Characteristics and chemical composition of organic fertilizers in agronomy

Organic fertilizers are the foundation for the reproduction of soil fertility and the comprehensive improvement of its properties. They simultaneously optimize the agrochemical, agrophysical, and biological indicators of the soil. The application of organic matter improves soil structure and regulates its water, thermal, and air regimes. In addition, organic matter serves as an energy source for beneficial soil microorganisms, while the carbon dioxide released during its decomposition provides additional plant nutrition.

Based on their chemical composition, all fertilizers are divided into three groups:

• organic;
• organomineral;
• mineral.

Organic fertilizers include substances of plant or animal origin that contain organic matter. These include manure, peat, poultry manure, sapropel, various composts, straw, and green manure crops. In agronomic practice, they are also traditionally called "tuks" (from an Old Slavic word meaning "fat" or "fertility").

• Cost of 1 kg of NPK in organic matter is 2.5 times cheaper
• Maximum nitrogen in sewage sludge is 3.9%
• Potassium in birch ash is 13.8%
• Calcium in birch ash is 36.3%

Composition and nutritional value of organic fertilizers

The chemical composition of organic matter varies significantly depending on its type and degree of decomposition. Nutrients in such fertilizers are predominantly in organic form. Their mineralization and transition to a state available to plants occur gradually throughout the entire growing season. This ensures a stable, prolonged effect of the fertilizers and reduces the risk of salt stress in crops.

Below are the average indicators of the chemical composition of the main types of organic and local fertilizers.

Fertilizer	N, %	P₂O₅, %	K₂O, %	CaO, %	Water content, %
Fresh manure: Cattle	0.45	0.23	0.50	-	77.6
Fresh manure: Horse	0.58	0.28	0.63	-	71.3
Fresh manure: Sheep	0.83	0.23	0.67	-	64.6
Fresh manure: Swine	0.45	0.19	0.60	-	72.4
Fresh manure: Mixed	0.50	0.25	0.60	-	75.0
Semi-decomposed: Mixed	0.60	0.30	0.75	-	68.0
Humus	0.98	0.58	0.90	-	-
Liquid manure	0.22	0.01	0.46	-	-
Poultry manure: Chicken	0.7-1.9	1.5-2.0	0.8-1.0	-	56.0
Poultry manure: Goose	0.60	0.50	1.10	-	82.0
Poultry manure: Duck	0.80	1.50	0.40	-	57.0
High-moor peat	0.52	0.05	0.01	-	50-60
Low-moor peat	1.15	0.15	0.1	-	50-60
Peat-manure compost	up to 1.80	up to 0.20	up to 0.38	-	65-75
Wheat straw ash	-	6.4	13.6	5.9	-
Birch wood ash	-	7.1	13.8	36.3	-
Green manure: Lupin	0.45	0.10	0.17	0.47	70-75
Green manure: Sweet clover	0.77	0.05	0.19	0.97	70-75
Green manure: Clover	0.50	0.14	0.38	-	75
Lake sludge (sapropel)	1.8-2.5	0.2-0.4	0.3-0.5	-	-
Pond sludge (sapropel)	0.2-2.0	0.1-0.5	0.1-0.3	-	-
Sewage sludge	1.9-3.9	2.3-3.9	0.01-0.21	-	-

Duration of action, stages of decomposition, and storage methods for manure

The positive influence of organic fertilizers on crop yield persists for 3–4 years. For this reason, they are applied periodically, maintaining an interval of every three or four years. Manure supplies plants with all essential nutrients and improves soil structure.

• Period of effect on yield — 3–4 years
• Nitrogen in 1 ton of semi-decomposed manure — 5 kg
• Phosphorus in 1 ton of semi-decomposed manure — up to 2.5 kg
• Potassium in 1 ton of semi-decomposed manure — 6 kg
• Calcium in 1 ton of semi-decomposed manure — about 7 kg

Physical properties and the rate of mineralization of the fertilizer directly depend on the species of animal. Based on moisture content, manure is divided into "hot" (horse, sheep) and "cold" (from cattle and pigs). Hot manure contains less water and decomposes faster; additionally, horse manure is initially richer in nitrogen and phosphorus. Bedding straw also contributes to plant nutrition, serving as an important source of micronutrients.

Micronutrient content in manure and straw, g

Micronutrient	In 10 t of manure	In 6 t of straw	Micronutrient	In 10 t of manure	In 6 t of straw
Boron (B)	50	36	Molybdenum (Mo)	4.0	2.5
Copper (Cu)	44	20	Zinc (Zn)	560	240
Manganese (Mn)	300	180	Cobalt (Co)	1.9	0.6

During storage, organic matter gradually decomposes, which causes the total mass of the fertilizer to decrease while the percentage of nitrogen, phosphorus, and potassium increases. Based on the degree of decomposition, four technological stages are distinguished: fresh, semi-decomposed, well-decomposed manure, and humus. Each stage has its own external characteristics and is characterized by a specific loss of initial mass.

• Fresh manure: straw retains its strength and natural yellow color.
• Semi-decomposed: straw darkens, breaks easily, the mass loses 25% of its initial weight, and the aqueous extract becomes thick and black.
• Well-decomposed: straw is completely decomposed, the mass becomes homogeneous, and its weight decreases by approximately 50%.
• Humus: a homogeneous, loose, earthy mass, of which about 25% remains from the initial weight.

Nitrogen and phosphorus content in cattle litter manure depending on the degree of decomposition, %

Indicators	Fresh	Semi-decomposed	Well-decomposed	Humus
Nitrogen (N)	0.52	0.60	0.66	0.73
Phosphorus (P₂O₅)	0.25	0.38	0.43	0.48
Organic matter losses	—	29.0	47.2	62.4

To preserve nutrients, it is necessary to strictly control the storage method. With loose stacking, the losses of dry matter and nitrogen over 4 months turn out to be several times higher than with compact, cold storage. The type of bedding also affects nitrogen preservation: peat binds it significantly more effectively than straw.

Average losses of organic matter and nitrogen with different storage methods over 4 months, %

Storage method	Manure on straw bedding		Manure on peat bedding
	Organic matter	Nitrogen	Organic matter	Nitrogen
Loose	32,6	31,4	40,0	25,2
Compact	12,2	10,7	7,0	1,0

Safety regulations for the use of poultry manure

Poultry manure is a concentrated, fast-acting fertilizer. In terms of nutritional value, chicken manure surpasses livestock manure, while the more watery manure of geese and ducks is close to it in effect. The nutrients in the manure are part of organic compounds and mineral salts, with a significant portion being in a readily available water-soluble form.

For safe use, fresh manure is applied to the soil in small doses in advance — in autumn or spring before sowing, under digging, so that ammonium nitrogen is converted into nitrate during the nitrification process. When preparing liquid top dressing, the raw material must be diluted with water and left to ferment for 5–7 days. Also, composting or thermal drying of the manure helps to reduce the concentration of ammonium nitrogen.

Poultry manure also serves as a rich source of micronutrients for crops. The nutrients in it are part of both organic compounds and mineral salts. The main part of these micro-components is in a readily digestible form.

Micronutrient content in the dry matter of poultry manure

Micronutrient	Content per 100 g of dry matter, mg
Iron (Fe)	300–400
Manganese (Mn)	15–38
Zinc (Zn)	12–39
Copper (Cu)	1–2,5
Cobalt (Co)	1–1,2

Peat, composts, and ready-made fermented fertilizers

For rapid soil enrichment with nutrients, one can use ready-made complex compositions. For example, Bionex-1, a dry fermented fertilizer based on composted chicken manure. It contains nitrogen, phosphorus, potassium, a full range of micronutrients, and is enriched with beneficial microflora.

Peat is a valuable soil amendment, but its effectiveness in pure form is limited. It contains a lot of nitrogen, but it is in a form unavailable to plants, and it is low in phosphorus and potassium. Peat has high water-holding capacity, low thermal conductivity, and poor water permeability. Without composting, it is applied mainly to soils poor in organic matter to improve their physical properties or under liming. In this case, the dose of peat is doubled compared to manure.

Composting mobilizes nutrients and increases the biological activity of the mixture. Tops, dry leaves, peelings, sawdust, shavings, ash, and weeds are suitable for preparing a mixed compost. The area for the pile is compacted, and components are laid in layers.

1. Compact the area for the compost and line it with dry peat, chopped straw, or dry leaves.
2. Lay out the available organic waste, alternating layers with peat or soil.
3. To accelerate decomposition, add manure, liquid manure, or fecal compost.
4. Apply phosphate rock and biologically active preparations (Compostin, Fitosporin, EM-preparations, AgroBriz, or Sternya).
5. Regularly moisten the compost mass during the maturation process.

• Dose of phosphate rock — up to 20 kg per 1 t of compost
• Degree of peat decomposition for direct application — from 30%
• Particle size of mature compost — no more than 2 cm
• Application rate of pure peat — 2 times the manure dose

Finished mature compost has a dark color and a uniform structure without visible layers. It crumbles well and emits a characteristic odor of garden soil.

Green manure: green fertilizer for soil improvement

Ploughing in the green mass of green manure crops enriches the soil with organic matter and nitrogen, improves its structure, and its water, air, and thermal regimes. Even when the above-ground mass is mown, the roots and crop residues of green manure crops decompose in the soil, replenishing the nutrient uptake. This technique is particularly effective when preparing plots for potatoes, root crops, and fruit-bearing crops.

The root system of green manure crops acts as a natural loosener. In heavy and compacted soils, mustard, cereals, and legumes loosen the deep layers of the subsoil. In light sandy soils, green manures increase water-holding capacity by accumulating organic matter. The green mass can not only be ploughed into the soil but also mown for mulching, composting, or liquid top dressing.

Leguminous crops are traditionally sown as nitrogen accumulators: lupin, pea, vetch, and serradella. Non-leguminous crops used include mustard, rapeseed, winter cress, oilseed radish, buckwheat, oats, and rye. Crop selection is carried out taking into account the growing season and heat requirements.

Crop	Period from sowing to max. productivity, days	Sum of active temperatures, °C	Drought resistance
White sweet clover	85–95	1200–1400	Very drought-resistant
Yellow sweet clover	85–95	1200–1400	Very drought-resistant
Perennial lupin	95–105	1400–1600	Low drought resistance
Annual lupin	70–80	900–1100	Low drought resistance
Field pea	75–85	900–1200	Low drought resistance
White mustard	50–60	700–800	Low drought resistance
Spring winter cress	40–50	600–750	Low drought resistance
Spring rapeseed	50–60	750–850	Low drought resistance
Oilseed radish	45–55	650–800	Medium drought resistance
Spring vetch	80–90	1100–1300	Moisture-loving

Selection and incorporation of green manure crops

The root system of legumes and mustard penetrates into the deep layers of the soil. Thanks to root exudates, these plants are able to absorb phosphorus from sparingly soluble compounds. They accumulate the element in their roots and above-ground mass, enriching the top arable layer with it.

Pre-sowing seed treatment of "BashInkom" green manure seeds with biological products Gumi and Fitosporin stimulates plant growth in the early stages. This technique increases emergence and increases the yield of the root system and above-ground green mass being incorporated by 30–40%.

• Incorporation depth in heavy soils — 6–8 cm
• Incorporation depth in light soils — 12–15 cm
• Biomass increase from seed treatments — 30–40 %
• Interval before planting the main crop — 2–4 weeks

1. Observe the incorporation phase. Carry out ploughing of the biomass during the budding period before the plants start flowering.
2. Consider the soil type. Incorporate the green mass to a depth of 6–8 cm in heavy soils and 12–15 cm in light ones.
3. Maintain the interval before planting. After the incorporation of young and fresh plants, the main crop can be planted in 2–4 weeks.

Crop	Period to max. productivity, days	Green mass, kg/100 m²	Root residues, kg/100 m²	Total biomass, kg/100 m²	N accumulated, kg/100 m²	P₂O₅ accumulated, kg/100 m²	K₂O accumulated, kg/100 m²
Annual lupin	80	526	80	606	2,31	6,3	2,09
Annual lupin (in sowing year)	80	187	41	228	1,04	3,8	1,55
Yellow sweet clover	90	334	172	506	2,30	7,2	3,10
Yellow sweet clover (in sowing year)	90	183	50	233	1,13	4,6	1,42
White sweet clover	90	420	120	540	2,51	9,6	2,99
Field pea	80	219	85	304	1,17	7,1	2,15
Vetch	90	257	54	311	1,60	7,3	2,01
Serradella	90	402	38	440	1,16	5,3	2,22
Oilseed radish	50	462	23	485	8,6	6,6	2,48
Winter cress	55	343	101	444	1,35	5,5	2,41
Phacelia	60	317	26	343	7,8	5,2	1,96
Fava bean	80	157	20	177	5,8	2,4	5,9

• Mustard. Suppresses soil-borne fungal and bacterial infections, repels wireworms and aphids. Loosens the soil well, preparing it for potatoes. Saturates the arable layer with organic matter, nitrogen, potassium, microelements, and phosphorus. Sowing times are from early spring to late autumn.
• Winter rye. Effectively suppresses weeds and improves soil structure. After spring ploughing, it enriches the soil with nitrogen, phosphorus, potassium, and microelements. It is sown in late summer or autumn and incorporated in the spring.
• Oats. Loosens the soil, suppresses weeds, and saturates the arable layer with nitrogen, phosphorus, potassium, and microelements.
• Vetch-rye. The mixture actively suppresses nematodes and weeds, loosens the soil well, and enriches it with nitrogen, phosphorus, potassium, and microelements.
• Vetch-oats. Improves soil structure, suppresses weeds, and saturates the soil with nitrogen, phosphorus, potassium, and microelements.

Humic preparations and their impact on soil fertility

The natural basis of soil fertility is humus — a product of the processing of organic matter by soil microflora under the influence of heat and humidity. Humic acids, as the main part of humus, convert sparingly soluble soil minerals into forms accessible to plants. Industrial humates are concentrated sodium, potassium, and ammonium salts of these acids.

The application of humates improves soil structure and converts phosphorus into easily digestible complexes. As a result, plants use nutrients more fully both from the soil itself and from applied mineral fertilizers. The preparations stimulate seed germination, accelerate crop growth, and advance harvest ripening dates.

Preparation	Preparation type	Content of active ingredients
Humate (powder)	Ballasted	19,8% humates
Gumix (powder)	Ballasted	25,2% humates
Humate-80 (tablets)	Ballast-free	75% humic acids
Floris (aqueous solution)	Ballast-free	65% humates
GUMI	Ballast-free	no less than 60% sodium humates on dry matter
Potassium humate	Ballast-free	45% humates
Humate+7	Ballast-free	37% humates + nitrogen, potassium, and 7 microelements

To optimize treatments, ready-to-use fertilizers and soils with added humates are produced: Urea humatized, Gumisol, Darina lignohumate, Orgum, Plodorodie, Tellura, Floris-compost, and the Gumi-Omi line.

Sapropel and humic preparations: biological soil activation

For pre-sowing treatment, root and foliar top dressing, humic preparations "Bogatyy", "Borogum-M", and "Gumi" are actively used. They are officially entered into the state catalog and approved for use. The "Gumi" preparation is manufactured from young brown coals using the technology of obtaining humus substances bioactivated by molecular weight (BMM). It contains salts of humic acids, macro- and micro-nutrients that accelerate seed germination, stimulate root formation, fruiting, and increase the resistance of crops to diseases and weather-related stresses.

Sapropel (freshwater silt) is a valuable source of organic matter and biologically active substances for field and greenhouse crops. In its natural state at the bottom of water bodies, it is a liquid colloidal mass with a dry matter content of only 1–10%. After freezing, sapropel quickly releases moisture to a level of 18–20%, becoming loose and convenient for application. The dry matter of the silt contains from 15 to 95% organic matter and from 19 to 88% ash components.

The organic matter of sapropel is rich in humic acids (11–38%), carbohydrates (20–32%), vitamins, enzymes, and hormones. The content of vitamin B12 is 3–73 mg/kg, and carotene is 0.44–4.42 mg/kg. The fertilizer also provides 1.3–6.0% total nitrogen and up to 1% phosphorus to the soil, with a pH ranging from 2.5 to 9.

• Manganese (Mn) in dry matter — 145–456 mg/kg
• Copper (Cu) in dry matter — 1547 mg/kg
• Boron (B) in dry matter — 4–17 mg/kg
• Zinc (Zn) in dry matter — 4–16 mg/kg
• Molybdenum (Mo) in dry matter — 1–20 mg/kg

Straw and manure: carbon balance and application methods

Ploughing in straw is the cheapest way to replenish humus reserves in the soil. When 100 kg of chopped straw is incorporated, 0.5 kg of nitrogen, 0.2 kg of phosphorus, 1.0 kg of potassium, and a complex of micro-nutrients are added to the soil. The humus-forming potential of 1 ton of straw with the addition of 10 kg of nitrogen is equivalent to 3.5 tons of litter manure. Implementing this technology on a farm costs 4 times less than applying an equivalent amount of manure of the same efficiency.

To compensate for the nitrogen deficit, one of the following compensating fertilizers must be added per every 100 kg of chopped straw during incorporation:

• 5 kg of "Gumi-Omi Nitrogen" fertilizer;
• 50 kg of "Bionex-1" preparation;
• 100–200 kg of manure, humus, or compost.

Systematic incorporation of straw reduces soil density, increases its biological activity and water-holding capacity. The rate of organic matter decomposition depends directly on the quality of raw material preparation: the finer the cut and the more crushed the stems, the faster the mineralization. In practice, three main methods of working with straw are used:

• Autumn ploughing of chopped material;
• Surface incorporation in heavy clay soils or under conditions of excessive humidity;
• Mulching to conserve soil moisture, prevent runoff, and improve the structure of the top layer.

Manure remains a traditional organic fertilizer, the properties of which change depending on the degree of decomposition. When working with fresh manure for root top dressing, a liquid solution is used.

1. Dilute the manure in water at a ratio of 1:10.
2. Allow the solution to steep for 5–7 days.
3. Apply the finished solution to the roots at 1–2 L per bush or 5 L per linear meter.

Detailed recommendations and dosages for different types of manure are provided in the table.

Type of fertilizer	Application features	Application rates
Fresh litter manure (straw has almost not changed color or strength)	Contains all nutrients, a lot of ammonium nitrogen, and viable weed seeds. Applied to all types of soils in autumn or spring before digging for cucumbers, zucchini, pumpkin, watermelons, and melons.	Up to 5 kg/m² (500 kg/100 m²).
Semi-decomposed and decomposed manure (homogeneous mass, organic matter loss is 30–50%)	Contains all nutrients, acts slowly and for a long time (up to 3–4 years). For root crops, it is applied under the preceding crop. For early potatoes and cabbage — from autumn; for late varieties of these crops and tomatoes — in spring before digging or directly into the holes at planting.	4–6 kg/m² (400–600 kg/100 m²).
Humus (loose earthy mass, organic matter loss up to 75%)	It is not recommended to specifically turn manure into humus due to high organic matter losses. It is most appropriate to use it for preparing soil mixtures for transplants.	2–3 kg/m².

Bird droppings Contain a large amount of all nutrients, more than cattle manure. Fresh bird droppings contain a lot of ammoniacal nitrogen, which inhibits the development of plants, especially seedlings (plant burns). Fresh droppings are best used in a diluted form. The optimal concentration of the solution is 12-20 parts of water to 1 part of droppings; use 1-2 liters per bush or 5 liters per linear meter. Dry droppings should be well crushed; in the form of powder, they are spread between rows and thoroughly mixed with the soil. 30-50 g/sq.m, 3-5 kg/100 sq.m