Effect of Fertilizers on Soil Properties
A detailed study of the interaction between soils, plants, and fertilizers is possible in long-term stationary experiments with systematic application of fertilizers. Such experiments create standardized conditions that make it possible to study the effect of climatic and agrometeorological conditions on crops, soils, and factors regulating soil fertility.
Main research directions in long-term stationary experiments:
- comparative assessment of rates, types, and forms of mineral fertilizers;
- assessment of the effectiveness of mineral, organic, and organomineral fertilizer systems in different types of crop rotations;
- determination of the optimal distribution of fertilizers among crops in a crop rotation;
- achieving maximum effectiveness when combining fertilizer systems with chemical amelioration, determining their effect on soil properties and crop rotation productivity;
- possibility of periodic application of phosphorus and potassium fertilizers;
- optimization of soil fertility and soil properties;
- regulation of the biological cycle and balance of biogenic elements in the agrocenosis;
- impact of agrochemicals on the environment.
In agrochemistry, the following methods are used to study soil properties in long-term stationary experiments.
Agrochemicals have a complex effect on soil fertility and soil properties:
- acidify or alkalize the soil solution;
- change agrochemical properties;
- affect the biological and enzymatic activity of the soil;
- enhance or weaken physicochemical and chemical absorption;
- affect the mobilization or immobilization of toxic elements and radionuclides;
- enhance the mineralization or synthesis of humus;
- affect the intensity of nitrogen fixation from the atmosphere;
- enhance or weaken the effect of other nutrients in soil and fertilizers;
- affect the mobility of biogenic macro- and microelements in the soil;
- cause antagonism or synergism of ions during uptake by plants.
Table. Methods for studying soil fertility (according to OST 10152-88 and the Methodological Guidelines for Comprehensive Monitoring of Soil Fertility of Agricultural Lands, 2003, with amendments).
| Indicator | Method and its characteristics | GOST of the research method |
|---|---|---|
| Physicochemical methods | ||
| pH of salt extract | Potentiometric (1 N KCl) | GOST 26483-85 |
| Exchangeable acidity | Potentiometric (1 N KCl) | GOST 26484-85 |
| Hydrolytic acidity | Kallen method (1 N CH3COONa extract) | GOST 26212-84 |
| Exchangeable (mobile) aluminum | CINAO method (1 N KCl extract) | GOST 26485-85 |
| Sum of absorbed bases | Kappen-Hilgowitz method for non-carbonate soils (treatment with 0.1 N HCl) Schmuck method for carbonate soils (1 N NaCl extract) | GOST 27821-88 |
| Exchangeable potassium | Maslova method (1 N CH3COONH4 extract) | GOST 26210-91 |
| Nonexchangeable potassium | Gedroits method (10% HCl extract with boiling) | — |
| Physical and water-physical methods | ||
| Particle-size distribution | Kachinsky method | — |
| Equilibrium density | Cutting-ring method or gamma-scopic method | — |
| Wilting point moisture | Method for determining moisture loss upon soil drying | GOST 28268-89 |
| Agrochemical methods | ||
| Total organic carbon content | Tyurin method modified by CINAO (oxidation of organic matter with chromic acid mixture solution) | GOST 25213-84 |
| Content of water-soluble humic substances | Hot water extract method | — |
| Content of mobile humic substances | Tyurin method. 0.1 N NaOH extract | — |
| Group composition of humic substances | Kononova-Belikova method (extract with a mixture of Na4P2O7 and NaOH) | — |
| Forms of mineral phosphates | Chang-Jackson method (sequential extracts with 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) | GOST 26107-84 |
| Mobile phosphates and mobile potassium: | ||
| - acid soils | Kirsanov method modified by CINAO (0.2 N HCl extract) | GOST R 54650-2011 |
| - chernozems | Chirikov method modified by CINAO (0.5 N CH3COOH extract) | GOST 26204-91 |
| - carbonate soils | Machigin method modified by CINAO (1% (NH4)2CO3 extract) | GOST 26205-91 |
| Degree of mobility of phosphorus and potassium in soils | Schofield method, 0.01 M CaCl2 extract | OST 10271-00 |
| Fixed ammonium nitrogen | Silva and Bremner method modified by Kudeyarov (colorimetric determination in an extract from a mixture of HF and HCl) | — |
| Vegetation experiments | ||
| Mobility and availability of nitrogen to plants | Vegetation experiment method using 15N | — |
| Mobility and availability to plants of “residual” phosphates and potassium compounds | Vegetation experiment method | — |
The physicochemical properties of soils influence the nutrient regime of soils and their biological activity, determine the transformation of fertilizers applied to the soil, and under conditions of a leaching 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 physicochemical properties of soils. The application of manure over many years usually increases the content of organic matter and the absorption capacity of soils, decreases exchangeable and hydrolytic acidity, and increases the degree of base saturation.
Table. Effect of systematic fertilizer application on agrochemical and agrophysical properties of soil (thick low-humus chernozem, soil layer 0–30 cm).
| Soil property indicators | Before establishment of the experiment (average over background, 1972) | At the end of the second rotation (1987). Variants: | |||
|---|---|---|---|---|---|
| Without basic fertilizer | Manure, 5 t + N49P56K53 | Manure, 10 t + N88P98K96 | Manure, 15 t + N128P141K139 | ||
| pH | 6,2 | 5,7 | 5,5 | 5,3 | 5,2 |
| H, mmol/100 g soil | 2,6 | 2,7 | 2,8 | 2,9 | 3,0 |
| S, mmol/100 g soil | 25,7 | 24,0 | 23,6 | 23,4 | 23,0 |
| V, % | 91,2 | 89,5 | 88,2 | 87,1 | 85,6 |
| P2O5, mg/kg soil | 127,4 | 121,2 | 141,6 | 157,2 | 164,0 |
| K2O, mg/kg soil | 70,3 | 66,4 | 80,6 | 87,8 | 93,6 |
| Humus, t/ha | 134,2 | 123,1 | 134,0 | 142,1 | 146,8 |
| Nitrogen, t/ha | 11,4 | 10,7 | 11,4 | 11,9 | 12,1 |
| Bulk density, g/m3 | 1,25 | 1,26 | 1,22 | 1,20 | 1,18 |
| Total water capacity, % | 49,2 | 48,9 | 50,4 | 51,1 | 52,2 |
| Capillary water capacity, % | 36,7 | 36,9 | 38,7 | 39,6 | 40,3 |
| Water permeability under field conditions, mm/(h·cm2) | 6,1 | 6,8 | 8,7 | 10,1 | 11,4 |
| Total porosity, % | 48,7 | 49,6 | 51,0 | 51,6 | 52,5 |
The combined application of manure and mineral fertilizers over 15 years increased the humus content by 12.6 t/ha and nitrogen by 0.7 t/ha, reduced soil density by 0.08 g/cm3, while total and capillary water capacity increased by more than 3%, water permeability by 4.3 mm/(h·cm2), and total porosity by 3%.
With long-term use of mineral fertilizers, soil properties may deteriorate. This is associated with acidification of the soil solution reaction as a result of displacement of hydrogen and aluminum ions from the absorbing complex, as well as the physiological acidity of some fertilizers. Proper application of fertilizers, that is, against the background of manure and liming, with the addition of amendments to neutralize the physiological acidity of fertilizers, makes it possible to maintain soil acidity at an acceptable level, and in some cases to reduce it. On neutral and near-neutral chernozem soils, slight acidification as a result of fertilizer application can be considered positive, since it increases the mobility and availability of many compounds.
Under conditions of a leaching water regime in soddy-podzolic and gray forest soils, changes in properties under the influence of fertilizers occur in the arable and deeper layers. This is associated with increased precipitation and soil acidification at high rates of mineral fertilizers, the formation of mobile organic compounds upon manure application, and peptization of soil colloids under the action of monovalent cations contained in fertilizers, and their leaching beyond the arable layer. The migration of nutrients into underlying layers due to peptization of colloids is promoted by fertilizer application in fallow and under row crops, as well as frequent soil tillage. The process is intensified by light particle-size soil composition and increasing fertilizer rates.
Systematic application of fertilizers leads to an increase in the amount of crop residues and roots, the decomposition of which causes the formation of new organic colloids in the arable layer and, simultaneously with the peptization of large soil particles, leads to an increase in the content of the silt fraction. In poorly buffered soils of light particle-size composition, leaching of colloids may predominate over new formation.
Changes in physicochemical properties in chernozem soils are concentrated mainly in the arable and subarable layers, which is associated with limited precipitation in the steppe zone and shallow wetting of the soil. Long-term fertilizer application on these soils leads to accumulation of the silt fraction and an increase in absorption capacity. At the same time, acidity decreases against the background of manure, but increases with the use of mineral fertilizers, which is explained by the physiological acidity of fertilizers and nonexchangeable absorption of monovalent cations in the absence of leaching of hydrogen and the acid residue. An increase in the acidity of chernozems promotes greater mobility of some nutrients and increases their availability to plants.
Systematic application of organic and mineral fertilizers on sierozems does not have a significant effect on the soil solution reaction because of their carbonate content and buffering capacity. A certain increase in the silt fraction and absorption capacity of these soils in the upper layers occurs due to the formation of colloids from organic plant residues. The arable layer of sierozems retains colloids because the large amount of calcium absorbed by colloids prevents their dispersion and leaching. The movement of fertilizer nutrients deeper along the profile in sierozems, as well as losses with groundwater and drainage waters during irrigation, are due to the leaching water regime and the solubility of some compounds.
Long-term application of organic and mineral fertilizers increases the carbon and nitrogen content in humus-poor soddy-podzolic and sierozem soils, while having little effect on humus-rich chernozems.
Table. Effect of long-term fertilizer application on the content of organic carbon and total nitrogen (Shevtsova L. K., 1993, 1998).
| Variants of the long-term experiment | C | N | C | N | C/N |
|---|---|---|---|---|---|
| % of air-dry soil | % of control | ||||
| Light loam, Belarusian NIIPA | |||||
| Control | 1,70 | 0,128 | 100 | 100 | 13,2 |
| Manure | 2,01 | 0,153 | 118 | 120 | 13,1 |
| NPK | 1,78 | 0,143 | 104 | 112 | 12,4 |
| Manure + NPK | 2,22 | — | 131 | — | — |
| Heavy loam, DAOS experiment with bare fallow | |||||
| Control | 0,71 | 0,107 | 100 | 100 | 6,6 |
| Manure | 1,00 | 0,124 | 141 | 116 | 8,1 |
| NPK | 0,79 | 0,110 | 111 | 103 | 7,2 |
| 1/2 Manure + 1/2 NPK | 0,89 | 0,122 | 125 | 114 | 7,3 |
| Weakly leached chernozem, light loam, Mironovsky Research Institute of Selection and Seed Production of Winter Wheat | |||||
| Control | 2,33 | 0,225 | 100 | 100 | 10,4 |
| Manure | 2,43 | 0,232 | 104 | 103 | 10,4 |
| NPK | 2,32 | 0,224 | 97 | 100 | 10,4 |
| 1/2 Manure + 1/2 NPK | 2,34 | 0,226 | 101 | 100 | 10,4 |
| Medium-thick chernozem, medium loam, Altai Research Institute of Agriculture and Seed Production | |||||
| Control | 3,47 | 0,305 | 100 | 100 | 11,4 |
| Manure | 3,65 | 0,308 | 105 | 101 | 11,9 |
| NPK | 3,64 | 0,300 | 105 | 98 | 12,1 |
| Manure + NPK | 3,65 | 0,309 | 105 | 101 | 11,8 |
In variants with manure application, an increase in organic matter content is noted in the upper horizons, while the weaker effect of mineral fertilizers is also manifested in the subarable soil layer. Manure and mineral fertilizers do not affect the group composition of organic matter in different soil types. The humus composition of long-term fertilized soils retains properties formed under regional soil-forming conditions. With long-term fertilizer application, soils are enriched in mobile organic matter in the early (hydrophilic) stages of humification, in more biochemically active organic compounds, and are also enriched in mobile and available nitrogen. The strongest effect of fertilizers on this indicator has been noted in soddy-podzolic soils, weak in chernozems, and very weak in sierozems.
The effect of mineral nitrogen and potassium fertilizers on soil fertility is associated with cation exchange. Systematic application of these fertilizers leads to fixation of the monovalent cations potassium and ammonium contained in the fertilizers by soil colloids, which is associated with the entry of cations into the crystal lattices of minerals. This process is influenced by the type of clay mineral, particle-size composition, organic matter content, soil solution reaction, 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 the hydrothermal conditions under which fixation occurs.
Nonexchangeable absorption of cations reduces their availability to plants and the utilization coefficient of nitrogen and potassium fertilizers.
The use of ammonium forms of nitrogen fertilizers is accompanied by fixation (nonexchangeable 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 amounts and must be taken into account in the overall nitrogen balance. Long-term use of nitrogen fertilizers leads to an increase in the amount of fixed ammonium. Ammonium fixation in soils of light particle-size composition is lower than in heavier soils, since fixation is associated with the silt fraction and the clay minerals composing it. Ammonium fixation occurs in the arable and deeper soil layers, especially in soils of light particle-size composition. Apparently, nonexchangeably absorbed ammonium is leached into lower layers together with colloids, whose content increases down the soil profile.
Table. Change in the content of nonexchangeable ammonium nitrogen in the soil profile of long-term stationary experiments, mg N/kg soil. Gray forest medium-loamy soil, Novosibirsk region (Yakimenko V. N., 2009).
| Variant | Soil layer, cm | |||
|---|---|---|---|---|
| 0-20 | 20-40 | 40-60 | 60-80 | |
| Virgin land | 165 | 188 | 192 | 215 |
| Fallow | 164 | 182 | 195 | 221 |
| Control (vegetable crop rotation) | 151 | 182 | 187 | 211 |
| Control (grain crop rotation) | 155 | 139 | 171 | 145 |
| NP (vegetable crop rotation) | 145 | 195 | 191 | 232 |
| NP (grain crop rotation) | 154 | 150 | 178 | 152 |
| NPK (vegetable crop rotation) | 209 | 190 | 197 | 225 |
| NPK (vegetable crop rotation) | 190 | 150 | 211 | 187 |
Crops, depending on the structure of the root system and its absorption capacity, influence the processes of migration of mineral forms of nitrogen and nonexchangeable absorption of ammonium.
When nitrogen and potassium fertilizers are applied simultaneously, ammonium fixation decreases due to the competing action of potassium.
Ammonium from mineral fertilizers is fixed faster than ammonium from manure, since it has greater mobility. When manure is applied, nonexchangeable absorption of ammonium is less pronounced than when mineral fertilizers are applied. This is associated with increased potassium fixation, improvement of the physicochemical properties of the soil, and enhanced nitrification capacity of soils.
Nitrogen retention in the form of nonexchangeably absorbed ammonium occurs in the first years of systematic fertilizer application, and once the fixation capacity is filled, no further increase in fixed ammonium from fertilizer application occurs. Potassium, like ammonium, is actively fixed in the first years of fertilizer application, and when the capacity for nonexchangeable potassium fixation is filled, it decreases, while its availability to plants and the coefficient of utilization by plants increase.
The nature of the transformation of fertilizer potassium depends on soil and climatic conditions. In soddy-podzolic and gray forest soils, the amount of exchangeable potassium increases, while the content of nonexchangeable potassium changes little. Accumulation of exchangeable potassium is noted in the arable layer and in deeper layers. In the arable layer of chernozems, nonexchangeable absorption of potassium predominates, while the amount of exchangeable potassium increases to a lesser extent. In sierozems, the content of exchangeable and nonexchangeable absorbed potassium increases.
Table. Content of various forms of potassium in soils under long-term fertilizer application, mg K2O/100 g soil.
| Soil, experimental institution | Experimental variant | Exchangeable potassium | Nonexchangeable potassium | ||
|---|---|---|---|---|---|
| Total content | Increase from fertilizers | Total content | Increase from fertilizers | ||
| Soddy-podzolic silty-sandy-loamy (MSKhA named after K. A. Timiryazev) | Control | 8,6 | — | 63,6 | — |
| Manure | 15,2 | 6,6 | 67,7 | 4,1 | |
| NPK | 14,8 | 6,2 | 67,1 | 3,4 | |
| Soddy-podzolic heavy-loamy (DAOS) | Control | 8,6 | — | 140 | — |
| Manure | 14,9 | 6,3 | 147 | 7,0 | |
| NPK | 14,8 | 6,2 | 146 | 6,0 | |
| Gray forest light-loamy (VNII of Bast Crops) | Control | 11,1 | — | 63,6 | — |
| Manure | 33,8 | 22,7 | 67,7 | 9,0 | |
| NPK | 30,0 | 18,9 | 67,1 | 3,0 | |
| Leached chernozem light-loamy (Mironovsky Research Institute of Wheat Breeding and Seed Production) | Control | 12,2 | — | 258 | — |
| Manure | 17,5 | 5,3 | 276 | 18,0 | |
| NPK | 16,4 | 4,2 | 272 | 14,0 | |
| Typical chernozem (Ak-Kavak experimental station) | Control | 33,8 | — | 527 | — |
| Manure | 55,4 | 21,6 | 557 | 29,0 | |
| NPK | 40,7 | 6,9 | 545 | 18,0 | |
The leaching regime of light-chestnut soils created by irrigation changes the content of nonexchangeable forms of potassium. The greatest changes are noted in the arable horizon, but the effect extends to the one-meter soil layer.
Table. Effect of systematic fertilizer application on the potassium regime of chestnut soils (Zhukova L. M., Nikitina L. V., 1986).
| Sampling depth, cm | Exchangeable potassium | Lightly hydrolyzable potassium | Nonexchangeable potassium | ||||||
|---|---|---|---|---|---|---|---|---|---|
| control | NPK | 2(NPK) | control | NPK | 2(NPK) | control | NPK | 2(NPK) | |
| Volga Research Institute of Irrigated Agriculture (NIIOZ), light-chestnut soil, irrigation experiment | |||||||||
| 0-25 | 27,5 | 30,1 | 33,9 | 119 | 128 | 131 | 403 | 424 | 447 |
| 25-40 | 26,3 | 28,0 | 29,1 | 129 | 130 | 129 | 413 | 422 | 431 |
| 40-60 | 18,1 | 20,6 | 22,4 | 103 | 109 | 110 | 319 | 326 | 363 |
| 60-80 | 16,2 | 18,8 | 20,5 | 97 | 83 | 92 | 293 | 298 | 305 |
| 80-100 | 16,7 | 19,2 | 19,5 | 85 | 85 | 100 | 289 | 300 | 296 |
| Issyk-Kul Agricultural Experimental Station (SKhOS), light-chestnut soil, irrigation experiment | |||||||||
| 0-20 | 23,4 | 24,4 | 26,0 | 262 | 273 | 276 | 270 | 281 | 299 |
| 20-40 | 21,2 | 20,7 | 23,5 | 243 | 251 | 268 | 267 | 272 | 284 |
| 40-60 | 16,0 | 18,9 | 18,3 | 236 | 234 | 238 | 264 | 295 | 320 |
| 60-80 | 14,2 | 17,8 | 20,7 | 197 | 207 | 231 | 265 | 292 | 266 |
Cation fixation is determined by soil type. For example, soddy-podzolic soils, despite the high dispersion of minerals, are characterized by a low ability to fix potassium. This is associated with the acidic reaction of the soil solution, unsaturation of soils with bases, low organic matter content, and increased soil moisture. Under such conditions, nonexchangeable absorption of potassium occurs in small amounts and only in the upper arable layer.
Liming and long-term application of manure increase the potassium-fixing capacity of acidic soils compared with mineral fertilizers, which is due to an increase in the amount of organic matter and the coagulating action of divalent cations contained in manure and lime fertilizers. With the combined application of nitrogen and potassium fertilizers, due to competition with NH4+ ions, potassium fixation decreases by 2–3 times.
Potassium fixation in soddy-podzolic soils is small and does not affect fertilizer application, since nonexchangeable potassium of soil colloids is a source of replenishment of exchangeable potassium reserves.
In gray forest soils, fixation of potassium and ammonium is more pronounced than in soddy-podzolic soils. The soil solution reaction, mineralogical composition, and increased organic matter content promote intensification of the process.
In chernozems, the conditions for nonexchangeable cation fixation are most favorable: high saturation of the absorbing complex with bases, high pH, high organic matter content, mineralogical composition of the colloidal fraction with a predominance of minerals of the montmorillonite group, and periodic drying of the upper layer, which leads to irreversible coagulation of colloids.
Simultaneous application of potassium and nitrogen fertilizers does not reduce potassium fixation, since nitrification processes actively occur in chernozems, which causes 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 sierozems, long-term fertilizer application leads to an increase in the amount of nonexchangeable potassium and ammonium. The transition of these cations into a nonexchangeably absorbed state is due to the predominance of hydromica minerals in the silt fraction. These minerals have a high fixing capacity with respect to monovalent cations. The alkaline reaction of the soil, saturation with divalent bases, and periodic drying of soils under the climate of dry-steppe and desert zones are also important.
The leaching regime promotes an increase in fixed cations in the lower layers of the soil profile. The combined application of nitrogen and potassium fertilizers has little effect on cation fixation, since the mineralogical composition of these soils has a high capacity for fixation of monovalent cations.
According to the content of exchangeable potassium and fixed ammonium, soils can be arranged in the following sequence: soddy-podzolic < gray forest < chernozemic < chestnut < sierozems.
Within one soil type, the amount of nonexchangeable cations increases from soils of light particle-size composition to heavy ones. Reserves of nonexchangeable cations must be taken into account when assessing soil fertility and calculating nutrient balances.
Natural phosphorus reserves in soils and their distribution along the profile depend on the phosphorus content in parent rocks and the nature of the soil-forming process. With systematic fertilizer application, the total content and amount of mobile forms of phosphorus increase. The degree of manifestation of changes is determined by fertilizer rates, 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 rates, the subarable layer is enriched in phosphorus, and in the case of light soils without liming and under irrigation, even deeper layers are enriched.
The composition of mineral phosphates along the profile is determined by the genetic characteristics of soils. Thus, in soddy-podzolic soils, phosphates of sesquioxides predominate, while in chernozems, calcium phosphates predominate.
When mineral phosphorus fertilizers are applied, more phosphates of sesquioxides accumulate in soils compared with manured soils.
Physiological Reaction of Salts
All mineral salts used as fertilizers can be divided by chemical properties into hydrolytically:
- acidic;
- alkaline;
- neutral.
The intensity of uptake of cations and anions during plant nutrition is different, as a result of which ions remain in the nutrient solution that cause acidification or alkalization of the medium.
Physiological acidity of fertilizer is the property of acidifying the soil solution reaction, associated with the preferential uptake by plants of cations from the composition of a mineral salt. Physiological alkalinity of fertilizer is the property of a fertilizer to alkalize the soil solution reaction, associated with the preferential uptake of anions from the composition of a mineral salt.
Thus, the change in the reaction of the medium is influenced not only by the reaction of the salts but also by their physiological reaction.
The physiological reaction of salts is more pronounced in water and sand cultures, that is, in media with low buffering capacity, therefore at high fertilizer rates it should be taken into account. When using physiologically acidic salts, anticipatory liming must be carried out.
Nitrogen is taken up by plants first. Ammonium salts are physiologically acidic, while nitrates are physiologically alkaline. For example, sodium nitrate dissociates into Na+ and NO3- ions; the NO3- anion is consumed by plants in larger amounts than the Na+ cation; as a result, the hydrolytically alkaline salt NaHCO3 accumulates in the solution. A similar reaction occurs when KNO3, Mg(NO3)2, and Ca(NO3)2 are applied.
Acidification of the solution occurs due to the more intensive uptake by plants of ammonium formed upon dissociation of NH4Cl and (NH4)2SO4. The application of these fertilizers requires neutralization of the acids formed by anticipatory liming. The physiologically acidic reaction of these salts was established in his works by D. N. Pryanishnikov.
The manifestation of the physiological reaction of ammonium nitrate depends on a number of factors determining nitrate and ammonium nutrition of plants. Usually the physiological acidity of ammonium nitrate is significantly weaker than that of other ammonium salts.
The physiological acidity of potassium fertilizers is even less pronounced than that of ammonium fertilizers. When growing crops with little need for potassium, for example, oats and barley, potassium salts proved to be physiologically neutral, whereas when growing sugar beet, sunflower, and maize, which consume large amounts of potassium, potassium salts proved to be physiologically acidic. Potassium-loving crops include potato, tobacco, and flax.
The ability to maintain the reaction of the nutrient solution depends on its composition. Thus, a solution containing a large amount of calcium bicarbonate Ca(HCO3)2, formed by the interaction of CaCO3 with carbon dioxide in water, eliminates excess acid through neutralization with calcium bicarbonate:
Such a solution is characterized by a certain buffering capacity, and noticeable changes in the reaction of the solution do not occur. The buffering capacity of soils depends on the absorption capacity and the composition of absorbed cations.
Effect of Fertilizers on Biological and Enzymatic Activity of Soils
Biological activity of soils is the totality of biological and biochemical processes occurring in the soil. It depends on the genetic characteristics of the soil, hydrothermal conditions, agronomic measures, the degree of mineralization and humification of plant residues, and the mobilization capacity of soils. Systematic application of fertilizers in crop rotations enhances the activity of soil biota.
On acidic soddy-podzolic soils, the application of lime influences the activity of biological processes. Periodic liming reduces the content of mobile aluminum and exchangeable hydrogen, creates more favorable living conditions for microorganisms in the soil, and intensifies the processes of organic matter mineralization.
Manure in pure form and in combination with mineral fertilizers and liming has a positive effect on biological activity. Liming enhances the effect of fertilizers on enzymatic activity.
Table. Effect of systematic fertilizer application on the biological activity of chestnut soil. Winter wheat and alfalfa. (Number of microorganisms, thousands per 1 g of dry soil on average over the growing season). Long-term experiment of Gorsky Agricultural Institute (Dzhanayev G. G. et al., 2005).
| Experimental variants | Ammonifying microorganisms | Spore-forming bacteria | Actinomycetes | Denitrifying bacteria | Bacteria assimilating mineral forms of nitrogen |
|---|---|---|---|---|---|
| Control | 3876 | 1462 | 5111 | 45 | 8509 |
| NPK | 4892 | 1623 | 5251 | 71 | 10698 |
| 2 NPK | 6576 | 1987 | 5814 | 89 | 15125 |
| Manure + NPK | 7958 | 2210 | 6136 | 122 | 18575 |
| 3 NPK | 6830 | 2007 | 6212 | 110 | 15021 |
The effect of fertilizers on the enzymatic activity of soddy-podzolic soils is similar to their effect on biological activity. Maximum enzyme activity is noted against the background of manure.
On chernozem, dark-gray forest soil, and sierozem, manure in pure form and together with mineral fertilizers has a positive effect on enzymatic activity. In most cases, an increase in urease activity is noted, which is due to the neutral or slightly alkaline soil reaction favorable for ureobacteria. Under the influence of fertilizers, invertase activity increases, and the activity of decomposition and synthesis of nitrogen-free organic substances increases to the same degree against the background of manure and mineral fertilizers.
References
- Mineev V. G., Sychev V. G., Gamzikov G. P., et al. (2017). Agrochemistry. Textbook. Edited by Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
- Bazdyrev G. I., Loshakov V. G., Puponin A. I., et al. (2000). Agriculture. Textbook for Universities. Moscow: Kolos Publishing House.
- Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Agriculture and Crop Production. Moscow: Bylina.
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Edited by B. A. Yagodin. Moscow: Kolos.
