occur, is discouraged, as long as there is ClO4- content in the soil.
• The research was not aimed at setting up norms for ClO4-content of the soil, although guidelines can be provided based on the data. For greenhouse soil and cucumbers a maximum content of 0.05 ppm per 0-25 cm soil is advised.