When it comes to salt and food, we're usually being told how much to add (or not add) to stay healthy. But the latest episode of MinuteEarth highlights a far bigger salt problem that could actually stop us from eating altogether - the increasing salinity in our soil. That might not sound like a very sexy topic, but it turns out that dry, drought-prone regions of the world produce nearly one-third of the global food supply, and rising salt levels are putting crops at risk of drying out. In other words, if we can't work out how to fix the issue, we're all going to get a whole lot hungrier.

So how does soil get salty in the first place? As the video explains, salt is a natural part of soil all over the planet. Normally this isn't a problem, because salt is either dissolved by rain in wet climates and washed down into the groundwater below, or it accumulates in lower soil levels of dry climates because native plant roots suck up all the rainwater around it.

These systems both work well… until you change either the plants, or the level of the water table. And this is the problem in dry areas, because farmers are rapidly swapping out deep-rooted native plants for shallow-rooted crops. This means that rainwater isn't sucked up as quickly, and more of it ends up making its way down to the groundwater, which causes the water table to rise.

On its way up, this groundwater dissolves all the salt deposits trapped in the deep soil layers, and brings them up to the crop roots. 

Why is that so bad? The video oversimplifies this point a bit (it's nothing to do with the size of the salt molecules), but it's because of the process of osmosis, which means that water will always move spontaneously across semi-permeable membranes, such as a plant root, into areas with higher concentrations of solutes - in other words, where it's saltier.

When soil water is mostly fresh, this works in a plant's favour, because the root contains more solutes than the soil and so water flows easily into the roots. And the leaves of a crop actually contain more solutes again, which means that osmosis 'pulls' the water up to the top of the plant, keeping everything nice and hydrated.

But when the soil water is saltier than the roots, it causes a huge problem, because even if there's plenty of water in the soil, very little of it is going to flow into the plant.

This means plants are dehydrating, even when there's enough rain. And dehydrated crops grow slowly, or die altogether, which means less food to feed our ever-growing population.

So is irrigation the answer? Unfortunately no. Watch the episode of MinuteEarth above to find out why using river and lake water just makes plants thirstier than ever. But don't worry, it's not all bad news: farmers have managed to come up with some pretty ingenious solutions to our salt problem, and they're better for the environment too. Thank you, native plants.