CHENNAI: Plants depend on 17 elements of the periodic table. They are classified into macronutrients, which are needed in large quantities, and micro-nutrients, which are essential too, but needed in only trace quantities. A skilled gardener needs to understand how to identify deficiencies of any of these, and how to remedy the situation.
One of the big boys from the list of macronutrients is nitrogen, which is absolutely critical for plant growth. Nitrogen is actually a component of the chlorophyll molecule itself, and plants need chlorophyll to carry out photosynthesis. This is why a nitrogen deficiency is often manifested in yellowing leaves because of lack of the green chlorophyll pigment. Moreover, it is also a key element present in amino acids, the building blocks of all proteins, DNA, RNA, etc.
There are a few ways in which this nitrogen is made available to plants: Some atmospheric nitrogen gets ‘fixed’ during lightning, which breaks the covalent bonds and forms nitrates, which are carried down to the soil by rain. This is a tiny percentage of overall soil nitrogen. Some nitrogen gets fixed by bacteria, which live in root nodules of leguminous crops like pulses. The plants provide them carbohydrates while the bacteria provide enzymes needed to break the triple covalent bonds.
Some nitrogen is also fixed by free-living soil bacteria. Dead plants and animals and other bio-mass like manure are decomposed to produce ammonium ions, which are then converted by nitrifying bacteria to nitrite and is further converted to nitrates by another group of bacteria. Chemical fertilisers: These have their basis in the Haber-Bosch process, which helps combined nitrogen and hydrogen to produce ammonia.
Now, some plants prefer to absorb their nitrogen as nitrates, while some plants prefer to absorb it as ammonium. Usually, plants that have a longer lifecycle like perennials, trees, shrubs etc prefer their nitrogen as ammonium, while short duration plants like vegetables prefer their nitrogen as nitrates.
How do you ensure whether your soil has more of nitrates or more of ammonium availability based on the crops that you are growing? A natural way to do this is by modifying the fungus and bacteria presence in the soil, by using compost prepared accordingly. In fungally dominated soils, the organic acids produce by the fungi, lower the pH of the soil, which reduces the number of bacteria working on producing nitrates, and the soil has more of nitrogen available as ammonium — which is what some plants prefer.
Vegetables and other short- term crops, on the other hand, prefer their nitrogen as nitrates. However, if you take a short-cut by using chemical fertilizers, which are predominantly salts that are nitrate based, you risk destroying your entire soil life. The plants do grow fast because they have access to nitrates — but the earthworms are driven off, beneficial microbes die away leaving your plant susceptible to disease, and so on. Just not worth it.
The author is CEO, Farmizen, a platform connecting organic and natural farmers to consumers with same-day delivery.
One of the big boys from the list of essential nutrients is nitrogen, which is critical for plant growth. Here’s how you can make sure that the soil in your garden contains the required nitrates and ammonium