Calcium deficiency (blossom end rot) is favored by both very low and high soil moisture, which inhibit calcium uptake and cause nutrient imbalances (e.g. excess nitrogen, high potassium or insufficient boron). When soil moisture is low, calcium will not move to the roots. And in case of high soil moisture, oxygen is unavailable for root growth and calcium will not be absorbed. So the key factor is maintaining proper soil moisture and avoid high levels of nitrogen.
It is recommended to "check calcium levels, and check that nitrogen levels are in balance with other nutrients, using a petiole sap test of the youngest mature leaves during early stages of crop growth."
Posted by: Dr. Ravishankar Narayana
Posted: November 13, 2017