eChapters

COEFFICIENT OF THE MEAN DEVIATION

A relative measure of dispersion based on the mean deviation is called the coefficient of the mean deviation or the coefficient of dispersion. It is defined as the ratio of the mean deviation to the average used in the calculation of the mean deviation.

STANDARD DEVIATION AND THEIR COEFFICIENT

The standard deviation is a measure of the spread of scores within a set of data. Usually, we are interested in the standard deviation of a population. However, as we are often presented with data from a sample only, we can estimate the population standard deviation from a sample standard deviation. These two standard deviations - sample and population standard deviations - are calculat- ed differently. In statistics, we are usually presented with having to calculate sample standard deviations.

FOR GROUPED DATA

Objective: The following data shows the marks of students and their frequencies find the standard deviation and its coefficient.

COEFFICIENT OF VARIATION:

The most important of all the relative measure of dispersion is the coefficient of variation. This word is variation not variance. There is no such thing as coefficient of variance. The coefficient of variation( C.V.) is defined

CORRELATION

In case of bivariate or multivariate normal distributions, we may be interested in discovering and measuring the magnitude and direction of the relationship between two or more variables. For this purpose we use correlation. The sys- tematic interrelationship between the variables is termed as correlation. When only two variables are involved the correlation is known as simple correlation. If more than two variables are involved the correlation is known as multiple correlation. An increase in one variable may cause an increase in the other variable, or a decrease in one variable may cause a decrease in the other vari- able, then they are said to be positively correlated. If a decrease in one variable causes an increase in the other variable or vise versa, the variables are said to be negatively correlated.

TEST OF SIGNIFICANCE FOR CORRELATION COEFFICIENT

Coefficient of correlation is a numeric characteristic of a population and is estimated from a sample of the bi-variate population. If ρ be the coefficient of correlation in the population and r be its sample estimate based on n pairs of observations, then standard error of r is given

t TEST FOR SINGLE MEAN

A t-test is any statistical hypothesis test in which the test statistic follows a Student’s t distribution if the null hypothesis is supported. It can be used to determine if two sets of data are significantly different from each other, and is most commonly applied when the test statistic would follow a normal distribution if the value of a scaling term in the test statistic were known. When the scaling term is unknown and is replaced by an estimate based on the data, the test statistic (under certain conditions) follows a Student’s t distribution.

t TEST FOR TWO SAMPLE MEAN:

Comparison of two sample means  and assumed to have been obtained on the basis of random samples of sizes n₁ and n₂ from the same population which is assumed to be normal.

t TEST FOR PAIRED OBSERVATION

This test is used for testing whether two series of paired observations are gen- erated from the same population on the basis of the difference in their sample means.

F TEST (VARIANCE RATIO TEST)

F distribution is applied in several tests of significance relating to the equality of two sampling variances drawn on the basis of independent samples from a normal population.

CHI- SQUARE TEST (χ₂ TEST)

The chi square test is used to determine if the two attributes are independent of each other. Chi square is a measure to evaluate the difference between observed frequencies and expected frequencies to examine whether the difference so obtained is due to a chance factor or due to sampling error.

In a contingency table if each attribute is divided into two classes it is known as 2×2 contingency table. When one attribute is divided into two classes and another into r or c resultant contingency table is known as r×2 or 2×c contingency table. Here, r denotes the number of rows and c the number of columns. For such data, the statistical hypothesis under test is that the two attribute are independent of one another. To test this hypothesis we use the test statistic

The chi square is a continuous distribution based on the assumption that the ul- timate class frequency is not less than 5 otherwise the value of χ₂ will be over- estimated and may cause too many rejections of null hypothesis. Therefore, to maintain the continuity of χ₂ and to draw the correct inference in 2×2 we apply a correction which is known as Yates’s correction for continuity.

A simple random sample (SRS) of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected.

A simple random sample is a subset of a statistical population in which each member of the subset has an equal probability of being chosen. An example of a simple random sample would be the names of 25 employees being chosen out of a hat from a company of 250 employees. In this case, the population is all 250 employees, and the sample is random because each employee has an equal chance of being chosen.

5.3.1. Main components

Shear tube: It absorbs heavy shocks and protects the components of rear transmission and main transmission from breaking.

Crown wheel and pinion: It transmits the drive from the main shaft to the rear axle shaft and inverts the direction of rotation to 90° from the main shaft. It reduces the speed and multiplies the torque.

Rear axle: It is a semi floating type. It transfers the drive from the sun gear to the rear wheel.

5.3.2. How does it work?

The drive from the main shaft of the gear box is taken to the rear drive shaft through the coupler planetary. Depending on the position of the high–low gear and lever which moves the coupler, power is transmitted directly or through epicyclic gear train. The drive from the rear drive shaft is transferred to a safety coupling also known as shear tube. The coupling is a safety device. In case the rear wheels encounter any shock loading, the coupling breaks and disconnects the gear box from the rear transmission. This prevents damage to costly parts in the transmission, clutch and engine. Power is transmitted from safety coupling to a pinion which has a spiral bevel gear at one end. The bevel pinion is supported on two tapered roller bearings carried in a housing which is mounted in the centre housing.

10.8.1. Function

A power take-off (PTO) is a splined drive shaft on a tractor that can be used to provide power to an attachment or a stand alone machine. PTO shaft gets the drive from hydraulic pump shaft. This in turn gets drive from engine. PTO is designed to be easily connected and disconnected (Fig 10.8.1.). It is used to operate implements, viz., rotavator, fertilizer spreader, duster and many more machines which are stationary such as threshers, water pump and portable flour mill. These shafts either run at 540 rpm with 6 splines in the shaft or at 1000 rpm with 21 splines in the shaft. But many old tractors have 540 rpm PTO. The present day equipment is designed to operate with 1000 rpm PTO shaft. The manufacturers of old tractor models provide an auxiliary gear box which increases the speed of PTO to 1000 rpm. Selection of implements, equipment and machinery should be done on the basis of available tractor PTO speed.

13.1. Types

Lamps: Head lamp, plough lamp, indicators

Switches: Safety switch, starter switch, etc

13.2. Components

Battery: A battery provides power to electrical or electronic circuits. The voltage rating of a battery tells how much electrical “pressure” the battery can provide. Battery energy is used to operate starter motor and to provide current to the ignition system during cranking. The electrolyte should always be maintained just below the maximum level, but should not go down below the 1/4^th level.

Alternator: Alternators are electromechanical devices used to convert mechanical energy to alternating current electrical energy. While some of the alternators use rotating magnetic field, some use linear. The functioning of alternators is similar to that of direct current generators. As the magnetic field around a conductor changes, a current is induced in the conductor. The rotating magnet or the rotor turns and cuts the field across the conductors. Thus, an electrical current is produced which causes the rotor to turn. This rotating magnetic field causes an AC voltage in the stator windings. In tractors, alternators are used to charge the battery and to power the electric system when its engine is running. An alternator is superior to a dynamo as it provides more precise output control, requires lesser maintenance, is more compact and requires no cut-out.

Farm tractor designs and styles differ greatly. Tractors are often used on a daily basis for several agricultural and non-agricultural tasks by attaching or operating light, medium to heavy implements, equipment and machineries according to the requirement and hp of tractors. Tractors are very versatile and can be used on sandy (light textured), loamy (medium textured) and clayey (heavy textured) soil at different topographic and agro-climatic conditions. Earlier, the proportion of tractor usage in agricultural and non-agricultural work was 70:30. This proportion has increased to about 55: 45 over the past two to three years. It is expected to reach 50:50 in (agricultural:non-agricultural applications) in the coming years. The major application of farm tractors for agricultural and non-agricultural sectors is given below.

22.1. What?

Threshing is the process of separating grains from the straw or pod by impact, friction or both. Threshing should be done at an appropriate time after harvest. Delayed threshing causes rapid deterioration of the grains, especially during field drying or when the crop is stacked in the field. Improper threshing leads to wastage of grains and reduces the quantity of final marketable produce. After threshing, the produce has to be winnowed to remove lighter materials such as unfilled grains, chaff, weed seeds and straw using a blower, air fan or wind. Winnowing improves the ability of the grain to be safely stored, milling output and quality.

22.2. Methods employed

Traditionally, threshing is done by beating the harvested crop on a threshing floor directly or with a stick. Another traditional method of threshing is to make a bull walk in circles on the grain on a hard surface. In some areas, the harvested panicle with grain is spread on the surface of a country road so that the grain may be threshed by the wheels of passing vehicles. In these methods winnowing is separately performed. However, with the development of technology, now it is mostly done by machine referred to as threshers, shellers and stripper. Some of these threshers have inbuilt facility for threshing. Thus, threshing and winnowing are completed in a single process.

24.1. What?

Most of the horticultural crops are raised by following special techniques such as budding and grafting. In case of landscape horticulture, frequent pruning and mowing are required to maintain the architecture. When new area is brought under cultivation, either jungle or unwanted plants have to be cleared. To perform all these operations, certain set of special tools are used. Some tools, though small, are of great need in raising and maintaining horticultural crops at various growth stages.

24.2. Special tools for horticultural crops

24.2.1. Manual

Axe, Dah, Hand shovel, Garden rake, Crow bar, Felling dao, Tea pruning dao, Billhook, Budding knife, Grafting knife, Budding and grafting knife, Pruning and slashing knives, Multipurpose chopping knife, Pruning secateurs, Pneumatic secateurs, Hedge shear, Hedge trimmer, Lopping shear, Forester shear, Grass shear, Garden sword, Flower scissors and coconut tree climber

This chapter deals with equipment and machineries that are used in certain specific operations/ areas.

25.1. Lac cultivation

High-capacity scraper cum grader, scraper cum grader

25.2. Mushroom production

Grain Cleaner, Grain boiler, Boiled grain and Chalk powder mixer, Bag/bottle filler, Spawn inoculators, Substrate mixer - manually operated

27.1. What?

Seed drills are designed to sow seeds at the recommended seed rate with precision and at the desired depth. Proper adjustments are made to the seed metering system to ensure efficient use of seed drills. This aspect is vital to have a good crop stand.

The seed size varies between crop and their varieties. In addition, the seed metering systems are based on volume displacement. Therefore, if one lot of seeds varies in size and weight from another, two different amounts or number of seeds will be metered if the drill setting is not changed. For this reason, metering systems should be calibrated each time when put to use.

The method of calibration will be given in detail in the manual provided along with the seed drill.

Genetic purity (trueness to type) of a variety can deteriorate due to several factors during production cycles. The best means to insure genetic purity therefore, would be to overcome to the greatest possible extent the various factors responsible for genetic deterioration. The important factors of apparent and real deterioration of varieties as listed by Kadam (1942) are as follows:

Developmental variations

Mechanical mixtures

Mutations

Natural crossing

Minor genetic variations

Selective influence of diseases

The technique of the plant breeder

1. SEED CLASSES

Generation system of seed multiplication is nothing but the production of a particular class of seed from specific class of seed up to certified seed stage. The choice of a proper seed multiplication model is the key to further success of a seed programme, which basically depends upon

1. SELECTION OF SITE

Select a location where one could ensure semi-shady conditions. Well drained medium-loam soil; rich in organic matter and neutral soil pH. An irrigation source in the vicinity with natural pH water is highly desirable.

1. SEED EXTRACTION

The processing of seeds starts from the extraction of seed material from the plant parts. The seed removal in dry fruits is known as threshing, while that of wet fruits is known as extraction.

2. METHODS OF SEED EXTRACTION

2.1. Dry extraction

Dry extraction is done either manually or mechanically. Manual extraction is by beating with pliable bamboo stick or by beating against a hard surface. Threshers are used for mechanical extraction. In this, care should be taken to avoid mechanical injury. Eg. All agricultural crops.

1. SEED DRYING

The process of elimination of moisture from the seed is called drying.

2. STAGE OF MOISTURE ELIMINATION

The moisture from the seed is eliminated in 2 stages

1. Surface moisture of the seed that initially removed by the drying air.
2. The removal of the moisture in the surface cause an imbalance in the moisture potential in the surface of the seed and the inner portion of the seed which leads to the migration of moisture from the inner organ to the surface.

The migration of moisture to the surface is slower than the evaporation and a moisture gradient is developed in the kernel. Elimination of moisture from the seed depends upon the relative humidity and temperature of the environment surrounding the seed.

1. MINIMUM SEED CERTIFICATION STANDARDS

In a seed quality control programme through seed certification, the minimum seed certification standards, in fact, are the minimum standard conditions which must be met. The minimum seed certification standards, thus are the standards required for the certification of seeds by the certification agencies.

The minimum seed certification standards can be broadly grouped into two groups.

1. SEED PURITY AND ITS COMPONENTS

Seed purity analysis from the working sample taken from submitted sample is made in accordance to ISTA rules. The uncertified seed sample is generally a mixture of pure seeds, inert matter and biological impurities including genetically impure seeds of the variety.

A buyer expects to have good seed and not a mixture of pure seed with a high percentage of chaff, straw, sand, weed seeds and other crop seeds and also genetically impure or mixed seeds.

Purity analysis is a test to estimate the extent of biotic and abiotic impurities present in the seed lot of a variety.

The relative long periods of time required for completion of germination tests delays the seed marketing. This necessiated the development of rapid methods for estimating the germination capacity of seeds. This test was developed by Lakon (1942) in Germany.

1. PRINCIPLE

It is a biochemical test, in which living cells are made visible by reduction of an indicator dye. The indicator used is 2,3,5 triphenyl tetrazolium chloride. Within the seed tissues, it interferes with the reduction processes of living cells and accepts hydrogen from the hydrogenases. By hydrogenation of the 2,3,5-triphenyl tetrazolium chloride, a red stable and non diffusible substance, triphenyl formazan is produced in living cells (Fig. 1).

1. FIELD OF APPLICABILITY

Grow-out test is the official measure for controlling the genetic purity of the seed lot. It serves as ‘pre-control’ as well as a ‘post control’ test for avoiding genetic contaminations. According to the official regulations in India, it is prerequisite for seed certification of hybrids of certain species such as cotton, castor, musk melon and brinjal.

The test is conducted for checking the sellers label with respect to genetic purity status of the seed lot under the provisions of the Seeds Act 1966. In addition, grow-out test can also be used as a measure to judge the efficacy of the certification agency or the inspector.

1. NEMATODES

Nematodes, also called eel-worms, are wormlike in appearance, but quite distinct taxonomically from true worms. They live freely in fresh or salt water or in soil. They are saprozoic and also parasitize animals (including man) and plants. Many species of nemotdes parasitize higher plants and cause disease symptoms. Plant parasitic nematodes are small (invisible to the naked eye), long, tubular, round in the cross section, unsegmented and smooth invertebrates. They inhibit different parts of plants, namely, roots, stem, flower buds and seeds. Depending on the host-parasite relationship, plant parasitic nematodes may be sedentary or migratory and ectoparasitic and/or endoparasitic in their feeding habits.

1.1. Nematodes

Seed-borne nematodes may be internal or may occur as seed infestation. Several saprozoic soil nematodes occur in beds of soil mixed with seed. Seed infestation by nematodes does not produce any specific symptoms on seed, but in those that occur as endoparasites, the floral structure may be modified into a seed gall (Anguina spp.) may produce symptoms such as discoloration of testa in groundnut (Ditylenchus destructor) or may be symptomless as in paddy kernels infected by Aphelenchoides besseyi. Neergaard (1979) listed five genera - Anguina, Aphelenchoides, Ditylenchus, Heterodora and Rhadinaphelenchus - that are seed-transmitted. Heterodora and Rhadinaphelenchus occur as endoparasites in roots, stems, and leaves. The latter also affects the growing apex, inflorescence and husks of dropped nuts.

Various physical, chemical and biological factors interdependently affect the fungal colonization or production of the mycotoxin. Physical factors such as temperature, relative humidity and insect infestations create ideal environment for fungal colonization and mycotoxin production. Stresses such as drought, an increase in temperature, and an increase in relative humidity may selectively alter colonization and metabolism of mycotoxigenic fungi and thus alter mycotoxin production (Russell et al., 1991). Cool and damp weather favours the germination of the sclerotia and thus ergot alkaloid formation in fescue and ryegrass.

Biological factors are categorized into intrinsic factor such as fungal species, strain specificity, strain variation and instability of toxigenic properties. Interaction between the toxigenic fungal species and substrate affect the fungal colonization and mycotoxin production. Some plant species are more susceptible to colonization and some resistant plant species may also get infestation due to favourable environmental conditions.

The ingestion of mycotoxin-contaminated feedstuffs by animals leads to adverse effect on animal health and the effects are more serious in monogastric animals depending on the species and the susceptibility to toxins within the species. Ruminants are less susceptible to mycotoxins than monogastric animals because of biotransformation of mycotoxins to non-toxic metabolites in rumen by rumen microbiota (Fink-Gremmels, 2008).

The economic loss in livestock arising due to mycotoxicosis is enormous apart from being a health risk. Indian economy is heavily affected by mycotoxins. It was estimated that 10 million dollars were lost in India’s export within a decade due to groundnut contamination with mycotoxins (Vasanthi and Bhat, 1998). Many developing countries have realized that reducing mycotoxin contamination in foods will not only improve the health and production in animal, but also increase the raw material exports (international trade) to other countries. The following strategies are to be adhered strictly to reduce the mycotoxins contamination of crops in the field.

1. Early harvesting

Early harvesting reduces the fungal infection of crop in the field. Early harvesting and threshing of groundnuts results in lower aflatoxin levels and higher gross returns of 27% than in delayed harvesting (Rachaputi et al., 2002).