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Molybdenum fertilizers

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Molybdenum in plant life

Among crops, the highest amount of molybdenum is found in legumes. Legume grass seeds contain from 0.5 to 20.0 mg Mo per 1 kg of dry weight, in cereals – from 0.2 to 1.0 mg per 1 kg of dry weight. In general, the content of molybdenum in plants can vary in the range of 0.1 to 300 mg per 1 kg dry weight; its increased content occurs with unbalanced nutrition of plants.

Plants consume molybdenum in smaller amounts than boron, manganese, zinc and copper. It is localized in young growing organs. Leaves contain more of it than stems and roots. Much molybdenum is concentrated in chloroplasts.

The lower limit of molybdenum content for most crops is 0.10 mg per 1 kg of dry weight, for legumes – 0.40 mg per 1 kg. The content in plants in smaller amounts indicates molybdenum deficiency. With an average yield of wheat, up to 6 g is taken from 1 ha, with the yield of clover – up to 10 g.

In plants, molybdenum is a member of nitrate reductase enzyme which is involved in the reduction of nitrates, reduction of nitrates to nitrites. It is a member of nitrogenase – the enzyme that binds atmospheric nitrogen during nitrogen fixation.

Molybdenum deficiency in plants leads to disruption of nitrogen metabolism and the accumulation of nitrates in tissues. Under the influence of molybdenum in the nodules of legume crops increases the activity of dehydrogenases – enzymes that provide the flow of hydrogen to bind atmospheric nitrogen. Molybdenum is involved in the biosynthesis of nucleic acids, photosynthesis, respiration, synthesis of pigments, vitamins. 

The role of molybdenum in the process of nitrogen fixation determines the improvement of nitrogen nutrition of legume crops when applying molybdenum fertilizers, increases the efficiency of phosphorus-potassium fertilizers. At the same time, the yield and protein content increase. The application of molybdenum to nonlegume crops by increasing the assimilation of nitrate nitrogen increases the use and assimilation of fertilizer and soil nitrogen and decreases unproductive losses of nitrogen by denitrification and nitrate leaching. This has been proven in studies with 15N on vegetable crops and cotton.

The crops most demanding of molybdenum fertilizers are clover, alfalfa, soybeans, peas, beans, beans, vetch, lupine, rape, some vegetable crops (lettuce, spinach, cauliflower, tomatoes). Molybdenum fertilizers are less likely to increase yields of nonlegume crops than legumes.

External signs of moderate molybdenum deficiency in legumes are similar to those of nitrogen deficiency. If the deficiency is more severe, the growth of plants slows down, roots do not develop nodules, plants turn pale green, leaf blades become deformed, and leaves die prematurely.

High doses of molybdenum are toxic to plants. Molybdenum content of 1 mg per 1 kg of dry weight in agricultural products is harmful to animals and humans. When the content of molybdenum in plants is more than 20 mg per 1 kg of dry weight, molybdenum toxicosis occurs in animals when eating fresh plants, in humans – endemic (molybdenum) gout. The toxic effect of molybdenum decreases when plants are dried or frozen, since this reduces the amount of soluble forms of molybdenum, as well as when copper is added to the food of animals and humans.

The positive effect on the yield and its quality of vegetable crops is due to the improvement of nitrogen nutrition of fertilizers and soil.

Table. Effect of molybdenum on lettuce utilization of soil nitrogen and fertilizer on sod-podzolic soil (by Muravin)

Experience option
Use for two repeated sowings per year (two-year average)
total, mg/vessel
from the soil
from fertilizer
mg/vessel
% of background PK
mg/vessel
% of fertilizer applied
РК
514
514
100
-
-
РК + Мо
612
612
119
-
-
NРК
992
712
134
280
39
NРК + Мо
1158
821
158
337
47

Improved nitrogen nutrition, in turn, contributes to a better use of other nutrients by crops. Application of molybdenum ensures a more complete incorporation of nitrogen received by plants into the composition of protein. In addition, it limits the accumulation in the products, especially in vegetables and pasture forage, nitrates when using high doses of nitrogen fertilizers and organogenic soils with intensive mineralization of nitrogen. This makes it advisable to apply molybdenum and nitrogen fertilizers together for nonlegume crops requiring molybdenum and legumes together with phosphorus-potassium fertilizers on soils with a lack of this element.

According to the data of field experiments, the average increase in pea yield from the use of molybdenum fertilizers on sod-podzolic, gray forest soils and leached chernozems is 0.26 t/ha, hay and clover seeds on sod-podzolic soils – respectively, 1.30 t/ha and 0.08 t/ha.

Table. Average yield gains of legume crops from molybdenum application (data of the All-Russian Institute of Fertilizers and Agrochemistry), t/ha

Crop
Sod-podzolic soils
Gray forest soils
number of experiments
increase from Mo
number of experiments
increase from Mo
Peas (grain)
34
0,29
22
0,36
Veatch:
- grain
10
0,51
14
0,49
- green mass
2
3,40
9
5,16
Soybeans (grain)
13
0,27
1
0,19
Fodder beans (grain)
22
0,49
5
0,32
Clover:
- hay
58
1,30
-
-
- seeds
18
0,08
-
-
Alfalfa (seeds)
15
0,93
9
1,82

High efficiency of molybdenum fertilizers with a sufficient supply of other nutrients is achieved when the molybdenum content in the soils of the Non-Black Earth zone is less than 0.15 mg per 1 kg of soil, in the Black Earth zone – less than 0.15-0.30 mg per 1 kg. The application of molybdenum fertilizers in legume-grass hayfields and pastures increases the number of legumes in the herbage, the protein content in the forage and the overall productivity of the lands.

Table. Action and effect of molybdenum on yield and botanical composition of herbage (by Sharov)

Experience option
Hay yield, t/ha
Botanical composition of the herbage, %
effect
aftermath
legumes
cereals
different-grass
Without molybdenum
2,46
2,51
27
46
27
Molybdenum foliar feeding (150 g/ha)
3,20
3,49
43
35
22

The average yield increase in pea grains is 0.2-0.3 t/ha, clover hay – 0.8-1 t/ha, vetch hay – 0.7-0.9 t/ha, cauliflower – up to 3 t/ha, tomatoes – 7 t/ha, potatoes – 2.5 t/ha, beets forage – 5 t/ha. Molybdenum contributes to an increase in protein content in peas, in hay clover, vetch, alfalfa, sugar content and vitamin content in vegetables are increased.

Molybdenum content in soil

The gross content of molybdenum in the soil varies in the range of 0.20-2.40 mg per 1 kg of soil, the mobile forms – from 0.10 to 0.27 mg per 1 kg of soil. As a rule, in the arable soil horizon the share of mobile forms of the gross content is 8-17%. Most poor in molybdenum are soils of light granulometric composition with low content of organic matter, in sod-podzolic, sandy soils, which contain 0.05 mg/kg of soil. Higher content of bulk and mobile forms is in black earth soils.

Molybdenum is contained in the soil in oxidized form as calcium molybdates. Mobility and availability to plants is affected by the reaction of the environment. In soils with pH < 5.5, molybdenum forms poorly soluble compounds with aluminum, iron, manganese, in alkaline soils – well soluble sodium molybdate. Liming promotes the transition of molybdenum from soil reserves in the mobile state, so molybdenum fertilizers on limed sod-podzolic soils reduce efficiency. At pH 7.5-8.0 even on calcareous soils mobility begins to decline due to an increase in carbonates.

Molybdenum deficiency can appear on sod-podzolic, gray forest, chernozem soils, dried acidic peatlands.

Table. Effects of manganese on crop yields (by P.A. Vlasyuk), t/ha

Crop
Yield without the use of Mn
Yield increase from Mn
Sugar beet (roots)
31,0
2,37
Winter wheat (grain)
3,34
0,21
Spring wheat (grain)
1,75
0,22
Corn (grain)
5,78
1,18

Molybdenum fertilizers

Ammonium molybdenum (ammonium molybdate, ((NH4)2MoO4) is mainly used as molybdenum fertilizer. In some regions, waste from the electric tube industry is used.

Molybdenum is a part of some industrial wastes. Thus, slags from ferroalloy plants contain 0.2-0.6% of molybdenum, wastes from molybdenum enrichment plants contain 0.002-0.05%, wastes from electric lamp factories contain 5-6%.

A promising form of fertilizer is molybdenized superphosphate designed for row application at a dose of 50 kg/ha, which corresponds to 50-100 g/ha of molybdenum.

Table. Assortment of molybdenum fertilizers

Fertilizer
Active substance
Content of the active substance in water-soluble form, %
Ammonium molybdate
Mo
52
Waste from the light bulb industry
Mo
5-8
Simple granulated superphosphate with molybdenum
P2O5
20
Mo
0,1
Double granulated superphosphate with molybdenum
P2O5
43
Mo
0,2

Application of molybdenum fertilizers

Among the ways of applying molybdenum fertilizers the pre-sowing treatment of seeds is effective and economically justified. For the treatment of 100 kg of large seeds 25-50 kg of ammonium molybdate or ammonium-sodium molybdate is used, for 100 kg of clover or alfalfa seeds – 500-800 grams.

Molybdenum fertilizers are used on sod-podzolic, gray forest soils, dried peatlands, leached chernozems and other soils, poor in available forms of molybdenum for plants. Application on calcareous sod-podzolic soils is less effective because lime promotes the transition of soil reserves of molybdenum in available forms. The efficiency increases with a good phosphorus-potassium background.

Molybdenum fertilizers can be used to apply to the soil, the pre-sowing treatment of seeds, foliar feeding of plants. The method depends on the type of fertilizer and culture. Doses of application are calculated at the rate of 1 kg of molybdenum per 1 hectare. Slags of ferroalloy plants in a finely ground bring in 50-60 kg / ha, the slag processing of oxidized ores and poor concentrates with a content of 3-8% bring in a finely ground in a dose of 12-30 kg / ha. Low-percentage wastes from enrichment plants are expedient to use in the area of their location due to insufficient transportability.

Molibdenized granulated superphosphate is introduced into the rows with the seeds of clover, alfalfa, peas and other crops at a dose of 50 kg/ha. The use of phosphorus and molybdenum increases with row application, as they contribute to a more complete mutual absorption. Molybdenum in the background of phosphorus increases the yield more than without it.

Table. Application of molybdenum microfertilizers for various crops[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.

Fertilizer
Crop
Application rate
Method of use
Molybdenum superphosphate (0,2% Mo)Leguminous50 kg per hectare in rows when sowingSoil application
Molybdenum ammonium (50% Mo)Peas, vetch, soybeans and other large-seeded crops25-50 g in 1.5-2.0 L of water per 100 kg of seedsPre-sowing seed treatment
Clover, alfalfa500-800 g in 3 liters of water per 100 kg of seedsPre-sowing seed treatment
Peas, fodder beans, clover, alfalfa, and other legumes grown for grain; vegetable, fruit-berry200 g per 100 liters of water (air treatment)Non-root fertilization during budding - beginning of flowering
Long-term cultivated pastures200-600 g in 100 liters of water (air treatment)Non-root fertilization during budding - beginning of flowering

Seeds are powdered or moistened before sowing. This method is the most promising because it is less labor-intensive and requires less fertilizer consumption. Seed pre-treatment is the most effective method of molybdenum application. Seed treatment is carried out before sowing or a few days or months in advance. Seeds are dried well after treatment. It is recommended to combine presowing treatment with seed dressing. Consumption is 25 g of molybdenum per 100 kg of seeds, or 50 g of molybdenum ammonium or 80 g of molybdenum-sodium ammonium per 1.2-2 liters of water. This amount of solution treats 100 kg of seeds of peas, vetch, soybeans, and other large-seeded crops. For 100 kg of clover and alfalfa seeds 500-800 g of ammonium molybdenum, which is dissolved in 3-5 liters of water, is used. The treatment is carried out evenly so that all the solution is absorbed by the seeds. For a hectare rate of vegetable seeds, depending on the size and seeding rate 60-100 grams of ammonium molybdenum, with a larger dose corresponding to the finer seeds.

For foliar feeding, 100-150 g per 1 ha of sowing is used. For long-term cultivated pastures, 200-600 g per 1 ha. For aerial spraying, a hectare standard is dissolved in 100 liters of water; when ground spraying of row crops – in 300-400 liters. Foliar feeding of legume grasses, peas and other crops grown for seeds or grains is carried out during the budding – blooming period. Fertilizing perennial grasses – clover and alfalfa in hay – is carried out in autumn in the year of sowing after removal of cover crop with well developed leaf surface. On natural meadows with a large proportion of legume component in the herbage, foliar feeding is carried out at the beginning of grass regrowth. In the absence of legumes in the grass mixture or a small amount, a good result is obtained by seeding meadows with a small amount of clover (6-8 kg/ha) with seeds pre-treated with molybdenum. In this case foliar feeding is not carried out.

When applying molybdenum fertilizers on seed crops of legume crops, boric fertilizers are applied together, which usually increases the efficiency of joint application.

In orchards, berry and vineyards, spraying in spring with 0.01-0.05% solution of molybdenum ammonium.

Phosphate fertilizers increase mobility of molybdenum in the soil and its availability to plants, as molybdate ions are replaced with phosphate ions. All processes that enhance mineralization of organic matter increase the mobility of soil molybdenum.

Sources

Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.

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.