The Story of NPK

If you’re a regular reader of this blog, you know that we think Konpòs Lakay, SOIL’s organic compost, is a pretty amazing thing. But unless you’re a farmer or avid gardener yourself, you may not know why! After all, when you’re surveying row after row of beautiful fresh produce at the grocery store or farmers’ market, it can be easy to forget that growing fruits and vegetables is no simple task.

But while those strawberries might look (and taste!) sweet, they’re actually very demanding organisms, requiring a precise diet of nutrients in the soil in order to survive. Of those nutrients, Nitrogen, Phosphorus, and Potassium (often referred to as NPK, their chemical element symbols) are the true building blocks of soil and are essential to growing healthy plants. As a result, it comes as no surprise that the majority of the world’s crops are fertilized with NPK – but where that NPK comes from has a huge impact on our environment, our wallets, and even our foreign policy.


NPK naturally occurs in compost made from human waste. This is known as the nutrient cycle: when we eat food, we absorb some nutrients and excrete the rest, which ideally end up back in the ground – growing more food for us to eat! Here at SOIL, this natural process is the foundation of our work transforming wastes from our sanitation projects into compost that will help grow more food. Unfortunately, the NPK used in chemical fertilizers is not part of the nutrient cycle. The industrial creation of nitrogen and extraction of phosphorous and potassium are environmentally devastating and economically unsustainable.

Nitrogen is essential for growing leaves and vegetation.

Nitrogen is essential for growing leaves and vegetation.

The ubiquitous “N”: Nitrogen is everywhere – it makes up 78% of the air around us. In the early twentieth century, scientists discovered how to extract nitrogen from the air and, in doing so, completely revolutionized modern agriculture. However, this process comes at a price: the extremely high temperatures required are achieved by burning natural gas or coal. The production of fertilizer nitrogen accounts for over 1% of the world’s annual energy consumption, and is responsible for 6% of greenhouse gas emissions associated with agricultural production (International Fertilizer Industry Association (2009) Energy Efficiency and CO2 Emissions in Ammonia Production 2008-2009 Summary Report).

Phosphorous encourages root and stem growth.

Phosphorous encourages root and stem growth.

The Fading “P”: Although chemical fertilizers are used across the globe, phosphate rock is highly concentrated in certain parts of the world. And like oil, it is a non-renewable resource. At some point – perhaps even within this century – the existing phosphate reserves will not be able to meet global demand; science writer Isaac Asimov has referred to phosphorous as “life’s bottleneck” (Asimov, I. (1974) Asimov on Chemistry. Garden City, NY: Doubleday).

Potassium works on plants’ cellular level to regulate the movement of water and nutrients, and is related to flowering and fruiting.

Potassium works on plants’ cellular level to regulate the movement of water and nutrients, and is related to flowering and fruiting.

The Exotic “K”:Potassium comes from potash, which is largely mined from reserves in Canada, Russia, and Belarus. As with phosphorous, the impact of mining and transporting massive quantities of potassium around the world is enormous.

Not only is the process of acquiring NPK for chemical fertilizers clearly environmentally and economically unsustainable, but the large amount of NPK they deliver to soil when used agriculturally actually does long-term damage to the soil’s productive capacity (in the same way that a jolt of sugar from an energy drink damages human health). In addition, the extra NPK from chemical fertilizer applications can run off, creating downstream “dead zones,” where NPK-fueled algae chokes out other forms of life.

That’s why SOIL’s experimental farms are so important: because we can demonstrate how compost improves the soil and increases crop yields – all without the destructive effects of chemical fertilizers. Ecological sanitation closes the loop on a broken nutrient cycle, recycling the building blocks of life through ecological processes instead of fossil fuel dependent extraction. You can help restore healthy nutrient cycles too, through home composting, supporting the recycling of human wastes and using organic fertilizers in your garden. 

If you’d like to learn more about our experimental farms, compost, or NPK, check out the links below:

1 “Sweet” News from our Experimental Farm – exciting results from sweet pepper trials on SOIL’s farm in Port-au-Prince.

2 Radio broadcast of the sordid story of Fritz Haber, the scientist who discovered the method for transforming atmospheric nitrogen into liquid nitrogen.

3 Introduction to the Gulf of Mexico’s dead zone, includes links to NASA satellite images of the world’s dead zones and educational resources.

4 Link to the European Commission’s overview of current and future global consumption of NPK.

5 Urine, like chemical fertilizers, contains huge amounts of nitrogen and phosphorous. This article from Scientific American reviews human urine as a crop fertilizer.

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