Subject and Methods of Agrochemistry
Agrochemistry, or agronomic chemistry, is the science of the interaction of plants, soil, and fertilizers in the cultivation of agricultural crops, of the cycling of chemical substances in agriculture, and of the use of fertilizers to increase yield, improve its quality, and enhance the fertility of the soil, taking into account the bioclimatic potential.
In the course of the development of agrochemistry, the meaning of the concept was constantly refined due to the tasks and the formation of its new functions, which reflects the complex interrelationship of plants, soil, climate, and agrochemical agents. The main task of agrochemistry is to study this interrelationship.
The goal of agrochemistry is to create optimal conditions for plant nutrition, taking into account the properties of types and forms of fertilizers, the characteristics of their interaction with soil, and to determine effective forms, methods, and timing of fertilizer use.
Subject of Agrochemistry
D. N. Pryanishnikov called the task of agrochemistry the study of the cycling of substances in agriculture and the identification of ways to influence the chemical processes occurring in soil and plants that affect yield and its quality.
Fertilizers create an optimal nutritional regime and purposefully regulate the metabolism of organic and mineral compounds, thereby making it possible to realize the potential productivity of plants. In turn, fertilizers are affected by plants; for example, plants can convert sparingly soluble forms into available ones, and the selective absorption capacity with respect to individual elements creates the physiological acidity or alkalinity of mineral fertilizers.
Agrochemical agents affect the chemical and physical properties of soil and the activity and direction of microbiological processes, while at the same time they themselves change under the influence of soil properties. Exchange reactions occurring in soil between the cations of mineral fertilizer salts and the soil absorption complex can lead to negative or positive results.
Scheme of relationships between plants, soil, and fertilizers as the essence of the subject of agrochemistry (according to D. N. Pryanishnikov):
D. N. Pryanishnikov showed the interrelationship between three interacting factors: soil, plant, and fertilizer in a simple scheme reflecting the essence of agrochemistry. The task of agrochemistry is to create optimal conditions with the help of fertilizers for plant nutrition. The same approach should be taken with respect to soil. By satisfying the biological requirements of plants, it is possible to realize the potential productivity of plants.
K. K. Gedroits noted that yield is determined by three factors: climate, soil, and the plant itself. Climate is difficult to change, but its effect can be mitigated by improving soil properties. By changing soil properties, the farmer can to a certain extent regulate the impact of climatic conditions on plants. K. K. Gedroits considered the effect of fertilizers indirectly, through changes in soil properties.
The development of theoretical principles of the quantitative and qualitative formation of cultivated plant production necessitated the introduction of bioclimatic potential into the concept of agrochemistry. The theory of obtaining programmed yields has been developed and is successfully applied; static models of soil fertility based on agrochemical and agrophysical indicators have been created and are being improved, taking into account the yield level of individual crops and the productivity of specialized crop rotations as a whole. Work is underway on modeling production processes for certain agricultural crops, the implementation of which will make it possible to achieve maximum high yields.
The dialectical interrelationship of the soil–climate–fertilizer–plant system in the modern understanding of the essence of the subject of agrochemistry:
Numerous experiments with fertilizers in various climatic zones of the country make it possible to a certain extent to take climate into account as one of the factors in the climate–plant system.
In the State Standard of 1983, climate was taken into account in the definition of the concept of “agrochemistry”: Agrochemistry is the science of the interaction of fertilizers, soil, plants, and climate, the cycling of substances in agriculture, and the rational use of fertilizers
(Resolution of the USSR State Committee for Standards of July 13, 1983, No. 3110).
Underestimation of climatic features in relation to a specific agricultural region can lead to errors in determining the value of mineral fertilizers.
Tasks of Agrochemistry
Cycling of substances in agriculture:
At the present stage of development, agrochemistry solves the task of studying the properties of various types of organic and mineral fertilizers and their influence on:
- the cycling and balance of nutrients in agriculture;
- soil properties and reproduction of fertility;
- plant nutrition and the metabolism of organic and mineral substances during vegetation;
- the biological activity of soil and its biodiversity;
- the formation of yield and product quality;
- the agroecological functions of agrochemistry in the soil–plant system;
- the economic and energy indicators of the efficiency of agrochemical agents.
The task of the modern agrochemist is reduced to determining the precise parameters of the cycling of biogenic elements, taking into account specific agroclimatic conditions and the specificity of agricultural plants and their varieties at given levels of productivity.
Methods of Agrochemistry
Laboratory Methods
Among the methods of agrochemistry, laboratory methods are of particular importance: chemical and physicochemical methods for analyzing plants, soils, and fertilizers. The creation of modern high-precision instruments for various methods of analytical chemistry has significantly expanded the range of possibilities in agrochemistry.
Among the methods of analytical chemistry, the following are widely used in agrochemistry:
- photometry;
- chromatography;
- spectroscopy;
- atomic absorption spectrophotometry;
- X-ray fluorescence;
- neutron activation analysis;
- mass spectrometry.
Methods of stable and radioactive isotopes are used to study metabolism in plants. High-performance modern analytical equipment and computers make it possible to process a large volume of routine analysis results. Portable measuring instruments make it possible to conduct rapid analyses directly in the field, quickly determine the content of chemical substances in plants or soil and soil properties, for example, acidity, and promptly adjust fertilizer application rates.
In recent decades, comprehensive soil–plant diagnostics of plant nutrition and fertilizer application has begun to be used, consisting of laboratory analysis of soil to determine optimal rates of applying the main fertilizer and subsequent correction of doses in top dressing during vegetation after analyzing plants in the field.
Physiological and Agrochemical Methods
Physiological and agrochemical methods include vegetation and lysimetric methods. In vegetation methods, experiments are conducted in special vessels placed in pavilions or greenhouses. In lysimetric methods, studies are carried out in large vessels, for example, with a volume of 1 m3, with walls isolated vertically to create conditions close to natural.
The lysimetric method has found wide application in research institutions around the world. With its help, the processes of migration and transformation of nutrients, changes in soil properties over time, balance experiments, as well as metabolism in plants and the formation of product quality are studied.
In practice, vegetation and lysimetric methods are often used in combination with each other. Physiological and agrochemical methods include experiments in phytotrons, in which all indicators of the plant production process are controlled and regulated: water supply, root nutrition, intensity and quality of light, temperature regime, photosynthesis, gas exchange, etc. These studies are conducted with full automation of processes and recording of parameters of plant growth and development. These methods are the most accurate and make it possible to reveal the process of metabolism with the participation of all factors of plant life, determine the potential productivity of plants and ways to realize it for a specific genotype, and create a dynamic model of the production process. Phytotrons are also used in breeding and genetic research. Phytotrons are used, as a rule, in large research institutions and higher educational institutions.
Field Experiments
Field experiment is an experiment conducted under field conditions to determine the effectiveness of fertilizers on the yield of agricultural crops, its quality, and soil fertility.
Small-plot experiments are carried out for deep, more often exploratory, experiments. As a rule, they combine vegetation and lysimetric experiments, but under conditions identical or close to natural. In small-plot experiments, labeled atom methods can be used; models of highly fertile soils are created and tested; types and forms of fertilizers and their combinations, including with other chemical agents or microbiological preparations, are tested. Small-plot experiments are conducted on plots with an area of up to 10 m2.
In short-term field experiments, the effect of fertilizers on yield and product quality is studied for at least three years under specific soil conditions. Data from the Geographical Network of Experiments in Russia are widely used to determine the need for different types and forms of mineral fertilizers in the zonal aspect, as well as to determine the country’s needs for mineral fertilizers.
Small-plot and short-term field experiments are also used to improve methods of comprehensive soil and plant diagnostics of plant nutrition and fertilizer application.
Stationary experiment is a field experiment with systematic application of fertilizers, which is conducted on one plot, in a crop rotation, in a link of a crop rotation, or under continuous cropping.
Long-term field experiment is a stationary experiment conducted over several rotations of a crop rotation. Long-term stationary experiments make it possible to obtain information for assessing the effectiveness of various fertilizer systems in crop rotations; the level of saturation of crop rotations with fertilizers; the optimal distribution of organic and mineral fertilizers among crops of the crop rotation and fertilizer forms. These experiments are the basis for developing static models of soil fertility, studying the patterns of changes in fertility and product quality during long-term use of fertilizers, conducting balance studies, migration of nutrient elements along the soil profile, and accumulation of ballast toxic elements, including heavy metals and agrochemical agents, that is, for solving environmental problems of agrochemistry. The experiments are set up under conditions close to production conditions.
Production experiments with fertilizers are conducted under production conditions to verify recommended application rates and to provide an economic assessment of fertilizers. They are short-term in nature and are intended for testing and refining scientific recommendations under production and specific soil-climatic conditions. The results of these experiments are of great importance in introducing and substantiating the effectiveness of a complex of agricultural chemicalization practices.
Relationship of Agrochemistry with Other Sciences
The content of agrochemistry as a science can be represented by three sections:
- plant chemistry;
- soil chemistry;
- fertilizer chemistry.
Plant chemistry is a section of plant physiology, soil chemistry is a section of soil science, and at the same time they are an integral part of agrochemistry. Fertilizer chemistry is fully part of agrochemistry. Scientific research in this section is conducted in combination with soil chemistry, plant physiology, and agriculture.
Agrochemistry cannot be considered separately from soil science, plant physiology, agriculture, and soil microbiology.
Agrochemistry emerged as an independent discipline due to theoretical and practical expediency.
The range of agrochemical research is very broad. It includes the study of the transformation of nutrients in soil and metabolism in plants, optimization of plant nutrition, reproduction of soil fertility, fertilizer application for planned yields, and regulation of product quality.
Relationship of Agrochemistry with Fundamental Sciences
Relationship of agrochemistry with fundamental sciences:
The relationship of agrochemistry with soil science lies in the fact that the effectiveness of fertilizers is determined by the chemical, physical, and physicochemical properties of soil and its biological activity, which in turn are related to the content and mobility of nutrients in soil. The interrelationship of soil properties and fertilizers is manifested in the processes of mobilization, immobilization, transformation, and migration of nutrients, which are influenced by plants of the agrocenosis.
The effectiveness and payback of fertilizers depend on the cultivation level of soils, humus content, absorption capacity, buffering capacity, and reaction of the medium. Therefore, the task of agrochemistry is to study the properties and fertility of soil, the balance of nutrients in the agrocenosis, and methods of regulating and reproducing soil fertility.
The relationship of agrochemistry with plant physiology is manifested in the influence of nutrients on all vital processes of the plant, which ensures the formation of product quality indicators. Such agrochemical practices as root and foliar top dressing make it possible to regulate plant nutrition, purposefully optimizing the conditions for active growth and development and the formation of a larger yield of better quality. Based on knowledge of the patterns of plant nutrition during vegetation, methods of plant diagnostics of crop supply with nutrients have been developed.
Many sections of agrochemistry are connected with soil biology and microbiology. Thus, the state and regulation of the nitrogen regime in agrocenoses is a task of agrochemistry, the successful solution of which is possible with a correct assessment of biological sources of nitrogen in the soil–plant system: symbiotic and associative nitrogen fixation or free-living microorganisms. The activity of these processes is determined by a correct fertilizer system. The same applies to the processes of humification and mineralization of humus and to phosphorus nutrition of plants.
The growing role of ecological aspects of agriculture links agrochemistry with ecology. For example, technogenic pollution of agrocenoses with heavy metals, radionuclides, and agrochemicals necessitates the development of a complex of agrochemical agents and practices aimed at reducing the entry of pollutants into plants and trophic chains.
Ecological assessment is especially necessary when using non-traditional types of fertilizers—industrial and municipal waste—and when using local organic and mineral raw materials as fertilizers.
Ecological functions of agrochemistry:
- maintenance of the biological cycling of substances;
- preservation of biodiversity and improvement of soil microbiocenosis;
- immobilization of toxic substances;
- preservation of soil biological activity;
- activation of the nitrogen-fixing capacity of soil;
- prevention of eutrophication of natural waters.
The creation of optimal cultivated agricultural landscapes in different natural zones is possible with the help of agrochemical agents. By applying fertilizers in a complex of landscape-adapted agriculture, humans create a cultivated agricultural landscape with an optimal geochemical regime, which is the best in hygienic terms and meets human living conditions.
The ecological function in agricultural landscape farming systems characterizes the relationship of agrochemistry with geochemistry. V. A. Kovda (1984) noted that the behavior of fertilizers in the landscape should be studied using biogeochemical methods—agrogeochemistry. He believed that studying the transformation of fertilizers in all components of the landscape makes it possible to obtain the greatest return from fertilizers with the least negative ecological consequences.
The relationship of agrochemistry with geography is manifested in the geographical patterns of fertilizer action, which in turn are determined by the soil, biological, and climatic conditions of the zones.
The relationship of agrochemistry with meteorology is determined by the dependence of the effectiveness of fertilizers and agrochemical agents on weather and climatic conditions.
Relationship with Applied Sciences
Relationship of agrochemistry with applied fields:
K. A. Timiryazev wrote in 1935 that agriculture became what it is thanks to agronomic chemistry and plant physiology. The relationship of agrochemistry with agriculture lies in the fact that the fertilizer system is the most important link in modern farming systems. Thus, the effectiveness of fertilizers is determined by the presence of mobile forms of nutrients in soil and the state of water and air regimes, which in turn depends on preceding crops and the tillage system. The same applies to the crop rotation system, which determines the application rates and ratios of fertilizers and the distribution of fertilizers and ameliorants among crops of the crop rotation.
The complex of agronomic practices used in cultivating a crop, including fertilizer application, is determined by the biological requirements of the crop, meteorological conditions, soil fertility, and the preceding crop, thereby linking agrochemistry with crop production.
The intensification of agriculture necessitates the comprehensive scientifically substantiated use in progressive cultivation technologies of agrochemical agents based on comprehensive soil–plant diagnostics of plant nutrition, fertilizer application, and chemical plant protection agents. In this case, the payback of mineral fertilizers and plant protection agents, in particular pesticides or herbicides, increases. This reveals the relationship between agrochemistry and plant protection.
The effectiveness of fertilizers under irrigation with an optimal combination of water and nutrient regimes of soils increases sharply. The same applies to the effectiveness of fertilizers when applied on reclaimed drained lands, especially with dual regulation of the water regime. This determines the relationship of agrochemistry with land amelioration.
Importance of Agrochemistry
For expanded reproduction of soil fertility and the creation of an active balance of biogenic macro- and microelements in the soil–plant–fertilizer system, it is important to make maximum use of local fertilizer resources. Particular importance is attached to manure. A well-established and properly organized technology for accumulating, storing, and using manure is an indicator of the culture of agriculture. High rates of chemicalization of agriculture require improvement of mechanization and automation, that is, improvement of transport means for transporting fertilizers; machines for fertilizer mixing and application; equipment for accumulating and storing manure, preparing composts, transporting and applying them.
The effectiveness of fertilizers is assessed primarily by economic indicators. It is possible to implement all practices of chemicalization of agriculture on a farm only by fulfilling a complex of organizational, economic, and farm measures with the appropriate material and technical base.
The results of the integrated use of all factors of agriculture can be represented by the example of the growth of wheat yields in Western European countries over the past 200 years.
In the Middle Ages, when the three-field farming system predominated, the average wheat yield was 0.7–0.8 t/ha. The introduction of crop rotation with clover made it possible to double yields. The Norfolk four-field crop rotation, which first developed in England in the 18th century, was typical of that time. The doubling of yields was achieved through biological nitrogen fixed by nodule bacteria on clover roots.
At the beginning of the 20th century, the doubling of wheat yields in Western Europe was associated with the widespread use of mineral fertilizers. In recent years, the dynamic growth of yields of cereal crops, reaching 5–6 t/ha and higher, is explained by a high culture of agriculture and the use of a scientifically substantiated fertilizer system based on soil and plant diagnostics, as well as crop rotation. An integrated plant protection system and achievements in breeding high-yielding crop varieties play a positive role.
Thus, by using a complex of agricultural practices in progressive crop cultivation technologies, the realization of their potential productivity is achieved. At the same time, there is a direct relationship between the level of fertilizer use and the yields of cereal crops.
The possibility of obtaining high grain yields of up to 7–8 t/ha under various soil-climatic conditions of Russia is confirmed by experimental production institutions, provided there is an optimal scientifically substantiated combination of all links of agriculture.
Taking into account the role of mineral fertilizers in increasing the productivity of Russian agriculture, in the second half of the 20th century measures were taken to increase their production and use.
Table. Dynamics of mineral fertilizer application (supply) in the Russian Federation.
| Years | Thousand t in terms of 100% nutrients | kg per 1 ha of arable land |
|---|---|---|
| 1965 | 2608 | 19,7 |
| 1970 | 4317 | 32,9 |
| 1975 | 7869 | 59,9 |
| 1980 | 8914 | 67,5 |
| 1985 | 12677 | 96,0 |
| 1986-1990 | 12800 | 99,0 |
| 1999 | 1200 | 10,0 |
| 2006 | 1510 | 27,0 |
| 2011 | 1970 | 38,0 |
Measures were taken to increase livestock numbers, which made it possible to increase the production and use of organic fertilizers.
Attention was paid to chemical amelioration of soils, in particular liming.
For example, the Ministry of Agriculture of the Republic of Kazakhstan has presented data on the use of mineral fertilizers.
In Belarus, in the period from 2006 to 2013, 250–313 kg/ha of a.i. of mineral fertilizers were used, or 1.3–1.5 million t of a.i. for all agricultural lands. In the near future, the technological need for mineral fertilizers for the planned productivity of arable land in the republic as a whole is 1939.1 thousand t of a.i., of which nitrogen fertilizers are 753.3 thousand t of a.i., phosphorus fertilizers 325.0 thousand t of a.i., and potassium fertilizers 860.8 thousand t of a.i.. Subsequently, as soil reserves of phosphorus and potassium increase, the need for these fertilizers may decrease to the level of removal of these elements with the planned crop yield, while the need for nitrogen fertilizers will remain.
In the 21st century, Russia and the CIS countries faced the need to raise agricultural productivity and achieve food independence. Based on the experience of countries worldwide, this goal can be achieved provided that agriculture is fully supplied with mineral fertilizers in the required volume and range, combined with the widespread use of all types of organic and local fertilizer resources, phosphorite application, and liming of acid soils.
Table. Use of mineral fertilizers in the Republic of Kazakhstan (according to the Ministry of Agriculture of Kazakhstan).
| Years | Fertilizers applied (NPK), thousand t | Applied kg a.i. per 1 ha | % fertilized | Fertilized area, thousand ha | |
|---|---|---|---|---|---|
| total | fertilized | ||||
| 1965 | 107,3 | 3,6 | — | 7,0 | — |
| 1986 | 1018,7 | 29,0 | 59,0 | 47,0 | 17253 |
| 1990 | 672,2 | 19,1 | 72,0 | 26,5 | 9332 |
| 2000 | 11,5 | 0,71 | 133,7 | 0,53 | 86 |
| 2005 | 58,5 | 3,17 | 89,4 | 6,23 | 1150 |
| 2010 | 99,4 | 4,14 | 40,2 | 12 | 2472 |
| 2015 | 81,1 | 4,3 | 33,1 | 10,3 | 2453 |
References
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. by B. A. Yagodin. Moscow: Kolos.
- Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. by Mineev V. G. Moscow: D. N. Pryanishnikov VNIIA Publishing House.
