Biotika April 2025
by Podkovyrov I.Y., Doctor of Agricultural Sciences, Associate Professor, Smirnov A.R., PhD student, Kravchenko E., Undergraduate student (Volgograd State Agricultural University, Volgograd, Russia)
Chestnut soils are common in the zone of intensive agriculture. Over a long period of their development, significant transformations have occurred in their properties, which is associated with the evolution of technology, the intensity of development, the use of land reclamation and climate change. The soils cultivated as a result of agricultural activity differ significantly in agrochemical properties from natural ones. The anthropogenic factor, while observing soil protection measures, has a positive effect on the agrochemical state of soils. Trends in increasing the uniformity of the soil cover and reducing the content of easily soluble salts in the arable horizon have been identified.
The region of chestnut soil distribution is strategically important for the development of intensive agricultural production. Despite the difficult soil and climatic conditions, obtaining stable yields is largely determined by soil fertility. The natural resource potential of chestnut soils remains insufficiently studied due to the peculiarities of soil formation and economic activity. Land reclamation significantly changes the agrochemical characteristics of the soil [1]. An example of this is the revealed changes in the Aral Sea area [2].
The generally accepted methods used are mainly aimed at determining agrochemical parameters in the content of nutrients and salts toxic to plants. Modeling makes it possible to predict changes in properties [3]. However, they do not provide a complete objective description of soil fertility, as they do not reflect the broad possibilities of providing crops with nutrition, moisture, and nutrients.
The aim was to study the agrochemical properties of chestnut soils in the territory developed for the cultivation of garden crops for a period of more than 40 years.
The object of the study is represented by the agro-industrial enterprise JSC "Gardens of the Pridonie" located in the Gorodishchensk district of the Volgograd region. Monitoring sites have been selected for the study. Coordinates of the center (block): 49.066114, 44.038542. According to the agro-climatic zoning, the study area belongs to a very warm, arid area. The lowest air temperatures are recorded in January -28.6 °C. The warmest months are July and August with average monthly temperatures of 24.2 °C and 21.3 °C, respectively. The average annual air temperature is 7.6 °C. The absolute maximum temperature reaches 43°C in August, the absolute minimum -40° starting in January, respectively. The annual precipitation is 385 mm. The greatest amount of precipitation falls during the warm period (June, July, and August) up to 118 mm.
Most of the territory is located within the East Don Range on the hills bounded from the north, east and south by the Don Range. The territory is hilly, hilly-flat, heavily indented by gullies and ravines. The separation of the territory by ravines and ravines is about 3 km2. The territory of the district is located in a zone of typical light chestnut soils. There are also soil complexes with meadow subtypes of chestnut soils and chestnut solonets. Most of the natural chestnut soils and their complexes have been transformed into agricultural soils under the influence of agricultural activity. Various agro-cane soils and agro-salt deposits have become widespread in the area.
Agrochemical studies on a set of indicators were performed in the laboratory of the Volgogradsky Agrochemical Service Center according to the methods established by regulatory documents: namely GOST 26107-84, GOST R 54650-2011, GOST 26490-85, GOST 26428-85, GOST 26484-85.
Laboratory analysis of soil samples from the site showed the following element content (Table 1). The content of mobile potassium in the soil varies significantly from 189.0 to 2490.0 mg/kg.
To assess the degree of availability of exchangeable potassium in the arable horizon of chestnut soil, a scale consisting of six classes (according to Machigin) was used:
- I – less than 100 mg/kg – very low;
- II – 101-200 mg/kg – low;
- III – 201-300 mg/kg – average;
- IV – 301-400 mg/kg – increased;
- V – 401-600 mg/kg – high;
- VI – more than 600 mg/kg – very high.
The site is marked:
- relatively low content on the soil site of 18;
- average content at soil sites 9 and 19;
- increased potassium content at control points 1, 3, 11, 14, 16, 20;
- high potassium content at control points 2, 4, 5, 6, 15, 17;
- very high potassium content at control points 7, 8, 10, 13.
Low values of the coefficient of variation in the potassium content in the soil were obtained – 30.49%, which is associated with cultivation, equalization of fertility through agrotechnical measures and land reclamation (irrigation).
The availability of exchangeable potassium in the soil is very high. Territories with a very high and high content of this element occupy more than half of the total surveyed area. The sites with medium and high potassium content are located locally and occupy small areas of about 500 hectares. There was also a multiple excess of the standard potassium content in two sites (at soil sites 8 and 10), which is also local in nature due to the complexity of soil differences. A low content of exchangeable potassium was found only in the site with the number 18.
The availability of mobile phosphorus in the soil is at a high level (on average, 115.15 mg/kg). The quantitative characteristics ranged from 23 to 731 mg/kg.
To assess the degree of availability of mobile phosphorus in the arable horizon of chestnut soil, a scale consisting of six classes (according to Machigin) was used:
- I – less than 10 mg/kg – very low;
- II – 11-15 mg/kg – low;
- III – 16-30 mg/kg – average;
- IV – 31-45 mg/kg – increased;
- V – 46-60 mg/kg – high;
- VI – more than 60 mg/kg – very high.
The survey results showed that a very high content of mobile phosphorus was detected on the soil sites. 2, 5, 4, 7, 8, 10, 11, 12, 13, 14, 17 and 20. A high content of this element was detected at soil sites 3, 6 and 16, and an increased one at site 18. Sites 1, 9, and 19 differ in the average content of phosphorus compounds.
The coefficient of variation in phosphorus content is quite high – 53.6%, which is associated with the low mobility of this element and local introduction into the soil during crop cultivation.
In general, high concentrations of mobile forms of phosphorus and potassium are characteristic of chestnut soils. These elements remained in the soil-forming rocks formed by the marine sediments of the ancient sea. Currently, they are involved in the biological cycle of matter by the activities of microorganisms, animals and plants. In the surveyed areas, there is no intensive crop production in modern conditions, leading to the removal of nutrients. The use of land for growing grain crops and haymaking leads to the assimilation of potassium and phosphorus compounds in the upper soil horizon. These compounds bind and are retained in soil complexes, which, in the absence of their systematic removal with the harvest, leads to accumulation.
Also, the accumulation of these compounds occurs as a result of regularly occurring landscape fires, leading to the salinization of vegetation on the soil surface and the conversion of organic compounds of phosphorus and potassium into mineral salts. These processes led to an increase in the content of mobile forms of phosphorus and potassium in the soils in the surveyed areas.
To assess the degree of availability of the arable horizon of chestnut soil with silk hydrolyzable nitrogen, a scale consisting of four classes (according to Cornfield) was used:
- I – less than 100 mg/kg – very low;
- II – 101-150 mg/kg – low;
- III – 151-200 mg/kg – average;
- IV – more than 200 mg/ kg – elevated.
The average content of alkaline hydrolyzable nitrogen in the selected samples was 15.5 mg/kg. At six sites (extremely low amount of nitrogen compounds was noted, less sensitivity of the detected equipment). In general, the nitrogen content is estimated to be very low (less than 10 mg/kg). Only in section 10 is the content of this element low (109.0 mg/kg). The remaining area has values ranging from 2.9 to 17.0 mg/kg. The availability of the arable soil horizon is generally very low in all surveyed areas.
A very low content of alkaline hydrolyzable nitrogen is a characteristic feature of light chestnut soils. These compounds are very mobile in the environment, are chemically active and quickly change from one form to another, washed out by precipitation. However, these compounds are derivatives of nitric and nitrous acids. They bind rapidly in soils that have an alkaline reaction to water-insoluble forms. The time of their existence in the environment is very short. This is confirmed by the results of laboratory soil analysis.
The hydrogen index of the pH water extraction allowed us to assess the degree of soil alkalinization. The average value for the site is 8.14. The pH of the arable horizon in the surveyed areas was fairly stable and varied between 8.0-8.2. A universal scale was used to assess the degree of soil alkalinity:
- pH less than 4.5 – strongly acidic;
- pH 4.6-5.0 – medium acid;
- pH 5.1-5.5 – slightly acidic;
- pH 5.6-6.0 – close to neutral;
- pH 6.1-7.0 – neutral;
- pH 7.1-10.5 – slightly alkaline;
- pH over 10.6 is highly alkaline.
According to the degree of alkalinity, soils are slightly alkaline, which is typical for light chestnut soils. The analysis showed a high degree of uniformity in this indicator. The coefficient of variation is 0.81%.
To assess the degree of availability of organic matter, the following scale was used for medium-loamy and heavy-loamy light chestnut soils:
- Up to 1.0% - less than the minimum content;
- 1.0-1.7 % - slightly humic;
- 1.8-2.5% - medium-low;
- More than 2.6% are highly humorous.
Laboratory analysis of the selected soil samples showed an organic matter content in the range of 0.7-1.2%. The average value within the area is 0.88%. Such soils are classified as slightly humic. Their supply of organic matter is very low. This is due to the predominance of the mineralization of organic residues in the arable horizon over the accumulation process. The coefficient of variation of the organic matter content is not high and amounted to 25.56%, which is due to the equally directed process of its transformation in the soil.
The main source of soil organic matter is plant residues formed when the surface is blackened by steppe plant communities. In the surveyed areas, the total projected grass cover is very low (in the range of 30-60%). The biomass formed by the herbage is used for animal feed and does not enter the soil. This led to a very low organic matter content in the arable horizon. In the fields of grain cultivation, only stubble and roots, which make up only 30% of the resulting organic matter, also enter the soil from plant residues. The rest is taken out with the harvest.
Depletion of the soil with nitrogen and organic matter was revealed in all the surveyed sites, which sharply reduces its fertility against the background of a high level of phosphorus and potassium supply. This should be taken into account when developing fertilizer systems for cultivated crops. Favorable soil conditions are considered to be conditions in which the soil contains the available nutrients necessary for the growth and development of cultivated plants, has a loose structure, and the required temperature and humidity are 60-80% of the total moisture capacity (OST 56-93-87).
The arable horizon contains very little humus, which is natural for heavy soils. When developing and performing crop rotations, it is necessary to provide the arable horizon with organic residues. The low content of macronutrients in the soil must be replenished by applying mineral fertilizers.
Studies have shown that a low coefficient of variation was detected in the content of potassium compounds (30.49%), organic matter (25.56%) and the hydrogen index of the aqueous extract (0.81%). The high level of phosphorus variability (53.60%) in chestnut soils is associated with the low mobility of its compounds and the formation of stable complexes that do not align with the chemical gradient. This is due to both the natural factor and the inefficient use of fertilizers, which plants do not fully assimilate. At the same time, the availability of organic matter and mobile forms of nitrogen remains low (in some cases below the limit of determination of devices), which is associated with insufficient intake into the soil and rapid assimilation by organisms.
Original paper, i.e. Figures, Tables, References, and Authors' Contacts available at http://journal-biotika.com/current-issues/2025-02/article_01.pdf