Colin,

I’ve played around with GSR calcium, both the Dormant and the Growing calciums, in California for 3 years or more with mixed results. On almonds, tree fruit, and various vegetables. It did seem to increase water penetration and soil flocculation on about half the soils tested, the other half showed no real differences. Never saw much of an increase in leaf Ca in any of the tests. We were applying 2-3 lbs per acre over the season, which is quite expensive. In the end, we felt that certain cover crop mixes and biological inoculants/stimulants tended to give a better plant-Ca response than the GSR calcium. I do still use some GSR at my place where I have well water that has 45 times more sodium than calcium in it (I constant-feed GSR dormant calcium in the water), and while the soil tests do not increase in ppm Ca, the soil has better aggregation vs without it. I’m dealing with very alkaline soils and water, around 8.3 pH, with sodium base saturation in the 7-10% neighborhood. Gypsum and micronized did not work at all, and only drove up the soil EC and sulfur levels. I have gotten the best results increasing plant-Ca with very high-quality compost, biological products, cover crop mixes, managed tillage, rock dusts, and where feasible alfalfa meal. That approach has worked the very best for me. It may be that it releases Ca from the soil, because I do have high Ca/high CEC soils but none of it is available due to pH/bicarbonate issues. Micronized sulfur has not worked either, fwiw. I can see it in the soil years later (yes, even the micronized versions).