10.2 - Fertilisers & Their Production

Why crops have to be fed, and the three nutrients

• Growing crops take nutrients from the soil as they grow.
• Harvesting removes these nutrients from the field instead of letting them decompose back into the soil.
• Over time, the soil becomes depleted, which slows plant growth and reduces crop yield.

What a fertiliser does

• A fertiliser is a substance added to soil to replace missing nutrients or supply more than the soil naturally contains.
• Replacing nutrients allows the same land to be cropped repeatedly and increases crop yields.

Why fertilisers matter

• The world's population is rising, but agricultural land is limited, so crop yield per hectare must increase.
• Most manufactured fertilisers are made using ammonia.

The three elements a plant needs most

• Plants need three main elements in large amounts: nitrogen (N), phosphorus (P), and potassium (K).
• If crops lack any of these, growth slows and yields fall.

The form they must be supplied in

Plants cannot absorb these elements directly; they must be dissolved in soil water and taken up through the roots as soluble compounds:

• Nitrogen - Ammonium salts and nitrates
• Phosphorus - Soluble phosphates
• Potassium - Soluble potassium salts

NPK fertilisers

• An NPK fertiliser is a formulation supplying nitrogen, phosphorus, and potassium.
• It's a mixture of salts, not a single compound.
• The proportions of N, P, and K are varied to suit different crops and soil types.