It is possible to study interaction of soils, plants and fertilizers in detail in long-term stationary experiments with systematic application of fertilizers. In such experiments conditions of standardization are created, allowing to study the effect of climatic and agrometeorological conditions on crops, soils and factors regulating soil fertility.
The main directions of research in long-term stationary experiments:
- comparative evaluation of doses, types and forms of mineral fertilizers;
- evaluating the effectiveness of mineral, organic and organomineral systems of fertilizers in crop rotations of different types;
- establishment of the optimal distribution of fertilizers on crops in the crop rotation;
- achieving maximum efficiency by combining fertilizer systems with chemical melioration, determination of their impact on soil properties and productivity of crop rotations;
- possibility of periodic application of phosphorus and potassium fertilizers;
- optimization of soil fertility and properties;
- regulation of biological cycle and balance of biogenic elements in agrocenosis;
- impact of agrochemical means on ecology.
Agrochemistry uses the following methods to study soil properties in long-term stationary experiments.
Agrochemical agents have a complex effect on soil fertility and properties:
- acidify or alkalize the soil solution;
- change agrochemical properties;
- Influence on biological and enzymatic activity of soil;
- strengthen or weaken physical-chemical and chemical absorption;
- affect mobilization or immobilization of toxic elements and radionuclides;
- increase mineralization or synthesis of humus;
- influence the intensity of nitrogen fixation from the atmosphere;
- strengthen or weaken the effect of other soil nutrients and fertilizers;
- influence the mobility of biogenic macro- and microelements in the soil;
- cause antagonism or synergism of ions when absorbed by plants.
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Agrochemical indicators of soil fertility
- Soil composition
- Absorption capacity of soils
- Soil acidity
- Base saturation and soil buffering
- Effect of fertilizers on soil properties (Русский Español)
- Agrochemical characteristics of Russian soils
Table. Methods of soil fertility research
| pH of salt extract | Potentiometric (1 n. KCl) | ГОСТ 26483-85 |
| Exchangeable acidity | Potentiometric (1 n. KCl) | ГОСТ 26484-85 |
| Hydrolytic acidity | Cullen's method (1 n. CH3COONa extraction) | ГОСТ 26212-84 |
| Exchangeable (mobile) aluminum | CRIASA method (1 n. KCl extraction) | ГОСТ 26485-85 |
| Sum of absorbed bases | Kappen-Hilgowitz method for non-carbonate soils (0.1 n. HCl treatment) Schmuck method for carbonate soils (1 n. NaCl extraction) | ГОСТ 27821-88 |
| Exchange potassium | Maslova method (1 n. CH3COONH4 extraction) | ГОСТ 26210-91 |
| Unexchanged potassium | Hedroitz method (10% HCl extraction with boiling) | |
| Granulometric | Kaczynski method | |
| Equilibrium density | Cutting ring method or gammascopic method | |
| Moisture of a steady wilting | Method for determining the loss of moisture during soil drying | ГОСТ 28268-89 |
| Total organic carbon content | Tyurin method modified by CRIASA (oxidation of organic matter with a solution of chromium mixture) | ГОСТ 25213-84 |
| Content of water-soluble humus substances | Hot water extraction method | |
| Content of mobile humus substances | Tyurin extraction method 0,1 n. NaOH | |
| Group composition of humus substances | Kononova-Belikova method (extracted with a mixture of Na4P2O7 and NaOH) | |
| Forms of mineral phosphates | Chang-Jackson method (sequential extractions 1 n. NH4Cl, 0,5 n. NH4F, 1 n. NaOH, 0,5 n. H2SO4) | |
| Total nitrogen content | Kjeldahl method (oxidation of soil with boiling concentrated H2SO4) | ГОСТ 26107-84 |
| Mobile phosphates and mobile potassium: Acidic soils Black earths Carbonate soils | Kirsanov's method modified by CRIASA (0,2 n. HCl extraction) Chirikov method modified by CRIASA (0,5 n. CH3COOH extraction) Machigin's method as modified by CRIASA (1% (NH4)2CO3 extraction) | ГОСТ Р 54650-2011 ГОСТ 26204-91 ГОСТ 26205-91 |
| Degree of mobility of phosphorus and potassium in soils | Scofield method 0,01 M CaCl2 extraction | ОСТ 10271-00 |
| Fixed ammonium nitrogen | Sylv and Bremner method modified by Kudeyarov (colorimetric determination in the extract from the mixture of HF and HCl) | |
| Nitrogen mobility and availability to plants | Method of vegetative experiment using 15N | |
| Mobility and plant availability of "residual" phosphate and potassium compounds | Vegetation experiment method | |
Physico-chemical properties of soils affect the nutrient regime of soils, their biological activity, determine the transformation of fertilizers introduced into the soil, under conditions of flushing water regime determine the possibility of movement of compounds into deeper soil layers.
Systematic application of organic and mineral fertilizers is accompanied by changes in the physical and chemical properties of soils. Application of manure for many years usually increases the content of organic matter and absorption capacity of soils, reduces metabolic and hydrolytic acidity and increases the degree of saturation with bases.
Table. Effect of systematic use of fertilizers on agrochemical and agrophysical properties of soil (powerful low-humus black earth, soil layer 0-30 cm)[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
| pH | |||||
| H, mmol/100 g soil | |||||
| S, mmol/100 g soil | |||||
| V, % | |||||
| P2O5, mg/kg soil | |||||
| K2O, mg/kg soil | |||||
| Humus, t/ha | |||||
| Nitrogen, t/ha | |||||
| Volume weight, g/m3 | |||||
| Total moisture capacity, % | |||||
| Capillary moisture capacity, % | |||||
| Water permeability in the field conditions, mm/(h·cm2) | |||||
| Total porosity, % | |||||
The combined application of manure and mineral fertilizers for 15 years increased the humus content by 12,6 t/ha, nitrogen – by 0,7 t/ha, reduced the soil density by 0,08 g/cm3, total and capillary moisture capacity increased by more than 3%, water permeability – by 4,3 mm/(h·cm2), total porosity – by 3%.
With long-term use of mineral fertilizers soil properties may deteriorate. It is connected with acidification of reaction of a soil solution as a result of displacement from an absorbing complex of ions of hydrogen and aluminum, and also physiological acidity of some fertilizers. Proper use of fertilizers, that is on the background of manure and liming, the introduction of additives to neutralize the physiological acidity of fertilizers allows you to keep soil acidity at an acceptable level, and in some cases reducing it. On neutral and near-neutral chernozem soils slight acidification as a result of fertilizer application can be considered positive, as it increases mobility and availability of many compounds.
In conditions of leaching water regime of sod-podzolic and gray forest soils changes of properties under the influence of fertilizers occur in arable and in deeper layers. It is connected with increased precipitation and soil acidification at high doses of mineral fertilizers, formation of mobile organic compounds at manure application and peptization of soil colloids under the influence of monovalent cations included in fertilizers, and their washout beyond the arable layer. Migration of nutrients to the underlying layers due to peptization of colloids promotes the application of fertilizers in the fallow and under row crops, as well as frequent tillage. The process intensifies with a light granulometric composition of the soil and an increase in fertilizer doses.
Systematic application of fertilizers leads to an increase in the amount of crop-root residues, decomposition of which causes the new formation of organic colloids in the arable layer and simultaneously with the peptization of large soil particles leads to an increase in the content of silt fraction. In low-buffered soils of light granulometric composition colloid leaching may prevail over new formation.
Changes of physical and chemical properties on black earth soils are concentrated mainly in arable and subsoil layers that is connected with limited precipitation in steppe zone and shallow soil soaking. Prolonged application of fertilizers on these soils leads to accumulation of silt fraction and the value of absorption capacity. At the same time acidity against the background of manure decreases, and with the use of mineral fertilizers increases, which is explained by physiological acidity of fertilizers and non-exchangeable absorption of monovalent cations in the absence of leaching of hydrogen and acidic residue. Increasing the acidity of chernozems increases the mobility of some nutrients and increases their availability to plants.
Systematic use of organic and mineral fertilizers on gray soils has no significant effect on the reaction of the soil solution due to their carbonation and buffering. Some increase of silt fraction and absorption capacity of these soils in the upper layers is due to the formation of colloids from organic plant residues. The arable layer of sierozem preserves colloids, due to the large amount of calcium, which is absorbed by colloids, prevents their dispersion and washout. Movement of fertilizer nutrients deep down the profile in gray soils, as well as losses with groundwater and waste water during irrigation, are caused by flushing water regime and solubility of some compounds.
Long-term use of organic and mineral fertilizers increases the content of carbon and nitrogen in humus-poor sod-podzolic and gray soils, while having little effect on humus-rich black soils.
Table. Effect of long-term fertilizer application on the content of organic carbon and total nitrogen (Shevtsova L.K., 1993, 1998).
| Control | |||||
| Manure | |||||
| NPK | |||||
| Manure + NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| 1/2 Manure + 1/2 NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| 1/2 Manure + 1/2 NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| Manure + NPK | |||||
In variants with the application of manure an increase in the content of organic matter in the upper horizons is noted, and a weaker effect of mineral fertilizers is also manifested in the subsoil layer. Manure and mineral fertilizers do not affect the group composition of the organic matter of different types of soil. The composition of humus long fertilized soils retains the properties formed in the regional conditions of soil formation. With prolonged use of fertilizers soil enriched mobile organic matter, which are in the early (hydrophilic) stages of humification, more biochemically active organic compounds, as well as enrich the soil with mobile and available nitrogen. The strongest impact of fertilizers on this indicator was noted on sod-podzolic soils, weakest – on black soils, very weak – on gray soils.
The influence of mineral nitrogen and potassium fertilizers on soil fertility is associated with cation exchange. Systematic application of these fertilizers leads to fixation of monovalent potassium and ammonium cations contained in fertilizers by soil colloids, which is associated with the entry of cations inside the crystal lattice of minerals. This process is influenced by the type of clay mineral, granulometric composition, organic matter content, reaction of soil solution, concentration of potassium and ammonium cations in the soil solution, composition and concentration of other cations, degree of saturation of the absorbing complex with these cations, and hydrothermal conditions under which fixation occurs.
Non-exchangeable absorption of cations reduces their availability to plants and the coefficient of utilization of nitrogen and potassium fertilizers.
Application of ammonium forms of nitrogen fertilizers is accompanied by fixation (non-exchangeable absorption) of nitrogen in the form of NH4+ by clay minerals, which reduces its availability to plants. Nitrogen fixation in the arable and deeper layers can reach significant sizes and should be taken into account in the total nitrogen balance. Prolonged use of nitrogen fertilizers increases the amount of fixed ammonium. Fixation of ammonium on soils of light granulometric composition is less than on soils of heavier granulometric composition because fixation is connected with silt fraction and clay minerals composing it. Fixation of ammonium occurs in the arable and deeper soil layers, especially on soils with light granulometric composition. Probably, non-absorbed ammonium is washed into the lower layers with colloids, the content of which increases down the soil profile.
Table. Changes in the content of non-exchangeable ammonium nitrogen in the soil profile of long-term stationary experiments, mg N/kg soil. Grey forest medium-loam soil, Novosibirsk region (V.N. Yakimenko, 2009)
| Virgin land | ||||
| Fallow | ||||
| Control (vegetable crop rotation) | ||||
| Control (grain crop rotation) | ||||
| NP (vegetable crop rotation) | ||||
| NP (grain crop rotation) | ||||
| NPK* (vegetable crop rotation) | ||||
| NPK* (vegetable crop rotation) | ||||
Crops, depending on the structure of the root system and its absorptive capacity, affect the processes of migration of mineral forms of nitrogen and non-exchangeable absorption of ammonium.
At simultaneous application of nitrogen and potassium fertilizers ammonium fixation decreases due to the competing action of potassium.
Ammonium of mineral fertilizers is fixed faster than ammonium of manure since it has greater mobility. When manure is applied, non-exchange absorption of ammonium is less pronounced than when mineral fertilizers are applied. It is connected with increased fixation of potassium, improvement of physical and chemical properties of soil and strengthened nitrification ability of soils.
Nitrogen fixation in the form of non-exchangeable ammonium occurs in the first years of systematic fertilizer application, and there is no further increase in fixed ammonium from fertilizer application when the fixation tank is filled. Potassium, as well as ammonium, is actively fixed in the first years of fertilizer application, and when filling the tank of fixation of non-exchangeable potassium – decreases, its availability to plants and the coefficient of use by plants increases.
The nature of potassium transformation of fertilizers depends on soil and climatic conditions. In sod-podzolic and gray forest soils the amount of exchangeable potassium increases, while the content of non-exchangeable potassium changes little. Accumulation of exchangeable potassium is noted in the arable layer and in deeper layers. In the arable layer of chernozems non-exchangeable potassium uptake prevails, the amount of exchangeable potassium increases to a lesser extent. In gray soils, the content of exchangeable and non-exchangeable, absorbed potassium increases.
Table. Content of various forms of potassium in soils during long-term fertilizer application, mg К2O/100 g of soil[2]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. - 854 с.
| Sod-podzol dusty-sandy-loam (Moscow Agricultural Academy) | Control | ||||
| Manure | |||||
| NPK | |||||
| Sod-podzolic heavy loam (DAOS) | Control | ||||
| Manure | |||||
| NPK | |||||
| Grey forest light loamy (All-Russian Research Institute of Bast Crops) | Control | ||||
| Manure | |||||
| NPK | |||||
| Leached light loamy black soil (Myroniv Research Institute of Wheat Breeding and Seed Production) | Control | ||||
| Manure | |||||
| NPK | |||||
| Typical black soil (Ak-Kavakskaya experimental station) | Control | ||||
| Manure | |||||
| NPK | |||||
Leaching regime of light chestnut soils created by irrigation changes the content of non-exchangeable forms of potassium. The greatest changes are noted in the arable horizon, but the effect extends to the meter layer of soil.
Table. Influence of systematic fertilizer application on potassium regime of chestnut soils (Zhukova L.M., Nikitina L.V., 1986).
Cation fixation is determined by soil type. For example, sod-podzolic soils, in spite of high dispersion of minerals, are characterized by low potassium fixation capacity. It is connected with acid reaction of soil solution, unsaturated soils with bases, small content of organic matter and high soil humidity. Under these conditions non-exchangeable potassium uptake occurs in small amounts and only in the upper arable layer.
Liming and long-term application of manure increase the fixing capacity of potassium in acid soils compared with mineral fertilizers, which is due to an increase in the amount of organic matter and coagulating effect of divalent cations contained in the manure and lime fertilizers. Co-application of nitrogen and potassium fertilizers due to competition with NH4+ ions decreases potassium fixation by 2-3 times.
Potassium fixation on sod-podzolic soils is small and does not affect the application of fertilizers, as non-exchangeable potassium colloids soil is a source of replenishment of exchangeable potassium.
In gray forest soils, potassium and ammonium fixation is stronger than in sod-podzolic soils. The reaction of soil solution, mineralogical composition, and increased content of organic matter contribute to the process.
In black earth conditions for non-exchange fixation of cations are the most favorable: high saturation of the absorbing complex with bases, high pH value, high content of organic matter, mineralogical composition of the colloidal fraction with the predominance of minerals of montmorillonite group, periodic drying of the top layer, which leads to irreversible coagulation of colloids.
The simultaneous application of potassium and nitrogen fertilizers does not decrease potassium fixation as the processes of nitrification are active in black soils, which is the reason for a slight increase in the amount of fixed ammonium against the background of fertilizers. Fixation of potassium and ammonium occurs in the upper layers of chernozems.
In chestnut soils and gray soils prolonged use of fertilizers leads to an increase in the amount of non-exchangeable potassium and ammonium. Transition of these cations to non-exchangeable absorbed state is caused by predominance of minerals of hydromica type in silt fraction. These minerals have a high fixing ability with respect to monovalent cations. Alkaline reaction of soil, saturation by divalent bases and periodic drying of soils in conditions of climate of arid-steppe and desert zones are of importance.
Leaching regime contributes to the increase of fixed cations in the lower layers of the soil profile. Joint application of nitrogen and potassium fertilizers has little effect on cation fixation, as mineralogical composition of these soils has high capacity of single-valent cations fixation.
According to the content of exchangeable potassium and fixed ammonium soils can be arranged in the following sequence: sod-podzolic < gray forest < black soils < chestnut soils < gray soils.
Within the same soil type the amount of non-exchangeable cations increases from light soils to heavy ones. Stocks of non-exchangeable cations should be taken into account when assessing soil fertility and calculating nutrient balances.
Natural reserves of phosphorus in soils and their distribution across the profile depend on the content of phosphorus in the parent rocks and the nature of the soil formation process. With systematic fertilization the gross content and amount of mobile forms of phosphorus increases. The degree of change is determined by the doses of fertilizers, the duration of their application and soil properties. Most of the phosphorus accumulated as a result of fertilizer application is retained in the arable layer. At high doses of phosphorus enriched subsoil layer, and in cases of light soils without liming and under irrigation and deeper layers.
The composition of mineral phosphates in the profile is determined by genetic features of soils. Thus, in sod-podzolic soils phosphates of semi-hydrous oxides prevail, in black soils – calcium phosphates.
When mineral phosphorus fertilizers are applied, more phosphates of metals forming oxides like R2O3 are accumulated in soils compared to soils where manure was systematically applied.
Effect of fertilizers on biological and enzymatic activity of soils
Biological activity of soils is a set of biological and biochemical processes occurring in the soil. It depends on genetic features of soil, hydrothermal conditions, agrotechnical measures, the degree of mineralization and humification of plant residues, mobilization capacity of soils. Systematic use of fertilizers in crop rotations enhances the activity of soil biota.
On sod-podzolic acidic soils the activity of biological processes is influenced by lime application. Periodic liming reduces the content of mobile aluminum and exchangeable hydrogen, creates more favorable living conditions for microorganisms in the soil, increases the mineralization of organic matter.
A positive effect on biological activity has a manure in pure form and in combination with mineral fertilizers and liming. Liming enhances the effect of fertilizers on enzymatic activity.
Table. Effect of systematic fertilizer application on biological activity of chestnut soil. Winter wheat and alfalfa. (Numbers of microorganisms, thousand per 1 g of dry soil, average for vegetation season). Long-term experience of Gorsky Agricultural Research Institute (Dzhanaev G.G. et al., 2005)
| Control | |||||
| NPK | |||||
| 2 NPK | |||||
| Manure + NPK | |||||
| 3 NPK |
The effect of fertilizers on enzymatic activity of sod-podzolic soils is similar to the effect on biological activity. Maximum enzyme activity is noted on the background of manure.
On black earth, dark gray forest soils and gray soil, manure in pure form and together with the use of mineral fertilizers has a positive effect on the enzymatic activity. In most cases, an increase in urease activity is noted, which is due to favorable for urobacteria neutral or slightly alkaline reaction of soil. Under the influence of fertilizers, invertase activity increases, and the activity of decomposition and synthesis of nitrogen-free organic matter increases to the same extent against the background of manure and mineral fertilizers.
Sources
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 с.