It could be time to feed your portfolio with some plant food stocks, but only if you are prepared to take a very long-term view.

The world’s grasslands, which is where much meat and milk production ultimately starts out, are being depleted of a vital mineral. Phosphorus is the chemical that farmers apply through fertilizer to replenish grassland after grazing.

A new study that in the Nature Communications journal warns that an acceleration in grassland degradation will require farmers to apply four times as much phosphorus — both from livestock manure and commercial products — to their pastures by 2050 to “achieve an anticipated 80 percent increase in grass production” and keep the soil fertile.

With a massive forecasted increase in food demand, particularly for more protein by consumers in developing countries, the production of commercial phosphorus must double by 2050, according to the study’s authors.

The potential agricultural crisis represents an opportunity for long-term investors. “When you get a scientific study, it can be bullish if the study is proven to be true,” says Jeffrey Stafford, an equity analyst at Morningstar in Chicago. “But it doesn’t happen overnight.”

The companies that would benefit if phosphate use increased are those that supply the mineral, such as Potash Corporation of Saskatchewan (ticker: POT), Mosaic Co. (MOS) and Agrium (AUG). None specialize solely in phosphates, but each supply it as part of their overall product lineup.

Unfortunately, these companies are currently suffering from an overall downturn in the agricultural market. Such businesses are always cyclical, given that demand for plant food is closely correlated with the price of the crops and other products such as milk and meat. When the farm economy weakens due to lower food prices, investors can expect these stocks to slump as well.

The good news is that such dips don’t last — eventually they come to an end and the bust turns back into a boom. How soon will the cycle turn? Stafford says it could be a couple of years.

That doesn’t necessarily mean that when the farm cycle turns up again that grassland will be given the extra phosphorus love that the study’s authors suggest. Farmers may need to have some additional incentives in order to start spreading the mineral on grassland.

“Often, things may be good from a scientific study basis,” says Christopher Muir, an equity analyst at S&P Global Market Intelligence in New York. “In order to get the business world to move often requires government regulations.”

There may be a way to get regulators to push for grassland protection because such pasture isn’t just vital to sustain meat and milk production. It is also important in helping reduce soil erosion. Grass shades the ground from the hot rays of the sun, allowing topsoil underneath to stay soft. That spongier earth is then able to absorb rain, says Joe D’Aleo, chief meteorologist for agriculture at Weatherbell Analytics in New York.

Without vegetation, the sun can scorch land into a hard surface to the point that rain simply runs off, taking some of the soil with it.

So should investors buy or take a pass? A recent report from Morningstar describes the industry as “volatile” with companies not being able to affect the price of fertilizer. That means the companies simply have to weather the economic ups and downs of the farm market.

The same report says Mosaic benefits, as “its mines in central Florida churn out about a tenth of the global production of phosphate rock, the key feedstock used to produce phosphate fertilizer.” Phosphate contains the element phosphorus.

Morningstar says the company has a fair value of $35 versus a recent price of $25. The company has market capitalization of $8.8 billion and has dropped in stock price by 53 percent in the last year, but carries an attractive price-to-earnings ratio of 9.

Potash “owns phosphate rock mines in the U.S. and benefits from not having to purchase expensive rock from third parties. Morningstar says the stock has a fair value of $24 a recent share price of $16. Potash is bigger than Mosaic, with a market cap of $13.5 billion, and its P/E ratio is 10.6. POT stock is also down more than 50 percent in the last year.

Agrium recently signed a deal to ensure the supply of feed material to its Ontario phosphate operations as one of its mines was becoming unprofitable. For that reason, Morningstar says profit margins in the phosphate business “will be pressured from the purchase of higher-priced offshore rock.”

Morningstar says the stock has a fair value of $98 a share versus a recent price of $83. Agrium has the highest P/E ratio of the three stocks, at 11.9, and carries a market cap of $11.5 billion. AGU stock has fallen 27 percent in the last 12 months.

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3 Stocks to Play to Shortage of Phosphorus originally appeared on usnews.com