Lockhart and Wiseman's Crop Husbandry Including Grassland

Steve Finch, Alison Samuel, Gerry P. Lane

• Publisher: Woodhead Publishing
• Year: 2002
• eBook ISBN: 9781855736504
• Edition: 8
• Topic: Technology & Engineering
• Subtopic: Agronomy
• Index: Technology & Engineering

First published in 1966, Lockhart and Wiseman's Crop Husbandry Including Grassland has established itself as the standard crop husbandry text for students and practitioners alike. Radically revised and expanded, and with a new team of authors, the eighth edition confirms and extends its reputation.Part one looks at the basic conditions for crop growth with chapters on plant structure and growth, soil analysis and management, and the use of fertilisers and manures. There is also a new chapter on the influence of climate and weather. Part two surveys general aspects of crop husbandry. As well as a discussion of cropping techniques, there are new chapters on the important new areas of integrated crop management and organic crop husbandry, as well as discussion of seed selection and production. Part three then looks at how these general techniques are applied to particular crops, with chapters on cereals, root crops, fresh harvested crops, forage crops and combinable break crops. Part four considers the use of grassland with chapters on classification, sowing and management, grazing and conservation for winter feed.Lockhart and Wiseman's Crop Husbandry Including Grassland remains the standard text for general agriculture, land management and agri-business courses, and is a valuable practical reference for the farming industry.- The eighth edition has been widely expanded and remains the standard text for general agriculture, land management and agri-business courses- Includes new chapters on cropping techniques, integrated crop management and quality assurance, seed production and selection and the influence of climate- Discusses basic conditions for crop growth, how techniques are applied to particular crops, the influence of weather and the use of grassland

Part 1

Conditions for crop growth

1

Plants

Abstract

Plants are living organisms consisting of many specialised individual cells. They differ from animals in many ways a very important difference is that they can build up valuable organic substances from simple materials. The most important part of this building process called photosynthesis, is the production of carbohydrates such as sugars, starch cellulose.

1.1 Plant physiology

1.1.1 Photosynthesis

In photosynthesis a special green substance called chlorophyll uses light energy (normally sunlight but sometimes artificial) to change carbon dioxide and water into sugars (carbohydrates) and oxygen in the green parts of the plant. The amount of photosynthesis per day which takes place is limited by the duration and intensity of sunlight. The amount of carbon dioxide available can also be a limiting factor. Shortage of water, low temperatures and leaf disease or damage can also reduce photosynthesis. The cells that contain chlorophyll also have yellow pigments such as carotene. Crop plants can only build up chlorophyll in the light and so any leaves that develop in the dark are yellow and cannot produce carbohydrates.

Oxygen is released back into the atmosphere during photosynthesis and the process may be set out as follows:

(a) The light stage (light dependent)

This takes place in the thylakoid membranes inside the ‘chloroplast’, an organelle found inside the cells of green tissue. Light provides energy for the chlorophyll molecule that releases electrons. These split water into oxygen and hydrogen.

The chemical reaction of this stage is:

$2{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{H}}_2+{\mathrm{O}}_2$

[1.1]

The hydrogen then moves into the next stage:

(b) The dark stage (light independent)

This takes place in the watery stroma of the chloroplast. Here the hydrogen is combined with carbon dioxide to give carbohydrates and water:

$2{\mathrm{H}}_2+{\mathrm{CO}}_2\to {\mathrm{CH}}_2\mathrm{O}+{\mathrm{H}}_2\mathrm{O}$

[1.2]

The carbohydrates are simple sugars, which can be moved through the vascular system of the plant in solution to wherever they are needed. This process not only provides the basis for all food production but it also supplies the oxygen which animals and plants need for respiration. The simple carbohydrates, such as glucose, may be built up to form starch for storage purposes or as cellulose for building cell walls. Fats and oils are formed from carbohydrates. Protein material, which is an essential part of all living cells, is made from carbohydrates and nitrogen compounds and also frequently contains sulphur.

Most plants consist of roots, stems, leaves and reproductive parts and need a medium in which to grow. These media could be soil, compost or even water where plants are grown hydroponically. In soil the roots spread through the spaces between the particles and anchor the plant. The amount of root growth can be phenomenal. For example, in a single plant of wheat the root system may extend to many miles.

The leaves, with their broad surfaces, are the main parts of the plant where photosynthesis occurs (Fig. 1.1). A very important feature of the leaf structure is the presence of large numbers of tiny pores (stomata) on the surface of the leaf (Fig. 1.2). There are usually thousands of stomata per square centimetre of leaf surface. Each pore (stoma) is oval-shaped and surrounded by two guard cells. The carbon dioxide used in photosynthesis diffuses into the leaf through the stomata. Most of the water vapour leaving the plant, as well as the oxygen from photosynthesis, diffuses out through the stomata.

Fig. 1.1 Photosynthesis.

Fig. 1.2 Stomata on leaf surface.

1.1.2 Transpiration

The evaporation of water from plants is called transpiration. It mainly occurs through the stomata and has a cooling effect on the leaf cells. Water in the cells of the leaf can pass into the pore spaces in the leaf and then out through the stomata as water vapour (Fig. 1.3).

Fig. 1.3 Cross-section of green leaf showing gaseous movements during daylight.

The rate of transpiration varies considerably. It is greatest when the plant is well supplied with water and the air outside the leaf is warm and dry. When the guard cells are turgid (full of water) the stomata are open. When the plant is under drought stress the guard cells lose water and the stoma closes, slowing down the loss of water vapour (transpiration) from the plant. It also slows down the rate of photosynthesis. The stomata also close in very cold weather, e.g. 0°C. Transpiration is also retarded if the humidity of the atmosphere is high because there is only a very small water vapour gradient between the inside of the leaf and the outside atmosphere. The stomata guard cells close (and so transpiration ceases) during darkness. This is because photosynthesis ceases and water is lost from the guard cells when some of the sugars present change to starch.

1.1.3 Respiration

Plants breathe, like animals, i.e. they take in oxygen that combines with organic foodstuffs and releases energy, carbon dioxide and water. Plants are likely to be checked in growth if the roots are deprived of oxygen for respiration, which might occur in a waterlogged soil. Respiration appears, superficially, to be the reverse of photosynthesis, with carbohydrates combining with oxygen to give carbon dioxide and water with a release of energy. However, it is much more complicated with a very different metabolic process taking place.

There are two main processes. The first is glycolysis where simple sugars are split to release energy and to form pyruvic acid, water and a carrier molecule. The second stage is the ‘Citric Acid’ or ‘Krebs’ cycle where the pyruvic acid is converted to citric acid, which cycles within the system through intermediate molecules releasing energy in the form of ATP (adenosine triphosphate), carbon dioxide and water. The energy-rich ATP can then be moved around the plant to provide it with the energy it requires for metabolism, growth and development.

1.1.4 Conduction

The conductive flow of water through the plant take...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Foreword
• Part 1: Conditions for crop growth
• Part 2: Crop husbandry techniques
• Part 3: The management of individual crops
• Part 4: Grassland
• Appendix 1: Soil texture assessment in the field
• Appendix 2: Nomenclature of crops
• Appendix 3: Nomenclature of weeds
• Appendix 4: Insect pests
• Appendix 5: Crop diseases
• Appendix 6: Crop seeds
• Appendix 7: Metrication
• Appendix 8: Agricultural land classification (ALC) in England and Wales
• Appendix 9: Weed control
• Appendix 10: Map of Ontario heat units showing areas most suited to growing maize
• Index