Most of the coir’s exchange sites are tied up with sodium and potassium. These ions are readily replaced by calcium. If calcium is applied, much of that calcium is going to be tied up in the exchange capacity taking out sodium and potassium. Therefore calcium is not in the substrate solution for utilization by the plants. There is a lag before the cation exchange capacity can be fully charged with calcium, potassium and magnesium. If a grower isn’t cognizant of this lag and doesn’t address it, it can cause deficiency problems. When 50 ppm calcium is incorporated in the fertilizer solution, the leachate may only contain 10 ppm calcium. Not that the plants utilized the other 40 ppm. Much of that 40 ppm was tied up at the exchange sites and will be available later.”
Once the cation exchange sites are charged with calcium and magnesium, then there is free exchange and there shouldn’t be any problems,” he said. “In the first two to four weeks, growers should probably start out with higher calcium and magnesium levels if they’re growing with coir. They should try to favor calcium and magnesium absorption at the exchange sites. This
is a precautionary step.”
