When fertilisation doesn’t work, is it the pH?
Often, despite the correct application of fertilisers, crops show signs of slowing down, such as delayed growth, yellowing of leaves or reduced production. In such cases, the problem is not necessarily due to a lack of nutrients, but to the reduced ability of the plant to absorb them, which is directly affected by soil pH.
What is pH and how it affects nutrition
The pH determines the acidity or alkalinity of the soil. A value of 7 is considered neutral. Values below 7 indicate acidic soil, while values above 7 indicate alkaline soil. Most crops thrive at a pH of 6-7,5. Outside this range, many essential elements (iron, manganese, phosphorus, zinc) are bound and unavailable to the plant, regardless of soil content.
Practical implications in the field
In alkaline soils (pH >7.5), the uptake of iron, manganese, zinc and phosphorus is limited. The plant shows symptoms of chlorosis and reduced growth, even if these elements are present in sufficient quantities.
In acidic soils (pH <5.5), the availability of calcium and magnesium is limited, while the toxicity of aluminium increases. The plant shows leaf drying, reduced rooting and general wilting.
In addition, pH affects nitrogen stability, with nitrate being less absorbed or more easily leached in acidic environments.
Effect on microbial activity
pH also plays a key role in the biological activity of the soil. Strongly acidic or alkaline environments limit the activity of beneficial micro-organisms, reducing the decomposition of organic matter and the release of nutrients.
Measurement methods and indicative periods
pH can be measured by simple soil analysis or with portable devices (pH meters, strips). Ideally, the measurement is carried out:
-before planting,
-when changing cultivation or fertilisation,
-in cases of suspected symptoms of food poisoning.
Accuracy is improved when the measurement is accompanied by a complete nutrient analysis.
What to do when the pH is out of range
In acidic soils: limestone or dolomitic lime is applied. The change is gradual, requires proper integration into the soil and constant monitoring.
In alkaline soils: immediate correction is difficult. The strategy is based on the use of acid-reaction fertilizers (e.g. ammonium sulphate), transbrominated chelating agents and an increase in organic matter. At the same time, phosphate or nitrate fertilisers that further raise the pH are avoided.
A decisive factor for the success of fertilisation
The pH value is a key tool in making good nutritional decisions. Monitoring it allows to prevent problems and optimize fertilizer efficiency. In any case, corrective actions require guidance from an agronomist and rational planning to produce high quality and high yields.
