Diagnosis of plant nutrition – a set of methods aimed at determining the availability of plant nutrients.
The purpose of plant nutrition diagnostics is to continuously monitor growing conditions and, if necessary, correct plant nutrition during vegetation.
Diagnosis of plant nutrition can be:
- comprehensive, involving regular agrochemical soil analyses, including an annual one to assess nitrogen availability;
- operational, which involves diagnosing nutrition during the growing season.
Methods of plant nutrition diagnostics:
- soil diagnostics – determining the quantitative content of nutrients in soils.
- plant diagnostics – determining the composition of chemical substances in the plant organism.
When correcting plant nutrition with the help of diagnostic methods we should take into account:
- high ordering of vital processes and their localization inherent in plants;
- the rate of plant growth and the onset of phases of development, which are determined by genetic factors;
- growing conditions;
- the impact of nutritional disturbances on the development and chemical composition of vegetative organs, which correlates with the chemical composition of reproductive organs;
- nutrients are activators, inhibitors or stabilizers, due to the lack or excess of which the processes of biosynthesis of physiologically active substances and their metabolism are disturbed;
- if the function of the nutrient is known, it is possible to control the reaction by dosage and ratio of nutrients;
- introduction of nutritional elements leads to changes in the chemical composition of plants, and it is possible to increase the content of other elements that were not introduced;
- decomposition of organic matter produces carbon dioxide, water and minerals that affect plant nutrition;
- correction of nutrition and cultivation technology in the early stages of development is most effective. Sufficient and balanced supply of nutrition helps to accelerate the initial stages of growth, which leads to a prolongation of each individual leaf;
- when distributing assimilates between competing same-type organs, the larger and closer to the source have an advantage.
Plant diagnostics
Plant diagnostics – determining the availability of chemical elements in plants by their chemical composition, taking into account the biological characteristics of the variety, growth rate and duration of growing season.
Diagnosis of plant nutrition is carried out taking into account the history of the field, soil and agrochemical maps, the results of experiments and zonal recommendations on the use of fertilizers for a particular crop. Diagnosis of plant nutrition is carried out taking into account the analysis of the chemical composition of leaves and roots. Normal provision of plants with nutrients is considered a state of internal saturation, accumulation in the reserve zones of the reserve of chemical elements.
For different conditions of soil and climatic zones the general optimal parameters of NPK content in grain crops using the methods of plant diagnostics have been developed.
Plant diagnostics includes:
- visual,
- chemical (tissue and leaf),
- functional, or physiological.
Visual diagnostics
The method of visual diagnosis is based on changes in the morphological signs of plants caused by deficiency or excess of nutrients in the soil.
The accuracy of the visual method is reduced due to the fact that often a sharp deficiency or excess of elements caused in the characteristic signs is rare, while a partial deficiency or excess may not be externally manifested. In addition, similar visual signs can be caused by deviations in temperature or water regimes, pest or disease damage.
Any disturbance of plant life processes is reflected in its appearance, which can be detected in various organs. But for each disorder, there are the most characteristic indicator organs, by which diagnosis is easier to make.
Plant starvation is noted when there is a short-term shift in the optimum ratio of elements, it can occur even on a high nutrient background with a combination of unfavorable external growth factors – light exposure, humidity, temperature, aeration.
In practice, quite often an excess of some nutrients, such as ammonium nitrogen, chlorine, and manganese, is observed in the plant.
The nutrient requirements of different crops vary, so in the same field rye can give a good yield without showing signs of potassium starvation, while potatoes cannot develop normally.
Indicator-plants – plants, by the appearance of which it is easiest to determine the lack or excess of any element of mineral nutrition.
Visual diagnosis of plant nutrition is one of the simplest, requiring no equipment method that allows in a relatively short time to draw a conclusion about the violations of plant nutrition, the causes (soil and weather factors), and to make recommendations for changes in cultivation technology.
In the visual diagnosis, in addition to the general provisions take into account the following:
- When assessing the plant is considered simultaneously in three temporal aspects: in the past, reflecting a set of measures for its cultivation, including environmental factors, in the present, assessing the growth rate and degree of development, and in the future, that is, making a forecast of the size and quality of the crop.
- Signs of starvation or excess of nutrients are more often manifested not on the entire area, but on individual plots, which is associated with different soil fertility, terrain features, the use of fertilizers, treatments.
- Examine the appearance of the plant better with the root system or its part for damage from pests, fungi, bacteria, viruses, pesticides and growth agents.
- Often the signs of deficiency and excess have outward similarities. However, deficiency is characterized by clearer signs.
- Plant damage caused by viruses often has similar signs to mineral nutritional deficiencies, but is characterized by a clearer boundary of the affected area.
- A final conclusion about the cause of the disturbance is made after eliminating it with appropriate treatments or fertilizers. On severely damaged leaves, external signs may persist.
In case of deficiency or excess of the element, the external signs may differ depending on the species and variety. However, there are common signs.
Many nutrients such as nitrogen, phosphorus, potassium, and magnesium have the ability to be reutilized, that is, reused. Deficiencies of these elements appear primarily on the lower, older leaves. Ability to reutilize calcium, sulfur, chlorine, boron and others is weaker, so their deficiency is manifested in the points of growth and on young leaves.
For visual diagnosis they evaluate:
- the general condition of the plants of the plot, field;
- weight, height of plants, correspondence of development to the period (phase) of vegetation;
- length of internodes (young plants have shorter internodes);
- stems are complete, resilient and mature, e.g. with a balanced nutrition the stem is more complete in a circle; maturity is estimated by the color of the cut at the level of the 3rd internode from above;
- leaf elasticity, coloration of leaves by tier, and nature of disturbances within the tier;
- development of roots, presence of root hairs, coloring of roots.
Based on the evaluation results, conclusions are made and recommendations are developed to change the cultivation technology. It is possible to correct unbalanced nutrition only partially, since the appearance of external signs of the lack of a mineral nutrient element indicates profound changes in plant metabolism, which subsequently cannot be eliminated completely.
In order to confirm the suspected nutritional disturbance in plants, injection and spraying methods are used for visual diagnosis. By spraying a leaf or by injection, the presumed missing element is injected into the stem (leaf gland). Observations are then made for several days. If the missing element is correctly identified, the signs of deficiency disappear, but not on the leaves on which it is identified, but on the newly formed ones.
To eliminate nutritional element deficiency, 0.5% solutions of potassium and calcium salts, 0.1% solutions of urea, sodium monophosphate, magnesium sulfate, 0.02-0.1% solutions of salts of trace elements are used.
Nitrogen
Nitrogen deficiency manifests itself:
- in the form of inhibition of vegetative growth and reproductive development,
- severe reduction in yields,
- leaves become light green, then yellow-green to yellow, with severe deficiency signs of nitrogen starvation spread to the whole plant. The aging of the lower leaves may be due to a lack of water, but at the same time there are signs of excess nitrogen.
Nitrogen starvation can easily be corrected by applying appropriate doses of fertilizer. If there is a lack of nitrogen in the soil, but with periodic fertilization, the plants are not deficient in this element.
Normal or increased nitrogen content in the soils of protected ground in spring and summer leads to increased pigmentation, can contribute to overheating of plants, closure of stomata and the termination of the entry of carbon dioxide, the increased decay of organic compounds.
Excess nitrogen is manifested by:
- a longer growing season;
- prolongation of the vegetative period, and its strong vegetative growth and, if there is a large excess of nitrogen, a complete halt to growth or even death of the plant;
- a reduction in resistance to disease;
- increased concentration of low-molecular nitrogen compounds, which worsen the fodder quality. For example, it was found that when nitrates are present in the feed more than 0.20%, milk yields decrease (Harker and Kaman, 1961), and at 0.34-0.45%, animal death is possible;
- formation of broad, succulent, dark green to bluish-green leaves (if the excess nitrogen is not due to lack of water);
- an increase in plant weight;
- poor development of the reproductive organs;
- damage to the product during storage;
- a gradual weakening of carbon dioxide uptake;
- decreased protein content and increased carbohydrate content;
- retardation of aging processes;
- increased outflow of nitrogen from old to young organs;
- decomposition of plasma proteins, the content of nucleic acids remains unchanged.
Cucumber and zucchini can be used as indicators of nitrogen excess, and white and cauliflower cabbage, corn, potato, black currant, apple tree, plum can be used as indicators of nitrogen deficiency.
Phosphorus
Phosphorus deficiency manifests itself as:
- decreased activity of the tricarboxylic acid cycle, protein synthesis,
- Increased accumulation of non-protein nitrogen compounds,
- decreased synthesis of starch and cellulose, and in severe deficiency the formation of sugars is slowed down,
- increased accumulation of sugars and anthocyanin.
Phosphorus deficiency appears well on tomato, apple, gooseberry, rutabaga, turnip.
Deficiency of phosphorus leads to inhibition of cell division, limitation of plant growth. Leaves turn dark green, dirty green, then reddish to purplish. Older leaves are the first to suffer. Forming leaves are small, ugly, and flowers are small. Premature fruit drop is noted in fruit and citrus crops, and crop thinning in cereals.
In field crops, the signs of phosphorus deficiency are more difficult to determine compared to others. Phosphorus deficiency can also be observed in soils with sufficient content, but with changes in other indicators, such as pH, humus and fine fraction, aluminum, calcium, iron. Phosphorus intake decreases during droughts and low temperatures, lack of oxygen.
Against a background of high doses of nitrogen and high yields, plant demand for labile phosphorus increases, especially during the phase of maximum growth.
Excess phosphorus is often observed in indoor conditions, much less often in field crops, leads to early aging of plants, starting with yellowing and dying off of old leaves, accelerated transition to the development of reproductive organs.
Application of high doses of phosphorus creates a deficit of calcium and trace elements such as, zinc, iron, boron, copper, manganese, the intake of toxic elements – aluminum and heavy metals is reduced.
Potassium
Potassium deficiency is often evident on light, acidic or high in three-layer clay minerals soils, which lose and fix potassium during intensive use. Potassium uptake worsens with desiccation and high doses of ammonium fertilizers that block potassium in three-layer minerals like vermiculite. Potassium deficiency can be caused by antagonism with calcium and ammonium.
Potassium deficiency leads to profound disturbances in structure and metabolism due to the participation of potassium in enzymatic processes and biological colloids. Hydrolysis processes are intensified, enrichment with low-molecular compounds of carbon and nitrogen increases, cell walls become thinner, water loss increases and its intake decreases.
Potassium-loving crops such as cabbage, potatoes, gooseberries, beets, alfalfa, beans, red currants and apple trees are most sensitive to potassium deficiency.
Signs of potassium deficiency include:
- stunted plant growth;
- normally colored or light green leaves are firm in the morning hours, wilting as light or temperature increases;
- young leaves small;
- leaves of lower tiers with normal or dark green coloration, become cup-shaped, dome-shaped, more often with marginal undergrowth. With severe potassium deficiency, these signs spread to leaves of the middle and upper tiers. In some plant species, pitting necroses along leaf margins are noted, which later merge into areas of light and dark brown color.
Excess of potassium is rare. Its signs are more often accompanied by signs of chlorine excess. Excess potassium may also appear as a lack of calcium and magnesium. High potassium content leads to lower intake of boron, zinc, manganese and ammonium, and increased intake of iron.
Calcium
Calcium deficiency increases synthesis of phenolic compounds. Cell membrane permeability increases, resulting in outflow of ions from the cell and further disturbance of nucleus structure, decrease in chromosome stability. Calcium is especially important for meristem tissue and its differentiation, directed action of phytohormones.
Plant species and varieties differ in their need for calcium and in their ability to absorb it from the soil. Disturbance of calcium nutrition in plants is often the cause of non-parasitic diseases.
Calcium accumulates in vegetative organs and in limited amounts in fruits. Its content in fruits and hoarding organs decreases with decreased transpiration, but high transpiration does not guarantee sufficient supply of calcium and water to plants.
Calcium nutrition of the plant is related to boron nutrition, the signs of deficiency of which are similar.
High calcium concentrations due to antagonism reduce the supply of other cations, which is important to consider in the presence of heavy metals in the soil. Calcium has a positive effect on elevated concentrations of soil solution macronutrients and most trace elements except molybdenum.
Calcium deficiency increases nitrate accumulation in plant tissues. The apical meristem, shoot and root, flowers and fruits are the first to suffer. Old leaves turn dark green, then turn yellow and die off. Roots remain short, slough, turn brown, and die off. In the upper, young leaves, the tip turns white at first, and the edges are affected with major disturbances.
With reduced transpiration, reduced calcium inflow leads to breakage of shoots of outwardly normal and intensively developing plants.
In fruit plants, when the ratio of ammonium nitrogen to calcium is increased, flower dieback occurs; increased potassium content intensifies this process. When calcium content in leaves is less than 3.0% and in fruits less than 0.15%, wilting of flowers begins.
Sufficient calcium content in leaves and fruits is not a guarantee of optimum conditions for further plant growth. Calcium must be in the form of free ions in the soil solution. The need for it increases with increasing light exposure.
An excess of calcium is rare, as a result of nutrient disturbance during liming. At the same time there may be a lack of potassium, boron, manganese, zinc, copper, sometimes magnesium, and an excess of chloride and sulfate. In such cases, in order to maintain the planned yields, the doses of all elements are increased and physiologically acidic fertilizers are envisaged.
Magnesium
Sufficient potassium nutrition of plants increases the content of magnesium in seeds and fruits; high doses of potassium fertilizers, on the contrary, suppress this process. A high potassium to magnesium ratio increases the manifestation of chlorosis, even if there is enough magnesium in the soil. High doses of ammonium have a similar effect.
Magnesium deficiency is observed in many soils, especially on dealluvial sandy, highly leached, acidic soils of high bogs, as well as on soils after liming in connection with the antagonism of calcium and magnesium. Lack of magnesium nutrition at optimal levels in the soil may be due to antagonism with hydrogen, potassium, ammonium, calcium, and manganese ions (Bergman, 1983).
Cabbage, potatoes, apple trees, gooseberries, blackcurrants, and grapes are susceptible to magnesium deficiency. Magnesium deficiency causes orange coloring of millet leaves, and purple-red coloring of blackcurrant and cottonseed.
Magnesium deficiency causes magnesium to drain from older leaves. Healthy plants have more magnesium concentrated in the lower leaves than in the upper leaves. Interstitial chlorosis is observed on the lower leaves, followed by brown and dark brown necroses. Magnesium deficiency reduces starch accumulation in potatoes, sugar in sugar beets, fat in oil-bearing plants, and protein.
Magnesium deficiency in vegetative organs leads to an increase in phosphorus, in seeds – to a decrease, and later in leaves. Nitrate reduction and phytohormone synthesis are slowed. In severe deficiency, carbon dioxide fixation stops, leaves become brittle, and accumulation of proteins, carbohydrates or fats in fruits decreases.
An excess of magnesium can be observed when the calcium-magnesium ratio is disturbed, especially when the root system is specifically damaged due to the lack of calcium, the yield is reduced, growth is slowed, potassium content and magnesium intake is reduced. Excess magnesium is also affected by high levels of nickel and chromium. Magnesium intake is facilitated by the nitrate ion.
Bor
Deficiency of boron leads to disturbances in the metabolism of nucleic acids, proteins and carbohydrates, respiration and photosynthesis processes; synthesis of phytohormones is reduced. Visual identification of boron deficiency due to its involvement in many metabolic processes and plant development is difficult.
Signs of boron deficiency are manifested primarily on young leaves and on the tips of growing shoots and roots. Boron content in older leaves is always higher.
Signs of boron deficiency may include:
- chlorosis, yellowing and then turning brown on the tips of young leaves; in tomato, blackening of the stem growth point;
- die-off of the growth cone, stunted formation of roots, flowers, seeds;
- desiccation of leaves, shredding, stopping the dominant development of the central shoot and sprouting of lateral shoots and roots.
Boron deficiency is stronger on rutabaga, turnip, sugar and fodder beets, sunflower, cauliflower and fodder cabbage, legumes, fruit crops, tomato, celery, flax, and rye.
Excess of boron leads to white-white edges of leaves, later they turn brown; sometimes pinpoint chlorosis appears on old leaves first. Excess of boron can coincide with signs of potassium deficiency.
Molybdenum
Molybdenum deficiency is manifested in the form of light coloring of leaves, especially along the central vein, similar to the signs of nitrogen deficiency and nitrate nitrogen excess, i.e. darker coloring and whitening of the leaf margin. Nitrogen supply to the reproductive organs is slowed, resulting in yield loss. Excess molybdenum leads to severe growth inhibition.
The deficiency is pronounced on cauliflower, legumes and green crops, tomato, and citrus. Most crops develop yellow leaf spotting, in cucumber – chlorosis of the edge of leaf blades.
Copper
In soil, copper is accumulated in organomineral complexes and partially in the exchange-absorbed state. Availability of copper decreases when the pH rises from 5.5 to 6.0. Deficiency of copper is clearly expressed on uncultivated wastelands, on light soils and soils of high bogs, sometimes on lowlands. Lack of copper in the feed leads to animal diseases.
Copper deficiency is more pronounced on clover, meadow millet, legumes, vegetables, oats, barley, wheat, cereal grasses, hemp, flax, forage and table root crops.
Copper deficiency is manifested by white tips of leaves, which later dry up; plants throw out panicles with high hollowness with a long delay; grains are formed sparsely.
Excess copper and phosphorus leads to zinc deficiency, sometimes iron deficiency. Excess appears on young leaves.
Iron
Iron deficiency is noted in soils rich in calcium and having an alkaline reaction, can occur in acidic soils with high magnesium content. Iron is absorbed by the plant throughout the growing season because it is not recycled from old leaves.
Iron deficiency shows up on young leaves, on fear, only when very deficient. Light green coloring of young leaves appears first, followed by yellowing and whitening. The veins and adjacent tissues remain green. The appearance of chlorosis decreases from top to bottom.
Excess iron is extremely rare, with leaves becoming dark green and bluish-green in color due to limited growth of shoots, leaves and roots. Symptoms of excess often coincide with symptoms of phosphorus deficiency, especially at low pH values.
Manganese
Manganese is contained in the humus layer and the silt fraction of the soil. In acidic soils, it is present in the form of a low-mobile divalent poorly accessible to plants. Mobility of manganese increases with the application of ammonia fertilizers.
Manganese deficiency manifests itself as point chlorosis, turning into necrosis on young leaves, and in excess – on old leaves.
Manganese deficiency is often observed in oats, wheat, potatoes, corn, table and forage root crops, cabbage, legumes, sunflower, fruit, citrus and vegetable crops. For example, oats have gray leaf spotting and sugar beets have spotting jaundice.
Excessive manganese content is eliminated by liming or high doses of iron.
Zinc
Zinc deficiency is manifested as reduction of growth, asymmetry of leaves, corrugation of leaf blade, inter-vein chlorosis.
Fruit crops, citrus, corn, soybeans, beans, buckwheat, beets, potatoes, meadow clover, and hops are susceptible to zinc deficiency.
Zinc deficiency is especially common in neutral and slightly alkaline soils. Systematic application of manure greatly reduces the risk of zinc deficiency. One way to prevent zinc deficiency is to plow weeds under corn.
An excess of zinc is extremely rare. Appears as chlorosis associated with iron deficiency, coloration of leaf veins is the same as in phosphorus deficiency; individual chlorosis along veins is located closer to leaf margins; leaf marginal chlorosis.
Chemical diagnostics
The method of leaf or tissue diagnosis is based on the relationship between changes in the nutritional regime and the chemical composition of leaves or tissues, the most responsive organs. Optimal concentrations of nutrients have been determined for different plants, at which crops show maximum productivity.
The accuracy of these methods for predicting fertilizer requirements is higher than soil analyses, because when determining the amount of nutrients in the soil, it is difficult to predict how much of them will reach the plants under changing plant life factors.
The disadvantage of chemical diagnostics, as well as of visual diagnostics, is the delay in obtaining information. Chemical diagnosis of plant nutrition under adverse meteorological conditions also gives distorted data on plant nutrition due to.
Tissue diagnosis
Tissue diagnosis of plant nutrition involves determining the content of nitrates, phosphates, sulfates, potassium, magnesium and other nutrients in tissues or extracts from plants. Tissue diagnosis can be carried out in the field with portable devices – portable laboratories, and in the laboratory. It is used for express analysis of nitrate, phosphate and potassium content in raw plant samples by the method of V.V. Zerling and to determine the ripeness of grain. For the same purpose you can use a portable express laboratory – a field bag of K.P. Magnitsky.
Determination of nitrate nitrogen in plant tissues under field conditions can be done by reaction with diphenylamine. This method is used to assess the need for nitrogen dressing.
Table. Determination of nitrate nitrogen
Indicator paper “Indam” can be used to diagnose nitrogen nutrition of winter cereals. Diagnostics is performed in tillering, heading, earing, and flowering phases. The following nodes are analyzed: in tillering phase – the tiller node, the second stem node – the second stem node, earing and flowering – the last stem node before the ear.
Table. Estimation scale of nitrogen availability of winter cereal crops
| White, pink-white | |||||
| Pink | |||||
| Pink intense, crimson | |||||
The method of determination in tissue slices is less accurate than in extracts.
Observations made under field conditions by B.A. Yagodin in 1993 of nitrate nitrogen availability in winter wheat in phases from the beginning of emergence to the beginning of grain formation using the method of tissue diagnosis allowed to establish the periods of highest demand for nitrogen fertilizers. It was found that the place of nitrate localization in the stem within the same phase of development is not constant, so it is necessary to pre-determine the stem node over which to make a cut for tissue diagnosis.
In this work, tissue diagnosis was performed according to the method of Wolring, Wehrmann (1981, 1983) using 0.5 g diphenylamine in 100 ml of concentrated H2SO4, which is similar to the method of Zerling (1978). A four-point scale was used to assess assurance:
- 0 – no staining,
- 1 – blue,
- 2 – light blue,
- 3 – dark blue.
The necessity of the second foliar nitrogen top dressing in the phase of emergence of the tube was justified by a decrease in the nitrogen content below 2 points. The dose was determined according to recommendations (Vielemeyer und a. 1985; Jakob und a., 1986): with an average score at the stage of 0 to 1.4, the dose is 40-50 kg N/ha, with 1.5-2.4 points – 30-40 kg N/ha. The third feeding with nitrogen fertilizers was carried out at the stage of milky ripeness in a dose of 30 kg/ha.
Leaf diagnostics
Leaf diagnosis of plant nutrition consists of gross analysis of the chemical composition of leaves of the whole plant or individual organs and comparison of the data obtained with reference values, the results of which make a conclusion about the availability of mineral nutrition, taking into account the state, growth and development of plants in a particular phase.
Plant samples are selected from areas typical for the given field, i.e. with a characteristic soil cover and the state of plants in certain phenophases.
Early diagnostic control taking into account the specific needs of crops by vegetation periods is the most informative.
When analyzing seedlings, sprouts or young plants, the whole above-ground part is determined, in adult plants, the lower part of the stem or petioles of the lower leaves are used to determine nitrates. To determine the total nutrient export all plant organs are analyzed. For leaf diagnostics, the indicator organs subject to the greatest changes in chemical composition depending on nutritional conditions can be analyzed. For example, in field tests with grain crops, a mixed sample is made up of 50-70 indicator leaves.
Table. Optimal gross content of nitrogen, phosphorus and potassium in plants, % on absolutely dry mass
| Winter wheat | Tillering | Above-ground part | |||
| Leaves | |||||
| Tubing | Above-ground part | ||||
| Barley | Tillering | Above-ground part | |||
| Leaves | |||||
| Tubing | Leaves | ||||
| Clover | Budding | Above-ground part | |||
| Blooming | Above-ground part | ||||
| Leaves | |||||
| Corn | Sprouting | Above-ground part | |||
| Phase 3-5 leaves | Above-ground part | ||||
| Leaves | |||||
| Phase of 6-10 leaves | Leaves | ||||
| Sugar beet | Phase 4-6 leaves | Leaves | |||
| Phase 10-18 leaves | Leaves | ||||
| Row closing | Middle leaves | ||||
| Potatoes | Before budding | Above-ground part | |||
| Leaves |
To determine the insufficiency of elements capable of reutilization, the upper, fully formed leaf is used, for the elements with low ability to reutilization the lower leaves are analyzed. Roots are analyzed in parallel and the ratio of mineral nutrients in the leaves and roots is determined.
For express analysis by the method of Zerling, a mixed sample is prepared from 10-20 whole plants in the tillering and trumpeting phase and from 20 plants in the earing and flowering phases. For biometric control of plant growth and development, 20 plants, including roots, are taken from each experimental plot, and 70-100 plants from each plot are taken for gross analysis in production crops; for biometric control, 25-30 plants are taken. Sampling is carried out in the morning hours, walking along the plot diagonals, no rainfall or irrigation for 2-3 days before sampling.
Storage, transportation, sample preparation and chemical analyses of plants are carried out in accordance with established methods.
The allowable content of nitrates in crop products is established by the state sanitary rules. For example, for potatoes, the allowable content of nitrates is 80 mg/kg raw weight or less, for cabbage no more than 300 mg/kg, tomatoes no more than 60 mg/kg, cucumbers no more than 150 mg/kg, carrots no more than 300 mg/kg, melons no more than 45 mg/kg, water melon no more than 45 mg/kg, table beets no more than 1400 mg/kg, onions no more than 60 mg/kg, chives no more than 400 mg/kg raw weight.
Particularly careful control of nitrate content should be carried out in the early phases of plant development and in leaf and green crops. By the end of the growing season, the nitrate content decreases. Their concentration is higher in the petioles and central veins of leaves which are analyzed. In reproductive organs and meristematic tissues, nitrate content is minimal.
Conclusions about the availability of plant nutrients are made on the basis of the relative content of nutritional elements, as well as the total accumulation by leaves or the whole plant by comparing with reference data.
To determine the removal of elements in plants, the content of nutrients is multiplied by the dry weight of the crop per 1 hectare. Also determine the ratio between the elements to establish the degree of balance of nutrition and compare them with the reference data.
Doses accepted in the system of fertilizers for the planned yield are specified by the results of plant diagnostics:
where D – adjusted dose of fertilizer, kg a.s./ha; A – average set dose, kg/ha; Copt – optimum content of nutrient in plants, % of dry matter; Cfact – actual content of nutrient in plants, % of dry matter. The Copt/Cfact ratio reflects the degree of plants’ need for a nutrient.
If the ratio of nutrients is unbalanced, the dose of one nutrient can be refined relative to the other.
For example, with a lack of nitrogen and an excess of phosphorus, the specified dose of nitrogen (DN) can be calculated by the formula:
Similarly, the dose of phosphorus (DP) in relation to potassium can be calculated by the formula:
Integrated diagnosis and recommendation system (DRIS)
The integrated diagnosis and recommendation system (DRIS) was developed in the United States. It is based on a probabilistic approach, based on the fact that the balance of nutrients in the tissues and organs of plants is subject to characteristic patterns. At the same time, it is assumed that the ratio of elements has diagnostic informativeness and better reflects the provision of plants.
In our country the first experiments with the use of this system, called the integrated system of operational diagnostics (ISOD), were carried out in the Soil Institute of them. V.V. Dokuchaev.
The integrated system of operational diagnostics is a set of methods used to diagnose fertilizer requirements, predict crop productivity and develop models of highly fertile soils. Influences of each factor on productivity indicators are expressed in indices. The basic basis for calculating the index is the optimal level of the factor under study.
The methodology of the system is reduced to determining the actual ratio of the amounts of nutrition elements (N : P, N : K, K : P, N : Ca, N : Mg, etc.) in the leaves and comparing the data obtained with the standards, which are constant for different types of soils. The index shows the degree of deviation of the factor under study from the optimum. The value and sign of the indices show the level of deficiency of an element of a nutrient.
Example. Norms of N:P, N:K, K:P ratios were obtained for the Moscow region by Elnikov et al., 1986. Corn was grown on leached chernozem in different weather conditions in different years. All leaves of corn in the flowering phase were taken for analysis. According to the method in 1963 with a favorable moisture regime in the variant without fertilizers, the soil was insufficiently provided with nitrogen, with an index of – 13.6, excessively provided with potassium (index +11.2) and close to optimal – with phosphorus (index +2.4). Thus, there was a strong imbalance of nutrients – the sum of the indices without taking into account the sign (13.6 + 2.4 + 11.2) = 27.2. Introduction of N60 reduced nitrogen deficiency, but at the same time increased the phosphorus deficiency (index – 5,8), and the total imbalance remained high (sum of indices 18,6). The addition of P60 increased the phosphorus supply and increased the nitrogen deficiency. Potassium application balanced nitrogen and phosphorus deficiency, but the overall imbalance remained.
Table. Fertilizer doses and N, P, K deficiency in corn leaves (by DRIS indexes)
| Control (without fertilizer) | |||||||
| N60P0K0 | |||||||
| N0P60K0 | |||||||
| N60P60K0 | |||||||
| N0P0K60 | |||||||
| N60P60K30 | |||||||
| N90P60K30 | |||||||
| N120P60K30 | |||||||
| N60P90K30 | |||||||
| N60P120K30 | |||||||
| N120P120K120 | |||||||
| Control (without fertilizer) | |||||||
| N60P0K0 | |||||||
| N0P60K0 | |||||||
| N60P60K0 | |||||||
| N0P0K60 | |||||||
| N60P60K30 | |||||||
| N90P60K30 | |||||||
| N120P60K30 | |||||||
| N60P90K30 | |||||||
| N60P120K30 | |||||||
| N120P120K120 | |||||||
Note. The indices are calculated according to the norms: N/P = 10.0, N/K = 1.26, K/P = 7.50 with coefficients of variation 10, 19, 15.
In a dry year, the elimination of excess potassium or reducing its content to a minimum in the absence of nitrogen deficiency (options N120P60K30 and N120P120K120) led to the highest corn yield, which fully corresponds to the characteristics of soil fertility in the option without fertilization. In the other variants a higher deficit of nitrogen was noted, which agrees with the position of the low efficiency of nitrogen fertilizers in years unfavorable in terms of moisture. In the experiments the corn yield was determined by the balance of nutrition elements, which was manifested in the conditions of relatively favorable moisture.
Functional diagnosis of plant nutrition
The uptake of nutrients is not always a consequence of their need for the plant. This is the main drawback of chemical diagnostic methods. In addition, a deficiency or excess of elements can lead to an impairment of plant uptake of other nutrients. For example, phosphorus deficiency leads to an accumulation of nitrates, and boron deficiency leads to a deficiency. However, this has nothing to do with nitrogen nutrition.
Functional diagnostic methods allow you to assess the need for plant nutrients by determining the intensity of physiological and biochemical processes. Thus, the level of supply and need for nitrogen is determined by the ability of tissues to reduce nitrates into nitrites, that is, by the activity of the enzyme nitrate reductase (Muravin, Slipchik, Pleshkov, 1978).
A.S. Pleshkov and B.A. Yagodin (1982) developed a diagnostic method for determining photochemical activity of chloroplasts, which was based on measuring photochemical activity of chloroplast suspension of an average leaf sample of diagnosed plants, followed by analysis with addition of nutrients. When the photochemical activity of the suspension increases with the addition of a nutrient compared to the control, the conclusion is made about the lack of this element, when it decreases – about the excess, and when the activity is the same – about the optimum content.
The proposed method allows for 40-50 minutes to establish the need of plants in 12-15 macro- and microelements and to make recommendations for root and foliar feeding. The method was introduced in 80 greenhouse farms, including Moscow (farm “Belaya Dacha”) and Ivanovo regions (farm “Teplichny”).
Soil diagnosis
Granulometric composition, organic matter content in soil, gross nutrient content, absorption capacity (AC) change slowly and serve as a characteristic of a particular soil difference.
The content of mobile forms of nutrients, soil reaction, composition of absorbed cations, the degree of saturation with bases change faster, especially under the influence of ameliorants and fertilizers. Therefore, agrochemical surveys of soils by these indicators are carried out at certain periods, as a rule, one in two years, or more frequently, depending on the amount of fertilizers and ameliorants applied. The results of such studies are presented in the form of agrochemical maps, field passports, or cartograms, and are used to determine the optimal norms, forms, timing, and methods of fertilizer application, as well as the need and doses of ameliorants.
Soil diagnosis of plant nutrition – periodic determination of relatively rapidly changing agrochemical indicators of soil. Soil diagnosis allows the most rational use of fertilizers and ameliorants, maximize their agrotechnical, economic efficiency and environmental safety.
The most dynamic indicator determined by soil diagnosis, which can change over several days, is the content of mineral forms of nitrogen. For this reason, this indicator is not used for agrochemical maps, cartograms and field passports. However, for economical and environmentally safe use of nitrogen fertilizers annual information about the reserves of mineral forms of nitrogen is necessary.
For regions of sufficient and excessive moisture soil diagnosis of nitrogen forms is carried out before the application of nitrogen fertilizers, in zones with insufficient moisture and arid climate – before the fall application. Depending on the depth of penetration of root systems of crops, water and air regimes of soils during the growing season, the content of mineral forms of nitrogen is determined in the soil layers to 100, 150, 180 cm. For the majority of agricultural regions of the country it is experimentally established that 60-80% of mineral nitrogen of 0-180 cm soil layer is concentrated in 0-60 cm layer. Conversion factors for mineral nitrogen reserves for 0-40, 0-60 cm layers in 0-100, 0-150 cm layers, etc. have been established for some regions.
There are several variants of correction or calculation of doses of nitrogen fertilizers based on the results of mineral nitrogen nutrition diagnostics. In all variants ammonia and nitrate nitrogen stocks in a definite layer are recalculated in kg/ha and taking into account possible nitrogen use coefficients by definite crops the received value is deducted from the value of crops general demand.
A simplified modification of nitrogen fertilizer doses correction was proposed by Y.P. Zhukov from the Agrochemistry Department of the Moscow Agricultural Academy. Mineral nitrogen is determined before the application of nitrogen fertilizers in the arable soil layer, i.e. 0-20 or 0-30 cm, the received result is recalculated in kg/ha and deducted from the set dose or the total crop requirement in nitrogen. This approach makes it possible to reduce the time for deep soil studies, moreover, the uncertainty of weather conditions does not allow us to make an accurate prediction regarding the stability of nitrate and ammonia forms of deep layers, especially in the first month after sowing the roots do not have time to penetrate to a sufficiently large depth.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.