Soil Science and Fertilizers

Bioremediation means cleaning of the environment of organic chemicals with the help of microbes, plant and animal species. The organisms involved in bioremediation are of two types, hyperaccumulators and detoxifying. Hyperaccumulators are used in bioprospecting and removal of minerals from wastes. The detoxifying agents metabolize the harmful chemicals through various biochemical reactions.

Soil salinity may be due to the presence of soluble salts in the soil water. This causes salt stress. Due to the presence of salts, the rate of absorption of water is decreased. The absorption of the water with salts may cause cell injury because the water is evaporated as transpiration. There is an accumulation of the salts which may result in cell injury. Hence, the plant will prevent the uptake of salt water and there will be a reduction in the water absorption.

Soil pollution is caused by the addition of substances and factors which decrease its productivity. It is caused by agrochemicals, industrial wastes, municipal wastes etc. It adversely affects the fertility of the soil. The industrial waste lingers in the soil surface for a long time and makes it unsuitable for use by changing the pH of the soil. Pesticides and herbicides are used in agricultural practices and these chemicals penetrate into the soil and change the pH of the soil, affecting its fertility.

Soil pollution is alteration in soil caused by removal or addition of substances and factors, which decrease its productivity and quality of plants and ground water. Negative soil pollution is reduction in soil productivity due to erosion and over use. Positive soil pollution is reduction in soil productivity due to addition of undesirable substances e.g., agrochemicals, industrial wastes, air pollutants washed down by rain, faulty sanitation etc. Pesticides and fertilisers are the two most important types of agrochemicals.

Presence of unwanted contaminant in soil is called soil contamination. The deposition of pesticides on fruits and vegetables lead to its accumulation in fatty tissues of the host. This phenomenon is called bio accumulation.

Xenobiotics are the unwanted chemicals or particles of compounds which are found in the regions where generally they are not present. These are the foreign particles like the herbicides, pesticides, agrochemicals like fertilizers, etc. These are the chemicals which might interact with the bacteria and other microorganisms in the soil. This might affect the absorption of nutrients by the plants.

Acidification is characterized by an increase in hydrogen ion concentration (H+), which mathematically corresponds to a decrease in the pH value (since pH is the negative log of H+ concentration).

Excessive use of artificial fertilizers leads to nutrient runoff that can contaminate water bodies (rivers) and degrade soil structure and fertility. It can also cause air quality issues through the release of gases like nitrous oxide.

While a nearly infinite variety of substances may be found in soils, they are categorized into four basic components: minerals, organic matter, air and water. Most introductory soil textbooks describe the ideal soil (ideal for the growth of most plants) as being composed of 45% minerals, 25% water, 25% air, and 5% organic matter. In reality, these percentages of the four components vary tremendously. Soil air and water are found in the pore spaces between the solid soil particles. The ratio of air-filled pore space to water-filled pore space often changes seasonally, weekly, and even daily, depending on water additions through precipitation, throughflow, groundwater discharge, and flooding. The volume of the pore space itself can be altered, one way or the other, by several processes. Organic matter content is usually much lower than 5% . Some wetland soils, however, have considerably more organic matter in them (greater than 50% of the solid portion of the soil in some cases).

• Climate affects soil formation because it determines the amount of water that is available for processes such as the weathering of minerals, the transportation of minerals and the release of elements. Climate also influences the temperature of the soil, which determines the rate of chemical weathering.
• Temperature and rainfall are the two main climatic factors responsible for soil formation. 
• Hence, Climatic factors affect soil profile and bring changes in soil structure.

Humus is dark brown amorphous gummy substance formed by partial decomposition of plant and animal matter. It constitutes the organic component of soil and is rich in lignin and cellulose. Humus is formed from organic remains through the activity of decomposer microorganism. The process of formation of humus from raw organic remains is called humification. Humus is quite resistant to microbial action. It is a reservoir of nutrients and is helpful in the maintenance of soil moisture as well as aeration. It is colloidal in nature. Nutrients are released slowly as the humus is decomposed slowly. Humus is further degraded by some microbes and release of inorganic nutrients occur by the process of mineralization.

All statements are true except the ability of roots to penetrate in sand and hummus are low as compared to clay.

Mineralization is the release of inorganic substances, both non-mineral(e.g., CO2, H2O) and mineral(e.g., Ca2+, Mg2+, K+, NH+4) from organic matter. The process is slow because of trapping of these nutrients in humus and their immobilization in decomposers/detritivores. It prevents their washing out or leaching. Nutrients immobilized in decomposer microbes and detritivores are again exposed to humification and mineralization after the death of these organisms.

Soil is the thin layer of material covering the Earth's surface and is formed from the weathering of rocks. It serves as the primary medium for plant growth.

While soil composition varies, the organic matter content in typical mineral soils is generally low, usually around 5% by volume, with the rest being minerals, water, and air.