Calcium: Plant Cell Strength and Nutrient Uptake
Calcium is an essential nutrient for all crops. It is what binds cell walls together, and gives strength and rigidity to stems and leaves. The disorder “blossom-end rot” found in tomatoes, watermelons, peppers and other fruiting crops is not a disease, but a failure of cell walls to form because of lack of calcium. With corn and other agronomic crops calcium deficiency shows up as weak stems and lodging (plants bending or falling over). Low calcium can result in low test weights of grains. Calcium is also important in helping to move other nutrients from the soil into plants. For a growing crop, tissue tests can determine the need for calcium. Also include boron in the tissue tests since boron is an important factor in calcium utilization by plants.
In soil tests calcium is typically reported in mg/kg or ppm (parts per million). While the quantity of calcium in the soil is useful, the relationship of calcium to other nutrients and soil pH are even more important in the calcium nutrition of crops. Calcium (Ca++), magnesium (Mg++), potassium (K+), sodium (Na+), and hydrogen (H+) are the primary bases attached to soil particles. Bases are nutrients that have a positive (+) charge and cling to soil particles, which have a negative (-) charge. This is similar to the way positive and negative ends of magnets attract and stick together.
The quantity of these base nutrients that can cling to soil particles determines the soil’s Cation Exchange Capacity (CEC). Calculating the percent of each base nutrient to the total quantity of bases (including H+) is how Percent Base Saturation (%BS) is determined. %BS is also a better indicator of which nutrient(s) may be limiting crop performance, than does just the concentration of each individual nutrient. %BS is a measure of the relative concentrations of these nutrients that is attached to soil particles and available to the crop for uptake.
For most crops the preferred %BS for calcium is 70%-75%. Good calcium levels in the soil is not only important for providing calcium to the growing crop, but also as a “carrier” nutrient that helps improve uptake of nutrients by roots. Low calcium reduces both cell wall formation and movement of nutrients throughout the plant. High levels of ammonium (NH4+), Mg++, K+, or Na+ in the soil can reduce the uptake of Ca++.
Lime application is the most common way to supply calcium to soil. However, most lime is ground limestone and is slow to release calcium to growing crops. It may take 2-3 years to get the full benefit of applied lime. As a result it may not be economical to apply lime on short-term rented farmland. Lime alone may not meet the calcium needs of a growing crop, especially if applied close to planting time.
Another method of getting calcium into a crop is to use AgriCal®, a liquid sugar-based chelated calcium product. It may be applied to soil or as foliar spray to a crop. The amount of AgriCal® applied to the soil is based on the soil’s %BS for calcium and the CEC of the soil. The table below shows the recommended soil application rates of AgriCal® based on these factors. Soil applied AgriCal® is typically applied shortly before planting or before emergence at rates of 1-5 gal/acre. For gardens or turf this equals to 2.9-14.7 oz/1000 sq. ft.
