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Plant fertilisers: It’s not what you use, but how you use it that’s important

Tan Ngai Paing

ANN/THE STAR – Chemical fertilisers are synonymous with food production, but public perception towards their ubiquitous use has not always been positive. Someone once asked me what it takes to remove chemical fertilisers from modern agriculture.

To that, I replied that Thanos (from the movie Avengers) would have to snap his fingers not once but twice to reduce the global population from nearly eight billion today to fewer than two billion. There’s truth in my jest. Without chemical fertilisers, we would not have enough food for everyone in the world today.

Why? Nitrogen is one of the most important nutrients for plant growth, and before the development of synthetic nitrogen fertiliser, through a process called Haber-Bosch, the major source of nitrogen fertiliser was from natural sources, such as guano and bone meal.

These sources, however, were limited in supply and could not keep up with the increasing global food demand. It was only through the advent of the Haber-Bosch process that the world’s population could expand beyond the pre-synthetic nitrogen fertiliser level of fewer than two billion people.

The importance of synthetic nitrogen fertilisers, together with other plant essential element chemical fertilisers, have allowed human civilisations to expand their populations rapidly and our societies to become increasingly sophisticated culturally, politically and economically.

A farmer applying foliar chemical fertilisers to improve the growth and production of durian trees. PHOTO: THE STAR

Chemical fertilisers have reduced global food insecurity and hunger. Tropical soils, such as ours, are inherently low in nutrients because our soils are susceptible to weathering from our warm and wet tropical climate.

Our soils require chemical fertilisers to provide the necessary amount of plant nutrients, as well as in their correct ratio or mixture tailored to specific crop needs.

This cannot be done if we use only manures or guano. Laboratory analyses have shown that the nutrient content derived from different organic sources can vary markedly between them.

Moreover, adding too much or adding only one type of organic matter may cause an imbalance of nutrients for plant growth.

So, what exactly are chemical fertilisers? Apart from nitrogen fertiliser, many chemical fertilisers containing phosphorus, potassium or magnesium are actually natural salts (not to be confused with table salt) and natural minerals that are mined from the earth.

For example, phosphorus is most abundant in northern Africa (particularly Morocco), while potassium comes from Canada and Russia. These natural minerals can either be processed to obtain a salt form or ground into fine particle sizes, which are then applied to soils.

Various chemical fertilisers can be mixed either physically or chemically to produce a combination of two or more elements to attain the required ratio recommended for crop production.

A balanced plant nutrition programme supplied with chemical fertilisers is one of the main reasons our agriculture can prosper, making a better nutrition diet accessible to almost anyone nowadays.

However, are chemical fertilisers harmful to our health? Can plant nutrients derived only from organic sources be safer?

Chemical fertilisers that contain heavy metals can have a negative impact on our health. But the same can also be said for organic manure, which can be contaminated with heavy metals.

Also consider this: plants cannot differentiate nutrients coming from chemical fertilisers and organic sources. What is important is that these nutrients must be in mineralised forms before being taken up by the plant.

For example, nitrogen must be in either nitrate or ammonium forms before the plant roots can absorb it, regardless if the nitrogen comes from chemical fertilisers or chicken dung.

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