Soil deterioration and soil conservation from the viewpoint of soil microbiology

The soil is not a dead, lifeless mass of rock constituents, but is in a true sense a living system. Numerous groups of micro-organisms inhabit the soil to the extent of hundreds of millions of individual cells in a single gram of soil. These organisms are responsible for most of the chemical changes which are taking place in the soil, many of these changes liberating the nutrient elements from the soil materials and making them available for plant growth. Changes in the physical and chemical soil conditions, as a result of cultivation and different cropping systems, are accompanied by corresponding changes in the numbers and activities of these micro-organisms. The microbiological state of the soil can rightfully be considered as an index of the fertility condition of the soil. The problems of water and wind erosion of the soil, as well as soil deterioration due to improper systems of cultivation, are closely associated with the problem of soil organic matter. A decrease in the organic matter content of the soil accompanies soil deterioration and is in itself a cause for further deterioration of the soil, while an increase of the content of organic matter and nitrogen is a symbol of soil improvement. Micro-organisms are closely associated both with the formation and with the destruction of the organic matter in the soil, and with an increase or a decrease of the available nitrogen. Any systems of permanent soil improvement or soil conservation must, therefore, consider the influence of soil treatment upon the activities of the soil-inhabiting micro-organisms, as well as the methods of utilizing their activities in order to bring about a permanent system of agriculture. Furthermore, soil erosion results in the loss of the "active" or "living" surface layer of the soil, leaving the "dead" subsoil. The latter, because of lack of aeration and lack of sufficient nutrients, limits the growth of the important micro-organisms. The soil may also become infested with pathogenic organisms as a result of certain systems of cropping, thus leading to a condition which characterizes "sick" or "exhausted" soils. This condition can be prevented or corrected by proper systems of crop rotation and soil improvement Soil conservation must keep a proper balance of the microbiological population of the soil and a proper state of microbiological efficiency.