eChapters

Walter Isard had given the location theory in 1956 vided publication entitled, Location and the Space Economy. Isard has modified the Loschian schema, in the attempt to make it more realistic. Isard linked location theory to the general theory of economics through the substitution principle.

In economic theory, capital can be substituted for labour, for example. Similarly, the selection of a manufacturing site from among alternative locations can be viewed as substituting expenditures among the various production factors such that the best site is chosen. (Fig.10.1) provides one simple illustration of Isard’s substitution principle.

This theory belongs to the ‘market area’ or ‘profit maximisation’ approach and has focused on spatial variations in scales potential. August Losch was a German economist and he proposed his theory in 1939 in a book entitled Die taumliches Ordnung Derwirt’s Chaff.

He disregarded spatial variations in production costs by holding them constant, and instead depicted optimal location as occurring where the largest possible market area is monopolised – that is, where sales potential and total revenue potential are maximised. Losch sought to explain the size and shape of market areas within which a location would command the largest revenue.

The social area analysis model of urban structure incorporates all three aspects of city structure, namely concentric zones, sectors and multiple nuclei. It is a more comprehensive statement of urban forms. The model was developed by R.A. Murdie in 1969. According to this model, the physical space of streets, buildings and roads are superimposed by three dimension of social space (Fig. 8.1). The social criteria are the following:

Family Status

Family status indicators include population and age variables, house ownership and age characteristics, family size and marital status and other life cycle. These exhibit a concentric zonal or ring pattern with older, smaller renter households located near the city centre and owner occupied newer larger family households near the outer fringe.

Economic Status

Economic status tends to include measure of income, occupation and education. This portrays a distinct sectoral pattern with definite high income and low income sectors.

Introduction

The search for order in the location and size of settlements continues. Certain geographers examined the size of distribution of settlements and described in graphical form the relationship between the number and size of settlements. Their methods were radically different in that they were not deterministic, rather than making a set of assumptions, deriving a theory and testing it against reality, they observed the size and number of settlements in various countries and noted a common characteristic, which was called the rank size rule. Having once observed this order in the real world, they then sought to explain it. A relationship which is observed on several occasions is called an empirical regularity. The rank size rule is one such empirical regularity.

The rank size rule was first observed by Auerbach in 1913 but was proposed and popularized by G.K. Zipf in his book “Human Behaviour and the Principle of Least Effort”. Since then, many writers have attempted to explain it but the basic aim has always remained the same: to find a graphical description to the size distribution of cities which would apply to the situation prevailing in many countries.

Rank Size Rule: Theoretical Base and Concept

Rank size rule is a theory describing numerical distribution of settlement, which recognises an empirical regularity whereby the product obtained by multiplying a city’s rank by its size is equal to a constant, the population of the country’s largest city such that for a given settlement system

Introduction

The characteristic features of a city are the result of the combination of various factors like topography, climate, history, economy, culture, etc. since these characteristics vary; every town/city is unique and has certain distinctive characteristics. These urban characteristics are, however, never static. They change both over time and space.

With the development of the economy, other factors like population growth, urbanization and improved technology have a combined effect on urban settlements, which grow bigger and more complex. The study of the internal structure of cities by urban geographers is a study of the structural and demographical variations (i.e., variations in building size, shape, height, function and social status) of urban settlement.

Theories on the Internal Structure of Cities

The internal structure of cities has attracted many generalizations in the form of theories. These theories have attempted to explain the city structure by examining cities at any location in a country largely from sociological viewpoint. The different theories on the internal structure of cities are the Concentric Zone theory of Burgess, Sector Theory of Hoyt, the Multiple Nuclei Theory of Ullman, the Social Area Analysis of Murdie and the Exploitative Model of William Bunge.

The scale of human settlements is dynamic; it ranges from farmstead to village to town to city and to metropolis. There is thus, a broad hierarchy of settlements. These hierarchies can be grouped according to size and function. Size hierarchies are ranked from the highest to the smallest settlements only in terms of population while functional hierarchies are essentially based on the extent to which settlements have an economic impact on their surrounding areas. Functional hierarchies rank the settlement according to the number of shops, the number of specialised services available or the most dominant financial organisations. Such hierarchies mayor may not have similar sized market areas. Despite their having the same population, one town might surpass another in functional importance.

In this context, two theories have been propounded-the Central Place Theory by Walter Christaller and its modified version by August Losch. These theories are two of the most important examples of the scientific approach to the study of settlements. These theories suggest that there is a definite link between the functions of a settlement and its spatial locations with regularity in the distribution pattern within an urban system.

The study of crop combination regions constitutes an important aspect of agricultural geography as it provides a good basis for agricultural regionalization. The crops are generally grown in combinations and it is rarely that a particular crop occupies a position of total isolation other crops in a given area unit at a given point of time.

The distribution maps of individual crops are interesting and useful for planners, but it is even more important to view the integrated assemblage of the various crops grown in an area unit.

For example, the demarcation of India into the rice region or wheat region does not explain the agriculturally significant fact that very often the wheat region also has a rice crop and vice versa, or wheat is often grown with gram, barley, mustard, lentil, peas and rapeseed.

For a comprehensive and clear understanding of the agricultural mosaic of an agroclimatic region and for the planning and development of its agriculture, a systematic study of crop combinations is of great significance.

In recent years the concept of crop combination has engaged the attention of geographers and agricultural land use planners. The studies made so far in this field range in approach from topical to regional and vary in extent from small areas of minor political units to the entire country.

The analysis of land use patterns has long been one of geography’s basic concerns. At first, it might appear as if agricultural land use is little affected by relative location, once the factor of a suitable market has been acknowledged. Indeed, the farmer does adapt his land use to site conditions, climate, land forms, and soils.

However, the effects of the market situation cannot be disposed of as easily as all that. Johann Heinrich Von Thunen (17831850), a German economist and estate owner of the early 19th century, developed a theory of agricultural location that is still worth considering.

This model is based on an econometric analysis of his estates in Mecklenburg, near Rostock in Germany. Most of the data used in explaining his theory were obtained by him through practical experience. He attempted to construct a theoretical model of land use pattern, giving a particular arrangement of towns and villages in a situation experienced in Mecklenburg.

The main aim of Von Thunen’s analysis was to show how and why agricultural land use varies with the distance from a market.

Isostasy is derived from the Greek word isostasios meaning ‘in equipoise’ or in a state of balance. American geologist Dutton was the first to use the term isostasy in 1889 for the state of gravitational equilibrium that exists between continents and ocean floor and the mountains, plateaus and plains on a rotating earth, in accordance with densities of their underlying rocks. Dutton was of the view that the height of these different features was related to their density. In other words, the higher features were composed of rocks of lower density and the features of lesser to height were made of rocks of higher density. For instance, the continental blocks whose average height is about 5 kms above the ocean floor are composed of lighter rocks than the latter, and to compensate for their higher height the continental blocks go deeper into the earth so that the continents and ocean basins may remain in equilibrium. The same argument applies to the mountain ranges. The excess mass of lighter materials which rises in the form of mountain chains on the earth’s surface is compensated by light materials extending as roots into the denser strata below. In other words, the upper part of the earth’s crust is built of lighter rocks which is floating on the substratum of denser rocks. The hypothesis of the sialic rocks floating over the sima of the sub-stratum had been first put forward by Sir George Airy of Britain in 1855. The use of the word floating, of course, did not imply that the sub-stratum was in a liquid condition.

The possibility of the drifting of continents was first suggested by the French scholar Antonio Snider in 1858, but this was so much opposed to the scientific view then prevailing that nobody took notice of it. In 1910 F.B. Taylor of America invoked the hypothesis of horizontal displacement of continents or continental drift with a view to explaining the distribution of mountain ranges, but for various reasons the hypothesis of Taylor received scant attention. German Professor Alfred Wegener was the first to put forward this idea in the form of a theory in 1912 and published a detailed discussion of it in 1915. But an account of the First World War (1914-18) this could not attract the attention of many scientists. In 1924 an English translation of Wegener’s book was published. Since then it has attracted much attention and publicity, and a huge literature has grown around this theory.

Wegener was primarily a climatologist and the main problem he wanted to explain was the change of climates in the geological past. There are several geological evidences to show that there have been important and large scale changes in the climates of the world in the geological past. The occurrence of coal in the cool middle latitudes indicates that the climate of these regions was hot and humid in the carboniferous times and the natural vegetation was dense forest which ultimately resulted in the formation of huge coal deposits. On the other hand, in India, South Australia, Brazil or South Africa where the climate is warm today, there are evidences of cold climate and the presence of glaciers in the carboniferous period. The only conclusion that can be reached from this is that either the climatic zones have moved or if they have not, then there has been movement of the landmasses. There are several difficulties in postulating shifts in the climatic belts of the world as their geographical distribution is governed primarily by the sun. It, therefore, appears to be more probable that the landmasses have changed their position.

Weed Management

The productivity of crops much depends on intercultural and weeding operation. The efficient management practices ultimately increases the yield level. The productivity is much dependent on various attributes starting from the variety, climate including human resource management and other factors known well to the farmers. It is estimated that nearly 30-50 per cent of the crop is lost due to weed menace in the agricultural fields. The farmers use various methods of weed control like cultural, mechanical, chemical and manual means. Encompassing all these control measures is known as integrated weed management.

Shifts or changes in the abundance and types of weeds within agricultural systems are common. These shifts can occur for a number of reasons and may result from cultural, mechanical, or chemical weed management strategies. The right combination of weeds and relying too heavily on any one practice is often the most common cause. Some of the concepts associated with weed species shifts are discussed below.

A weed shift is the change in the composition or relative frequencies of weeds in a weed population (all individuals of a single species in a defined area) or community (all plant populations in a defined area) in response to natural or human-made environmental changes in an agricultural system. Weed shifts occur when weed management practices do not control an entire weed community or population. Some species or biotypes are killed by (or susceptible to) the weed management practice, others are not affected by the management practice (tolerant or resistant), and still others do not encounter the management practice (dormant at application).

Those species that are not controlled can grow, reproduce, and increase in the community; resulting in a weed shift. Any cultural, physiological, biological, or chemical practice that modifies the growing environment without controlling all species equally can result in a weed shift. Weed shift may be due to introduction of new species or change in relative proportion of members of the existing community. Latter is the most common.

A. Species shift: Change in density of one or more species in field

B. Biotype shift: Change in density of biotypes within a species. These shifts often found noticed since biotypes typically are similar in appearance. Herbicide resistantbiotypes are the most frequently studied.

Resistance

The intensive and continuous use of herbicides over the last five decades has resulted in the development and evolution of weeds resistant to the normally phytotoxic chemicals. Although herbicide resistance was reported as early as 1957 against 2, 4-D from Hawaii the first confirmed report of herbicide resistance was against triazine herbicide in common groundsel (Senecio vulgaris) was reported in l968 from U.S.A. Over the years, more than 150 weed species have been identified as having developed biotypes resistant to at least one or more herbicide classes. Resistance to at least 15 classes of herbicides have been noted. Moreover, the area of land infested with resistant weeds is increasing rapidly. Reports of evolution of newly resistant biotypes continue to emanate from all over the world, including developing countries, e.g., India, where extensive use of herbicides in grain crops began only in the late 1970s. These reports indicate that herbicide resistance problems are accelerating and, consequently, management of weeds is becoming increasingly more difficult and complex.

The phenomenon of herbicide resistance in plants, especially in weeds, is analogous to the evolution of changes that arise in insects and pathogens in response to the continuous use of insecticides and fungicides. Herbicide resistance is the result of selection for traits that allow weed species to survive specific herbicide usage, which would otherwise cause mortality. Herbicide resistance contributes a trait of resistance within the plant species to a herbicide and resistant weeds are those plant species that express the genetic variation required to evolve mechanisms to escape control. Like other crop pests (insects, pathogens, etc.) with reference to pesticides (insecticides, fungicides, etc.), herbicide-resistant weeds are the result of intensive selection pressure in weed populations.

Generally, resistance is defined as the ability of a plant species to withstand the phytotoxicity of a chemical. This is the trait normally found in crop plants, as against weeds, thus forming the basis for herbicide selectivity. Crop resistance to a herbicide is often different from the one that exists in the phenomenon of herbicide resistance in weeds.

Herbicide resistance in the context of weeds is defined as a characteristic of the weed species to withstand a herbicide dosage substantially higher than the wild type of the same plant species can withstand. It is the inherent or acquired ability to withstand the dosage of herbicide normally used for satisfactory weed control. Resistant weed populations are unharmed by a concentration of herbicide that completely kills all unselected populations. This herbicide concentration is the one that in field practice produces an effective kill.

Herbicide susceptibility represents the other end of the scale, encompassing natural variability in sensitivity to herbicides within the unselected populations. Tolerance, on the other hand, indicates reduced susceptibility (or conversely enhanced resistance) which may sometimes result from selection by herbicides. It is a response rather less than 100% survival accompanied by zero reduction in growth at herbicide concentrations, which normally give 100% Kill of susceptible biotypes. Tolerance may also be considered the natural or normal variability of response to-herbicides that exists within a species and can easily and quickly evolve.

Persistence of Herbicide in Soils

Most of the herbicides are applied to soil as pre-emergence for weed control under different situations. For effective weed control, herbicides must remain in soil in active and available form until their purpose is served. Larger persistence poses hazard to subsequent land use and is undesirable. The length of time that an herbicide remains active in the soil is called persistence or soil residual life. The quantity of herbicide that remains in the soil after its mission is accomplished is referred as residue. The term residue infers the continued presence of herbicide in the soil in very small quantities even though it may not be present in herbicidal quantities or available for plant absorption. Herbicide residues in soils are undesirable mainly because they may

Injure sensitive crops in a cropping system,

Be absorbed by succeeding crops and residues accumulated in unlawful amounts in the produce,

Result in building up of herbicide residues following repeated treatments that exceed their rate of dissipation, and

Inhibit growth of soil micro-organisms.

Knowledge of persistence and carry over residual effect of herbicides is essential to use them safely and effectively. Persistence of herbicides in soils pose hazard when

Highly persistence herbicides are used,

Crop failure necessitates replanting,

A susceptible crop follows a short term crop which received a persistence herbicide, and

Decomposition of the applied herbicide proceeds very slow.

Herbicide Mixtures

A mixture of two or more herbicides could be more effective for controlling different weed species. In horticultural and plantation crops, weed free situation is needed during the entire year over several years. In such situations, herbicides are to be rotated to take care of all the species of weeds. A mixture of herbicides, due to chemical reaction, may enhance or reduce the efûciency of one or more compounds. Hence, knowledge of herbicides interactions is essential for efûcient use of herbicides in weed control.

Mode of Action

The term mode of action refers to the sequence of events from absorption into plants to plant death. The mode of action of the herbicide influences how the herbicide is applied. For example, contact herbicides that disrupt cell membranes, such as acifluorfen (Blazer) or paraquat (Gramoxone Extra), need to be applied post emergence to leaf tissue in order to be effective. Seedling growth inhibitors, such as trifluralin (Treflan) and alachlor (Lasso), need to be applied to the soil to effectively control newly germinated seedlings.

To be effective, herbicides must 1) adequately contact plants; 2) be absorbed by plants; 3) move within the plants to the site of action, without being deactivated; and 4) reach toxic levels at the site of action. The application method used, whether pre-plant incorporated, pre-emergence, or postemergence, determines whether the herbicide will contact germinating seedlings, roots, shoots, or leaves of plants.

Mode of Action of Herbicides

Herbicides perform a vital role in the management of weeds. As the name indicates, herbicides are chemicals that kill or control vegetation. Although the ultimate effect of most herbicides is the same (usually death of weed), the way they control weeds is vastly different. Physiologists use the term mode of action to describe the way the herbicides affect weeds. It includes the entire sequence of events that occur from the time the weed absorbs the herbicide to the final plant response (usually death). The term mode of action is the broad term under which all aspects of herbicidal action including the mechanism of action is included, while the mechanism of action refers to only the biochemical and biophysical responses of plants that appeared to be associated with herbicidal action.

Thus, mode of action includes absorption, translocation to an active site, inhibition of a specific biochemical reaction, degradation or breakdown of the herbicide in the plant and soil and the effect of the herbicide on plant growth and physiology.

Although two herbicides may differ chemically, they may still possess the same mode of action example trifluralin (a dinitroaniles herbicide) and propanamide (an amide herbicide) are inhibitors of microtubule/spindle apparatus. Each herbicide family (class or group) has a primary site of action which may be different in its action from others example sulfonylureas herbicides are ALS or AHAS inhibitors while glyphosate and sulfosate are ESPS inhibitors. Some may have more than one site of action, but the mostinhibitory of these will be affected first. The other site(s) may be considered secondary. Fluometuron, a urea group herbicides act by inhibiting photosynthesis at photosystem II and carotenoid biosynthesis.

Herbicide Application

Generally, herbicides are applied in the form of solution or granules. Of the two, spraying solutions of herbicides formulated as wettable powders, soluble powders and emulsifiable and solution concentrates is more common. When herbicides are formulated as granular or encapsulated materials, they are applied by hand or with the help of a granular applicator.

History on Classification of Herbicides

Copper sulphate (CuSO₄) was the earliest inorganic salt used as selective herbicide for controlling dicot weeds in cereal crops during 1896 in France, Germany, and USA. Sulphuric acid (H₂SO₄) was used as herbicide in cereals during 1909. In selective killing action depends on the fact that it runs off the leaves of the cereals and scorches rough surfaces of certain seeds. Sodium chlorate (NaClO₃) under the name mort-herbs is used in France for killing deep rooted perennials. Another non-selective herbicide, ammonium sulphamate (NH₄SO₃NH₂) was introduced in 1945 as ammate for the control of woody plants. Organic herbicides are more effective and selective.

Classification of Herbicides

Classification of herbicides is modified periodically as and when new herbicides are developed. Herbicides are classiûed based on their method of use (soil and foliage applied), mode of action (systemic or translocated and non-systemic or contact herbicide) and chemical key structure (aliphatic-aromatic, dinitrophenal, etc. Some herbicide molecules contain more than one classifying key structure and they are put into the group most likely to be contributing activity.

Any approved herbicide is known by three names: common name, chemical name and trade name. Common name of herbicide is a technically accepted abbreviation of its chemical name. Chemical name reads out its full molecular structure. Trade names refer to their formulations offered by the chemical companies for the consumers.

Herbicide History and Development

Common salt, ash, smelter waste, and like cheap materials have been used for centuries to control weeds on roadsides, fence rows, and pathways. But Chemical weed killing was born in 1896 when Bonnet, a French grape grower, observed that the Bordeaux mixture which he used against downy mildew of grape turned the leaves of Sinapis arvensis (a weed) black. Soon it was found that copper sulphate present in the Bordeaux mixture was responsible for its weed killing effect. Further tests in France, Germany, and U.S.A. established that copper sulphate could indeed be used for selective control of broadleaf weeds in small grains; wheat, barley, and oat. Between 1896 and 1908, several other inorganic salts, as also sulphuric acid, were found selective to small grain cereals. Of these, in Europe, a 6 to 10 per cent solution of sulphuric acid continued for considerable time as a satisfactory herbicide for broadleaf weed control in cereals, but it corroded the containers and sprayers. In the U.S.A., salts like sodium chlorate, carbon bisulphide, sodium arsenite, kainite, and calcium cyanamide were developed for non-selective eradication of perennial weeds, particularly, Convolvulus arvensis ‘field bind weed’ and Cirsium arvense ‘Canada thistle‘. In Hawaii, sodium arsenite solution was found highly effective for weed control in sugarcane plantations. Between 1930 and 1940, some boron compounds, thiocyanates, dinitro phenols (DNC and DNBP), ammonium sulphate, and certain mineral salts were developed in the west for selective and non-selective weed control. DNC and DNBP wereused extensively in Europe in small grains for broadleaf weed control, even though these chemicals dyed the hands and clothes of the users to yellow colour, almost permanently. Further milestones in weed control were introduction of organic chemical, 2-methyl-4, 6-dinitrophenoll (DMOC), in 1932 and discovery of hormone type selective weed killers. Selective residual chemicals such as substituted phenyl ureas and triazines, and non-residual chemicals diquat and paraquat are more recent discoveries.

The discovery of the herbicidal activity of 2, 4-D (2, 4-dichlorophenoxyacetic acid) first synthesized in 1941, triggered the development of modern herbicide technology. 2, 4-D proved to be an outstanding herbicide.

Integrated Method of Weed Management

Definition

1. An integrated weed management may be defined as the combination of two or more weed-control methods at low input levels to reduce weed competition in a given cropping system below the economical threshold level. It has proved to be a valuable concept in a few cases, though much is still to be done to extend it to the small farmers’ level.
2. When more than one method is employed for controlling weeds, it is termed as integrated method weed management.

FAO Definition

It is a method whereby all economically, ecologically and toxicologically justifiable methods are employed to keep the harmful organisms below the threshold level of economic damage, keeping in the foreground the conscious employment of natural limiting factors.

IWM is the rational use of direct and indirect control methods to provide cost-effective weed control. Such an approach is the most attractive alternative from agronomic, economic and ecological point of view.

Methods of Weed Control

Prevention, eradication and control are the fundamental principles of weed control.First basic step is to prevent the infestation of a weed(s) in a locality in order to avoid their further spread. If one fails in preventing spread of weeds, eradication step must be adopted. Eradication is limited on a very small scale and adopted only when suitable methods of complete weed removal are available as eradication is cent per cent control of weeds alongwith its root system and other propagative parts. Further, if one fails in prevention and eradication techniques then different weed control methods must be strictly followed in which the objective is to bring down the weed population (with any method) to a level that economical crop yields are possible. The aim of each weed control method is to achieve reasonable good control of weeds. Following methods for controlling weeds are very common:

Preventive Methods

Try to prevent spread of weed seeds/vegetative parts with the adoption of following preventive techniques.

Weed monitoring is conducted to detect significant weed problems, rank them for relative severity and sort them by management type annuals, biennials, perennials, grasses and broadleaves. Weed monitoring provides information to tailor weed management efforts that reduce the impact of the weeds. The primary objective of weed survey and mapping is to accurately identify and delineate land with populations of unwanted plants. These surveys are conducted so that scientists and managers can predict those areas potentially subject to weed invasion; understand the biology of the invasion process and determine means by which weeds spread; develop, implement and evaluate weed management plans; assess the economic impact of weed invasion and increase public awareness, education and weed management efforts. Weed survey information is collected and compiled into maps showing the distribution and severity of infestation. Weed monitoring involves repetitive surveys to track weed populations over time. A standardized system of weed surveying and mapping is necessary to provide consistently reliable information that can be compared from year to year. Further, a standardized system allows weed survey data to be incorporated into a state wide weed survey database for the production of state wide noxious weed maps.

Weed Ecology

Ecology is the study of reciprocal relationship between organisms and their environments. The ecology of weed is thus concerned with growth characteristics and adaptations that enable weeds to exploit the ecological niches left open in those environments altered by man for his use and the survival mechanisms where by weeds persist in such environments. In simple words weed ecology is reciprocal relationship of weeds with their environments. Weeds grow voluntarily in all crops raised by human beings since ancient ecology of weeds is divided into two categories (types).

1. Weed Auto Ecology

It is study of only one population i.e. how an individual species in a population interacts with its environment at all stages of its life cycle. So, in case of auto ecology competition within same species (intraspecific) or with crop plants (inter specific competition) is studied.

2. Weed Synecology

The study of relationships between communities of different weed species with their environment is called weed synecology. Different weed species grow in certain combinations and in specific patterns in the ûeld. The population of different weed species interact with the external environmental conditions and among themselves. Weed communities differ from field to field and crop to crop in the same locality. The community character is dynamic and changes in form and composition of weed flora takes place in course of time due to some external and internal factors prevailing in the community. This process is called ecological succession. With the passage of time there will be series of changes in the composition of weed community which ultimately results in stable community. This is termed as climax community.

Weed Biology

Weed biology is the study of the establishment, growth, reproduction, and life cycles of weed species and weed societies/vegetation. Weed biology is an integrated science with the aim of minimizing the negative effects, as well as using and developing the positive effects, of weeds.

Life Cycle - Based on life cycle weeds are classified as annuals, biennials or perennials.

Annuals

Annuals complete their life cycle from seed in less than one year. There are two types: summer and winter annuals. Summer annuals germinate in the spring, mature, produce flowers and seeds and die before fall. Winter annuals germinate in the fall, overwinter in a seedling or rosette stage, mature, produce flowers and seeds, and die in the spring or early summer. Because of the seedling stage, annual weeds are generally easy to control. There are usually few annual weeds present in low bush blueberry fields.

Biennials

Biennials generally complete their life cycle over two years. The first year the seeds germinate and form a basal cluster of leaves and a tap root. The plant overwinters in this stage. During the second year the weed produces a flower stalk, sets seed and dies. Examples of biennial weed are evening primrose and wild carrot.

The association of weeds with field crops was started when ancient man started cultivating plants as crops commercially. However, type of weed flora went on shifting with the passage of time, due to changing climatic conditions, cropping pattern, agronomic practices, crop cultivars etc. When crops are cultivated invariably a variety of volunteer undesirable vegetation come up simultaneously which competes with the crop for all growth factors viz., nutrients, soil moisture light, space etc.

Definition of Weed

Weed is a plant that originates under a natural environment and in response to imposed and natural environments, evolved and continues to do so as an interfering associate with our desired plant and activities.

Weed is a plant growing out of place. They are unwanted not useful, persistent and prolific, effectively competing with the beneficial and desirable crop plants for space, nutrients, sunlight, and water, interfere with agricultural operations and thereby reducing the yield and quality of produce.

Weeds are unwanted and undeserved plants that interfere with the utilization of the land and water resources and thus adversely affect crop production and human welfare. Thus a plant out of its place or a plant growing where it is not desired is a weed. This definition was given by Buchholtz in 1967. E.g. Bajra is a weed in pulse, pulse is a weed in bajra, tomato is a weed in brinjal field. Weed is defined as the unwanted, undesirable plant growing out of their proper place which interfere with the utilization of natural resources, prolific, persistent, competitive, harmful and even poisonous in nature and can grow in adverse climatic conditions (Jethro Tull: Father of Weed Science).

Weediness: Weediness is defined as the state or condition of a field, flower beds, lawns and so forth in which there is an abundance of weeds.

Weeds are plants that are unwanted in a given situation and may be harmful, dangerous or economically detrimental. Weeds are a serious threat to primary production and biodiversity. They reduce farm and forest productivity, displace native species and contribute significantly to land and water degradation. The costs of weeds to the natural environment are also high, with weed invasion being ranked second only to habitat loss in causing biodiversity decline.

Growth: Growth involve cell division subsequently cell elongation. Increase in volume that is associated with fruit growth largely result of cell division or cell elongation or both. In some fruit such as apple, extension of intercellular space may also contribute the growth. Generally growth by cell division in early stage whereas, cell elongation during later stage.

Two distinct type of growth curve are observed when increase in such variable such as fresh weight, volume and dry weight of fruit.

1. Single sigmoid curve
2. Double sigmoid curve

In case of single sigmoid growth curve firstly there is rapid increase in size then after decline so there is only one rapid growth is observed e.g. Apple, pear, tomato, cucumber and strawberry.

In case of double sigmoid two rapid growth period are separated by an intermediate period that is less growth or no increasing growth curve. Double sigmoid growth curve can be used as two successive sigmoid curve thus there are three clearly define stage of growth.

Jam: Jam is a product made by boiling fruit pulp with sufficient sugar to a reasonably thick consistency. Jam is mainly prepared by apple, pear, sapota, apricot, peach, papaya, karonda etc. It can be prepared from one kind of fruits or from two or more kind of fruits. In general jam contains 0.5-0.6% acid and invert sugar should not be more than 40%.

Drying- Removal of water from product by influence of non conventional energy source like sun and wind.

Dehydration- Process of removal of moisture by the application of artificial heat under controlled condition of temperature, humidity and airflow etc.

Advantage of dehydration over sun drying

The process of dehydration is much more rapid than sun drying.

Dehydration requires less floor area.

Dehydration is done under very hygienic condition.

Sun drying is not possible in cloudy weather or during rain while dehydration or mechanical drying is not dependent on weather.

The colour of dehydrated or mechanically dried fruit and vegetable remain uniform due to uniform drying temperature.

Canning: Canning is the process by which sealing of the food product and sterilizing them by heat for long storage is known as canning.

History: The term canning was first invented by N. Appert (1804) in France. In honour of the inventor canning is also known as appertization (Appart is known as the father of canning) and Saddington (1807) in England first described the method of canning. Peter Durand (1810) got first british patent on canning of food in tin container and William under wood introduced canning of fruit on a commercial scale in U.S.A.

Principle of canning: The main principle of canning is destruction of spoilage organism by means of heat.

Proper handling, packaging, transportation and storage reduce the post harvest losses of fruits and vegetables. For every one percent reduction in loss will save 5 million tons of fruit and vegetable per year. Processing and preservation technology helps to save excess fruit and vegetable during the glut season (off season). The technology has become a necessity to improve the food safety and strengthen nation’s food security. The technology helps to boost export of agricultural commodities in the form of preserved and value added products e.g. mango, pineapple, citrus, grapes, tomatoes, peas, potato and cucumber being processed on a large scale.

Principles and Methods of Preservation of Fruits

Preservation: Preservation means just protect the foods against the spoilage, but scientifically it may be defined as a science which deals with the process for prevention of decay or spoilage of the food is called preservation. In other words, just controlling the physical, chemical or microbial changes in the foods is called preservation.

Climbers

Climbers are group of plants which have weak stems and ability to climb up the support with the help of modified organs for sunlight and air, twiners differ from climber in the way that they do not posses such modified organs but twine around the support cover it and reach the top. Climber are woody or herbaceous plant which climb up the trees and other tall objects with the help of support of their special modified organ, such as tendrils, root, thorns, rootlets, hooks etc.

Tendrils- Bigonia gracilis, Clematis paniculata etc.

Thorns- Bougainvillea species, Climbing roses etc.

Rootlets- Ficus repens etc.

Hooks- Gallium aperine, Rubus australis etc.

Climbers and twiners are important group of plants. Climbers and twiners add the beuty, colour or fragrance in the garden and artificial structure like garden wall, topiary, arches, pergola etc. are made with the help of climbers.

Trees

A trees is a woody perennial plant with clear stem or trunk. Trees trend to be long leaved living up to several 100 year.

TREE- logical meaning of each letter

T - Temperature and micro-climate moderation.

R - Removal of air pollutant.

E- Erosion control.

E - Energy conservation.

Annuals Border

In this type of border annuals are planted according to their height to beauty of the garden. Annuals border are found two types.

• Single face border.
• Double face border.

Single face border- In this type dwarf plant is kept on front of beds, medium height annuals are planted in the centre while the taller annuals are planted in the back.

Double face border- In this type tall annuals are planted in the center and medium and dwarf annuals are planted in both sides of tall annuals so that full view can be seen from both side.

Annuals

Annuals or seassonals are the group of plants which complete their life cycle in one season or in one year. Annuals are commonly known as seasonal as they complete the process of life like germination, growth flowering and seed formation in one season and finally the plant without. Annuals are widely used for garden decoration, cut flower and pot plants. They are frequently grown as bedding plant and in rock garden on the sides of lily pool and in shrubberies.

Garden Walls : A garden lover will never like to block the view of his garden by putting a wall along its periphery. A garden as it is enjoyed from inside should also be visible from outside.

• Low brick or concrete or stone wall of say 60-90 cm height and to put over it some grills.
• Alternatively walls from 1.8-5.0 m may also be erected depending upon the size of garden.
• One may grow creepers such as Ficus repens over the wall.

Flower Beds: The most essential criterion of a flower beds is display the flowers in the best way possible. It may be born in mind that flowers look best when massed in a bed. The flower beds are of special importance under condition of the plains of India since they can be kept planted throughout the year unlike those in England or other parts of Europe where nothing can be grown in the open between November-March. Annuals and herbaceous, perennial flowers, flowering plants are grown in flower beds to provide massing effect of different colours borders is continuous beds of more length than width containing plant of one kind only.

Hedge

When shrub is planted on boundary for fencing, it is also called as hedge. In other word shrubs or trees planted at regular intervals to form a continuous screen is called a hedge. It may be ornamental or protective or both. Hedge also become an important feature of formal layout to serve various function as screening of the area out building, tennis court, vegetable garden, hardening of unwanted place etc. All the shrubs cannot be planted for making an ideal hedge due to different nature of growth.

Garden

Garden is a place where vegetables, fruits and ornamental plants are grown mainly for recreation. The garden incorporates both natural and man-made materials.

Types of garden

The major garden types which shall be discussed are: English garden, Mughal garden, Persian garden, Italian garden, French garden, Japanese garden etc. Out of these the Mughal, Persian, Italian and French styles fall in the category of formal gardens, whereas the English and Japanese gardens are classified in the informal style of gardening.

Lawn

Lawn is a natural green carpet, and it is important feature of a landscape and a garden without a lawn is not considerd complete. Lawn is an area of land closed mowed grasses it is primarily developed for aesthetic and recreational purpose. A lawn is an integral part of a garden and landscape besides aesthetic and recreational purpose and several other purposes. Lawn provides a place for taking rest after tiring of the day, holding parties, social functions, passive and active recreation. Distinguishing characteristic of turf grasses is the ability to with stand close mowing and still providing a functional dense healthy ground cover. Lawn is also called as heart of garden. Lawn can be called as turf pitch a field, sod, yard, are green depending upon the plantation usage continent. Lawn is a ground cover of perennial grass, ditch, persists enclose mowing and require proper management practice.

J.B. Olcoth designed first experiment in lawn grass at Monchester in USA in the 19th century. Festuca and Agrostis species were used to make turf (Lawn) during 1880 in U.K. In the early 19th century lawn become wild spread out side of parks golf course. Now a day in many metro cities of India lawn has become a cultural of the passion of many homes.

The planning of a garden is an art. It is said that a poet is born, and in that sense a garden architect is also born. But that does not mean that a garden architect has nothing to learn. On the contrary he should learn enough of geology, geography, garden history, styles of gardening, and above all should have a profound knowledge about plants. It is imperative to know at the outset what is meant by landscape gardening. A landscape may be defined as any area, either big or small, on which it is possible or desirable to mould view or a design, whereas landscape gardening may be described as the application of garden forms, methods, and materials with a view to improving the landscape. The art of designing is known as “landscape architecture,” although the older term landscape gardening” is also popular.

Before discussing the principles of gardening in detail, it will be worthwhile to make some useful suggestions. The first and the foremost thing are not to imitate another garden which has secured a prize in a competition. One has to develop one’s own design giving due consideration to the local conditions. One more mistake which is commonly made is to plant many more specimens than a garden can accommodate causing overcrowding. In a landscape garden any difference in levels has to be taken advantage of, but in a perfectly flat land it will be costly to create artificial undulations. In each garden the care should be at least one feature or there be a second these two should harmonize with each other. Before planning a design are must be sure for what purpose the garden is utility or beauty or both.

Vegetable crops: A seed is borne on fruit and fruit is a mature ovary and ovary is a typical part of flower. Flower in angiosperm, consists of four parts these are calyx/sepal, corolla/petals, androecium/stamens and gynocium/pistil, outer whorl of flower is collectively referred to as calyx. The individual components of calyx are called as sepal. Petals are collectively referred to as corolla. Petal is a unit of second inner whorl after sepals. Stamen is part of flower bearing the male reproductive parts composed of anther and filaments. Pistil is part of flower bearing the female reproductive parts composed of stigma style and ovary.

Seed Production Techniques in Vegetable Crops

Share (%) of F₁ hybrids- Cabbage 85%, Watermelon 70%, Okra 23%, Tomato 80%, Chilli 80%, Cauliflower 50%. Among the Asian countries, India is the 2^nd largest production of hand pollinated hybrid seed in vegetables.

The purpose and the mode of marketing of vegetables determine the type of vegetable gardening. The various types of vegetable gardening are as follows.

Home or Kitchen gardening

Market gardening

Truck gardening

Processing gardening

Vegetable forcing

Seed production gardening

Floating vegetable gardening

Seed

A seed is a mature ovule consisting of an embryo together with stored food, all enclosed by a protective coat. It is product of the ripened ovule of gymnosperm and angiosperm plants which results as a consequence of fertilization and some growth within the mother plant formation of seed completes the cycle of reproduction. The embryo develops from zygote and the seed coat from the integument of ovule. A seed has three main parts these are seed coat, endosperm and embryo. Embryo includes the root, the cotyledon and embryonic leaves. Seed is located inside fruit and a fruit is a mature ovary. In broad sense any plant part which is used for commercial multiplication of crop is called seed. Thus in case of potato stem and tuber are also known as seed. Improved seed results in (1) Better germination (2) Vigorous seedling growth (3) Higher crop stand (4) Better quality of produce (5) Ultimately in higher crop yield.

Development of seeds: Successful pollination and fertilization are the prerequisites to produce a viable seed. During pollination the pollen grains are transferred from anther to the stigma and get stuck there in the sticky fluid secreted by the stigma. The fluid contains sugar which induces germination of pollen grains. The pollen tube grows downward through the style in the ovary until it reaches the embryo sac and discharges two male gametes-one is fused with a female gamete and forms the zygote (2n) and the other is united with two pollar nuclei to produce endosperm (3n). The zygote develops and gives rise to embryo embedded in nutritive tissue developed from endosperm. The nucellus tissues surrounding these structures provide necessary energy for their proper development. Like fruit, the seed also exhibits sigmoid and sometimes double sigmoid pattern of growth. Various changes occur during the course of seed development and the sequences of development may vary from species to species keeping the basic theme unaltered.

Seedlings of several vegetables are first raised in well prepared nursery beds, followed by transplanting in the field. Raising of seedling in the nursery beds is economical as well as easier to take care of young, tender seedlings against pest and diseases. Further, raising of seedlings in nursery allow more time for land preparation.

Site and soil for nursery

In selecting a site for nursery beds, following points should be considered viz sunny situation, good drainage and irrigation facilities. Sandy loam soil with plenty of organic matter are ideal for starting nursery beds. In case of heavy soils it is desirable to add coarse sand to modify the soil condition. Before sowing seed it is essential to sterlize the beds by steam or formaldehyde or any other chemical to do away with problem of damping-off disease. Burning of leaves or straw in the beds is quite helpful in controlling certain soil borne diseases and pests.

Physiological disorders are abnormalities in plants which are associated to non-pathogenic factors. A plant or its parts may show unusual growth, function or deformity. Such abnormalities are widely referred to as disorders. These may be incited by nutrients deficiency or excess, hormonal imbalance, abnormal growing conditions etc. Some commonly observed disorders have been dealt in here suitably.

The current status of advances in fruit breeding is through the development of different scientific approaches augmented by ever-increasing knowledge and application of genetics, statistics and biotechnology. These innovative approaches very specific for a species in most of the cases, are the major tools of the fruit breeders to tackle the different objectives of fruit improvement programme at present Fruit improvement is a very slow process due to the long generation cycle varying from species to species, thereby reducing the chances of exploiting genetic recombination. Besides this factor, most of the fruit species are either highly heterozygous or polyploidy in nature. Due to this reason the asexual propagation of fruit plants is a conventional means while wide segregation occurs upon sexual reproduction. Such expectation is not unlikely because the types selected as commercial varieties are definitely to be vigorous ones, and a positive correlation exists between vigour and heterozygosity.

This discussion on breeding of fruit plants involves different aspect of the species concerned is so essential as well as fundamental that discussion of them must procede any consideration of breeding methods themselves. The plant species are grouped into two-self-pollinated and cross-pollinated. These two groups have emerged on the basis of pollination mechanism which plays significant role in the method of breeding application. To emphasize the difference in the reproductive systems of these two groups one should know the details about floral biology, mechanism of pollination control, reproduction by asexual and sexual means and self and cross-pollinated plants.

The quantitative increase in plant body such as increase in the length of stem and root, the number of leaves etc., is referred to as plant growth whereas, the qualitative changes such as germination of seed, formation of leaves, flowers and fruits, falling of leaves and fruits is referred as development. Utilization of these substances for proper development of the plant is regulated by certain chemical messengers called plant growth substances or plant growth regulators, which in minute amounts increase or decrease or modifies the physiological process in plants. Plant growth substances are the chemical other than nutrient which required in very small amount but without which plant can not complete their physiology.

The two sets of internal factors, viz., nutrition and hormone control the growth and development of the plant. The raw material required for growth is supplied by nutritional factors which include the minerals, organic substances the protein, carbohydrates, etc.

Phytohormones: These are the hormones produced by plants which in low concentrations regulate plant physiological process. These usually move within the plants from a site of production to a site of action.

Plant growth regulators: These are organic compounds other than nutrients, which in small amounts promote, inhibit or otherwise modify any physiological process in plant.

It may be defined as any organic compounds which are active at low concentrations (1-10 ml) in promoting, inhibiting or modifying growth and development in plants. The naturally occurring (endogenous) growth substances are commonly known as plant hormones, while the synthetic ones are called growth regulators.

Plant hormones: It is an organic compound synthesized in one part of plant and translocated to other parts, wherein very low concentration causes a physiological response.

The plant hormones are identified as promoters (auxins, gibberellin, and cytokinins), inhibitors (abscisic acid and ethylene) and other hypothetical growth substances (Florigen, death hormone, etc.).

Bearing

Bearing is connotation of flowering and fruiting. When a fruit tree flowers and fruits, it is said in bearing condition. Different fruits have different bearing habits, inflorescences, types of flower, mode and medium of pollination, pollen viability and all these account a lot for the bearing of fruit plants.

Bearing habit

If one observes a mango tree, he/she may find it does produce the fruits terminally on a shoot and it citrus he/she finds the fruits always produced laterally in the leaf axils. The manner or patter in which a plant produces its fruit is known as bearing habit or fruiting habit. Bearing habits are specific to the kind of plant. In determining the bearing habit of any plant three points are to be considered.

Horticultural plants are grown for their produce like fruit, vegetable, flower, medicinal component, spices etc. Therefore, these plants should be managed in such a way that human desires for the purpose of growing them are fully satisfied in terms of quality and quantity of produce. This demands direct manipulation of plant growth itself or plant environment through various inputs. In manipulation of plant development, training and pruning are important for which our knowledge about plant development and its phenology has to be complete. These practices are important in fruit crops.

Planting System

Main objective of layout is maximum number of plant accommodated in per unit area without affecting the efficiency of production. If more than one fruit is included in the orchard plan, each kind should be grouped into individual block. Similarly fruit ripened in particular season should be grouped to facilitate convenience in watch and ward, harvest and post harvest handling. Some kind of fruit trees need pollinators/pollinisers for improving the fruit set.

Orchard

Establishment of orchard is a long term investment. It is require a proper planning, any mistake during the selection of site, planting distance, choice of crop/variety, quality of nursery stock etc. reflect greatly on the orchard performance and efficiency.