Manure

Effect of manure on soil

Soils systematically fertilized with manure are characterized by lower acidity, a higher content of plant-available forms of phosphorus, an increased amount of humus and total nitrogen, and a greater degree of base saturation. According to a summary by A. D. Khlystovsky (1992), over 55–65 years on an uncultivated soddy-podzolic heavy loamy soil of the Dolgoprudnaya Agrochemical Experimental Station named after D. N. Pryanishnikov, doses of litter manure averaging 9 t/ha per year led to a doubling of the yields of winter rye and wheat, potato, oats, and grasses compared with the unfertilized control. At the same time, the average annual productivity of the crop rotation was 2.3–2.6 t/ha of grain units; at doses of 15 t/ha, 2.8–3.0 t/ha of grain units.

Over 52 years, annual application of litter manure at a dose of 12 t/ha had a neutralizing effect on soil acidity equal to the application of 100 kg/ha CaCO₃, reduced hydrolytic and exchangeable acidity in the 0–20 cm layer compared with the control by 0.5 mg-eq/100 g, reduced aluminum content by 2 times, increased the sum of absorbed bases by more than 1 mg-eq/100 g of soil, and increased the degree of base saturation by 10%. The neutralizing effect of manure also manifested in the sub-arable horizon (20–40 cm) of the soil.

Increasing the proportion of manure in crop fertilization and the transition to systematic application of increasing doses improve agrochemical indicators, fertility, and cultivation of poor soddy-podzolic soil. In combination with systematic application of high doses with liming, it turns poor soil into fertile soil that does not differ in agrochemical indicators from chernozems. However, as a rule, such a strong increase in fertility is economically unprofitable and environmentally hazardous. Given economic possibilities, it is advisable to raise the fertility of specific poor soils to an optimal level that ensures maximum productivity of good-quality crops with scientifically based application of fertilizers and ameliorants.

The positive effect of manure on the physicochemical properties of soils is confirmed by numerous experimental data obtained in various soil-climatic zones of the country.

Under the action of manure organic matter, microbiological processes in the soil are activated, which help increase the solubility and availability of nutrients to plants. Under the influence of microbiological processes decomposing cellulose, the content of available phosphate forms in Krasnozem increased 2–3 times. Under the action of microbial metabolic products, insoluble phosphates of calcium, iron, and aluminum pass into soluble compounds. Manure affects soil biological activity, nitrification capacity, and proteolytic activity.

Manure is especially important in the regions of the Non-Chernozem zone of Russia, whose soils are poor in humus and contain few nutrients.

Source of soil humus

In soil systematically manured for more than 50 years, the humus content compared with the control without fertilizers after 15 years was higher in the arable horizon by more than 0.2% carbon, total nitrogen by 0.02–0.05%; in the sub-arable horizon (20–40 cm), carbon by 0.04–0.05% higher, nitrogen by 0.02–0.05%.

Under conditions of intensive agriculture, it is impossible to achieve a deficit-free humus balance in the soil without the use of organic fertilizers. With systematic application of manure in a crop rotation, humus content increases in all soil types. Mineral fertilizers have little effect on humus and nitrogen accumulation, since the source of humus when mineral fertilizers are applied is mainly root and crop residues.

Depending on the soil type, long-term fertilizer application affects humus and nitrogen accumulation differently. For example, in humus-poor soddy-podzolic soils this process is more noticeable. The low humus content of serozems makes it possible to increase soil humus through organic fertilizers. On humus-rich chernozem soils, fertilizers provide smaller yield increases.

The composition of humus in different soils changes little under long-term fertilizer application; an increase in carbon content is accompanied by accumulation of all groups of humic substances. The ratio between humic and fulvic acids is a characteristic feature of a specific genetic soil type. The absence of fertilizer influence on this indicator is due to the fact that the group composition of humus is characterized by fully humified organic compounds of the soil. Fertilizers affect soil organic matter at early stages of humification.

For example, in soddy-podzolic soils over 36 years, systematic application of manure increased the content of water-soluble humus by 17–34%, in weakly leached chernozem by 5–18%, in typical serozem by 23–50% compared with the control. These mobile organic substances are at early stages of humification and enrich the soil with available nitrogen compounds. In soils with low humus content, longer manure application led to greater accumulation of water-soluble humus.

Accumulation of mobile humic substances also occurs in chernozem soils under long-term fertilizer application. This is explained by mobilization of chernozem humus due to the acidifying effect of mineral fertilizers. Thus, long-term application of manure and mineral fertilizers enriches soils poor in organic matter with total carbon and nitrogen and increases in all soil types the content of mobile forms of organic substances at early stages of humification.

When calculating the humus balance in soil, one takes into account organic matter formed through humification of manure, as well as that formed from root and crop residues of plants. Annual humus replenishment in soils from crop and root residues depends on the soil-climatic zone, biological characteristics of plants, and yield. For example, in the Non-Chernozem zone after cereals, humus is replenished on average by 0.4 t/ha, in chernozems of the European part by 0.5–0.7 t/ha, in the Urals, Siberia, and the Far East by 0.3 t/ha. Row crops replenish humus reserves on average half as much as cereals. Perennial grasses on non-irrigated soils by 0.5–1 t/ha, under irrigation more.

The humification coefficient of manure depends on the soil-climatic zone, agricultural practices, irrigation, dry matter content in manure, and type of manure. Overall it is 15–30% on a dry matter basis. The humification coefficient of plant residues of cereal crops and perennial grasses is equated to that of litter manure, while for row crops it is half as much. Knowing manure application rates in a crop rotation, one can calculate humus accumulation in soil.

Annual humus mineralization depends on soil-climatic conditions, structure of sown areas, intensity of soil tillage, and level of chemicalization. Soils under cereals lose 0.5–1 t/ha of humus annually; under row crops 0.8–3 t/ha. Maximum humus mineralization occurs in bare fallows up to 3–5 t/ha. Humus mineralization is greater on soils of light granulometric composition and under irrigation.

Application of organic fertilizers improves the nitrogen regime of soils, since 1 gram of carbon is used by microorganisms to fix from 15–20 to 20–40 mg of atmospheric nitrogen.

Bedding-free manure is a source of readily soluble nutrients for plants and increases humus and nitrogen content in soil. However, the organic matter of bedding-free manure differs in composition and humus reproduction capacity from litter manure and straw. The C:N ratio in bedding-free manure ranges from 5:1 to 10:1. Bedding-free manure has a high content of readily decomposable organic compounds. Therefore, it has less effect on humus reproduction than litter manure.

Nitrogen content in manure

Nitrogen of organic compounds is converted into ammonium through ammonification or nitrified to nitrates. Under conditions of increased soil moisture and lack of oxygen in an alkaline environment, denitrification and formation of molecular nitrogen may occur, which is irreversibly lost to the atmosphere. With proper manure management, nitrogen losses due to denitrification are sharply reduced.

The content and forms of nitrogen in manure of each animal species are determined by the ratio of solid and liquid excreta and bedding material. Nitrogen of feces and bedding contains slowly decomposing nitrogenous compounds, so it is poorly available to plants in the first year; urine contains readily soluble compounds that quickly turn into ammonia and are available to plants immediately after application. The more urine and ammonia the bedding absorbs, the higher the content of total and ammonium nitrogen; therefore, manure on peat bedding, or stored or covered with peat, is richest in total and ammonium nitrogen. In semi-rotted manure of dense storage, the total nitrogen content, depending on animal species and feed quality, ranges from 0.3 to 1.0%, and ammonium nitrogen, depending on type and amount of bedding, from 20 to 40% of total nitrogen.

In the first year, plants take up on average 20–30% of nitrogen from the total content in manure. This depends on the content of ammonium nitrogen and the ratio between soluble and protein nitrogen, the amount of carbohydrates in manure, and the time between application and the beginning of intensive crop consumption. A large amount of carbohydrates promotes the development of microflora, which also consumes ammonium nitrogen from manure, so its uptake by plants is lower. When manure is applied in fallow or under main autumn tillage, it decomposes more completely and crops take up more nitrogen than with pre-sowing and spring application.

Compared with mineral fertilizers, total nitrogen in manure is taken up by the first crop 3 times less, but it provides plant nutrition with this element for 3–4 years, sometimes longer depending on dose, manure quality, and soil-climatic conditions.

Nitrogen use from litter manure in the first year is highest (on average 30% of total) from sheep (goat) manure, less from horse (20%) and cattle manure (18%), and minimal (10%) from pig manure, although with abundant pig fattening, nitrogen use in the first year may exceed 20% of total content.

Plants take up nitrogen from sheep manure most quickly, as it contains little water and much nitrogen.

Phosphorus content in manure

Due to the organic matter of manure, microbiological processes in soil are intensified, resulting in increased solubility and availability to plants of mineral nutrition elements. Thus, insoluble phosphates of calcium, iron, and aluminum pass into mobile forms. Phosphorus consumed by microorganisms and fixed in plasma, when they die, passes into compounds available to plants.

Increased mobility of insoluble phosphates can occur as a result of interaction with humic and other organic acids. Therefore, phosphorus applied with manure is more mobile. Thus, in soddy-podzolic soil, phosphorus accumulated as a result of systematic manure application in crop rotation is less bound by sesquioxides of iron and aluminum than with mineral fertilizers. In organic-matter-poor serozems, manure partially prevents fixation of residual phosphorus by carbonates. The acidifying effect of nitrogen-potassium fertilizers does not manifest in an alkaline environment. Under these conditions, phosphorus accumulated from long-term manure application is more mobile than phosphorus accumulated from mineral fertilizers.

The bulk of residual phosphates accumulates in the upper soil layers (0–20, 20–40 cm). In some cases, phosphorus penetration into deeper layers is observed.

The content of mobile phosphorus in soil (by Kirsanov) with manure application after 4 years in the arable layer increased by 12 mg/kg compared with the control without fertilizers. After 52 years, the difference was 16 mg/kg at a dose of 9 t/ha manure, and 24 mg/kg at a dose of 15 t/ha manure. At the same time, phosphate mobility increased. After 40 years, similar changes in the content of mobile forms and mobility of phosphates were found in the sub-arable horizon.

Most of the phosphorus in manure is in the solid excreta of animals and bedding and is taken up by plants as they mineralize. The organic matter of manure prevents chemical fixation of mineralized phosphorus in soil and allows it to remain in forms available to plants longer. Therefore, in the first year after application at equivalent phosphorus doses, plants take up 1.5–2.0 times more phosphorus from manure (on average 35% of total, sometimes up to 50–55%) than from mineral fertilizers.

Plant uptake of manure phosphorus, depending on its dose and quality, as well as soil-climatic conditions, continues for 3–4 years. Moreover, the initial advantage of manure phosphorus over mineral fertilizers decreases over time.

Potassium content in manure

Potassium in all components of litter manure is in mobile and plant-available forms. Potassium from manure is taken up by plants in the first year in the same way as from equivalent doses of mineral fertilizers. Its total effect in manure persists on average for 3–4 years; with increasing doses and on fertile soils, more than 4 years. The duration of action of potassium from manure and mineral fertilizers at equivalent doses over several years is similar or with some advantage of manure, depending on crops grown, fertilizer doses, and soil-climatic conditions.

Systematic application of manure and liming reduce potassium mobility, as they lead to its fixation in soil. In chernozems, this occurs due to nitrification processes, which reduce ammonium content and consequently its competitive ability. Application of manure on chernozems, as on soddy-podzolic soils, promotes accumulation of exchangeable potassium compared with mineral fertilizers, while processes of potassium fixation into non-exchangeable form simultaneously increase. Exchangeable potassium in chernozems is less mobile, and with manure application its mobility decreases, whereas with mineral fertilizers it increases.

On serozems, systematic fertilizer application leads to an increase in exchangeable and non-exchangeable potassium. The leaching regime of soils promotes accumulation of these potassium forms along the soil profile to a depth of 1 m. Differences in the action of manure and mineral fertilizers manifest in changes in the mobility of exchangeable potassium: against the background of manure, mobility decreases; against the background of mineral fertilizers, it increases.

Over 52 years, manure doses averaging 9 t/ha increased, compared with the control without fertilizers, the content of exchangeable potassium in the arable layer by 15–36 mg/kg; at a dose of 15 t/ha over 18–20 years by 31–52 mg/kg. In the sub-arable horizon (20–40 cm), exchangeable potassium content after 40 years increased by 100 mg/kg, after 50 years by 120 mg/kg.

In the first year, plants take up 60–70% of potassium applied with manure.

Carbon, calcium, magnesium, sulfur

During decomposition of manure organic matter, at least 70% of carbon is mineralized, turning into carbon dioxide; the remaining 30% is used for new humus formation. Carbon dioxide, dissolving in soil solution, increases the mobility of soil phosphates and calcium, which improves plant nutrition with these elements; calcium also improves soil structure. For example, during decomposition of 30–40 t of manure, 35–55 (100–200) kg of carbon dioxide is released daily, which enriches the near-soil atmospheric air and improves plant air nutrition. All trailing crops, for example, cucumber, zucchini, pumpkin, with a dense herbage completely absorb the released soil carbon dioxide. This is especially important for crops grown in protected ground. For a grain yield of 4.0–4.5 t/ha, 180–200 kg of carbon dioxide is required daily.

Yield increases from manure as a source of carbon dioxide applied at 20–30 t/ha under vegetable and row crops reach 30–40%. Application of 60 t/ha of manure under cucumbers on sandy loam soil increased the yield by 43%, 20% of which was due to carbon dioxide formed from manure decomposition. The additional carbon dioxide increased the yield of sugar beet roots by 24%, sugar collection by 25%.

The availability to plants of calcium, magnesium, sulfur, and micronutrients from manure is generally no worse than from mineral fertilizers. The duration of uptake depends on doses and quality of manure, composition and productivity of crops, and soil-climatic conditions.

Micronutrients in manure

Manure is a source of micronutrients. When applied, the soil is less depleted of micronutrients at high yields than when using mineral fertilizers. The content of micronutrients in manure varies widely.