Geography & History Notes | KCSE, NECTA, ZIMSEC & GCSE

  Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal residues at various stages of decomposition, cells, and tissues of soil organisms, and substances synthesized by soil organisms. The following are factors affecting decomposition of soil organic matters: Temperature: Cold periods retard plant growth and OM decomposition. Warm summers may permit plant growth and humus accumulation.  Soil moisture: Extremes of both arid and anaerobic conditions reduce plant growth and microbial decomposition. Near or slightly wetter than field capacity moisture conditions are most favourable for both processes.   Nutrients: Lack of nutrients particularly N slows decomposition.   Soil PH: Most of the microbes grow best at pH 6 – 8, but are severely inhibited below pH 4.5 and above pH 8.5.   Soil Texture: Soils higher in clays tend to retain larger amounts of humus.   Other Factors: Toxic levels of elements (A...

  Soil is the mixture of minerals, organic matter, gases, liquids, and the countless organisms that together support life on Earth. Soil composition is an important aspect of nutrient management. While soil minerals and organic matter hold and store nutrients, soil water is what readily provides nutrients for plant uptake. Soil air, too, plays an integral role since many of the microorganisms that live in the soil need air to undergo the biological processes that release additional nutrients into the soil. Soil is composed of both organic and inorganic matter, and it is essential for life on earth to exist.  Soil is composed of: Mineral Particles: Mineral particles are the largest ingredient and make up approx 45% of soils . They are the original rock that got broken down by weathering and erosion to form the basis of soil. The type of rock that was broken down to form it is called the parent rock. The broken down rock produces minerals such as calcium, phosphorus, and potas...

  soil water is water available for consumption by plants . Soil water has been classified from a physical and biological point of view as Physical classification of soil water, and biological classification of soil water.   Physical classification of soil water Gravitational water Gravitational water occupies the larger soil pores (macro pores) and moves down readily under the force of gravity. Water in excess of the field capacity is termed gravitational water. Gravitational water is of no use to plants because it occupies the larger pores. It reduces aeration in the soil. Thus, its removal from soil is a requisite for optimum plant growth. Soil moisture tension at gravitational state is zero or less than 1/3 atmosphere. Factors affecting gravitational water Texture: Plays a great role in controlling the rate of movement of gravitational water. The flow of water is proportional to the size of particles. The bigger the particle, the more rapid is the flow or movement. B...