Why test your soil before you fertilise — and how to take a good sample

Many farms fertilise by habit: the same product, the same rate, every season. When yields stall, the reflex is to add more. Without knowing what the soil already has, that can mean paying for nutrients the crop does not need while the real shortage goes uncorrected.

Soil testing is an essential tool for determining soil fertility. Its results are the basis for nutrient recommendations that help make crop production profitable while protecting water quality.^[1]

Common reasons fertiliser gives a poor return, all of which a soil test can reveal:

• Wrong pH. Standard soil tests measure pH. In very acidic soils, nutrient-holding capacity is lowest, and it rises as pH is corrected with lime.^{[2, 3]}
• Low nutrient-holding capacity. Cation exchange capacity (CEC) is how much of the positively charged nutrients — potassium, calcium, magnesium, ammonium — a soil can hold. Clay and organic matter provide it. Sandy, low-organic-matter soils have low CEC and lose nutrients through leaching.^{[3, 4]}
• One nutrient short, others plentiful. Standard test packages report phosphorus, potassium, calcium and magnesium, so you can correct the one that is actually limiting.^[2]
• Too much of a good thing. Excess nitrogen, for example, weakens rice stems, harms the environment and lowers farm profits.^[5]

A soil test is only as good as the sample. Follow these steps:

• Sample each area separately. Divide the farm into areas that look and are managed alike. Avoid unusual spots such as wet patches; if they are large, sample them separately.^[1]
• Take many subsamples. Collect at least 15 to 20 subsamples from each area; more subsamples reduce variation further.^[1]
• Walk a zigzag. Take the subsamples at random in a zigzag pattern across the whole area, each at the same depth and of the same volume.^{[1, 2]}
• Sample to the right depth. For cultivated fields, extension guidance is to sample to plough depth (about six to seven inches, roughly 15–18 cm). For tree crops, ask the lab or your agronomist which depth and position to use.^[1]
• Mix and send. Mix the subsamples well in a clean bucket and send one combined sample per area, clearly labelled.
• Repeat regularly. Extension guidance suggests testing sandy soils every two to three years and clay soils every three to four years.^[2]

In Malaysia, the Department of Agriculture runs a soil fertility advisory service that farmers and agri-entrepreneurs can apply to, and our team can arrange a test and walk you through the results.^[6]

NEXGROW is a bio-organic, phosphate-solubilising fertiliser. It converts insoluble soil phosphorus into forms plants can absorb, and adds organic matter and beneficial microbes to the soil. The official booklet gives rates by crop and age — and for paddy, by soil CEC, which you can only know from a soil test.

See the NEXGROW crop programs for the booklet rates for each crop.

Get a test before planting a new block, before liming, before changing your fertiliser programme, and whenever one part of a field performs worse than the rest. After that, re-test on a regular cycle so you can see whether your programme is moving the soil the right way.^[2]