eChapters

1.The fine earth covering land surface acts as a reservoir of nutrients and water Soil.
2.The word ‘Soil’ is derived from Latin.
3. Study of origin, classification, morphology of soil is known as Pedology.
4. The study of soils in relation to crop growth Edaphology.
5. The father of Soil Science Dokuchalev.

Important Points to Remember

• The active factor of soil formation is : Climate
• Black soils (Vertisols) are formed mainly from the weathering of: Basalts
• Which soils have the highest cation exchange capacity : Black soils
• Plants wilt when soil water content goes below: 15 bar
• Available phosphorus in fertilizer is the fraction: Water soluble + Citrate soluble P

INTRODUCTION

Soil-borne pathogens cause heavy losses to most agricultural crops. Repeated planting of a crop in the same piece of land results in a high inoculum build-up, which forces the farmers either to change the crop or the land. Thus, the search for new, effective, inexpensive and non-hazardous methods for the control of soil-borne diseases is a continuous one. Over the years, efforts have been made to manage the soil-borne pathogens by employing fumigants, chemical pesticides, biological control agents, different type of soil amendments and also by causing modifications in different cultural practices. But, pathogen control is often hampered by the fact that both the inoculum of the pathogens and the lethal agents applied to the soil are affected by the soil’s physical, chemical and biological environment. Keeping in view the bottlenecks with different methods of management of soil-borne pathogens; harnessing of solar energy i.e. soil solarization is an effective method to control soil-borne pathogens.

Abstract

Wilt of gladiolus caused by Fusarium oxysporum f.sp. gladioli is a serious disease in Himachal Pradesh and disease incidence ranged between 19.0 to 50.5 at different gladiolus growing areas of the state during 2002 and 2003. Soil solarization of the infected field by covering it with transparent  polyethylene mulch (25 µm) for 40 days in summer months (March-April) was found effective to control the pathogen in soil.  Soil solarization resulted in average maximum temperature of 39.9oC in 2002 and 41.4oC in 2003 with an increase of 11.9 and 9.8^ºC, respectively in comparison to unsolarized soil. Increase in the average maximum soil temperature was found lethal to the Fusarium wilt pathogen of gladiolus. Soil solarization for 40 days resulted in significant reduction (84.6 %) in the colony forming units of the pathogen at 5 cm soil depth in comparison to unsolarized control. Soil solarization also resulted in 63 per cent reduction in disease incidence, recorded increase in different growth parameter of crop and also resulted in early flowering of the spikes.

Vegetables have got an important place in agriculture development, human diet and economy of the country. All the developed and developing countries realized the importance of vegetables an essential diet due to medicinal and nutritional value for human health. There is a steady upward trend in vegetable production. China is ranking first in the world and currently produces 237 million tonne of vegetables. India has made a quantum jump in vegetable production securing the second position in the world. The total production of vegetable is more than 91 million tonne in the country. Diseases and pests are the most important factors for low vegetable production. Various fungi, bacteria, viruses, phytoplasmas, nematodes and weeds are responsible for causing diseases in vegetables resulting heavy reduction in yield and quality.

Soil structure is highly important for maintaining favourable conditions for water movement, aeration, root development and crop production. In irrigated agriculture, inappropriate management practices can cause structural degradation through compression, puddling, compaction and crust formation. This chapter examines the major processes responsible for deterioration of soil structure and their effects on soil physical properties and crop performance. Soil compaction is discussed in relation to agricultural machinery, pressure distribution, formation of compacted layers and restrictions to root growth and water movement. The chapter also explains soil crusting, its mechanisms, effects on seedling emergence and methods for evaluating crust strength. Slow-permeable soils, including Regur soils, highly permeable soils and soils with shallow water tables are considered from a management perspective. Appropriate management practices are emphasized to restore permeability, improve soil structure and maintain favourable soil-water relationships. The chapter provides an integrated understanding of structural degradation and its management for sustainable irrigated agricultur

Soil Structure Defined

Soil structure is defined as the arrangement of individual soil particles with respect to each other into a pattern. Structure describes the gross, over-all arrangement ofthe soil solids. In other words, soil structure is the ‘architecture’ of a soil.

Soils are composed of structural units, called “peds”. The peds consist of many individual particles, bound together by cementing agents like organic matter, clay and hydrous oxides of iron and aluminium. However, the strength of the bonds, the size and shape of the peds and the proportion of the soil particles involved in the peds differ considerably among soils.

Soil survey is essentially a systematic examination of morphological, a set of other variable soil characteristics, description, classification and mapping of soil in an area alongwith a report making an interpretation to predict their potentials for various uses particularly for crop production.

Activities of Soil Survey Soil survey is composed of the following activities –

1. Anticipation of soil variability - The initial activity of soil survey is obtained by classifying the surveyed data according to different land forms and existing land uses either through field traversing, or aerial photo or by satellite images of the concerned area.

2. Characterisation and classification – This is done on the basis of soil profile description supported with soil analytical data.

3. Soil mapping - This is performed by showing the distribution of types of soil or soil mapping units based on already classified soils with their landforms, and land uses or their combinations.

4. Interpretation - It is the process of making prediction about the potentials of soils for various uses like choice of farm practices – agriculture, horticulture, forestry, pastures etc. and their management practices.

In recent times, the interpretations cover a wide spectrum of soil uses, both for agricultural and non agricultural (sewage and human waste disposal, high way construction, water and gas supply, recreation, wild life, urban and industrial structures) and many specialized uses. Soil survey if correctly carried out according to scientific principles, can provide the data base for various interpretations. This is because the same soil properties determine the behaviour of a soil for a variety of different uses. For instance, the content of clay, silt and sand, the shrink and swell behaviour, the permeability of soil to water and air, content of calcium carbonate, salts, organic matter, gypsum, soil depth, depth of ground water, hard pan formation, co-efficient of linear extensibility, water holding capacity etc. are examples of such properties that are important to plant growth and these properties also strongly influence non farm uses. Some examples in support are

A hard or petrocalcic horizon or other slowly permeable layer (clay-pan) in a soil restricts the movement of air and water, thus adversely affecting the plant root growth. Such a layer limits the soils suitability for septic tanks and other onsite waste disposal. It also makes a poor sub grade for high way construction.

A soil high in soluble salts is a poor medium for plant growth; it is also corrosive to iron and steel structures, such as pipelines and fences, causing high maintenance and repair costs.

High organic matter content is generally favourable to plant growth, but it is a limitation for road construction.

The strongly gypsiferous soils (gypsum content >10%) are considered unsuitable for arable crop cultivation because of its dissolution under irrigated or even moderate rainfall and making the surfaces uneven through the developments of sink holes. Such soils are unsuitable for irrigation and drainage canal networks and also for construction of roads, bridges etc.

The shrink- swell soils of India (vertisols) because of summer monsoon rains are suitable for growing a “kharif” crop but are very dangerous for construction of roads, air strips, buildings, laying gas, water pipelines which get distorted, develop cracks and lead to sunken floors etc.

Soil survey is essentially a study and mapping of soils in their natural environment. It is the systematic examination, description, classification and mapping of soils of an area.

2.1. History of Soil Survey in India

The original investigations on Indian soils were carried out by Voelcker dates back to 1893 and by Leather to 1898.They classified the soils of the country into four major groups, namely the Indo-Gangetic alluvium, the black cotton soil or regur, red soil and laterite soil. Schokalskaya (1932) has published a soil map of India based on the Russian concept which describes 16 soil groups such as climate,vegetation, soil-forming materials, salinity, alkalinity, swamps and peats (Bhattacharyya et al. 2013). In 1935,Wadia and his co-workers collected a soil map of India with significance on geological formations and classified the soils as red, black (regur), laterite and lateritic soils of Peninsular India and also Indo-Gangetic Plains (IGP) which includes delta, desert, bhabar, terai and alkali soils. Vishwanath and Ukil (1943) published a soil map of India by placing the soils in different climatic zones for the first time. This was prepared by Imperial Agricultural Research Institute, New Delhi, and published in the year 1943. There were 17 kinds of soils identified, viz., deep black soils, black clay soils, black loamy soils, black sandy soils, red sandy soils, brown sandy soils, red and yellow soils, dark reddish brown soils, mixed soils (white and yellow), alluvium (Indus, Gangetic, Brahmaputra), coarse alluvium, soils of swamp lands, calcareous soils, usar soils, kallar soils, coastal alluvium soils and soils of Great Himalayan Ranges.

Soil survey works were started in 1954, in most of the states as a part of their agricultural development programme, and Bihar (Soil Survey and Land use Planning Scheme, Sabour) was pioneer. In 1954, the soil survey work was started under the leadership of Dr. P. P. Jha following the conventional procedures in Bihar (including Jharkhand) to delineate the soil associations based on geology, relief, physical and chemical characteristics of soils for the first time in India by the then Soil Survey Scheme at Sabour (Mishra et al. 2001; Mishra 2015, 2016). Meanwhile, the National Atlas Organization, Kolkata, prepared a soil map of India in 1957 classifying Indian soils into six major groups and 11 broad types. Murthy and Pandey (1983) applied the working principles of the USDA 7^th Approximation in classifying the Indian soils with available data on soil classes and thus used the US system for the first time at great soil group level, which was transformed into a soil map of India on 1:6.3 million scale. Mishra et al. (1994) attempted to propose “Fluvisols” as the 13th Order in USDA Soil Taxonomy for active floodplain soils frequently occurring in different parts of India and elsewhere. Mishra (2015, 2016) proposed a framework of Indian system of soil classification mainly based on land use options.

13.1. Soil survey and soil mapping

Refers to study and mapping of soils in the fields.

Process of classifying soil types and other soil properties in a given area and geo-encoding such information.

Draws information on geomorphology, theories of soil formation, physical geography, analysis of vegetation and land use patterns.

Primary data for the soil survey are acquired by field sampling and by remote sensing.

Remote sensing principally uses aerial photography (Illuminating the object/ target with pulsed laser light and measuring the reflected pulses with sensor), but LiDAR ( Light Detection and Ranging) and other digital techniques.

AERATION, SOIL: The exchange of air in soil with air from the atmosphere. The air in a well aerated soil is similar to that in the atmosphere; the air in a poorly aerated soil is considerably higher in carbon dioxide and lower in oxygen.

Introduction

Soil resource catalogue provides an insight into the capability and the constraint

of mapped area for its optimum exploitation towards developmental planning.

For this motive soil survey series as an essential tool. Soil survey is essentially

a study and mapping of soils in their natural environments and systematic

examination, description, classification and mapping of soil of area.Soil survey

contains a group of compound operation involving

•             To study important properties of soils and associated land features.

 •            Define taxonomic units through correlation and classifications of soils.

•             To establish and draw a border of different kinds of soils on standard

topographical base map through mapping of soils.

 •            Transfer of technology from research farm to farmer ‘s field under

different soil condition and management practices.

Soil classification, or soil taxonomy as it is called, is grouping of soils in an orderly and logical manner based on soil properties (differentiating characters) for the purpose of studying and identifying them. The following are the purpose of soil classification:

To organize our knowledge of soils

To bring out and understand the relationships among the soils

To remember the properties of soils

To learn new relationships and principles in different soil groups

Temperature is a fundamental property of usually used to characterize the thermal condition of a system. The growth of any biological system is optimal within certain ranges of temperature and inhibited or ceased beyond this boundary. In addition to plant growth, the significance of temperature on agriculture can be ascertained by its role on physical, chemical and biological processes occurring in soil. Therefore, to study these soil properties intensively measurement of soil temperature is essential.

10.1 Measurement of Soil Temperature

Temperature of any system cannot be directly measured. It can only be estimated by its influence on some properties (thermometric properties) which respond to the variation in the intensity of heat of that system. These thermometric properties include volume, pressure, length, electrical resistance, thermal emf of the matter. Instruments built to take the advantage of any of these thermometric properties of the matter are called thermometer.

15.1. Soil Temperature

Soil temperature affects plant growth directly; influences soil moisture, aeration, structure, microbial activity, decomposition of plant residues and availability of plant nutrients. Intermediate temperatures, near optimum for each crop, are the desirable temperatures for crop growth. Extreme temperatures are undesirable, lest crop growth would be retarded and weeds and germs may be favoured. Moderate daily variations are desirable as they lead to soil moisture distribution and aeration.

15.1.1. Factors Affecting Soil Temperature

The mean annual soil temperature is about 1°C higher than the mean annual air temperature. Soil temperature is influenced mainly by climatic conditions. The factors which affect the transfer of heat through atmosphere from the Sun also affect the soil temperature. The following are the factors that affect soil temperature:

Temperature is the measure of the thermal state of a body with respect to its ability to transfer heat. Soil derives its heat almost entirely directly from the sun and losses much of it back into the atmosphere. The major processes for heat transfer in soil are: Radiation, Convection, Conduction and Latent heat exchanges between soil and atmosphere. The most important source of which is the incident radiation supplying almost all the heat energy for the biosphere and also determines the thermal regime of soil. Soil temperature or thermal regimes of soil is an extremely important property of soil as it regulates plant growth directly and influences moisture and aeration status in soil, soil structures, microbial activities and decomposition of plant residues and the availability of plant nutrients . It is controlled mainly by its thermal properties and radiation exchange over the surface and their variations within the soil. The quantity of incident solar radiation and heating the soil depends on the several factors such as exposure and latitude, albedo, soil colour, slope vegetation and composition of soil.

Soil temperature is an important environmental parameter for plant growth and development. It has direct effects on microbial growth and development, organic matter decay, seed germination, root development, and water and nutrient absorption by roots. In general, the higher the temperature the faster these processes occur. Variation in soil temperature is much more pronounced because of varying characteristics and composition of soil.

The soil gains heat by absorption of solar radiation and longwave counter radiation from the atmosphere, downward transfer of sensible heat and horizontal transfer of heat from the surroundings. On the other hand, soil loses heat by longwave radiation to the atmosphere, upward transfer of sensible heat to air when the soil surface is hotter than air and with evaporation and horizontal transfer of heat from the column to surroundings.

The population of India is estimated to touch 1.4 billion by the year, 2025, which will need at least 300 million tonnes of food grain. This necessitates the production of additional food grain from the same land without loosing the production potential of the soil. This, in turn, requires extensive research to provide a scientific basis for enhancing and sustaining food production as well as soil productivity with minimum environmental degradation. In order to attain this it is essential that the amount of nutrients removed from the soil should be replenished through judicious use of fertilizers and manures. This needs a more comprehensive approach for fertilizer use, incorporating components like soil test, field research and economic evaluation ofthe results. Soil testing is one of the best scientific means for quick and reliable determination of soil fertility status. Soil test crop response study in the field provides soil test calibration between the level of soil nutrients as determined in the laboratory and the crop response to fertilizers as observed in the field for predicting the fertilizer requirements of the crop.

Objectives of soil testing.

Soil testing provides a sound information about the suitability, fertility and productivity of the soil. This enables the farmers to make the most profitable use of some of the costly inputs in farming. However, lack of information among the farmers about soil testing and their importance in management of resources necessitates that the work of soil testing should be taken extensively. Soil testing is a useful tool for making fertilizer recommendations for various crops and cropping sequences as well as reclamation of problem soils. Thus the major objective of soil testing are to identify the type of soil related problems like salinity, alkalinity, and acidity and to suggest appropriate reclamation/amelioration measures and to evaluate the fertility status in terms of available nutrients for making soil test based fertilizer recommendations.

Maximum potato yield occurs when sufficient P is available during early vegetative development and the entire period of tuber growth. Total plant P uptake increases rapidly during tuber initiation, levels off to a constant rate during tuber bulking, and ceases with plant maturation occurs primarily through the transfer of P reserves from the vine and roots. Phosphorus uptake by potatoes is relatively low compared with uptake of potassium or nitrogen but similar to uptake of sulfur. The amount of P in the soil solution that is readily available for plant uptake is very small compared with the total amount of P in the soil.

A general blanket application of fertilizer leads to its poor efficacy and wastage of costly resources as well as of environmental pollution. This becomes more relevant in case of P as unlike nitrogen applied P remains in soil and adds to its build up. In addition, this has resulted in severe imbalance of nutrients in soil (Kumar et al., 2009).

Keeping this in view, a multilocation experiment was conducted in the major potato growing states of India under the All India Coordinated Research Project on Potato to evaluate suitable dose of P based on soil test on P economy in potato (table 52). Exact quantification of phosphorus fertilizer based on soil test is very important.

Introduction

In order to cater to the nutritional needs of a rapidly growing population, it is imperative to increase food grain production on the same land while maintaining the soil’s productive capacity. This necessitates comprehensive research to establish a scientific foundation for enhancing and sustaining food production and soil productivity with minimal environmental impact (Rathore et al., 2010). Balanced nutrition extends beyond the application of nitrogen, phosphorous, and potassium in specific quantities through fertilizers. It entails ensuring that the soil contains the right proportions of available nutrients to meet the crop’s requirements for optimal yield (Rathore et al., 2010).

Scientific agriculture is the only solution for increasing productivity of various crops and the input resources most effectively. Fertilizer, the most efficient and often the most expensive input can be applied to crops on the basis of generalized state level fertilizer recommendations. However, state level fertilizer recommendations do not take into consideration fertility status of the field which is neither uniform nor constant and which varies from field to field. Sometimes more fertilizers are added leading to unnecessarily higher investment, while under another situation, inadequate quantities of fertilizers may be added, resulting in lower returns. Inefficient and imbalanced uses of fertilizers affect both soil health and agricultural productivity.

Therefore, the best and most effective method for fertilizer recommendation is soil testing. It is a mode of assessing the nutrient supplying capacity of a soil.

Sustainable agriculture warrants a wise management of natural resources and inputs to satisfy human needs in the fast changing scenario while maintaining, if not improving, the quality of environment. Soil as a natural resource is facing more and more serious degradation threats under modern agriculture. Incidence and expansion of multi-nutrient deficiencies in Indian soils owing to inadequate and unbalanced nutrient input through fertilizers is considered one of the major reasons for decline in factor productivity of crops. The problem of soil fertility depletion is spectacular across the soil types and agro-climatic zones, but it is more acute in intensively cropped areas, where annual nutrient removal by the crops often far exceeds replenishments. Recent diagnostic surveys indicate that in several high productivity areas of irrigated ecosystems like, Trans-and Upper Gangetic Plain zones, farmers are resorting to even excessive use of fertilizers, especially N, to maintain the yields at levels attained previously with lower fertilizer application rates. With an unabated deterioration in soil health in general, and soil fertility in particular, and a mounting pressure on finite land resources due to increase in population, the interest in soil fertility and soil health has revived due to several reasons:

Stagnation in growth rates of production and productivity of staple foodgrains - threat to food security

Decline in factor productivity, thus increasing cost of production

Nutrient withdrawals in excess of replenishment

Low nutritional value of food and feed grown on nutrient-starved soils - threat to nutritional security

Poor quality of produce fetching low price - threat to economic security

Introduction

It is well-known that soil testing is agronomically sound, beneficial and environmentally responsive tool for monitoring the nutrient as well as pollutant status of soils, and also for making precise fertilizer recommendations for various crops and cropping sequences. Soil testing with associated plant and water analysis is the only tool known which helps to control soil fertility. Nutrient supplying power of soils, crop responses to added nutrients and fertilizer and amendment needs can safely be assessed through sound soil testing programme. Monitoring of soil fertility, against depletion and accumulation of certain elements in toxic proportions over time, is also possible through appropriate soil tests. This also helps to economize on cost of fertilizers and also in increasing fertilizer use efficiency.

Soil texture refers to the relative distribution of sand, silt and clay on a sample of <2 mm size. It is an intrinsic soil property and basically refers to the particle size distribution in a soil. A number of physical characteristics and chemical properties of a soil are influenced by texture or particle size distribution. To estimate the content of sand, silt and clay particles, the soil samples are first brought into a dispersed state by mechanical and chemical treatments so that different binding agents are removed. In the dispersed soil samples, the soil particles settle down at a differential settling rate according to their size. In laboratory, the common methods for analysis for particle size distribution are : Buyoucos hydrometer method and International pipette method. In this chapter, the procedure of Buyoucos hydrometer method is described.

Principle

This method is based on the principle of variable rate of settling of particles as per their size and as described by Stokes’Law. Large particles shall settle fast. The measurement of density of the suspension is done at different times using a hydrometer (ASTM 152H-Type hydrometer is preferred). The measurement in this hydrometer is based on a standard temperature of 20 _oC and a particle density of 2.65 Mg m_-3 and the units are expressed in grams of soil per liter.The principal source of error in this procedure is the incomplete dispersion of soil clays as the clay particles are cemented by agents such as organic matter, CaCO and iron oxides. Incomplete dispersion results in low values for clay and high values for silt and sand. Thus, soils with higher organic matter (>1.0%) should be first treated with 6% hydrogen peroxide (H₂O₂) for removal of organic carbon. The rate of sedimentation is also affected by temperature and the density of the dispersing solution.

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.

2.1. Particle Size Distribution Analysis

Soil is composed of particles of varying size and shape. The expression of the proportion of the different size 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.

Physical properties of a soil greatly influence plant growth. The plant support, root penetration, drainage, aeration, retention of moisture and availability of plant nutrients are all linked with the physical condition ofthe soil. The physical properties of a soil which depend on the amount, size, shape, arrangement and mineral composition of its particles, also influence its chemical and biological behaviour.

Q. 1 If the forward speed of a tractor drawn seed drill is increased twice,
then the seed rate delivered will be
(A) Reduced to half            (B) Double
(C) Increased by four time (D) Remains the same

In modern times, soil tillage has emerged as an integral part of a crop system. Soil tillage or soil surface management has been found important in alleviating soil related constraints encountered in crop production. An important effect of soil tillage on crop productivity is through its influence on soil processes, soil Soil Tillage 39 properties and crop growth. At the same time, soil tillage has its impact on the environment e.g. soil degradation, water quality, emission of green house gases from soil related processes etc.

The plants draw water from the soil for growth and development. The soil acts a reservoir for soil moisture (Fig.5.1). The basic aim of a soil water balance model is to quantify the manner in which the water supplied to the soil either through precipitation and irrigation is disposed off. In the process, the soil water balance models were found to be extremely useful to determine the amount of water utilized by the crop for evapotranspiration.
The concept of water balance was originally developed by Thornthwaite, an American geographer and it formed the basis for development of more scientifi c advances due to its wide range of applicability including
• Choice of crops/ cropping systems based on water availability
• Irrigation scheduling
• Optimisation of limited water resources for higher productivity
• Characterization of droughts and agricultural droughts
• Assessment of crop yield and pre harvest forecasting of crop yields
• Designing irrigation projects
• Development of water storage structures
There are quite a large number of water balance models available in literature nowadays. Several of these models may be applicable for regions where there are developed. There were considerable efforts to develop water balance models can be used by the crop on daily basis in case of different crops as well. The choice of a water balance model to a large extent depends on the availability of data required for running the model. It may not be possible to cover all models available in

5.1 Kinds of Soil Water

The following re the three main classes of soil water:

(i)  Hygroscopic water. Water held tightly to the surface of soil particles by adsorption forces.

(ii) Capillary water. Water held by forces of surface tension and continuous films around soil particles and in the capillary spaces.

(iii) Gravitational water. Water that moves freely in response to gravity and drains out of the soil.

Water can move in the liquid and gaseous phases:

1. Liquid water

i) Saturated flow: Most pores are filled with water; water in this condition is tension free

ii) Unsaturated flow: Pores are partially filled with air; the water is under tension.

2. Water vapour

i) Diffusion: Water vapour moves by diffusion as a result of vapour pressure differences (partial pressure)

ii) Mass flow: Water vapour flows in a mass with other gases of the system in response to differences in total pressure.

The movement of water through soil is fundamental to irrigation efficiency, drainage, nutrient transport and plant water availability. This chapter examines the principles governing water movement in both saturated and unsaturated soil conditions. It introduces the movement of water through the soil profile and discusses saturated hydraulic conductivity as an important parameter describing the ability of soil to transmit water. Water flow under unsaturated conditions is considered in greater detail, including the relationship between soil-water content and hydraulic conductivity. The chapter presents the equation for unsaturated flow and describes experimental approaches for studying water movement. Unsaturated hydraulic conductivity, represented as K(θ), provides an important basis for understanding the changing ability of soil to transmit water as soil moisture conditions vary. The chapter also considers prediction of soil-water flux, linking theoretical concepts with practical irrigation and soil-water management. Understanding water movement helps in determining irrigation requirements, reducing water losses, improving drainage and maintaining favourable soil-water conditions for crop growth.

Plant Relationship with Soil in Climate Change

1. Gravimetric Moisture

Significance of Gravimetric Analysis

Gravimetric moisture analysis, being the foundation of soil water assessment, allows for a meticulous examination of the water content in the soil. The process involves obtaining a representative soil sample, subjecting it to controlled drying conditions, and determining the weight loss after moisture removal. This method not only quantifies the total water content but also helps in understanding the soil’s water-holding capacity and drainage characteristics. Gravimetric analysis is indispensable in precision agriculture, aiding farmers in optimizing irrigation schedules and preventing overwatering or underhydration.

5.1 Soil

Soil and water are the two most important natural resources required for crop production. Without soil, no crop can be produced even if there is availability of plenty of water. It is vital not only for agriculture but also very vital for sustenance of life. No building can stand on any place without soil. Soil gives foundation support for any building. The term ‘soil ’is defined in various ways depending on the general professional field in which it is used. However to an agriculturist, soil is the substance existing on the earth surface, which grows and develops plant life. It contains all vital elements including its inherent fertility contents that support the growth of plants. For an engineer, soil is the unaggregated deposits of mineral and organic particles covering major part on the earth crust. It includes widely different materials like boulders, sand, gravel, clays and silts. Soil is produced by the weathering of solid rocks. The formation of soil is due to geologic cycle continuously taking place on surface of the earth. The geologic cycle comprises weathering or denudation, transportation, deposition and upheaval, again followed by the above mentioned processes. Weathering may be natural or artificial. In natural weathering, physical processes like temperature changes, flow of water, ice, wind and rain play the role. In artificial weathering animals especially human beings interference causes soil erosion and formation. It is obvious that it takes hundreds of years to form one inch of soil.

The phenomena related to the retention and movement of water in soils, its uptake and translocation in plants and its loss to the atmosphere are all energy related. The more strongly water is held in the soil, the greater is its energy. It means that if water is to be removed from a moist soil, work has to be done against the adsorptive forces. The water movement is always from a zone where the free energy of water is high (standing water table) to one where the free energy is low (a dry soil). This is called soil water energy concept.

17.1. Soil Water Potential

The free energy of soil solids for water is influenced by:

i) Matric force: the attraction of the soil solids for water (adsorption) which markedly reduces the free energy (movement) of the adsorbed water molecules.

Water is the elixir of life. It is required for the evapo-transpiration of growing plants. Water acts as a solvent and, together with dissolved nutrients, makes up soil solution from which plant roots derive nutrients. Soil water content controls soil air and soil temperature.

16.1. Forces of Water Retention

The forces responsible for water retention in soils are adhesion and cohesion. Adhesion refers to the attraction of solid surfaces for water. Cohesion refers to the attraction of water molecules for each other.

The force with which the soil particles retain water is defined in terms of pF scale (Schofield, 1935). pF is defined as “the logarithm to the base 10 of the numerical value of the negative pressure of soil moisture expressed in centimetres of water.”

Water is absolute necessary constituents for the survival and growth of all the living substances on earth. It is the most essential ingredients for many of the physiological and metabolic process in plants, like photosynthesis to form sugars, translocation of cell constituents and maintenance of cell turgidity. Soil, being an adsorbent of water received from precipitation or rainfall acts as reservoir to meet requirement by plant during growing season. Water retained in the soil serves as solvent to dissolve salts and nutrients and as a carrier to translocate them for absorption by plants. It plays significant role in weathering reaction, soil forming processes and profile development. Water is also important for growth and activities of microorganisms influencing decomposition of organic matter, transformation of mineral nutrients and other physical, chemical and biological properties in soil. This chapter deals with the retention and movement of water in soils to obtain better understanding of soil-water-plant-atmosphere relationships.

The soil consists of many solid particles of different sizes and is capable of absorbing and retaining water in the soil within certain limits when water is received through either from precipitation or by irrigation. The water that is held in the soil is called soil water (Fig.4.1). It can exist also in the form of water vapour as well. The crop production depends upon the soil water. All the water that is present in the soil may not be available for plants.
The water availability to the plants from the soil depends upon some physical properties of the soil as well as on the physical processes that govern the existence of water in the soil. Therefore, it is necessary to understand about the relationships that govern the water availability in the soil as explained in the following text-
4.1. Energy Concept of Soil Water
Soil water energy concept is all about potential energy, gravitational potential, osmatic potential, pressure potential energies.
4.1.1. Soil Water Energy: The total energy state of soil water is defined by its
equivalent potential energy as determined by various forces acting on the water per unit quantity. Different energies are involved including kinetic and potential energy.

The soil is a heterogeneous, polyphasic viz., solid, liquid and gaseous, particulate, disperse and porous system (Fig. 3.1). The solid phase constitutes the soil matrix, the liquid phase consists of soil water, which always contains dissolved substances so that it should properly be called as soil solution and the gaseous phase is the soil atmosphere.

Increasing susceptibility of vegetables to various biotic and abiotic stresses and very high cost of hybrid seeds has warranted the attention of the vegetable growers to improve the nursery raising technology of vegetables. Now-a-days protected nursery raising of vegetables has become a full flagged industry in several developed countries like Israel, Japan, Spain, Netherlands, USA etc. In countries like Israel no vegetable grower is growing his own nursery, but they are getting the required kind of seedlings from an established nursery owner on pre- order basis. Similar system of nursery raising is also prevalent in several other advance countries. In those situations where vegetables are being grown under protected conditions it becomes pre-requisite to raise the required vegetable seedlings only under protected environment to get virus free healthy seedlings.

Raising nursery from seeds provide an easy and convenient way to nourish tender and young seedlings in a well managed, small and compact area for better germination of small and costly seed. In general, vegetables crops are divided into three groups according to their relative ease for transplanting. Beet root, broccoli, brussels sprouts, cabbage, cauliflower, tomato and lettuce are efficient in water absorption and rapidly form new roots after transplanting. Vegetables crops that are moderately easy for transplanting are brinjal, onion, sweet pepper, chilli and celery which do not absorb water as efficiently as crops that are easy to transplant, but they form new roots relatively quickly. The vegetable crops which are difficult to transplant are: all cucurbits and sweet corn which require special care during nursery raising and transplanting. Seedlings not only reduce the amount of time of the crop but it also increases the uniformity of the crop and harvesting as compared to direct sowing of the crops. Transplanting of seedlings also eliminates the need for thinning and provides very good opportunities for virus free, vigorous and even off-season seedlings if grown under protected conditions in soil-less media. So it becomes necessary to know the protected structures which can be efficiently used for successful raising of vegetable seedlings, suitable types of containers and growing media, method of seeding in containers in soil-less media, growing conditions and water and fertilizer requirement of seedlings along with hardening and transplanting to the field. Protected nursery raising technology is highly suitable and can be established as a small scale industry in major vegetable growing areas of our country by progressive farmers especially in peri-urban areas. By this way the vegetable growers will get virus-free healthy and off season nursery as per their requirement and it generate extra employment in rural areas.

Cation exchange: The ‘soil cations’ essential for plant growth include ammonium, calcium, magnesium, and potassium. There are three additional ‘soil cations,’ which are not essential plant elements but affect soil pH. The additional ‘soil cations’ include sodium, aluminum and hydrogen.

The major distinguishing characteristic of cations is their positive charge. Just like a magnet, a positive charge is strongly attracted to a negative charge. When soil particles have a negative charge, the particles attract and retain cations. These soils are said the have a cation exchange capacity. Although most soils are negatively charged and attract cations.

The ‘soil cations’ are further divided into two categories. Ammonium, calcium, magnesium, potassium, and sodium are known as the ‘base cations,’ while aluminum and hydrogen are known ‘acid cations.’ Unlike the other base cations, sodium is not an essential element for all plants. Soils that contain high levels of sodium can develop salinity and sodicity problems.

The words ‘base’ and ‘acid’ refer to the particular cation’s influence on soil pH. As you might suspect, a soil with a lot of acid cations held by soil particles will have a low pH. In contrast, a highly alkaline soil predominately consists of base cations.

Cations in the soil compete with one another for a spot on the cation exchange capacity (Table 42 and Fig 18). However, some cations are attracted and held more strongly than other cations. In decreasing holding strength, the order with which cations are held by the soil particles follows: aluminum, hydrogen, calcium, potassium and nitrate, and sodium.

The soil–plant relationship is central to crop productivity because soil conditions directly influence root development, water uptake, nutrient availability and plant growth. This chapter focuses particularly on the problems associated with salt-affected soils, including saline, sodic and acid soils. It explains the formation, distribution and characteristics of saline soils and describes the production constraints created by salinity stress. The effects of salinity on plant growth, evaluation of saline soils, reclamation and leaching are discussed together with leaching requirements and crop salt tolerance. Water and nutrient management strategies for saline soils, including the use of biofertilizers, are considered. Sodic soils are examined through their formation, characteristics, exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR), followed by reclamation practices and amendment use, particularly gypsum. The chapter also addresses acid soils, their formation, chemical characteristics, nutrient availability, plant-growth constraints and amelioration through liming. Calcareous soils and their management are also included, providing a comprehensive treatment of problematic soils affecting soil–plant interactions

The soil-plant-water relationship is a critical aspect of agricultural science, encompassing the interactions between soil properties, plant health, and water dynamics. This article examines the intricate connections that influence plant growth and crop productivity, highlighting the roles of soil texture, structure, and organic matter in water retention and availability. It explores how plants uptake water through root systems and how transpiration affects water distribution within the soil. The study also addresses the impact of irrigation practices and soil management techniques on optimizing water use efficiency in agricultural systems. Understanding these relationships is essential for developing sustainable farming practices that enhance crop yield while conserving water resources.

Water is the most abundant compound on the earth but its sufficient availability is always a big constraint in crop production, particularly in arid and semi-arid areas since agriculture is the last priority for good quality water due to severe competition with public health and industrial demand, hence, the judicious and efficient use of water for irrigation in agriculture needs through knowledge of soil-plant-water relationship. The integrated approach for water management in rain fed areas or irrigated agriculture in soil-plant-atmosphere system helps in the selection of suitable crops and varieties and also helps in improving the crop yield and water use efficiency in relation to water supplying capacity of soil profile depending on its texture and rhizosphere depth. Similarly, atmospheric demand of evapotranspiration by various weather parameters via temperature, relative humidity, radiation, rainfall and wind speed is highly variable during the crop season depending on geographical location and is highly area specific. In irrigated area, the saving of irrigation water through improved management practices will further help in extending the irrigated areas with same amount of water, which will further boost agricultural production and sustainability.

Most of the earth’s total water is contained in oceans (96%), a small portion (2%) as snow and ice and the rest (2%) in the water bodies of the continents. Oceans, lakes, rivers and other water bodies of the earth are called hydrosphere. Continuous circulation of water between hydrosphere, atmosphere and lithosphere is known as hydrological cycle (Figure 12.1). Schematic diagram illustrating the earth’s water cycle– the hydrological cycle.

The soil–plant–water relationship integrates the major concepts of soil-water availability, root water uptake and plant transpiration into a unified system. Water movement through the soil and plant is governed by differences in water potential and by resistance within the water-conducting pathway. This chapter examines water uptake by roots and the process of transpiration, emphasizing the continuous movement of water from soil through the plant and ultimately to the atmosphere. Variations in water potential and water flux within the soil–plant system provide the basis for understanding how water is transported under different environmental and soil conditions. The resistance of the water-conducting system is considered as an important factor controlling water movement. The chapter separately discusses water movement through soil and within plants before connecting these processes with water movement from the leaf surface to the atmosphere. Control of transpiration is also examined, linking plant water relations with environmental conditions and crop water use. The chapter provides an integrated framework for understanding soil–plant–water interactions essential for efficient irrigation, crop productivity and sustainable management of water resources.

The plants collect water by its root system available in the soil medium. A soil rich in nutrients cannot ensure success of crops unless the presence of satisfactory state of water and air, mechanical attributes and thermal regime. The physical properties of soil and plants greatly influence the movement, retention and use of water. The soil should provide sufficient pore spaces and size distribution and decomposition of rocks and for the movement and retention of water for plant needs. Rainwater, irrigation, groundwater, seepage, etc. , contribute in replenishing the water in dried up soils. In all the cases thorough understanding of behavior of water is required to ensure the need of water to plants and optimize the use of irrigation water.