eChapters

Purpose: The ash content of plants represents the deposition of minerals elements in the plant or in its parts. The value of ash content in the plant tissue indicates the health of the plant. Plant ash is also used both in qualitative and quantitative estimation of mineral elements.

Material and Equipments: Crucible, oven, chemical balance and weight box.

Boron occurs as anion in soils and isrequired by plants in very small quantity. Water soluble B makes the estimate of its availability to plants. Total boron in soils varies from 20 to 200 mg kg^-1 and available (water soluble) boron in soils ranges from 0.03 to 12 mg kg^-1 respectively. The threshold value ranging from 0.1 to 0.5 mg kg^-1 (water soluble B) depends upon the soil type, crops, and other factors, below which the response to applied boron may be expected. Its availability is affected by soil pH as under:

Soluble chloride (Cl) concentration in the extract is determined by silver nitrate titration. This method quantifies the concentration of Cl (meq/L) in the saturation paste extract. Chloride may be determined using anion selective electrode (potentiometric). Plant tolerance to Cl can be related to its concentration in the soil saturation paste extract. The method detection limit is approximately 0.1 meq/L, dependent on the method of analysis, and is generally reproducible within ± 10 %.

Apparatus Required

Burette, pipette, conical flask and mechanical shaker etc

Diethylene tetramine penta acetic acid (DTPA) being a chelating agent is used in the determination of available Fe, Mn, Cu and Zn. When the soil is shaken with a solution of DTPA, it combines with metal ions in the solution and form soluble complexes of Fe++, Mn++, Cu++ and Zn++. The CaCl2 and triethanolamine (TEA) solution slightly raise and buffer the soil pH and mitigates the effect of Ca++ and Mg++.

[Alkaline Permanganate / Subbiah and Asija (1956) Method]

Introduction

Nitrogen (N) is found in the arable horizon of the soil, mostly in organic material. In the soil solution, organic N is gradually transformed into ammoniacal (NH₄ ⁺), nitrite (NO₂ ^–) and nitrate (NO₃ ^–) nitrogen by microbial processes. Organic-N is, in itself, of very little use to plants, as it can not be absorbed as such. It is, therefore, necessary to estimate the different forms of mineralized or available N. The NO₃ ^–_N and NO₂ ^–-N together, hardly, exceed 1 % of the total N in normal soil.

The available N in soil refers to a fraction of the total N which is converted into forms accessible to the plants. This constitutes, on an average, only 0.5-2.5 % (rarely 5 %) of the total N in a soil at any given time. Nitrogen is, generally, absorbed by plants as NO₃ ^–, under oxidized environment (upland condition), and as NH₄ ⁺, under reduced condition. NO₂ ^– is sometimes, detectable, but the amount is, generally, very small vis-a-vis NH₄ ⁺ or NO₃ ^– and, hence does not warrant its determination. The sum total of NH₄ ⁺ and NO₃ ^–- N is smaller than the total N, which becomes available to plants and the difference being attributed to the mineralization of the organic N, during the crop growth cycle.

The Kjeldahl method is mainly divided into three main steps. This method needs to be carried out in proper sequence. 

The major part of soil nitrogen exists in complex combination in the organic compounds. It becomes available to plants after breakdown to simple form followed by mineralization. The chemical methods for determination of soil nitrogen availability involve either direct or indirect of total nitrogen or measurement of a fraction of easily hydrosable nitrogen by employing solution of dilute acid or alkali. Distillation of alkaline potassium permanganate solution has often been adopted for estimating the ox disable and reactive form of soil nitrogen. The available nitrogen in soil is determined by alkaline permanganate method as per procedure suggested by Subbiah and Asija (1956).

Principle

A known weight of the soil is mixed with alkaline potassium permanganate (KMnO₄) solution and distilled. The organic matter present in soil is oxidized by the nascent oxygen, liberated by potassium permanganate, in the presence of sodium hydroxide and the released ammonia is condensed and absorbed in known volume of a boric acid with mix indicator to form ammonium borate, the excess of which is titrated with a standard sulphuric acid.

In Bray’s method a mixture of ammonium fluoride and hydrochloric acid (NH4F + HCl) act as the extracting agent. It works in two ways, firstly, the hydrogen ions from HCl have a solubilising effect, especially on Ca-P, which makes phosphate get extracted. Secondly, the fluoride ions (from ammonium fluoride) complex with the Al3+ and Fe3+ ions, thereby releasing the Al and Fe bound phosphorous into the extract.

Olsen P were found to bear a quadratic relationship, with Olsen’s extractant underestimating the content in phytoavailable P of soils with high Olsen P contents relatively to soils with low contents. The ‘‘change point’’ at which phytoavailable P began to increase rapidly per unit change in Olsen P was 53 mg Olsen P kg–1 soil. For the acid soils, a significant quadratic relationship was found between the amount of P desorbed to water and Olsen P at the three soil:solution ratios studied.

The term available phosphorus (P) refers to the inorganic form, occurring in soil solution, which is almost exclusively ‘orthophosphate’. The available P is considered to be a fairly good indicator/measure of the P supplying capacity of a soil. A knowledge of available P content of soils is important for determining its critical limit , based on soil-test-crop response calibration study.

Principle

In soil, phosphorus exists in the form of various types of orthophosphates. A very small fraction of these is available to plants at a given time. Available phosphorus content of soil consists mainly of Ca-P, Al-P and Fe-P. In the neutral and alkaline soils particularly, Ca-P is the dominant fraction. Organic –P fraction is also considerable amount, but is usually not include in the determination of available phosphorus. A large number of extractions, buffer solutions, acids and chelating agents have been suggested for available phosphorus from time to time. However, no single extractant appears to be suitable for all types of soils. Two types of extraction methods are more popularly adopted. Under acidic soil conditions, Bray No.1, which involves soil extraction with a solution consisting of 0.003 N NH₄F and 0.025 N HCl is widely followed. The fluoride complexes Al and Fe in soil, thus releasing some bound p besides the easily acid soluble P (largely Ca-P). This extraction is suitable for soils containing less than 2% calcite or dolomite because in calcareous soils, carbonates quickly neutralize the acid, resulting in less extraction of P.

Potassium is extracted from the soil with the help of suitable extractant CH3COONH4 by shacking followed by filtration or centrifugation & is determined in the extract using flame photometer. The analysis photometer is based on the measurement of the intensity of characteristic lime emission given by the element to be determined .

The total potassium content (K) of a soil varies from 0.05 to 2.5%. The total K is distributed in mineral form (90-98%), fixed non-exchangeable (1-10%) and exchangeable plus water soluble K(1-2). Exchangeable K represents an average of 2-15% of the sum of exchangeable bases and 1-3% of the total capacity of cationic exchange.

Principle

It is based on the principle of the equilibrium of the soils with an exchangeable cation mode of the solution of neutral ammonium acetate, in a given soil:solution ratio. During the equilibrium, ammonium ions exchange with the exchangeable K ions of soil.The K content in the equilibrium solution is estimated with a flame photometer.

Soil is shaken with 0.15 % CaCl2 solution. Chloride ions displace adsorbed sulphate during extraction. Calcium ions suppress the extraction of soil organic matter and hence eliminate the contamination caused by extractable organic S.

Soil is shaken with 0.15 % CaCl2 solution. Chloride ions displace adsorbed sulphate during extraction. Calcium ions suppress the extraction of soil organic matter and hence eliminate the contamination caused by extractable organic S.

Sulphur (S) occurs in different forms in soil viz., sulphites, sulphates , sulphides and in organic compounds. Plants absorb S in the form of sulphate(SO₄ ^2-) . The organic forms of S compounds become assimilable, especially following microbiological transformation into SO₄ ^2-. The mineralization of organic sulphur in a soil depends primarily upon the N:S ratio and any SO₄ ^2- formed may be fixed against extraction, particularly if much Fe and Ba is present or if soil is very acidic.

Principle

Beside some amount in the soil solution, available sulphur in mineral soils occurs mainly as adsorbed SO₄ ^2- ions. Both CaCl₂ and phosphate solutions (as monocalcium phosphate) are generally used for replacement of the adsorbed SO₄ ^2- ions. Use of Ca salts have a distinct advantage over those of Na or Na, as Ca prevents deflocculating in heavy textured soils and leads to easy filtration. SO₄ ^2- in the extract can be estimated turbid metrically using a spectrophotometer. Sulphur in the extract can also be measured by colorimetric method using barium chromate but the turbimertic method given below is mainly used in the soil testing laboratories.

Introduction

In recent years, the boom in industrialization has revolutionised the countries but has also added much of sufferings. There is tremendous increase in the water and air pollution. Large amounts of effluents from industries containing organic substances of different nature are discharged and enter the aquatic systems resulting in water pollution. Biological Oxygen Demand (BOD) is the amount of dissolved oxygen required by the aerobic microflora to oxidise the organic matter of dirty water. Increased organic matter results in more oxygen requirements by microorganisms to oxidise it and it results in enhancement of BOD of water. As the BOD of water rises, due to decrease in dissolved oxygen (DO), there is increase in death of fish due to suffocation. Determination of biological oxygen demand (BOD) only is insufficient to give a clear picture of organic content of water bodies and the presence of toxic chemicals in the sample so the chemical oxygen

Bulk density is the ratio of oven-dry mass of soil to its total volume before drying. Knowledge of bulk density is useful in calculating moisture content by volume, porosity using particle density, volume of a known weight of soil, and weight of a furrow-slice. Bulk density is a direct measure of soil compaction. Bulk density is highly dependent on any kind of physical manipulation, degree of wetness, and kind and arrangement of soil particles. For this reason, preservation of original structure in the sample is most essential aspect of the methodology for determination of bulk density. Common methods of determining soil bulk density use soil cores or clods in their natural state.

Theory

Bulk density of the food material play an important role in many applications such as drying, storing, separation of undesirable material, determining the purity of seeds, grinding, maturity evaluations, design of storage structures, etc. It is an important parameter in packaging requirement and is often 2-20% of true density. Bulk density is the density of material when stacked or packed in bulk. Bulk density of powder can be determined under loose conditions. Loose packing is defined as the state obtained by pouring a powder sample into a vessel without any consolidation.

Bulk density

Bulk density of the food material can be defined as the ratio of weight of an untapped material to its volume including the contribution of the inter-particulate void volume. There are two kinds of voids, voids between particles and void within particles. Weight of the material can be determined by weighing balance. Volume can be determined by measured dimensions or using liquid or gas or solid displacement methods.

Pore space or porosity : Porosity is an index of the relative pore volume in the soil or volume fraction of pores. Its value generally lies in the range of 0.3-0.36 (30-60%). Coarse textured soils tend to be less porus than fine textured soil, though the mean size of individual pores is greater in the former than in the latter. The total porosity, in any case, reveals nothing about the pore size distribution which itself is an important property.

Bulk density is the mass per unit volume of soil including pore space. The normal range of bulk density in most soils is ranging from 1.02 to 1.80 g / cm³. The bulk density of coarse textured soils will be on the higher side while organic soils will have lower bulk density.

Particle density is the mass of soil per unit volume excluding pore space. Pore space is that fraction of soil volume not occupied by solid particles.

Principle

The bulk density and percent pore space are determined from the apparent and true volumes of the soil measures by adding a known quantity of water to a measuring cylinder contain a weighed quantity of soil.

Aim : To determine the Calcium in plant sample.

Principle

Carbonate (CO₃) and bicarbonate(HCO₃) ions are species of the same acid, carbonic acid. Their proportionate content is a function of pH. The CO₃ starts to form as pH rises above 8.4. Carbonate and bicarbonate are generally determined in soil saturation extract by titration with 0.01 N H₂SO₄ to pH 8.3 and 4.5, respectively.

Apparatus Required

Burette, pipette, conical flask and mechanical shaker etc

Introduction

Carotenoids are pigments found in plants that contribute to photosynthesis and provide various health benefits. Measuring carotenoid content in leaves can help assess plant health, productivity, and the effects of environmental conditions. The determination of carotenoids typically involves extraction followed by spectrophotometric analysis.

Materials and Equipments

• Fresh leaf samples

• Acetone, hexane, or a mixture of acetone and hexane (for extraction)

• Mortar and pestle or homogenizer

• Centrifuge and centrifuge tubes

• Spectrophotometer • Volumetric flasks and pipettes • Analytical balance

Seafood has grown in consumption as it has become an important part of a diet. Simultaneously their safety is a rising concern for human health. However, seafood may contain harmful chemicals as well as biological agents that could pose health risks to consumers. Fishes are harvested from waters that are contaminated by varying amounts of industrial chemicals, heavy metals, pesticides and antibiotics. These contaminants may accumulate in fish at levels that can cause human health problems (e.g. carcinogenic and mutagenic effects).The seafood may also get contaminated with various pathogenic bacteria due to unhygienic handling practices, cross contamination of raw foods with cooked or ready-to eat foods, and lack of proper temperature control. Pathogenic bacteria can cause illness in human, either by infection or intoxication. Food borne infections are caused by swallowing live pathogens that grow within the body, usually in the intestinal tract. Intoxication is a condition caused by swallowing preformed toxins i.e. toxins produced by microorganisms in the food before it is eaten. Food can become contaminated at any point during production, distribution and preparation. Everyone along the production chain, from producer to consumer, has a role to ensure the safety of seafood.

Chlorophyll content serves as a vital indicator of plant health and photosynthetic efficiency, with higher levels reflecting robust photosynthesis and overall plant vigor, while lower levels may signal nutrient deficiencies, diseases, or environmental stresses. Assessing chlorophyll content helps evaluate plant productivity, as chlorophyll is essential for absorbing light and converting solar energy into chemical energy. Additionally, the chlorophyll-a to chlorophyll-b ratio provides insights into how plants adapt to various light conditions, revealing their light absorption efficiency and ability to cope with environmental changes. Measuring chlorophyll on a fresh weight, dry weight, and leaf area basis allows researchers and agronomists to gauge the effectiveness of agricultural practices such as fertilization, irrigation, and crop management strategies. It also aids in monitoring the impact of stress factors like drought, salinity, pollution, or pest attacks, which is crucial for developing strategies to enhance crop resilience.

Reagents: 80% acetone: - 80 ml acetone + 20 ml water = 100 ml

Procedure for Chlorophyll Extraction from Leaves

1. Sample Collection: Collect fresh, healthy leaves from the plant to be analyzed. Ensure that the leaves are free from dust, pests, and diseases.

2. Preparation of Leaf Samples: Rinse the leaves thoroughly with distilled water to remove any surface contaminants. Pat them dry with a clean paper towel. Weigh an exact amount (usually around 0.1-0.5 grams) of fresh leaf tissue using an analytical balance. Record the fresh weight accurately.

Abstract

The geochemical signature and vulnerability of groundwater of the East Coastal aquifers of  India from Pondicherry to Nagapattinam were determined. The coastal aquifers are fragile and this situation becomes more intense in aquifer systems like that of the Pondicherry to Nagapattinam region. A total of 136 water samples were collected during pre and post monsoon of 2008 and 2009 respectively. Out of which 45 samples for each pre and post monsoon from shallow groundwater and 23 samples for each pre and post monsoon from deeper groundwater.. The samples collected were analysed for major, minor cations and anions. Selected samples were also analysed for stable isotopes (d¹⁸O and dD). The analysed samples were studied for; their utility for different purpose, the nature of the geochemical classification, their variations in ion ratios, extent of sea water intrusion and the percentage of mixing, The study reveals that chief mechanism controlling shallow groundwater is the salts precipitated in the pore spaces during the Pre monsoon were leached and dissolved during the subsequent monsoon apart from sea water intrusion. Southern part of the study area  is more vulnerable than the Northern part of the study area.

Materials Required

Spectrophotometer, ethyl alcohol, beakers, pestle and mortar etc. 

Procedure

    1.     Preparation of sample extracts
        a.    Liquids : Centrifuge the juice at 5000 rpm for 4-5 min., and collect the supernatant. For liquid samples prepare a 40 % solution in ethyl alcohol. To 30 ml of the sample add 45 ml of ethyl alcohol and mix thoroughly. Filter through Watman 
No. 1 paper.

        b.    Semi-solid samples: To 15 g of blended sample add 15 ml of distilled water and 45 ml of ethyl alcohol. Mix thoroughly and filter through Watman No. 1 paper.
        c.    Dried products: Extract known quantity of sample (4-6 g) with 100 ml of 60% ethyl alcohol for 12 hrs and filter through Watman No. 1 filter paper.
    2.     Measure the absorbance of the samples at 440 nm for non-enzymatic browning and 400 or 420 nm for measurement of colour.
    3.     Prepare 60% ethyl alcohol solution as blank. Add 30 ml of distilled water to 45 ml of absolute alcohol and use as blank.

Aim

To determine the contours by cross-section method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To determine the contours by grid method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To determine the contours by radial line method using dumpy level.

Materials required

Dumpy level
Leveling staff
Measuring tape
Wooden pegs/chain pins
Field book

Description

Bucket elevator is one of the equipments used in the material handling to convey the material vertically. The lab model bucket elevator (Fig.34.1) consists of number of buckets/cups arranged to an endless flat belt. The belt with cups run vertically and cups are placed at a particular interval in the belt. The belt is wrapped over two pulleys, one at the top is called head pulley which receives power from an electrical motor 0.5 hp through suitable power concentration and rotates at required rpm. The belts, cups and pulleys are mounted on a steel frame. The grain from the hopper is reaches to the bottom pulley. The bucket is filled with grains during upward movement and is discharged at the top due to the centrifugal force. An outlet is provided at the top to collect the discharge grain. The capacity depends on the bucket size and seed of operation. For proper discharge of the material, the weight of the material in each cup should be equal to the centrifugal force created due to rotation.

Description

Screw conveyor is one of the equipment used in material handling to convey the material horizontally. The screw conveyor consists of screw blade, screw shaft, coupling, tubular trough, cover, inlet and outlet gates, bearings and drive mechanism. A shaft with spiral screw revolves in the tubular trough. The screw shaft is supported by end and hanger bearings. The rotation of screw pushes the grain along the trough. The pitch of a stranded screw which is the distance from the center of one thread to the center of the next thread is equal to its diameter

Materials Required

Soxhlet apparatus, petroleum ether, water bath, sample, grinder, weighing balance, filter paper, threads.

Procedure

    1.    Take the given sample and weigh it (A)
    2.    Dry the samples in an oven till there is no more weight loss and weight it (B)
    3.    Grind the sample into powder.
    4.    Place a weighed quantity of sample in filter paper, wrap the paper and tie it tightly with a thread so that no powder comes out of the paper during extraction. 
    5.    Pour approximately 100 ml of anhydrous ether into the bottom flask. Turn the heaters on. Set the temperature at about 40ºC.  
    6.    The ether will evaporate and circulate through the sample and again will come back to the flask. 
    7.    Repeat the process for about 16 – 18 hrs for complete extraction. 
    8.    Remove the sample and evaporate most of the ether from the mixture of crude fat and ether obtained during extraction.
    9.    Evaporate excess of ether from the crude fat sample by evaporation on a water bath. Evaporate till it is free from the fumes of ether. Record the weight (C).

Materials Required

Sample, Liebig condenser, digestion flasks (700-750 ml cap), conical flasks, filtering cloth (thick linen cloth for clear filtration) reagents, muffle furnace, crucibles.

Reagents

    1.    0.255 N Sulphuric acid solution : Dilute 2.5 g (1.36 ml) of concentrated H₂SO₄ to 200 ml. Ensure correct concentration by titration.
    2.    0.313 N Sodium hydroxide solution: 2.504 g NaOH / 200 ml water nearly free from sodium carbonate. Ensure correct concentration by titration.
    3.    Asbestos Chips: gooch grade, medium fibre, acid wash and ignited
    4.    10% Potassium sulphate (K₂SO₄) solution: Dissolve 10 g of Potassium Sulphate (AR) in water and make up to 100 ml.

Breaking of soil aggregates and dispersion followed by a rapid drying leads to rearrangement and coherence of soil solids in the form of surface crust. The cohesion exhibited by soil upon drying is directly related to surface crusting and clod formation. The formation of soil crusts and hard clods is a major structural feature of soils. Seedling emergence of cereal crops is generally controlled by point resistance around the shoot tip (Richards, 1953). Penetrometer, which measures the resistance to vertical penetration in soil, is an effective instrument to evaluate the crust strength. A relationship between penetration resistance and seedling emergence would serve as a guide to ensure optimum soil condition for a desired plant density.

Apparatus and Accessories

Penetrometer, moisture box, trowel, electronic balance and oven.

(Method of Olbrich et al., 1971)

Jones and Ekman (1960) showed that ¹⁴⁴Ce is absorbed to a very small extent in the gut of the ruminant and suggested its use as a marker in digestibility trials. Huston and Ellis (1968) studied the affinity of radioactive cerium for feedstuffs and digesta particles in vitro experiments and found that cerium is rapidly absorbed onto and remained tenaciously bound to  digesta particles. Ellis and Huston (1968) tested radioactive cerium as a particulate flow marker in sheep with favourable results.

Experimental Procedure
Three Holstein bulls weighing 315, 239 and 305 kg and one Holstein steer weighing 327 kg are used. Twice daily, at 9.00 am and 9.00 pm, they are fed 3.4 kg of a balanced ration, meeting NRC requirements for normal growth and maintenance.

The quantity of space available for product storage is referred to as warehouse capacity. Understanding the distinction between theoretical working capacity and storage capacity can be aided by warehouse capacity. In warehouses and other storage facilities, space is perhaps the most valuable resource for online retailers. By making the most of their warehouse space, businesses can significantly increase the quantity of goods they can store there. Having more things in storage at once can save them money on transportation and other expenses.
It also makes it easier for the warehouse KPI staff to access the products, which helps them process orders faster and deliver the goods to customers sooner. Because space can be limited in a warehouse setting, warehouse managers and business owners should take the time to assess how much space they have and how well they’re using it.
STEP TO CALCULATE WAREHOUSE STORAGE CAPACITY
Understanding your warehouse’s current capacity is the first step in
determining how to increase it. This brief guide will show you how to calculate a
warehouse’s capacity in feet:
• Calculate the total square footage of your warehouse complex. Let’s assume that it is 10,000 square feet in this case.
• Determine the total amount of space devoted to non-storage purposes, such as offices, loading areas, restrooms, and break rooms. Assume for the moment that this is equivalent to 2,000 square feet.
• Subtract the total square feet of non-storage space from the total square feet of your warehouse to determine the usable space. The following is the equation:
USABLE SPACE-TOTAL SQUARE FEET – NON-STORAGE SPACE SQUARE FEET
Determine the total usable storage space by identifying the maximum stack height or clear height. This should account for the lowest-hanging overhead

Aim

To study the determination of drying rate of agricultural products

Problem

In a drying experiment on paddy at an air temperature of 60ºC, the following data were obtained. Prepare a drying rate curve for the experiment. Initial weight of the sample is 1250 gm and initial moisture content is 35% (d.b).

Electrical conductivity of the soil is the quantity of electricity in coulombs that passes per second per cm3 of the soil solution under an applied potential difference of 1 volt. It is written as EC in abbreviated form and is expressed in millimohs cm-1 or dS m-1 (deciSiemen m-1). Current flows in the soil solution due to presence of soluble salts like Cl- , SO2- 4 and NO3 - of Na+, K+ Ca++ and Mg++. These salts fully dissociate in water to their constituent cations and anions and the current is carried by those cations anions in the soil solution.

1. Introduction

Organisms are known to experience stress when environmental conditions, such as temperature, photoperiod, and humidity deviate from their optimal range. Organisms that respire aerobically constantly generate reactive oxygen species (ROS) through metabolism and employ antioxidants to reduce excess ROS formation and maintain a redox balance (Juan et al., 2021). ROS play crucial roles in cell signaling (Sies and Jones, 2020), homeostasis, cell death, immune defense against pathogens, and the induction of mitogenic responses (Dröge, 2002). Therefore, optimal environmental conditions maintain a balance between ROS formation and antioxidant processes in all living organisms.

Procedure

• Take 1 g soil in a 50 ml beaker

• Add 25 ml 1M KCL solution 

Reagents

• Buffer solution : Dissolve 67.5 g of Ammo. Chloride in 200 ml distilled water. Add 570 ml Ammonium solution. The volume make up to 1 ltr.

• EBT : 0.2 g in 25 ml methanol.

Calcium (Ca) and magnesium (Mg) are the two most abundant alkaline earth cations in soils. They both occur as soluble ions in soil solution, exchangeable, non-exchangeable and in organic material. Soils from arid regions are richer in Ca (1-2% CaO), while those from humid zones have a low content (0.01-0.02% CaO). On the other hand exchangeable Mg is found in very small quantities in calcareous soils. Sometimes, in acid soils, Mg²⁺ represents the largest quantity of the sum of exchangeable bases.

Principle

The method is based on the principle that calcium, magnesium and a number of other cations form stable complexes with versenate (ethylendiaminetetraacetic acid disodium salt, EDTA) at different pH. A known volume of standard calcium solution is titrated with standard 0.01N EDTA solution using murexide (ammonium purpurate) indicator in the presence of NaOH solution.

The end point is a change of color from orange red to purple at pH 12 when the whole of Ca forms a complex with EDTA. Calcium plus Mg are also present in the solution and can be titrated with 0.01N EDTA using buffer solution and a few drops Eriochrome Black T indicator. The end point is a change of color from red to blue at pH 10. Beyond pH 10, magnesium is not bound strongly to Erichrome Black-T indicator to give a distinct end point.

Carbonate is a natural constituent of many soils occurring as sparingly soluble, alkaline earth carbonate, chiefly as calcite and dolomite. Most carbonate minerals found in local soils are calcite and account 90% of total soil carbonates. The determination of total carbonate such as CaCO₃in soil is of great interest on account of high useful ess for diagnosing soil status in terms of structure, texture, biological activity or nutrient content. In calcareous soils carbonates exert a major influence on the chemical properties. Also carbonate content is used as a differentiating criterion for some classes at the family level of soil taxonomy.

Principle

A qualitative rapid test for free calcium carbonate is made by adding 10 mL of diluted HCl(1:3) to about 5 g of air dry soil on a watch glass and observing the intensity of effervescence which results from the evolution of CO Based on the . degree of effervescence the amount of calcium carbonate present in the soil can be broadly categorized into “traces or negligible, low, medium, high and very high”. Soils having traces to low amounts of calcium carbonate do not pose any problem. But those showing medium to very high degree of effervescence, a separate quantitative analysis should be carried out using Puri’s rapid titration method.

54.1. Aim

To determine crude fibre in given samples.

54.2. Theory

Fibres can be classified into four categories like crude fibre (cellulose); acid detergent fibre (cellulose + lignin); neutral detergent fibre (cellulose + lignin + hemicelluloses) and total dietary fibre (Cellulose + lignin + hemicelluloses + pectic substances). Crude fibre is the organic residue of a sample. A fat free sample is treated with boiling sulphuric acid and subsequently with sodium hydroxide. The residue after subtraction of ash is regarded as crude fibre.

54.3. Reagents/ Apparatus/Glassware

1. 0.255 N Sulphuric acid solution

2. 0.313 N Sodium hydroxide solution

3. 10% Potassium sulphate solution

4. Ethanol

Limitation of Weende Method

The partition of carbohydrate into fiber (CF) and nitrogen free extract (NFE) is presumed to represent a separation of less digestible starch and sugars. However, in 20 to 30 percent feeds listed by Morrison, the NFE is less digestible than the CF. This comes about for several reasons, the most important of which is the CF method (successive boiling with dilute sulphuric acid and sodium hydroxide) does not recover all the fiber and large portions of fibrous constituents  are extracted into the NFE. The most  important of these fractions are lignin and hemicellulose are dissolved by both acid and alkali. The basic error of the NFE concept is the assumption that if constituents are soluble they are digestible. Lignin, the rigid component of wood, not only is indigestible but lowers the digestibility of substances with which it is associated.

Another portion of the indigestible part of NFE arises from an artifact in the calculation of faecal NFE, where it is presumed that faecal nitrogen is protein (N x 6.25). Actually, 80-90 percent faecal nitrogen is NPN and is composed of bacterial residue in which the ratio of organic matter to nitrogen is about 1:4. Thus, part of the faecal NFE arises by an underestimation of the organic matter associated with faecal nitrogen.

Fructose, a keto-hexose (called as fruit sugar), is usually accompanied by sucrose in fruits and estimated by the methods of Ashwell (1957).

Materials

Resourcinol reagent: Dissolve 1g resorcinol and 0.25 g thiourea in 10 ml glacial acetic acid. This is stable in the dark.

Dilute HCl: Mix five part of conc. HCl with one part of distilled water.

Standard fructose solution: Dissolve 50mg of fructose in 50 ml water. Dilute 5 ml of this stock soln. to 50 ml for a working standard.

[Schoonover (1952) Method]

Introduction

Sodic (Alkali) and Saline-Sodic soils are characterized by the presence of large amounts of sodium, as high as 15% or more, on their exchange complex. As a result of this, the pH of soils increases beyond 8.0, causing nutritional imbalances, elimination of soil organic matter, deterioration of soil physical condition, etc., besides affecting the soil biotic community. Gypsum (CaSO₄. 2H₂O) is commonly used for the management of such soils, when applied in right amounts and size.

Principle

A given weight of soil is equilibrated with a known amount of Ca solution, and the amount of Ca, left in the solution is determined by EDTA titration. The difference between the amount of Ca added and the Ca left in the solution, gives the amount of Ca exchanged. In practice, gypsum of about 1/3 of the value, obtained by this method, is satisfactory in most cases.

Hydraulic conductivity is an important soil property that determines the ability of a soil to transmit water. A method of measuring hydraulic conductivity of saturated soil using undisturbed soil core is described in this exercise.

Principle

Flow of water across a soil layer or a sample of known dimension can be best described by Darcy’s law expressed as:

Infiltration rate refers to the volume of water entering into the soil per unit area in the unit time, when the soil is subjected to a shallow depth of ponding at the surface. Under continued ponding, the high infiltration rate in the beginning decreases to a constant value, known as final infiltration rate. The reduction in infiltration rate is due to combined effects of reduced hydraulic gradients, dispersion of aggregates, blocking of pores, cracks and channels, and swelling of colloids. Numerous techniques for measurement of infiltration rate have been developed to meet specific needs but use of double-ring infiltrometer has given consistent result in a variety of conditions.

Principle

In double-ring infiltrometer method, a small representative area in the field is bounded by two concentric metal rings (Figure 17.1) which permit impounding of water over the soil within the rings. The rate fall of surface of water ponded on the soil in the inner ring is taken as the rate of water intake or infiltration rate. In the cropped field, infiltration rate can be measured only within the rows and for which the diameter of the cylinders may be changed to meet the specific needs. The measurements under wetland conditions should be made from a distance of about 40-50 cm to avoid pressure effects.