Soil is made up of solid, gaseous and liquid phases. In the latter, the pH of the soil is measured, since it is the place where the dissolved chemical products make the soil in conditions of acidity or alkalinity. So soil pH is an indicator of the acidity or alkalinity of the soil and is measured in pH units. In more specific terms, pH is the negative logarithm of the hydrogen ion concentration and its measurement scale goes from 0 to 14, considering 7 as the value of neutrality.

Castellanos (2000) mentions that in general, there are four pH intervals that are particularly informative; a pH less than 4.0 indicates the presence of free acids commonly produced by the oxidation of sulfides, a pH below 5.5 strongly suggests the occurrence of exchangeable aluminum and/or excess manganese, a pH between 7.3 to 8.4 indicates the possible presence of CaCO 3 and a pH greater than 8.2 the possible presence of high concentrations of exchangeable sodium. It also indicates as ideal pH a range that goes from 6 to 6.5, since it is where there is a reasonable availability of nutrients.

The pH of a soil will change over time, as it is influenced by factors including parent material, environment, and most importantly, current agronomic practices. The pH condition can even fluctuate during the growing year and significantly affect the growth and development of plants.

How to measure the pH?

The determination of soil pH is suggested to be done in the first 10 cm of soil, this can be done directly in the field through a test kit or portable potentiometers that are very common today for crop nutrition monitoring. Even with the practicality of this equipment, it is always advisable, in terms of greater accuracy, to send the sample to a laboratory for pH determination. In addition to an accurate pH measurement in the laboratory, it is the best way to detect acidity or alkalinity problems and initiate soil management strategies.

PH and nutritional availability

Soil PH sensor affects nutrient availability and how nutrients react with each other. At low pH some elements such as molybdenum, phosphorus, magnesium and calcium become less available to plants. As values cross the acidity range, elements such as aluminum, iron, and manganese may become more available, and aluminum and manganese may reach levels that are toxic to plants. On the contrary, when the pH is greater than 7.5 (calcium chloride), there may be affectations in the availability of phosphorus due to the effect of calcium and micronutrient deficiencies, especially zinc, are frequent. Logically, these changes will affect the growth and development of the plants, and will ultimately affect the final yield of the crop.