Soil organic matter: the quiet multiplier

Soil organic matter holds water, holds nutrients in a form roots can reach, keeps soil structure open so roots and air can move, and feeds the microbial life that makes nutrients available. Two fields given identical fertiliser can return very different yields for this reason alone.

Continuous cropping with only chemical fertiliser gradually draws organic matter down. The first sign is usually physical rather than nutritional: the soil crusts after rain, water stands or runs off instead of soaking in, and the crop shows stress sooner in a dry spell.

Rebuilding it is slow but not complicated. Return crop residue rather than burning it, use farmyard manure, compost, PROM and bio-organic inputs where you can, and keep a legume in the rotation. Green manuring in the summer gap is one of the cheapest interventions available to most farmers.

This is long-term work — measured in seasons, not weeks. But it is the one investment that raises the return on every other input you buy, season after season.