Form 1 Agriculture Notes

FORM ONE NOTES

Soil Fertility ll

(Inorganic Fertilizers)

Introduction

Plant nutrients occur in the soil in form of soluble substances.

These substances are taken in by the plants in different quantities depending on their roles in the plant tissues.Essential Elements
These are nutrients needed by plants for various uses.
They are divided into two broad categories namely:
> Macronutrients
> micronutrients.Macro-nutrients
These are also referred to as major nutrients.
They are required by the plant in large quantities.They include;
carbon,
hydrogen,
oxygen,
nitrogen,
phophorus,
potassium,
sulphur,
calcium
magnesium.> Nitrogen, phosphorus and potassium are referred to as fertilizer elements,
> Calcium, magnesium and sulphur, are referred to as liming elements.
Role of Macro nutrients in Plants
Nitrogen (N03,NH4“)
Sources
Artificial fertilizers
Organic matter
Atmospheric fixation by lightning
Nitrogen fixing bacteria.Role of Nitrogen in Plants
Vegetative growth
Chlorophyll formation
Build up of protoplasm.
Improves leaf quality in leafy crops such as tea and cabbagesDeficiency Symptoms
I Yellowing of the leaves/chlorosis.
I Stunted growth.
Premature ripening.
Premature shedding of the leaves.
Light seeds.Effect of Excess Nitrogen
Scorching of the leaves.
Delayed maturity.Loss of Nitrogen From the Soil:
Soil erosion.
Leaching.
Volatilization.
Crop removal.
Used by microorganisms.Phosphorus (H, P04, HPO”4 P105)
Sources:
Organic manures
Commercial fertilizers
Phosphate rocksRole of Phosphorus
Encourages fast growth of the roots.
Improves the quality of the plant.
Hastens maturity of the crops.
Influences cell division.
Stimulates nodule formation in legumes.Deficiency symptoms
Growth of the plant is slow.
Maturity is delayed.
Leaves become grey, purple in colour.
Yield of grains, fruits and seed is lowered.Loss of Phosphorus From the Soil
Soil erosion.
Leaching
Crop removal
Fixation by iron and aluminium oxide.Potasium (K‘, K20)
Sources;
Crop residue and organic manures.
Commercial fertilizers
Potassium bearing minerals e.g. feldspar and mica.Role of Potassium in Plants
Increases plant vigour and disease resistance.
Increases the size of grains and seeds.
Reduces the ill-effects due to excess nitrogen.
Prevents too rapid maturation due to phosphorus.Deficiency Symptoms
Plants have short joints and poor growth.
Plants lodge before maturing.
Leaves develop a burnt appearance on the margin.
Leaves at the lower end of the plant become mottled, spotted or streaked.
In maize, grains and grasses firing starts at the tip of the leaf and proceeds from the edge usually leaving the midrib green.Loss of Potassium From the Soil
Crop removal.
Leaching.
Soil erosion.
Fixation in the soil.Calcium (Ca2+)
Source:
Crop residues and organic manures.
Commercial fertilizers.
weathering of soil minerals.
Agricultural limes for example dolomite, limestone.Role of Calcium in Plants
Improves the vigour and stiffness of straw.
Neutralizes the poisonous secretions of the plants.
Helps in grain and seed formation.
Improves the soil structure.
Promotes bacterial activity in the soil.
Corrects the soil acidity.Deficiency symptoms
Young leaves remain closed.
There are light green bands along the margins of the leaves.
Leaves in the terminal bud become hooked in appearance there is a die-back at the tip and along the margins.Loss of Calcium
Crop removal
Leaching
Soil erosionMagnesium (Mg2+)
Sources:
Crop residues and organic manures
Commercial fertilizers
Weathering of soil minerals.
Agricultural limes.Role of Magnesium in Plants
Forms part of chlorophyll.
Promotes the growth of the soil bacteria and enhances the nitrogen fixing power of the legumes.
Activates the production and transport of carbohydrates and proteins in the growing plant.Deficiency symptoms
Loss in green colour which starts from the bottom leaves and gradually moves upwards.
The veins remain green.
Leaves curve upwards along the margins.
Stalks become weak and the plant develops long branched roots.
The leaves become streaked.Sulphur (S04 2′ ,SO,)
Sources:
Commercial fertilizers.
Soil mineral containing sulphides
Atmospheric sulphur from industries.
Rain waterRole of Sulphur in Plants
Formation and activation of coenzyme-A.
Sulphur is a constituent of amino acids.
Influence plant physiological processes.Deficiency Symptoms
Small plants/stunted growth.
Poor nodulation in legumes.
Light green to yellowish leaves/ chlorosis.
Delayed maturity.Micro-nutrients
Also referred to as trace or minor nutrients.
They are required in small quantities/traces.
They are essential for proper growth and development of plants.They include;
Iron,
Manganese,
Copper
Boron,
Molybdenum
Chlorine.Role of Micronutrients and Their Deficiency Symptoms
Copper> Role in oxidation-reduction reactions.
> Respiration and utilization of iron
> Deficiency symptoms-yellowing of young leaves.
Iron> Synthesis of proteins.
> Takes part in oxidation-reduction reactions.
> Deficiency symptoms – leaf chlorosis
Molybdenum> Nitrogen transformation in plants.
> Metabolization of nitrates to amino acids and proteins
> Deficiency symptoms –leaf curl and scathing.
Manganese – Same as molybdenum.
Zinc> Formation of growth hormone.
> Reproduction process
> Deficiency symptoms – white bud formation.
Boron> Absorption of water.
> Translocation of sugar
Inorganic Fertilizers
These are chemically produced substances added to the soil to improve fertility Classification According to:
Nutrients contained> Straight – contain only one macronutrient.
> Compound fertilizers – contain more than one macronutrient
Time of applicationSome applied when planting.
Top dressing after crop emergence
Effects on the soil pH.> Acidic fertilizers.
> Neutral fertilizers.
> Basic fertilizers.

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Properties and Identification of Fertilizers
Nitrogenous Fertilizers
Characteristics
Highly soluble in water.
Highly mobile in the soil hence it is applied as a top dress.
Easily leached because of the high solubility hence does not have residual effect on the soil.
Has scorching effect on young crops during wet seasons.
Easy to volatilize during hot season.
They have a tendency to cake under moist conditions.
They are hygroscopic hence should be stored in dry conditions.Examples:
Sulphate of Ammonia (NH4) 2 SO4-Physical appearance:
> white crystals,
> Has acidic effect,
> Contains 20% N.
Ammonium Sulphate Nitrate [(NH4),SO4+ NH4 NO;]> Colour: granules which appear yellow orange,
> less acidic,
> contains 26% N.
Calcium Ammonium Nitrate (CAN)> Colour: greyish granules,
> neutral in nature,
> contains 21 % N.
Urea> Colour: small whitish granules
> Easily leached or volatilized,
> contains 45- 46%N.
Phosphate Fertilizers
Has low solubility and immobile.
Non-scorching.
Has a high residual effect hence benefit the next season’s crop.
Easy to store because they are not hygroscopic.Examples;
Single super-phosphate> Appearance: whitish, creamy white granules,
> contains 20-21 % P,O5
Double super-phosphate> Appearance: dark greyish granules,
> Contains 40-42% P205
Triple super-phosphate> Appearance: small greyish granules,
> Contain 44-48% P205
Potassic Fertilizers
Characteristics:
Has moderate scorching effect.
Moderately soluble in water.
Most Kenyan soils have sufficient potassium.Examples;
Muriate of Potash (KCI)> Contain 60 – 62% K10
> Slightly hygroscopic.
> Appearance amorphous white.
Sulphate of Potash (50% K10)Compound or Mixed Fertilizers
These are fertilizers which supply 2 or more of the macronutrients.Examples;
Mono ammonium phosphate.
Di-ammonium phosphate
20:20:20, 23:23:23Advantages of application of compound fertilizers
Saves time and money.
Mixture gives improved storage properties and better handling.Disadvantages of compound fertilizers application
Expensive.
Wasteful.
Mixing may not be thorough.
Incompatibility of the individual fertilizers.Methods of fertilizer application
Broadcasting – random scattering of the fertilizers on the ground.
Placement method – application of fertilizers in the planting holes.
Side dressing – fertilizer is placed at the side of the plant within the root zone, in bands or spot-rings.
Foliar spraying – specially formulated fertilizer solution applied on the foliage in spray form.
Drip method – applied through irrigation water.Determination of Fertilizer Rates
Contents of fertilizers are expressed as fertilizer grade or fertilizer analysis.
Fertilizer grade indicate the guaranteed minimum of the active ingredients (N, P205, K 20) in the mixture.
It is expressed as a percentage on a weight to weight basis or percentage by weighExample 10:20:o means for every 10kg of the mixture there are 10kg of nitrogen, 20kg of P10 5 and okg of K20.
Example
A farmer was asked to apply fertilizers as follows:
60 kg/ha nitrogen (top dressing)
60 kg/ha P205 (in planting hole).
60 kg/ha K20. How much sulphate of ammonia (20%) would be required per hectare? How much double super-phosphate (40%) P2O5would be required per hectare? How much muriate of potash (50% K20) would be required per hectare?Answer/Solution
Sulphate of ammonia (SA) which gives 60kg/ha N60/20 x 100 = 300 kg SA
Double super phosphate (40% P2O5)which gives 60kg/ha P20560/12 x 100 = 150 kg DSP
Muriate of potash (60% K20) which gives 60kg/hK2O=60/60 x 100 = 100 kg muriate of potash
Example
A farmer was asked to apply fertilizers as follows:
200kg/ha of DSP (40% P205
150kg/ha of muriate of potash (60% K20)
150kg/ha of sulphate of ammonia (20% N)How much P205 did the farmer apply per acre?
How much K20 did the farmer apply per hectare?
How much N did the farmer apply per hectare?
Solution/Answer
P205 applied per hectare from 200kg of DSP 40/100 x 200 = 80 kg/ha P205
K205 applied per hectare from 150 kg of muriate of potash = 60/100 x 150 = 90 kg/ha K20
N applied per hectare from 150 kg/ha sulphate of ammonia 20/100 x 150: 30 kg/ha NSoil Sampling
Refers to obtaining of small quantity of soil that is representative in all aspects of the entire farm.Soil Sampling Procedures
Clear the vegetation over the site.
Dig out soil at depths of 15-25cm.
Place the dug out soil in a clean container.
Mix thoroughly the soil in the container.
Take a sample and send it to National Agricultural Laboratory for analysis.
The container carrying the sample should be properly labeled as follows:> Name of the farmer,
> Location,
> District
> Address of the farmer.
Sites to Avoid
Dead furrows, ditches.
Swamps
Near manure heaps.
Recently fertilized fields
Ant hills.
Under big trees.
Near fence lines or foot paths.
Do not put them in containers which are contaminated with fertilizers or other chemical containers.Methods Of Soil Sampling:
Zigzag method
Traverse methodSoil Testing
Soil testing is the analyzing of the soil sample to determine certain qualities of the soil.Importance of Soil testing:
To determine the value of the soil hence determine the crop to grow.
To determine the nutrient content hence find out the type of fertilizer to apply.
To determine whether it is necessary to modify the soil pH for a crop.How Soil pH affects Crop Production
Influences the physical and chemical properties of the soil.
Affects the availability of nutrients.
Influences the incidences of soil borne diseases.
Determine the type of crop to be grown at a given area.Methods of pH Testing
Universal indicator solution
pH meter> Know the course of action to be taken in the event of a disease and maintenance of good health.
> Know the prevalent diseases.
> Calculate the cost of treatment.
Marketing Records show commodities sold, quantities and value of all the sales.Labour Records – show labour utilization and labour costs.
Crop production ii
(Planting)
Planting is the placement of the planting material in the soil for the purpose of regeneration in order to produce more of the plant species.Types of planting materials
Seeds
Seeds are produced by flowering after pollination and fertilization. They contain the part of the plant that germinates and subsequently grows in to new plants. Advantages of using seeds as planting materials.
Seeds are easily treated against soil borne pests and diseases.
They are not bulky therefore storage is easy.
They are easy to handle during planting making operation easy.
When planting seeds, it is easy to use machines like seed planters and drillers.
It is easy to apply manures and fertilizers together with seeds during planting.
Fertilizers and manures application can be easily mechanized.
It is possible to develop new crop varieties due to cross pollination.Disadvantages of using seeds as planting materials.
Some seeds have long dormancy and they may need special treatment in order to germinate.
Plants raised from seeds have variations from the mother plant due to cross pollination,
This may introduce undesirable characteristics.
Soil borne pests may damage seeds if left for sometime in the soil before rain falls.
Some seeds may lose viability if stored for a long time. This leads to gaps in the farm.1. Vegetative materials.
These are plant parts which have the ability to produce roots, they grow and develop in to new plants.
Plant parts such as leaves, roots or stems can be used for planting as long as they are capable of rooting. Advantages of using vegetative materials for planting.
Crops originating from vegetative materials matures fasterthan those from seeds.
The crops shows uniformity in such qualities as disease resistance, seed size, colour, keeping or storing quality and chemical composition.
It is possible to produce many varieties of compatible crops on the same root stock.
Use of the vegetative materials is easier and faster, especially where seeds show prolonged dormancy.
The resulting plant has desired shape and size for ease of harvesting and spraying.
It facilitates the propagation of crops which are seedless or those that produce seeds which are not viable or have a long dormancy period.
Such crops include sugar-cane, bananas, Napier grass and others.Disadvantages.
Vegetative propagation does not result in new crop varieties.
Keeping the materials free of diseases is difficult.
Materials cannot be stored for long.
The materials are bulky and there fore difficult to store and transport.Plant parts used for vegetative propagation.
i) Bulbils.
These are tiny sisal plants produced in the inflorescence almost at the end of the plant growth cycle.
They resemble the mother plant except that they are smaller in size.
They are produced by the branches of the sisal pole.
When manure they mature they develop rudimentary roots and fall off to the ground just below the pole.
They are the collected and raised in the nurseries before they are transplanted t\o the main field.
One sisal pole may produce as many as 3,000 bulbils. They are usually 10cm long. They make good planting materials and are better than suckeii) Splits
These are plantlets divided from the existing mother plant with complete with complete leaves and rooting system.
They are used to propagate most pasture grasses and pyrethrum.
Pyrethrum splits are raised ﬁrst in nursery and then transplanted to the field.iii) Crowns and slips
These are materials used to propagate pineapples
Crowns are born on top of the fruits and are broken off and prepared for planting.
They are more preferred to suckers because they give uniform growth and take two years to reach maturity.
Slips are borne to the base of the pineapple fruits.
They are cut and prepared for plantings.
Their growth rate is faster than for crowns giving average uniformity.
They take 22 months from planting to maturity.
Crowns and slips are planted in the nurseries first before transplanting to the main seed bed.iv) Suckers
These are small plants that grow from the base of the main stem.
They have adventitious roots which grow quickly when planted to form a new plant.
They are used to propagate bananas, sisal, and pineapples.
When planted, suckers give uneven growth leading to maturity at different times.
They should be planted when they are young.v) Tubers
These are underground food storage organs which are short and thick.
They are used as vegetative propagation materials because they sprout and produce roots for growth.
There are mainly two types of tubers, the stem and root tubers.
Root tubers develop from the thickening of the adventitious roots.
Root tubers are not commonly used for propagation since they produce weak stems.
A good example of a root tuber is the sweet potato.
On the other hand stem tubers have some auxiliary buds which are sometimes referred to as ‘eyes’.
These eyes sprout to produce stems which grow into plants. Stem tubers are therefore swollen stems with scales leaves.
A good example of a stem tuber is Irish potato.vi) Vines.
These are soft wood cuttings which produce roots easily upon planting to give rise to new plants.
They are cut from the mother plants and planted directly into the field.
Soft wood cuttings (vines) are taken from rapidly growing shoots.
The soft upper parts of the shoots are preferred.
When preparing the cuttings, some leaves and nodes are included.
Roots are produced from the nodes.vii) Cuttings and setts
Cuttings are portion of plants parts which are cut and then planted.
They may be from stems, roots or leaves.
A stem cutting must have a bud which develops into shoot.
The root cutting must have an eye. Cutting must have an eye.
Cuttings must produce leaves as soon as possible so that they can start making their own food.
Sometimes cuttings are induced to produce roots by use of rooting hormones.
Once the cuttings have developed roots, they give rise to new plants.
In some crops, the cuttings are big enough to be planted directly to the main seedbed whereas there are some plants whose cuttings are first raised in special nurseries before they are transplanted to the seedbed.
The cuttings of Napier grass and sugar-cane are planted directly on the seedbed but those of tea; have to be raised in special nursery before they are transferred to the seed bed.
Examples of crops which are propagated by use of stem cuttings include: tea, cassava, and sugar-cane and Napier grass.
The stem cuttings used to propagate sugar-cane are known as ‘setts’. Setts are stem cuttings which have 3-5 nodes are usually 30-45 cm long.Factors affecting rooting of cuttings.
Temperature: for the cuttings to produce roots warm temperatures are required around the root zone while cool temperatures are important for the aerial part of the cuttings. For most species optimum day and light temperatures for rooting are 22 -27°c and 15-21° c respectively.a) Relative humidity: Proper rooting of cuttings requires high humidity which lower the transpiration rate. it also increases and maintains leaf turgidity all the time. As such, cuttings should be rooted in green houses or under shady conditions, where relative humidity can be regulated. Sometimes the propagation area can be sprayed with water to keep it moist.
b) Light intensity: soft wood cuttings need high intensity light to produce roots. This is because light promotes the production of roots since it affects the rate of photosynthesis. Hard wood cuttings do well in dark conditions since they have high amount of stored carbohydrates and therefore rooting is excellent in darkness.
c) Oxygen supply: plentiful supply of oxygen is required for root formation. The rooting medium used must therefore be capable of allowing proper aeration.
d) Chemical treatment: these rooting hormones which promote the production of roots in cuttings. The common ones include [AA (indoleacetic acid).
e) Leaf area: Soft woods cuttings require a lot of leaves for photosynthesis while hardwood cuttings will produce roots better without leaves.
Selection of planting materials
When selecting materials for planting the following factors must be considered:
Suitability to the ecological conditions — the selected planting materials should be well adapted to the soil conditions, temperatures and amount of rainfall in the area. There are many varieties of maize, for example, which are suitable to different ecological conditions. Hybrid 622f or example is mainly for the high altitudes areas of Kenya 513 for the medium altitudes and the Katumani composites for the low rainfall areas while the coast composites are suitable for the coastal conditions each variety will grow well and produce high yields if grown under the correct conditions
Purity of the materials – planting materials should be pure and not mixed with other off types the percentage purity of planting materials will affect the seed while higher seeds rates are used for impure seeds.
Germination percentage – This is a measure of the germination potential of seeds it is expressed as a percentage for example a germination percentage of 80 means that for every 10 seeds planted 80 of them are expected to germinate. Germination percentage helps to determine the seed rates of crops lower seed rates are used for crops with higher germination percentage while higher seed rates are used for those with lower germination percentage.
Certified seeds – These are seeds which have been tested and proven to have 100 germination potential and free from diseases and pests they give high yields after the first planting but the subsequent yields decline if replaced therefore in this case it is always advisable to buy new seeds which are certified every time planting is done In Kenya certified seeds are produced by the Kenya seed company(KSC) and distributed by Kenya Farmers Association (KFA) and other agents.Preparation of planting materials.
After the planting materials are selected they are prepared in different ways before they are planted. Some of the methods used to prepare planting materials include the following:
(a)Breaking the seed dormancy.
Some seeds undergo a dormancy period between maturity and the time they sprout. The dormancy period is the stage whereby a seed cannot germinate, the stage of inhibited growth of seed. it should be broken before the seed is planted.
Methods of breaking seed dormancy.
The following methods are used to break seed dormancy:
(i) Mechanical method: This is a method which aims at scratching the seed coat to make it permeable to water. Scarification is done by rubbing small sized seeds against hard surface such as sand paper, while filling or nicking the seed coat with a knife is done to large sized seeds such as croton seeds.
(ii) Heat treatment: this involves the use of hot water or burning the seeds lightly. It softens the seed coat making it permeable to water and thus is able to germinate. The seeds are soaked in hot water about 80’c for 3-4 minutes after which the water is allowed to drain off. Example of seeds treated in this way include: leucean 7a2 + 32 = 22 calliadra and acacia.
Light burning also serves the same purpose as hot watertreatment. In this case trash is spread over the seeds which are already covered with a thin layer of soil. The trash is burned, after which the seeds are retrieved and planted. Examples include acacia and wattle tree seeds. Overheating should be avoided as this will cook the seeds.
(iii)Chemical treatment: seeds are dipped in specific chemicals such as concentrated sulphuric acid, for two minutes and then removed. The chemical wears off the seed coat making it permeable to water. Care should be taken not to leave the seeds in the chemicals for too long as this will kill the embryo. Cotton seeds are normally treated with chemicals to remove the lint or fibres.
iv) Soaking in water: seeds are soaked in water for a period of between 24 — 48 hours until they swell. They are then removed and planted immediately. The seeds treated thus germinate very fast. Pre-germinated seeds are used when raising rice in the nurseries.
b) Seed dressing
This is the coating of seeds with fungicides or an insecticide or a combination of the two chemicals. This is particularly common with cereals, sugar-cane and legumes. The chemicals protect the seedlings from soil-borne diseases and pests. Certified seeds which are sold by seed merchants in Kenya have been dressed with these chemicals. Farmers can also buy the chemicals and dress their own seeds.
c) Seed inoculation
In areas where soils are deficient in nitrogen, legumes such as beans, clovers and peas should be coated with an inoculant. An innoculant is a preparation which contains the right strain of Rhizobium depending on the type of legume and encourages nodulation, hence nitrogen fixation. Below is a table showing different legume crops and their right strain of Rhizobium.
Crop inoculation group
Lucerne
Clover
Pea
Bean
Lupin
soyabeanRhizobium Species
R.melioti
R.trifoli
R.leguminosarum
R.phaseoli
R.lupini
R.japonicumWhen handling inoculated seeds, care should be taken to prevent them from coming in contact with chemicals. This means that inoculated seeds should not be dressed with chemicals as these will kill the bacterium. They should also be planted when the soil is moist to avoid dehydration which kills the bacterium.
d) Chitting
This practice is also referred to as sprouting. The selected seed potatoes ‘setts’ which are used as planting materials are sprouted before planting to break their dormancy. The setts of about 3-6 cm in diameter are arranged in layers of 2 or 3 tubers deep in a partially darkened room. The setts should be arranged with the rose» end facing upwards and the heel-end downwards. Diffused light encourages the production of short, green and healthy sprouts.
If Chitting is done in complete darkness, long, pale thin sprouts develop which break easily during planting. During Chitting potato aphids and tuber months should be controlled by dusting or spraying the sett with dimethoate.
Sometimes a chemical known as Rendite is used to break dormancy, thus inducing sprouting. Chitting is done mainly to make sure that growth commences immediately the seed is planted so as to make maximum use of rains for high yields.
Time of planting
The timing of planting or sowing is inﬂuenced by the type of crop to be planted and the environmental conditions of the area.
Factors to consider in timing planting.
The rainfall pattern/moisture condition of the soil.
Type of crop to be planted.
Soil type.
Market demand.
Prevalence of pests and diseases.
Weed control.
Timely planting is necessary and should be done at the onset of rains. in some areas where rainfall is scare dry planting is recommended.Advantages of timely planting.
Crops make maximum use of rainfall and suitable soil temperature, leading to vigorous growth.
Crops usually escape serious pests and diseases attack.
Crops benefit from nitrogen flush which is available at the beginning of the rain.
For horticultural crops, proper timing ensures that the produce is marketed when prices are high.
Crops establish earlier than the weeds, hence smothering them.Methods of planting.
There are two main methods of planting :-
Broadcasting.
Row planting.Broadcasting.
This method involves scattering the seeds allover the field in a random manner. It is commonly adapted for light tiny seeds such as those of pasture grasses.
It is easier, quicker and cheaper than row planting. However, it uses more seeds than row planting and the seeds are spread unevenly leading to crowding of plants in some places.
This results in poor performance due to competition. Broadcasting gives a good ground cover, but weeding cannot be mechanized. For good results, the seedbed should be weed-free, firm and have a fine tilth.
Row planting.
The seeds or other planting materials are placed in holes, drills or furrows in rows. The distance between one row to the other and from one hole to the otheris known.
In Kenya, both large and small — scale farmers practice row planting. It is practiced when planting many types of crops, especially perennial, annual and root crops.
Advantages of row planting.
Machines can be used easily between the rows.
It is easy to establish the correct plant population.
Lower seed rate is used than if broadcasting is adopted.
It is easy to carry out cultural practices such as weeding, spraying and harvesting.Disadvantages of row planting.
It does not provide an ample foliage cover. Thus the soil is liable to being eroded by wind and water.
It is more expensive than broadcasting because of consuming a lot of labour and time.
It requires some skill in measuringthe distances between and within the rows.Seeds can also be planted by dibbling where the planting holes are dug by use of pangas or jembe, or by a dibbling stick (dibbler). Most of the dibbling is done randomly although rows can also be used when using a planting line.
Random dibbling is not popular in commercial farming due to low levels of production. It is only common among conservative farmers in planting of legumes such as beans, pigeon peas and cow peas.
Over-sowing.
This is the introduction of a pasture legume such as desmodium in an existing grass pasture. Some form of growth suppression of existing grass such as burning, slashing or hard grazing plus slight soil disturbance is recommended before over sowing. A heavy dose of super phosphate, preferably single supers at a rate of 200- 400 kg/ha is applied.
The grass must be kept short until the legume is fully established. Regardless of the method of establishment, the pastures and fodder stands should be ready for light grazing 4-5 months after planting if rainfall and soil fertility are not limiting.
Under-sowing.
This refers to the establishment of pasture under a cover crop, usually maize. Maize is planted as recommended and weeded 2-3 weeks after the onset of rains. Pasture seeds are then broadcasted with half the recommended basal fertilizer.
No further weeding should be done and maize should be harvested early to expose the young pasture seedlings to sunlight. The benefits of under sowing include facilitating more intensive land utilization and encouraging an early establishment of pastures.
Fodder crops and vegetetively propagated pasture species may also be under sown as long as rainfall is adequate for their establishment. Timing is not very crucial in this case and planting can be done as late as 6-8 weeks after the onset of rains.
Plant population
This refers to the ideal number of plants that can be comfortably accommodated in any given area, without overcrowding or too few to waste space.
Agricultural research has arrived at the optimum number of various crop plants to be recommended to farmers. Plant population is determined by dividing the planting area by spacing of the crop. This may be simpliﬁed thus:
Plant population = Area of land divided by Pacing of crop
Example
Given that maize is planted at a spacing of 75 x 25 cm, calculate the plant population in a plot of land measuring 4 x 3 m.
Working
Area of land = Plant population divided by Pacing of crop
Area of land = 400 cm x 300 cm
Spacing of maize = 75 cm x 25 cm
Therefore, plant population = 400 cm x 300 cm
75 cm x 25 cm
= 64 plants.
Spacing
It is the distance of plants between and within the rows. Correct spacing for each crop has been established as shown in table below.
Crop
Maize (Kitale)
hybrids
spacing
75-90 cm x 23—30 cm
Crop
Coffee
(Arabica) tall varieties
spacing
2.75 cm v 2.75 m
Crop
Tea
spacing
1.5 m by 0.75 m
Crop
Beans (erect type)
spacing
45 -60 m by 25 cm
Crop
Bananas
spacing
3.6 — 6.0 m by 3.6 — 4.5 m
Crop
Coconut
spacing
9 m x 9 m
Crop
Tomatoes (Money maker)
spacing
100 x 50 cm
Crop
kales
spacing
60 x 60 cm
Spacing determines plant population and the main aim of correct spacing is to obtain maximum number of plants per unit area which will make maximum use of environmental factors.
Wider spacing leads to a reduced plant population which means lower yields, whereas closer spacing could lead to overcrowding of plants and competition for nutrients and other resources would occur. Correctly spaced crops produce yield of high quality that are acceptable in the market.
Spacing is determined by the following factors:
The type of machinery to be used.The space between the rows should allow free passage of the machinery which can be used in the field. For example, the spacing between rows of coffee is supposed to allow movement of tractor drawn implements.
Soil fertilityA fertile soil can support high plant population. Therefore closer spacing is possible.
The size of plantTall crop varieties require wider spacing while short varieties require closer spacing, for example, Kitale hybrid maize is widely spaced than Katumani maize.
Moisture availability.Areas with higher rainfall are capable of supporting a large number of plants hence closer spacing than areas of low rainfall.
Use of crop.Crop grown for the supply of forage or silage material is planted at a closer spacing than for grain production.
Pest and diseases control.When crops are properly spaced, pests might find it difficult to move from one place to the other, for example, aphids in groundnuts.
Growth habit.Spreading and tillering crop varieties require wider spacing than erect type.
Seed rate.
Seed rate is the amount of seeds to be planted in a given unit area governed by ultimate crop stand which is desired.
The objective of correct spacing of crop is to obtain the maximum yields from a unit area without sacrificing quality. Most crops are seeded at lighter rates under drier conditions than under wet or irrigated conditions.
Seeds with low germination percentage are planted at higher rates than those which have about 100% germination percentage. There is an optimal seed rate for various crops.
For example, the seed rate for maize is 22 kg per hectare, wheat is 110 kg per hectare and cotton is between 17 to 45 kg per hectare.
Factors to consider in choosing seed rates.
Seed purity.When planting seed which is pure or with a high germination percentage, less seed is required. On the contrary, more seeds are required when using impure or mixed seeds.
Germination percentage.Less seed is used when its germination percentage is higher. Seed of lower germination percentage is required in large amounts.
Spacing.At closer spacing, more seeds are used than in a wider spacing.
Number of seeds per hole.When two or more seeds are planted per hole, higher seed rate is required than when only one seed is planted per hole.
The purpose of the crop.A crop to be used for silage making is spaced more closely than one meant for grain production. This would require use of more seeds. Maize to be used for silage making, for example, requires more seeds than that meant for production of grain.
Depth of planting.
This is the distance from the soil surface to where the seed is placed. The correct depth of planting is determined by:
Soil type: seeds Will emerge from grater depths in sandy soil that are lighter than in clay soils.
Soil moisture content: it is recommended that one plants deep in dry soils in order to place the seeds in a zone with moist soil.
Size of the seed: Larger seeds are planted deeper in the soil because they have enough food reserves to make them shoot and emerge through the soil to the surface.
Type of germination: seeds with epigeal type of germination (carry cotyledons above the soil surface) such as beans, should be planted shallowerthan those with hypogeal type of germination (leave cotyledons under the soil) such as maize.Suggested Activities.
1.Learners to carry out planting using broadcasting method and planting rows.
2.Learners to identify different vegetative propagation materials displayed by the teacher.
3.Learners to determine the correct plant population for a given area by mathematical calculations.
4.Learners to collect samples of different tree seeds and prepare them for planting by various methods of breaking seed dormancy.
5.Learners to determine the germination percentage of different samples of cereals and legume seeds.
Crop Production Ill
(Nursery Practices)
Introduction
Planting materials are either planted directly in a seedbed or indirectly through a nursery bed.
A seedbed is a piece of land which could be small or large and prepared to receive planting materials.
A nursery bed on the other hand is a small plot of land specially prepared for raising seedlings or planting materials before transplanting.
It is usually 1m wide and any convenient length depending on the quantity of seedlings to be raised.
A seedling bed is a special type of nursery bed used for raising seedlings pricked out from the nursery bed due to overcrowding before they are ready for transplanting.
Pricking out refers to the removal of seedlings from a nursery bed to a seedling bed.
Nursery practices refer to all the activities carried out throughout a nursery life to raise seedlings.Importance of Nursery Bed in Crop Production
To facilitate the production of many seedlings in a small area.
It is easy to carry out management practices in a nursery than in the seedbed.
It facilitates the planting of small seeds which develop into strong seedlings that are easily transplanted.
It ensures transplanting of only healthy and vigorous growing seedlings.
It reduces the period taken by the crop in the field.
Excess seedlings from the nursery may be sold to earn income.Selection of a Nursery Site
Factors to consider;
Nearness to the water source.
Type of soil.-should be well drained, deep and fertile, preferably loam soil.
Topography.-it should be situated on a gentle slope to prevent flooding and erosion through surface run-off.
Previous cropping.-to avoid build up of pests and diseases associated with particular plant families, consider the preceding crops.
Security.-select a site that is protected from theft and destruction by animals.
Protection against strong winds and heat of the sun.-select a sheltered place. i.e. to avoid excessive evapotranspiration and uprooting seedlings.

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