Soil is not just an inorganic mass, it is a natural environment that contains air, water, organic matter and various living things (various macro and micro organisms). The number of microorganisms in the soil can reach up to one billion in one gram of soil, and in this respect, scientists define soils as living beings.
Agriculturally dead plant and animal wastes are considered as organic matter. In general, the source of organic matter is animal manure (feces), plant roots, branches, leaves, stems, straw, stubble and various organic urban wastes. Peat, leonardite and gidya (immature coal) formed by the accumulation of organic compounds in aqueous environments in the past are important sources of organic matter. Organic matter has many important biological, physical and chemical functions in soils.
The soils of Turkey (except the Black Sea region) are generally poor in terms of organic matter content, and the organic matter content of 65% of our country's soils is low and very low. In terms of soil quality and production, it is desirable that the organic matter content in the soils be more than 3% (at a good level).
The Effect of Organic Matter (Fertilizers) on the Biological Properties of Soils
The most important element of soil quality is soil organic matter and the number of microorganisms in the soil. Scientists emphasize that the number of living things in the soil is an important criterion in terms of soil fertility and quality. They are of the opinion that the higher the number of living things in the soil, the more fertile the soil. Microorganisms in soils need nutrition and energy to survive. The main food and energy source of microorganisms in the soil is organic matter. In terms of production, the land can be compared to a factory. If the workers working in a factory go on strike or lighten the work due to insufficient wages, it cannot be expected that that factory will operate at full capacity and produce. Similarly, the land is a factory, and the creatures that live there are our production workers. Living things in the soil must be fed at a sufficient level in order to work at full capacity. The higher the organic matter content of a soil, the higher its agricultural production capacity. In an environment where the food source is low, the number of living things decreases and only those who can adapt to difficult conditions and those who are strong can stay in the environment. If the organic matter in the soil is insufficient, the number of living things in the soil will decrease and therefore the production capacity of the soil will decrease. The purpose of artificial fertilizers applied to the soil at various times is to feed only the plants in the short term and does not have any significant benefit for soil creatures. Continuous production with artificial fertilizers is not possible in terms of sustainable agriculture. After a certain point, the tiredness seen in people starts to be seen in the soils and the yield decreases over time.
The Effect of Organic Matter on the Physical Properties of Soils
One of the important factors determining the cultivation and use of soils in agricultural production is the physical properties of the soil. Soil properties such as structure, texture, aeration, water holding capacity, bonding of individual soil particles are considered as physical properties. Organic matter improves the physical properties of soils and provides a suitable environment for plants (Figure 1). In the research carried out with barn manure on this subject, it was determined that organic fertilizers increase the water holding capacity of the soil, and two times more water enters the soil in the areas where barnyard manure is given than in the areas that are not given. This is due to the fact that organic fertilizers bind individual soil particles together, giving the soil a spongy structure.
Organic fertilizers bind individual soil particles in soils and provide a good soil structure. Good soil structure also reduces soil erosion. On the other hand, in clay soils, it reduces the soil compaction and reduces the loose structure of the soils and the formation of cream layer. Good soil structure ensures the retention of water and plant nutrients in the soil. On the other hand, in clayey (sticky and muddy) soils, the soil structure improves and the soils reach the pan (appropriate moisture amount for the cultivation of the soil) faster and ease of cultivation is provided. In soils with good organic matter content, plant growth is better because aeration in the root zone of the plant (oxygen entry from the atmosphere to the soil, carbon dioxide output from the soil) is good. With the decomposition of organic materials, the soils take on a dark color. Dark-colored soils retain more sunlight than light-colored soils and the soil temperature increases. With the increase in soil temperature, plant root development and chemical reactions in soils increase.
The Effect of Organic Matter on the Chemical Properties of Soils
Organic matter is the main source of many plant nutrients. Although the plant nutrient content of different organic substances varies, if no artificial fertilizers are added from the outside, soil organic matter provides 90-99% of the total soil nitrogen, 33-37% of the soil phosphorus and 70-80% of the sulfur in the soil. Along with these, soil organic matter also contains other different plant nutrients such as potassium, manganese, boron, copper, zinc, molybdenum. The plant nutrients contained in organic substances gradually become available to plants during the decomposition of organic substances, and plants can take these nutrients continuously for up to 3-5 years.
Organic compounds released during the decomposition of organic materials in soils make plant nutrients that cannot be taken up by plants in soils available. At the same time, organic compounds cling to the clay surfaces that hold the plant nutrients in the soil, reducing the adhesion of nutrients by the clays and preventing them from turning into a position that cannot be taken by the plants (Figure 2). Thus, soil fertility and plant growth increase.
Organic materials increase the buffering capacity of soils. With its buffering feature, the addition of lime, fertilizer, toxic compounds and other substances prevents sudden changes in the soil (such as increase or decrease in blood pressure in humans).
How to Protect and Increase Organic Matter Content of Soils
Toprak organik maddesinin sürekliğini sağlamak için organik madde artışını sağlayan bitkilere (yeşil gübreler) ekimde yer verilmelidir. Yeşil gübreleme yani bitkilerin çiçeklenme döneminde sürülerek toprak ile karıştırılması 3-5 yılda bir yapılmalıdır. Tahıl, sebze ve yem bitkisi münavebesi toprakların organik madde kapsamını korumakta ve artırmaktadır. Mümkün olduğu kadar topraklarda daha fazla anız artıkları bırakılmalı ve yakılmamalıdır. Özellikle tahıllarda ürün hasat edildikten sonra, anız artıkları daha sonraki ekim sırasında sorun yaratıyorsa, mümkünse toprak gölge tavında işlenmeli ve anız artıklarının toprak ile karışması sağlanmalıdır.
For the continuity of agricultural production, animal manures and other organic materials must be given to the fields and gardens. Soil organic matter can be increased by mixing straw and straw wastes, various plant and animal wastes and organic fertilizers with the soil. Animal manures and organic fertilizers must be mixed with the soil after they are applied to the soil. Otherwise, nitrogen, especially in animal manure, turns into gas and disappears.
Conclusion
In order to obtain high yields by preserving the quality and vitality of the soils, the organic matter content of the soils should be increased or at least the current situation should be maintained. The quality of fruits and vegetables grown in soils with good soil quality due to their organic matter content is also good.