eChapters

Ecology of a place is influenced by a number of biotic and abiotic factors. An agroecological zone is broadly homogeneous in climatic and edaphic factors, but not necessarily contiguous, where a specific crop exhibits roughly the same biological expression. On the other hand, the characteristics of an agroecological zone influence the crops and cropping patterns of the zone. Thus, there are considerable variations in the types and management practices of agroforestry systems being followed in different agroecological zones.

AGROFORESTRY FOR HUMID AND SUBHUMID TROPICS

Humid and subhumid tropical regions have much variation in biological, social and economic parameters. The characteristics of humid tropics include high mean annual rainfall of more than 1500 mm, dry season of less than four months in a year and mean annual temperature of more than 22° C. Rainfall usually exceeds the evapotranspiration. However, demographic pressure has caused excessive deforestation and overgrazing which developed soil related problems like low soil fertility, low organic matter, high acidity and high rainfall erosivity. The agroforestry practices designed for this region should aim for improved fallows, soil fertility improvement and conservation, food production, etc. Thus, the common agroforestry systems in this zone are taungya, homegardens, alley cropping, plantation-crop combination, windbreaks, silvipastoral systems and various intercropping systems. Shifting cultivation is a common practice in tropics which should be discouraged as it causes environmental degradation and ecological imbalance, soil erosion and soil nutrient loss.

A watershed is a geohydrological unit or all the land and water area bounded by a divide which contributes runoff to a common point. Watershed is considered to be synonymous with ‘catchment basin’ and ‘drainage basin’. In watershed management approach, development is not only confined to agricultural lands but also covers the area, starting from the highest point of the land to the outlet of the natural stream. Watershed management becomes increasingly important as a way to improve livelihood of people while conserving and regenerating their natural resources.

Watershed management is the process of creating and implementing plans, programmes and projects to sustain and enhance watershed functions that affect the plant, animal and human communities within a watershed boundary. It implies the judicious use of all the resources, i.e., land, water and vegetation in an area to prevent soil erosion, improve water availability and increase food, fodder, fuel and timber on sustained basis.

India shares 17.4% of the world population, while its land is only 2.4% of the total geographical area of the world. Naturally, the pressure on the land is often beyond its carrying capacity. Therefore, the productive lands, especially the farmlands in India are in the constant process of various degrees of degradation and are fast turning into wastelands. At present, approximately 55.76 million hectare area of the land is lying as wastelands in India. Out of these lands, about 50% lands are such non-forest lands, which can be made fertile again if treated properly. In the last 60 years India’s lush green village forests and woodlots have been deforested to the maximum. To restore this ecological imbalance by developing the degraded non-forest wastelands, Government of India had created the Department of Wasteland Development during July, 1992 under the Ministry of Rural Development, which has been subsequently reorganized and renamed Department of Land Resources, with a broader mandate.

National Wasteland Development Board was established in 1985 mainly to tackle the problem of degradation of lands, restoration of ecology and to meet the growing demands of fuelwood and fodder at the national level. The Board was reconstituted in August, 1992 and was made responsible for development of wastelands mainly in non-forest areas in totality by involving local people at every stage of development. It aims at creating a scenario where the Government acts as a facilitator and the people at the grass root level become the real executioner of the programme. The degradation of environment in the fragile Indian subtropical ecosystem is basically attributed to the following factors.

Human societies over the ages have depleted natural resources in different ways and degraded their local environments. Indiscriminate cutting down of trees and accelerating the construction works lead to global warming and climate change. Climate scientists believe that human-induced deforestation is responsible for 18-25% of climate change. Accumulation of greenhouse gases in the lower atmosphere is the main cause of global climate change. The concentration of these gases in the earth’s atmosphere is increasing, mainly due to deforestation and the combustion of fossil fuels which release carbon dioxide.

The earth receives heat energy constantly from the sun through radiation. Some of the heat is absorbed and some is reflected. Carbon dioxide works like an invisible blanket that wraps around the earth and traps the heat inside, similar to the function of a greenhouse. A greenhouse is a structure that is used in colder climates to grow plants. Even when outside temperatures drop below freezing point, greenhouses are still warm enough inside to grow plants. Greenhouses are made of glass, which allows solar radiation to enter. The heat is trapped inside the greenhouse, allowing plants to grow all the year round. Increasing concentrations of carbon dioxide in the earth’s atmosphere insulate it like a greenhouse, leading to a gradual warming of the earth’s atmosphere. Carbon dioxide is the major greenhouse gas, but there are others as well, including methane and nitrous oxide.

Mitigation means addressing the causes of climate change, while adaptation attempts to tackle its effects. The Intergovernmental Panel on Climate Change defines mitigation as an anthropogenic intervention to reduce the sources or enhance the sinks of greenhouse gases and adaptation as the adjustment in natural or human systems to a new or changing environment (IPCC, 2007).

Greenhouse gas emission is likely to rise by 25-90% by 2030 relative to 2000 and the earth could warm by 3° C at the end of this century. Even with a temperature rise of 1-2.5° C, the Intergovernmental Panel on Climate Change predict serious disastrous effects, including reduction in crop yields in tropical and subtropical areas leading to increased risk of food shortage, spread of climate responsive diseases such as malaria, and an increased risk of extinction of 20-30% of all biodiversity present on earth (IPCC, 2007). Carbon dioxide is the most important among all greenhouse gases. Carbon sequestration may be defined as the process of removing C from the atmosphere and depositing it in a reservoir. It entails the transfer of atmospheric carbon dioxide, and its secure storage in long-lived pools (UNFCCC, 2007).

From the agroforestry point of view, carbon sequestration involves primarily the uptake of atmospheric CO₂ during photosynthesis and transfer of fixed carbon into vegetation and soil pools for ‘secure’ storage. It occurs in two major segments of agroforestry systems; aboveground and belowground. The total amount sequestered in each part differs greatly depending on a number of factors including the region, the type of system, site quality, and previous land-use (Nair, 2012). On average, the soil and aboveground parts are estimated to hold major portions, roughly 60 and 30%, respectively, of the total carbon stored in tree-based land-use systems (Lal, 2010). Sequestering CO₂ from atmosphere through natural techniques such as afforestation, reforestation, natural regeneration of forests and the adaptive agriculture is more economically and ecologically sound in increasing the carbon storage capacity of the terrestrial ecosystems (Dhyani, 2014). Although carbon sequestration through afforestation and reforestation of degraded natural forests has long been considered useful in climate change mitigation, agroforestry offers some distinct advantages (Murthy et al., 2013). The carbon in the aboveground and belowground biomass in an agroforestry system is generally much higher than the equivalent land use without trees. An agroforestry system has higher carbon sequestration potential than pastures or field crops (Kirby and Potvin, 2007).

In agroforestry systems the various components like tree, crop and pasture exist in different proportions and orientations. It is difficult to find out which agroforestry system is the best suited for a given land situation. Similarly, it is to be decided which technologies are required for refinement and improvement of the existing agroforestry practices. But without sufficient knowledge of the existing system in a particular land situation, it is very difficult to set the research priorities for modification and development of this system.

Diagnosis and Design (D & D) is a systematic and objective methodology developed by International Centre for Research in Agroforestry (ICRAF) to initiate, monitor and evaluate agroforestry programmes. D & D is based on the philosophy that knowledge of the existing situation (diagnosis) is essential to plan and evaluate (design) meaningful and effective programmes in agroforestry research for development. The methodology plays a strategic role in all the phases of the agroforestry research process. D & D in agroforestry is unique and it has been specially developed for the following purposes.

Agroforestry systems are more complex than the agricultural systems. The long-term nature of trials involving woody species and the varying objectives of agroforestry trials demand that adequate caution be exercised in their design. Several characteristics of the trees like slow growth, long-term effects on their surroundings, long life, age of trees, the area over which the influence of trees extend, etc. complicate the issue of designing experiments for these systems. Agroforestry experiments are often established on marginal sites which include sloping lands, and sites with infertile and degraded soils. It is thus difficult to find homogeneous sites of such problem areas, especially sloping lands where plots along contour lines are long and linear. Germplasm of many agroforestry tree species are usually collected from different origins which lack uniformity. Therefore, experimental materials in an agroforestry experiment may not be of uniform quality.

There are several features of agroforestry systems that require some modification of the methods usually used in agricultural experiments. Important issues related to agroforestry experiments include

Economic analysis provides a rational basis for making decisions in allocating scare resources among various options to achieve competing goals. If resources were not limiting, there would be no need for economic consideration. Some important basic principles of economic analysis are outlined below.

PRINCIPLES OF ECONOMIC ANALYSIS

Optimization criteria

The additional return obtained from using one additional unit of an input should be considered to optimize net income from several possible production options. If option ‘x’ gives a higher return to land than other options, then additional units of land should be allocated to option ‘x’.

Agricultural extension is a term that has long been used to describe a non-formal educational system aimed at improving the livelihood of farmers. Extension education aims at three main types of behavioural changes in relation to knowledge (things known), attitudes (things felt) and skills (how to implement the things). This can be achieved through persuasion and motivation for the changes. The core activities in extension are education and training. Extension is now being regarded as a much wider task of integrating indigenous and new skills and techniques, derived from study or research, into an overall framework of discussion and cooperation between the people and the extension organisation. The extension worker is primarily engaged in the ‘selling’ of ideas to bring about changes in the knowledge, attitudes and skills of the individual. Functions of extension in a broader sense include

Multipurpose trees and shrubs are defined as all woody perennials that are purposefully grown to provide more than one significant contribution to the production and/or service functions of a land-use system that they occupy. In agroforestry systems, different species of trees and shrubs can be planted with many types of crops in a variety of patterns. Thus, it is required to know about the methods of propagation and nursery raising, planting and other silvicultural management practices along with the diverse uses of multipurpose trees and shrubs of tropical and subtropical areas before their selection for forestry and agroforestry activities. It is important to select the most suitable tree species since it is not easy to replace them once they have been planted.

MANGIUM (Acacia mangium)

Acacia mangium is a single-stemmed evergreen tree that grows to 25-35 m in height and up to 60 cm in diameter. The bole is usually straight, often fluted near the base, free of branches for up to half its height. Mangium is native to Australia, Indonesia and Papua New Guinea. However, it tolerates varied site conditions and has adaptability to different planting objectives. Mangium shows most vigorous growth on well-drained, fertile soils in high rainfall areas in the humid tropics. It is valued for its rapid growth and has been planted throughout the humid tropics and is a major plantation species in the Asia-Pacific. Provenances from Papua New Guinea consistently show better growth in height and diameter.

1.1. What is Earth?

The Earth is a layered body consisting of three parts: core, mantle, and crust. The radius of the Earth is nearly 6370 km of which crust, mantle and core share a depth of 40, 2850 and 3480 km, respectively (Figure 1.1). Exterior of the Earth contains the outer lithosphere which is surrounded (70% of surface) by water (hydrosphere). Solid and liquid sphere are surrounded by gas (atmosphere). The atmosphere is of 320 km above the lithosphere / hydrosphere. It is believed that there is a progressive increase in temperature with depth, if one goes to the core from the Earth crust. There is a rise of approximately about 1°F for every 64 feet depth on an average. Therefore, one could imagine that the interior of the earth is in molten condition.

2.1. Minerals

Primarily, minerals are usually inorganic substances possessing a definite chemical composition and a definite molecular arrangement which is usually expressed in geometric form. The mineral matter is made up of various elements, combined to form compounds. Usually, minerals consist of more than one constituent elements. Quartz contains two elements, silicon and oxygen. Other minerals may contain many elements, such as amphibole consists of several elements that include sodium, calcium, magnesium, iron, aluminium, silicon, and oxygen. Some elements exist as such without forming compounds. They contain exceptionally one element. Graphite (C), diamond (C), and Sulphur (S). Minerals are naturally occurring crystalline solid where the atoms are arranged in a regular three-dimensional array. A crystal is a solid, formed by a repeating three-dimensional pattern of atoms, ions, or molecules & possessing fixed distances between the different parts. Minerals that do not grow in these regular or crystalline patterns are called amorphous solids. When we talk about ‘naturally occurring’, we exclude the laboratory-synthesized crystalline solids. Glass and amber are also naturally occurring solid, but they are not crystalline and thus, they are not considered as minerals, rather they are referred as amorphous solids.

3.1. What is weathering?

Weathering may be defined as the transformation process of solid rocks, involving the disintegration and decomposition of rocks and minerals, into soil.

There are different types of weathering: physical, chemical and biological.

3.1.1. Physical weathering

In physical weathering the chemical composition of the weathered products remains same as that of the parental rocks. It is involved in fragmentation of rocks into comparatively smaller sizes. It does not transform the parental rock into a newer one that may differ from the parental rock in chemical composition. The process is totally physical in nature. But this is also true that physical weathering encourages chemical weathering, and both may be carried out simultaneously because physical weathering promotes more surface area of parental rocks for more interaction with agents of chemical weathering.

4.1. What is pH?

pH is used to classify substance as acidic, neutral and alkaline, based on the prevalence of free H⁺ ions. Water molecules on autoionization dissociate to produce H⁺ and OH^- in equal number, although degree of dissociation is very small because of its stability (about one molecule in 10 million is ionized at any one time). H⁺ ions later attached to un-ionized water molecule to give rise hydronium ions, (H₃O)⁺

5.1. What is soil organic matter?

Plant and animal residues which are not yet added to the soil are considered as organic materials. However, once they are added to soil, they become soil organic matter. Therefore, organic materials contributing to the soil matrix are referred as Soil Organic Matter (SOM). Sometimes SOM is also used to highlight only the non-living organic materials produced by living organisms. But SOM should be regarded as a broad term that includes biomass, partially decayed residue, and highly decomposed and transformed organic substances, humus. Agricultural soil contains nearly 1-5% of SOM, which is regarded as least amount in soil as compared to other three soil components, minerals (45%), air (25%) and water (25%). However, it contributes enormously to soil productivity. Soil productivity and fertility exhibit direct positive relationship with SOM content in soil. Plants and animals are considered as primary and secondary sources of soil organic matter, respectively. Plant residues and application of organic manures e.g., farmyard manure, compost or green manuring help to build up organic matter in soil and thus, enrich the soil with organic carbon and other plant nutrients. Under natural conditions, roots of grasses in grasslands, the leaves including shoot portion of the large trees in forest lands and after harvesting the crop remnants in agricultural field provide enough incorporation of organic materials in soil. SOM plays a vital role to maintain sustainability in agricultural production through producing healthy soils and thus, healthy crops.

6.1. What is colloid and colloidal system?

A colloidal particle may be defined as a substance which is microscopically dispersed evenly throughout another phase and is possessing a size of 10^-7 to 10^-3 mm and representing a larger surface area per unit mass. Thus, a colloidal system refers to a two-phase system in which small particles of one phase which might be of solid, liquid or gas is suspended evenly in the second phase of solid, liquid or gaseous material. These colloidal systems may be of solid in liquid or solid in gas or liquid in liquid or liquid in gas. Unique examples of liquid in liquid colloidal system includes the fat droplets dispersed in water of milk. When you put floor disinfectant liquid in water, it forms a white emulsion. Thus, emulsion becomes a colloidal system of liquid in liquid. Likewise, in fog, water droplets are suspended in gaseous air. So, fog is an example of a colloidal system, constituting of liquid dispersed in gas. When we refer smoke, it contains carbon particles (solid) suspended in air (colloidal system of solid and gas). However, smog is composed of smoke and fog. In case of soil colloidal system, soil colloids, which are of tiny particles (<0.001 mm size) and may be of organic and inorganic nature, are suspended in soil solution (water) and referred to as sol. Colloidal chemistry, which involves in the surface reactivity and charge characteristics of colloids, plays a pivotal role in total soil chemistry.

7.1. Introduction

Like all other living organisms such as humans, animals, and microorganisms, plants also need elemental nutrients for their growth and development. They assemble the nutrients from soil, water and air. However, to obtain economical crop yield, nutrients are also supplied to the crops from external sources such as chemical fertilizers and manures and using biofertilizers. It is the present-day need to handle the soil fertility status in a more realistic and careful way to obtain maximum crop harvest. Under poor management practices, soil may become infertile and loose its importance in agricultural use. In modern days, huge food demand for the burgeoning human population does not permit to show luxury to use only fertile soil. Moderately fertile soil or even degraded soil should also be managed properly so that they may be used to grow crops. For this, plant nutrients status of the soil plays a significant role along with other soil properties. For sustainable soil fertility management, parameters such as crop to be raised, its nutrient demand at various growth stages, current nutrient status of the soil, amount of nutrient application based on the soil testing results etc are important to be considered. Balanced nutrition to the plants is the prerequisite to obtain maximum benefit. If nutrients supplied to the plants are low in quantity than their requirement, crop production is lowered down. Similarly, if the nutrients are provided in more amount in the soil or unbalanced way through fertilizer or manure applications, total crop yield is suffered. It is a very common example that excess of phosphorus leads to zinc deficiency in most crop plants and it has been observed that excess N is responsible for potassium starvation in potato. Again, excess of iron, manganese, zinc, copper shows plant toxicity. Addition of nutrients to soils in excess also causes environmental pollution when the excess nutrients are lost from soil by leaching, surface run-off and volatilization. Unscientific way of soil fertilization leads to increasing cost of cultivation and imparts adverse effect to the environment instead of doing any good. Therefore, one should have a clear knowledge on soil fertility to obtain a sustainable productivity.

8.1. What is an ion exchange reaction and its application in soil system

Ion exchange is a reversible chemical reaction between two substances, either between two electrolytes or between an electrolyte solution and a solid complex as well as between two solid phases (if in close contact with each other), where ions of equal charge may be interchanged in equivalent proportion.

Organic colloids and inorganic micelles (clays) are sites of ion exchange. Soil contains silicate clay minerals which exhibit charges due to isomorphous substitution as well as due to the pH dependant charges for ionisation of hydrogen and hydroxide functional groups. Organic matter present in soil also contributes to the pH dependent charges due to the presence of various active functional groups. Thus, the organic and inorganic colloids present in soil bear positive or negative charges. Electric charge on soil particles is neutralized by equivalent amount of oppositely charged exchangeable counter ions, held by coulomb forces and van der Waals forces. Ca⁺², Mg⁺², H⁺, K⁺, Na⁺, NH₄ ⁺, Al⁺³, Fe⁺³, Fe⁺², Mn⁺², etc. are the common cations present in soil where Ca⁺² serves as the dominant ion. However, Na⁺ and Al(OH)₂ ⁺ are the dominant cations found in the exchangeable phase in strong alkali and strong acid soils, respectively. SO₄ ^- 2, Cl^-, HCO₃ ^-1, NO₃ ^- etc. are the most common anions found in soil to neutralize positively charged soil colloids.

9.1. Introduction

Soil biology is a branch of science that studies the soil inhabiting organisms in relation to their ecology, functions, behaviour and impact on various soil processes and plant growth. Soil fertility is directly dependant on humus content as well as the presence of microorganisms in soil, although surface soil does not contain more than 0.5% by weight of living organisms. However, such a small portion of soil constituent as compared to other organic and inorganic constituents plays a significant and major role in transformation of plant nutrients from their unavailable to available form from organic wastes, soils and fertilizers. They have a direct role in improving soil tilth, providing an appropriate environment for root growth, decomposing organic residues to form humus and in turn releasing nutrients for plants use, releasing many plant growth promoters, fixing inert atmospheric nitrogen in plant usable forms and they promote many other important processes without which plants cannot survive. Absence of living organisms in soil leads to its infertility. An understanding of microbial processes in soil environment, keeping in view of soil nutrient status, carbon sequestration, soil health and quality, overall sustainability in agriculture and also global warming in respect of greenhouse gas emissions (nitrous oxide and methane) through agricultural practices, is very important in regulating nutrient release at different plant growth stages. If we are in a state to understand how various biological processes influence various changes in soil environment or in the opposite way that how different soil conditions alter the soil biota in number as well as in their functions and diversity, it is easier to implement soil management practices that promote to gain more benefits.

Microorganisms are ubiquitous in nature. Possessing a diverse habitat, they are found everywhere in soil, air and water at a varied temperature and pH. One may find the highest genetic diversity of life within the domain of microorganisms. But unfortunately very few are known to us, so far only 1% of the microbial species on the earth are culturable. However, it is believed that soil of one gram may contain hundreds of millions to billions of microbes which may represent several thousand microbial species. In respect of the population, bacteria top the list followed by actinomycetes, fungi, algae and protozoa in accordance with a decreasing numerical order. Out of three important soil fertility components viz. physical, chemical and biological; the biological component is least understood due to its wide complexity.

10.1. Introduction

The soils possessing characteristics that are not suitable and economical for crop growth are termed as Problem soils. These characteristics may be of physical, chemical and biological. For cultivation of crops in these soils, it is necessary to follow specific management interventions and proper reclamation measures. Frequently we come across another term, ’degraded soil’. Degraded soil is also a problem soil. However, there exists a hair-line difference between problem and degraded soil. Problem soils refer to the soils in which the inherent soil characteristics, obtained from its genesis, pose problems for their optimal use, while degraded soils are developed due to anthropogenic activities by unwise management interventions.

10.2. Types of problem

Mainly there are four types of problem that may exist in soils: physical problems, chemical problems, biological problems and nutritional problems as a result of physical, chemical and biological constraints in soils.

11.1. What is acid soil?

Acid soils refer to those soils that are characterized with the presence of higher concentration of H⁺ in soil solution and at exchangeable sites or characterized with its high proton donating capacity such as aluminium (Al³⁺) on hydrolysis gives rise to proton. Both H⁺ and Al³⁺ are responsible to contribute soil acidity. Al³⁺ causes soil acidity indirectly by generating H⁺ through its hydrolysis, while H⁺ contributes directly. Therefore, due to more abundance of H⁺, they exhibit low soil pH and low base saturation (Ca²⁺, Mg²⁺, Na⁺ and K⁺). Such soil is considered as problematic soil because plant growth is affected adversely under acidic conditions and they suffer root injuries when grown in acid soils. Besides, soil acidity interferes in the soil nutrients availability to plants, making them either deficient to plants (such as phosphorus, calcium, magnesium, molybdenum) or toxic to plants for their more availability. Under acidic condition, Al, Mn and Fe are found in more soluble form. Thus, they are taken up by the plant in such a higher level that they become toxic to plants. Phosphorus becomes immobile due to the formation of insoluble compounds with aluminium and iron under acidic conditions. Ca, Mg and Mo also become unavailable in acid soil and show their deficiency symptoms. Soil acidity also affects soil microbial growth and thus, in turn, affects the nutrient dynamics in soil. Soil acidification is induced heavily under intensive agricultural practices such as increasing leaching due to more irrigation practices, addition of fertilizers, build-up of soil organic matter and many other possible ways.

12.1. Introduction

All soils invariably contain soluble salts. However, physico-chemical and biological soil properties start degrading when excessive amount of salts are accumulated in soil, particularly in rhizosphere, due to several anthropogenic activities and environmental conditions, and crop production is severely affected. Then we refer those soils as salt-affected soil.

The need of intensive agriculture to keep pace with the increasing world population for their food requirement necessitates to bring more agricultural land area under irrigation. However, irrigation system without taking enough drainage provision and poor water quality and its poor management may make the situation worst due to the development of salt-affected soils that ensue unproductive soil and low crop yield. Crops grown on salt-affected soils suffer from high osmotic stress, nutritional disorders due to nutrient (N, Ca, K, P, Fe, Zn) deficiency, specific ion toxicities, poor soil physical conditions and as a consequence, a reduced crop productivity.

Although it is considered that the rocks and minerals on weathering lead to salt accumulation in the soil, but the salt-affected soils are not truly originated from the accumulation of such salts in situ. On the contrary, occurrence of salt-affected soils is due to receiving salts that come from other locations with water. Sea water inundation in coastal belt, irrigation with poor quality water including saline groundwater, poor drainage system, irrigation adopting unscientific ways leading to waterlogging, shallow water table etc. contribute heavily toward development of salt-affected soils. Salt-affected soils may occur under almost all climatic conditions. Their distribution, however, is relatively more extensive in the arid and semi-arid regions compared to the humid regions because of poor precipitation to leach soluble salt adequately. Since evapotranspiration greatly exceeds precipitation in these climatic conditions, the soluble salts move upward with water due to capillary action and are left behind on the surface soil and the rhizosphere, once water is evaporated. The commanding ions of accumulated salts in affected soil are sodium, potassium, magnesium, calcium, chlorides, sulphates, carbonates and bicarbonates. The nature and properties of salt-affected soils are so diverse that they require specific approaches for their reclamation and management. Therefore, it is necessary to know their origin, formation, nature, chemistry and properties in detail to classify them into groups for their proper management to maintain sustainable agriculture.

13.1. Introduction

Water is chemically benign. However, its interference in free gas exchange in soil becomes detrimental to crop growth when soils are subjected to waterlogging or plants are submerged with water.Waterlogging of soil refers to a soil condition when the soil attains a moisture regime to such an extent that oxygen is not available in the pore space in enough quantity for plant roots to respire adequately. On the contrary, detrimental gases such as carbon dioxide, methane, hydrogen sulphide, ethylene etc. accumulate in the root zone and adversely influence the growth of plants. Thus, anaerobic condition prevails in waterlogged soil causing depletion of oxygen and increase of CO₂ in root zone, which severely affects aerobic micro-organisms while harmful organisms proliferate and restrict the plant growth. Waterlogging leads to nutrient deficiencies or nutrient toxicities, root tip decomposition and eventually, reduced growth or death of the plant. Physical, chemical and biological activities in the soil are also disturbed due to low temperature. However, this is important to note that plants differ among themselves in their demand for oxygen. Even oxygen demand for same plants differs with its growth stage. Therefore, it is well understood that there is no universal level of soil oxygen that can identify waterlogged conditions for all plants. Mostly waterlogging prevails in the land due to non-permeability of the soil material, the presence of an impervious layer in soil horizon, or a high-water table.

14.1. Introduction

Environmental pollution primarily deals with five types of pollution: soil pollution, water pollution, air pollution, sound pollution and light pollution. However, soil, water and air pollutions are considered very important as the pollutants from the environmental compartments may be cycled within themselves, enter the food web and interfere the biological processes adversely of any living species. Soil supplies nutrients and water to plants which, in turn, act as the nutrient supplier to animals and humans. Thus, maintenance of soil quality is considered prerequisite for growth of plants, animals and humans. If soil, water and air are polluted through various mechanisms, living components in the environment are suffered adversely. Soil, water and air pollutions are associated with the build-up of soil contaminants such as toxic organic and inorganic compounds, petroleum hydrocarbons, radioactive materials, salts, disease causing agents etc. above the permissible limit, so that their presence will cast adverse effects on physicochemical and biological properties of soil which in turn exert negative impact on crop growth and on any non-targeted organisms. Common soil contaminants include heavy metals, pesticides, petroleum hydrocarbons, fertilizers if used in excessive amount, and many others. Contamination of the soil, air and water results from intensification of farming activities. Primarily nutrients (particularly nitrogen and phosphorus), sediment, wastes, pesticides and salts are regarded as agricultural nonpoint source pollutant. Realistically, most of the pollutants originate from anthropogenic activities, although there exists many naturally occurring mineral components that may exhibit toxicity towards living system at higher concentration. Land disposal of municipal and industrial wastes, automobile emissions, mining activity, and application of fertilizers and pesticides to agricultural field cause a continuous accumulation of heavy metals and other pollutant components in soils. These pose threats of environmental degradation via soil erosion, loss of biodiversity, climate change etc.

In modern agriculture, use of synthetic chemical fertilizers are essential in agriculture for sustainable yield but, these have resulted in environmental pollution. The use of synthetic fertilizer could result in serious human health issues and also affects the soil microflora, besides being costly due to high production cost. Further, excess use affects soil processes and result in nutrient imbalances in plants with increased susceptibility to pests and diseases and also affects the symbiotic associations. Under these circumstances, biofertilizers could be an alternative for integrated nutrient management system in horticulture. The entire crop production system depends on soil beneficial microflora and their activities, which makes them highly potential alternatives to synthetic chemical fertilizers.

Biofertilizers or microbial fertilizers are essential for eco-friendly and sustainable cultural practices. The term “biofertiliser” has been defined in several ways due to its unique relationships between the plant and rhizosphere microflora. Biofertilizers mainly include nitrogen fixing bacteria, phosphate solublizing and potash solubiling bacteria.

2.1 Nitrogenous biofertilizers

These biofertilizers augment nitrogen to the plants through fixation of atmospheric nitrogen, either symbiotically or asymbiotically. The major nitrogenous biofertilizers are:

2.1.1 Rhizobium

The word Rhizobium is a Greek word where “rhiza” refers to root, and “bios” refers to life. Rhizobium was first named by Frank (1889) which means ‘root living’ in Latin (Fig. 3). Some species of Rhizobium were later moved to new genera based on phylogenetic analysis. It consists of 49 rhizobial species and 11 non-rhizobial species.

Biofertilizers improve the plant growth due to changes in the microbial community of rhizosphere by production of several substances. Normally, biofertilizers promote plant growth either by facilitating nutrient absorption or by secretion of plant hormones. Biofertilizers also cause inhibitory effects by acting as biocontrol agents on various pathogens so that the growth of plant is enhanced. The mode of action could be either direct or indirect methods

Benefit of biofertilizers have been extensively studied for various agricultural and horticultural crops. However, the effectiveness of inoculated biofertilizers are influenced by several factors. If the use of biofertilizers have to be popularized in horticultural crops, the major factors affecting their performance particularly in relation to soil, plant, quality of the product and application methods have to be addressed. Factors affecting the performance of biofertilizers are:

4.1 Quality of the product

4.1.1 Production process

The high quality of biofertilizers are determined by the production process (Bashan et al., 2014). At the same time, the population density of mother culture and the quality of the final products are directly related (Stephens and Raskm, 2000). As the inoculum consists of a strain, the relationship among the microorganisms interaction in the rhizosphere have to be understood. In the case of more than one microorganisms, the efficiency depends on the various mode of action by various microorganisms which might overlap with antagonistic acitivities (Vassilev et al., 2001, 2006 b). The relationship of microorganisms with plants is not based on the taxonomic diversity, but their functional diversity (Maherali and Klironomos, 2007).

The efficiency of biofertilizers could be assured by enhanced shelf life of the inoculant and biological traits which are a challenge for developing a formulation (Bashan, et al., 2014). Hence, either single or consortia of microorganisms formulation with or without additives determines the efficacy of the biofertilizers. The formulation determines shelf-life during storage and transport, which enhances the persistence of the strain in soil and get maximum benefits to the host plants after inoculation (Manikandan et al., 2010; Schoebitz et al., 2012). Different kinds of carriers are used in the formulation process which affects the overall quality and efficacy of the biofertilizers (Bashan et al., 2014; Herrmann and Lesueur, 2013). Granular inoculants showed good results under stressed soil conditions (Clayton et al., 2004; Lupwayi et al., 2006). Encapsulation of the microbial strain into polymers allow diverse compositions and structures (Vassilev et al., 2005) but, have limitations for commercial production (Bashan, et al., 2014; John et al., 2011). Use of additives might improve the shelf life of the product (Bashan et al., 2014; Malusà et al., 2012; Herrmann and Lesueur, 2013) with introduction of specific substances to enhance the efficacy of biofertilizers.

The inoculum dosage and method of application determines the efficacy of biofertilizers. The quantity of biofertilizers to be applied depends on the type of crop, seed rate and soil edaphic factors. There are 3 methods for inoculation of biofertilizers

Seed treatment: One packet containing inoculant (200 g) is mixed with 200 ml of rice gruel or 40 % gum arabic solution to make a slurry (Fig. 23). Then the seeds required for an acre are mixed in the slurry in such a manner that they have a uniform coating of the inoculant over the seeds. Then, the inoculated seeds are shade dried for 30 minutes. The shade dried seeds should be sown within 24 hours. One packet of the inoculant (200 g) is normally sufficient to treat 10 kg of seeds.

Fruits, vegetables, ornamentals, plantation crops and spices, medicinal and aromatic plants, tubers, are the major horticultural crops contributing to the economic growth in India. Even though the horticultural sector is growing fast, with India being the second largest producer of fruits and vegetables in the world, the productivity and quality have to be improved in order to meet the demand of increasing population. Under these circumstances, ecofriendly techniques needs to be adopted which could ensure food security and sustainable production. Indiscriminate application of agrochemicals and chemical fertilizers in horticultural crops and their residues could harm the human health, soil and environment. Horticultural crops need an ecofriendly technique, as most of the horticultural products are directly consumed. Hence, there should not be any residues of agrochemicals in food products. In the current context, use of ecofriendly, cost effective and organic-based inputs like biofertilizers can maintain health of the soil and good quality in horticultural crops. The application of biofertilizers offers an attractive and sustainable means of improving the quality of food products. Biofertilizers like Azotobacter, Azospirillum and AMF and PGPRs not only supplies the required nutrients to plants, but improves the fruit quality and quantity (Pathak et al., 2017).

Biofertilizers can directly or indirectly influence the growth of plant. The direct influence can be through production of phytohormones or making the nutrients available to plants. The indirect effect can be through management of plant pathogens through biological control. Therefore, the purposeful introduction of biofertilizer inoculants to plant microbiome represents an environmentally sound option that holds a prominent position in order to reduce the dependency on agrochemicals (Adesemoye and Kloepper, 2009; Abhilash et al., 2016; Aloo, et al., 2019).

Microbes in soil can rarely exists as single cells and survive near the plant root canopy or in bulk soils or endophytes or even on plant surfaces (Lorito, 2006). The soil microflora occurs as complex members of microbiota (Hacquard, 2015). Microbial consortia (MC) are unique mixture of organisms which respond to the environment stress and adapt to stresses due to internal beneficial interactions among the microbial community. Ecosystem’s physiological functions by microflora is carried out by more than one microbial species with the functional diversity and succession among different microbial components. The microbial balance among the different microflora of a MC will consist of a continuous shift between actively growing cells and non-dividing cells of the microbial consortia. It has been reported that different microbial populations “talk” to each other by “quorum sensing” mechanism in a given environment by exchanging specific chemical signals (Thompson, 2015). Natural microbial consortia holds many specific properties like stability, functional diversity and perform complex functions. The natural consortia have generated an interest in manpulating synthetic consortia for the benefit of application (Minty, et al., 2013).

Biofertilizer is already proven to be beneficial for agricultural and horticultural crops. The most important pre-requisite for the success of biofertilizer application is the presence of high population of viable cells which will show the desired effect on plants. Biotic interactions along with competition from native microflora is a major challenge to an applied strains of biofertilizers. The formulation is an important parameter for biofertilizer production containing efficient microbial strain with suitable carrier material and additives. The microbial strain needs suitable protective environment to increase their efficiency at the target site and also make it user-friendly. Performance of biofertilizers under field condition is the major requirement for inoculants. Inadequate formulations and poor inoculant quality are the major hurdles for the successful use of biofertilizers.

Formulation of biofertilizers has to be consistant during production, distribution, storage and transport to the farmer/end users. The shelf-life of inoculated microbial fertilizer depends on the formulation with suitable carrier material. If local production and distribution of an efficient native biofertilizer formulations are developed, the present problems in the field performance of biofertilizers could be significantly solved. Specific formulations of native strains for use in saline soils, acid soils, drought, high temperature and eroded soils requires specific formulations. Therefore,use of native strains of biofertilizer formulations which are tolerant to the abiotic stress is an important approach. The formulations of biofertilizers are challenging and limited success has been observed in the commercialization of new biofertilizers. Hence, the search for new formulations has been a continuous approach. However, the choice of the formulation depends on the application method, available equipment, farmer’s convenience, plant inherent characteristics and developmental stage, cost, mode of action and colonization pathway of the inoculated strain. Conventionally, solid based formulations are used, which have problems of low viability during storage and application.

Quality Control is very important in biofertilizer production, which determines the efficiency of microbial strains. Generally, the quality control based on BIS are voluntary in nature. However, some of the biofertilizers are brought under the ambit of Fertilizer Control Order 1985 (FCO) during 2006 (Yadav and Chandra, 2014). At present, biofertilizers are under the FCO with specific quality standards. Biofertilizer production and its sales can be regulated and is a mandatory requirement for registration of manufacturing unit with the State Fertilizer Controller (who is generally the Commissioner or Director of Agriculture Department) under the statutory provision of FCO. Moreover, some officers of the Agriculture Department have been declared as Fertilizer Inspectors at the district level, who are authorized to inspect production and storage facilities and draw samples for quality analysis. National Centre of Organic Farming (NCOF), Ghaziabad under the Govt. of India and its six Regional Centre’s located at Bhubaneswar, Bangalore, Jabalpur, Nagpur, Hissar and Imphal have been declared as testing laboratories. Under the provisions of the FCO act, State Governments can also develop their own quality control laboratories and notify them under the FCO (1985). Peat, lignite, peat soil, humus, wood charcoal or similar material favouring the growth of microbial strain could also be used. The FCO specifications for different biofertilizers are presented below:

It has been well established that the biofertilizers are beneficial to plants and are cost-effective inputs for sustainable production system. However, there are some constraints with respect to its production, which are presented below:

10.1 Production constraints

10.1.1 Raw material

Eventhough there are large number of biofertilizer formulations, only few are considered as good carrier materials for biofertilizers such as peat and lignite. Moreover, its availability in India is limited and the quality is lacking for these carrier materials. Hence, a cost effective and locally available material with increased shelf-life is the need of the hour.

10.1.2 Specificity and availability of strains

As the microbial strains used as biofertilizers are specific to soil and agro-ecological conditions, availability of specific strains for the specific host and soil edaphic factors are inadequate.

Microbes present in the biofertilizer formulations help in microbial processes in the soil which augment the availability of nutrients to be taken up by plants. They are of different types based on their nature and function such as nitrogen fixing, phosphate solubilizing, phosphate mobilizing or biofertilizers for micronutrients. Plants use different strategies for growth promotion at different stages of plant growth and development. Biofertilizers are mass multiplied cultures of specific beneficial microbial strains which improves the fertility of soil and productivity. The nutrients are added through natural processes of nitrogen fixation, solubilization of phosphorus and synthesis of growth promoting substances to stimulate the plant growth. The main sources of biofertilizers are bacteria, fungi and cyanobacteria.

11.1. Bio-enrichment of chemical fertilizers- A new approach

Yield response of different host plant depends on the mineral fertilizer and its fertilizer use efficiency. Generally, such fertilizers are low in efficiency due to environmental and soil factors. A large portion of synthetic fertilizers are lost due to fixation, leaching, run-off, erosion, volatilization, denitrification and precipitation without reaching plants. Hence, there is an economic loss and water and environmental pollution.

Microbial inoculants applied to the soil enhances the uptake of nutrient by plants and increase the efficiency of synthetic or organic fertilizers. In this context, it is possible to impregnate mineral fertilizers with specific microbial strain. A new approach is to incorporate the microbes or microbial compositions into fertilizer compositions.

The soil fertility is depleting in the current scenario of gap between nutrient removal from soil and supplies. Moreover, increase in the fertilizer prices has become unaffordable to small and marginal farmers. There is also a growing concern about the environmental hazards and its threat to sustainable crop production. Indiscriminate use of synthetic fertilizers for intensive crop production has resulted in large quantity of nutrient (particularly P) accumulation in soils which has resulted in generating a dead soil. In this context, the long term use of biofertilizers are considered to be economical, eco-friendly, more efficient, productive and accessible to marginal and small farmers over chemical fertilizers (Subba Rao, 2001). Biofertilizers mainly consists of specific living cells which supplies nutrients to plants through their root system. Microbes in these fertilizers provide nutrients to the plants by nitrogen fixation, phosphate solubilization, phosphate mobilization, and promotion of beneficial rhizobacteria (Bhat et al., 2010). Biofertilizer application improves the supply of nutrients, organic carbon, accumulation of soil enzymes, productivity, soil fertility index, economy of farmers, and maintenance of sustainability in natural soil ecosystem and horticultural crops. The production of efficient and sustainable biofertilizers for crop plants needs to be undertaken to make the biofertilizers popular and efficient. The important and specific research in future may be focused on the following aspects.

There are many manufacturers of biofertilizers in both government and private sectors. Only some of them have been listed here for the information

The biofertilizer technology has paved way for the manufacturers and entrepreuners to establish a biofertilizer production unit due to an increasing demand and awareness among farmers. Biofertilizer production units have already been started with most of them in the southern states of India. The biofertilizers can be produced using different kinds of carrier materials (peat, coal, lignite, clays, inorganic soil), organic materials (composts, soybean meal, wheat bran, sawdust, etc.), or inert materials (e.g., vermiculite, perlite, kaolin, bentonite, silicates). Natural carriers like peat, plant waste materials, composts, sawdust, sludge lignite, clays, coal, vermiculite, perlite and bentonite and mixture of organic and inorganic materials may also be used.

The Government of India is also encouraging a low cost technology by providing a subsidy to establish a biofertilizer production unit . The major equipment’s and other materials required for a biofertilizer production unit with the capacity of 150 metric tonnes/annum are given below

1.1 Importance of Water for Agriculture

All animals and plants require water for their survival. Animals cannot prepare their own food. They depend on plants for their food. Plants need water for preparation food by the process of photosynthesis. Majority of this water requirement of the crops is met from different forms of precipitation. However, when the water requirement is not fully met from precipitation, then growth of the crops is affected. Water requirement of crops depend on many factors. It depends on the type of crops, irrigation schedules practiced, soil texture, position of groundwater table below effective root zone of the crop and management practice followed in crop cultivation. The dry land crops need less water compared to rice which is a water loving crop. The perennial crops like sugarcane, banana etc. need more water than other crops like cereals, pulses, oilseeds etc. Water requirement of crops is partly met by the upward flux of groundwater. The capillary rise of shallow water table in the form of upward flux helps in meeting the water requirement of crops to some extent. The upward flux depends on the type of the soil, effective root zone depth of the crop, depth of water table below effective root zone depth of the crop and potential gradient of soil moisture suction. If the soil is heavy like clay, effective root zone depth of the crop is more (deep rooted crop) and position of ground water table is near to ground level (shallow water table), then the upward flux is more.

Due to rainfall or application of irrigation water, some amount of water is recharged to soil reservoir. This recharged water is stored in the soil as soil moisture content. The stored moisture or called as water in the soil reservoir helps in supporting water requirement of crops also. The heavy soil like clay has more moisture retention capacity than the light soils like sandy soil. The residual soil moisture held in clay soil is released slowly and supports more soil moisture to the crops for a longer period than the sandy soil which has less soil moisture retention capacity. After meeting the water requirement of crops from all sources including different forms of precipitation, ground water contribution by capillary rise and residual soil moisture, if there is any shortage of water, then this shortage should be met from other sources which are called as irrigation. It is to be noted that irrigation is not the natural phenomenon of supply of water; rather it is the artificial means of supply of water to the crops. Irrigation may, therefore, be defined as the science of artificial application of water to the crop in accordance with the crop requirement for better nourishment of the crops.

2.1 Introduction

Rain and snow are the two chief sources of water of the earth. In-situ conservation of rainwater helps the plants to meet some of their consumptive uses directly. Not all the amount of rainwater that falls at a point is conserved by the soil reservoir to support the plant growth. Some part of it flows over the soil surface as surface runoff and some seeps down as infiltration and finally adds to the underground reservoir. Therefore, rain or snow, which is not used directly by the plants, becomes a potential source of either surface or ground water for irrigation. In areas with extreme low temperature, snow contributes major source of water supply wherever, in humid and sub humid regions, rain is the principal source. Precipitation, rain or snow, is the first stage of the continual cycle of water in its round from atmosphere to the earth and return by evaporation from water bodies, snow surfaces and land surfaces. The continual cycle of distribution of water is governed by the process called as hydrologic cycle. Thus, precipitation or atmospheric water is the first form of water above the earth’s surface, the second form being the surface water on earth and the third form is the subsurface water or underground water. The study of occurrence, distribution and circulation of precipitation through the unending hydrologic cycle forms the basic part of study of hydrology. As mentioned above, the part of precipitation that is not used by the plants in-situ flows over the soil surface as runoff and contributes to either surface or ground water supply.

Engineering hydrology is the science that deals with the estimation of runoff and its transmission from one place to the other, besides dealing with the properties of water in nature. For, an engineer, surface and groundwater are the two most important components to deal with. But due to lack of data of stream flow, it is usually necessary to study precipitation, evaporation and percolation to indirectly determine the availability of surface and groundwater. For planning and management of water resources systems, an engineer has to estimate (i) water resources potential of a basin, (ii) dependable yield for irrigation and hydel power generation and industrial water demand (iii) probability of occurrence of floods with their magnitude, (iv) sediment yield and transportation (v) hydrometeorology (vi) new sources of water for irrigation (vii) stream flow forecasting by use of precipitation data (viii) water control, navigation, control of soil erosion and control of pollution of water bodies and (ix) operation and maintenance of river valley projects. For estimation of the above mentioned parameters, it is important to understand the hydrologic cycle properly.

3.1 Introduction

Irrigation water that is supplied to crop fields is defined by a term commonly called as discharge which is also called as rate of flow. Discharge is defined as the volume of water flowing through a cross section in a unit time. It can be expressed as cubic metre per second (cumec), cubic feet per second (cusec), litre per sec (lps) etc. one cumec is equivalent to 35.5 cusecs or 1000 lps. The measurement of discharge is very important in everyday life starting from deciding the amount of irrigation to be supplied to a crop at a particular growth stage, or amount of water supply for domestic and industrial uses, for flood control and power generation etc. It plays a vital role in water resources planning.

3.2 Methods of Discharge Measurement

The various methods of discharge measurement can be broadly classified into the following types: (i) volume method of discharge measurement (ii) flow measuring structures such as orifices, mouthpieces, flumes and weirs.

4.1 Introduction

A reservoir that collects and harvests in-situ rainfall as well as runoff from the catchment area can be used for many purposes: the most important of which is the supply of water to crops as supplemental irrigation. The water of the reservoir can be used for domestic and industrial uses. It is also a good source for recreational use. Total water demand of the reservoir including irrigation to different crops in different seasons, domestic and other non-agricultural uses are to be assessed. While estimating the crop water requirement and irrigation requirement, various crops to be grown in the service area of the reservoir, their water requirements, crop duration, extent of coverage and water management practices followed are to be taken into consideration. Multiplying the irrigation requirement with crop coverage area, volumetric irrigation water requirement of crop can be found out. Summation of irrigation requirement of all crops grown in service area of the reservoir gives total irrigation demand of the reservoir.

4.2 Water and Irrigation Demand of Crops

Of the various demand of water from the reservoir, irrigation demand of crops grown in the command area of the reservoir is very important. Most of the crop water demand is met from rainfall. However, when the rainfall is deficient to meet the crop water demand, then the deficit is met from the stored water of the reservoir in the form of irrigation, more commonly called as supplemental irrigation. The irrigation to the crops is required mostly to meet the evapotranspiration requirement of the crop. Before discussing the water and irrigation demand/requirement of crops, it is essential to know some commonly used terms frequently used.

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.

6.1 Introduction

In order to increase the production and productivity of crops, provision of irrigation system is highly essential. A project that makes use of weir or a barrage for providing irrigation to fields is called as direct irrigation system. On the other hand, a storage irrigation system makes use of storage reservoir by construction of dams. In order to provide irrigation by both the schemes, it is necessary to have a network of canal systems. A canal is an artificial channel, generally trapezoidal in shape constructed on the ground to carry water to the fields. The canal systems that provide water to the fields include main canals, branch canals, distributaries, minors and watercourses. It is imperative to design the canal systems properly for a certain realistic value of peak discharge that must pass through them so as to provide sufficient irrigation to the command areas. The flow irrigation that provides irrigation water to the fields may be of two types i.e. Inundation irrigation and Perennial irrigation.

7.1 Introduction

The entire amount of water that is diverted at the canal head regulator does not reach at the field for use of irrigation. Major amount of it is lost on way during its movement in the canal systems. During the passage of water from main canal to outlet at the head of the water course, water may be lost either by evaporation from the surface or by seepage through the peripheries of the channel. These losses are sometimes very high, and may go up to 50 % of the total water diverted into the main canal. Evaporation losses are low and may go to a maximum of about 7 percent of total losses. The major loss of water in the conveyance system is the seepage loss. Seepage loss depends on the channel geometry and evaporation loss is proportional to the area of free surface. In determining the designed channel capacity, a provision of these water losses must be made. The provision for the water lost in the watercourses and in the field however, already made in the outlet discharge factor, and hence no extra provision is made on that account. However, excluding the above two losses, there is operational loss which when added to the evaporation and seepage losses, the total losses goes up the maximum 50 percent level. The operational loss includes spillage, over-toping, leakage through rodent holes, dead storage, initial infiltration and evapotranspiration from the vegetation along the watercourse. Evaporation and seepage losses of the canals are discussed below.

8.1 Introduction

For maximization of yield of crops, it is essential to provide irrigation to crops. When either the natural sources like rainfall, dew, snowfall and other forms of precipitation or when the capillary rise of groundwater is not sufficient to meet the crop water demand, then there is need to supply irrigation. This irrigation water is a precious resource and need to be used cautiously. There are three important things need to be understood for optimum utilization of irrigation water with basic purpose to maximize the yield and returns. 

9.1 Introduction

After knowing when to irrigate and how much to irrigate, next important thing is how to irrigate the crop field. Methods of irrigation plays a very crucial role in deciding how to irrigate the crop fields since all the crops do not require same methods of irrigation. Depending on the sources of water available for irrigation, type of crop to be irrigated, quantity and quality of water to be applied and other economic considerations, methods of irrigation will vary. Irrigation water may be applied to the crops by flooding it on the field surfaces as surface irrigation, by applying it beneath the soil surface as sub irrigation, by spraying it under pressure as sprinkler or overhead irrigation or by applying it in drops around the root zone of the crop as trickle irrigation. The commonly used methods of irrigation are described in schematic diagram as follows

10.1 Application Efficiency and Irrigation Uniformity

All irrigation systems have some non-uniformity. This non-uniformity influences yields and irrigation efficiency especially application efficiency. If the net amount of water applied during irrigation is the same as that required to fill the soil water deficit, then because the distribution of water is never perfect, half of the field will receive too much water while the other half will receive too less water. In such a context, a farmer will try to apply more irrigation water to his field so that a larger fraction of the field has an adequate amount. This will tend to have higher percolation and runoff and thereby declining the application efficiency. An alternative to adding extra water is to improve the uniformity of water application. A major advantage when the uniformity is improved is that the amount of deficit in the area under irrigation is reduced and the potential for water logging and salinization is also reduced.

11.1 Performance of Farm Irrigation Systems

The performance of farm irrigation systems is determined by the efficiency with which water is delivered to the field and utilized to the fullest amount possible with minimum losses due to seepage and percolation, runoff, evaporation and other operational losses. The efficiency of the irrigation system will increase if the conveyance losses, application losses and other losses are reduced to a great extent.

11.1.1 Overall Efficiency

The overall efficiency of a farm irrigation system is defined as the percent of water applied to the farm that is used for irrigation on the farm. Irrigation efficiency otherwise called as overall system efficiency is defined.

Bone is an integral part of musculo-skeletal system of body. In the living animal it is bluish pink, whereas, fresh dead bone is yellowish-white in colour. It is hard and resistant to pressure but also have certain amount of elasticity. Its tensile strength is equal to the cast iron, though bone three times lighter and ten times flexible to cast iron.

Number of bones: The number of bones of the skeleton varies with age and species. Number of bones in cattle-210; Horse-208; Dog-271; Fowl-166 and human-208 (207-212)

Composition of bone: Bone contains different bone cells, organic and inorganic matrix and water. Organic matrix is about one-third and Inorganic matrix is two-third weight by volume. The organic material consists of 90% collagen [type-I (maximum), type V and type XII] and 10% non-collagenous glycoprotein and bone specific proteoglycans (osteocalcin, osteonectin, sialoprotein, bone phosphoproteins and small proteoglycans) and bone growth factors [TGF-beta family; Insulin-like growth factor-1, 2; bone morphogenetic protein (BMP); platelet derived growth factor (PDGF); Interleukin -1 (IL-1); Interleukin-6 (IL-6); colony stimulating factor]. Organic matrix of bone resembles the matrix of dense fibrous tissues such as tendons, ligament and joint capsule. It is not certain whether all of these proteins are synthesized by bone cells or whether they are synthesized by cells outside of the bone and then incorporated into the bone matrix. However, their presence within bone and their potential to affect the activity of bone cells suggests they have important role in controlling bone cell functions. Inorganic matrix of bone or mineral component of bone serves as an ion reservoir and gives bone of its stiffness and strength. It reserves 99% of body calcium, 85% body phosphorus and 40-60% body sodium and magnesium. Inorganic matrix of bone is composed of 85% calcium phosphate, 12% calcium carbonate, 3% of magnesium phosphate, calcium fluoride and magnesium carbonate. It also contains traces of chlorine, sodium, potassium. These minerals remain as hydroxyapatite crystal form within bone. However, bone mineral crystal is not pure hydroxyapatite, instead they contain both carbonate and acid phosphate groups (HPO₄) and bone crystal does not contain OH groups. Bone matrix has such great durability and stability that it can remain essentially unchanged and retain much of its strength for centuries after death. Removal of organic matters renders the bone fragile, brittle and shattered, whereas, decalcification renders bone soft and pliable and resistant to fracture.