Why does soil acidity matter to crop productivity?

Acidity has the following effects on soil: It decreases the availability of plant nutrients, such as phosphorus and molybdenum, and increases the availability of some elements to toxic levels, particularly aluminium and manganese. Essential plant nutrients can also be leached below the rooting zone.

Wallace MukokaWallace Mukoka January 06 · 2 min read
Why does soil acidity matter to crop productivity?
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Toxicity to crop: as the pH decreases below 5.5, the availability of aluminum and manganese increase and may reach a point of toxicity to the plant. Excess aluminium ions in the soil solution interfere with root growth and function, as well as restricting plant uptake of certain nutrients.

Effect on phosphorus availability Acid soils cause phosphorus to form insoluble compounds with aluminium and iron. Liming of soils with low pH dissolves these insoluble compounds and allows phosphorus to be more available for plant uptake.

Micronutrient availability Acidic soils affect the availability of micronutrients in the soil and ultimately general crop development and productivity.

Soil organisms Some micro-organisms e.g. important bacteria and fungi in the soil associated with nitrification require a certain soil pH level to function efficiently in acidic soils (low pH).

Soil physical condition Liming improve soil physical structure by reducing soil crusting/capping and this promotes better emergence of small-seeded crops and ultimately result in better crop stands. Remember population stand is key in attaining higher yields generally in all crops.

When is the right time to lime?

Lime should be applied at least 3 to 6 months before crop establishment since it takes a significant amount of time for lime to dissolve and react with the soil to cause the desired adjustments in ph. In other words, a week after harvesting is the best time to apply lime.

However, farmers should note that, application of lime can still be done even during crop establishment and the lime can act as a 'buffer' which works as a conduit for nutrient uptake from soil to crop through the roots and adjust the pH during the later stages of the crop cycle.

Frequency of subsequent liming should be determined by soil tests.

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