Soil fertility is the ability of soil to meet the needs of cultivated plants by earthly factors of life, is the resultant indicator of the state of soil processes.
In a more expanded sense, soil fertility is the ability of soil to provide optimal factors of plant life, including sufficient nutrients in mobile form and transform them into soil stock and back; to exhibit phytosanitary properties, to be resistant to adverse factors and suitable for the use of modern cultivation technologies.
Soil fertility is not the only factor of crop yield, besides it biological features of plants, climate, agricultural technology, etc. affect crop yield. However, other things being equal, it will determine the productivity of crops.
Soil fertility management, which consists of regulating soil processes to ensure optimal plant life factors in the long term, is a key task of farming.
Modern farming systems pay considerable attention to the ecological aspect. The task of preserving and improving fertility should be solved taking into account the resistance of soils to degradation.
Natural soil fertility
Natural fertility is fertility resulting from the natural soil formation process over a long period of time and is determined by such factors as the granulometric and chemical composition of the soil and climate.
Under conditions of natural fertility, some of the nutrients are inaccessible to plants. In some cases, there is a permanent deficit of some elements, such as nitrogen.
Human impact on soils with natural fertility through its treatment, led to a change in regimes, which affected the provision and availability of plant life factors.
Due to the influence of natural factors and human activities consisting in tillage, use of fertilizers, irrigation, use of crop rotations, etc., effective soil fertility was formed.
Soil fertility indicators
The fertility of even one type of soil is determined by a large set of conditions, such as relief, steepness and exposure of slopes, chemical composition of soil-forming rocks, hydrological regime, etc. Which requires a differentiated approach to their use.
Quantitatively, soil fertility is usually assessed by three types of indicators:
- agrophysical;
- biological (composition and amount of organic matter, biota activity, phytosanitary state);
- agrochemical.
Fertility indicators are in correlation with yield and in most cases are interrelated with each other. Some of them are fundamental, determining the state of all soil processes, for example, granulometric and mineralogical composition, phytosanitary state, others are their derivatives.
Agrophysical indicators of soil fertility
Main article: Soil fertility: Agrophysical indicators of soil fertility
Agrophysical indicators of soil fertility include:
- granulometric composition;
- mineralogical composition;
- soil structure;
- thickness of arable layer.
Agrophysical indicators determine the mechanical properties of the soil, which directly or indirectly affect all factors of plant life and soil conditions.
The most favorable for growth and development of plants are formed on soils of medium granulometric composition.
Optimal soil structure is considered lumpy or granular, consisting of aggregates of 0.25-10 mm, with an optimal ratio of solid phase and total porosity of 50:50 for sod-podzolic soils and 40:60 – for black earth.
The thickness of the tilled layer is the depth of tillage. Increasing tillage depth increases moisture capacity and creates favorable conditions for root system growth and soil microflora activity. However, increasing the depth of tillage leads to a sharp increase in economic and resource costs. Therefore, the optimal thickness of the arable layer is considered 27-30 cm for most soils.
Granulometric and mineral compositions, as a rule, do not change over time, and their reproduction is very difficult. The structure and thickness of the arable layer, on the contrary, indicators that can be reproduced by appropriate agricultural practices.
Agrochemical indicators of soil fertility
Main article: Agrochemistry: Agrochemical indicators of soil fertility
Agrochemical indicators of soil fertility include:
- nitrogen content and availability;
- content and availability of phosphorus;
- content and availability of potassium;
- content and availability of microelements;
- the reaction of the soil environment.
Agrochemical indicators of fertility determine the availability and provision of nutrients required for plant growth and development.
Nutrient content can vary greatly depending on the type of soil and the adopted agricultural technology. For most soils the content of fixed nitrogen ranges from 130 to 350 kg/ha, phosphorus – from 0.01% for poor sandy to 0.20% for highly humus, potassium – up to 2-3% for clay and loamy, on poor sandy its content decreases sharply.
The availability of nutrients is influenced by a number of factors, one of which is the reaction of the soil environment.
The arrival of nutrients in natural conditions proceeds quite slowly due to the processes of nitrogen fixation, receipt with precipitation, dust, groundwater and runoff. In conditions of cultivated lands agrochemical indicators are regulated by the application of fertilizers and ameliorants.
Soil organic matter
Main article: Soil fertility: Soil organic matter
In most cases, the integral indicator of fertility is the content of organic matter and its qualitative state.
The choice of this particular indicator is explained by the functional importance of organic matter in soil-forming processes. The development of soil as a natural-historical body of the planet is the result of a constant process of synthesis and destruction of organic matter, providing a continuous manifestation of the cycle of substances and energy during soil formation. Soil formation process and the development of soil fertility are the key factors of stable and efficient production.
Organic matter has a significant impact on the most important agronomic properties of soil: agrophysical, biological and agrochemical, as well as phytosanitary state.
Increasing the content of organic matter in the soil is a long-term task, which should be based on the real possibilities of reproduction of organic matter of arable soils. Effective implementation of this task is possible with long-term, planned and systematic impact of a set of practical methods.
The optimal content of organic matter is determined by the type of soil, the effect of quantitative yield increase and the cost of reproduction of this indicator.
Biological activity
Biological activity characterizes the intensity of soil biological processes. Useful soil microorganisms take part in the nutrient cycle, secrete enzymes, antibiotics, growth stimulants and other organic substances affecting plant development.
Phytosanitary condition of soil
Main article: Soil fertility: Phytosanitary condition of soil
Phytosanitary state consists in the ability to reduce the effect of phytotoxic substances, microorganisms, phytopathogens and maintain a balance between beneficial and harmful entomofauna, to have a minimum supply of seeds and vegetative organs of weed plants.
Phytosanitary state of the soil is determined by the activity and composition of soil biota, the predominance of which of useful organisms is conditioned by the provision of optimal soil regimes, created by scientifically sound system of industrial activity, adapted to local conditions.
Reproduction of fertility
Cultivation of newly developed soils
Cultivation of soils – improvement of natural properties of soil by means of agro ameliorative measures.
Cultivation of a field – improvement of soil properties of a particular plot using cultural and technical impact on arable land, increasing the size of field contours, leveling, removal of stones, etc.
Cultivation of soils is used for newly developed lands with very low natural fertility, for example on podzolic, solonchak, highly washed away soils, with plowing of unfertilized subsoil horizon. In these cases, there is not reproduction, but creation of fertility. This task is relevant when restoring soil in mountainous areas or peat developments.
Land recultivation – restoration of cultural fertility on previously used soils.
Reproduction of fertility
In the process of agricultural activities related to alienation together with crop yields, the soil consumes mineral and organic substances, deteriorates water and air regimes, phytosanitary state, microbiological activity. In connection with this there is a loss of fertility, which in conditions of intensive farming is required to maintain at an acceptable level, and ideally should strive for optimum provision of plant life factors.
Restoration of soil fertility is based on the achievement of optimal soil fertility indicators in relation to specific conditions of production and technology of fertility reproduction. It is based on the law of return.
Reproduction of fertility can be divided into simple and expanded.
Simple fertility reproduction – measures aimed at return of soil fertility to original parameters.
Extended fertility reproduction – measures aimed at restoring soil fertility above their original parameters.
Extended reproduction is especially relevant in conditions of intensive farming, in which lands with low natural fertility are included in turnover. For sod-podzolic soils expanded reproduction is a necessary condition of stable agricultural activity.
Soil fertility management is a complex of measures aimed at control of soil fertility and its simple or expanded reproduction in conditions of a particular enterprise. It is based on a model built on the basis of actual values of fertility indicators, which are in correlation with yields, soil and climatic and production conditions.
Example of fertility model on sod-podzolic medium-loam soils of the Non-Chernozem zone of Russia. Productivity of the model is 4.5-6.0 tons of grain, or 6500-7500 fodder units.
| Fertility indicators and their parameters | Technological and material factors of simple reproduction of fertility |
| Agrophysical | |
1. Density – 1.1-1.2 g/cm3, porosity – 50-55%, air capacity – 25-30%. | Equal-depth tillage, a combination of mouldboard and non-moldboard methods, conservation tillage, with elements of minimization |
2. Structure – fine crumbly, macrostructure water strength – more than 40%. | |
3. The thickness of the arable layer is 25-30 cm. There is no podzolic horizon. | |
| Biological | |
1. Content of humus in arable layer – 2.5-3%, stock – 75-90 t/ha. | Application of organic fertilizers – 10-12 t/ha. |
2. The activity of soil biota is high. | Sowing perennial grasses – 25-30% of the total cropping pattern |
3. Phytosanitary condition – number of weed plants is at the level of economic threshold of harmfulness, pathogens and pests are absent. | |
| Agrochemical | |
1. State of soil absorption complex and acidity: pH = 6.0-6.5, 7-12 mg-eq, V = 80-90%. | Liming by full hydrolytic acidity once in 5-6 years. |
2. NPK content, mg/kg soil: mineral nitrogen – 30-50; mobile forms of phosphorus – 150-250; mobile forms of potassium – 200-250. | Mineral fertilizers application: NPK – 250-300 kg/ha of crop rotation area. |
3. Content of microelements, mg/kg of soil: copper – 0,8-1,2; molybdenum – 0,2-0,4; boron – 0,5-0,6; zinc – 5-7. | Ratio N:P:K = 1 : 0.5-0.6 : 1.2-1.3. |
Methods of fertility reproduction
Reproduction of fertility in modern agriculture is carried out in two ways: material and technological.
Material method of fertility reproduction is based on the application of fertilizers, ameliorants, pesticides, etc. It has the most complete and diverse effect on soil fertility by replenishing nutrients.
Technological method of reproduction is based on the use of crop rotation, various methods of tillage and methods of sowing, intermediate crops, etc. It mobilizes soil resources, but does not replenish them, so the use of this method alone is not able to provide a long-term effect of fertility reproduction.
Fertility optimization
Thanks to the developments of research institutions and data from long-term stationary experiments of the Geographic Network (agronomic stations), it became possible to optimize soil fertility by agrochemical and agrophysical indicators. Fertility indicators are optimal if they ensure high yield and product quality of all crops of the crop rotation, promote economic efficiency and improve the ecological situation.
Table. Indicators of the fertility of different soils and crop yields [1]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| Tillage layer, cm | ||||
| Density, g/cm3 | ||||
| Total porosity, % | ||||
| Moisture capacity, % of mass | ||||
| Water resistant aggregates 0.25 mm, % | ||||
| Humus, % / t/ha | ||||
| Nitrogen, % / t/ha | ||||
| Phosphorus mobile, mg/kg soil | ||||
| Potassium exchange, mg/kg soil | ||||
| Winter wheat | ||||
| Barley | ||||
| Perennial grasses | ||||
| Potatoes | ||||
| Cottonwood | ||||
Soil fertility is evaluated by a set of indicators in accordance with the specialization of crop rotation.
Optimal fertility indicators are achieved by using a set of agrotechnical methods and agrochemical means. Soil Institute named after V.V. Dokuchaev Soil Institute proposed the parameters of soil fertility indicators to ensure high crop yields.
Table. Optimal parameters of the properties of the arable horizon of soils in the forest-steppe zone (according to N.I. Karmanov, 1993)
| Depth, cm | ||
| Density, g/cm3 | ||
| Total porosity, % | ||
| Number of water resistant aggregates (fraction with a particle size of 0.25 mm) | ||
| Humus content, % | ||
| Humus stocks, t/ha | ||
| Type of humus Сhumic : Cfulvic | ||
| Amount of labile humic acids, mg C/kg | ||
| Saline pH | ||
| Hydrolytic acidity mmol/100 g soil | ||
| Amount of absorbed bases, mmol/100 g soil | ||
| Base saturation degree, % | ||
| Mobilizable forms of phosphorus, mg/kg soil | ||
| Mobilizable forms of potassium, mg/kg soil | ||
For sod-podzolic soils, an important indicator is the level of acidity, which is determined taking into account the specialization of crop rotation, biological features of crops, granulometric composition of the soil, the amount and composition of absorbed cations.
One of the causes of plant sensitivity to acidic soil reaction is the presence and mobility of aluminum, and crops respond to the content of active forms and to the ratio of exchangeable calcium and aluminum or the sum of calcium, magnesium and aluminum. The higher this ratio, the less aluminum action is manifested.
The problem of optimizing the reaction of the soil solution is due to the use of physiologically acidic mineral fertilizers, which lead to the depletion of the arable layer by calcium. Maintenance of optimum reaction of acidic soils is connected with scientifically grounded technology of liming.
First of all soil fertility is determined by the content of organic matter. Optimum parameters of humus content in sod-podzolic soils depending on granulometric composition are established: in sandy – 1.8-2.0, sandy loam – 2.0-2.5, loam – 2.6-3.0. To maintain a deficit-free balance of humus it is necessary to annually apply 16-18 t/ha, 13-15 t/ha and 10-12 t/ha of manure, respectively.
To maintain an optimal humus content in acidic sod-podzolic and gray forest soils combine liming, the introduction of organic and nitrogen fertilizers in doses which cover more than 90% of the nitrogen removal with crops, the inclusion of legume-grass mixtures in the structure of cultivated areas. Doses of organic fertilizers are determined depending on the content of humus and granulometric composition. Assessment of the nitrogen regime of soils is carried out by the content of mineral nitrogen.
One of the characteristics of soil fertility is the content of mobile phosphorus. It should be guided by crops of the crop rotation, the most demanding to phosphorus nutrition, for specific soil and climatic conditions.
The lower limit of mobile forms of phosphorus is determined by assessing the content of phosphorus at the maximum yield of a particular crop and the lack of effect of additional application of phosphorus fertilizers. According to generalized long-term experiments, the lower limit of P2O5 content is 100-150 mg/kg for sod-podzolic loamy soils, 50-100 mg/kg – for sandy and sandy loam soils, 100-150 mg/kg – for gray forest soils. A further increase in the content of mobile phosphorus does not provide a significant increase in yields.
Table. Crop rotation productivity and content of mobile forms of phosphorus in long-term experiments of the Geographic Network of Agronomic Stations (1993)
| CES of the All-Russian Institute of Fertilizers and Agrochemistry, sod-podzolic heavy loam | Control | |||
| NPK - reduced dose | ||||
| NPK - основная доза | ||||
| NIISKh North-East, sod-podzolic medium-loamy | Control | |||
| NPK | ||||
| NPK | ||||
| VNII of flax, sod-podzolic loamy | Control | |||
| NPK | ||||
| Manure + NPK | ||||
| Sudogodskaya ES, sod-podzolic loamy sand | Control | |||
| NPK | ||||
| 2 NPK | ||||
| Manure + NPK | ||||
| Vladimir ES, gray forest | Control | |||
| NPK | ||||
| NPK | ||||
| 2 NPK |
The importance of optimizing the phosphorus nutrition regime is due to the fact that significant areas of arable land are characterized by low content of mobile phosphorus.
For the optimum content of mobile phosphorus in soil is considered that in which not less than 90-95% of the maximum yield is achieved, the missing 5-10% is replenished by phosphorus fertilizers, compensating the removal.
Irrigated conditions require higher levels of mobile phosphorus supply. Increasing the content of mobile phosphorus from low (2-4 mg/100 g soil) to medium (8-10 mg/100 g soil) gives the highest yield increases. Further increase leads to a decrease in the value of gains, and reaching optimum values, crop yields stabilize.
Table. Fertilizer rates to increase the content of mobile phosphorus by 10 mg P2O5/kg of soil (by Litvak Sh.I., 1990; Sychev V.G., Shafran S.A., 2013)
| Sod-podzolic | sandy and sandy loam | by Kirsanov | ||
| light loam | ||||
| medium loam | ||||
| heavy loam | ||||
| Grey Forest | sandy and sandy loam | by Kirsanov | ||
| loamy | ||||
| heavy loam | ||||
| Podzolized black earth | light loam | by Chirikov | ||
| loamy | ||||
| Leached black earth | heavy loam | by Chirikov | ||
| Typical black earth | heavy loam | by Chirikov | ||
| Common black earth | loamy | by Chirikov | ||
| heavy loam | ||||
| Carbonate black earths | On average | by Machigin | ||
| Chestnut | On average | by Machigin | ||
* Taking into account the removal of phosphorus by the crop and its return coefficients
Table. Gradations of soil mobile phosphorus availability, mg/kg of soil (Methodological guidelines for comprehensive monitoring of soil fertility of agricultural lands, 2003)
| Very low | ||||
| Low | ||||
| Medium | ||||
| Increased | ||||
| High | ||||
| Very high |
An indicator of plant potassium availability is its content in the soil in the exchangeable form. There are reserves of potassium in the soil and there is a dynamic equilibrium between the potassium of the soil solution, exchangeable and non-exchangeable (fixed and potassium of natural clay minerals). In the process of plant nutrition dynamic equilibrium is broken and all forms of soil potassium are involved. The mobility of exchangeable potassium and the rate of its recovery from non-exchangeable forms are important.
Table. Gradations of soil provision with mobile (exchangeable) potassium, mg/kg of soil (Methodological Guidelines for Comprehensive Monitoring of Soil Fertility of Agricultural Lands, 2003)
| Very low | |||||
| Low | |||||
| Medium | |||||
| Increased | |||||
| High | |||||
| Very high |
Provision of soils with mobile potassium is determined by different methods depending on soil type.
Optimal levels of provision with exchangeable potassium can be specified by specialization of crop rotation, liming of acidic soils, provision with nitrogen, phosphorus, biological characteristics of crops.
Table. Provision of soils with exchangeable potassium and productivity of crop rotations[2]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| Sod-podzolic sandy loam and loam | ||
| Grey forests | ||
| Leached and typical black earths (forest-steppe) | ||
| Strong, common and carbonate black earths (steppe) | ||
| Common and carbonate black earth (steppe, with irrigation) | ||
| Chestnut, light and dark chestnut (steppe, with irrigation) |
Potassium fertilizer consumption to increase potassium content in the soil are presented in the table.
Table. Fertilizer rates for increasing the content of mobile K2O by 10 mg/kg of soil (by Litvak Sh.I., 1990)
| Sod-podzolic | sandy loam | by Kirsanov | |
| Light and medium loam | |||
| heavy loam | |||
| Grey Forest | sandy loam | by Kirsanov | |
| Light and medium loam | |||
| heavy loam | |||
| Podzolized and leached black earth | in average | by Chirikov |
M.H. Shaimukhametov and D.S. Travnikov (1977) proposed the optimal parameters of the content of exchangeable potassium depending on its share in the capacity of cation exchange (CCE) of soils with different granulometric composition.
Table. Optimal indicators of exchangeable potassium content in soils (M.Kh. Shaimukhametov, L.S. Travnikova, 1997).
(granulometric composition) | ||
|---|---|---|
| Sandy | ||
| Sandy loam | ||
| Loamy | ||
| Heavy loam and clay | ||
The limits of variation of the minimum content of exchangeable potassium for sod-podzolic soils are shown in the table.
Table. Variation levels of the minimum content of exchangeable potassium for sod-podzolic soils of different granulometric composition (Nikitina L.V., 2011)
| Sandy loam | ||
| Light loam | ||
| Medium loam | ||
| Heavy loam |
On the basis of generalized experimental data the gradations of the degree of soil provision of soil-climatic zones of Russia with mobile forms of trace elements were determined.
Table. Gradation of soil provision with mobile forms of microelements in Russia (Yagodin, Zhukov, and Kobzarenko, 2002).
On average, the use of microfertilizers can increase crop yields by 10-12% on soils with low content.
Table. Effectiveness of microfertilizers application for the main agricultural crops according to the generalized data of field experiments (1993)[3] Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
| Wheat, barley (grain) | ||||||
| Corn, green mass | ||||||
| Sugar beets, root crops | ||||||
| Potatoes, tubers | ||||||
| Clover, seeds | ||||||
| Perennial grasses, green mass | ||||||
Research institutions of Belarus conducted research to determine the optimal indicators and developed a model of fertility of sod-podzolic loamy soils.
Fertility management systems
Construction of soil fertility management system begins with determination of optimal parameters of fertility model. In order to build a feasible model, experimental characteristics of specific farming areas should be taken into account for objective agronomic evaluation of soils.
Assessment of effectiveness of differentiated, experimentally determined models of fertility should be supplemented with economic assessment, which allows to objectively compare the effect obtained from the model with the costs of its maintenance in specific natural and economic production conditions.
Agro-economic assessment of fertility models allows to determine the levels of fertility reproduction, as a whole, and by individual indicators – simple or expanded reproduction.
Reproduction of fertility in intensive farming should be carried out on all indicators of fertility, but paramount importance should be given to the most important of them for specific soils and conditions of agricultural production.
Sources
Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov, etc., ed. by V.G. Mineev. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.