Soil Study

Wheat Choice has Lasting Effect on Soil health and Yield Researchers at the John Innes Centre in Norwich and Rothamsted Research in Harpenden, examined the effects of growing high and low take-all building susceptible wheat on the make-up of the soil bacterial community associated with the second wheat crop. To their surprise, the impact on the soil from wheat grown in the first year of the experiment completely overrode any expected influence of the second year crop. They found that the variety of wheat grown in year one sets the scene in the soil and what is going on in the soil long after harvesting the initial wheat crop determines the subsequent year's root health and yield. Dr Jake Malone, of the John Innes Centre said: "We knew that plants and microbes in the soil interact in a multitude of ways but we didn't realize just what an impact growing different varieties of the same crop could have on the communities of microbes living in soil. We hope to ta...

Gully Erosion Gully erosion is the removal of soil by water from large channels. These channels carry water during and immediately after rain. Gullies cannot be removed by tillage as in the case of rill erosion. Gully erosion is well developed in unstable and unprotected steeper lands. Gully erosion is quite pronounced in Balochistan and Pothohar area. Gullies not only take the land out of cultivation and reduce area under crops, but also create problems in trafficability, efficient management and use of land. Major factors influencing the gully development include type and condition of soil, presence of compacted layer on or near the surface, type and intensity of storm, absence of protective vegetative cover etc.

Rain-drop Erosion Rain drop erosion resulting from the impact of water drops directly on soil particles. Soil particles get displaced from their moorings and may become part of runoff. In fact, it is the point of initiation of water erosion. The kinetic energy of falling rain drops disintegrates the soil crumb into finer component particles, and then splashes away to down hills. The moving particles also cause scaling of pore spaces, which in turn tend to increase runoff, thus accelerating erosion process.

Soil Moisture Limits for Plant Growth Field Capacity                 The soil moisture content at which all the gravitational water has been drained out of root zone. Usually the moisture content at 1/3 atmosphere tension is considered to be field capacity that is usually to be attained approximately 2 to 3 days after irrigation. Permanent Wilting Point                 The moisture content at which plant roots cease to extract soil moisture is called permanent wilting point. Usually the soil moisture contents at 15 atmospheres are considered to be permanent wilting point. Available Moisture                 The difference in moisture content between field capacity and permanent wilting point is considered available moisture. This is the moi...

Hard Clayey Soils These are the soils in which clay particles constitute over 35% or more of the total weight.  These soils are extensively distributed in salt range foot hills of Punjab and western Kohistan of Sindh.  The plants that grow in these soils have to face the following problems. Soil is compact. There is lack of aeration and drainage. Root penetration and respiration is restricted. Soil is usually shallow due to presence of Ca pan in the lower horizons. This leads to reduced water storage in the thin surface layer of the soil which is exhausted very soon. Because of high adsorptive power of clay, even a slight but continuous addition of Na is enough to cause deflocculation which is very harmful phenomenon for plants. Some kind of help will have to be provided during establishment of vegetation and initial growth stages. Once establishment and having gained complete control of site, the vegetation will by itself bring rapid improvements in s...

Waterlogged Soils These are the soils where water-table rises high and reaches within 3 feet of ground surface most of the time and thus affects crop roots. In extreme cases, the water-table rises even higher than ground surface. Waterlogging is very extensive problem in irrigated areas. It is caused by addition of huge amount of percolation and seepage water from canals, distributaries and water channels as well as inefficient irrigation practices and absence of any effective drainage system. The intensity of water logging is variable and depends on season, general land slope and soil porosity etc. Presence of gravitational water in the root zone for a long period of time excludes the soil air. Plant roots are therefore, unable to respire properly. Oxygen dissolved in soil water gets exhausted very soon because there is no new addition of oxygen to the standing water. In some cases, the ground water may pick up excessive amount of carbon dioxide and salts and intensif...

Wind Eroded Soils In arid sandy areas such as deserts and sea coast, strong wind bellow frequently and cause soil erosion as well as flagging of tree crowns. This is very acute problem in Thal, Cholistan, Tharparker and deserts of Balochistan. The plants that grow in such situation have to face some or all of the following problems. Since the soil is unstable, therefore; the plants are continuously faced with either exposure of their root system due to blowing away of sand or burial of their shoots due to deposition of new sand. Moving sand particles cause mechanical damage to tender shoots and foliage. The transpiratory load is extremely high. Light intensity tends to be very high due to its reflection from shining sandy surface. Water holding capacity of sandy soil is very low which leads to water deficiency for most of the time. The problem of soil erosion by wind can be successfully tackled by considering the following points: A species shou...

Salt affected Soils These soils are those in which either the salt contents of lower horizons concentrate in or on the soil surface or normal proportion of various cations and anions present in soil is disturbed in a big way by excess or shortage of certain ions. This redistribution of salts of salts in soil profile is generally caused by the rising of water table accompanied by intensive evaporation from the surface. The saline water moves up through capillaries and evaporates into the atmosphere while leaving the salts on the soil surface. These salts are frequently seen in the form of thin white crust in the saline area. This crust is quite conspicuous during winter. It has been estimated that about 1/4 to 1/3 of our irrigated area has gone out of production because of salinity. Product vising these areas by tree planting is a major breakthrough. Salinity of soils is rightly considered as enemy number one of World’s Agriculture. In Pakistan about 16.75 million acres area ...

 Soil Problems There are generally three soil problems: Soil salinity and sodicity Soil erosion Waterlogged soils Soil Salinity and Sodicity                 Soils affected by salinity and sodicity are called salt-affected soils. These soils adversely affect the growth of most crop plants because of the presence of excess soluble salts or exchangeable sodium or both. Salt-affected soils are generally divided into three classes i.e. saline, sodic and saline sodic. 1.       Saline Soil                                 A soil having sufficient amount of soluble salts but not excessive exchangeable sodium to adversely affect the growth of most crop plants is saline soil. Saline soils have: Electrical conductivity of ...

Essential Plant Nutrients Plants need food for their growth and development like other living thing. Humans and animals depend on plants for their food from natural raw material. Seventeen elements have been found to be indispensable for plant growth, development & reproduction.  Criteria of Essentiality                 An element should meet following three criteria to be termed as an essential nutrient: ·          Plant is unable to complete vegetative or reproductive stage of its life without that element. ·          The need of such a nutrient is specific and its deficiency symptoms can be corrected by supplying only the same nutrient. ·          The nutrient plays a direct role in plants active process and meets its nutritional needs. Essential nutrients can be divid...

Organic Matter Soil organic matter is composed of decomposing residues (plants and animals), by-product formed by decomposition, microorganisms and materials resistant to further decomposition. Generally, a mineral soil contains 2-5 %organic matter. Organic matter plays a variety of roles in nutrient, water and biological cycles in soil system. Source of organic matter: common organic waste materials which could be used to increase soil organic matter include animal manures, crop residues, composts, green manure, sewage sludge, food processing wastes, industrial organic wastes, wood manufacturing wastes and municipal wastes. Factor Affecting Organic Matter in Soil The amount of organic matter in soil is the result of two processes: the addition of organic matter and the loss of organic matter through decomposition. The following four factors affect both addition and losses. Management                ...

Importance of Soil pH pH is the negative log of the hydrogen ion activity of a soil.                                                                  pH  = -log (H + ) Here H +  represents the hydrogen ion activity in mol L -1 . The pH scale is the logarithm to the base 10 o the reciprocal o the hydrogen ion activity. As the pH of a solution goes from 7 to 6, the hydrogen concentration increases 10 times and OH ions decrease by 10 times. The pH scale extends from 1 to 14. Soils with pH less than 7 are acidic and those with a pH above 7 are alkaline or basic.   It is major factor in determining which trees, shrubs or grasses will dominate the land ...

Basic Process of Soil Genesis During soil formation, the unconsolidated weathered material under goes many changes. These changes are brought about by variations in the four basic soil forming processes. Time required for a soil to develop the distinct layers (horizons). Horizons tend to develop more rapidly under warm, humid and forested conditions where there is enough water to move clay, humus and other colloids downward. Under ideal conditions recognisable soil profile may develop within 200 years and under less favourable conditions the time may extend to several thousand years. These four basic processes often referred as soil forming or pedogenic processes. They are responsible of soil genesis under all kind of environments. Addition                 Inputs of materials to the developing soil profile from outside sources are considered additions. For example, fallen plant leaves, dust, twigs, animal ...

Role of Living Organisms in Soil Formation Soil formation means both the production of parent material and soil profile development. The process of weathering and soil profile development occurs simultaneously. The formation of soil happens over a very long period of time. It may take thousands of years. Soil is formed as results of weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with organic matter. Over time this creates a thin layer of soil and then lower plants grow and soil development is enhanced. Later on higher plants grow and attract animals. When the plants and animals die their bodies decay/decompose. Decaying matter makes the soil thick and rich. This continues until soil is fully developed. The activities of living plants, animals and the decomposition of their wastes and residues have marked influence on soil development. Soil organisms play a major role in soil profile differentia...

Soil Morphology Soil morphology is the visual observation of morphological features of soil i.e. soil colour, texture and structure of horizon and arrangements of these horizons in the soil profile. This can be studied in the field by the naked eye (macro morphology), with the aid of hand lens and binocular stereoscope (meso morphology), with the electron microscope (micro morphology). Soil Profile                                 A vertical section of the soil showing different layers and extending into the C-horizon or parent material (R layer) is called soil profile. Horizon                                 It is a layer of soil approximately parallel to the soi...

Physical Properties of Soil The soil properties that we can see or feel and are relatively more permanent than chemical properties are called physical properties of soil. Such properties are difficult to change. Soil physical properties include texture, structure, particle and bulk density, porosity, air and water content, consistency, colour and temperature. Soil Texture and its Significance                                                                    It refers to relative proportions of the three primary soil separates (sand, silt and clay). Texture is important because it determines the ease of tilling the soil, the amount of aeration, water intake rates and water storage in the soil. It also influences soil fertility. For instance, a fine textured clayey soil is difficult to till, has poor aerati...