eChapters

9.1 Determination of Oxygen Diffusion rate (ODR) of Soil

The rate of movement of oxygen from atmosphere to respiring plant root cells is important for root respiration and thereby the growth and development of plant. While diffusion through the air-filled pores maintains the exchange of gases between the atmosphere and soil, diffusion through water films maintain the supply of oxygen and disposal of carbon dioxide from active root tissues which are typically hydrated.

Principle

Lemon and Erickson (1952) introduced a method for measuring oxygen diffusion in soil with the help of platinum electrode. The process measures the extent of chemical reduction of oxygen by the platinum electrode maintaining a constant potential of 0.65V with a reference electrode.

Soil consistency is a term used to designate the manifestation of different physical forces acting within the soil at various moisture levels. The consistency limits, also known as ‘Atterberg Limits’ (Atterberg, 1911; 12) are defined by the water content of the soil to create specified degree of consistency. These limits are – (i) Liquid limit or upper plastic limit, (ii) Plastic limit or lower plastic limit and (iii) Sticky limit.

8.1 Determination of Liquid Limit or Upper Plastic Limit

Equipments and Materials

Liquid limit device (Casagrande, 1932) and accessories, spatula, dish, oven, moisture box, balance, desiccator

7.1 Determination of Hydraulic Conductivity of Saturated Soil Laboratory Methods

Hydraulic conductivity of a saturated soil indicates the ease with which water is transmitted through the soil pores. If a constant water head (h) is maintained on a saturated soil column of length (L) and the volume of water (V) percolating per unit time (t) through per unit cross sectional area (A) to the other end, then according to Darcy’s Law, the rate of flow of liquid or flux (q) is proportional to the hydraulic gradient (ÄH/L) across the length of soil column.

6.1 Determination of Soil Moisture

6.1.1 Determination of Soil Moisture Content by Gravimetric Method (Direct method)

Traditionally, water content in soil is expressed as the ratio of the weight of water present in the soil to the weight of dry soil. When this ratio is multiplied by 100, it becomes the percentage of water in the soil sample on dry weight basis.

Equipments and Materials

Soil auger, aluminium moisture box with air tight lid, balance, oven and desiccator

In natural condition primary soil particles cohere to each other to form a cluster or an aggregate through the cementing action of various agents like organic matter, carbonates, oxides of iron and aluminium, etc. Aggregate analysis tells one about the structural status, pore geometry which in turn influences the movement of air and water in soil, amount of water stable secondary particles (aggregate) as well as the extent of finer particles aggregated to the coarser particles and the erodibility status of surface soil against wind and water.

4.1 Determination of Specific Surface Area of Soil

Specific surface area of a soil is defined as surface area per unit weight of soil and is expressed as m² g^-1. The specific surface of soil greatly influences the physical and chemical properties such as retention of water at high suction, swelling, plasticity, soil strength, cation exchange capacity and availability of nutrients. The basic principle of determination of specific surface is based on the amount of gas or polar liquid required to form a monomolecular layer on the soild. Knowledge of molecular size (diameter) and the mass of the adsorbate enables one to calculate specific surface of the adsorbent.

Principle

Dyal and Hendricks (1950) introduced a method for estimating specific area based upon the adsorption of ethylene glycol (EG) to form a monomolecular layer over the entire soil surface. The method involves adding EG to pretreated soil or clay sample and evaporating the excess EG in an evacuated system. The quantity of EG retained at the moment the evaporating rate decreases is proportional to the surface area. Later on Carter et al. (1965) suggested the use of ethylene glycol monoethyl ether (EGME) having high vapour pressure at room temperature than EG for determining surface area of the layer silicate minerals and soils.

3.1 Determination of Bulk Density of Soil

3.1.1 Determination of Bulk Density of an undisturbed Soil

Bulk density of soil is expressed as the ratio of the mass (weight) of soil particle to their total volume including the pore space between the soil particles. Alternately, it is the weight of unit volume of dry soil. It is usually expressed in the unit of gram per cubic centimeter (g/cc) or mega gram per cubic meter (Mg/m³). In fine textured soil bulk density varies from 1.00 to 1.60 g/cc, whereas in coarse textured soil from 1.20 to 1.80 g/cc.

2.1 Particle Size Distribution Analysis

Soil is composed of inorganic particles and organic molecules of varying size and shape. The expression of the proportion of the different size inorganic particles is termed as ‘soil texture’. It is one of the most important basic characters being little changed by cultivation or other practices. Particles are arbitrarily distinguished into following groups on the basis of their diameters.

Soil is a mass of large variability and thus its sampling is the most challenging problem for any soil analyst. Practically, soil sampling is a two step process which includes (i) collection of soil from homogeneous unit and (ii) processing which in turn includes drying, grinding, sieving, mixing, partitioning and storing.

Wide hybridization (interspecific/intergeneric) is basically attemped to introduce new genetic variability from wild or distantly related species into cultivated ones or to synthesize new plant type/s like Triticale and Raphanobrassica. Majority of the commercial crop plants are usually deficient for one or the other desirable traits which are usually available in their wild relatives. However, crossability between commercial varieties and their wild relatives is very limited which is naturally imposed by certain genetically controlled reproductive barriers. These reproductive barrier/s usually operate either at pre or post fertilization stage/s in plant species (Stebbins1958). Since a species is constituted of individuals who share a common gene pool, reproduce among themselves only / exchange genes and share a common habitat. Hence at natural level gene flow remains strictly confined only among members of a particular species otherwise among the members of unrelated species a genetic barrier exists to create reproductive isolation. Therefore, wide crossing basically requires the overcoming of such barriers whch are imposed by temporal and spatial isolation of parents. The reproductive isolation consists of premating and post mating isolation mechanisms like habitat isolation or geographical isolation, sexual isolation and mechanical barrier depending upon incompatibility or mismatching of ganitalia (animals). Sexual isolation in animal kingdom is usually enforced by type of sexual displays and mating calls which are attractivce only to particular members of a species , however other potential intermating species also do exist in the same habitat or locality at that particular period of time.

The newly synthesized autopolyploids, having few or more undesirable features, e. g; meiotic instability, low seed setting and late maturity etc, are usually not suitable for immediate commercial use, are known as raw polyploids. This is specifically more applicable for those sexually propogated polyploids which are developedfor seed. In early generations due to polyploid chromosome constitution and polysomic inheritance they predominanantly do not breed true. Further more, due to meiotic instability chromosome number in their progeny is not always constant or equal to as in synthesized autotetraploid which may vary from few more to few less than the standard autotetraploid. The raw polyploids usually reverts back to diploid parental constitution due chromosome elimination (Randolph and Fischer, 1939). The mechanism responsible for reverting back to diploid status is similar to that of which give rise haploids from diploids. Presently cases are known where either spontaneously or due to specific treatments the chromosome number was reduced to half in somatic tissues. The phenomenon causing such chromosomal reduction is termed as somatic reduction or reduced mitosis Earlier reports suggested it probably to be caused due to spindle organizer abnormalities or some other unknown mechanism/s. The treatment of seed or seedling by colchicine, chloramphenicol and paraflurophenylalanine are reported to have induced chromosome reduction and production of haploids.

The intervarietal chromosome substitution lines of wheat (T. aestivum) are utilized to study the effects of individual whole chromosome/s on agronomic characters of interest to improve crop plants to be selected for preferred traits (Law and Worland 1973). The common method to develop subsitutiion lines involves development of monosomics lines first of that variety which are used later as recipient variety or recurrent parent for substitution. Presently monosomic lines of several wheat varieties are available. However, the development of substitution lines for a specific chromosome by using monosomics sometimes may be erroroneus due replacement of specific monosome by another one of the 21 chromosome set from the donor to the recipient and consequently monosomic becomes monosomic for another chromosome or a recombined chromosome (univalent shift.). Therefore, to maintainand confirmthe identityof a chromosome involved in monosomy are tagged with either genetic marker/s or confirmed cytologically or with the help of molecular markers.

The chromosomes provide physical basis by which genetical stability and continuity of individuals and populations are maintained in each generation. Chromosomes also play an important role to generate variation which is an essential component of evolutionary process. Although crossing over during meiosis is responsible for generation of variability, but structural changes in chromosome too are important for causing variation and evolution, since genetic and cytological analysis of individuals of related species or isolated populations within the species have shown that they may differ by various kinds of changes in their chromosomal structure. The structural changes usually may result from spontaneous chromosome breakage. But under normal condition/s such breakage is an rare event and its frequency is dependent upon environmental conditions, i.e., temperature, various high energy radiations (e.g. X, λ and β-rays) and some chemicals. Chromosome breakage is reported to be higher in some hybrids and in presence of particular genes. Certain chromosomes and chromosomal segments (centromeric and other heterochromatic regions) are more likely to undergo breakage. But stability and continuity of structural changes in the chromosomes depend on the behavior of the broken ends. There is no change if broken end rejoins at the same chromosome but a change may occur if it rejoins with the end of other chromosome or if remains unattached. In case of a pair of homologous chromosomes if one chromosome has any structural change and other one is normal we customarily call it a structural hybrid.

The relationship between gene and chromosome was suspected at the time of rediscovery of Mendelian^, Laws. During that period Montgomery (1901) and Walter Sutton (1902) working on grasshoppers showed that chromosomes occur in distinct pairs, often of recognizable shape and size, and that synapsis involves the union of maternal and paternal chromosomes, while Winiwarter (1901) concluded from his studies in rabbit ovaries that bivalents in the first meiotic division resulted from the chromosome pairing side by side and not end to end as believed by some other workers of that time . Theodor Bovery (1902) showed from his work on polyspermy in the fertilization of sea urchin eggs that the chromosomes of an individual were not equivalent (genetic information) to one another and hence a full chromosomal complement is essential for normal development of cell. Correns (1902) and Cannon (1902) pointed out close parallelism between Mendelian segregation and chromosome reduction during meiosis and concluded that genes are located on chromosomes but they, like de Vries, supposed that maternal and paternal chromosomes move to opposite poles during meiosis. In the same year Guyer established an understanding that random assortment between different pairs of chromosomes would give the independent assortment of genes required by Mendel. Ultimately Sutton (1903) brought together the ideas from cytology and genetics to clearly show the role of chromosomes in heredity and hence to establish the field of cytogenetics. Boveri also through his work, advanced many of the same ideas and thus the hypothesis correlating genes and chromosome transmission was established, which is known as the “Sutton-Boveri Hypothesis or chromosome theory of inheritance”.

Most of the DNA of an living organism is packaged and organized in a chromosome as well as in mitochondria and cell organelles (Feulgen and Rossenbeck 1924). DNA is not found on its own but rather is structured in long strands wrapped around protein complex called nucleosome consisted of a protein called histone. During most of the duration of cell cycle a chromosome consists of long double helix DNA molecule (with associated proteins)During S phase the chromosome gets replicated resulting in X –shaped structure (chromatids) and still attached to a single centromere. The basic role of the chromosome is to provide a frame work which allows each linear segment of the genome to replicate and segregate efficiently. Failure in either of processes cause chromosome imbalance in daughter cells. Three specific cis-acting sites are required for stable chromosome maintenance, i.e., an origin of replication, a centromere and telomeres.

Classical studies of the morphologyof individual chromosomesof the plant species begun by S. Nawaschin 1910-16 and continued by Taylor (1925), Sharp (1929) and Mc Clintock (1929-30). And eventually it was possible to set up working models which account for the internal structure and chemistry of the chromosome and the genetic material as well as genetical facts. The use of aceto-carmine with iron (Belling, 1921) and application of heat greatly improved the staining differentiation of chromosomes. Smears have practically replaced the paraffin techniques of studying chromosome. The gross morphology of chromosomes is generally worked out either at prophase stages of meiosis or metaphase in somatic tissues. The chromosomes may differ in thickness, total length, position of centromere or spindle fiber attachment region, chromomere pattern and number and position of secondary constriction. The total length of chromosomes at metaphase also differs in different tissues of a species and also in certain tissues chromosome present may be very different in appearance. Figure 1 shows various morphological features of a eukaryotic chromosome

The influence of water quality on the soil and plant growth is related to the chemical and physicalproperties of the soil, the salt tolerance of the crop, the climaticregime of the area and the method,frequencyand the amount of irrigation water applied. Irrigation water quality refers to its suitability and sustainability for use in agricultural crops. The problems thatresultfrom the use of a particular irrigation water, vary both in kind and degree, and are modified by soil, climate and crop as well as by the skill and knowledge of the water user. As a result there is no set limiton water quality, rather itssuitability for use is determined by the conditions of use which affects the accumulation of water constituents andwhichmayrestrictcrop yield.The soilproblems mostcommonlyencountered and used as a basisto evaluate water quality are those related to salinity, water infiltrationrate,toxicityanda group of other miscellaneous problems. Numerous guidelines are available for evaluation of water quality. Time to time some of theseguidelines has been updated with modification of some criteria like SAR to Adj. SAR and the Adj. R_Na and development of new concepts like water qualityIndex (WQI) whichhave increasedour predictability. Thenewguidelines are relied heavily on old ones.The modified guideline by Ayers and Westcot (1985) was foundto be themost reliabletopredict thewaterqualityforirrigation.

Irrigated agriculture is playing a major role in enhancing food and livelihood security of a country. Supply of fresh water which is an importantinput for the sustainable and economic development of agriculture are not enough to meet the requirement of all sectors of economy. Reduced water availability to agriculture from the present share of 85% of country’s water resources to about 70-75% by 2020AD wouldaffect the capacity of the country to meet the food production target, unless supplies are augmented from unconventional sources. For future agriculture there are no alternatives but to rely on non conventional sources for partial alleviation of the forecasted water scarcity. Amongthese sources extraction of marginal quality groundwater and the waste water generatedfromurban and industrial activities have thepotential to augment the water supplies. Many associatedsoil, plant and environmental problems come up when these sources of water are directly used for irrigation. For addressing theseproblems and to get more benefit from thesesourcesof water, the first step is to understand how an irrigation water source affects the soil plantsystem.Thereforeknowledge of irrigationwaterqualityiscriticaltodevelop appropriate site and crop specific comprehensive short term and long term management programs.

3.1 Concepts of Soil Sampling

Samplinginvolvesthe selection fromthe total populationof a subset ofindividuals upon which measurements will be made. The measurements made on this subset (or sample) will then be used to estimate the properties (or parameters) of the total population.Samplingisinherent toanyfield research programinsoilscience because the measurement of the total population is impossible for any realistic study.

Samplingdesign involves theselection of the mostefficient method forchoosing the samples thatwill be used to estimatethe properties of the population. The definition of the population to be sampled is central to the initial formulation of the research study. The sampling design defines how specificelementswill be selected from the population, and these sampled elements form the sample population.

Pedogenetic and soilgeomorphic studies focus on determining the processes thatformed the soilproperties or landscapes under study and the environments that controlled the rates of these processes. Pedonscale studies are closely associated with thedevelopmentof soil taxonomic systems andfocus onvertical, intrapedon processes. Soil geomorphic studies are the interface between quaternary geologyand soil science and soil geomorphologistsfocus on lateral transferprocesses and the historical landscape evolution. Hence sampling is difficult for a particular population and is differentfor differentstudy.

Advances in analyticalchemistry and instrumentalanalytical chemistry in the pastfew decades have significantlyimproved, makingelemental determinations in soil extracts and water samples easier, faster and less challenging for the analyst. For most of the elemental analysis procedures, the more traditional wet chemistryprocedures havebeenreplaced byvarious analytical instrumental procedures that employ either emission or absorption spectrophotometry. The elemental concentration in prepared soil extracts and water samples can be determined by a number of instrumentalanalyticalprocedures.

The trend today is toward greater analytical sophistication, to multielement computer controlled analytical instrumentation, resulting in a less ended understandingof the analytical principlesinvolved, and “black box” concepts of instrument calibration, maintenance, and operation. Preparation of the analyte and suitable adaptation for a method of analysis requires an understanding, by the analyst, of the principle of the method as well as its requirements and limitations. Adequate testing is usually required before putting the method to use, following procedures such as those that have been adapted by the Association of Official Analytical Chemists (AOAC).

It is not possible to cover in adequatedetail every method of analysissuitedfor the elemental concentration determination in soil extracts and water samples. Therefore, the objective here is to provide sufficient background information about the instrumentalprinciples to guide the reader.

Manychemicalreactions innature,particularlyinlivingsystems,occur inaqueous solutions. Reactions are often carried out in the laboratory in aqueoussolution becausethese aregenerallymore rapid in solutionthanwhen puresolid reactions are mixed. Analysisof substancesmaybe qualitative or quantitative in nature. A quantitative analysisis one inwhich the amountor concentrationof a particular species in a sample is determined accurately and precisely.

1.1 Volumetric Analysis

Volumetric analysis is a quantitative analysis. It involves the measurement of the volume of a known solution required to bring about the completion of the reaction witha measuredvolume of the unknown solution.

The reaction used in volumetric analysis must fulfil the followingconditions;