Soil erosion – is the process of detachment and displacement of soil particles from land surface. Agencies involved – water, wind, sea waves and animals. 2 broad categories – (i) The Natural erosion or the geologic erosion or the normal erosion; (ii) Accelerated erosion or soil erosion – By soil erosion we mean accelerated soil erosion only. Reasons (1) Destruction of forests, (2) unscientific cultivation practices, (3) Heavy grazing in pasture and grass lands. Harmful effects – (1) Convert the fertile lands to barren and unproductive, (2) causes frequent floods and diversion of course of flow of rivers through fertile river banks due to deposition of soil in river basins, (3) silting of dams due to deposition of sand and silt. Types of Erosion – (1) Rainwater erosion includes – splash erosion, sheet erosion, hill erosion and gully erosion – out of these Gully erosion is the most serve for. (2) Land slides erosion – Earthquakes, heavy rainfall, etc., are the major factors – Heavy destruction of forests also (takes places is sloppy and mountainous areas). (3) Stream Bank Erosion – due to torrential rains in hilly areas causes flooding of rivers and streams causing large scale erosion throughout the stream banks. (4) Sea shore erosion – due to turbulent waves in the sea during heavy rains and winds. (5) Wind erosion – in low rainfall areas – due to strong winds – soil particles are deposited on fertile soils of far of places. Causes expansion of deserts to fertile areas. Winds cause movement of soil particle in 3 ways – (i) Saltation, (ii) Suspension, (iii) surface creep. Saltation – soil particles having a size of between 0.1 to 0.5 mm diameters are directly hit by wind which lead to a bouncing action of the particles- this bouncing action is …

Soil Testing Facilities in Kerala There are 14 soil-testing labs in Kerala, i.e., one for each district. A central soil testing labs is functioning at Parottukonam, Nalanchira to supervise, coordinate and control the activities of the different soil testing labs in the state. There are 9 mobile soil-testing labs with a testing capacity of 50 samples per day one each in 9 districts (except districts of Ernakulam, Pathanamthitta, Idukki, Wayanad and Kasargodu). Soil Test Crop Response correlation Studies Interpreted S.T. Data – best basis for fertiliser recommendation. But the response of the crop depends on other factor like plant population, crop variety, soil moisture, etc.- many methods were suggested to improve ST interpretations. The all India Coordinated Project for investigation on ST – crop response – started in 1967. The studies have indicated significant regression equation for different soil types for predicting crop response and for preparing suitable fertiliser schedules based on ST data. The purpose of ST crop response studies is securing and selecting the best ST method and the calibration of ST values for fertiliser recommendation – the studies enable to know the type of response curve operating in a set of soil-crop-agro-climaric condition, e.g., of each curves – linear, mitscherlich-bray, sigmoid, etc – curves are useful to determine fertiliser does to obtain economic yield – different approaches – critical level approach, percentage yield approach, targeted yield/prescription method . Soil Test Summaries and Soil Fertility Map Soil test data can be summarized to provide information on overall fertiliser requirements for specific areas and on the kinds of fertiliser materials and mixture most suitable for those areas. Helpful for planners and administrators in determining policies of fertilizer production, distribution and consumption – useful for researchers also – can be prepared soil wise, village wise, block wise or district wise. …

Soils which contain high levels of particular clays, such as smectites, are often very fertile. For example, the smectite-rich clays of Thailand’s Central Plains are among the most productive in the world. Many farmers in tropical areas, however, struggle to retain organic matter in the soils they work. In recent years, for example, productivity has declined in the low-clay soils of northern Thailand. Farmers initially responded by adding organic matter from termite mounds, but this was unsustainable in the long-term. Scientists experimented with adding bentonite, one of the smectite family of clays, to the soil. In field trials, conducted by scientists from the International Water Management Institute in cooperation with Khon Kaen University and local farmers, this had the effect of helping retain water and nutrients. Supplementing the farmer’s usual practice with a single application of 200 kg bentonite per rai (6.26 rai = 1 hectare) resulted in an average yield increase of 73%. More work showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years. In 2008, three years after the initial trials, IWMI scientists conducted a survey among 250 farmers in northeast Thailand, half of whom had applied bentonite to their fields. The average improvement for those using the clay addition was 18% higher than for non-clay users. Using the clay had enabled some farmers to switch to growing vegetables, which need more fertile soil. This helped to increase their income. The researchers estimated that 200 farmers in northeast Thailand and 400 in Cambodia had adopted the use of clays, and that a further 20,000 farmers were introduced to the new technique. If the soil is too high in clay, adding gypsum, washed river sand and organic matter will balance the composition. Adding organic matter to soil which is depleted in nutrients and too high in sand will boost its quality.

Here, land degradation refers to a human-induced or natural process which impairs the capacity of land to function. Soils are the critical component in land degradation when it involvesacidification, contamination, desertification, erosion or salination. While soil acidification is beneficial in the case of alkaline soils, it degrades land when it lowers crop productivity and increases soil vulnerability to contamination and erosion. Soils are often initially acid because their parent materials were acid and initially low in the basic cations (calcium, magnesium, potassium and sodium). Acidification occurs when these elements are removed from the soil profile by normal rainfall or the harvesting of forest or agricultural crops. Soil acidification is accelerated by the use of acid-forming nitrogenous fertilizers and by the effects of acid precipitation. Soil contamination at low levels is often within soil’s capacity to treat and assimilate. Many waste treatment processes rely on this treatment capacity. Exceeding treatment capacity can damage soil biota and limit soil function. Derelict soils occur where industrial contamination or other development activity damages the soil to such a degree that the land cannot be used safely or productively. Remediation of derelict soil uses principles of geology, physics, chemistry and biology to degrade, attenuate, isolate or remove soil contaminants to restore soil functions and values. Techniques include leaching, air sparging, chemical amendments, phytoremediation, bioremediation and natural attenuation. Desertification is an environmental process of ecosystem degradation in arid and semi-arid regions, often caused by human activity. It is a common misconception that droughts cause desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Soil management tools include maintaining soil nutrient and organic matter levels, reduced tillage and increased cover. These practices help to control erosion and maintain productivity during periods when moisture is available. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands accelerates desertification. Erosion of soil is caused by wind, water, ice and movement in response to gravity. Although the processes may be …

A taxonomy is an arrangement in a systematic manner. Soil taxonomy has six categories. They are, from most general to specific: order, suborder, great group, subgroup, family and series. The soil properties that can be measured quantitatively are used to classify soils. A partial list is: depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content and salt content. In the United States, soil orders are the top hierarchical level of soil classification in the USDA soil taxonomy . The names of the orders end with the suffix -sol. There are 12 soil orders in Soil Taxonomy: The criteria for the order divisions include properties that reflect major differences in the genesis of soils. Alfisol – soils with aluminium and iron. They have horizons of clay accumulation, and form where there is enough moisture and warmth for at least three months of plant growth. They constitute 10.1% of soils worldwide. Andisols – volcanic ash soils. They are young and very fertile. They cover 1% of the world’s ice-free surface. Aridisol – dry soils forming under desert conditions which have fewer than 90 consecutive days of moisture during the growing season. They include nearly 12% of soils on Earth. Soil formation is slow, and accumulated organic matter is scarce. They may have subsurface zones of caliche or duripan. Many aridisols have well-developed Bt horizons showing clay movement from past periods of greater moisture. Entisol – recently formed soils that lack well-developed horizons. Commonly found on unconsolidated river and beach sediments of sand and clay or volcanic ash, some have an A horizon on top of bedrock. They are 18% of soils worldwide. Gelisols – permafrost soils with permafrost within two metres of the surface or gelic materials and permafrost within one metre. They constitute 9.1% of soils worldwide. Histosol – organic soils, formerly called bog soils, are 1.2% of soils worldwide. Inceptisol – young soils. They have subsurface horizon formation but show little eluviation and illuviation. They …

Soil is classified into categories in order to understand relationships between different soils and to determine the suitability of a soil for a particular use. One of the first classification systems was developed by the Russian scientist Dokuchaev around 1880. It was modified a number of times by American and European researchers, and developed into the system commonly used until the 1960s. It was based on the idea that soils have a particular morphology based on the materials and factors that form them. In the 1960s, a different classification system began to emerge which focused on soil morphology instead of parental materials and soil-forming factors. Since then it has undergone further modifications. The World Reference Base for Soil Resources (WRB) aims to establish an international reference base for soil classification.

A horizontal layer of the soil, whose physical features, composition and age are distinct from those above and beneath, are referred to as a soil horizon. The naming of a horizon is based on the type of material of which it is composed. Those materials reflect the duration of specific processes of soil formation. They are labelled using a shorthand notation of letters and numbers which describe the horizon in terms of its colour, size, texture, structure, consistency, root quantity, pH, voids, boundary characteristics and presence of nodules or concretions. Few soil profiles have all the major horizons. Some may have only one horizon. The exposure of parent material to favourable conditions produces mineral soils that are marginally suitable for plant growth. That growth often results in the accumulation of organic residues. The accumulated organic layer called the O horizon produces a more active soil due to the effect of the organisms that live within it. Organisms colonise and break down organic materials, making available nutrients upon which other plants and animals can live. After sufficient time, humus moves downward and is deposited in a distinctive organic surface layer called the A horizon.

The production, accumulation and degradation of organic matter are greatly dependent on climate. Temperature, soil moisture and topography are the major factors affecting the accumulation of organic matter in soils. Organic matter tends to accumulate under wet or cold conditions where decomposer activity is impeded by low temperature or excess moisture which results in anaerobic conditions. Excessive slope may encourage the erosion of the top layer of soil which holds most of the raw organic material that will eventually become humus.

Humus refers to organic matter that has been decomposed by bacteria, fungi, and protozoa to the final point where it is resistant to further breakdown. Humus usually constitutes only five percent of the soil or less by volume, but it is an essential source of nutrients and adds important textural qualities crucial to soil health and plant growth. Humus also hold bits of undecomposed organic matter which feed arthropods and worms which further improve the soil. Humus has a high cation exchange capacity that on a dry weight basis is many times greater than that of clay colloids. It also acts as a buffer, like clay, against changes in pH and soil moisture. Humic acids and fulvic acids, which begin as raw organic matter, are important constituents of humus. After the death of plants and animals, microbes begin to feed on the residues, resulting finally in the formation of humus. With decomposition, there is a reduction of water-soluble constituents including cellulose and hemicellulose and nutrients such as nitrogen, phosphorus, and sulfur. As the residues break down, only complex molecules made of aromatic carbon rings, oxygen and hydrogen remain in the form of humin, lignin and lignin complexes as humus. While the structure of humus has few nutrients, it is able to attract and hold cation and anion nutrients by weak bonds that can be released in response to changes in soil pH. Lignin is resistant to breakdown and accumulates within the soil. It also reacts with amino acids, which further increases its resistance to decomposition, including enzymatic decomposition by microbes. Fats and waxes from plant matter have some resistance to decomposition and persist in soils for a while. Clay soils often have higher organic contents that persist longer than soils without clay as the organic molecules adhere to and are stabilised by the clay. Proteins normally decompose readily, but when bound to clay particles, …

The organic soil matter includes all the dead plant material and all creatures, live and dead. The living component of an acre of soil may include 900 lb of earthworms, 2400 lb of fungi, 1500 lb of bacteria, 133 lb of protozoa and 890 lb of arthropods and algae. Most living things in soils, including plants, insects, bacteria and fungi, are dependent on organic matter for nutrients and energy. Soils have varying organic compounds in varying degrees of decomposition. Organic matter holds soils open, allowing the infiltration of air and water, and may hold as much as twice its weight in water. Many soils, including desert and rocky-gravel soils, have little or no organic matter. Soils that are all organic matter, such as peat (histosols), are infertile. In its earliest stage of decomposition, the original organic material is often called raw organic matter. The final stage of decomposition is called humus.