Crop Production and Soil Management Techniques for the Tropics

By Dominic J. Udoh

The book is a compact and easy-to-use source of technical information on crop production and soil management. It is meant for use by students and teachers of agriculture at the college and the undergraduate levels; also farmers and agriculturists. It is presented in two parts (1 and 2).

Part 1 discusses the principles and factors that determine success in crop production, such as the roles of soil, climate and technology adoption. In discussing the nature and properties of soils, specific attention is given to examples in the calculations of quantities, especially in the aspects of soil physics and soil chemistry. The roles of fertilizers, manures and soil amendments in the sustenance of soil fertility are discussed and illustrated with field data. Methods of converting soil test values of fertilizers to quantities and rates per hectare are given; so also are the procedures for ameliorating the challenges posed by soil pollution. There is also a discussion on the recently approved World Reference Base (WRB) for soil resources as to how it has enabled correlations among similar soil Groups and Orders across the different national classification systems that are in use. The 32 Reference Soil Groups (RSG) of the WRB are listed to create awareness on this very useful report provided by the FAO and UNESCO.

Part 2 of the book deals with discussions on the nature, uses and cultivation processes for the wide range of crops produced in the tropical and subtropical regions of the world. National production levels are given with the perspective that such information reveals the relative popularity of some crops in certain countries and also their economic importance. This section on crop production covers two-thirds of the book and provides very handy briefs for quick and easy sourcing of information on a wide array of crops.

The book ends with appendices that provide frequently required information on scientific values, constants, equations and terminologies. It is a handbook of general information on the issues of managing soils and producing relevant crops successfully in the face of a multiplicity of challenges.

• Language: English
• Publisher: Tellwell Talent
• Release date: Oct 26, 2021
• ISBN: 9780228849919

Dominic J. Udoh

Dominic J. Udoh (Ph.D.) is a Soil Scientist, Agronomist and practicing farmer. He is a former Rector of Akwa Ibom State College of Agriculture, Obio Akpa, now a campus of Akwa Ibom State University. He also formerly served as Hon. Commissioner for Agriculture, Akwa Ibom State, Nigeria.Dr Udoh studied at the University of Ife, Ile-Ife, for his B.Sc. degree, and later earned his postgraduate degrees at the Universities of Wisconsin and Mississippi State, USA. He lectured in the Universities of Uyo and of Akwa Ibom State, where he served as Head of Department, Soil Science. He presently resides in the City of Red Deer, AB, Canada.Bassey A. Ndon (Ph.D.) is an Agronomist and Crop physiologist. A Professor and former Dean, Faculty of Agriculture, University of Uyo, Nigeria, he obtained his doctorate degree at the University of Wisconsin, Madison. Prof. Ndon had served as Director, School of Continuing Education, University of Uyo, and also as Research Physiologist at the Nigerian Institute of Oil Palm Research, Benin City. He is currently involved in consultancy and the development of tertiary education in West Africa.

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Copyright © 2021 by Dominic J. Udoh • Bassey A. Ndon

All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author, except in the case of brief quotations embodied in critical reviews and certain other non-commercial uses permitted by copyright law.

Tellwell Talent

www.tellwell.ca

ISBN

978-0-2288-4992-6 (Paperback)

978-0-2288-4991-9 (eBook)

Crop Production and Soil Management Techniques for the Tropics

Examples of Profiles of Two Orders of Tropical Soils

Dominic J. Udoh

Bassey A. Ndon

Table of Contents

Dedication

Foreword

Preface

Acknowledgements

Part 1: Agricultural Soils, Principles of Plant Nutrition and Methods of Soil Fertility Management

Chapter 1: Factors Affecting Crop Production

1.0 Introduction

1.1 Climatic Factors

1.2 Soil Factors

1.3 Plant Genetics factor

1.4 Pests and Diseases

1.5 Farm Management Practices

1.6 Farm Infrastructural Facilities

Chapter 2: The Soil, a Medium for Plant Growth

2.1 Introduction

2.2 The Formation of Soil

2.3 Soil Composition and Properties

2.4 Soil Microbiology

2.5 Soil and Land Classification

Chapter 3: Soil Fertility and Plant Nutrition Management

3.1 Introduction

3.2 Plant Nutrition

3.3 Sources of Plant Nutrients and Factors that Affect Availability/Uptake

3.4 Managing Soils for the Sustenance of Fertility

3.5 Problem Soils and Methods of Managing Them

Chapter 4: Methods of Controlling Pests, Diseases and Weeds in Crop Production

4.1 Introduction

4.2 Crop Pests and Diseases

4.3 Methods of Pest and Disease Controls

4.4 Weeds and Methods of Control

4.5 Problems Associated with the Use of Agro-chemicals

Chapter 5: Farm Mechanization Practices

5.1 Mechanization Power, Equipment and Tools

5.2 Specialized Farm Machines

5.3 Farm Implements

5.4 Summary

Chapter 6: Methods of Seed Production and Handling

6.1 Introduction

6.2 Stages of Seed Production and Certification

6.3 Organization of a National Seed Production System

6.4 Regulation and Control of Seed Production Practices in Nigeria

Part 2: THE PRODUCTION OF FIELD AND

PLANTATION CROPS

Chapter 7: Cereal Crops Production

7.1 Maize (Zea mays L.)

7.2 Rice (Oryza sativa L.)

7.3 Guinea Corn [Sorghum Bicolor (L.) Moench or S. Vulgare]

7.4 Pearl Millet (Pennisetum glaucum or Cenchrus americanus)

Chapter 8: Leguminous Crops Production

8.1 The production of Cowpea (Vigna unguiculata (L.) Walp)

8.2 Soybeans (Glycine max L. Merr)

8.3 Groundnut (Peanut) – (Arachis hypogaea L.)

8.4 Bambara Groundnut (Vigna subterranea L.)

Chapter 9: Root and Tuber Crops Production

9.1 Yams (Dioscorea spp.)

9.2 Cassava (Manihot esculenta Crantz)

9.3 Cocoyam (Colocasia Esculenta, and Xanthosoma sagittifolium)

9.4 Irish Potato (Solanum tuberosum)

9.5 Sweet Potato (Ipomea batatas)

Chapter 10: Vegetable Crops Production

10.1 Fluted Pumpkin (Telfairia occidentalis Hook. f., and Telfairia pedata)

10.2 Water Leaf (Talinum triangulare, L.)

10.3 Lettuce (Lactuca saliva)

10.4 Cabbage (Brassica oleracea, L. or B. oleracea var. capitata)

10.5 Gnetum africanum (Local names are: Koko, Eru, Afang and Ukazi)

10.6 Eggplants (Solanum melongena L.)

10.7 Tomatoes (Solanum lycopersicon)

10.8 Okra (Abelmoschus esculentus L.)

10.9 Benniseed or Sesame (Sesamum indicum, L.)

10.10 Melon (Citrullus vulgaris)

10.11 Carrot (Daucus carota)

Chapter 11: Spice Crop Production

11.1 Pepper (Capsicum Frutescens L.)

11.2 Ginger (Zingiber officinale Roscoe)

11.3 Onion (Allium cepa)

11.4 Basil Leaf Plant (Ocimum spp.)

Chapter 12: Fibre Crops Production

12.1 Cotton (Gossypium spp.)

12.2 Jute (Corchorus capsularis)

12.3 Kenaf (Hibiscus cannabinus)

Chapter 13: The Production of Tree and Other Plantation Crops

13.1 African Oil Palm (Elaeis guineensis Jacq.)

13.2 Coconut Palm (Cocos nucifera L.)

13.3 Raphia Palm (Raphia hookeri P. Beauv.)

13.4 Date Palm (Phoenix dactylifera)

13.5 Para-rubber (Hevea brasiliensis L.)

13.6 Sugar Cane (Saccharum officinarum L.)

Chapter 14: The Production of Fruits

14.1 Pineapples (Ananas comosus, L., Men.)

14.2 Mango (Mangifera indica, L.)

14.3 Guava (Psidium guajava L.)

14.4 Orange (Citrus spp.)

14.5 Avocado Pear (Persea gratissima Gaertn or Persea americana Mill.)

14.6 Cashew (Anacardium occidentale, L.)

14.7 Pawpaw (Carica papaya L.)

14.8 Plantains and Bananas (Musa spp.)

14.9 African Pear (Bush Butter Tree: Dacryodes edulis)

Chapter 15: The Production of Beverage and Stimulant Crops

15.1 Cocoa (Theobroma cacao, L.)

15.2 Tea (Camellia sinensis, L.)

15.3 Coffee (Coffea Arabica L.),

15.4 Kola (Cola nitida (Went) Schott & Endl.)

15.5 Tobacco (Nicotiana tabacum, L.)

Chapter 16: The Challenges that Face Agricultural Development in the Humid Tropics

16.1 Introduction

16.2 A Review of the Efforts Made so Far

Appendix1: Tables of Measures, Conversions and Equivalents

Appendix2: Abbreviations and Acronyms of Some Agricultural Organizations, Parastatals and Institutions

Bibliography

Dedication

To

The Lord God Almighty, who created mankind and placed him on earth to work it for food production and to also manage it properly to its productivity and usefulness as both a garden and a place for safe and cheerful habitation. It is in connection with this that we decided to write a book to guide those involved with soil management and successful crop production.

Foreword

There is an overwhelming global consensus that a virile agricultural sector plays indispensable roles in food security, poverty reduction and economic development. In Nigeria, the crop production subsector is a major driver of the agricultural sector, as it contributed about 75 percent to the growth of the sector in recent years.

The crop subsector is however yet to attain its optimum potential due to challenges imposed by a paucity of arable and fertile lands, low yields and climate change, among others. Indications are that overall crop yields in Africa and South Asia could decline by as much as 40% by year 2050, and yet during this period, demands for food is expected to surge as diets change and populations increase in the developing world.

The Food and Agriculture Organization of the United Nations (FAO) asserts that increased productivity on sustainable intensification of crop production based on enhanced levels of soil fertility management and a shift from subsistence farming to a market-oriented production. The authors of this epoch making book must be commended for combining theoretical offerings in a practically oriented manner, the focus being to produce a fresh set of agricultural practitioners with a market-oriented mindset. The rich contents of this book are to be expected with respect to the pedigree of the two authors who are practicing agriculturists with wealth of experience in the public sector.

The updated offering is an obvious improvement on the first edition, published in 2005 and the second edition published in 2016. It is divided into two sections and sixteen chapters and covers the whole gamut of actual crop production, the factors that affect sustainable crop production, and the management of the input resources required for intensification of the production of about fifty-two tropical crops.

The book, written in lucid and free-flowing prose, is suitable for undergraduate and postgraduate students of agriculture. It is useful for teachers and lecturers taking early soil, crop and agronomy classes; also farmers and practising agriculturists will find it a good source of information on many general topics on soil fertility, fertilizers and manures, isuues of crops and production data, as well as disease and pest management. It is my great pleasure and privilege to recommend Crop Production and Soil Management Techniques for the Tropics, written by accomplished scholars, toall relevant stakeholders and aspiring agriculturists.

Prof. Ini Akpabio

Dean, Faculty of Agriculyure,

University of Uyo,

Uyo, Nigeria.

Preface

Agricultural production in the tropical world has seen serious adoption of modern technologies in farming methods in the last three decades. What had therefore been feared concerning food sufficiency, other than natural disasters, is no longer of major concern to several countries. Rather, interest and effort are shifting to increased production for the purposes of export earnings and industrial development. This third edition of the book is presented to encourage the sustenance of effort in the adoption of modern farming approaches and practices, especially in the management of soil fertility and in crop husbandry.

In the first edition of this book material had been presented in a much summarised form in order to enable the reader pick his information quickly. The same approach is still followed, generally, in this third edition but there is expansion in content and scope such as will help the reader obtain fuller information on the various subjects and topics. Such expansion is most prominent in the chapters dealing with the soil. Effort has been made to update information on soil classification, including information on the recently published (2015) revision of the World Reference Base for soil resources. The chapters on crop production have new entries, and improved information on crop nutrient contents. For people in urban areas who are not familiar with the physical form of some crops, more illustrative photographs have been added.

In view of the speed of generation of new scientific information in modern times one would hardly hope to have very effectively kept abreast with most of the changes but it is hoped that sufficient material has been covered to enable the student, teacher and farmer who uses this book to find it a helpful tool for the performance of their academic and farming tasks.

The authors accept responsibility for the contents of this book and will welcome suggestions for further improvement and updating. We may be contacted by email as indicated below.

January, 2021

Acknowledgements

We remain grateful to Almighty God for his help in the execution of this project and we also request God to bless all those who have helped in one way or another in the production of the book. Special thanks goes to all those who helped in the production of the first edition of the book, and so we appreciate the contributions of Professor N. U. Ndaeyo, Dr P. E. Asuquo and other colleagues who offered useful advice on content and presentation. We like to still thank Ekomobong Nyong, Lucy G. Johnson, Pauline Obot and Arit Etiefe for the original typesetting of the book. Finally, we thank Edidiong D. Udoh, Idopiseabasi E. Asuquo, Esther Bassey, Imaobong D. Udoh and Obong-Ofiok Udoh for help in the preparation of the revised manuscript.

Dominic J. Udoh

Bassey A. Ndon

PART 1

Agricultural Soils, Principles of Plant Nutrition and Methods of Soil Fertility Management

Chapter 1

Factors Affecting Crop Production

1.0 Introduction

Levels and intensities of crop production are largely controlled by the prevailing factors of the natural environment, edaphology, ecosystem dynamics, plant genetics and human intervention. The interdependence among climatic, edaphic, plant and human factors makes it mandatory for agriculturalists to have in-depth knowledge of the conditions required for the successful production of crops.

It is well known that crop growth depends on the ability of green plants to transform, with the help of solar energy, inorganic compounds into organic compounds such as carbohydrates, proteins, fats and oils. These are then stored in the different organs and tissues of the plant and used in support of plant growth, the generation of physiological energy and the synthesis of plant products.

The factors that most affect crop production shall therefore be discussed under six major headings, namely:

(1)Climatic factors

(2)Soil (edaphic) factors

(3)Plant genetics factors

(4)Pests and diseases

(5)Farm management practices

(6)Farm infrastructural facilities

1.1 Climatic Factors

These include all the natural forces of the physical environment, namely: rainfall, solar radiation (light and temperature), relative humidity (R.H.), wind and wind velocity, and air flow/quality. The impacts of each of the factors, as they affect plant growth and development, can be explained as follows:

(a)Rainfall

This is a critical factor in the supply of water to plants. Where it does not rain adequately, crops cannot be grown, except under irrigation, which is an expensive system of crop production. Plant germination, growth and development are activated and sustained by soil water which is supplied by rainfall or by an irrigation system. Irrigation water is normally obtained from lakes, rivers, wells and boreholes by various technological methods. The seepage/percolation of water through soil during rainfalls builds up underground water reserves, which becomes the source of water that is tapped from wells and boreholes. Farming in arid areas or in the dry season usually depends either partly or wholly on irrigation systems.

Wetlands or marshlands are also used for cropping in the dry season when the water table drops adequately to allow proper aeration of plant roots. Some varieties of crops like rice and sugar cane can thrive in wet soils or under irrigation. Again, short season crops, such as the leafy vegetables and some cereals, are widely grown on drained wetlands by river banks and under irrigation. Success in growing a crop does not only depend on the amount of water supplied to the soil, it also depends on the rate of evapo-transpiration, which is, in turn, affected by the prevailing ambient temperature, relative humidity, vegetation cover or mulching.

When considered in detail, every part of the tropics has variations in the frequency, intensity and duration of rainfall, from as low as 100mm in the hinterland or desert fringe areas of West Africa to as high as 5,000mm in the monsoon ravaged Bay of Bengal in Southeast Asia. Rainfall duration may vary from 6 to 9 months; intensity may range from drizzle to heavy downpours or rain storms driven by very strong winds. Typhoons, tornadoes and hurricanes commonly occur in the coastal regions of the wet tropics during the rainy season. Rainfall intensity and duration generally decreases as one goes inland in most areas of the tropics, except where desert fringes reach the coast.

Several areas of the tropics frequently suffer heavy soil loss on account of erosion, landslides and floods. Drainage practices are required to remove excess water and enable crop cultivation where land is scarce. Also crops may be selected for those species or varieties that are adapted to wetland ecology. Such crops include the palms (Family: Arecaceae), the mangroves (Family: Rhizophoraceae) and rice (Oriza spp.), among others. Species of these three families, especially, are widely distributed in the wetland forest zones of the African, Asian and American tropics.

Based on experience and extant agricultural data provided by FAO and national data sources it has been established that most crop production, as well as highest yields around the world depends on soil water obtained from direct rainfall. Crop failures or very poor yield normally result whenever rainfall fails or reduces significantly. Irrigation is an excellent substitute where technology is available, relatively cheap and water source available. We can conclude, therefore, that the best success in growing crops depends ultimately on the supply of adequate amounts of water by rainfall.

The amount of water available for a crop is usually calculated by deducting the total estimated loss of water (by evapo-transpiration, crop uptake, surface runoff, seepage or percolation) from the estimated input of water (rainfall and irrigation water, where applied).

(b)Solar Radiation

i)Light

Solar radiation is the ultimate source of all terrestrial and atmospheric energy. As much as 12% of the visible spectrum could be converted to plant energy when growing conditions are optimal and a green crop surface is present. The rates of photochemical processes are influenced more by variations in light intensity than by differences in species, although both are important. Indeed higher yields and greater mean growth rates are obtained from crops adapted to production of vegetative rather than grain products. Exposure to radiation, such as up to 9 hours of daylight - as determined by day length and season – actually plays the most important role in crop productivity. The photosynthetic process continues as long as there is irradiation; and carbohydrates are synthesized as represented by the equation:

When plants are well exposed to sunlight, and not shaded, they will grow more stoutly and luxuriantly, with well differentiated leaves and branches. They will also fruit abundantly and yield more highly. This happens because stronger light intensity enhances the activity of growth hormones in plants. Shaded crops, on the other hand, have etiolated stems; weak, broad leaves and poor capacity to withstand stress.

ii)Temperature

Each crop has its suitable temperature span: that is, its own optimum temperature range for growth and development. A range of 15°C—32°C supports the good growth of most tropical and subtropical region crops. Lower or higher temperatures limit seed germination and also affect flowering, fruit and seed development, grain filling and maturation, and tuber or seed survival.

In most tropical areas – with their relatively small annual variations in diurnal and seasonal temperature ranges – there is never a temperature limitation to crop growth, except in the drier inland regions or desert fringe areas where very high ambient temperatures often raise evapo-transpiration and soil temperature to very high levels such that crop growth and yield are reduced by moisture stress. Soil water reserves are also quickly depleted in such circumstances. Therefore only short season or early maturing crops species or varieties of the cereal legume and leafy vegetable families are favoured. This is why cereals, pulses and spice crops constitute the most predominant crop-groups grown in the savannah and dessert fringe zones of the tropics; whereas tubers and tree crops abound in the humid, coastal rainforest zones.

iii)Relative Humidity (R.H.)

This is the amount of water vapour that is held by air at a given temperature relative to the total amount the air can hold at the same temperature. The value is calculated as a ratio percentage. Temperature affects R.H. and vice-versa, and under irrigated agriculture the water needs of plants increase with reduction in R.H. High R.H. is not desirable because it favours attacks on crops by pests and disease pathogens.

iv)Wind

Wind influences plant growth in arid regions mostly if there is a frequency of strong winds. Wind affects both the soil and the plant. Heavy sand particles carried by windstorms cause soil erosion by scouring the soil surface through saltation. The sand and dust particles carried by the wind also damage plant leaves and tissues and can destroy seedlings by completely covering or uprooting them. In the tropical forests and coastal areas winds and rainstorms blow down young plants, and several hectares of crops are often destroyed through stem breaking (plantains and bananas, especially).

Physiologically, lodging, branch tearing and foliage damage caused by strong winds weaken photosynthetic capacity, which then causes reduction in plant growth rate and yield. Hot, dry winds adversely affect photosynthesis by causing the stomata to close, while moderate breezes can enhance photosynthesis by continuously replacing the carbon dioxide absorbed by the leaf surface.

v)Other environmental factors

Air quality - this is important when there are risks of air pollution. Air pollution is caused by the release of obnoxious, polluting gases such as SO2, NO2 and CO2, as well as gases of the hydrocarbon ((HC) group. These gases are released at point sources, viz: industrial plants, mining operations, vehicle and plant operations, petroleum oil and gas production, oil refining, gas flaring and poor urban waste disposal. When these gases are released into the air and atmosphere they cause green house effects and also poison plants. The necrotic spots and tissue-death symptoms often observed on plant leaves and twigs are frequently caused by the impacts of these gasses on the living tissue of plants.

Altitude – this is also relevant since some crops perform better or optimally only at higher elevations, while others grow well at low elevations.

1.2 Soil Factors

Soils provide the medium and suitable environment for plant growth and anchorage. When the soil is fertile—that is, contains adequate amounts of the essential nutrients in the right proportions; is in the right pH range; is free from toxic substances, and is well drained to favour effective aeration— plants will grow well and yield highly, if the supply of water is also adequate. When nutrients are deficient or soil pH is unfavourable, plants will not grow or yield well. High contents of organic matter, high cation exchange capacity and base saturation are indicators of fertile soils.

The physical characteristics of soils, like the chemical properties, are equally significant. Loamy to clayey soils support crops better than sandy or wet clay soils because of better availability of nutrients, better soil-plant-moisture interrelationships and higher levels of microbial activity. The properties of soils, as they generally affect plant growth and production, are explained in more detail in the chapters on soils and soil fertility management, but emphasis at this point is that it is important to adopt soil management practices that promote the sustenance of high fertility.

1.3 Plant Genetics factor

Crops that belong to different genetic families, genera, species and varieties may differ greatly in their need for nutrients and water, growth rate and yield, and also in their response to the general environment due just only to their differences in genetic makeup. The differences may be in terms of yield capacity; days to seed or product maturation; tolerance to pests, diseases, drought, flood, soil acidity and salinity; quality of seed or product, and size or height of plant at maturity. This is the reason why plant breeders carry out several adaptation trials at multiple locations before they recommend crops of certain families, genera, species and varieties to the different climatic or geographic zones of a country or the world. Much plant breeding effort is also directed to producing crop varieties that give high yields under relatively lower levels of nutrient and environmental profiles.

1.4 Pests and Diseases

Other factors that affect crop production are pests and diseases. The most important crop pests are the grasshoppers, birds, caterpillars (of butterflies and moths, especially), leaf miners, beetles and weevils; while the most common causal factors of diseases are fungi, bacteria, viruses, and nematodes. Amongst these, fungi are the most common causal factor.

Crops that are rich in proteins (pulses and cereals) are the most susceptible to pest and disease attacks. Farmers spend much money to buy agrochemicals if they must control these pests/diseases. As many chemicals are poisonous to livestock and humans great care is required in the use agrochemicals. Materials meant for use as seed are usually handled separately, treated well with appropriate chemicals and stored in special rooms, while the lots meant for consumption would not be treated at all except with mild and very short duration chemicals whose effect wear off within specified time durations and thereby pose no health hazards to humans. There are some biological procedures for controlling pests and diseases and theses are elaborated upon at Chapter 4 of this folio.

1.5 Farm Management Practices

Good yields of crops cannot be obtained even under the most favourable environmental and soil conditions if farm management practices are poor or inappropriate. The basic or fundamental management practices that must be recognised and handled properly include:

(1)Selection of suitable location (fertile soil, suitable topography, etc.) for the farm.

(2)Use of appropriate seedbed.

(3)Use of healthy, disease free seeds and other planting materials to establish the crop.

(4)Adoption of appropriate technologies in the conservation of or enhancement of soil Fertility (use of fertilizers, manures, lime, agro-chemicals, crop rotation, etc.)

(5)Efficiency in soil water management. The farmer should plant in time to optimise water use from rainfall. He must also select crop varieties in relation to water use efficiency and income generating capacity if cropping under irrigation.

(6)Adherence to good agronomic practices–timely weeding, farm hygiene, pest control, timely harvests, proper processing, handling and storage of products.

(7)Effective training of farm staff in the best techniques of soil and crop management.

From the foregoing, it is clear that farmers need to understand the impact of the factors of crop production and to adapt their management practices to fit into the prevailing conditions. Conversely, they should select projects that, though not the most desirable from their personal viewpoint, but nevertheless the best choice in terms of economic returns.

1.6 Farm Infrastructural Facilities

Modem farming methods require interventions, whether mechanical or electrical, in some stages or steps of the production process. When properly utilised, mechanization reduces, and may even completely remove the tedium and drudgery associated with manual operations and allow more work to be accomplished more efficiently.

Some of the infrastructural facilities that could enhance modern scientific crop production are:

a)Provision of roads, lanes and paths on the farm. These are crucial to farm operations and should be wide enough to allow for vehicular movement to all parts of the farm. A minimum width of 2.0m is recommended for lanes and paths. Side paths (used only for access to plots, including when moving with carts and wheelbarrows) may be about 1m wide. The surfaces of the roads, drives and lanes or paths should be firm and well drained to provide all weather accessibility to all activity centres.

b)Provision of adequate quantity of clean water is very essential in a modern farm. The water source can be a river, stream, municipal supply system or borehole at the farm. Another approach that can be feasible in a heavy rainfall area is to create water storage ponds and tank where runoff and rain water may be collected and stored for irrigation and other uses after rainfall ceases.

To supply irrigation water to crops during the dry season or at other times when crops must be irrigated, there is often a need to construct mini-canals/channels for the conveyance of water from the source(s) of supply to the fields to be irrigated. Alternate arrangements could be the use of hoses, pipe lines or sprinkler systems.

c)Provision of electricity - this may be obtained from the public grid or from a farm owned generator. Electric power in the farm is required for water pumping, lighting of workshops and storehouses, farm products processing, drying of products like grains, and operation of electronic equipment. The standard of living of the farmer and other operators is also raised when they can use modern conveniences like the TV, radio and the phone within the farm environment. Graduate levels workers will more readily accept to work on a farm when electric power is available to enable them use electrical appliances. The ability to use the phone enables easy communication with input supplies and product customers, as well as contacts with hospitals or the police in the event of emergencies such as accidents, theft and fire.

d)There is need to provide first aid equipment and medicines at the farm for initial attention to injuries and other health emergencies before better help can be obtained from a clinic or hospital.

Chapter 2

The Soil, a Medium for Plant Growth

Food comes from the earth. The land with its waters gives us nourishment. The earth rewards richly the knowing and diligent farmer, but punishes inexorably the ignorant or lazy farmer. This partnership between land and farmer is the rock foundation of our successful social structure.

(W. C. Lowdermilk, 1940)

2.1 Introduction

From the viewpoint of agriculture, the soil is that natural body of weathered rock material mixed with organic matter and air which occupies the topmost layer of the earth’s crust, and which can support plant growth when watered. The soil is the medium for plant growth. It provides both nutrients and anchor to plants whose roots ramify in all directions. The roots absorb water (which supplies H) and 15 other essential nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Co, Cl and Ni) from the soil, and these constitute the plant’s nutrients. The other nutrients (C, O) are obtained from the air. Soils vary greatly in terms of depth, physical and chemical properties, fertility status and general characteristics, depending on their age, since formation; they vary also in climate, topography of associated land form, parent materials, etc. It is obvious that without productive soils there could be no agriculture and the state of human development that we see today.

In concluding this brief introduction to this chapter we like to point out to readers that many terms, as previously defined in the ‘Soil Science Glossary of Terms’, have been declared obsolete or been redefined by a Committee of Experts set up for the purpose by the Soil Science Society of America whose terminologies we use. A few examples of obsolete terms are:

active acidity, potential acidity; alkali soil, soil alkalinity (use alkaline soil); capillary potential, capillary water (use matric potential or soil water tension or suction); use gravitational potential instead of gravitational water; Pascal as pressure unit instead of bar; wetland soil instead of hydromorphic soil; salination instead of salinization, saline-sodic instead saline-alkali; etc.

The initial, formal publication of major redefinitions of terms was done in 1987, with various updated versions following that first effort. With the most recent revision published in 2015 it is obvious that the matter will remain a slow but continuous exercise. We therefore advise soil scientists, agronomists and other stake holders to continually access updated versions of the glossary in order to remain abreast with changes. In this book we have tried to exclude obsolete terminologies but many unidentified examples may be seen by readers, in which case we ask for tolerance. Future editions will make more corrections.

2.2 The Formation of Soil

Soils are formed when weathered rock material (parent material) undergoes further physical and chemical Soil Soil is formed by the weathering of rocks and addition of organic matter to the broken down rock materials under the influence of the five factors of soil formation, viz: parent material, climate, topography, living organisms, and time. The great variability of soils, in terms of forms and properties, is due, therefore, to the effects of these five factors and the intensities of their expression.

These factors can be explained briefly as follows:

i)Parent Material (pm): Disintegrated and decomposed igneous, metamorphic or sedimentary rock materials, which constitute the mineral phase of soil. It occurs in-situ or as transported sediment. Parent material can also consist of decomposed organic material (histic).

ii)Climate (cl): The regime of rainfall, temperature, wind, and relative humidity that prevails

iii)Topography (p): The shape, slope and positional orientation of the land upon which the soil is forming.

iv)Living Organisms (o): The microscopic, small and large plants and animals whose activities contribute to the soil formation process and whose decomposed dead bodies constitute the organic fraction of the soil.

v)Time (t): The period over which climate, topography and living organisms act upon parent material and interact together so that the formation of soil results. The soil formation process begins when temperature and pressure changes cause rocks to crack and chip. Further physical and chemical disintegration under the influences of heat, wind storm and rainfall, running water, mineral and organic acids, finally reduce the rock materials to very small sizes. The exposure of these small mineral particles, which have rather large specific surface areas, to the atmosphere over long periods of time results in more chemical reactions that involve carbon dioxide, oxygen and organic acids. Ultimately, the reactions cause the conversion of the rock and organic materials to agricultural soils.

In general, the predominant characteristics of soils depend therefore on:

(a)Type of dominant rock material from which its parent material was derived:

Whether it was igneous, metamorphic, sedimentary or mixtures of these rocks? Rocks that are rich in basic mineral elements (Ca, Mg, K and Na) contribute parent materials that form the more naturally productive soils. On the other hand, rocks that contain mostly silica (Si), aluminium (Al), sodium (Na) and similar non-nutrient materials usually give rise to soils of low native fertility.

(b)The intensity of the effects of the pm, cl and p soil-forming factors: This refers to the quantitative and qualitative impacts of the five soil-forming factors on the soil formed, e.g.:

(i)Effects of pm will differ in accordance with the preponderance or absence of certain kinds of minerals present in the parent material – whether rich in basic or acidic types, and in fine or coarse minerals. Soils from organic materials have a histic epipedon while others have only mineral horizons.

(ii)Climatic factors – differences in climatic conditions (temperature, rainfall, humidity, etc. generate significant differences in the type of soils formed.

(iii)The topography – soils formed on hill tops and steep slopes are usually thin and young compared with those on flats and valleys.

(c)Duration of the process: This determines the extent of soil horizon development. In some soils, only the ‘A’ and ‘C’ horizons have been differentiated. In others, there are ‘A’, ‘B and ‘C,’ horizons, while in yet others (old, highly-weathered soils), there are the ‘A’, ‘B1’, ‘B2’, ‘B2t’ and ‘C’ horizons.

(d)Extent of the Activity of Living Organisms: This is directly related to the availability of moisture and energy sources. Soils under thick grass or forest vegetation differ from those on sparsely vegetated land. Under moist soil conditions microorganisms, insects, earthworms and the arthropods are very active once sources of energy, such as organic wastes, are available. They greatly modify soil composition and properties through their activities in the decomposition of organic material – which include tunnelling through, and mixing subsoil and topsoil materials, releasing mucilage, humus acids or gels. The growth of roots also greatly modifies soil structure: grasses, especially, promote granulation while trees foster the recycling of subsoil minerals to the top soil. The top soil is therefore usually thicker where the activity of soil organisms is enhanced by an abundance of organic litter.

2.3 Soil Composition and Properties

2.3.1 The Composition and Components of Soils

(a)Composition of Soil

The topmost portion (15cm) of most well-watered and well drained mineral soils is composed as follows:

Mineral fractions – 45% ii) Organic Matter – 5% iii) Water – 25%, and Air – 25% (Fig.21). The wavy line separating the air and water components indicates a dynamic and inverse relationship between the two. Before discussing the component fractions of soil, we first to appreciate the structural profile of an ideal, mature soil type, which then constitute a template for defining the individuality of most soils.

Fig. 2.1 Soil composition

The Soil Profile – when a vertical section of soil is cut and examined, a typical layering pattern is observed, with each layer differing from the others in thickness, colour, texture, structure and chemical reactions.

The different layers are called ‘horizons’ and the whole vertical section is called a Soil Profile. All well-developed, undisturbed soils have their own distinctive profiles. Measures in the field indicate that profiles and their horizons may vary in depth from a few centimetres to several meters although profiles per se usually range between one and two meters.

A schematic representation of an idealized, highly differentiated soil profile, which includes the litter layer, is given in Fig. 2.2. The horizons are described briefly as follows, starting with the ‘A’ horizon:

Fig. 2.2: Schematic Outline of a Well Stratified Soil Profile

i)‘A’ horizon: this is the topmost mineral layer of soil that lies immediately below the ‘litter’ or ‘O’ layer. The ‘A’ horizon is dark in colour due to the presence of humus (residual organic matter). It constitutes the topsoil, which carries most of the plant available nutrients. The feeding roots of plants grow and ramify there. ‘A’ horizons may, in some well-developed soils, show sub delineations designated as A1 and A2, due to the eluviation (leaching out by rainwater) of materials like organic matter, clay and soluble minerals from the upper to the lower part of the horizon or down the profile to the B-horizon. ‘A’ horizon is the layer that is most exposed to disturbances and ruin by rainfall, wind storm, pollutants and human activity.

ii)‘B’ horizon: This layer underlies the ‘A’ horizon of an undisturbed soil, and is termed the subsoil. For most cultivated soils, however, it may not be correct to automatically equate the ‘A’ and ‘B’ horizons as being respectively separated into ‘topsoil’ and ‘subsoil’, by reason of the fact that soil tillage during seedbed preparation may mix the ‘A’ and ‘B’ horizons, except in limited situations where ‘A’ horizons are deeper than 25 cm or where only shallow tillage is required. Topsoil on frequently cultivated land is actually the ‘plow-layer’, which is composed of the ‘A’ and part of the ‘B’ horizons of soil. The organic matter and fine minerals leached from the ‘A’ horizon are deposited in the ‘B’ horizon in the processes of illuviation. When this happens, the ‘B’ horizon may be differentiable into 2 or more sub-horizons identified as B1, B2, or B2t and B3. Deeply penetrating roots can absorb some soluble minerals from the ‘B’ horizon and such minerals are recycled back to the ‘A’ horizon when dead plant matter is deposited on the soil surface.

iii)‘C’ horizon: This is the unconsolidated material below the solum (the ‘A’ and ‘B’ horizons). The ‘C’ horizon may or may not fully constitute the whole parent material from which the soil solum was formed. This horizon is least affected by the factors of rock weathering and soil formation. There is greater accumulation of Ca, Mg, and CO3-2 in this horizon. Other than the three standard horizons described above two other horizons may be described as follows, viz:

‘O’ horizon – this is the litter layer that lies or sits above the ‘A’ horizon like a cap. It consists of dead and decaying but unincorporated plant and animal residues. Materials, especially soluble elements like K+, leach from the litter layer to the ‘A’ horizon as bacteria, fungi and soil arthropods invade this litter layer for fresh supplies of organic energy sources. The ‘O’ horizon may be described as ‘O1’ and ‘O2’ to separate the layer of relatively fresh and easily identifiable litter/organic material from the layer where most of the litter/organic materials are decomposed and identification of source is more difficult.

‘R’ horizon – this is the underlying bedrock or unconsolidated deposits upon which the profile rests or was developed. The underlying bedrock of soil profiles may be sandstone, granite, limestone, basalt or unconsolidated rocky or sandy sediments deposited by floodwaters, landslides or mudflows.

In general, soil profiles and their horizons vary in depth from a few centimetres to several meters, although most have depths of only one to two meters. Soils with deep ‘A’ horizons are usually more fertile than similar soils with shallow ‘A’ horizons. The depths of ‘A’ and ‘B’ horizons, the texture, pH, nutrient assay and chemical behaviour of soils usually determine their value for crop cultivation.

(b)The Components of Soil:

The soil mineral fraction:

The mineral component of the soil is made up of soil particles (particulates) that are less than 2.0 mm in diameter, which are identified and classified by size fractions as sand, silt, and clay. In many classifications, the ‘sand’ is subdivided into subgroups: very fine, fine and coarse sand. Most classification systems agree on < 200 µm diameter as the boundary between the clay and silt fractions (see section 2.3.2a below for more details).

Depending on the rock materials from which they were derived, the assorted mineral particles of soil contain or carry nutrient elements, which become available for plant nutrition. Such elements include phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), iron (Fe), copper (Cu), Zinc (Zn) and manganese (Mn). The mineral fractions, especially the colloidal fraction (particles of < 0.001mm or 1µm diameter) play important roles