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Scientific basis for the use of straw as an organic fertilizer

Straw can be used as an organic fertilizer. For this purpose, it is widely used in foreign and domestic agriculture, in farms specializing in grain production. Scientific prerequisites for the use of straw as an organic fertilizer:

1. Straw is a source of nutrients. The chemical composition of straw varies depending on soil and weather conditions. On average, at 16% moisture content contains: 0.5% nitrogen, 0.25% – phosphorus (P2O5), 0.8-1.0% – potassium (K2O), 35-40% carbon, as well as sulfur, calcium, magnesium, boron, copper, manganese, molybdenum, zinc, cobalt.

At an average cereal yield of 2.0-3.0 t/ha, 10-15 kg of nitrogen, 5-8 kg – phosphorus (P2O5), 18-24 kg of potassium (K2O) return into the soil with straw.

2. Straw serves as energy material for the formation of humus and increase the microbiological activity of the soil. The chemical composition of straw of cereal crops includes a large amount of nitrogen-free substances (cellulose, hemicellulose, lignin) with a small content of nitrogen and mineral elements. The C:N ratio (70-80:1) in straw affects its decomposition in the soil. Straw provides soil microflora with available carbon, but cellulosic microorganisms have a great need for nitrogen, so, given its small amount in the straw, microorganisms consume mineral nitrogen of the soil, i.e. there is a process of nitrogen immobilization. With a lack of nitrogen the processes of straw decomposition are inhibited. For normal decomposition of straw, the ratio C:N should be 20-30:1.

The effectiveness of straw fertilization increases with additional nitrogen application. A comparative evaluation of fertilization with straw with additional nitrogen compensation and manure shows their equal effectiveness. It is important that with the applied straw and nitrogen the C:N ratio is achieved equal to 20:1. For this purpose, when plowing straw, additional 0.5-1.5% nitrogen from its weight, or 5-15 kg N per 1 ton of straw mineral or organic fertilizer.

When composting straw in aerobic conditions, humus yield is 7.9%, with the addition of mineral nitrogen – 8.5% of the mass of the straw. The most intensive humus formation occurs in the first 4 months of composting, during the decomposition of cellulose and hemicellulose. And humus is accumulated in the maximum amount during the period of the highest number of microorganisms.

In combination with mineral fertilizer, liquid manure or legumes used as green manure, straw has the same effect on humus content as an equivalent amount of manure.

3. Straw for fertilizer improves the physical and chemical properties of the soil, reduces nitrogen loss, increases the availability of phosphate and soil biological activity, improves nutrient conditions for plants. The positive effect of straw is possible when favorable conditions for decomposition are created. For example, the rate of microbial decomposition of straw depends on the presence of food sources, their number, species composition and activity, soil type, cultivation, temperature, humidity, aeration. Thus, straw decomposition increases with the addition of nitrogen, phosphorus, manganese, molybdenum, boron, and copper.

The intensity of cellulose decomposition increases from sod-podzolic soils to gray forests and chernozems. Optimal temperature of cellulose decomposition is 28-30 °С with soil moisture content 60-70% of full moisture capacity. The intensity of decomposition in the upper soil layer is higher due to good aeration, large number and diversity of species composition of microorganisms.

Straw increases the nitrogen-fixing capacity and enzymatic activity of the soil.

4. Often in the first year after the application of straw yield of cereal crops decreases due to contained and formed in the decomposition of toxic compounds, as well as a deterioration of nitrogen nutrition of plants.

Of particular importance is straw fertilization for legume crops. The effectiveness of straw increases with the treatment of legume seeds with nitragin, so on areas fertilized with straw, first try to place legume or row crops. Early applied straw stimulates nitrogen-fixing ability of legumes and increases their yield. Nitrogen nutrition of row crops is provided as a result of mobilization of soil nitrogen during inter-row cultivation.

5. Nitrogen from mineral fertilizers reduces the depressing effect of straw on cereal crops. Nitrogen of mineral fertilizers immobilized in the presence of straw is more mobile, less resistant to acid hydrolysis and mineralized faster than nitrogen immobilized without straw, especially humus nitrogen. Subsequently, straw enhances the processes of nitrogen mobilization, increases the use by plants of both immobilized nitrogen and soil nitrogen, which determines the positive effect on the yield of subsequent crops.

Ways to use straw

  1. Chopped and scattered over the field straw is ploughed in autumn during ploughing or in spring in areas with sufficient moisture. This method can be combined with green fertilizer, which eliminates the application of mineral nitrogen fertilizer and also creates favorable conditions for humus formation after plowing.
  2. On soils of heavy granulometric composition and in humid climatic conditions scattered straw is not ploughed in, but is incorporated superficially by disk-tillers, disc harrows or mills. This method of embedding gives a better effect compared with ploughing. Where possible, after superficial embedding, sow an intermediate crop, preferably a legume.
  3. Straw is also used as a mulching material to combat water and wind erosion. Mulching creates favorable conditions for water absorption into the soil, reduces, and sometimes completely eliminates the danger of surface runoff, promotes uniform distribution of water over the soil surface, improves the structure of the arable layer, and reduces moisture evaporation.
  4. Leaving stubble and straw in place of conventional tillage with non-moldboard tillage reduces wind speed over the soil surface by 40-60%, reducing the risk of wind erosion, so in areas prone to wind erosion, non-moldboard tillage is carried out without embedding straw.
  5. On areas fertilized with straw, first of all, it is sought to place leguminous or row crops. When sowing cereal crops on these areas nitrogen fertilizer is applied at the rate of 8-10 kg of nitrogen per 1 ton of straw. Nitrogen brought with straw in the balance of mineral fertilizers is not considered, since it is included in the general turnover of soil nitrogen, and plays a role only with the systematic application of straw for fertilization in the rotation.

Plowing straw into the soil with the addition of nitrogen is more effective in autumn, as the toxic phenolic compounds formed during decomposition for plants during the autumn-winter-spring period are washed out and decomposed from the root layer.

High efficiency of application of straw with addition of nitrogen gives for row crops with long period of vegetation, at its systematic application in crop rotations its efficiency in time increases: the increase of yield of crops of crop rotation from 0,1 t/ha of fodder unit increases to 0,2-0,3 t/ha of each ton of straw.

According to generalized G.E. Merzla results of long-term experiments of the All-Russian Institute of Fertilizers and Agrochemistry, straw when aligned with mineral fertilizers on nutrient elements of application rates, the effect on crop yields and soil fertility is equal to manure. For example, on the powerful low-humus black earth in experiments Drabivska experimental station when aligning the rates of nutrients in the straw and manure for sugar beet yield was 40.8 and 40.5 t/ha, whereas when making only straw in the amount of 4-6 t / ha – 35.7 t / ha, when adding to the straw 90 kg/ha of nitrogen – 37.9 t/ha, in the version without fertilizers – 33.5 t/ha.

In studies of the Sumy experimental station on black earth when applying to corn straw, litter and litter-free manure in equivalent rates of nutrients, green mass yield was 54.5 t/ha; 52.9 t/ha; 53.2 t/ha, respectively, in the control without fertilizers – 41.4 t/ha.

In the experiments of the Krasnodar Research Institute of Agricultural Sciences on leached black earth yield of winter wheat at the application of 5 t/ha of straw was 2.66 t/ha, 5 t/ha of straw and N50 – 3.20 t/ha, in the control without fertilizer – 2.80 t/ha.

On typical micellar-carbonate black earth in the experiments of the Stavropol Research Institute of Agricultural Sciences, the yield of winter wheat in the background was 2.89 t/ha, background + 10 t/ha of straw – 3.00 t/ha, background + 10 t/ha of straw + N20 – 3.13 t/ha.

Systematic application of straw increases its efficiency, and the lack of nitrogen appears only in the first years. In subsequent years, nitrogen is released more than fixed, so the effect of straw is also observed without additional nitrogen application.

Methods of applying and embedding straw

Mineral nitrogen fertilizers can be replaced by litter-free liquid manure at the rate of 6-8 tons per 1 ton of straw. This combination has an effect similar to litter manure.

On the straw, left evenly on the field after combine harvester, you can make a half-liquid, liquid manure, slurry, sewage, or other organic fertilizer at the rate of 15-20 kg/ha of nitrogen with embedding disk-tiller to a depth of 6-8 cm. In this case, its decomposition is accelerated, not accompanied by the accumulation of toxic substances. The main tillage of the soil to a certain depth is carried out in the usual for a particular zone terms.

The effectiveness of using straw for fertilization with the addition of mineral nitrogen or in combination with litter-free manure or green fertilizer is confirmed in many soil and climatic conditions. For example, in Belarus, on typical sod-podzolic, strongly podzolic, light loamy loam and light loamy soils, separate introduction of 3 t/ha of chopped straw and 27 t/ha of liquid manure had the same effect on the crop yield of the crop rotation (potatoes, barley, perennial grasses), as 30 t/ha of litter manure.

Application of straw as fertilizer in the world is much more than in Russia. For example, the proportion of straw in the total amount of organic fertilizer in Germany is now: for sugar beet – 72%, under wheat – 71%, under winter barley – 58%, whereas at the beginning of 70-ies this figure did not exceed 15-25%.

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 Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.