eChapters

Cross-pollinated species, or outbreeders, are highly heterozygous, heterogeneous and carry a higher mutation load than the inbreeders. Their mode of reproduction bestows upon them considerable heterozygous balance under panmitic population structure. Inbreeding such species disturbs the natural rhythm and leads to inbreeding depression. It is, therefore, essential that if selfing has created any disturbance in outbreeders, the heterozygous structure be restored. Since artificial selfing and outcrossing can be carried out in such crops at will, all breeding methodologies, even those meant for self-pollinated crops, can be used for their improvement. In fact, allogamous crops have provided opportunities for innovating breeding procedures to achieve the maximum efficiency by combining selfing and outcrossing cycles.

Thus, the classical separation of breeding procedures for self- and cross-pollinated crops has become unnecessary, particularly, for outbreeders which are amenable to selfing. Exploitation of heterosis has been the major objective in cross-pollinated crops and most breeding procedures developed earlier aimed at maximising heterosis. In later years, with better understanding of genetic structure of populations and availability of efficient biometrical methods of estimating genetic parameters, newer procedures of accumulating desirable genes have been developed. The presently available breeding procedures for cross-pollinated crops can be broadly classified under two heads: (1) Hybrid development, and (2) Population improvement. Both these methodologies, though independent, are not mutually exclusive. The steps for operating the two procedures, however, have contrasting requirements. For hybrid development, fixation of genes through cycles of selfing is necessary whereas such fixation is avoided while developing populations. As can be seen from the scheme given below, in both cases the homozygosity attained through initial selfing is converted to heterozygosity at the end of breeding programme. Irrespective of whether hybrids, synthetics or composites are being developed, great emphasis is placed on the attainment of homogeneity in the end products.

1) Origin and distribution

Pearl millet (Pennisetum americanum (L) Leeke, 2n-14) originated in west Africa from where it was introduced into India. Large variability is still found in Africa. Pearl millet is a dual purpose crop; its grain is used for human consumption and its fodder as cattle feed. It is cultivated mainly in Africa and Asia, primarily as a grain crop in an area of 26 million ha with a production of 13 million tonnes. As a poor man’s bread, it sustains a large population of Africa and Asia. It also contributes to the economy of countries like the U.S.A. where it is grown as a forage crop.

In India, Pennisetum americanum (bajra) is cultivated on 11 to 12 million ha land with a production of about 6 million tonnes. It is grown on marginal lands and in areas of scanty rainfall. Rajasthan, Gujarat, Maharashtra, Uttar Pradesh and Haryana account for about 90 per cent of the total area under this crop.

A close relationship between the mode of reproduction of a cultivated plant and the methods to be employed for its improvement is now well accepted. Crop plants are broadly placed in two groups according to the mode of their reproduction: sexually reproduced and asexually propagated or reproduced plants. Asexual reproduction does not involve the union of gametes and/or reduction in chromosome numbers.

Plants may reproduce asexually in a variety of ways. In 1980, Mayo has identified the following methods of asexual reproduction on the basis of the classification made earlier by Stebbins in 1941 and Brown in 1972.

Plant diseases, in spite of the various measures adopted to control them, continue to be a major cause of crop losses. At times these losses have been so heavy that they have caused severe famines. Diseases are caused by a wide variety of organisms such as fungi, bacteria, viruses, mycoplasma and nematodes. The diseases may be partially or completely controlled by chemical, cultural and genetic methods. When no single method is effective in controlling a disease, integrated control constituting a combination of the three methods of disease control (chemical, cultural, genetic) may be effective. If host resistance alone is sufficient to check a disease, then it is to be preferred to other methods because it is the least expensive, has no adverse environmental effects and involves no specific action on the part of the farmer, even when only partial, genetic resistance supplements chemical control and makes it more effective in comparison with chemical control on a completely susceptible cultivar.

Many plant diseases have been successfully controlled by exploiting genetic resistance especially where differentiation in the pathogen with respect to resistance genes in the host is lacking. In some cases, even when pathotype differentiation occurs in the pathogen, genetic resistance in combination with other methods has given adequate control. Breeding for resistance to highly variable air-borne fungal pathogens has claimed much time and effort of plant breeders and success has often been transient. The reasons for the shortlived success have become clear from research during the last quarter of a century.

The immediate and long-term objective of modern plant breeding in all countries irrespective of the state of their advancement is increasing the availability of food to meet the calorie-protein requirement of their people. In the past, breeders have concentrated their efforts on increasing the yield of the important crop species. Better adaptation to local environmental conditions, high production and better resistance to the major pests and diseases have been among the priority goals of genetic plant improvement. Yielding ability and stability undoubtedly deserve high priority but enough attention also needs to be paid to improving nutritional characteristics of the plant produce for their maximum utilisation. Awareness of nutritional requirements and the optimal characteristics of crop products to be utilised as food and feed, therefore, becomes an important parameter of breeding effort.

The main source of food in the developing world is cereals which provides 45 to 85 per cent of the total calories and 50 to 80 per cent of the total protein requirements. The consumption of animal proteins, which are nutritionally well balanced, is low and costly and beyond the reach of the low income groups. On the other hand, plant proteins are cheaper to produce and easier to store and transport. All these factors go in favour of increasing the quantity and quality of cereal proteins in order to improve the dietary and nutritional status of the masses in the developing world.

Proteins are made up of about twenty different amino acids. For man, eight of these amino acids, valine, methionine, leucine, isoleucine, threonine, phenylalanine, lysine and tryptophan, are essential (EAA) for constituting a well balanced diet. In impioving the grain quality of cereals consideration should, therefore, be given apart from the content of carbohydrates, fats, minerals and vitamins in the grains, to improving the protein content as also the amino acid composition of the protein.

Most varieties of fruit plants have originated as chance seedlings or through somatic mutation and have been maintained and multiplied through vegetative propagation by fruit growers. The improvement of fruit plants through breeding has not yet attracted the serious attention of the research workers. Unlike field crops, fruit plant breeding is time consuming and laborious. Studies on the mode of inheritance of important economic characters of fruit plants are difficult because of the heterozygous nature of the plants. Moreover, varying degrees of sexual incompatibility have complicated the situation. Due to a long juvenile phase, it takes a long time to identify a useful hybrid. This factor has become a serious handicap because most research workers leave or shift from the programme before tangible results are obtained.

During the last two decades, considerable useful information has been generated on breeding methodology for the improvement of some of the important fruit crops. In this chapter fruits like mango, banana and papaya have been included.

Introduction

Tree improvement through the application of genetic principles is directed towards modifying the heredity of tree populations so that they are able to meet the needs of the forester and the wood based industry. The breeder of annual crop plants resorts to hybridisation, selection, testing of the improved strains, multiplication of improved seeds and finally their release for commercial planting in that logical sequence. But the tree breeder, whose career may be shorter than the life cycle of the tree species taken up for improvement, tends to carry out the above operations in a modified form and often some of the operations are carried out concurrently.

Many of our tree species are wild unselected populations. They are, therefore, expected to exhibit considerable natural variability for many characters and also to respond well to selection for further improvement. Further, altitudinal and latitudinal variation in many characters between populations are expected for those tree species which have a wide geographical distribution. So, the selection of desirable seed sources or provenances is an essential step that is basic to all tree improvement programmes. The right provenance is identified through well laid out provenance trials at a number of locations in the area where the improved selection is to be grown. Further improvement is then planned and executed for exploiting the naturally available intrapopulation variation. The variation normally measured is the phenotypic variation which is the result of interaction of the genotype of the individual with the environment. However, what is essential for selection to be effective is genetic variation for the character under consideration. Genetic variation is assessed by appropriate progeny trials. Since many of the economically valuable characters of tree species are polygenically controlled and exbibit continuous variation, measurements have to be in metric units. The use of biometrical techniques for assessing and analysing this variation, therefore, becomes an essential requirement.

Forage crops are plant species used to feed domestic animals (such as cattle, sheep, goat, pig, and poultry). Both cultivated and wild plants can serve as forage. The domestic animals feed on forages either by grazing or stall feeding (cut fodder eaten in stalls).

Grazing, that is pasturing of animals, is cheaper and allows production of both livestock and dairy produce at a lower cost because no expense is involved in growing, cutting, transporting or feeding. In North and South America, Australia, New Zealand, and in many other temperate countries pastures are widespread and popular because sufficient land is available. While land is cheap and plentiful, labour is scarce and expensive; hence management of natural, and in recent years sown pastures has received much attention.

Until about fifty years ago, the natural grasslands in the Western countries met the minimum needs of the farmers and grassland management was operated at a level comparable to subsistence agriculture of many developing countries. In other words, emphasis was laid on exploitation of natural productivity of the grassland, using a low level of management based on minimum use of inputs like chemical fertilizers. However, it was soon realized that productivity of native grasslands will have to be greatly improved if the high demands for meat and milk were to be adequately met.

In India, however, out of a total cultivable area of about 131.11 million ha less than 2 per cent is utilized for forage crops because feeding the large human population takes the first preference for land use to produce grain and cash crops. It is, therefore, necessary to intensify efforts, particularly in over-populated countries, for a more efficient production of high yielding forage crops to get maximum return out of minimum land.

Breeding methods for vegetable crops are basically similar to those adopted in others like cereals, oilseeds or pulses. Certain aspects, peculiar to vegetables, however, require specific attention: (i) In many cases, the edible part of the plant is not the seed (as cauliflower, cabbage, carrot and onion) and hence while breeding for improved plant part that is used as vegetable, its seed production capacity needs due consideration, (ii) Vegetables like tomato, garden pea and onion are consumed in different forms (fresh or processed) and the end use of the product (like processing quality) has to be taken into account in breeding programmes, (iii) Consumer preferences (as for example in eggplant) size, colour and shape of the vegetable has to be given due emphasis, (iv) Being perishable in nature, keeping quality and suitability for long distance transportation are important attributes in vegetable crops unlike grain crops where bulk handling and haulage can be mechanised, (v) Another peculiarity with vegetable crops is that they vary widely in modes of reproduction necessitating appropriate choice of breeding methods. In addition to vegetatively propagated crops like potato, sweet potato, cassava (tapioca), garlic, pointed gourd or “Parwal (Trichosanthes dioica L.) and ivy gourd or ‘Kundru’ (Coccinia cordifolia L.), there are many seed propagated vegetable crops which are auto- or allogamous or intermediate (Table 1).

Within these broad groups, variations in the extent of cross- or self-pollination, namely, 15-20 per cent natural cross-pollination in chillies and 20-25 per cent natural self-pollination in muskmelon have been recorded.

Since genetic variability is essential for any crop improvement programme, the creation and management of genetic variability becomes central to crop breeding. Experimentally induced mutations provide an important source of variability. An advantage of such created variability is that the starting point can be an agronomically accepted cultivar rather than a genetic stock of no direct commercial value with many undesirable attributes. It should, however, be realized that none of the imposed treatments in a plant system has so far been able to direct a specific change. As a result, following mutagenic treatments, a mixed bag of induced variants is found and many of these may not be of any value. Also, many events take place concurrently in a treated cell to produce variation at several loci within a genome. Because of these reasons it will be unrealistic to expect miracles out of a mutation breeding programme. The desired results can be achieved only when the objectives are clearly defined and the experiments are specifically designed to achieve those objectives. When a mutant of the required type is obtained, we only reach the step of identification of a desired recombinant in a conventional breeding programme and all the succeeding steps of evaluation of the mutant are in no way different from those in the conventional breeding procedures.

Genetic resources deal with germplasm of a given species that provides the necessary genetic variation for the improvement of that species in terms of particular products, increased efficiency and higher levels of productivity. Genetic resources are, in this sense, the building blocks, fundamental not only to a crop improvement programme, but also for the very survival of the species in time and space (Swaminathan, 1983).

As agriculture is becoming more and more intensive and location-specific, plant breeding objectives are becoming more and more complex. Besides high yield, a modern variety is often expected to combine specific duration, nutritional attributes, adaptation to varying soil and water regimes, and resistance to ever-multiplying pests and diseases—to mention only a few of the character combinations. To meet these objectives, a wide range of germplasm must exist, and the plant breeder should have an easy access to the genetic resources.

In conventional breeding for genetic upgradation of yield and other desirable attributes of crop plants, favourable assemblages of genes from two or more parents are made to develop a commercial variety. The important steps of this exercise are: locating the right kind of parents that possess the desired characteristics; making crosses between or among them; handling the segregating generations in an appropriate manner so as to identify the required recombinants; stabilizing the recombinants and finally evaluating their performance in a series of trials. This approach has been very successful in the sense that it has provided increments in productivity continuously. In an analysis done by the American Society of Agronomy on the genetic contributions to yield gains of five major crop plants, it was concluded that sorghum yields increased due to genetic improvements at the rate of 1.2 per cent per year between 1950 and 1980. For corn, the corresponding yield increase was 90 kg/ha/year between 1930 and 1980, which is equivalent to a rate of increase of 1 per cent per year. It was also estimated that 70 per cent of the total gains in corn yields are attributable to genetic improvement and 30 per cent of the yield gains are due to non-seed inputs like fertilizers, pesticides and cultural practices.

In India also, the improvement of productivity of the major food, fibre and several cash crops has been very impressive. The success is due to intensive research in plant breeding resulting in the evolution of varieties with very high genetic yield potentials and the concurrent support from other disciplines that has provided the package of practices which help in the realization of the created potential. In all crop plants, where the breeding efforts have been intensive, the phenomenon of plateauing of yields has become apparent. Wheat provides, perhaps, the best example of the situation. Since the 1970s, when the gains from genetic restructuring of the plant type had been established, major yield increases have not occurred. Since the demands of the future will be undoubtedly much larger, and additional cultivable land will not be available, ways will have to be found for a sizable increase in productivity per unit area in the immediate future. This requirement calls for the development of strategies and procedures that will make dramatic yield gains possible. For meeting the challenge, a continuous search is being made for innovative methods which will give yield increments of a much higher order than those provided by the conventional approach. In this chapter, an attempt has been made to introduce some such promising approaches.

Precise collection and processing of soil sample is the first and foremost step for carrying out any soil study, therefore it is essential to collect the coil sample very accurately keeping in view the variations in slope, colour and texture of the soil management aspects. Soil sampling should be avoided from non-representative sites like recently fertilized plots, bunds, channels, marshy tracts and spots near trees, wells, compost piles etc. It should be kept in mind that erroneous samples will never yield accurate result in spite of very improved method of analysis. The depth of sampling may vary according to the need of soil study and extent of rhizosphere. However, in general the sampling depth for field crops is the plough layer (0 - 15 cm) but it could be up to one meter or as per the purpose of the study. Soil samples in dry farming areas should be taken depth wise as the roots of the crops in this conditions reaches to deeper layers in search of water and nutrients.

Mainly two types of soil samples (disturbed and undisturbed) are used for determining the physical properties of soil. The disturbed soil samples are used for determination of particle size distribution, particle density, aggregation, column studies for diffusion-dispersion coefficients and soil-water diffusivity. Whereas, undisturbed (core) soil samples are used for the estimation of bulk density, porosity, retention and transmission characteristics of air and water.

Particle-size distribution is one of the stable soil characteristics, being little modified by agricultural management practices. The particle-size distribution expresses the proportion of various size particles in a soil, especially sand, silt and clay that determine soil texture (Hillel, 2004). Soil texture is closely related to soil physical properties such as water retention and release characteristics, surface area, swelling and shrinking, soil strength and tillage properties. There are two common methods being employed for particle-size (<2.0 mm) analysis namely international pipette method and the hydrometer method. Both the methods are based on Stokes’ law which establishes a relationship between particle size and the rate of sedimentation. Thus, particles are assessed by their settling velocities from suspension in a water solution that can be used to quantify particle size. Size range of soil particles (sand, silt and clay) according to two most adopted systems i.e. U.S. Department of Agriculture (USDA) and International Union of Soil Science (IUSS) formerly known as International Society of Soil Science (ISSS) are given below:

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

Particle density of soil is the ratio of mass and volume of soil solids. Particle density of soil is an important physical characteristic because the interrelationships of porosity, bulk density and air space, and rates of sedimentation of particles in fluids depend on particle density.

Principle

The determination of particle density (ρ_p) requires the measurement of mass of the solid and its volume. The mass is obtained by weighing the oven- dry soil sample and volume by calculating from the mass and density of water displaced by the sample in a pycnometer. The pycnometer is a glass flask with a ground glass stopper having a capillary opening. The particle density can be calculated using the following equation:

Bulk density to which a soil can be compacted is dependent on water content and force of compaction. Adsorbed water on soil particles acts as lubricant and every addition of water increases ease of compaction to progressively a greater density. However, this increase in density will occur only to a certain value of water content beyond that it decreases with further addition of water in soil. The moisture content at which maximum dry density is obtained for a limited and fixed effort is called as proctor moisture and the density at that point is known as maximum or proctor density”.

Principle

A soil at varying water contents, compacted with a specific amount of compaction energy, would result in a bulk density-water content relationship. The maximum bulk density obtained at the proctor water content represents 100 % compaction. The test can be performed in laboratory on various soils using Abbot’s compactor

Proportion of solid, liquid (water), and gas (air) components in a soil mass indicates physical conditions such as soil structure, porosity and water content. A well Structured soil may have a high pore volume whereas a compacted soil may have little pore-space for other phases to occupy. In general, soil solids may occupy 50 % of the soil volume in a well-aggregated fertile loam and the remaining volume may be occupied by liquid and gases interchangeably.

Soil aggregates refer to a group of two or more primary particles which cohere to each other more strongly than to surrounding particles. Under field conditions, these units also cohere to some degree with neighboring aggregates and form larger aggregates. The aggregates form and break easily into smaller aggregates during tillage and by disruptive action of water and air. The aggregates maintaining their identity are those in which the cohesive forces among particles are greater than the disruptive forces. A quantitative characterization of aggregates is being done by determining aggregate stability and size distribution of aggregates. The aggregate stability refers to the resistance of soil aggregates to breakdown by water, air, and mechanical manipulations. Numerous methods have been proposed to determine size distribution and stability of soil aggregates (Kemper and Rosenau, 1986). The size distribution of wet and dry aggregates determines overall tilth, size of pores and susceptibility of aggregates to movement by water and wind.

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

Apparatus and Accessories

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

The variable amount of moisture contained in a unit mass or volume of soil and is the key factor affecting the growth of plants. Numerous other soil properties depend very strongly upon moisture content. Gravimetric (direct) and sensor based (indirect) methods are generally employed for soil moisture determination.

9.1 Gravimetric Method (Direct)

Principle

The gravimetric method is based on the principle that the water in the porous material is lost by evaporation on heating and the porous material undergoes an equivalent loss in its weight. However, the water loss may be limited by the internal operation within the complex porous material such as soil. This method is simple, routine, reliable, inexpensive, and easy to use. The major limitations of this method are that it is destructive, laborious and time consuming.

Soil consistency refers to the resistance offered by soil against forces that tend to deform it. The soil consistency varies with texture, kind of clay and moisture content. The efficiency of agricultural implements, animals and labour is largely affected by soil consistency as it directly inf luences the workability of a soil. Operations at suboptimal or supraoptimal water contents lead to clod formation, compaction, poor drainage and aeration. The common terms suggested by Atterberg (1912) to describe consistency are liquid limit, plastic limit, plasticity index, and sticky point. The physical basis of consistency limits is related to the interaction of water with soil. The water content at which plasticity is exhibited is the plastic limit or lower plastic limit of soil.

10.1 Liquid limit

Principle

The liquid limit refers to the water content at which resistance to f low becomes negligible and soil represents a semi f luid. A trapezoidal groove of specified shape cut soil held in a special cup will close in 25 taps on a hard rubber plate. The soil in the cup is 1.0 cm deep and the groove is 2.0 mm wide at the bottom with slopes outward at a 60^° angle horizontally. The soil in the walls of the groove f lows under the impact of the cup on the hard base and close the groove.

Soil pores differ greatly in size, shape, tortuosity, and continuity. They are characterized generally in terms of total porosity, air-filled porosity, and pore-size distribution. The characterization of pore space is important in understanding the storage and movement of water and gases, the development of plant root systems, the flow and retention of heat, and soil strength. The observation that bulk density is considerably lower than the average particle density indicates that only part of the bulk volume is occupied by soil solids and the remainder is occupied by a lighter material, such as air and water.

Total Porosity

Total porosity (n) is the percentage of the bulk volume not occupied by solids and can be computed using following relationship:

Tensiometer is a device to measure soil moisture tension or equivalent negative pressure of water in the soil. A tensiometer consists of a tube sealed at one end by a porous ceramic cup which is in contact with the soil and a vacuum gauge or a manometer connected at the other end above the soil surface. When the tensiometer is filled with water, the manometer or gauge will read zero tension. When such a tensiometer is placed in an unsaturated soil, the soil in contact with the porous ceramic cup will immediately start sucking water through the porous cup wall. The water in the soil pores immediately establishes hydraulic equilibrium with the water in the cup through saturated pores of the cup wall. Water and solutes can f low through the pores of the cup wall but not the air within the working range of the tensiometer. Water could be sucked from the tensiometer by the soil until vacuum created inside the tensiometer is just sufficient to overcome the suction of the soil. At equilibrium, the tensiometer reads directly the amount of soil suction. The outf low of water from the cup is very little. The effective range of the tensiometer is 0 to 0.85 bars depending on quality of the porous cup.

As water enters the soil, air is displaced and the soil pores in the upper part of the profile become saturated. A continuous supply of water leads to an increasing depth of saturation. If the supply of water at the soil surface is cut off then the rapid downward movement of water may essentially ceased within 48 hours. The soil is then said to be at its field capacity. At this stage macropores are drained off but micropores are still filled with water for use by plants. Since it is difficult to draw a boundary line between macro-and micropores and there is no sudden change in the profile drainage rate for many soils, it is not easy to specify a depth and time after which soil water movement is negligible. Therefore, measurements are necessary in each soil to specify the time and depth of sampling after wetting. Special care would be necessary in soils with impeded drainage and sand lenses, which produce perched water tables.

Over most of the wetness range in which plant roots normally function, all the water in soil is controlled by matric forces. A relationship between water content and matric or soil water suction is referred to as water characteristics of the soil. Increase in matric suction is associated with decrease in water content in the soil and the process is known as desorption. On the other hand with decrease in suction soil moisture content increases and this process is known as sorption. The curves showing relationship during progressive intake and withdrawal of water are known as sorption and desorption curves respectively.

Tensiometer is suitable for finding out soil water characteristic at tension values below 2.0 kPa, whereas gas phase pressure is required for higher tensions. A pressure chamber containing a porous membrane or a ceramic plate with all its accessories to provide regulated compressed air is most convenient. A detailed methodology to determine water characteristic curve by pressure plate apparatus is described below.

Water holding capacity of soil is the amount of water that a given soil can hold against the force of gravity. Soil texture and organic matter are the key components that determine the water holding capacity of a soil. Soils with smaller particle sizes (silt and clay) have larger surface area and can hold more water as compared to sand which has large particle sizes and smaller surface area. It is an important hydro-physical characteristic of a soil because it provides simple means of determining useful moisture levels to maintain soil for good plant growth. Detail procedure for determination of water holding capacity of soil using Keen box method (Piper, 1966) is described here.

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

Principle

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

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

Principle

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

Soil aeration signifies the ability of a soil to supply oxygen to actively growing roots and soil organisms. Because of constant biological activity causing oxygen consumption and carbon dioxide evolution, the oxygen present in a soil pore or oxygen renewal by mass flow becomes inadequate to meet the plant demand. A continuous diffusion of oxygen from atmosphere to soil and to plant roots through the wetted pores plays an important role. The oxygen reaching plant roots has to diffuse not only through the gaseous phase in the soil pore and wetted pore neck but also through a water film that is present on the hydrated root surface.Lemon and Erickson (1952) suggested a platinum microelectrode method that simulates the field situation. In this method measurement of the rate of oxygen diffusing through the liquid phase to a reducing surface similar to the plant root.

The ratio of soil air-to-soil water permeability indicates the magnitude of breakdown of structure as a result of wetting. A value of one indicates no change in structure and a value greater than one reflects a deterioration of soil structure.

Principle

The permeability of soil to air can be obtained essentially in the same way as the permeability of soil to water. The measurement of permeability of soil to air involves the preparation and placement of the soil in a suitable container with provision for monitoring pressure differential across the sample and the rate of flow of air through it. For steady state case, this involves measurement of inlet and outlet pressures and the volume flux of air. The suitable form of the Darcy’s equation for calculating permeability of soil to air is:

Soil temperature plays an important role in plant growth. Solar radiation received on the earth surface raises the temperature of the soil surface from morning to solar noon followed by a decline until the next morning. Soil temperature gradients established on the surface lead to flow of heat downwards causing a rise in temperature of lower layers. These variations in temperature affect germination, emergence and further growth of plants. Several types of thermometers such as mercury or liquid in glass, bimetallic, bourdon gauge, thermocouples and electrical resistance have been used in soil research but the use of thermocouples and thermistors has been found most useful. A brief description of different types of thermometers used in measurement of soil temperature is given below:

Liquids in Glass Thermometer

A liquid-in-glass thermometer (Figure 20.1) consists of a capillary glass tube with a bulb at one end filled with a thermometric liquid (mercury), vacuumed and sealed. By reading the position of the liquid level on a scale the temperature value can be obtained.

Garden Rakes

1.For use with moving debris.

2.Aids in the cleaning process.

3.Proper use is with two hands.

Classifications and Nomenclature

Plants can be classified according to the following criteria: (1) botanical, (2) descriptive and (3) agricultural. Botanical classification is based on the morphological characteristics of plants as well as on their anatomy, physiology and DNA sequences. Descriptive classification is based on the environmental adaptation, growth habit and other observable features. In agriculture, plants can be broadly classified as either useful or useless. Those which are useful are called crops while those which are not useful are called weeds.

A common, well-defined system of crop classification is important in crop science and agriculture. Grouping of plants following established systems will simplify plant collection initiatives, research and breeding specialized development efforts. Having standardized botanical names will also facilitate efficient communication, dissemination and retrieval of scientific information. Additionally, the grouping of crops will indicate that these crops may have similar uses, adaptation, growth habits and methods of culture. Classifying crops by family is likewise important in intergeneric grafting. To students of crop science, a list of crops under the various agricultural classifications will be a useful reference in crop names and identification and as a review guide. To the farm manager himself, the same list will offer innumerable benefits in finding alternative crops for specific uses.

Despite these advantages, however, classifications of crops in agriculture vary from place to place and from one country to another due to differences in the primary usage of certain crops, intensity of care, extent of cultivation and other criteria under consideration. It is not uncommon to find crops having two or more classifications, used simultaneously, alternatively or sequentially. FAO(2010) in its report entitled “Crops Statistics - Concepts, Definitions and Classifications”, expressed its difficulty in the collection and presentation of statistical data due to differences in the concepts, definitions, coverage and classifications” of crops which are grown in different countries.

Climate and Ornamental Crops

There are many factors which affect the production of the ornamental crops. It may be internal or external factors. Climate and soils are the chief natural factors on which the success or failure of ornamental crops production is dependent. A knowledge of the effect of various soil and climatic conditions on ornamental crops production is very essential for every prospective to grower, climate includes several factors like temperature, relative humidity, rainfall, wind, hail, light whereas, soil covers such factors as moisture supply texture, pH etc.

Temperature: The rate of development of a plant (the leaf unfolding rate) is a function of temperature. As temperatures increase, the leaf unfolding rate increases. If the temperature exceeds the maximum temperature, plants experience stress and leaf unfolding rate declines. Given the high costs of fuel, many growers are tempted to reduce the greenhouse temperature to save money on fuel. Because the rate of crop development is dependent on temperature, reducing temperatures increases production time of all crops. However, some crops will be more severely delayed than others. Reducing temperatures from 20°C to 16°C increased time to flower of Salvia farinacea by 13 days. This same temperature drop only increased days to flower of pansy by four days. For crops that are severely delayed by lower temperatures, reducing the growing temperature may actually increase total fuel costs for producing that crop. Every plant has fairly well defined range of temperature to which it is tolerant and below which the plants of that variety are liable to be injured to a more or less extent.

Annual flowers are a group of herbaceous plants which grow from seeds, produce flowers, set seeds and complete their life-cycle within one year or one season. They provide a beautiful display of colours in the garden. Whether it is a small home garden or a big public garden, it is incomplete without beds of annual flowers. They enhance the decorative value of a garden within a short span of time. At their blooming time, one feels elated when a rain of beauty drizzles in the garden.

Classification of Annuals

Based on season, the annual flowers are divided into 3 groups—winter season, summer season and rainy season.

Winter season annuals

This group includes a large number of seasonal flowers. The important ones are acroclinium, agrostemma, amaranthus, anchusa, annual carnation, annual chrysanthemum, antirrhinum, arctotis, bells-of-Ireland, brachycome, calceolaria, calendula, campanula, candytuft, celosia, China aster, cineraria, clarkia, cornflower, daisy, delphinium, dianthus, dimorphotheca, echium, eschscholzia, gazania, godetia, helichrysum, helipterum, hollyhock, gypsophila, limonium, linaria, linum, lupin, marigold, matricaria, mesembryanthemum, mignonette, mimulus, myosotis, nasturtium, nemesia, nicotiana, nemophila, nigella, pansy, petunia, phlox, pimpinella, poppy, rudbeckia, salvia, saponaria, scabiosa, schizanthus, senecio, stock, sweet alyssum, sweet pea, sweet sultan, sweet william, venidium, verbena, viola and wall flower.

Climbers can be used to break the bareness of long walls, soften posts, frame doors and windows and beautify window boxes. With a fence or trellis, they can be used for screens, making a background for flower garden or quickly turning an ordinary porch or patio into a private, shady living centre. Some slower growing climbers are useful as container plants for patios. On the down side, most vine species have the potential to become invasive, spreading to areas where they may not be desirable or becoming too large for the intended area.

Types

Climbers are characterized as three types based on how they cling to a support. The kind of support needed depends on whether the Climbers cling by twining stems, orby specialized structures such as tendrils, adhesive disks and aerial roots. Climbers with twining stems wind around a support as they grow (Fig. 5.2). Examples of plant with twining stem sinclude bitter sweet, wisteria and trumpet creeper.Tendrils resemble thread like stems that wrap around any structure they contact (Fig. 5.1). Examples of plants with tendrils include grape, pea, and cucumbers. Some Climbers have specialized structures for clinging to a support with a disk-like suction cup (Fig. 5.3). Examples include Boston ivy and Virginia creeper. Other Climbers cling by means of small, aerial roots that attach to rough surfaces such as mortar, wood, and tree trunks (Fig. 5.4). Examples include English ivy, trumpet creeper and winter creeper euonymus.

Shrubs are usually woody or semi-woody perennial plants; their branches arise from the base of the plants and grow up to the height of 3 to 4 meter. Many shrubs, which are more or less prostrate, make excellence ground flower. Availability of a large number of species & cultivars, a wide range of variation in shape & size of the plants, diversified types of leaves, growth habit, remarkable ranges of size, shape, colour of flowers & the variety of fragrance have made the shrubs as important garden plants. Several species of shrubs have unusually attractive colours.

Most of the shrubs are hardy & grow in all types of soil with little attention. Although some plants flower almost throughout the year, in most cases they are seasonal. A selection can be made in such a way that some plants in the shrubbery will be in bloom in any season of the year. Most of these plants are fairly quick growing and when vegetatively propagated, start flowering in the first year. Plants like Bauhinia acuminata (Kanchnar), Cassia alata (Candle Bush), Vinca rosea,which are usually grown from seeds also produced flowers in the first year.Shrubs can be classified into three groups according to the requirement of the sunlight for growth & flowering:

Bulbs

Floriculturists use the term “bulbous” to include a wide array of perennial plants that grow from underground organs, including bulbs, corms, tubers and rhizomes. Any plant described as bulbous will normally have a swollen root or stem or even leaves underground (Some orchids and other plants have swollen stems – above ground). Bulbs, corms, tubers and rhizomes are perennial plants organ that are part of a plant type called bulbous plants in which part of the plant has evolved into a below-ground storage unit where food created one year is used to nourish the plant in the next. They are valuable in the garden for many reasons. Spring bulbs appear early, before most perennials have started to grow again after the winter. They can also add color to containers when other plants are not ready to face the danger of frost. In summer, bulbous plants such as Alliums and lilies can provide stately interest, while autumn crocuses and tiny hardy cyclamen can cheer up the garden toward the end of the season. The purpose of the bulbous part of the plant is to store food for the plant parts that live above ground to enable the plant to survive adverse conditions. The leaf bases may resemble scales, or they may overlap and surround the centre of the bulb. A modified stem forms the base of the bulb and plant growth occurs from this basal plate. Roots emerge from the underside of the base, new stems and leaves from the upper side. Most true bulbs have their scales closely packed together such as Hyacinthus but some types, such as the Lily (Lilium), they are loose and swollen. Most popular bulbs have a papery skin, the tunic, whose function is to protect the tissues within. Some true bulbs such as the Lily do not have a tunic and are therefore, easily damaged by rough handling. Cardio crinums dies after flowering but other bulbs are perennial. Vegetative reproduction in true bulbs is by means of offsets called bulblets.

The term essential element was proposed by Arnon and Stout (1939).They concluded three criteria must be met for an element to be considered essential. These criteria are:

1.A plant must be unable to complete its life cycle in the absence of the mineral element.

2.The function of the element must not be replaceable by another mineral element.

3.The element must be directly involved in plant metabolism.

The number of elements considered essential for the growth of higher plants now varies from 16 to 20 or more, depending upon the definition of essentiality. Other scientists such as Nicholas (1961) believed that an element should be considered essential if its addition enhances plant growth even though it merely substitutes for one of the 16 elements that Arnon declares to be essential. For example, sodium can substitute in plant nutrition for some potassium and vanadium for some molybdenum, Nicholas would consider both sodium and vanadium as essential, but Arnon would not. On the basis of the criteria used, Arnon specifies 16 elements and Nicholas 20 elements as being essential for the growth of higher plants. Three other debated nutrients are nickel (urea transformations), cobalt (N₂ fixation) and silicon. These criteria are important guidelines for plant nutrition but exclude beneficial mineral elements. Beneficial elements are those that can compensate for toxic effects of other elements or may replace mineral nutrients in some other less specific function such as the maintenance of osmotic pressure. The omission of beneficial nutrients in commercial production could mean that plants are not being grown to their optimum genetic potential but are merely produced at a subsistence level.

Weed is a plant that is growing in the wrong place. Weeds have many mechanisms and characteristics that enable them to compete, having thick waxy cuticle leaves that can be resistant to some chemicals, fast reproduction methods, the ability to reseed in 6 week cycles and deep tap roots enabling the weed to survive in compacted dry ground conditions.

There are many reasons to control weeds in annuals/biennial and perennial ornamentals. Weeds compete with the plants by absorbing essential nutrients and water, or by blocking light or air circulation. Weeds dramatic reduce the growth of the plants. The greatest damage is often done when the weeds and ornamental plants are small. Weeds also interfere with harvesting by physically hindering. They lower flower quality further by harbouring insects, such as whiteflies, thrips mites, slugs, snails and/or diseases.

Growing under optimal conditions for the flower will reduce the ability of weeds to compete against the crop. Controlling humidity/ventilation, water, light, pH, nutrients and temperature all figure prominently in providing flower optimal conditions. A plant health strategy to greenhouse weed control contains three principal elements, prevention/sanitation, evaluation of water quality and using all controls available physical, cultural and chemical. Prevention and sanitation can include the use of mulches in orchidhouse weed control. Rice hulls, perlite, pumice, corn gluten meal bark, Penn Mulch - pelletized recycled paper and human hair have all been used for this purpose. Prevention also includes, eliminating air borne weed seeds from entering the greenhouse by screening vents and other openings and preventing perennial weeds from growing under foundations. A 1-3 meter weed free zone should be maintained immediately adjacent to the greenhouse.

Pruning is a regular part of plant maintenance involving the selective removal of specific plant parts. Although shoots and branches are the main targets for removal, roots, flower buds, fruits and seed pods may also be pruned. Pruning wounds plants, but plants respond differently to wounding than do animals. In plants, damaged areas are covered by callus tissue to close wounds. Another response to pruning occurs inside plants. Chemical boundaries form around wounded areas, walling off or compartmentalizing the wounds. Compartmentalization limits any decay that results from wounding, or from the natural death of branches. Use pruning techniques that minimize plant wounding and speed wound closure.

Lawn

The lawn is a plot of closely mowed grasses. It is composed of thousands of individual plants crowded and forced into a very unnatural growth habit. It is an integral part of the garden. It is basically an area of land planted between gardens covered with grass and other low lying plants.

Lawn is one of the most important features of a garden. A well kept lawn makes a garden look extremely beautiful. It looks like a beautiful green carpet amidst colourful flowers in a garden. Lawn can be called as turf, pitch, field or green depending upon its plantation and usage. Selection of lawn grass depends upon it usage and its season of plantation. Though a well maintained lawn requires a little of patience and care, the final results are always very beautiful and soothing. Scientific reports say that lawns reduce energy consumption through it soothing effects and the green grass prevents soil erosion as well as cut down noise pollution in the urban areas.

Any substance or mixture of substances intended through physiological action, for accelerating or retarding the rate of growth or maturation, or otherwise altering the behaviour of plants or the produce thereof are known as plant growth regulators. It does not include plant nutrients, trace elements, nutritional chemicals, plant inoculants and soil amendments.

Plant hormones are organic compounds other than nutrients, synthesize by plants and regulate plant growth and development. They are active in very low concentrations, produced in certain parts of the plants and are usually transported to other parts where they elicit specific biochemical, physiological and morphological responses. They are also active in tissues where they are produced. The term plant growth regulator is usually used to denote a synthetic plant hormone, but most of the synthetic compounds with structures similar to those of the natural hormones have also been called hormones. For instance, the synthetic cytokinin, kinetin is considered a hormone.

Ornamental pot plants should be potted in small pots according to the size of the plants. Any kind of pot/container which can hold medium and provide aeration is suitable. The most common container is the plastic or clay pots. Plastic pots should be preferred because it retains moisture longer than mud pots. Plants should not be disturbed frequently and re-potting done only when absolutely necessary.

Potting media

Different types of growing media may be used for ornamental pot plant cultivation, but it is crucial that it must retain a certain amount of moisture and be well draining. Different plants require different substrate in which they would thrive. Conditions of the plant experiences in nature should think before choosing the media. Tropical plants require more water naturally compare to subtropical and temperate ones. For irrigating with sprinkling can or hose, it is better to use materials that drain well and decompose slowly while for drip irrigation heavy potting material should be used. The most important thing is to match watering habits to the potting material. Growing conditions play a most significant role in deciding on a medium. If there is no problem in providing a constantly humid environment due to climate or if growing in a greenhouse, the moisture retention on thepart of media is less of a concern. Ambient temperatures play a role here, as well, as warmer temperatures tend to increase the evaporation of water and along with the drying rate of the medium. The personal tendencies and how much time might be spending to water plants is another significant factor in choosing a medium. The combination of potting materials that will work best for garden plants mainly on Plant structure and root structures:

Bonsai is a Japanese art form using miniature trees grown in containers. The first documented evidence of an oriental word for container planting emerged approximately 1600 years ago in China. Bonsai is a Japanese pronunciation of the earlier Chinese term pen zai. A bon is a tray-like pot typically used in bonsai culture. The purposes of bonsai are primarily contemplation (for the viewer) and the pleasant exercise of effort and ingenuity (for the grower). Bonsai is not intended for production of food, for medicine, or for creating yard-sized or park-sized gardens or landscapes. Instead, bonsai practice focuses on long-term cultivation and shaping of one or more small trees in a single container.

The practice of bonsai is sometimes confused with dwarfing, but dwarfing more accurately refers to research and creation of plant cultivars that are permanent, genetic miniatures of existing species. Bonsai does not require genetically dwarfed trees, but rather depends on growing small trees from regular stock and seeds. Bonsai uses cultivation techniques like pruning, root reduction, potting, defoliation and grafting to produce small trees that mimic the shape and style of mature, full-sized trees.

Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species. Which produces true branches and can be cultivated to remain small through pot Some species are popular as bonsai material because they have characteristics, such as small leaves or needles that make them appropriate for the compact visual scope of bonsai. Some of the plants highly suited for making bonsai

Ikebana

Flowers are generally known as the symbol of beauty around the world. Many people stick flowers in vases to wreath their rooms, houses and other places. Japanese FlowerArrangement is essentially different from the Western style of flower arrangement. The western style involves symmetrical arrangement of flowering plants in a vase whereas, the Ikebana, which means “flowers kept alive”, is much more intricate, complex and asymmetric. This style of flower arrangement is one of the famous cultural traditions of Japan known around the world. Generally, all Japanese flower arrangement styles are lumped together as ikebana but we cannot say they are all the same. Ikebana is a disciplined art form in which nature and humanity are brought together. Though it is a creative expression, it has certain rules governing its form. The main rule is that all the elements used in construction must be organic, be they branches, leaves, grasses, or flowers. The artist’s intention behind each arrangement is shown through a piece’s colour combinations, natural shapes, graceful lines and the usually implied meaning of the arrangement. They arrange flowers to recreate nature in miniature to see individual flowers which have been left behind. Ikebana is like one of the ways to communicate with nature. Another aspect present in ikebana is its employment of minimalism. That is, an arrangement may consist of only a minimal number of blooms interspersed among stalks and leaves. The structure of a Japanese flower arrangement is based on a scalene triangle delineated by three main points, usually twigs, considered in some schools to symbolize heaven, earth and man and in others sun, moon, love & earth. The container is also a key element of the composition and various styles of pottery may be used in their construction. Over time, the ways and styles have changed but there is still the basic idea of ikebana remain same.

Plants are important to humankind not only economically, environmentally and industrially but also spiritually, historically and aesthetically, they sustain human life through direct and indirect gains by providing a wide range of products for survival and prosperity. Bio-aesthetic planning to a large extent is a product of the age. With the advancement in agriculture and increase in population, large settlements developed, marking the beginning of urbanization. More and more people moved to urban areas for comfortable life. Increasing human needs resulted in large-scale exploitation of natural resources, great reduction in forest cover and extinction of many species of flora and fauna. The extent of forest cover is a good indication of the health of the land. The large scale deforestation in recent decades has rendered the sensitive catchment areas and hilly areas particularly vulnerable to soil erosion. Professor Lancelot Hogben coined the term ‘Bio-aesthetic planning’ defined as planning of flora and fauna with the object of beautifying the piece of land (country). Bio-aesthetic planning is an aesthetic branch of Horticulture which deals with planting of ornamental plants in such a way that it creates a picturesque effect. It is a very fascinating and interesting subject. With the greater realization of environmental, ecological and socio- economic benefits of plants, scope of Bio-aesthetic planning has increased further. Bio-aesthetic planning can play important role in environmental amelioration of urban and industrial areas along with their beautification.

Landscape Gardening

Landscape gardening is an aesthetic branch of Horticulture which deals with planting of ornamental plants in such a way that it creates a picturesque effect. According to Chambers’ dictionary, the definition of landscape is the appearance of that portion of land which the eye can view at once and landscape gardening is the art of laying grounds so as to produce the effect of a picturesque landscape. Landscape gardening can be defined as the decoration of a tract of land with plants and other garden materials so as to produce a picturesque and naturalistic effect in a limited space. According to Bailey, Landscape gardening is the application of garden forms, methods and materials to the improvements of the landscape and the landscape in this connection is any area large or small on which it is desirable to develop a view or design. So landscape may or may not include plants.

Landscape gardening can also be defined as the beautification of a tract of land having a house or other object of interest on it. It is done with a view to create a natural scene by the planting of lawn, trees and shrubs. Landscape gardening is both an art and science of the establishment of a ground in such a way that it gives an effect of a natural landscape. It can be also defined as the imitation of nature in the garden. It can also be defined as improving of total living environment for the people. In light of all the foregoing definition landscape gardening can be defined more appropriately as art of creating gardens, parks and other green areas.

Landscape design seeks to create balance between living and natural environments in order to derive the greatest use and enjoyment from outdoor space. A landscape to a landscape designer is like a slab of marble to a sculptor or the insides of a home to an interior decorator; a landscape is the canvass on which the landscape designer crafts his or her masterpiece. Since the landscape gardening is the making pictures on the ground with plant and other material, landscape designer should be proficient in art, ornamental gardening, ecology and physiology. He should be an architect and engineer to appreciate the relationship between plant form, colours and buildings.

The term “low-maintenance” refers to a plant that does not require frequent maintenance such as regular watering, pruning, or spraying to remain healthy and to maintain an acceptable aesthetic quality. A low-maintenance plant has low fertilizer requirements and few pest and disease problems. In addition, low-maintenance plants suitable for India must also be adapted to or at least tolerate our poor, alkaline, sand or limestone-based soils. Both native and non-native species are included herein. Also, a variety of plants that are not commonly available in Indian nurseries or garden centres were intentionally included with the hope that increased demand will generate increased supply. Putting the right plant in the right place is of foremost importance in creating a healthy and successful low-maintenance landscape. However, this principle is dependent upon one’s ability to accurately select the right plant species for a given location. Common names are often misleading and sometimes more than one plant species may be referred to by the same or similar common name.