CIGR handbook of agricultural ENgineering volum III

Importance of Human-Powered1.1.2 Human-Powered Tools and Machines for Field Operations 5 Economics of Human-Powered Tools/Machines 1.1.3 Human-Powered Tools and Machines for Some Common

of Agricultural Engineering

Volume III

i

CIGR Handbook

of Agricultural Engineering

Volume III Plant Production Engineering

Edited by CIGR—The International Commission of Agricultural Engineering

Ministry of Agriculture, Fisheries and Food, France

Published by the American Society of Agricultural Engineers

iii

Front Matter Table of Contents

➤

➤

All rights reserved

LCCN 98-93767 ISBN 1-892769-02-6

This book may not be reproduced in whole or in part by any means (with the exception

of short quotes for the purpose of review) without the permission of the publisher.For Information, contact:

Manufactured in the United States of America

The American Society of Agricultural Engineers is not responsible for statements andopinions advanced in its meetings or printed in its publications They represent the views

of the individual to whom they are credited and are not binding on the Society as a whole

iv

Editors and Authors

M´ecanisation agricole, CIRAD-CA Programme GEC,

BP 5035 34090 Montpellier Cedex 1, France

Standards Coordinator, American Society of Agricultural Engineering,

2950 Niles Road, St Joseph, MI 49085-9659, USA

M Havard

CIRAD-SAR, BP 5035, 73, Rue J.F Breton, 34090 Montpellier, Cedex 1, France

H J Heege

Christian-Albrechts-Universit¨at Kiel, Institut f¨ur Landwirtschaftliche

Verfahrenstechnik, Max-Eyth-Strasse 6, 24118 Kiel, Germany

R O Hegg

Agricultural and Biological Engineering Department, Clemson University,

McAdams Hall, Box 340357, Clemson, South Carolina 29634-0357, USA

E U Odigboh

University of Nigeria, Faculty of Engineering, Nsukka,

Enugu State, Nigeria

J Ortiz-Canavate

E.T.S.I.AGRONOMOS, Dpt Ing Rural, Universidad Polit´ecnica de Madrid,

Ciudad Universitaria s/n, 28040—Madrid, Spain

M´ecanisation agricole, CIRAD-CA Programme GEC,

BP 5035 34090 Montpellier Cedex 1, France

E.T.S.I.AGRONOMOS, Dpt Ing Rural, Universidad Polit´ecnica de Madrid,

Ciudad Universitaria s/n, 28040—Madrid, Spain

Editorial Board

Fred W Bakker-Arkema, Editor of Vol IV

Department of Agricultural Engineering

Michigan State University

Michigan, USA

El Houssine Bartali, Editor of Vol II (Part 1)

Department of Agricultural Engineering

Institute of Agronomy

Hassan II, Rabat, Morocco

Egil Berge

Department of Agricultural Engineering

University of Norway, Norway

Jan Daelemans

National Institute of Agricultural Engineering

Merelbeke, Belgium

Tetuo Hara

Department Engenharia Agricola

Universidade Federal de Vicosa

Wageningen, The Netherlands

Osamu Kitani, Editor-in-Chief and Editor of Vol V

Department of Bioenvironmental and Agricultural EngineeringNihon University

Kameino 1866

Fujisawa, 252-8510 Japan

Hubert N van Lier, Editor of Vol I

Chairgroup Land Use Planning

Laboratory for Special Analysis, Planning and Design

Department of Environmental Sciences

Agricultural University

Wageningen, The Netherlands

ix

The late Richard A Spray

Agricultural and Biological Engineering Department

Clemson University

Clemson, South Carolina 29634-0357, USA

Bill A Stout, Editor of Vol III

Department of Agricultural Engineering

Texas A & M University

Texas, USA

Fred W Wheaton, Editor of Vol II (Part 2)

Agricultural Engineering Department

University of Maryland

Maryland, USA

Importance of Human-Powered

1.1.2 Human-Powered Tools and Machines for Field Operations 5

Economics of Human-Powered Tools/Machines

1.1.3 Human-Powered Tools and Machines for

Some Common Tools for Crop Processing by

1.1.4 The Sociology and Future of Hand Tool

1.1.5 Efficient Use of Energy Potential by a

1.1.7 Farm Equipment for Transport, Tillage, Secondary

xi

Equipment for Tillage 31

1.1.19 Differences of Farming Principles Between Upland

Planting Systems and the Principle of a Transplanting

1.1.22 Description and Types of Two-Wheel Tractor Designs 951.1.23 Production and Concentration of Two-Wheel Tractors 101

1.1.26a Management of Two-Wheel Tractors 1101.1.26b Trends in the Development of Two-Wheel Tractors 114

Mechanics of Two-Axle Tractors Pulling

Mechanics of Hillside Operation and Overturning Stability 125

Traction Tires: Requirements, Design, Specifications 127

Introduction: Role of Comfort, Health and Safety 153

Technical Aids for the Operator: Survey and

Beginnings of Implement Control by Hydrostatic Hitches 165

Concept and Dimensions of the Three-point Hitch 166

Appropriate Tillage According to Soil Conditions 185

Site Specific Spreading 267

Timed-flow Method for Calibrating Boom Sprayers 304

Traction and Flotation Assistance for Combines

Throw-in Threshers That Chop the Straw for Stockfeed 344

Low-height Herbaceous Structures

Bushy Structures (Small Fruits, Wine Grapes) 416

Trailers with Hydraulic Tippers 464

Trailers Used for Transporting Combine Harvesters

1.10.1 Standardization on Workplace Health and Safety in

1.10.2 Relationships Between European and

1.10.3 E.U Standards for Environmental

2 Mechanizations Systems 5212.1 Systems Engineering, Operations Research, and

2.2.5 Basic Guidelines and Principles

2.2.8 Key Policy Instruments for Formulation of an AMS 547

2.3 Transfer of Technology 554

Prerequisites and Constraints Connected with

The Role of Farm Machinery Industries for

Examples of TT Successfully Carried out in

The Protection of Intellectual Property and the

3.2.3 Concepts of Precision Farming Systems and Required

Data Management and Geographic

This handbook has been edited and published as a contribution to world agriculture atpresent as well as for the coming century More than half of the world’s population isengaged in agriculture to meet total world food demand In developed countries, theeconomic weight of agriculture has been decreasing However, a global view indicatesthat agriculture is still the largest industry and will remain so in the coming century.Agriculture is one of the few industries that creates resources continuously fromnature in a sustainable way because it creates organic matter and its derivatives byutilizing solar energy and other material cycles in nature Continuity or sustainability

is the very basis for securing global prosperity over many generations—the commonobjective of humankind

Agricultural engineering has been applying scientific principles for the optimal version of natural resources into agricultural land, machinery, structure, processes, andsystems for the benefit of man Machinery, for example, multiplies the tiny power (about0.07 kW) of a farmer into the 70 kW power of a tractor which makes possible theproduction of food several hundred times more than what a farmen can produce manu-ally Processing technology reduces food loss and adds much more nutritional values toagricultural products than they originally had

con-The role of agricultural engineering is increasing with the dawning of a new century.Agriculture will have to supply not only food, but also other materials such as bio-fuels,organic feedstocks for secondary industries of destruction, and even medical ingredients

Furthermore, new agricultural technology is also expected to help reduce environmental

destruction

This handbook is designed to cover the major fields of agricultural engineering such

as soil and water, machinery and its management, farm structures and processing cultural, as well as other emerging fields Information on technology for rural planningand farming systems, aquaculture, environmental technology for plant and animal pro-duction, energy and biomass engineering is also incorporated in this handbook Theseemerging technologies will play more and more important roles in the future as bothtraditional and new technologies are used to supply food for an increasing world popula-tion and to manage decreasing fossil resources Agricultural technologies are especiallyimportant in developing regions of the world where the demand for food and feedstockswill need boosting in parallel with the population growth and the rise of living standards

agri-It is not easy to cover all of the important topics in agricultural engineering in alimited number of pages We regretfully had to drop some topics during the planningand editorial processes There will be other requests from the readers in due course Wewould like to make a continuous effort to improve the contents of the handbook and, inthe near future, to issue the next edition

This handbook will be useful to many agricultural engineers and students as well as

to those who are working in relevant fields It is my sincere desire that this handbook will

be used worldwide to promote agricultural production and related industrial activities.Osamu Kitani

Editor-in-Chief

xxv

Effective crop production requires machines—hand tools, animal-drawn implementsand engine-powered equipment This volume presents the fundamentals of various agri-cultural tools and machines and describes the types most commonly used for variousoperations The scope of crop production is defined rather broadly to include green-house production and forestry in addition to field crops Important peripheral top-ics also are covered, such as transport machines, machine systems, and technologytransfer

Since machines for crop production represent a substantial capital investment forindividual farmers, principles and guidelines are given for proper selection and machinemanagement to achieve the greatest return On a broader scale, policies and strategies aregiven for effective national or regional mechanization programs Transfer of technologyfrom industrialized to developing countries is also discussed

Standards are crucial in the design, testing, marketing and use of agricultural chines Globalization of the agricultural machinery manufacturing industry requires thatmachines built by one manufacturer operate effectively with power units built by another.Also, safety issues require standards to assure protection of the operator and the generalpublic

ma-The future is always hard to predict, but one thing is certain: If humans are to surviveand thrive on planet Earth, agricultural practices must be sustainable over the long term.Machines and associated farming practices can have a profound impact—both positivelyand negatively—on soil erosion, precise chemical application, air quality and otherenvironmental aspects Precision farming techniques are designed to vary the fertilizerand chemical application rates in accordance with the crop needs and thereby save moneyand help maintain the environment

Many individuals and agencies have contributed to this handbook The various ters were written by 41 individuals—all of whom are experts in their particular area ofspecialization These authors are from 12 countries and represent many languages otherthan English Although every effort was made to standardize the format of each chapter,

chap-it is hoped the reader will overlook minor variations in format and terminology resultingfrom the broad authorship

It is not possible to acknowledge individually the hundreds of authors of the referencescited, although their work contributed significantly to this volume

The chapter manuscripts were reviewed by two world renowned experts in the field

of agricultural mechanization Their questions and comments were considered by thechapter authors and resulted in substantial improvement in the manuscripts In addi-tion, all the chapter manuscripts were reviewed by Ms Lynette James, Department ofAgricultural Communications at Texas A&M University, a very capable editor whohelped standardize the format and make the volume more readable

xxvii

A project of this type would have been impossible without many competent anddedicated research assistants, typists, reviewers and other helpers The editors extend asincere thanks to everyone who contributed to this volume.

B A Stout, Editor Volume III

B Cheze, Co-Editor Volume III

1 Machines for Crop

Production

1.1 Power Sources Human-Powered Tools and Machines

E.U Odigboh

1.1.1 Technical Characteristics of Human Power

Introduction

To mechanize means to use machines to accomplish tasks or operations A machine

may be as simple as a wedge or an inclined plane, or as complex as an airplane tural mechanization, therefore, is the use of any machine to accomplish a task or operationinvolved in agricultural production It is clear from this definition that agriculture any-where has always been mechanized, employing a combination of three main sources ofpower: human, animal and mechanical/engine, giving rise to three broad levels of agricul-

Agricul-tural mechanization technology classified as hand-tool technology (HTT), draft-animal technology (DAT) and mechanical-power or engine-power technology (EPT).

Hand-tool technology is the most basic level of agricultural mechanization, where

a human being is the power source, using simple tools and implements such as hoes,machetes, sickles, wooden diggers, etc A farmer using hand-tool technology can cul-tivate only about one hectare of land He cannot do more than that because of certainscientifically established facts

Power Production and Consumption by Humans

As a source of power, the human being operates essentially like a heat engine, withbuilt-in overload controls or regulators Chemical energy input in the form of food isconverted into energy output, some of which is useful for doing work On the average, ahealthy person in temperate climates consumes energy at a sustainable rate of only about

300 W, while in tropical climates, as a result of heat stress the rate is reduced to onlyabout 250 W Many tasks for agricultural production can be performed only at higherrates of energy consumption, however, as shown in Table 1.1 Some actual manual workrates for certain field operations are presented in Table 1.2

The fact that many primary agricultural production operations demand higher rates ofenergy than the maximum sustainable rate of energy consumption by humans necessitates

1

Table 1.1 Human Power Consumption for Various Farming Activities

Gross power Activity consumed (Watts) Clearing bush and scrub 400–600

Source: mainly from Dumin and Passmore,

1967, Energy, work and leisure Heineman as given by Inns (1992).

Table 1.2 Some Field Operation Rates by Farmers

Using Hand-Tools

Average manual work rate Operation (man days/ha)∗Land clearing 32.6 (20.1–47.8) Ridging for cassava 43.8 (29.7–64.5) Mound making for yams 57.8 (35–93) Cassava planting 28.3

Yam planting 17.3 Weeding root crops 36.7 (22.3–77.6) Weeding general 40.0

Cassava harvesting 28.5 Yam harvesting 32.0

∗ Range values in parenthesis [1].

rest periods in manual work The rest period required can be estimated using the mula [2],

where,

Using the formula, it follows that the manual ridging operation which demands 400–

1000 W (Table 1.1) requires rest periods of between 22.5 and 45 minutes per hour ofwork Note that at the 1000 W rate of energy consumption, the farmer can work only for

15 minutes, and must rest for 45 minutes, per hour of work It must be noted here alsothat an appropriate rest period, as estimated using the above formula, is a physiologicalnecessity inherent in manual work

Figure 1.1 Sustainable Physical or Power Output by Humans

(Inns, p 2).

Human Work Output

Only about 25 percent of the energy consumed when handling relatively easy taskssuch as pedaling, pushing or pulling is converted to actual human work output Undermore difficult work conditions, the efficiency of converting consumed energy to physicalwork may be as low as 5 percent or less This means that, at the maximum continuousenergy consumption rate of 0.30 kW and conversion efficiency of 25 percent, the phys-ical power output is approximately 0.075 kW sustained for an 8–10 hour work day.Naturally, higher rates can be maintained for shorter periods only, as shown in Fig.1.1[2]

Some Compensating Attributes of Human Labor

The discussion thus far and the facts given in Tables 1.1 and 1.2 make it dantly clear that power is the major limitation to increasing the area cultivated by thehand-tool farmer It should be noted that the problem is not necessarily with the toolsused, especially for primary production operations, since efforts made to redesign themhave yielded no significant improvements [3, 4] The toil, drudgery, and severe powerconstraint on timely field operations, which limit production and earning capacity, arethe inherent characteristics of peasant farmers using hand-tool technology; change thetechnology and you change the farmer’s status [5]

abun-Still, the peasant farmer and his hoe and machete are efficient companions in cropproduction at the subsistence level where he operates This is so because of certain human

attributes that compensate significantly for the limited physical power that the farmercan generate The relevant human attributes are exhibited when the farmer:

• Adopts a working mode that incorporates appropriate rest periods

• Makes instantaneous decisions as to how much force to exert to accomplish a task,thereby conserving energy

• Chooses the most appropriate tools for a given production unit operation

• Changes from one task to another readily and rationally, exhibiting a versatility that

no other power source is capable of

In spite of the inherent compensating characteristics, however, the power needed

to operate any human powered tool or machine should not be more than the farmercan potentially supply; the farmer should employ the preferred modes of human powerapplication such as pedaling or simulated walking

Importance of Human-Powered Agricultural Tools/Machines in the LDC’s

All three levels of technology, HTT, DAT and EPT, are used in the mechanization ofagriculture in most countries of Africa and the other less developed countries (LDC’s)

of the tropical world But HTT predominates, especially for production field operationssuch as land preparation, as shown in Table 1.3

Table 1.4 also shows that for overall agricultural production, human power accountsfor the lion’s share of work in most African and Latin American countries It has beensuggested that a power-use intensity of 0.4 kW/ha is required for effective levels ofagricultural mechanization While that figure may well be controversial, the facts andfigures presented in Tables 1.3 and 1.4, and especially those in Table 1.5, show that thepower-use intensity in Africa is so low that it should be of serious concern to all Consid-ering the natural limitations of human powered tools and machines, their predominance

in the agriculture of developing countries is an important factor to address when dealingwith overall economic development of those countries

Table 1.3 Sources of Power for Various Primary Land Preparation Operations in Various Countries

% of Total Land Cultivated Draught EngineCountry Human animal (Mech.)

Table 1.4 Sources of Power for Overall Agricultural Production in Latin America and

Africa (% Share)

Latin Source of Power America Africa Nigeria Human power 59 89 90 Animal power 19 10 8

Source: [7, 8].

Table 1.5 Engine Power Available for Agriculture

in Different Countries and Continents

Country/Continent W/ha (Hp/acre)

Source: Adapted from [9].

1.1.2 Human-Powered Tools and Machines for Field Operations

Definitions

The description of a machine in the introduction to Section 1.1, which grouped a wedgetogether with an airplane, may be valid only at a certain level of conceptualization But

in a more formal sense, a machine is a device or mechanical contrivance consisting of

two or more relatively constrained components which is energized by a power source to

transmit and/or modify force and motion to accomplish some desired kind of work In

contrast, a tool is a human powered instrument or implement usually without parts that move relative to one another, like a hoe, a dibber, or the like, used to facilitate mechanical

manual operations

Classification by Field Operations

Field operations are tasks performed in the field at different phases of crop tion The major operations include land preparation, planting, weeding, and harvesting.Based on these operations, the tools/machines used are classified into: land prepara-tion tools/machines; planting tools/machines; weeding/cultivation tools/machines; andharvesting tools/machines

produc-Hand-Tools for Land Preparation

Hoes

Naturally, soil preparation is usually the first task in crop production, undertaken

to achieve a variety of basic interrelated objectives such as seedbed preparation, weed

control, soil and water conservation, soil compaction amelioration, etc In peasant culture, soil or land preparation to achieve a combination of these objectives usuallyinvolves tilling with a hoe, and constitutes the most significant characteristic of thehand-tool (mechanization) technology.

agri-Curiously, no manually operated machine for land preparation is commonly able The hoe is the most popular and most versatile tool used in developing coun-tries of the world, where peasant farmers account for close to 90 percent of the areaunder cultivation The hoe is the tool used almost exclusively in land preparation ofpeasant agriculture, for combined primary and secondary tillage, and for land-formingoperations such as ridging, bedding, mounding, bunding, ditching, etc Hoes for landpreparation come in different sizes, weights and peculiar shapes, having evolved overthe years to suit widely varying crops and conditions of soil, farming culture, farmers’physiques and temperaments Described generally as long-handled implements with thin,flat blades set transversely, common technical features of hoes include long handles andheavy heads carrying the cutting blades or shares Handles vary a great deal in length,shape and curvature Blades also vary a great deal in shape, size and curvature, lead-ing to an intriguingly varied world of hoes, as illustrated by the small sample given inFig 1.2 Wide-bladed hoes are used for digging, ridging and mounding under normalsoil conditions; narrow-bladed ones are used for hard soil conditions; while tined hoes,which are not very common, are used for stony conditions

avail-Machetes/Spades

Other hand tools used to complement the hoe in land preparation under peasantagriculture include machetes, axes, spades, forks, and rakes, which also vary in sizesand shapes, as illustrated in Fig 1.2 Next to the hoe, the machete is one of the mostimportant tools in peasant agriculture, where it is indispensable in land clearing and ahost of other crop production operations

Manual Planting Tools and Machines

Hoes

The hand hoe of appropriate size and shape is the most versatile tool used by thepeasant farmer in planting cereals, root crops and other crops The farmer with the handhoe can use his judgment and experience to place the seeds or planting materials atoptimum depths and appropriate spacings within and between rows, and provide justthe right firming pressure to achieve good yields Hoes used for planting, while varyinggreatly according to diverse cultural preferences, usually are lighter and smaller thanthose for primary tillage or ridging, mounding, bedding or ditching operations, becauseless energy is demanded (see Table 1.1) and closer attention required

Manual Planters

Unlike the case for land preparation, there are many hand-operated machines availablefor planting and sowing, often with improved results in terms of uniformity of plantspacing and row configuration The manual planters may be as simple as dibbers, whichare pointed instruments made of steel or wood tipped with steel, used to place seeds inthe ground Or they may be as sophisticated as the various types of jab planters or pushed

Figure 1.2 A Variety of Hand Tools for Land Preparation A - Hoes; B - Machetes; C - Shovels,

spades, forks and rakes.

or pulled seed drills with more complex seed metering devices In this case, differentmetering mechanisms give rise to such planter types as seed-roller, fluted-roller, slide-roller and chain- and- sprocket driven seed drills/planters Illustrations of some of themajor types of manual planting tools and machines are given in Fig 1.3.

It is important to state here that the more sophisticated pushed or pulled planters,which usually are equipped with seed coulters or other furrow openers, do require well-prepared seed beds, which a typical peasant farmer usually is not able to provide Infact, a peasant farmer, whose only or major means of land preparation is the hand hoe,

is not likely to prepare enough land area to make the ownership or use of the moresophisticated hand-operated planters economical As a result, adoption of these pushed

or pulled planters by peasant HTT farmers is very limited indeed

Manual Weeding Tools and Machines

Hoes

What is said about the hand hoe with respect to planting applies to weeding andcultivation Generally speaking, in peasant agriculture, the heavy work of land prepara-tion using big hoes is handled by the men while subsequent field operations, especiallyweeding, are undertaken by women and children, using the smaller and lighter hand hoesthat come in three major types: digging hoes, chopping hoes and pushing/pulling hoes.Most peasant farmers own only the digging hoe type, which they use for different tillageoperations, often with designs that are peculiar to certain traditional communities, such

as the design called ikeagwu-agadi (literally meaning “exhaustion free for the aged”) by

Igbo-speaking people of Nigeria, which is a very popular hoe (see Fig 1.4) for weedingunder all soil conditions, soil topography and cropping patterns

By implication, the chopping hoes, used to chop the weeds and soil, though suitableunder hard or friable soil conditions and all conditions of soil topography and croppingpattern, are much less popular Still less popular are the pushing/pulling hoes, used tocut weeds under the soil surface but suitable only under friable soil conditions Someexamples of weeding hoes are given in Fig 1.4

Rotary Hoes and Wheeled Cultivators

Human-powered rotary hoes for weeding do exist but are mainly used for row croppedpaddy rice or upland crops in friable soils Also, many designs of human-poweredwheeled cultivators, with different kinds of weeding shares (tines, hoes, etc.) are avail-able but are suitable only for row crops in friable soils Some examples of rotary hoesand wheeled cultivators are given in Fig 1.4 Naturally, use or ownership of these moresophisticated human-powered weeders is very much restricted, thereby severely lim-iting their impact on the activities of peasant or small-holder farmers of the tropicalworld

Slashers

For completeness, human-powered slashers, most commonly in the form of machetes

or cutlasses, should be mentioned as important human-powered weeding tools used bypeasant farmers Slashers are used to cut down above-ground parts of weeds and areespecially useful in controlling weeds in plantations or perennial crops

Figure 1.3 Some Examples of Manual Planting Machines A - Hand-pushed centrifugal grain/fertilizer broadcaster; B - Hand-pushed rotary injection planter; C - Hand-pushed seed drill

D - A variety of jab planter.

Figure 1.4 Some Examples of Weeding Tools and Machines A - Weeding hoes

(Ikeagwuagadi); B Improved weeding hand hoe; C Handpushed rice weeder; D Wheeled hand-pushed weeder; E - Hand-pushed ridge-profile weeder.

-Manual Harvesting Tools and Machines

From discussions thus far, it is evident that tools and machines for field operationsused by peasant farmers have retained their pristine forms and sizes as developed bytheir ancestors centuries ago This is particularly true of harvesting operations for whichthe hoe, various diggers, machetes and knives, sickles and scythes, persist as the majortools available to peasant farmers of the developing countries of the world A few man-ual harvesting machines have been developed here and there, but they cannot competefavorably with the manual harvesting tools in terms of cost and efficiency

Hoes

If the hoe is thought ubiquitous in peasant agriculture, well so it is It is the principaltool used by small holder farmers to harvest root and tuber crops (yams, cocoyams,potatoes, corn, cassava, etc.) as well as all crops that develop underground, such asgroundnuts Of course, the type of hoe used depends on the crop, the topography (flat,beds, ridges or mounds) and the soil type or condition (hard or friable, plastic or muddy).Happily, in most cases, a suitable hoe is always available

Diggers and Lifters

A variety of simple tools consisting of long-handles with sharpened or speared diggingtips made wholly of wood, wooden with steel tips, or made wholly of steel, form a secondgroup of tools known as diggers, which are used to harvest root and tuber crops, especiallyyams Often they are used together with hoes to deal with roots and tubers that develop

at considerable depths in the ground Sometimes, shovels and forks, where available, areused in place of wooden diggers There are also a number of designs of hand tools calledlifters, used for root crops, especially cassava, as illustrated in Fig 1.5

Machetes and Knives

For harvesting cereals (millet, corn, rice, sorghum) peasant farmers use various types

of machetes or knives developed over the centuries to cut the plant stalk or grain heads, in

a once-over operation or selectively, with the special advantage that shattering losses areminimized Another advantage is that inclusion of unnecessary vegetation is drasticallyreduced, making for lower transport costs and safer storage The main disadvantage isthe inherently high labor requirements, which can be considerably higher than those forsickles, especially for heavy crops Special knives have been developed for some crops,such as sugar cane and oil-palm

Scythes

A scythe is a variant of a sickle, composed of a long, curving blade with a sharp edge,made fast at one end to a long, bent shaft with a handle forming a unit called the snath

Figure 1.5 Some Examples of Harvesting Tools other than Hoes and Machetes A - Different traditional sickle shapes; B - Some Nigerian sickles; C - Various harvesting hooks; D - Scythe handles; E - Different scythe blades; F - Sickle dimensions; G - Cassava lifter.