Molybdenum fertilizers
Molybdenum fertilizers — micronutrient fertilizers that meet the needs of agricultural crops for the micronutrient molybdenum.
Molybdenum content in soil
The total molybdenum content in soil ranges from 0.20–2.40 mg per 1 kg of soil, and that of mobile forms from 0.10 to 0.27 mg per 1 kg of soil. As a rule, in the arable horizon the proportion of mobile forms in the total content is 8–17%. The poorest in molybdenum are light-textured soils with low organic matter content—soddy-podzolic and sandy soils, which contain 0.05 mg/kg of soil. Higher contents of total and mobile forms are found in chernozem soils.
Molybdenum is present in soil in oxidized form as calcium molybdates. Mobility and availability to plants are affected by the soil reaction. On soils with pH < 5.5, molybdenum forms poorly soluble compounds with aluminum, iron, and manganese; in alkaline soils, it forms readily soluble sodium molybdate. Liming promotes the transition of molybdenum from soil reserves into a mobile state, therefore molybdenum fertilizers on limed soddy-podzolic soils have reduced effectiveness. At pH 7.5–8.0, even on limed soils, mobility begins to decrease due to an increase in the amount of carbonates.
Molybdenum deficiency may occur on soddy-podzolic, gray forest, chernozem soils, and drained acidic peat bogs.
Molybdenum fertilizers
As molybdenum fertilizers, ammonium molybdate ((NH4)2MoO4) is mainly used. In some regions, wastes from the electric lamp industry are used.
Molybdenum is a component of some industrial wastes. Thus, slags from ferroalloy plants contain 0.2–0.6% molybdenum, wastes from molybdenum concentrating plants contain 0.002–0.05%, and wastes from electric lamp plants contain 5–6%.
A promising fertilizer form is molybdenized superphosphate, intended for band application at a rate of 50 kg/ha, which corresponds to 50–100 g/ha of molybdenum.
Table. Range of molybdenum fertilizers.
| Fertilizer | Active ingredient | Content of a.i. in water-soluble form, % |
|---|---|---|
| Ammonium molybdate | Mo | 52 |
| Electric lamp industry wastes | Mo | 5-8 |
| Simple granular superphosphate with molybdenum | P2O5 | 20 |
| Mo | 0.1 | |
| Double granular superphosphate with molybdenum | P2O5 | 43 |
| Mo | 0.2 |
Application of molybdenum fertilizers
Among the methods of applying molybdenum fertilizers, pre-sowing seed treatment is effective and economically justified. For treatment of 100 kg of large seeds, 25–50 kg of ammonium molybdate or ammonium sodium molybdate is consumed; for 100 kg of clover or alfalfa seeds, 500–800 g.
Molybdenum fertilizers are used on soddy-podzolic, gray forest soils, drained peat bogs, leached chernozems and other soils poor in plant-available forms of molybdenum. Application on limed soddy-podzolic soils is less effective, since lime promotes the conversion of soil molybdenum reserves into available forms. Effectiveness increases against a good phosphorus-potassium background.
Molybdenum fertilizers can be applied to the soil, for pre-sowing seed treatment, and for foliar feeding of plants. The method depends on the fertilizer type and crop. Application rates are calculated at 1 kg of molybdenum per 1 ha. Slags from ferroalloy plants are applied in finely ground form at 50–60 kg/ha; slags from processing oxidized ores and low-grade concentrates with a content of 3–8% are applied in finely ground form at 12–30 kg/ha. Low-percentage wastes from concentrating plants are best used in the area where they are located because of insufficient transportability.
Molybdenized granular superphosphate is applied in rows with seeds of clover, alfalfa, peas and other legumes at a rate of 50 kg/ha. With band application, the utilization coefficient of phosphorus and molybdenum increases, since they promote more complete mutual uptake. Molybdenum against a phosphorus background increases yield more than without it.
Table. Application of molybdenum micronutrient fertilizers to various crops.
| Fertilizer | Crop | Rate | Method of application |
|---|---|---|---|
| Molybdenum superphosphate (0.2% Mo) | Grain legumes | 50 kg per 1 ha in rows at sowing | Soil application |
| Ammonium molybdate (50% Mo) | Peas, vetch, soybean and other large-seeded crops | 25–50 g in 1.5–2.0 L of water per 100 kg of seeds | Pre-sowing seed treatment |
| Clover, alfalfa | 500–800 g in 3 L of water per 100 kg of seeds | Same | |
| Peas, fodder beans, clover, alfalfa and other legumes grown for grain; vegetables, fruit and berry crops | 200 g per 100 L of water (aerial treatment) | Foliar feeding during budding — beginning of flowering | |
| Long-term cultivated pastures | 200–600 g in 100 L of water (aerial treatment) | Same |
Before sowing, seeds are dusted or moistened. This technique is the most promising, since it is less labor-intensive and requires less fertilizer consumption. Pre-sowing seed treatment is the most effective method of applying molybdenum. Seed treatment is carried out before sowing or in advance, several days or months beforehand. After treatment, the seeds are dried well. Pre-sowing seed treatment is recommended to be combined with dressing. Consumption is 25 g of molybdenum per 100 kg of seeds, or 50 g of ammonium molybdate or 80 g of ammonium sodium molybdate, in 1.2–2 L of water. This amount of solution treats 100 kg of seeds of peas, vetch, soybean and other large-seeded crops. For 100 kg of clover and alfalfa seeds, 500–800 g of ammonium molybdate is used, which is dissolved in 3–5 L of water. Treatment is carried out evenly so that all the solution is absorbed by the seeds. For the per-hectare seeding rate of vegetable crops, depending on seed size and seeding rate, 60–100 g of ammonium molybdate is used, with the larger dose corresponding to smaller 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, the per-hectare rate is dissolved in 100 L of water; for ground spraying of row crops, in 300–400 L. Foliar feeding of seed crops of leguminous grasses, peas and other crops grown for seed or grain is carried out during budding — beginning of flowering. Feeding of perennial grasses — clover and alfalfa for hay — is carried out in autumn in the year of sowing after removal of the cover crop, when the leaf surface is well developed. On natural meadows with a large proportion of the 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 when their amount is small, a good result is obtained by overseeding meadows with a small amount of clover (6–8 kg/ha) using seeds previously treated with molybdenum. In this case, foliar feeding is not carried out.
When molybdenum fertilizers are used on seed crops of legumes, boron fertilizers are applied together, which usually increases the effectiveness of the combined application.
In orchards, berry fields and vineyards, spring spraying is carried out with a 0.01–0.05% solution of ammonium molybdate.
Phosphorus fertilizers increase the mobility of molybdenum in soil and its availability to plants, since molybdate ions are replaced by phosphate ions. All processes that enhance the mineralization of organic matter increase the mobility of soil molybdenum.
References
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.
- Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. Mineev V. G. Moscow: Publishing House of the D. N. Pryanishnikov VNIIA.
