eChapters

Objective: The distribution of age of males at the time of marriage was as follows

Paratition Value

Median is calculated for dividing the series into two equal parts. If the series is divided into four, eight, ten or hundred parts then the measures are called Quartile, Octile, Decile and Percentile respectively denoted by Q_(1,2,3), O_(1,2..7), D_(1,2…9) and P_(1,2…99).

A relative measure of dispersion based on the quartile deviation is called the coefficient of quartile deviation. It is defined as

MEAN DEVIATION

The mean deviation is the first measure of dispersion that we will use that ac- tually uses each data value in its computation. It is the mean of the distances between each value and the mean. It gives us an idea of how spread out from the center the set of values is.

The mean deviation is based on all the observations, a property which is not possessed by the range and the quartile deviation. The formula of the mean de- viation gives a mathematical impression that is a better way of measuring the variation in the data. Any suitable average among the mean, median or mode can be used in its calculation but the value of the mean deviation is minimum if the deviations are taken from the median.

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

FOR GROUPED DATA

Objective: Data regarding lives of two new models of refrigerators collected in a recent survey are

MOMENTS

The term moment in mechanics refers to the measure of a force with reference to its tendency to produce rotation. The strength of this tendency is depen- dent upon the amount of the force and the distance from the origin at which the force is applied. If on both the sides of the origin the force are equal than there will be a balance, at a balanced position the positive product equals the negative product.

Moment is used in Statistics in a quite analogous sense. The class frequencies are looked upon as the forces and the deviations of the different values from the mean are taken as the distances. In other words, moment is the mean of the first, second, third, fourth, etc. powers of deviations of the different values from the arithmetic mean. The first moment about the mean is always zero and second moment about the mean is variance.

If the moment calculated from arithmetic mean are called central moments and denoted by μ with a subscript which indicate the order of the moment. Moments are the mean values of powers of the deviations in any frequency distribution taken about three points

SKEWNESS

Skewness means lack of symmetry. Skewness denotes the tendency of a distri- bution to depart from symmetry. A frequency distribution is said to be skewed if the frequencies decrease with markedly greater rapidity on one side of the central maximum than on the other side. This characteristic of a frequency distribution is known as skewness and the measures of asymmetry are usually called measures of skewness.

The main object of measuring skewness is to know the direction of the varia- tion from an average and to compare the frequency distribution and the shape of their curves.

There are two types of skewness

(i) Positive Skewness (ii) Negative Skewness

KURTOSIS

Kurtosis refers to the extent to which unimodal frequency curve is peaked. Kurtosis is a measure that refers to the peakedness of the top of the curve. Kurtosis gives the degree of flatness in the region about the mode of a frequency distribution.

Types of Kurtosis

There are three categories of kurtosis that can be displayed by a set of data. All measures of kurtosis are compared against a standard normal distribution, or bell curve.

The first category of kurtosis is a mesokurtic distribution. This type of kurtosis is the most similar to a standard normal distribution in that it also resembles a bell curve. However, a graph that is mesokurtic has fatter tails than a standard normal distribution and has a slightly lower peak. This type of kurtosis is considered normally distributed but is not a standard normal distribution.

The second category is a leptokurtic distribution. Any distribution that is leptokurtic displays greater kurtosis than a mesokurtic distribution. Characteristic of this type of distribution is one with extremely thick tails and a very thin and tall peak. The prefix of “lepto-” means “skinny,” making the shape of a leptokurtic distribution easier to remember. T-distributions are leptokurtic.

The final type of distribution is a platykurtic distribution. These types of distributions have slender tails and a peak that’s smaller than a mesokurtic distribution. The prefix of “platy-” means “broad,” and it is meant to describe a short and broad-looking peak. Uniform distributions are platykurtic.

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

REGRESSION

Regression means to revert or return back. The term was first introduced by Sir Francis Galton in1877. Regression technique is applicable in all those fields where two or more relative variables have the tendency to go back to the mean. Regression analysis refers to the methods by which estimates are made of the values of a variable from the knowledge of the values of one or more other variables and to the measurement of the errors involved in this estimation pro- cess.

In statistical modeling, regression analysis is a statistical process for estimat- ing the relationships among variables. It includes many techniques for mod- eling and analyzing several variables, when the focus is on the relationship between a dependent variable and one or more independent variables. Regres- sion analysis helps one understand how the typical value of the dependent variable (or ‘criterion variable’) changes when any one of the independent variables is varied, while the other independent variables are held fixed. Most commonly, regression analysis estimates the conditional expectation of the dependent variable given the independent variables – that is, the average value of the dependent variable when the independent variables are fixed.

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.

STANDARD NORMAL DISTRIBUTION

If μ = 0 and σ = 1, the distribution is called the standard normal distribution or the unit normal distribution, and a random variable with that distribution is a standard normal deviate. The approximate test is given by

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.

ANALYSIS OF VARIANCE

Analysis of Variance (ANOVA) is a hypothesis-testing technique used to test the equality of two or more population (or treatment) means by examining the variances of samples that are taken. ANOVA allows one to determine whether the differences between the samples are simply due to random error (sampling errors) or whether there are systematic treatment effects that cause the mean in one group to differ from the mean in another.

Most of the time ANOVA is used to compare the equality of three or more means, however when the means from two samples are compared using ANOVA it is equivalent to using a t-test to compare the means of independent samples.

ANOVA is based on comparing the variance (or variation) between the data samples to variation within each particular sample. If the between variation is much larger than the within variation, the means of different samples will not be equal. If the between and within variations are approximately the same size, then there will be no significant difference between sample means.

The two-way ANOVA compares the mean differences between groups that have been split on two independent variables (called factors). The primary purpose of a two-way ANOVA is to understand if there is an interaction be- tween the two independent variables on the dependent variable. For example, you could use a two-way ANOVA to understand whether there is an interac- tion between gender and educational level on test anxiety amongst university students, where gender (males/females) and education level (undergraduate/ postgraduate) are your independent variables, and test anxiety is your depen- dent variable. Alternately, you may want to determine whether there is an in- teraction between physical activity level and gender on blood cholesterol con- centration in children, where physical activity (low/moderate/high) and gender (male/female) are your independent variables, and cholesterol concentration is your dependent variable.

The interaction term in a two-way ANOVA informs you whether the effect of one of your independent variables on the dependent variable is the same for all values of your other independent variable (and vice versa). For example, is the effect of gender (male/female) on test anxiety influenced by educational level (undergraduate/postgraduate)? Additionally, if a statistically significant interaction is found, you need to determine whether there are any “simple main effects”, and if there are, what these effects are (we discuss this later in our guide).

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.

1.1. Definition

A tractor is a specific vehicle designed to deliver a high tractive torque at slow speeds, for the purposes of haulage or for pulling an agricultural implement or equipment or machinery. This vehicle is also used as a source of power for stand-alone agricultural machineries. The word tractor is taken from Latin being the agent noun of trahere “to pull”.

1.2. History of evolution

The first engine-powered farm tractors used steam and were introduced in 1868. These engines resembled small road locomotives. They were used for general road haulage and in particular for timber trade. The most popular steam tractor was the Garrett 4CD.

In 1887, gasoline-fuelled engines were tried as an alternative to steam engines. Later, Henry Ford produced his first experimental gasoline powered tractor in 1907, under the direction of his chief engineer Joseph Galamb. It was referred to as an “automobile plow”. While unpopular at first, these gasoline powered machines began to catch on. In the 1910, the size of the tractor was smaller than the earlier introductions and also became more affordable. In 1917, Henry Ford introduced the first mass-produced tractor. These were built in the U.S.A., Ireland, England and Russia. The unique feature of these tractor consisted of the strength of the engine holding the entire machine together. By 1920, tractors with a gasoline powered internal combustions engine had become a norm.

1.3. History in India

The level of mechanization in Agriculture was very low at the time of independence in 1947. But, the initial few five-year plans implemented by the Government of India gave an impetus to the improvement in the production and productivity of major crops including mechanization via joint ventures and tie-ups between local industrialists and international tractor manufacturers. It was three decades after independence that the domestic production of 4-wheel tractors grew slowly. In 1990, the tractor production was nearly 2,70,000 units per year and by the 2013, the volume approached to about 6,96,000 units per year. India has presently overtaken the United States as the world’s largest producer of four-wheel tractors with over 16 national and 4 multinational corporations engaged in its production. But still the Food and Agriculture Organization estimates that from out of the total agricultural area, less than 50% is under-mechanized land preparation. This indicates that potential for large tractorization still exists. Credit facilities for farmers have been improving steadily over the years. This is one of the prime drivers of the sale of tractor in India.

2.1. Introduction

The engine is the source that generates power. It transforms chemical energy in fuel into mechanical energy for power. Diesel internal combustion engines are invariably used in all the tractors. In these engines, very high compression of the air ignites the fuel as compared to spark plug that ignites fuel in petrol engines. The air in the diesel engine is compressed with a compression ratio typically between 15 and 22 resulting in a 40 bar (about 600 psi) pressure as compared to 8 to 14 bar (about 200 psi) in the petrol engine. This high compression heats the air to 550°C (1022°F). At about this moment, small droplets of fuel are sprayed in an atomized form directly into the compressed air in the combustion chamber.

2.2. How does it work?

Any engine will work with four strokes, namely suction, compression, power and exhaust (Fig 2.1). It will also complete two revolutions of the crankshaft. In the suction stroke, pure air is drawn into the cylinder through the inlet valve. The exhaust valve gets closed and the crankshaft completes half a revolution. In the compression stroke, the piston moves up while the valves remain closed. The air which is drawn into the cylinder during the suction stroke is compressed. There is a rise in temperature. The hot air ignites the fuel injected into the cylinder. The crankshaft again completes half a revolution. In the power stroke, the hot products of combustion, viz., carbon dioxide and nitrogen expand. The piston is forced down. The valves remain closed and the crankshaft completes half a revolution. In the exhaust stroke, the exhaust valve opens while the piston reaches the lowest point of travel. Then the burnt gases are swept out.

3.1.1. Introduction

Clutch is a device which is used to connect and disconnect the tractor engine from the transmission gears and drive wheels. It is fitted in between the engine and gear box. The clutch transmits power by means of friction between driving members and the driven members.

4.2.1. Gear boxes

It is a unit fitted after the clutch. Forms a part of transmission and provides speed and torque conversions from a rotating power source to another device using gear ratios. Its primary function is to change the speed of the tractor to cater to varying field, road and load condition. It also helps in reversing the tractor.

Gears are usually made of alloy steel. Since the tractor has to transmit heavy torque all the time, the best quality lubricants, free from sediments, grit, alkali and moisture, are used for lubrication. SAE 90 oil is generally recommended for gear box.

The description about gear boxes stated below pertains to major tractors manufactured in India. The number of teeth in each of the gear and the engagement between gears of the main shaft and the corresponding gear on the counter/lay shaft also change in different tractors evolved over a period of time. Hence, information hosted in this section is only indicative.

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.

6.4.1. Function

The brake is used to stop or slow down the motion of a tractor. It is mounted on the driving axle and operated by two independent pedals. Each pedal can be operated independently to assist turning of the tractor during field work or both the pedals can be locked together.

6.4.2. Principle of operation

The brake works on the principle of friction. When a moving element is brought into contact with a stationary element, the motion of the moving element is affected. This is due to frictional force which acts in the opposite direction of the motion and converts the kinetic energy into heat energy.

7.5.1. Functions

The two primary functions of tyres, especially rear ones, are to provide maximum work output while ploughing the field and for haulage.

8.6.1. Function

It steers the tractor in the required direction. The rotation of the steering wheel moves the steering column, which in turn rotates the sector shaft. This rotation pulls the pit man arms on one side and pushes at the other side. This motion is conveyed to the wheels by the drag link and makes the front wheel turn in the requisite direction.

9.7.1. Function

The front axle is the unit on which the front wheel is mounted. This wheel is an idler wheel by which the tractor is steered in various directions. The function is to assist the steering and support the tractor. It is a rigid tubular or I-section steel construction, pivoted at the centre. The pivot pin is housed on bushings on a support bolted to the front of the engine. As the track width of a tractor is adjustable, the front axles have provision to be extended on both sides. The tubular front axles have telescopic arrangement for extension, whereas the I-section type of front axles are three-piece axles.

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.

11.1. Hydraulic system

It is a mechanism in a tractor to raise, hold or lower the mounted or semi-mounted equipment by hydraulic means. All the present day tractors are equipped with a hydraulic control system for operating three point hitches. Some of the tractors are fitted with a hydraulic brake system and a few others are fitted with a hydraulic steering system. Tipping trailers, front mounted loaders or dozers are examples of multi use of hydraulics.

11.2. Principle

The working principle of a hydraulic system is based on Pascal’s law (Fig 11.1.) This law states that the pressure applied to an enclosed fluid is transmitted equally in all directions. A small force acting on a small area can produce higher force on a surface of larger area.

12.1. Instruments panel

12.1.1. Oil pressure gauge

Indicates oil pressure in Kgf/cm²

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.

1. Introduction

Agricultural mechanization refers to usage of any improved tool, implement and machine by the farm workers to improve the efficiency of any operation to increase productivity. It also helps to reduce drudgery or stress which adversely affects human mental faculties leading to errors, imprecision and hazards and eventually loss of efficiency if done manually. In developed countries, however, mechanization is synonymous to automation. There is scope to mechanize every operation of crop production, post harvest and agro-processing.

17.1. What?

The soil is prepared to a fine tilth, which is referred to as land preparation or preparatory cultivation. This enables proper sowing of seeds, planting of seedlings and precise application of fertilizers to the crop. Various implements are used to prepare the land. The basic ones are ploughs, harrows, cultivators or tillers, and land levellers. These implements are manually operated or by animals or tractors. Various improvements have been made to increase the efficiency of each one of the implements by research workers. Many products are also available to suit the local regions and soil condition.

17.2. Plough

It has been the basic implement used for decades in agriculture to open up and invert the soil for initial cultivation. While inverting the soil, it also buries the weeds and the remains of the previous crops and allows them to decay. In the process of inverting, it also aerates the soil. Ploughs were initially used with animal power. Later on, many improved implements with heavy weights have been developed. These are drawn by tractors.

18.1. What?

The basic objective of sowing is to place the seed in rows at the desired depth, to maintain proper spacing between seed to seed, cover the seeds with soil and provide proper compaction over the seed if required. Precise sowing/planting helps in better crop stand. This helps to achieve optimum yields. Traditional sowing methods include broadcasting manually, opening furrows by a country plough and dropping seeds by hand (i.e.) dibbling. In the present day, improved seed-cum-fertilizer drills are used for sowing and fertilizer application. These are provided with seed and fertilizer boxes, metering mechanism, furrow openers, covering devices, frame, ground drive system and controls for variation of seed and fertilizer rates.

18.2. Types of sowing/planting equipment

Sowing equipment include seeders and transplanters. Various types of sowing equipment, viz., manually operated, animal drawn, power operated and tractor drawn are used throughout India.

18.2.1. Seed drills

Seeders are available for sowing seeds of various crops. Some seeders have been designed with adjustable metering mechanism which makes them versatile for sowing two or three kinds of seeds. For example, a multicrop planter developed by CIAE is used for sowing garlic, maize, moong, peas and groundnut. Similarly, the institute has developed a small seed sowing drill which is used for sowing small seeds such as bajra, rapeseed and mustard.

19.1. Need for weeding

Weeding is the critical operation to be carried out to obtain a good crop. Weeds are plants which grow in places where they are not wanted. They grow in the fields competing with crops for water, soil nutrients, light and space and thus reduce crop yields. They also harbor insect pests and micro-organisms. Certain weeds release the inhibitors or poisonous substances into the soil which are harmful to plants, human beings and livessecks. They increase the expenditure on labour and equipment, render harvesting difficult and reduce the quality and marketability of agricultural produce. When grown in water channels, they block and or reduce the flow of water.

The weed seeds germinate earlier and grow faster than the crop plant. This phenomenon is more pronounced when coupled with favourable environment like fine soil tilth and the soil receiving adequate water and fertilizers. Weeds flower earlier and produce seeds profusely ahead of the crop. So, these seeds get mixed up with the harvested crop and are distributed to the next season or transported to other places along with the harvested produce.

20.1. What?

Sprayer is equipment used for applying insecticides, fungicides, herbicides and in some cases fertilizers as foliar sprays to agricultural crops. Sprayers range in size from man-portable units (backpacks) to Self propelled units with boom mounts covering 60-150 feet length. Sprayers include the ones used for spraying liquid formulations, dusters for dusting dust formulations and granular applicators for delivering granules.

20.2. Principle of working

Sprayers work based on Bernoulli’s principle. Basically, the sprayers have a storage tank, a plunger, lance and a nozzle. When the plunger is pushed in, the air flows at a high velocity through the nozzle. The flow of air at high velocity creates a region of low pressure just above the lance. The higher atmospheric pressure acts on the surface of the liquid insecticide causing it to rise up the lance and the insecticide leaves out through the nozzle as a fine spray.

Sprayers are fitted with hollow cone nozzles for spraying pesticides and with flat fan nozzles for herbicides.

21.1. What?

Harvest is the process of gathering the end produce from mature crops in the fields. Harvest marks the end of the growing season, or the growing cycle for a particular crop. Harvesting is the most labour-intensive activity. Moreover, timely harvest before shattering of the produce or before rain assumes significance. As adjacent fields sown at the same time come to harvest simultaneously, farmers face great problem in getting manual labour for harvesting and cleaning their produce. To overcome these difficulties, different types of harvesters have been developed from time and again to suit different crops, situation and conditions.

21.2. Harvester and reaper

Harvesters are used to cut the crop after they mature. In such cases, threshing is to be done separately. Harvesters are available for a wide range of crops belonging to cereals, pulses, millets, oilseeds, fruits and plantation crops. Reapers are used to harvest crops such as rice, wheat, soybean, mustard, rapeseed, safflower and other thin stemmed crops. Reapers are operated using power tiller.

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.

23.1. What?

Post harvest and agro-processing refers to activities carried out after harvesting a crop. These include milling, grading, processing and packing of the produce before it reaches the end users. This is also referred to as value addition, as it increases the marketable quality of the harvested produce.

23.2. Milling

It is the process of separating edible portion of the grain after removal of the husk or seed coat. This converts the products into a form that can be readily used for cooking, e.g. rice milling and dal milling.

23.3. Grading

Grading is the process of segregating the harvested produce based on the physical appearance including size and colour. Grading increases the market value of the crop.

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