Which of the following is not provided to the soil by a chemical fertiliser?

To determine which of the following is not provided to the soil by a chemical fertilizer, we need to understand the role of chemical fertilizers in soil nutrition. Chemical fertilizers are typically used to supply essential nutrients to the soil, promoting plant growth and productivity. These nutrients include nitrogen (N), phosphorus (P), and potassium (K), commonly referred to as NPK.

Now, let's examine the options to identify the nutrient that is not provided by a chemical fertilizer:

1. Nitrogen (N): Chemical fertilizers often contain nitrogen compounds such as ammonium nitrate or urea. These compounds supply nitrogen to the soil, which is crucial for plant growth and the development of proteins and chlorophyll. Therefore, nitrogen is provided by chemical fertilizers.

2. Phosphorus (P): Chemical fertilizers also contain phosphorus compounds, such as monoammonium phosphate or diammonium phosphate. Phosphorus is essential for root development, energy transfer, and overall plant growth. Therefore, phosphorus is provided by chemical fertilizers.

3. Potassium (K): Chemical fertilizers also include potassium compounds like potassium chloride or potassium sulfate. Potassium is necessary for various plant functions, including water regulation, enzyme activation, and disease resistance. Therefore, potassium is provided by chemical fertilizers.

Based on the information above, we can conclude that all three nutrients (nitrogen, phosphorus, and potassium) are typically provided to the soil by chemical fertilizers. Therefore, none of the options listed is not provided by a chemical fertilizer.