Who Cares about Salinity?
Who Cares About Salt?
We use them in our foods for taste, on sidewalks to melt ice, and in our houses for drywall. Salts are some of the most commonly used minerals found on the planet, and yet not many think of them as a threat to our global food security. Just like humans cannot drink seawater, plants have difficulty using the water they need from the soil when too many salts accumulate in their root zones. Nearly 2,800 soccer fields worth of food-providing land is lost each day because of the over-accumulation of salt in farm ground as a result of poor irrigation management and contaminated groundwaters found all over the world.
What do salts do to plants?
These corn cobs show the dramatic differences that we observe because of the effect salt has on plants. The cob on the left experienced very little to no soil salt effects, and the one on the right experienced very high concentrations of soil salts. The cause of this yield reduction can be threefold:
Salt holds onto water harder than the plants can suck it up, and this makes the corn thirsty. We experience that as humans too! It's why we can't drink salt water out of the ocean for nourishment.
The chemical compounds that make up salts can poison plants, making them become sick and reduce yield significantly, if not cause death.
Salt will physically "get in the way" of other essential nutrients in the soil when roots are trying to uptake their food. It will also cause toxic levels of salt to accumulate in the plant, causing it to suffer.
The combination of these three things is what makes soil salinity one of the biggest threats to global security we face as humans.
Where do salts come from?
Salinity manifests itself in several ways in our environment: in saline irrigation and drainage waters, saline and sodic soils, saline groundwaters, seawater intrusion, brines from natural salt deposits or geologic formations, and brines from oil and gas fields and mining. The primary source of salts into natural waters and soils is from the chemical weathering of minerals. Mineral solubility is the principle regulator of the extent of salt accumulation in soils and waters. Natural secondary sources of salt include atmospheric deposits of oceanic salts along coastal areas, seawater intrusion into groundwater basins, saline water from rising groundwaters, inland saline lakes, and leaching of saline landforms. Human sources of salts include irrigation and drainage waters, soil and water amendments, manures and sewage, chemical fertilizers, and oil and gas field brines.
Continuing to proceed in agriculture as we are, with deficit irrigation in times of scarcity, over-fertilization with saline chemicals, and re-using tailwater effluent for irrigation will inevitably lead us to our own demise if nothing is done to manage this. Perhaps the most famous example of mismanaged irrigation is the fall of ancient Mesopotamia. This once productive land, known as the “fertile crescent”, diverted river flows into canals that ran through the region, and used the water to irrigate their fields. Consequently, seepage from the earthen canals, coupled with over irrigation, led to a rising water table. Along with that came excessive accumulations of soil salts from the natural waters. The farms had to switch to wheat (a more salt-tolerant crop), and then to barley (an even more salt-tolerant crop!) before their land simply could not provide any longer. This led to an economic collapse and the ultimate downfall of society. This too, is our fate if we continue down the path that we are, but luckily, many scientists over time have come up with trusted strategies, as well as some new and more innovative ones, that could provide management tools to farmers around the world for managing salinity.