Calcium (Ca)
Ca is often applied in a form of gypsum (calcium sulphate) and/or lime (calcium carbonate) to correct high-sodium, compacted soils
- High-sodium soils are characterized by a high proportion of sodium ions relative to other cations (i.e., Ca, Mg, K). Excessive sodium levels affect soil structural stability, reducing infiltration rates and soil moisture-holding capacity and increasing soil compaction.
- These soils are formed when Ca and Mg ions bound to clay particles in saline soils are displaced by sodium and are then leached from the soil profile. Sodium ions attached to the clay remain and tend to accumulate in the soil.
- High-sodium soils can be improved by the addition of Ca and/or organic matter — the best remedy is usually gypsum + humic substances + biology + water.
- Calcium displaces the adsorbed sodium from the exchange complex and this improves the structural stability of the soil.
KEY FACTS
- Calcium (Ca) is a relatively large divalent cation, classified into a group of alkaline earth metals.
- A high proportion of the total Ca in plant tissues is often located in cell walls (apoplast).
- The mobility of Ca in plant tissues is rather low.
- Calcium can be supplied at high concentrations and can reach more than 10 percent of the dry weight (e.g., in mature leaves).
FUNCTION
- Involvement in cell-wall integrity (calcium pectinate) as well as stabilization of membranes and the cytoskeleton
- Essential role as a secondary messenger in cell-signaling pathways
- Role in cell signaling and nutrient sensing
- Involved in stress response and antioxidation (neutralization of reactive oxygen species)
AVAILABILITY
- A high level of phosphorus (P) in alkaline soil limits Ca availability.
- Overfertilization with Mg or K reduces the Ca uptake rate in the rhizosphere.
- Soil organic compounds have a tendency to bind Ca and reduce the exchangeable pool.
- Boron (B) deficiencies reduce calcium mobility in the soil
