- N (nitrogen) drives leafy growth — key for grass and cereals — and washes out easily.
- P (phosphate) supports roots and establishment.
- K (potash) helps water balance and crop quality.
- Lime corrects acidity. Below the right pH, nutrients are locked up however much you apply — so test the soil first.
The three numbers on a bag (for example 20:10:10) are the percentages of N, P and K. Applications are regulated near watercourses and in some zones, so check the current rules before you spread.