Final answer:
Soil can easily become deficient in calcium, as these ions do not stick to negatively charged soil particles. Plants absorb calcium as cations dissolved in the soil solution.
Step-by-step explanation:
Soil can easily become deficient in calcium, because these ions are negatively charged and do not stick to negatively charged soil particles. Plants absorb Ca²+ as cations dissolved in the soil solution. These ions are generally derived from the breakdown of organic material and as soil minerals are weathered and put in solution.