Formation of arid soil and chemical composition of forest soil
Arid soils are formed from the fragmentation of adjacent rocks and are largely blown from Indus valley area and coastal regions. They mainly can be seen developing western Rajasthan. It mainly ranges from red to brown in colour. It is generally sandy to gravelly in texture, and have a high percentage of soluble salts. These also said to be saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water. Because of the presence of dry climate, accelerated evaporation and high temperature, these lack moisture and humus. These soils are deficient in nitrogen and humus. The phosphate and iron content is normal. They are mineral rich soils but the main limitation is the lack of water. The soils exhibit poorly developed horizons. Plants are widely spaced. Chemical weathering is limited. Lower horizons of the soil are occupied by ‘kankar’ layers because of the increased calcium content downwards. It limits the penetration of water, and when irrigation is made available, then the soil moisture is readily available for a sustainable plant growth. They give high agricultural returns if irrigated properly. The availability of water from the Indira Gandhi canal has transformed the agricultural landscape of desert soils of western Rajasthan. These soils are mainly cultivated for bajra, fodder, pulses, and less water requiring crops.
Soil formation when influenced by forest vegetation, are generally characterized by deeply rooted trees, significant ‘litter layers’ or O horizons. Recycling of organic matter and nutrients, that includes wood, and wide varieties of soil-dwelling organisms are generally called forest soils. There are also soils now covered with forest vegetation, often plantations, on lands that were not naturally forested. These soils are probably undergoing processes that give them ‘forest soil-like’ characteristics, e.g., litter layers from trees, woody organic residues from deep roots, and associated soil microbe and fauna populations. Like other soils, forest soils have developed, and are developing, from geological parent materials in various topographic positions interacting with climates and organisms. Forest soils have been studied by many generations of soil scientists. Some studies have been focused mainly on ecologic characteristics, for example on surface organic layers in forests in Denmark, which introduced the terms ‘mor’ and ‘mull’; while other investigations have dealt with nutrients, water supplies, soil organisms (especially mycorrhiza-forming fungi), fertilizer additions, and other impacts of forest management. The chemical composition of forest soils is pH, anion-exchange capacity (AEC), electrical conductivity, cation-exchange capacity (CEC), base saturation (BS) percentage, exchangeable sodium percentage (ESP), and redox potential. These indices characterize the forest soils and affect the growth and distribution of forest tree species.