Soil composition varies depending on where you collect samples, and farming practices can shift that composition significantly. You gather surface samples from three sites — a forest, a conventionally farmed field, and a field treated with compost — and observe structure, color, texture, and earthworm activity in the field. Back in the lab, you dry and sieve each sample, then test pH, nitrogen, phosphorus, and potassium. The forested soil comes out darkest with the most earthworm activity. The conventionally farmed soil is lighter, shows surface crusting, and registers higher nitrogen from added fertilizer. The differences across these three sites map directly onto how farming changes the rock bits, organic matter, and biological life that make up the soil.

Soil nutrients are the food in the dirt — nitrogen, phosphorus, and potassium — that feed plants and support their growth. Farming practices change how much of this food the soil holds. Comparing forest, farm, and compost-treated soils shows that conventional farming raises nitrogen levels through added fertilizer but may reduce overall soil health.