This book aims to provide the soil testing laboratory with sustainable technical literature on various aspects of soil testing, including testing methods and formulations of fertilizer recommendations etc, this book has been planned and it provides elaborated information on major soil types of India, their composition, plant nutrient and their function, typical deficiency symptoms of nutrients in plants, apart from procedure of sample collection and methods of analysis.
This book contains analytical concepts on nutrients covering principles, materials, equipment’s, methods, calculations and interpretations, with clear and easily understandable words/ sentences which provide better clarity of the analytical methods used.
This book will be a useful tool for soil testing in research laboratories for advancing research and preparing Soil Health Card for the farmers.
In Odisha most of the area (41.16%) is under cultivable land. Most of the people are dependant on farming. They use huge amount of fertilizers without applying balanced fertilizers. They do not test soils and apply unbalanced fertilizers which leads to less growth of crops and yields. Despite our best and diverse efforts for sustainable crop production, the imbalance use of major nutrients (N, P, K, Ca, Mg & S) and micronutrients (Fe, Mn, Cu, Zn & B) decreases the production of the crop.
Soil testing identifies various constraints in soil that limit crop production. Fertilizer recommendation and soil management practices to be adopted are based on the soil test report. Soil testing starts with collection of soil samples from the field and ends with interpretation of soil test results leading to necessary recommendations for increasing crop production.
Aim of the Experiment: The composite soil samples, collected, are air-dried and processed before analysis in the laboratory.
Soil texture is the relative proportion of sand, silt and clay in soil by weight. As per the classification of the inorganic soil particle by the International Society of Soil Science, diameters of the sand, silt and clay particles vary from 2 to 0.02 mm, 0.02 to 0.002 mm and less than 0.002 mm, respectively. There are 3 broad textural groups i.e sand, loam and clay and each broad textural group is subdivided into different textural classes depending upon the proportion of sand, silt and clay.
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.
Primary particles tend to adhere under natural condition so as to form secondary unit called aggregates. It is very difficult to determine the diameter of the individual aggregated particle. So the mean weight diameter is calculated as a single value constant, which indicate the wetted average value for a group of aggregates.
The soil water plays an important role in the physical, chemical and biological activities taken place in the soil which directly or indirectly affects the crop growth. The water content of the soil can be measured by different methods. These methods are gravimetric method, neutron scattering method and electrical resistance method.
Field capacity may be defined as the amount of water held in soil after excess water has drained away and the rate of downward movement of water was materially decreased which usually taken place within two to three days after heavy rain or irrigation. In this condition water was moved out of the macropores and air has moved into take its place.
Infiltration is the entry of a fluid from one medium into another. Soil water plays an important role in nature. The entry of rain or irrigation water into soil is called infiltration. Infiltration rate is defined as the amount of water entering into a soil per unit area per unit time under one atmospheric pressure. The infiltration rate depends upon initial moisture content of soil, condition of soil surface and permeability of various layers.
The maximum water holding capacity is the amount of water, expressed as percentage on oven dry basis held by a soil when it is completely saturated with water. At this moisture content, all the pore spaces are completely filled with water.
Determination of soil texture mainly depends on the complete dispersion of soil aggregates into their individual primary particles without triturating the particles themselves, accurate fractionation of the sample into various separates, sedimentation of different particles in the viscous medium as well as measurement of individual particle by the hydrometer.
Atomic weight of an element is defined as the relative average weight of its atom as compared to the weight of an atom of C12 (stable isotope) taken as 12 on the a.m.u. (atomic mass unit) scale.
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.
In the detection of soil organic carbon a known weight of soil is heated with an excess volume of standard K2 Cr2 O7 in the presence of Con. H2 SO4 . The soil is slowly digested at the low temperature by the heat of dilution of H2 SO4 and the organic carbon in the soil is thus oxidized to CO2 . The highest temperature attained by the heat of dilution reaction produced with the addition of Con. H2 SO4 is approximately 12o C which is sufficient to oxidize the active forms of the soil organic carbon but not the more inert forms of carbon that may be present.
The lime requirement (LR) of an acid soil is the amount of lime needed to neutralize the acidity from an initial condition to some target soil pH, like 7.0. Different methods are used to calculate a LR for specific soils. Lime requirement tests will always recommend adding enough lime to neutralize all the acidity associated with soil pH, much of the salt-replaceable acidity, and some of the residual acidity.
The statement is still valid as long as it is understood that in an aqueous solution the substances involved are subject to dissociation, which changes the ionization state of the substances.
The Kjeldahl method is mainly divided into three main steps. This method needs to be carried out in proper sequence.
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.
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 .
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.
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.
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++.
Procedure • Take 1 g soil in a 50 ml beaker • Add 25 ml 1M KCL solution
Take 1 g phenolpathalin powder in a 100 ml volumetric flask. Then add volume up to 100 ml by ethanol (Ethyl alcohol).
Digestion Mixure : This is a mixture of two salt. That is potassium sulfate and cupper sulfate with 9:1 ratio (90 g Potassium sulfate + 10 g Copper sulphate).
100 ppm ‘P’ : By dissolving oven dry KH2 PO4 salt. Take 0.4393 gm of KH2 PO4 and volume to 1 ltr that gives 100 ppm ‘P’.
Take 5 ml/2.5 ml aliquot in a 25 ml volumetric flask.
6.25 HNO3 (for 2 ltr) : Take 181 ml of conc HNO3 and diluted to 2 ltr in a volumetric flask.
Aim : To determine the Calcium in plant sample.
Aim : To determine the Magnesium in plant sample.
