I’m from holland and the soil in my marijuana greenhouse was tested and showed high levels of dissolved salts and sulfur. How did this happen, and what can I do to fix it?
In Holland, the water table is regulated with pumps and dams and is generally kept about a half-meter (18 inches) below ground level. Any marijuana fertilizers you might add to the soil usually stay right in place instead of draining like they would with a groundwater level that was lower. Adding fertilizer crop after crop will force salt levels to accumulate. The soil will also be affected by dairy herds in the form of manure contamination. The levels of manure dropped in the fields are generally so high that nitrogen and other salts also build up to high levels. In addition, cows are fed salt which is excreted through the urine and increases the sodium chloride levels in the soil.
The sulfur was contained within the fertilizers and could also show up as a result of its repeated use as a fungicide. Commercial marijuana growers in The Netherlands will occasionally leach the soil. First, they dig large holes in the ground at which point the soil is flooded with uncontaminated water. The water fills the holes and is pumped out along with the dissolved salts. This process is quite costly and you might consider using units that keep the marijuana plants above the ground level (e.g. containers or hydroponic systems).