Help! We’re running out of phosphorus

Over the last few years, there has been much discussion about the availability of phosphorus: one of the key nutrients needed for plant growth. Like water, it’s becoming increasingly scarce (see graph in figure 1 below). With so much focus on the shortage of water we tend to overlook the fact that plant nutrients (or fertilizers) are just as essential. Europe has a limited supply of extractable phosphorus. At the moment, the Netherlands is the only European country with a phosphorus surplus. In the Netherlands, the Nutrient Platform was set up to promote phosphate recycling. Prices of this commodity are expected to rise as shortages continue to grow. Will we run out of phosphorus? Is this concern justified and what can we do about it?  

Figure 1: Peak phosphorus ‘Hubbert’ curve, indicating that production will eventually reach a maximum, after which it will decline (source: Cordell, Drangert and White, 2009)

In addition to our dwindling phosphorus reserves, there are a limited number of phosphate mines worldwide. The vast majority of phosphate in the world comes from just three mines. In fact, eighty percent of world reserves is exported from Marocco, China and Jordan (see Figure 2).

Figure 2: Global phosphorus reserves as reported in 2008. Remaining reserves are highly geographically concentrated and are under the control of only a handful of countries. Note: units are in phosphate rock, not P. Data: Jasinski ((2009).

Phosphate as a fertilizer
Phosphate is one of the key fertilizers required for plant growth. Phosphate is essential for root development, the photosynthesis process and the production of sugars in plants. It also plays an important role in plant respiration and assimilation (assimilation is a plant’s production of nutrients using light). Plants deficient in phosporus usually suffer from stunted growth. This is shown by the figure below.

Figure 3: Phosphate deficiency severely affects plant growth

But if phosphorus is so important, and its availability and extractability so limited, what can we do to ensure adequate supplies in the future? There are various measures that can be taken, divided below into macroeconomic and microeconomic measures.

Macroeconomic measures
Every country should draw up and monitor their phosphate balance. Cheap fertilizers are a thing of the past. We asked the former chairman of the Nutrient Platform for his view: ‘The horticultural industry should accurately determine the current input and output levels of phosphorus in its sectors and sub-sectors. Such a balance will show you where the losses are occuring and allow you to work out the costs of reducing those losses. Since Europe has a limited supply of extractable phosphorus, it will have to recycle its waste flows. There are three types of waste flows: agricultural waste, waste from the food and stimulant industries (including expired products) and sewage sludge.’ Smaling continues: ‘You should compare those three to determine the most efficient method of retaining phosphorus within the production system. Whether recycling vegetable waste (such as tomatoes) weighs up against recovering phosphorus from water would make an interesting study case.’

Microeconomic measures
These microeconomic measures could be taken now:

1. The first measure is switching from soil-based to soilless growing media. This would be a major step forward and dramatically improve crops yields. It would also allow significant savings to be made on fertilizers.
2. The next step is recycling drain water and the fertilizers it contains, for instance by disinfecting the drain water with UV light. Two important benefits of UVc light is that it’s efficient and doesn’t affect the composition of the drain water. The latter enables the fertilizers in the water to be reused. What’s more, the cost of the disinfection equipment can be recouped within two years! 
Figure 4: Example of closed loop recycling. A HortiMaX FertiMiX is used to add fertilizers, while the HortiMaX VitaLite is used to disinfect the drain water.

3. The third step is to give the plants exactly what they need by accurately controlling the application of fertilizers. Technical developments in sensors and control systems continue to advance. Most growers nowadays control fertigation based on the EC level. There are, however, new methods for dosing fertilizers more precisely. These prevent fertilizers from accumulating in the system, so water can be recycled more frequently. An example of one of these methods is illustrated in figure 5.

The peak in our phosporus production is coming. As the global population continues to grow, and with it the demand for food, careful management of our phosphorus supplies is essential.    From a macroeconomic viewpoint, we have to monitor our phosphate balance. From a microeconomic viewpoint, we can take measures in the short term. Collecting and then disinfecting and recycling drain water are now feasible options and usually provide a high return on investment.

About the author
Ir. Michiel Suurmond
Product Manager for Water & Nutrition
Tel.: 00 31 6 55 70 73 96

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