The Higher the Sodium, the Higher Need for Calcium
The Impact Calcium has on Sodium
Previously we have stated the importance of calcium and the balance of nutrients in soils being the key for maximum crop production and ultimate soil health. In this blog we look into the impact calcium has on sodium. This is an important example of nutrient balance and the effect one nutrient can have on another.
Sodium levels in our soils here in Australia is a growing issue and one that is causing loss of production across both dryland and irrigated crops.
The estimated loss in agricultural production from salt-affected farms is approximately $130 million (across Australia) and rising. (https://www.qld.gov.au/environment/land/soil/salinity/impacts)
So what does excess salt do to plants and soils? The below is a little technical but does help explain the role of calcium on salt toxicity.
Salt toxicity comprises osmotic and ionic components both of which can severely affect root and shoot growth. Uptake of Na+ across the plasma membrane is very fast resulting in physiological effects on extracellular as well as intracellular sites. Sodium reduces binding of Ca2+ to the plasma membrane, inhibits influx while increasing efflux of Ca2+, and depletes the internal stores of Ca2+ from endomembranes. These changes in the cell Ca2+ homeostasis are suggested here to be the primary responses to salt stress that are perceived by root cells. Salt would almost instantly reduce the amount of Ca2+ being transferred to the leaf cells, with Ca2+ activity dropping and Na+ activity rising in the apoplasm of leaf cells. This Ca2+signal would be transported to leaves together with, if not preceding, the signal of limited water supply. (Z. Rengel, Department of Plant Science, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, SA 5064, Australia.)
There is a quick chemistry and plant physiology lesson for us.
Excessive levels of soluble salts in the soil, particularly sodium chloride, cause poor plant growth. A build-up of salts in the soil interferes with water and nutrient uptake by plants because of osmotic effects (i.e. high concentrations of salts in the soil make the soil water less available for plant uptake). Affected plants wilt or show salt burn symptoms on the older leaves. Crops vary in their tolerance to soil salinity.
Nutrient uptake is effected on a number of levels with the main cause being the physical problems in soils (such as dispersion) and the restriction of rooting depth and root hair development which then obviously limits plant growth.
Sodium tends to displace exchangeable cations, such as calcium, from the sites where they are attached to soil particles. Exchangeable calcium helps to keep soil particles bound together in aggregates, but in soils with excess sodium, the sodium causes clay particles to break away from soil aggregates and disperse. This has the effect of reducing pore spaces and reducing the movement of water through the soil profile. In sodic topsoils, a hard crust may form when the soil surface dries out.
The Solution – More Calcium
The solution is reasonably simple, the higher the sodium in a soil, the more calcium is needed. Lime and gypsum are the obvious choice and need to be part of a longer term focused program. There is also technology today that can enhance and improve these longer term product applications. This works on a crop by crop basis as well as making more available the calcium in our soils. Through combinations of chelated and complexed calcium ions in high quality products, soil calcium levels can be significantly increased on a per crop basis making a big difference to the effect of sodium.