h�bbd```b``�SA$�J�����3��`�D��ճ�����L��E���E`��H�(�9� 2b�4e����@ln��7��O��=�@����L��_�.d`$������@� �n Fusarium lini which causes wilt of flax (Alasi) secretes HCN, a deadly poisonous substance and Fusarium udum a fungus causing wilt of pigeon pea (Arhar) secretes fusaric acid in the roots of the host plants These toxic chemicals secreted by fungi may be responsible for causing wilt in the flax and arhar (Cajanus cajan). Decomposition of dead organic matter primarily helps in the feeding and growth process of these micro-organisms and secondly, increases the nutrient contents of the soil. Not all the soil organisms are beneficial in their properties and behavior. 7. Oxygen of soil is absorbed by plant roots and soil micro organisms in respiration and CO2 is given out which accumulates in spaces. However, the soil has more bacteria and it is their natural habitat. Daubenmire, “soil is the upper part of earth crust in which plants are anchored.” He defines soil as weathered superficial layer of earth crust with which are mingled living organisms and products of their decay. The important factors which bring about changes in the soil atmosphere are temperature atmospheric pressure, wind and rainfall. Plants absorb a small quantity of ram water and dew directly from their surfaces but most of water absorbed by them comes from the soil. It is usually differentiated into horizons of minerals and organic constituents of variable depths which differ from the parent materials in morphology, physical constitutions, chemical properties, composition and biological characteristics.”, According to Russian school, “soil is natural body differentiated into horizons of usually unconsolidated minerals and organic constituents of variable depths.”. TOS4. In some forests their number may reach up to 10,000 per square foot. Anabaena Nostoc Microcystis are important nitrogen fixing blue-green algae. De and Fritsch (1938) have found that certain blue-green algae are able to fix 20 lbs of atmospheric nitrogen per acre in a rice field. Many rodents, insects and earthworms turn over the soil and sometimes also expose the rock surface for physical and chemical weathering. The core is the central fluid or vapounsed sphere having diameter of about 2 500 kms from the centre and is possibly composed of nickel-iron (Urey, 1952). Knowledge of soil is helpful in agricultural practices, such as cultivation, irrigation, artificial drainage and use of fertilizers. It is water of chemical compounds held by chemical forces of molecules (as for example, CuSO4.5H2O). Heavy accumulation of CO2 in the soil is harmful for the plant growth Presence of oxygen in the soil is important in the sense that it helps in the process of breakdown of resoluble rocky mass into soluble minerals and also in the humification (a process in which insoluble minerals and organic nutrients locked up in the dead remains of plants and animals are converted into soluble forms). Soil biology is the study of microbial and faunal activity and ecology in soil. Temperature and atmospheric pressure cause expansion and contraction of the soil air. Fertile soils teem with microorganisms, which directly contribute to the biological fertility of that soil. Actinomycetes prefer saline soils and soil bacteria grow fairly well in the neutral soils richly supplied with organic nutrients. ‘ The quantity of water available in the soil varies from place to place. According to R.F. Content Guidelines 2. Soil water plays very important role in the plant growth. The crust is very complex. Important group of soil organisms are given below (Fig. (c) On complete decomposition, it forms several organic acids which serve as solvents for soil materials. (ii) Below the litter may be found a layer of partially decomposed organic matter which is known as duff layer. This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. It need not be emphasized here that the actual moisture content of a soil has little meaning in respect to plant growth unless: (ii) The permanent wilting percentage of the soil are also known. A major fraction of total water absorbed from the soil is transpired by the plants and only a small quantity of it enters the composition of protoplast. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes.
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