The importance of biomass in sustainable agricultural soil management
Authors: Tunguz Vesna , Pržulj Novo 
Published: April 2024

Soil formation is a long-lasting natural process, but quickly destroyed by degradation which leads to decrease in soil potential, as a condition for the survival of mankind and the living world on the planet. In order to increase yield of cultivated plants and food production in the second half of the 20th and the beginning of the 21st century, agrochemicals - chemical fertilizers and pesticides were intensively applied, which led to deterioration of the dynamic balance of soil ecosystems and water pollution. Surface layer of agricultural arable land is loose and often insufficiently protected by vegetation during the year, and it is exposed to water and wind erosion. In addition to natural, anthropogenic factors contribute to the reduction of agricultural land and the reduction of the quality of arable land. Although it is the most important natural resource of mankind, excessive or irresponsible use of soil leads to a decrease in its productivity and finally permanent degradation. The increase in the use of artificial fertilizers, manures and slurry produced on farms, and changes in land use are the main factors causing progressive increase of nitrates and nitrites in water in last 25 years. During intensive use, the fertility of the soil changes - mainly caused by depletion due to plant yields and loss of plant nutrients, acidification or alkalization and reduction of organic matter content. Soil fertility is strongly correlated with soil quality and represents the ability of soil to enable cultivated plants to optimally accumulate biomass with minimal use of manure and mineral fertilizers. Concern for soil, its natural resources and biological divergence is becoming the subject of interest of an increasing part of human population, and not just the ones engaged in agriculture, and thus becomes the responsibility of a society as a whole. Due to his activities, most often agricultural production, men can increase or decrease the fertility of the soil. Protecting the soil from erosion and increasing the amount of organic matter in the soil are particularly important measures in the sustainable management of agricultural soil. Incorporating crop residues increases the content of organic matter in the soil, and the application of green manure and cover crops in the crop rotation protects the soil from erosion and improves its physical, chemical and biological properties. Ploughing crop residues increases the content of nutrients, organic matter and humus, and microbiological activity in the soil, improves water, air and physical properties of the soil, improves soil structure, which consequently contributes to increase in soil fertility and ultimately yields. Harvest residues are a valuable product due to high energy content necessary for microorganisms, which should not be removed, but used on the plot by ploughing. The nutrients in the crop residues are at the place of their application, transport is unnecessary, and they have the same nutritional value as manure. Depending on the plant species, ploughing crop residues provides 20–25% of nitrogen, 25–50% of phosphorus, and 30–80% of potassium for the next crop. Decomposition of crop residues in the soil is done by two processes: (1) decomposition to water, carbon dioxide, ammonia and minerals that can be used by the next crop and (2) transformation into humus. The application of nitrogen fertilizers with ploughed aboveground biomass significantly contributes to the increase of humus content and the efficiency of carbon retention in the soil. Planned input into the soil of aboveground biomass of a crop grown exclusively for that purpose is called green manuring or sideration, and the crop itself used for green manure is called green manure or siderate. Siderates have numerous positive effects on the soil - organic matter enrichment, improved biological activity in the soil, effect on pedohygiene, physical, chemical and biological properties, absorption of more difficult-to-access nutrients and prevention of nutrient leaching, especially nitrogen. Planting of green manure, included in the crop rotation, contributes to the control of pests and diseases and reduces weeding of arable land, which would otherwise be unsown. Growing green manure in the summer months has a positive effect on reducing soil temperature, water retention, preservation of microorganisms from direct sunlight and protection of the soil from erosion. Plants used for green manure should have a strong root system and be characterized by rapid growth and rapid development of green mass. It is desirable that they have the ability to bind atmospheric nitrogen and absorb more difficult-to-access nutrients from deeper soil layers. The selected crop for green manure should create the maximum green mass in a certain climate. In organic agriculture, the main source of nitrogen is leguminous plants, living in symbiosis with Rhizobium bacteria, which have the ability to fix airborne nitrogen and convert it into a form accessible for plant absorption. It is desirable to use mixtures of legumes with non-legumes for green manure for better adaptation and creation of biomass as large as possible. The application of green manure also has certain disadvantages: additional costs for seeds, cost of soil cultivation and sowing, lack of income-producing crops, additional seasonal field labour, possible problems with pests and diseases due to the "green bridge" effect and the possibility that green manure becomes weed. Cover crops have a large capacity to contribute to sustainable agricultural soil management and the realization of sustainable agricultural production. These crops primarily maintain and improve soil properties and capacity through its protection against water and wind erosion, improvement of soil structure (aggregate stability), improvement of soil hydraulic properties (water infiltration), increase in soil organic carbon content and microbiological activity, and decrease of nitrogen leaching, thus reducing groundwater pollution. Cover crops play a useful role in adapting to climate change and mitigating greenhouse gas emissions. The different benefits of cover crops depend on the plant species used as cover crops (legumes, non-legumes, grasses, Brassicaceae), the time of sowing and termination of vegetation of cover crops and the manner of termination of vegetation - mechanically or chemically. Cover crops that have an adventitious root are more effective in protecting the soil from erosion than cover crops with an axial root. Cover crops manifest their positive economic effect after long-term use. In addition to the main effects on the soil, cover crops have other effects, such as allelopathic and the effects of using different mixtures of cover crops on the health and quality of the soil.