Necessity of foliar top dressing and practical methods for measuring Ph soil

Always recommending one or another technology for replenishing field crops, in addition to the biological characteristics of the crop itself, the pH of the soil is equally important. Because it largely determines the availability of macro- and microelements for plants.

ph 1

Actually, the pH itself is a negative logarithm of the concentration in the soil solution of hydrogen (H +) ions. The reaction of the soil solution, first of all, depends on the parent (Ground-forming) rock, on which the soil was formed, and further and from other factors – climate, vegetation, economic activity and the like.

According to the indices of acidity, soils are divided into classes:

pH 3.0-4.0. The strong acid reaction of the soil environment is characteristic of strongly podzolic, brown mountain-forest and marsh soils. Availability of phosphorus is reduced. Iron, aluminum and manganese are mobile and affect most plants toxicly, that is, these elements inhibit the absorption by plants of phosphorus, calcium, potassium, iron, sodium and boron, as the permeability of the protoplasm of the root cells decreases. The activity of bacteria is suppressed, so in such soils a low content of nitrogen also shows an increased activity of low fungi. Soils with such pH can be rationally used for crops that grow well on acidic soils.

pH 4.0-5.0. The medium- acid reaction of the medium is characteristic of sod-podzolic, boggy and brown mountain-forest soils. The state of phosphorus, iron, aluminum, manganese, calcium, potassium, boron, cobalt compounds is similar to that for very strongly acidic soils. Reduced microbiological activity, activated mushroom. Soils with such a pH in loamy and clay granulometric composition (characteristic mainly for the western regions) tend to compact.

pH 5.0-6.0. Weak acid reaction of the medium, characteristic of gray forest, Viluguvani and podzolized chernozems. Phosphorus is in an accessible state, the toxicity of aluminum and manganese is reduced or absent, the deficiency of sulfur, calcium, potassium, boron, cobalt is low. Nutritional conditions close to optimal. They are inclined to small compaction, they observe an increased level of vital activity of microorganisms.

pH 6.0-7.0. Neutral reactions of the medium, typical for chernozem soils. They have a favorable level of fertility, optimal conditions for nitrogen, phosphorus, potassium and microelement, excellent soil structure, intensive microbiological activity.

pH 7.0-8.0. Weak alkaline reactions of the medium. Characteristic for southern chernozems, carbonate soils. Phosphorus, iron, zinc and manganese can be in short supply. There is an easy antagonism (competition) between the supply of phosphorus, zinc and copper. With the systematic use of phosphorus fertilizers, zinc and copper deficiency occur. Microbiological activity, nitrogen supply conditions are good.

pH 8.0-9.0. Medium alkaline soil reactions . An elevated pH is characteristic of the parent rocks of many chernozems and chestnut soils. Such a reaction is not harmful to the growth and development of most field or vegetable crops, but is unfavorable for fruit trees, especially apple and sweet cherry. In alkaline conditions with a pH above 8.5, there is a shortage of nitrogen and phosphorus, an excess of readily soluble salts, a lack of trace elements such as iron, manganese, copper and zinc.

pH more than 9.0. The strongly alkaline reactions of the soil solution, characteristic of solonetzes, soda solonchaks. The availability of phosphorus is reduced, iron and manganese are in short supply, an excess of boron is possible. It is characterized by very unfavorable properties: unstructured, high viscosity and stickiness in the wet state, high hardness in the dry state, low water permeability, suppressed microbiological activity.

Optimal soil solution pH ranges for basic crops

Agricultural Plants

Optimum solution pH range

Wheat (spring and winter)


Corn, peas



6.0 – 6.8


5,0 6 5



Sugar beet



6.5 -7 1

Nitrogen-fixing bacteria, fungi



Nodule bacteria


So from the foregoing it becomes clear that a micronutrient deficiency can occur in unfavorable soil-climatic conditions. On light sandy soils, the washing of boron and magnesium can be observed. Copper is inaccessible to peat. In alkaline soil, the availability of most microelements (Zn, Cu, B, Mn, Fe) is limited. Acidic medium is a serious barrier to absorption by plants N, P, K, Mg. The most effective way to eliminate micronutrient deficiencies is foliar top dressing, fertilizers in which trace elements are in chelate form.

Methods for determining pH

Several methods are widely used to determine the pH value. The hydrogen index can be estimated approximately by means of indicators, accurately measured with a pH meter or determined analytically by conducting an acid-base titration.

Universal indicator

To extend the working interval for pH measurement, a so-called universal indicator is used, which is a mixture of several indicators. The universal indicator successively changes the color from red through yellow, green, blue to violet when changing from the acidic region to the main one.

Solutions of such mixtures – “universal indicators” are usually impregnated with strips of “indicator paper”, with the help of which it is possible to determine the acidity of the aqueous solutions under study with an accuracy of one pH.

This method involves the preparation of an aqueous extract from the soil.

ph 2

The analytical volumetric method

The analytical volumetric method – Acidimetry – also gives accurate results of determining the acidity of solutions. A solution of a known concentration (titrant) is added dropwise to the test solution. When they mix, the chemical reaction proceeds. Equivalence point – the moment when the titrant is exactly enough to completely complete the reaction, is fixed by means of an indicator. Further, knowing the concentration and volume of the added titrant solution, the acidity of the solution is calculated.

This method is carried out in laboratories.

ph 3


Using a special instrument – pH meter – allows you to measure pH over a wider range and more accurately (up to 0.01 pH units) than with universal indicators. The method is convenient and highly accurate, especially after calibration of the indicator electrode in the selected pH range. Allows you to measure pH directly in the ground without first preparing the water extract, which greatly facilitates and speeds up the work.

ph 4


The most accurate and convenient method for determining the acidity of soil in the field is the pH meter. To date, the choice of Ph-meters is very large, the most accurate instrument will be the one with a glass pH electrode-constructively, this electrode is a glass cylinder in the middle of which there is a chloride-electrodes electrode and segregations with 0.1 M HCl solution. It is also good when a standard temperature sensor is included in the device, the use of which allows automatic temperature compensation.

Agronomist-consultant of the
department of microfertilizers
Ivan Valerievich Gordienko