Green fertilizers (green manures)

Scientific basis for the use of green fertilizers

1. Green fertilizer is a source of organic matter and nitrogen in the soil. When the green mass of green manures is plowed in at 35-40 t/ha, 150-200 kg of nitrogen enters the soil, which is equivalent to 30-40 t of manure. The nitrogen utilization coefficient of green fertilizer in the first year is 2 times higher than that of manure. Leguminous green manures enrich the arable layer with available phosphorus, potassium and other elements. For example, on light soils in Woburn (UK), annual plowing in of green manures over 7 years increased the organic matter content by 10%; at Rothamsted Experimental Station, the use of green fertilizer for 30 years accumulated 35 t/ha of organic matter in the soil. In Bavaria (Germany), the use of green fertilizer on loamy soil for 25 years increased the humus content from 2.2-2.3% to 2.8%, whereas applying only mineral fertilizers reduced the humus content to 1.9%.

Green fertilizer influences the fractional composition of humus. For example, in long-term experiments on soddy medium-podzolic medium-loamy soil, the green mass of lupine increased the content of humic acids by 20-30%, while the absolute and relative content of fulvic acids decreased. In Central Asia on typical serozems, intermediate crops for green fertilizer together with alfalfa in cotton-alfalfa rotations improved the humus balance and promoted the mobilization and accumulation of plant-available phosphorus from sparingly soluble phosphates.

2. Green fertilizer improves the agrochemical, physicochemical and physical properties of the soil: excess soil acidity is neutralized, the sum of absorbed bases increases, hydrolytic acidity and the content of mobile aluminum decrease, and the cohesion of sandy and sandy loam soils increases.

On gray forest medium-loamy soil of the Northern Trans-Urals, plowing in green manures reduces the bulk density of the 10-cm layer by 0.07-0.11 g/cm³, and in the 10-20 cm layer by 0.06-0.12 g/cm³. According to data from the Don zonal SRI of Agriculture, in reducing bulk density green manures are equivalent to 20-30 t of manure per 1 ha. In Dagestan, green fertilizers during terracing of slopes over 4 years on average reduced the bulk density in the 40 cm layer by 9.5%, and the humus content in the arable layer increased by 0.54-0.71%.

3. Due to the increased humus content and improved agrochemical and agrophysical properties of the soil, the biological activity of soils increases, the soil and above-soil air is enriched with carbon dioxide, air nutrition of plants improves, and the activity of soil microflora is activated. The number of microorganisms in the 30-cm layer after plowing in green manures increases 1.5-2 times compared with the control, and when combined with mineral fertilizers, 2-3 times.

Plowing in post-harvest buckwheat for green fertilizer on soddy weakly podzolic medium-loamy poorly cultivated soil of Moscow Oblast with a mass of 20-30 t/ha increased the biological activity of the soil and increased the nitrate nitrogen content as a result of intensive mineralization of organic matter.

A positive effect from sowing before winter rapeseed, mustard, rye, barley, and Turkmen vetch was obtained in the conditions of Uzbekistan. Sown in September-October, by the beginning of April they accumulate over 25-40 t/ha of aboveground green mass; plowing in such an amount of organic mass improves soil properties, activates microbiological activity, and increases the content of nitrates, saprophytic microorganisms and actinomycetes. All this contributes to the improvement of the phytosanitary condition of the soil, including the control of wilt, therefore winter sowings of intermediate crops into growing cotton are recommended, primarily on wilt-infested fields.

According to field experiments of the Timiryazev Agricultural Academy, the use of green fertilizers in pure form and in combination with straw leads to a change in the species composition of spore-forming bacteria: the share of bacilli using mineral soil nitrogen grows, which is an indicator of intensive decomposition of organic material.

4. Green fertilizer is a link in intensive agriculture that performs the function of protecting the environment from pollution. With the development of the chemicalization of agriculture and the increase in the use of mineral fertilizers, losses of biogenic elements increase as a result of washout from the surface, migration into deep soil layers, and increased denitrification. Moreover, the more arable land is not occupied by vegetation, the greater these losses. Intermediate green manures, primarily perennial lupine, vegetating in autumn and spring between crop rotation crops, prevent losses of nutrients and protect against water and wind erosion, thus being elements of a soil-protective farming system.

Post-harvest sowings are used in irrigated regions of Central Asia, in the humid subtropics of the Black Sea coast of the Caucasus and Transcaucasia.

5. Green fertilizer performs a phytosanitary role. For example, plowed-in plant mass of perennial lupine reduces damage to potato tubers by scab, which is especially important when growing seed potatoes. In experiments of the SRI of agriculture and animal husbandry of the western regions of Ukraine, on plots where lupine was plowed in during years with large amounts of precipitation, the share of affected tubers was 1-2%, whereas on plots without lupine it was 7-8%.

Great harm to crops is caused by phytopathogenic fungi that cause root rots. Carriers of root rot infection are plant residues and seeds. The faster organic residues decompose in the soil, the faster the fungus is removed from dormancy, and the soil is freed from infection. Post-harvest green manures contribute to an increase in the number of actinomycetes, which are antagonists of the root rot pathogen, as well as saprophytic microflora that accelerates the mineralization of plant residues.

Systematic scientifically grounded use of green fertilizer in combination with other agrotechnical practices contributes to an increase in the profitability of agricultural production. Especially high efficiency of green fertilizers is noted on light sandy soils with poor agrochemical, physicochemical, biological and water properties. In the regions of the Central Non-Chernozem zone, light soils account for about 20% of arable land; in some oblasts, for example, Bryansk and Vladimir, up to 50-60%.

Chemical composition

According to data from various sources, 1 t of raw mass of leguminous green manures on average contains:

• in lupine — 210 kg dry matter; 4.5 kg N; 1.3 kg P₂O₅; 1.8 kg K₂O; 5.0 kg CaO;
• in sweet clover — 220 kg dry matter; 7.7 kg N; 0.5 kg P₂O₅; 2.0 kg K₂O; 10.0 kg CaO;
• in serradella — 210 kg dry matter; 6.2 kg N; 2.2 kg P₂O₅; 5.5 kg K₂O;
• in sainfoin — 200 kg dry matter; 6.2 kg N; 1.2 kg P₂O₅; 3.2 kg K₂O.

Compared with the chemical composition of mixed manure of dense storage, 1 t of which contains 5 kg N, 2.5 kg P₂O₅ and 6 kg K₂O, leguminous green manures are richer in nitrogen and poorer in phosphorus and potassium. Mixtures of legumes with cereals, as well as non-leguminous green manures, are also poorer in nitrogen.

The decomposition processes of green fertilizers in the soil proceed faster than those of other organic fertilizers containing slowly decomposing substances.

Application of green manures

There are separate and compacted (mixed) sowings of green manures.

With separate sowings, the field is occupied by leguminous plants from spring throughout the growing season. It can be plowed in both for winter and spring crops. Green fertilizer occupies a separate field of the crop rotation.

Domestic farming practice shows that as soils are cultivated and specialized crop rotations are introduced, it is advisable to introduce intermediate green fertilizer without disrupting crop alternation in rotations. The use of green-manure fallows (separate green fertilizer) is more suitable on uncultivated soils poor in organic matter. Therefore, the practice of using bare fallows in the Non-Chernozem zone is not an agrotechnically progressive technique. In this zone, green-manure fallows are more effective. To accelerate the cultivation of podzolic soils, green fertilizer is combined with the application of manure, composts and mineral fertilizers.

Compacted (mixed) sowings can be continuous, when part of the field is entirely occupied by green manure, and strip sowings with band or row alternation of the main crop and green manure. For example, green manures planted in the interrows of orchards and berry fields or row crops, across slopes for erosion control.

Depending on the time (before or after harvesting the main crop), there are undersown, i.e. sown under the main crop, and intermediate (post-harvest), i.e. sown after harvesting one crop and before sowing another. This green fertilizer includes post-harvest sowings, autumn and pre-winter sowings. The latter are sown in September-October and plowed in in spring; they are used in irrigated regions of Central Asia, in the humid subtropics of the Black Sea coast of the Caucasus and Transcaucasia.

Post-harvest intermediate green manures are sown after harvesting an early ripening spring crop, for example, barley, and plowed in for fall plowing. For these purposes, harvesting is carried out quickly, and after soil preparation, sowing of plants for green fertilizer is carried out. In this case, green manures manage to accumulate significant mass.

Green manures are also used for undersowing to the main crop, for example, sweet clover is undersown in spring to a grain crop, after harvesting which, before the onset of cold, sweet clover manages to accumulate sufficient mass.

Methods of using green manures: full, mown and aftermath green fertilizers.

With full green fertilizer, the entire mass of green manure is plowed in on site.

Mown fertilizer is grown in an outlying field, then transported to rotation fields and plowed in. Perennial lupine is suitable for this, an advantage of which is also that it ripens for seeds even in the northern regions of the Non-Chernozem zone.

Aftermath green fertilizer is plowed in after the removal of the cut or eaten mass of regrown stubble and root residues of green manures. It is used on sowings of soddy-podzolic soil, primarily of light granulometric composition. It is used in Siberia and the Far East. As aftermath green manures in the irrigated regions of Turkmenistan, Tajikistan, Uzbekistan, Transcaucasia, Kyrgyzstan and Kazakhstan, winter and forage peas and chickling vetch are sown; in the irrigation regions of the Trans-Volga region — chickling vetch and sweet clover.

The main regions of green manure application are soils poor in organic matter with unfavorable properties in different zones requiring cultivation. They are also used when organic fertilizers are lacking.

Green fertilizer is widely used in many countries of the world. Almost everywhere, intermediate crops are used as green fertilizer; separate ones only on depleted soils and on plots remote from livestock farms.

Separate green fertilizer is also used on plots that have come out from uprooting tree and shrub vegetation during the development of new lands and the enlargement of arable land.

In the conditions of intensive agriculture of Belarus and the Non-Chernozem region of Russia, the key green manure crop is perennial lupine. It grows on poor uncultivated soils. When used for soil cultivation, without disrupting the crop alternation scheme, 30-50 t/ha are plowed in at one time. With 3-fold plowing in an 8-field rotation, it ensures an average annual application of plant mass of at least 14-19 t/ha; in a 10-field rotation, 11-15 t/ha.

Green fertilizer has a good effect on potatoes placed after winter rye with undersowing of perennial lupine as an intermediate crop.

Usually perennial lupine is undersown under winter rye. After harvesting rye, lupine grows until late autumn. In spring, vegetation begins immediately after snow melt. Before plowing in for potatoes in spring, lupine manages to grow up to 20 t/ha of green mass, and together with root residues, 30-50 t/ha. After green fertilizer, buckwheat, maize or sunflower for silage, and vetch-oat mixture for green fodder can also be placed in the rotation.

Green fertilizer can be used in the zone of sufficient moisture on all soils, as well as in conditions of irrigated agriculture, for example, in the regions of the Volga region, Central Asia and the subtropics of Transcaucasia, whose climatic conditions promote the rapid accumulation of organic matter. In the Volga region, Rostov Oblast, Krasnodar and Stavropol Krais and other regions of irrigated agriculture, post-harvest and undersown green manures are advisable.

In the central oblasts of the Non-Chernozem region, after harvesting winter and early spring grain crops, fields may remain unoccupied for more than 60 days at a sum of active temperatures of 800-1000 °C, which constitutes 30-40% of the agroclimatic resources of the warm period of the year. Also, a reserve of such resources is available in spring before sowing late spring crops. This amount of precipitation and heat is sufficient for cultivating undersown and post-harvest crops. This can be done south of the line St. Petersburg — Tver — Ivanovo — N. Novgorod — Kazan — Ufa.

In the Non-Chernozem zone, as a green manure crop, annual narrow-leafed lupine (alkaloid), annual forage (low-alkaloid) and perennial (alkaloid) are used. Due to the introduction of forage lupine into cultivation, two-way use of green manures is practiced:

• the green mass of forage lupine is harvested for silage, and post-harvest and root residues are plowed in for winter crops;
• forage lupine is grown for grain, and straw and root residues are plowed in;
• the green mass is mowed at the beginning of budding or flowering and used for fodder.
• e field is left unplowed for aftermath regrowth. In good weather, lupine regrows, and the resulting aftermath is plowed in for green fertilizer. This method allows collecting 20-30 t/ha of green mass for silage and 10-15 t/ha of aftermath for green fertilizer.

Green manures

As green manures, leguminous crops are used: lupine, serradella, sweet clover, vetch, chickling vetch, sainfoin, astragalus, peas, field pea, lentil, clover, alfalfa. Less often, mixtures of leguminous and cereal grasses or intermediate (inserted) non-leguminous crops are used: mustard, colza, rapeseed, buckwheat, winter rye, phacelia.

The use of legumes for green manuring is due to their ability to enrich the soil with nitrogen through nitrogen fixation.

Lupines

Main page: Lupine

Annual and perennial lupines with different alkaloid content are the most common green manures for acidic soils of the Non-Chernozem zone of the European and Asian parts of Russia. Alkaloid lupine is used only for fertilizer; non-alkaloid lupine — aboveground mass for livestock feed, and post-harvest and root residues as aftermath fertilizer. All lupines have the ability to assimilate phosphorus from hard-to-access soil phosphates and phosphorite and bone meal, and to improve the phosphorus nutrition of subsequent crops in the rotation. Lupines are also symbiotically capable of fixing molecular nitrogen from the atmosphere, thereby improving the nitrogen balance in agrocenoses even on poor sandy and sandy loam soils.

Lupines grow well on acidic soils; on very acidic ones, liming is required; sometimes annual lupines tolerate liming poorly, and perennial ones only at the beginning of vegetation. One of the reasons for the suppression of lupines on very acidic soils after liming is the deterioration of phosphorus nutrition: lime prevents the assimilation of sparingly soluble phosphates. Therefore, under lupines, lime and phosphorite meal are applied in layers: lime — to the depth for plowing with skimmers; phosphorite meal — for pre-sowing treatment.

Layer-by-layer application of lime and phosphorite meal in combination with potassium fertilizers under lupine is an effective method of soil cultivation.

Annual alkaloid lupines — blue narrow-leafed and yellow — are grown in separate and mixed sowings and plowed in as full fertilizer during the period of maximum nitrogen accumulation, i.e. during the formation of shiny beans on the main stem. In occupied fallows, the green manure is chopped with disks and plowed in no less than 2-3 weeks before sowing winter crops. Before sowing the latter, the field is rolled so that the soil settles and does not lead to exposure of the tillering node. With the development of forage (non-alkaloid) lupines, the areas of cultivation of alkaloid lupines remained only in the northern oblasts — Vologda, Kostroma, partly Smolensk, Vladimir, Nizhny Novgorod.

Annual forage lupines are more valuable with combined use; they are an additional protein feed for animals and at the same time an aftermath green manure. They are effective as green fodder and post-harvest aftermath fertilizer after harvesting winter rye for green fodder.

The aboveground mass of forage lupines with combined use is mowed in the budding or flowering phase at a high (8-20 cm) cut, which ensures fodder quality with good aftermath regrowth.

Perennial lupine, due to its cold resistance, ripens everywhere, up to Arkhangelsk, with a high multiplication coefficient. It flowers and forms seeds in the second year, and gives maximum green mass without fertilizers in the 3rd-4th year of life.

Perennial lupine in rotations is sown in green-manure fallows or under the cover of winter rye. Pre-winter undersowing is also used as an intermediate crop in the link occupied fallow, winter rye with pre-winter undersowing of perennial lupine, potatoes.

On very poor soils for cultivation, perennial lupine is sown in outlying fields, wastelands, interrows of fruit and berry nurseries, orchards and berry fields, forest nurseries and on ravine slopes. Lupine is left on such plots for 6-8 years and used as mown green fertilizer on nearby fields, berry fields and nurseries, in the tree trunk circles of orchards.

Sweet clover

Main page: Sweet clover

Sweet clover can be annual and biennial, white and yellow, with white being more productive and yellow ripening earlier. This crop grows well on calcium-rich neutral soils. On limed soddy-podzolic soils, sweet clover is more productive than annual and perennial lupine. Due to its powerful root system, it is very drought-resistant and cold-resistant, and is valuable as full and aftermath fertilizer even with poorly developed aboveground mass.

It is also used as animal feed. Increased coumarin content reduces fodder quality, but there are varieties that do not contain coumarin.

For complex use, annual and biennial species are used; on fields with a large slope, biennial is better. Forms of use of undersown and separate sowings:

• mowing at the beginning of flowering for feed and aftermath fertilizer;
• the green mass of the first cut is used for fertilizing other fields (mown fertilizer), the second — for feed, and the aftermath — for feed or aftermath fertilizer;
• the green mass of the first cut — for feed, the second cut — for mown fertilizer, and the aftermath — for feed or fertilizer;
• separate sowing as a fallow-occupying crop with plowing in for fertilizer under winter crops.

Serradella

Main page: Serradella

Serradella — an annual moisture-loving leguminous grass, prefers light slightly acidic (pH_sol 5.0-5.5) soils, and is capable of using sparingly soluble phosphates and phosphorite meal. On sandy and sandy loam soils, it responds well to potassium and magnesium fertilizers. On moisture-provided soils, it is more effective as an undersown crop under the cover of spring and winter (in spring) grain crops. The earlier the cover crop is harvested, the higher the productivity of serradella. On fields clean of weeds, sufficiently moistened and early harvested, post-harvest cultivation of serradella is also effective.

Separate or inserted (intermediate) sowings of serradella are used as full, mown and aftermath fertilizer; complex use is more effective: for livestock feed (cut or aftermath) and green fertilizer (cut, aftermath or root and post-harvest residues).

Use of post-harvest residues as green fertilizers

Post-harvest plant residues (stubble and roots) are an income item in the organic matter balance and are a variety of aftermath green fertilizer.

The quantity and quality of post-harvest residues depend on the biological characteristics of crops, and within one species — on the variety, productivity, and soil and climatic conditions. Possible amounts of post-harvest (crop) residues vary (in t/ha dry matter):

• annual lupines 0.5-1.5 t/ha;
• perennial 2.0-3.0 t/ha;
• clover 3.0-7.0 t/ha, alfalfa 4.0-9.0 t/ha;
• peas 1.5-3.0 t/ha;
• winter rye and wheat 2.2-6.5 t/ha;
• barley 2.0-4.5 t/ha;
• maize 1.5-6.0 t/ha;
• potatoes 0.8-1.2 t/ha;
• sugar beet 1.0-1.5 t/ha;
• rye for green fodder 1.0-2.0 t/ha;
• winter colza 0.5-1.5 t/ha;
• mustard 0.4-1.0 t/ha;
• perennial cereal grasses 5.0-11.0 t/ha.

By decrease in the quantity of post-harvest and root residues, crops are arranged in the following sequence: perennial cereals — cereal-legume — legume grasses — maize — winter grains — spring grains — winter crops for green fodder — sugar and fodder beet — potatoes — inserted (intermediate) crops.

The nitrogen balance due to symbiotic nitrogen fixation is influenced only by legumes and grain legumes in pure and mixed sowings. The nitrogen content in the roots of leguminous crops reaches 2.0-2.5%, and in non-leguminous crops — no more than 0.5-1.0% of dry mass. Therefore, the post-harvest residues of perennial alfalfa in terms of dry matter and nitrogen content are equivalent to 40 t/ha of manure, and clover and clover-timothy mixture — to 20-25 t/ha.

Perennial cereal grasses occupy first place by mass of post-harvest and root residues, but due to their low nitrogen content (0.5-0.7%), their C:N ratio is wider than that of legumes. Therefore, during the mineralization of residues, microorganisms immobilize soil and fertilizer nitrogen forms in the same way as when plowing in straw for fertilizer.

The quantity and quality of post-harvest residues entering the soil is regulated by the structure of sown areas and intermediate crops, which is taken into account when determining the need and places for applying organic fertilizers in the agrocenosis.

Effectiveness of green fertilizers

The effectiveness of green fertilizers depends on the species, productivity and method of use of the green manure. The larger and better quality the green mass of the green manure plowed in for fertilizer, the higher the effect and aftereffect.

The rate of decomposition of green fertilizers depends on the granulometric composition and moisture of the soil, the phase of plant development at the moment of plowing in, and the depth of embedding. With increasing depth of embedding, age of green manures and content of clay particles in the granulometric composition, the mineralization of green fertilizers slows down. The addition of small doses of manure, poultry manure, fecal masses and other microorganism-rich components to green manures during plowing in accelerates mineralization rates.

Ensuring a favorable reaction of the environment and an optimal nutrient regime is a factor in increasing the effectiveness of crops and methods of using green fertilizers.

Leguminous green manures, due to symbiosis with nodule bacteria, are able to satisfy their own and partially subsequent crops' needs for nitrogen. Methods of increasing the nitrogen-fixing ability of leguminous crops are inoculation of seeds with active races of nodule bacteria and treatment with molybdenum fertilizers (20-25 g Mo per hectare norm of seed sowing).

Nodule bacteria are specific and can actively interact only with a particular species of leguminous crops. Strains of nodule bacteria differ in virulence, i.e. the ability to penetrate the root and form nodules, and activity, i.e. the ability to assimilate molecular nitrogen from the atmosphere. Bacterial preparations for treating legume seeds include nitragin and rhizotorfin, which are specific for each crop and contain virulent and active bacterial strains.

Per hectare norm of seeds, 500 g of preparation is used, and only that part of the seeds which is sown on the same day is treated. Inoculation can be combined with treatment with molybdenum fertilizer; for this, the fertilizer and bacterial preparation are dissolved in one portion of water. However, it cannot be combined with seed dressing, which must be carried out 3-4 weeks before sowing; it can also be combined with treatment with molybdenum fertilizers.

The increase in grain yield of rye from lupine green fertilizer is 4.2 c/ha on sandy soils, 4.7 c/ha on sandy loam, and 7.7 c/ha on loamy soils (average of 36 experiments). Green fertilizers show high effectiveness on other crops as well, on light soils, and their aftereffect is noted over a number of years.

List of sources

1. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
2. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.