BRE 211: Principles of Agriculture and Forestry

Lecture 4

Principles of Agricultural/ Crop Production They include:

Land preparation Plant propagation Nursery establishment Transplanting seedlings Field Planting Fertilizer application Crop protection Harvesting Post harvest handling and storage

Land Preparation Involves:

Land Clearing Drainage Preparatory cultivation

Land Clearing Existing vegetation is cleared. Intensity of clearing varying from clear

felling to selective thinning depending on the crops to be grown.

Intensively grown crops usually require total clearance of the vegetation.

Techniques of Land ClearingNormally two techniques including:

Slash and Burn Clear Felling and Stumping

Slash-and-burn involves: Slashing the herbaceous undergrowth

followed by burning of the debris and standing shrubs and trees.

In some instances the bigger trees are pruned or ring barked and fired to kill them in places where they endanger the growing crops.

Advantages of Burning

Releases nutrients bound in the plant tissues in readily soluble ash and the planted crop may subsist on such nutrients immediately on germination.

Acts as a disinfectant that destroys pests, disease causing organisms and weed seeds.

Disadvantages of Burning Destroys the potential organic matter in vegetation by

releasing the volatile nutrients such as nitrogen and sulphur.

Some forest litter may resist burning thus result in poor land clearing.

However, Burning is becoming less frequent on intensively farmed

areas near homes and villages. Burning of clearings is still practiced in the establishment of

tree crops. Clear felling and stumping: This is rare but under intensive or mechanized

cropping it is done thoroughly in order to facilitate mechanical cultivation.

After clearing, soil conservation and drainage works commence.

Drainage

Causes of Poor drainage: Some soils have a water table permanently or

seasonally high enough to adversely affect crop growth thus need drains to lower the water table.

Physical condition of one or more horizons of the soil checks the downward movement of excess surface water thus impeding the drainage of excess surface water to a depth below the root range of crops.

If the soil is wet and especially if it is high in clay content, a barrier impeding water percolation can also be formed by the smearing action of tractor wheel slip or of an implement which destroys structure and seals coarse pores and cracks.

Conditions for Drainage Where rainfall in abundant and well distributed

throughout the year, it might be desirable to keep the water table below crop rooting depth at all times.

Although it is necessary to improve drainage during part of the wet season in drier areas, it is undesirable to lower the water table more than is necessary since in such areas the objective is to conserve water.

On peat soils, it is usually desirable to maintain the water table as high as crop requirements permit because draining peat too deeply enhances its tendency to dry, shrink and reach a high temperature during the day.

Conditions for Drainage Tree crops that need to develop a deep root

system to anchor them firmly against strong winds will require a lower water table than some annual crops or surface-rooting perennials such as pineapple.

Main effect of improving drainage is to improve the aeration of the soil enabling the crop to develop a deeper root system so that it can tap a larger volume of soil for nutrients and is better able to withstand periods of draught

Methods of improving drainage Sub-surface drains of tile, plastic pipe, rubble (bits

of broken stone) and brushwood. Uncommon due to initial and maintenance cost

Open surface drains: Made mechanically with scrapers, bulldozers, and drainage ploughs or dragline excavators. Cheaper in cost but take up land, inconveniences mechanized tillage operations, harbour obnoxious weeds and rodents requiring constant maintenance.

Ridge and furrow system: Land is formed into broad ridges with a slight gradient on the furrows or ditches between them.

Cambered bed system: This is a modification of the ridge and furrow system in which the land is raised into beds.

Drainage

Drains cannot help once the structure of the surface soil has been destroyed

They only reduce the risk of such damage occurring by keeping the surface layer drier and thus prolonging periods during which it is not too wet for mechanized tillage.

Preparatory Cultivation

It is better to cultivate at the end of the rains in order to expose weed seeds, pests and pathogens to desiccation during the dry season.

Extent and efficiency of preparatory cultivation depends on the type of soil and the cultivation equipment.

Simple and light tools such as the hoe, panga, slasher, etc are associated with cultivation of soils in small-scale tropical agriculture.

Human supplies the energy used in cultivation although farmers in the savanna also commonly use animal power.

Tractors and their associated implements such as ploughs, harrows, and ridges are associated with highly developed agriculture of industrialized countries .

Effects of Cultivation Eliminates competition by weed species. Incorporates organic and inorganic manure. Improves the tilth or granular condition of the soil,

which facilitates aeration, water percolation and easy rooting of seedlings.

Helps destroy some pests and pathogens present in the soil by exposing them to the sun.

Buries some weed seeds too deep for germination. However may turn up previously buried weed seeds

which can dominate the re-growth after cultivation.

Plant Propagation Objectives:

To increase the number of plants To preserve the useful characteristics of the

plants.

Types: Sexual Propagation (Propagation by seed) Asexual Propagation (by use of specialized

vegetative parts of the plants or by artificial techniques such as grafting, layering, cutting or budding)

Propagation by seed

Commonest way of propagating self-pollinated and many cross-pollinated crops.

Advantages: Seeds are usually not expensive Seeds can be stored for long periods Seeds can remain viable at least until the next

planting season when stored in a cool dry place Seed does not usually carry over diseases and

pests, which attack growing crops although some fungal spores infect seeds.

Propagation by seedDisadvantages:

Development of off-types and variation in plant populations when cross-breeds are grown

Long juvenile period when plant is unable to produce seeds especially in tree crops

Some seeds do not produce plants that resemble their parent plants

Some seeds cannot produce yields during the first year e.g. Root and tuber crops.

Vegetative propagation Depends on the ability of plant parts to regenerate

roots and shoots; and grow into new plants having the same characteristics as their parent plant.

Advantages: Eliminates the problems of dormancy and reduces the

juvenile period of plants Yields are obtainable easier and faster than seed

propagated plants. Produces seedless crops e.g. banana easily through Maintains crossbred plants in heterozygous condition

indefinitely. Disadvantage:

Danger of transferring diseases to the new plants or locations.

Methods of Vegetative Propagation Use of specialized vegetative parts or

modified stems and roots such as bulb, corm runner, rhizome, suckers, tubers and root.

Induction of adventitious roots and shoots by cutting or layering the stem e.g. in tea and sweet potato propagation.

Grafting: Two plant parts are joined by regeneration of their tissues.

Budding: Only the vegetative bud is joined to another plant where it regenerates a new plant.

Ratooning: Outgrowths from stools of a harvested crop are used.

Nursery Establishment A Nursery phase is an important part of the

planting operation for most trees and some field crops.

Seedlings can be better cared for and conveniently watered with less effort to increase growth and development.

Characteristics of a good nursery site Should be near a source of water Should be as near as possible to the site of field

planting Site should not be subject to planting other crops. Ground should be level or terraced.

Nursery Requirements Water:

A small nursery can be watered using watering cans by family labour while a larger one may require more workers or the use of a pump and hose system.

Polythene bags: Most widely used containers for nursery seedlings

because they are cheap and durable and make handling of seedlings at planting very easy.

size of bags used depends on the seedlings. Shade:

Young seedlings do better under partial shade at the early stages. they will become self-shading when they get larger

Nursery Requirements Fertilizer:

Usually nursery seedlings will grow faster if fertilized. The easiest way to fertilize seedlings is to dissolve a nitrogen fertilizer containing all the major nutrients in water and water lightly once every week.

Fertilizer scorch can be avoided by immediately re-wetting with water alone.

Sometimes micronutrient deficiencies will occur and these are best dealt with by watering with a complete/compound fertilizer dissolved in water and given periodically.

Transplanting seedlings Should be done during a sufficiently wet

season. Before planting the seedlings, any weak,

slow-growing, diseased, deformed or otherwise abnormal plants should be discarded as it affects the long-term yield of the field planting.

Seedlings grown in Polythene bags are easy to transport to the field and lorry, tractor, trailer or hand may carry them depending on the situation.

Transplanting seedlings Use a box and double poles carried on the

shoulders of two workers to carry seedlings over rough ground.

Before planting the Polythene bags must be stripped off by slitting lengthwise with a razor blade or a very sharp knife.

Although Polythene bags are widely used for nurseries some farmers may still prefer to plant seedlings directly in the soil.

This often means that considerable damage is done to the seedling on extraction, thus delaying its development.

Field Planting Seed or planting material largely determines

the quantity and quality of the harvested produce.

Good stocks of planting materials ensure Reduced costs of cleaning, standardization and

disinfection Uniform germination thus eliminating replanting or

supplying missing stands Vigorous seedling growth which reduces weed

and disease damage Uniform growth rates, maturity and produce

Field Planting Low grade or poor-quality planting materials

lead to: Uneven germination and establishment which may

necessitate replanting or supplying missing stands Feeble seedling growth susceptible to disease and

insect damage Costly disinfection or grading of planting materials

against seed-borne diseases and pests Uneven growth rates due to lack of uniformity in

genetic composition. Uneven maturity which affects the cost and

efficiency of harvesting Lack of uniform produce due to a combination of

all the above factors.

Field PlantingThis affects not only the efficiency of

primary processing but also the quality and market value of the products.

Most farmers in the tropics still provide for their planting materials from their own harvests or purchase them from unregulated markets.

Methods of planting Broadcast:

This is limited to crops that will be transplanted particularly small seed crops. It is unsuitable for large seeds and vegetative cuttings

Drilling: This is planting seed in small furrows

Dibbling: Holes are made and the seeds placed in these

holes and covered. The crops could be planted in scattered like beans.

Sowing Practices The successful establishment of seedlings of annual

crops depends upon Viable seed of adapted cultivar Uniform sowing & placement depth Firm seed-soil contact Availability of moisture and nutrients in the soil

The factors involved in sowing management can be divided into two broad groups: Mechanical factors such as depth of planting,

emergence habit, seed size, seedbed texture, and seed-soil contact.

Biological factors such as companion crops (in mixed cropping and pastures) and competition for light.

Spacing and plant population Spacing crops optimally reduces interplant

competition for sunlight, moisture, air and nutrients. The ultimate yield from a unit land area is contributed

to by all the plants growing on it. Excessively wide or narrow spacing leads to

reduction in yield. The exact spacing for any crop depends on:

Soil productivity Location Time of planting.

On fertile moist soils, closer spacing will give better results than on poor soils or soils susceptible to moisture stress.

This explains the sustained high yields from close spacing and high plant populations in irrigated as compared to rainfed crops.

Fertilizer ApplicationFertilizers are chemical compounds

containing the elements that are added to the soil to supplement its natural fertility.

Fertilizers containing only one of the major elements (N, P, and K) are single, simple or straight fertilizers

Those containing two or three elements are classified as mixed compound or complex fertilizers.

Fertilizer Application Nutrients in fertilizers must come within the

feeding range of plants’ roots for maximum benefit from the application.

The soluble constituents of fertilizers diffuse through the soil vertically and only slightly in a lateral direction.

The method of application therefore must ensure distribution in a moist soil to reach the plant roots.

Thus method of applying fertilizer is important.

Methods of Fertilizer Application Broadcast before planting: Fertilizer is spread as uniformly as

possible over the field after ploughing land then mix it with soil by ploughs or cultivators.

Gives good results with crops like millet which are planted in narrow rows.

Suitable for those crops whose seeds are usually broadcast. However, it stimulates weeds.

Row Placement: Fertilizer is placed in bands or in localized areas along rows at a calculated distance for maximum absorption by the plants.

Advantages Fertilizer comes in contact with minimum amounts of soil

particles reducing phosphorus fixation. Fertilizer is within reach of the roots and the plant can feed on it

easily Fertilizer placed in bands does not supply nutrients to the weeds

near the surface

Methods of Fertilizer Application Top-dressing: Second application by broadcasting

on the soil surface close to the plants when the crop is 3-4 weeks old.

Drill placement – Fertilizer is applied along with the seed.

Good for crops like wheat, maize and other cereals, which can withstand contact with the fertilizer.

Band Placement: Fertilizer is placed in bands on one side or both sides of the row about 5cm below the seed and 4cm away from the seed or plant.

The method is useful for cotton, tomato and potato crops that are sensitive to direct contact with fertilizer.

Side-dressing: Second application when the crop is partly grown (4-8 weeks) given as a continuous band near the crop row to a depth of 4-5 cm.

Methods of Fertilizer Application Application by plough: Fertilizer is placed in

a continuous band at the bottom of the plough furrow. Each band is covered as the succeeding furrows are turned over.

Applying liquid fertilizer: Fertilizer is mixed with most fungicides and pesticides and applied simultaneously or dissolved in irrigation water and applied together in a process referred to as fatigation

Used for high-value crops by direct spraying. Carbamide (urea) is the most commonly used in

this way.

Types of Fertilizers Nitrogenous fertilizers Phosphatic fertilizers Potassium fertilizers Mixed or compound fertilizers. Farmyard manure

Nitrogenous Fertilizers All major inorganic fertilizers in common use

are synthetically produced. Many nitrogenous compounds are made from

ammonia in an atmospheric nitrogen manufacturing process known as the harber process. Hydrogen is combined with nitrogen in the ratio

3:1 by volume at high temperature (400-500 o C) and pressure (200-1000 atmosphere) in the presence of catalyst form ammonia.

This ammonia is used directly as fertilizers or is converted into various nitrogen fertilizers.

Phosphatic fertilizersAre of three grades depending on their

solubility. Water-soluble phosphate Citrate-soluble phosphate Phosphates that are only soluble in strong

mineral acids such as sulphuric acid and nitric acid.

The solubility depends on the chemical composition or formula of the phosphate and the degree of fineness.

Potassium Fertilizers Manufactured from natural deposits of potassium

salts found in various parts of the world. The crude potash minerals are dissolved in water

and the various salts separated by fractional distillation.

All are soluble in water and the potassium content is readily available to plants unlike the nitrogen fertilizers.

Most potash fertilizers have no effect on soil pH. Most important potash fertilizer materials are:

Muriate of potash Sulphate of potash

Mixed or compound fertilizers Contain at least two of the three major elements N, P,

K. Advantages of compound fertilizers include:

Can be applied by hand as well as a fertilizer drill since it is usually dry with fine and well-mixed granules.

Is stable and does not cake up, form lumps or deteriorate in any way over time.

Contains all the major plant nutrients in the right proportions. The ready-made mixture saves farmers the labour of mixing

fertilizers. Save time and labour when applied in the calculated amount

instead of using separate straight fertilizers. Disadvantages include: Cost slightly more than the total cost of three

equivalents of NPK. May be unsuitable for many soils.

Farmyard Manure (FYM) FYM refers to all the refuse from farm animals. It is a by-product consisting of two components: solid and liquid

in a ratio of 3:1. Solid part is made up of dung and straw that has been used

for animal bedding while the liquid comes from the urine. Dung comes mostly from undigested material and the urine

from the digested material that is absorbed by the animal and then excreted.

More than 50% of the organic matter contained in dung is in the form lignin and protein similar to those contained in humus.

This material is quite resistant to further decay and therefore the nutrients present in this fraction of dung are liberated very slowly.

Nutrients present in the urine are readily available either directly or after simple decomposition.

Over half of nitrogen, almost all the phosphate and about two fifths of potash are found in the solid portion.

Farmyard Manure (FYM) Manure is essentially a nitrogen-potash fertilizer. Manure supplies nutrients required by plants. Because it originated from plants, FYM naturally

contains all mineral constituents including trace elements.

FYM improves the physical properties of the soil by increasing humus content and consequently the water holding capacity of the soil.

Carbonic acid helps to release minerals present in FYM.

It releases these nutrients fastest when the soil provides warm moist conditions favourable for microbial decomposition.

Factors affecting Fertilizer Use Crop factors

Certain crops need larger amounts of particular nutrients than others e.g. Legumes require large amounts of P whereas grains require proportionately more N.

Crop variety: Recently developed varieties are more responsive to higher doses of fertilizer than traditional crop varieties.

Soil Factor Soils differ in their potential for production. Large applications of fertilizer can be profitable on soils that have

high potential but are low in fertility Climatic factor

Soils in areas of low rainfall lose little by leaching thus nutrients level remains stable. If fertilizers are added, the limited amount of water available means that the plants are unable to respond.

Soils of humid regions lose nutrients through leaching and weathering but their water supply is adequate for high crop production. Here, fertilizer application will show good results.

Factors affecting Fertilizer Use Economic factor

Fertilizer use is increase by low prices and decreased by high prices.

Crop prices have the opposite effect: High price for the crop will give a profitable return from large fertilizer application yield but follow a curve of diminishing returns

Management factor Managers choose the input-output levels at which they will

operate. Increased crop outputs usually require increased fertilizer inputs.

Top yields depend on many factors including soil type, climate, cropping history, fertilizer history and soil amendments, tillage practices, weed control and timing of operations. Most of these are managerial factors.

Effects of Fertilizer Application on Agriculture

Use of mineral fertilizers boosts crop growth which harvested provides a considerable amount of residue adding the organic content of the soil.

When well fertilized, cereals e.g. millet, maize and sorghum leave behind considerable organic residue in the form of roots, stumps and stalks

When nitrogen is applied or a cereal-legume rotation is adopted, the organic residue undergoes rapid microbial decay to produce humus.

Thus the use of fertilizers in conjunction with farmyard manure increases the efficiency of crop plants.

Crop Protection Crops are protected against:

Fire Pests Diseases Weeds

Pests and diseases are among the most serious limiting factors to economically efficient crop production and utilization of natural resources in tropical agriculture.

Crop losses through pests and diseases may sometimes be negligible but at other times total loss especially as a result of sporadic outbreaks of non-economic pests and diseases.

Pests and disease-causing organisms or pathogens include rodents, bats, birds, insects, mites, molluscs, nematodes, weeds, parasitic plants, fungi bacteria, mycoplasma, viruses and sometimes humans.

Some diseases are, however, caused by physical or soil factors.

Crop Pests Arise in two major ways.

Natural occurrence: Sudden attack of crops by insect e.g. locust outbreaks in arid and semiarid regions.

Alteration of the ecosystem: People attempting to change the ecosystems for their own benefit creating conditions that favour the development of pests. Some of these human activities

Classification of Pests According to damage they

cause Biting and chewing insects Piercing and Sucking insects Boring insects

Classification of Pests

According to Severity of damage c Key or major pests: cause

serious and persistent economic damage in an ecosystem in the absence of effective control measures.

Minor pests: Cause economic damage only under special circumstances in their local environment.

Classification of Pests Numbers of organisms involved Frequency of occurrence

Occasional pests Potential pests Migrant pests

Fundamental Principles of Crop Protection

Control of pests and plant diseases means the reduction in the amount of damage caused.

Perfect control is rare, but there is economic control when the increase in yield more than covers the cost of chemicals, materials and labour used for the control operations.

The fundamental principles of control include. Exclusion

Preventing entrance and establishment of pests in farms, states or countries.

Involves using certified seeds or plants, discarding any that are doubtful, possibly treating seeds or tubers before they are planted.

For states and countries, exclusion also includes quarantine prohibition by law.

Fundamental Principles of Crop Protection Eradication

Eliminating pest once already established on a plant or in a farm through.

Removal of the diseased specimens or cutting off cankered tree branches eradication could be aided by control viral diseases

Cultivation and deep ploughing to bury plant debris Rotation of susceptible with non-susceptible crops in an

attempt to starve out the pest Disinfection with chemicals Heat treatment Spraying or dusting foliage with pesticides Treating soil with appropriate chemicals to kill insects,

nematodes and fungi Trapping rodents

Fundamental Principles of Crop Protection Protection

Placing a protective barrier between the susceptible part of the host and the pest.

In most instances this is a protective spray or dust applied to the plant in advance of the arrival of the pest.

Sometimes it means killing insects or other inoculating agents,

Storage of food surpluses, preservation by freezing, canning, salting etc. can also protect the food items from pest damage.

Fundamental Principles of Crop Protection Immunization

Control by the development of resistant varieties or by inoculating the plant with something which will inactivate the pest or pathogen.

Avoidance Growing crops during period when the pest

population is low or absent in the field. Crop is planted to avoid the damaging pest

population. The use of early and rapidly maturing varieties can

also have profound effect on the degree of pest damage experienced by the crop

Insects and other arthropods are the most serious pests of crop plants in tropical agriculture.

Pest Control Objective

To reduce the population of the offending pests below the economic threshold when its damage becomes uneconomical i.e. does not cause losses in yield.

A pest control method will therefore be considered successful if it can maintain the pest population well below the economic threshold.

Complete eradication of a pest from an ecosystem is not readily practicable or even desirable.

Basic principles of pest control include Preventing pests from gaining access to the host/ Pest-

host interaction prevention. Killing the pest directly reduces the population of the

pest on the host.

Methods of Pest control Include:

Physical control Legislative control Cultural control Biological control Chemical control Integrated pest management (IPM)

Physical control Includes the use of various barriers to prevent pests from

physical contact with their hosts and mechanical removal or destruction of the pest.

Barriers may be mechanical, chemical or behavioral. Mechanical barriers include:

Wire fences Mosquito nets Fine nylon net sleeves Nylon or paper bags Sticky bands Boots for waders Concrete foundation - prevent termites. Hand picking Flooding Lethal temperatures Hermetic storage – Tightly closed bins Radiation

Physical control Chemical barriers include: Prophylactic chemical treatment carried out

on crops leaving a residual poison that is lethal to the pest.

Behavioral barriers exploit the fact that pests locate their hosts by responding to external stimuli such as sight and oduors.

They include Frightening devices. Traps Attractants Anti-feedants – inhibit feeding of pests

Legislative Control Is the use of laws and regulation to prevent

the importation of pest organisms into a country and to restrict the spread of pests from areas where they are already established.

Main objective is to prevent dangerous pests from colonizing new areas.

Include: Quarantine: Restricts movement of produce

from areas of infection to other areas Eradication regulations Certification regulation

Cultural Control Is the manipulation of regular agronomic practices to

influence on the incidence and populations of crop pests. The basic principle of cultural control is the disruption of the

development and life cycles of pests either by denying them their food or by exposing stages in then life cycle to adverse conditions so that they are killed.

Advantages: Relatively cheap and effective. Poses minimal danger to the environment.

Cultural control involves: Cultivation of the soil Variation in planting and harvesting dates Crop rotation Close season Trap cropping Resistant crop varieties Mixed cropping Good husbandry practices

Biological Control Is deliberate use of organisms (parasites,

predators and pathogens) to reduce populations of pests.

Such natural enemies may be arthropods (insects and mites), bacterial protozoan, fungi, viruses, nematodes or even vertebrates (birds, toads, fish).

Method is usually used as a supplement to other methods of control.

Successful biological control requires that: Pest population is reduced to levels well below the

economic threshold. Population is maintained sufficiently low to allow

the survival of the biological control agent.

Biological ControlBiological control requires thorough

knowledge of the ecosystem, the ecology and behaviour of the target pest and the bio-control agent.

Advantages: It is safe and cost-effective Is devoid of environmental pollution

problems associated with chemical control.Care must be exercised, however, not

to upset the ecosystem of the area by the manipulation of controlling species.

Chemical control Most common and easily applicable method for

reducing or preventing economic pest damage is the use of toxic substances or pesticides to kill or repel pests on their host crops.

Continues to play a significant role in solving the food and wealth problems of tropical countries.

Advantages: Relatively easy method of pest control Produces quick and easy results Can be repeated as often as desirable Is cheap and individual farmers can take independent action

on their own farms The broad-spectrum action of many pesticides makes it

possible to control a complex of pests with one or a combination of pesticides.

Chemical control Disadvantages

Is repetitive and must be applied whenever there is a pest outbreak. Thus it is wasteful

Pesticide applied rarely kills all the pests and the residual population which survives soon develops to cause economic damage

Pesticides can be toxic to beneficial insects especially parasites, predators and pollinators. They are potentially toxic to wildlife, fish and humans

Cause environmental pollution and ecological disturbance. Toxic residues may remain in agricultural produce.

Pests may develop resistance to a pesticide which reduces the effect of that pesticide on that pest

Chemical control provides only a temporary solution to pest problems

Pesticides are expensive to manufacture and usually have to be imported by tropical countries.