Some people argue that CaCO3 (Trical 35-SP) should not be used in a high P situation because the Ca and P tie-up. They recommend using gypsum instead.
We have been discussing and demonstrating for 10+ years that the calcium in CaCO3 is only released when root acids or microbes break down the CaCO3. Further, gypsum is not broken down into Ca (calcium) and SO4 (sulfate) by any mechanism in the soil.
High P (phosphorus) in the soil does not automatically mean ‘high availability”. However, when P is released it is very reactive and will tie-up readily.
The data from years of Analync testing has shown some interesting phenomena:
Primarily, calcium ties up mainly with sulfate and CO3 (carbon trioxide) while phosphorus ties up with micros–especially Fe (iron).
Without being too scientific, this happens because of the valence (charge) of the Ca and Fe ions. Calcium is always +2 and SO4 and CO3 are always -2; a match made in heaven. Fe on the other hand has multiple valences but prefers +3 in the soil, and PO4 (phosphate ion) has a valence of -3. So, it is significantly easier for Fe and PO4 to combine as FePO4.
KEY POINTS TO REMEMBER
- Calcium carbonate is the most abundant calcium mineral.
- Plants get their calcium from calcium carbonate by biological activity and root exudates.
- Gypsum’s calcium solubility is far less than what the plant needs.
- Calcium carbonate does not affect pH to the extent that other things do (like irrigation water)