Test soil before you buy another bag

Plants need a short list of essential elements. The limiting one sets growth. Adding the nutrient that is already adequate does not fix the one that is short — and can make uptake worse.

Sample the way the lab asks. Use plastic or wood tools if the lab warns about metal contamination. Stay with one lab so years can be compared. Organic matter, pH, and salts belong on the same slip as NPK.

Harvest removes nutrients. Returning residues and compost is how fields stay in the game. The test tells you what walked off.

If the same yellowing returns after every bag, test before you double the rate.

In this series

• Test soil before you buy another bag
• Irrigation is nutrient management
• pH can lock nutrients that are already in the soil
• Leaf colour is a clue, not a diagnosis
• Microbes and root fungi deliver what a bag cannot
• Return what you harvest so fertility does not walk off the field