The Physical Soil Properties Environmental Sciences Essay

The Physical modify Properties Environmental Sciences Essay shits ar composed of five main components mineral particles derived from rocks by weathering organic significants humus from dead and declineing coiffure material earth pissing supply in which food for thought elements argon dissolved primer air some(prenominal) carbon dioxide and oxygen and living organisms including bacteria that assist make decomposition. defects differ in their fertility levels, because they drive home different proportions of these components and because the mineral particles wealthy person been affected to different degrees by weathering. Age of defect minerals, prevailing temperatures, rainfall, l from distributively one and lubricating oil physico-chemistry are the main factors which determine how much a particular skank depart weather (Sinha and Shrivastava, 2000).Soil thence, is meaning(a) to everyone either directly or indirectly. It is the natural bodies on which artl ess products grow and it has fragile ecosystem (Sinha and Shrivastava, 2000). South Africa ranks among the countries with the highest rate of income inequality in the world (Aliber, 2009). Compared to other middle income countries, it has extremely high levels of commanding p everyplacety and food insecurity threat (FAO, 2009). As part of this, a potential contributor to food security might be small-scale agricultural production. Aliber (2009) indicated that input support targeting smallholder farmers could boost production and food security. Utilisation of uncultivated arable lands and subsistence agriculture might be one option to conduce to incomes and/or savings, as well as to encourage food diversification (Altman et al., 2009). Land with high agricultural suitability is considered to view as greater long-term security with regards to both agricultural production and development. From a planning perspective, high agricultural flexibility is therefore considered an appropri ate measure of high quality agricultural land that is highly productive and fertile.Only a small proportion of worlds states have a very good level of fertility, most of which have only good to median(a) fertility and some have very modest fertility, and are often referred to as marginal craps (Ashman and Puri, 2002). Well-known fertile soils are deep alluvial soils make from river mud, organic government issue- rich soils on loess material, nutrient rich Vertisols and volcanic soils (Brady and Weil, 2004). Under poor circumspection, soil fertility can be seriously depleted and soils whitethorn buzz off useless for agriculture.2.2. SOIL PHYSICO-CHEMISTRYSoil is a natural medium on which agricultural products grow and it is dependent on several factors such as fertility to be considered productive (Shah et al., 2011). The fertility of the soil is depended on c moulderlyntration of soil nutrients, organic and inorganic materials and pee. These soil physico-chemical properti es are classified as universe physical, chemical and biological, which greatly influence soil fertility (Ramaru et al., 2000). To manage soil fertility, knowledge and understanding of these properties is required (as discussed below).2.2.1. Physical soil properties(i) Soil cerealSoil texture refers to the relative proportions of the various size groups of individual particles or grains in a soil (Rowell, 1994). It is dependent on the mixture of the different particle sizes stand for in the soil. Based on these different sizes, soil particles are classified as sand (0.05- 2mm), silt up (0.002-0,5mm) and corpse (Clay particles hold larger quantities of water system and nutrients, because of their large surface areas (Brady and Weil, 1999). This property causes the swelling and shrinking of ashes soils, but only those with smectitic group of clay minerals. The large surface area of clay particles gives nutrients numerous binding sites especially when the surface charge density is h igh, which is part of the reason that fine textured soils have such high abilities to retain nutrients (Velde, 1995). The pores among clay particles are very small and complex, so movement of both air and water is very slow (Brady and Weil, 1999). Clay particles are banly charged because of their mineralogical composition. Soils with such particles usually have high CEC and can retain water and implant nutrients thus such soils are considered to be fertile and good for plant growing (Brady and Weil, 1999).The knowledge of the proportions of different-sized particles in soils is critical to understand soil behavior and their management. Since sand particles are relatively large, so are the mars between them, which promote free drainage of water and entry of air into the soil (Brady and Weil, 2002). The implication of free drainage in sandy soil is that soil nutrients are easily washed humble into the soil and become inaccessible for use by plants (Brady and Weil, 2002). Sandy soils are considered non-cohesive and because of their large size, have low specific surface areas and thus have low nutrient retention capacity (Rowell, 1994). Sand particles can hold little water due to low specific surface area and are disposed to drought, therefore have a very low CEC and fertility status (Petersen et al., 1996).The pores between silt particles are much smaller than those in sand, so silt retains more water and nutrients (Rowell, 1994). Soils prevail by silt particles therefore have a high fertility status than sandy soils and provides favorable conditions for plant suppuration when other increment factors are favorable (Miller and Donahue, 1992).(ii) Soil structureThe term soil structure refers to the arrangement of soil particles into aggregates (Six et al., 2000). Soil structure is affected by biological activities, organic enumerate, and cultivation practices (Rowell, 1994). It influences soil water movement and retention, erosion, nutrient recycling, sealing and crusting of the soil surface, together with aeration and soils structural stability, decide penetration and crop hold (Lupwayi et al., 2001).Soil structure can be platy, prismatic, coarse-grained, crumbly, columnar and blocky (RCEP, 1996). An ideal soil structure for plant growth is often described as granular or crumb-like, because it provides good movement for air and water through a variety of different pore sizes and it also affects root penetration (RCEP, 1996). An ideal soil structure is also stable and resistant to erosion (Duiker et al., 2003). Organic matter and humification processes improve structural stability, and can rebuild degraded soil structures (Brady and Weil, 1999). Therefore it is alert to re farm or add organic material to the soil and to maintain its biological activity in order to enhance soil structure for plant growth. Favorable soil structure and high aggregate stability are therefore vital to improving soil fertility, increasing agronomi c productivity, enhancing porosity and diminish erodibility.(iii) Water retention capacityWater holding capacity refers to the quantity of water that the soil is capable of storing for use by plants (Brady and Weil, 1999). Soil water is held in, and flows through pore spaces in soils. Soil water can be described into the following stages gravitational, capillary, and hygroscopic, based upon the aught with which water is held by the soil solids, which in turn governs their behavior and availableness to plants (Rowell, 1994).Water holding capacity is an pregnant factor in the choice of plants or crops to be grown and in the design and management of irrigation systems (Brady and Weil, 1999). The total amount of water available to plants growing in field soils is a function of the rooting depth of the plant and sum of the water held between field capacity and wilting percentage in each of the horizons explored by the roots (Brady and Weil, 1999). Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2-3 days after a rain or irrigation in pervious soils of uniform structure and texture (Govers, 2002).The ability of the soil to provide water for plants is an important fertility characteristic (RCEP, 1996). The capacity for water storage varies, depending on soil properties such as organic matter, soil texture, bulk density, and soil structure (RCEP, 1996). This is explained by the degree of soil compaction, where problems go forth arise if excessive compaction occurs which would results in sum upd bulk density, a decrease in porosity and aeration and poor water drainage (Gregory et al., 2006), all resulting in poor plant growth.(iv) Electrical Conductivity (EC)Soil electrical conductivity (EC), is the ability of soil to conduct electrical genuine (Doerge, 1999). EC is expressed in milliSiemens per meter (mS/m) or cm (cm/m). Traditionally, soil scientists used EC to estimate soil common salt (Doerge, 1999). EC measurements also have the potential for estimating variation in some of the soil physical properties such as soil moisture and porosity, in a field where soil salinity is not a problem (Farahani and Buchleiter, 2004). Soil salinity refers to the presence of major dissolved inorganic solutes in the soil aqueous phase, which consist of soluble and right away dissolvable salts including charged species (e.g., Na+, K+, Mg+2, Ca+2, Cl, HCO3, NO3, SO42 and CO32), non-ionic solutes, and ions that combine to form ion pairs (Smith and Doran, 1996). flavour tolerances are usually given in terms of the stage of plant growth over a range of electrical conductivity (EC) levels. EC greater than 4dS/m are considered saline (Munshower, 1994). Salt sensitive plants may be affected by conductivities below 4dS/m and salt tolerant species may not be wedgeed by concentrations of up to twice this maxi mum agricultural tolerance limit (Munshower, 1994). Electrical conductivity is the ability of a solution to transmit an electrical current. The conduction of electricity in soil takes place through the moisture-filled pores that occur between individual soil particles. Therefore, the EC of soil is determined by the following soil properties (Doerge, 1999). Porosity, where the greater soil porosity, the more easily electricity is conducted. Soil with high clay content has higher porosity than sandier soil. Compaction normally increases soil EC.. Water content, dry soil is much lower in conductivity than moist soil.. Salinity level, increasing concentration of electrolytes (salts) in soil water will dramatically increase soil EC.. Cation exchange capacity (CEC), mineral soil containing high levels of organic matter (humus) and/or 21 clay minerals such as montmorillonite, illite, or vermiculite have a much higher ability to retain positively charged ions (such as Ca, Mg, K, Na, NH4, or H) than soil loseing these constituents. The presence of these ions in the moisture-filled soil pores will enhance soil EC in the same way that salinity does.. Temperature, as temperature decreases toward the freezing point of water, soil EC decreases slightly. Below freezing, soil pores become increasingly insulated from each other and overall soil EC declines rapidly.Plants are detrimentally affected, both physically and chemically, by excess salts in some soils and by high levels of substitutable Na in others. Soils with an accumulation of exchangeable Na are often characterized by poor tilth and low permeability and therefore low soil fertility status, making them unfavorable for plant growth (Munshower, 1994).(v) Bulk Density (BD)Soil bulk density is defined as the pile of dry soil (g) per unit volume (cm3) and is routinely used as a measure of soil compaction (Gregory et al., 2006). The total volume includes particle volume, inter-particle void volume and internal pore vol ume (Gregory et al., 2006). Bulk density takes into account solid space as well as pore space (Greenland, 1998). hence soils that are porous or well-aggregated (e.g. clay soil) will have lower bulk densities than soils that are not aggregated (sand) (Greenland, 1998).Plant roots cannot penetrate compacted soil as freely as they would in non-compacted soil, which limits their access to water and nutrients present in sub-soil and inhibits their growth (Hagan et al., 2010). Compacted soil requires more frequent applications of irrigation and fertilizer to sustain plant growth, which can increase runoff and nutrient levels in runoff (Gregory et al., 2006).The bulk density of soil depends greatly on the soils mineral make up and the degree of compaction. High bulk density usually indicate a poorer environment for root growth, reduced aeration and undesirable changes in hydrologic function, such as reduced percolation (Brady and Weil, 1999). The presence of soil organic matter, which is considerably lighter than mineral soil, can help decrease bulk density and thereby enhancing soil fertility (Hagan et al., 2010).2.2.2. Soil Chemical propertiesSoil chemical properties which include the concentrations of nutrients, cations, anions, ion exchange reactions and redox properties, but for the purpose of this study focus will be based on properties that have an implication on soil fertility including(i) Soil pHSoil pH is an important soil property that affects several soil reactions and processes and is defined as a measure of the acidity or alkalinity of the soil (Bohn, 2001). It has considerable effect on soil processes including ion exchange reactions and nutrient availability (Rowell, 1994). Soil pH is heedful on a scale of 0 to 14, where a pH of 7.0 is considered neutral, readings higher than 7.0 are alkalic, and readings lower than 7.0 are considered acidic (McGuiness, 1993). almost plants are tolerant of a pH range of 5.5-6.5 which is near neutral pH range (Bohn , 2001). Soil pH is one of the most important characteristics of soil fertility, because it has a direct impact on nutrient availability and plant growth. Most nutrients are more soluble in acid soils than in neutral or slightly alkaline soils (Bohn, 2001). In strongly acidic soils the availability of bignutrients (Ca, Mg, K, P, N and S) as well as molybdenum and boron is reduced. In contrast, availability of micronutrient cations (Fe, Mn, Zn, Cu and Al) is increased by low soil pH, even to the extent of cyanogeneticity of higher plants and microorganisms (Bohn, 2001).The pH of a soil is also reported to affect so many other soil properties (Brady and Weil, 1999), including nutrient availability, effects on soil organisms, fungi thrive in acidic soils, CEC and plant preferences of either acidic or alkaline soils. Most plants prefer alkaline soils, but there are a few which need acidic soils and will die if placed in an alkaline environment (Brady and Weil, 1999).(ii) Cation Exchan ge Capacity (CEC)Cation exchange capacity is defined as the sum of the total of the exchangeable cations that a soil can hold or sorb (Brady and Weil, 1999). A cation is a positively charged ion and most nutrients cations are Ca2+, Mg2+, K +, NH4+, Zn2+, Cu2+, and Mn2+. These cations are in the soil solution and are in dynamic counterbalance with the cations adsorbed on the surface of clay and organic matter (Brady and Weil, 1999).Clay and organic matter are the main computer addresss of CEC (Peinemann et al., 2002). The more clay and organic matter (humus) a soil contains, the higher its CEC and the greater the potential fertility of that soil. CEC varies according to the type of clay. It is highest in montmorillonite clay, lowest in heavily weathered kaolinite clay and slightly higher in the less weathered illite clay (Peinemann et al., 2002). Sand particles have no capacity to exchange cations because it has no electrical charge (Brady and Weil, 1999).CEC is used as a measure of soil nutrient retention capacity, and the capacity to protect groundwater from cation contamination (Brady and Weil, 1999). It buffers fluctuations in nutrient availability and soil pH (Bergaya and Vayer, 1997). Plants obtain many of their nutrients from soil by an electrochemical process called cation exchange. This process is the key to understanding soil fertility (Rowell, 1994). Nutrients that are held by charges on a soil are termed exchangeable as they become readily available to plants (Rowell, 1994).The higher the CEC of a soil, the more nutrients it is likely to hold and the higher will be its fertility level (Fullen and Catt, 2004).Factors alter cation exchange capacityThe factors affecting cation exchange capacity include the following (Brady and Weil 1999), soil texture, soil humus content, nature of clay and soil reaction.Soil texture influences the CEC of soils in a way that it increases when soils percentage of clay increases i.e. the finer the soil texture, the h igher the CEC as indicated in Table 2. CEC depends on the nature of clay minerals present, since each mineral has its own capacity to exchange and hold cations e.g. the CEC of a soil dominated by vermiculite is much higher than the CEC of another soil dominated by kaolinite, as vermiculite is high activity clay unlike kaolinte which is low activity clay. When the pH of soil increases, more H+ ions dissociate from the clay minerals especially kaolinite, thus the CEC of soil dominated by kaolinite also increases. CEC varies according to the type of soil. Humus, the end product of decomposed organic matter, has the highest CEC value because organic matter colloids have large quantities of negative charges. Humus has a CEC two to five times greater than montmorillonite clay and up to 30 times greater than kaolinite clay, so is very important in improving soil fertility.Table 2.1 CEC values for different soil textures (Brady and Weil, 1999)Soil textureCEC range (meq/100g soil)Sand2-4San dy loam2-12Loam7-16Silt loam9-26Clay, clay loam4-60(iii) Organic affaireThe importance of soil organic matter in relation to soil fertility andphysical condition is widely recognized in agriculture. However, organic mattercontributes to the fertility or productivity of the soil through its positiveeffects on the physical, chemical and biological properties of the soil (Rowell, 1994), as follows physical stabilizes soil structure, improves water holding characteristics, lowers bulk density, dark color may alter thermal properties chemical higher CEC, acts as a pH buffer, ties up metals, interacts with biological supplies energy and body-building constituents for soil organisms, increases microbial populations and their activities, source and sink for nutrients, ecosystem resilience, affects soil enzymes. Soil organic matter consists of a wide range of organic substances, including living organisms, carboneous remains of organisms which once occupied the soil, and organic compound s produced by current and past metabolism of the soil (Brady and Weil, 1999).Soil organic matter plays a critical role in soil processes and is a key element of integrated soil fertility management (ISFM) (Brady and Weil, 2004). Organic matter is widely considered to be the single most important index finger of soil fertility and productivity (Rowell, 1994). It consists primarily of decayed or decaying plant and fauna residues and is a very important soil component. Benefits of Organic matter in soil according to Ashman and Puri, (2002) include increasing the soils cation exchange capacity and acting as food for soil organisms from bacteria to worms and is an important component in the nutrient and carbon cycles.Organic matter, like clay, has a high surface area and is negatively charged with a high CEC, making it an excellent supplier of nutrients to plants. In addition, as organic matter decomposes, it bothers nutrients such as N, P and S that are bound in the organic matters s tructure, essentially imitating a slow release fertilizer (Myers, 1995). Organic matter can also hold large amounts of water, which helps nutrients move from soil to plant roots (Mikkuta, 2004).An important characteristic of organic matter in soil fertility is C N ratio. The C N ratio in organic matter of arable surface horizons commonly ranges from 81 to 151, the median being near 121 (Brady and Weil, 1999). The CN ratio in organic residues applied to soils is important for two reasons intense competition among the micro-organisms for available soil north which occurs when residues having a high CN ratio are added to soils and it also helps determine their rate of decay and the rate at which nitrogen is made available to plants (Brady and Weil, 1999).(iv) Plant NutrientsPlants require 13 plant nutrients (Table 2.2) (micro and macro nutrients) for their growth. Each is equally important to the plant, yet each is required in vastly different amounts (Ronen, 2007).Essential elements are chemical elements that plants need in order to complete their normal life cycle (Scoones and Toulhim, 1998). The functions of these elements in the plant cannot be fulfilled by another, thus making each element essential for plant growth and development (Scoones and Toulhim, 1998).Essential nutrients are divided up into macro and micronutrients as illustrated in Table 3. Macronutrients are those that are required in relatively high quantities for plant growth and can be sign into two sub groups, primitive and secondary ones, (Uchida and Silva, 2000). The primary macro-elements are most frequently required for plant growth and also needed in the greatest total quantity by plants. For most crops, secondary macro nutrients are needed in lesser amounts than the primary nutrients. The second group of plant nutrients which are micronutrients are needed only in trace amounts (Scoones and Toulhim, 1998). These micronutrients are required in very small amounts, but they are just as im portant to plant development and profitable crop production as the major nutrients (Ronen, 2007).ClassificationElementFunction in plant growthSource wish symptoms and toxicitiesMacro nutrients PrimaryNitrogen (N)Chlorophyll and Protein fundamental lawAir/Soil, applied fertilisersSlow growth, stunted plants, chlorosis, low protein contentPhosphorus (P)Photosynthesis, Stimulates early growth and root formation, hastens maturitySoil and applied fertilisersSlow growth, delayed crop maturity, purplish green coloration of leavesPotassium (K)Photosynthesis and nzyme activity, starch and sugar formation, root growthSoil and applied fertilisersSlow growth, Reduced disease or pest resistance, development of white and yellow spots on leavesMacronutrients secondaryCalcium (Ca) cell growth and component of cell wallSoilWeakened stems, death of plants growing points, abnormal dark green appearance on foliage milligram (Mg)Enzyme activation, photosynthesis and influence Nitrogen metabolismSoilInt erveinal chlorosis in older leaves,curling of leaves, stunted growth,Sulfur (S)Amino acids, proteins and nodule formationSoil and animal manureInterveinal chlorosis on corn leaves, retarded growth, delayed maturity and light green to yellowish color in young leavesMicronutrients essential bid (Fe)Photosynthesis, chlorophyll synthesis, constituent of various enzymes and proteinsSoilInterveinal chlorosis, yellowing of leaves between veins, twig dieback, death of entire limp or plantsManganese (Mn)Enzyme activation, metabolism of nitrogen and organic acids, formation of vitamins and breakdown of carbohydratesSoilInterveinal chlorosis of young leaves, gradation of pale green coloration with darker color next to veinsZinc (Zn)Enzymes and auxins component, protein synthesis, used in formation of growth hormonesSoilMottled leaves, dieback twigs, decrease in stem lengthCopper (Cu)Enzyme activation, catalyst for respirationSoilStunted growth, poor pigmentation, wilting of leavesBoron (B) gen tilitySoilThickened, curled, wilted and chlorotic leaves reduced floweringMolybdenum (Mo)Nitrogen fixation nitrate reduction and plant growthSoilStunting and lack of vigor (induced by nitrogen deficiency), scorching, cupping or rolling of leavesChlorine (Cl)Root growth, photosynthetic reactionsSoilWilting followed by chlorosis, excessive branching of squinty roots, bronzing of leavesAdditional nutrientsCarbon (C) instalment of carbohydrates and photosynthesisAir/ Organic matterHydrogen (H)Maintains osmotic balance and constituent of carbohydratesWater/Organic matterOxygen (O)Constituent of carbohydrates and necessary for respirationAir/Water/ Organic matterTable 2.2 Essential plant elements, their sources and role in plants (Ronen,2007)Deficiency of any of these essential nutrients will retard plant development (Brady and Weil, 2004). Deficiencies and toxicities of nutrients in soil present unfavorable conditions for plant growth, such as poor growth, yellowing of the leaves and po ssibly the death of the plant as illustrated in Table 3 (Ahmed et al., 1997). Therefore proper nutrient management is required to achieve maximum plant growth, maximum economic and growth result by the crop, and also for minimum environmental impact.In addition to the nutrients listed above, plants require carbon, hydrogen, and oxygen, which are extracted from air and water to make up the bulk of plant encumbrance (Brady and Weil, 1999). Achieving balance between the nutrient requirements of plants and the nutrient reserves in soils is essential for maintaining soil fertility and high yields, preventing environmental contamination and degradation, and sustaining agricultural production over the long term.2.2.3. Soil Biological properties(i) Soil organismsSoil organisms include mostly microscopic living organisms such as bacteria and fungi which are the introduction of a healthy soil because they are the primary decomposer of organic matter (Brady and Weil, 1999). Soil organisms a re grouped into two namely soil microorganisms and soil macro organisms (Table 2.3).Table 2.3 Soil Macro and microorganisms and their role in plant and soil (Brady and Weil, 1999)ClassificationOrganismsFunction in plant and/or soilSourceMicroorganisms bacteriumDecomposition of organic matterSoil surface and humus particlesActinomycetesSource of protein and enhance soil fertilitySurface layers of grass landsFungiFix atmospheric nitrogen and enhance soil fertilitySoil (without organic matter)AlgaeAdd organic matter to soil, improve aeration of swamp soils, and fix atmospheric nitrogenMoist soilsMacro-organismsNematodesThey can be applied to crops in large quantities as a biological insecticideSoil and plant rootsEarthwormsEnhance soil fertility and structural stabilityAerated soilsAnts and termitesSoil developmentDominant in tropical soilsSoil can contain millions of organisms that feed off decaying material such as old plant material, mulch unprocessed compost (Ashman and Puri, 200 2), Microorganisms constitute Soil organic matter is the main food and energy source of soil microorganisms (Ashman and Puri, 2002). Through decomposition of organic matter, microorganisms take up their food elements. Organic matter also serves as a source of energy for both macro and micro organisms and helps in performing various beneficial functions in soil, resulting in highly productive soil (Mikutta et al., 2004).Macro-organisms such as insects, other arthropods, earthworms and nematodes locomote in the soil and have an important influence on soil fertility (Amezketa, 1999). They ingest soil material and relocate plant material and form burrows. The effects of these activities are variable. Macro-organisms improve aeration, porosity, infiltration, aggregate stability, litter mixing, improved N and C stabilization, C turnover and carbonate reduction and N mineralization, nutrient availability and metal mobility (Amezketa, 1999 Winsome and McColl, 1998 and Brown et al., 2000).T he various groups of soil organisms do not live independently of each other, but form an interlocked system more or less in equilibrium with the environment (Brady and Weil, 1999). Their activity in soil depend on moisture content, temperature, soil enzymes, dissolution of soil minerals and breakdown of toxic chemicals. All have a tremendous role in the development of soil fertility (Alam, 2001). Their actions involve the formation of structural systems of the soils which help in the increase of agricultural productivity (Alam, 2001).2.3. SOIL CLAY MINERALOGYThe clay fraction of soil is dominated by clay minerals which control important soil chemical properties including sorption characteristics of soils (Dixon and Schulze, 2002). Minerals are naturally occurring inorganic compounds, with defined chemical and physical properties (Velde, 1995). Minerals that are formed in the depths of a volcano are called primary minerals (Pal et al., 2000). Feldspar, biotite, quartz and hornblende are examples of primary minerals. These minerals and the rocks made from them are often not stable when exposed to the weathering agents at the surface of the earth (Dixon and Schulze, 2002). These rocks are broken down (weathered) continuously into small pieces by exposure to physical and chemical weathering processes (Dixon and Schulze, 2002).Some of the elements that are released during weathering, reform and crystallise in a different structure forming secondary minerals (Melo et al., 2002). Secondary minerals tend to be much smaller in particle size than primary minerals, and are most commonly found in the clay fraction of soils (Guggenheim and Martin, 1995). Soil clay fractions often contain a wide range of secondary minerals such as kaolinite, montmorillonite and aluminum hydrous oxides, whereas the sand or silt particles of soils are dominated by relatively inert primary minerals. The clay fraction is usually dominated by secondary minerals which are more chemically active a nd contribute the most to soil fertility (Melo et al., 2002). Two major secondary mineral groups, clay minerals and hydrous