SOIL FERTILITY: ORGANIC MANURES.
SOIL FERTILITY: ORGANIC MANURES, Soil fertility.
The ability of the soil to provide crops with the required nutrients in proper proportions and form for high production.
Characteristics of fertile soils.
- Good depth.
Deep soils give plant roots greater volume to obtain plant nutrients and provide strong anchorage.
ii. Proper drainage.
A well-drained soil is properly aerated promoting healthy root development. They allow root respiration and reduce the buildup of carbon (iv) oxide to toxic levels.
iii. Good water holding capacity.
This ensures that enough water is retained for plant use.
iv. Adequate nutrient supply.
Should supply the nutrients needed by plants in the correct amounts and in a form that is available to the crops.
v. Correct soil pH.
Different crops have different soil pH requirements. Certain plant minerals are only available at a specific soil pH.
vii. Free from excessive infestation of soil borne pests and diseases.
SOIL FERTILITY: ORGANIC MANURES
HOW SOIL LOSES FERTILITY.
As water infiltrate into the soil it dissolves soluble minerals. The dissolved minerals are carried to lower horizons beyond the reach of many plant roots. A soil with many nutrients that have been leached is infertile.
It is the carrying away of the top fertile soil. Leads to loss of good soil and plant nutrients rendering soil infertile.
- It is growing one type of crop on a piece of land over a long time (monoculture). The crop uses only those nutrients it require while other nutrients remain unused.
- This leads to exhaustion of some particular nutrients.
- The crop grown utilizes nutrients from a certain zone thus soil in that zone become infertile as far as that crop is concerned.
- There is build-up of pests and diseases if one crop is grown continuously.
Harvested crops remove large amounts of nutrients from the soil.
The nutrients removed from the soil are taken away making soil deficient in these plant nutrients.
Change in soil pH.
Changes in soil pH affects the activity of soil micro-organisms as well as the availability of soil nutrients.
Burning of vegetation cover.
- When vegetation is burnt, organic matter is destroyed leading to the destruction of soil structure.
- Accumulation of ash formed after burning cause nutrient imbalance which may lead to unavailability of some nutrients.
- Micro-organisms are also destroyed thereby interfering with microbial activities such as nitrogen fixation and decomposition or organic matter.
- The soil is also left exposed to the agents of soil erosion.
Accumulation of salts.
- Soil water contains dissolved mineral salts which comes from parent rock. Other salts comes from decomposition of organic matter.
- Where rainfall is irregular and insufficient to remove salts from the soil, coupled with high evaporation rates and poor natural drainage, results in salt accumulation or salinization on the soil surface.
- Soils with a lot of salts are saline and the state of having too much salts in the soil is referred to as soil salinity.
- The salts causes water deficiency and may lead to change of soil pH.
MAINTENANCE OF SOIL FERTILITY.
Control of soil erosion.
The measures to control soil erosion aims at promoting good water infiltration and reducing runoff. Includes: terracing, contour cultivation, strip cropping, cut-off drains and planting cover crops.
Practice of growing crops of different families on the same piece of land in an orderly sequence.
Helps to control crop pests, diseases and weeds.
Ensures maximum utilization of soil nutrients by growing a variety of crops which have different nutrient requirements.
Legumes in a rotation programme improves the soil nitrogen.
Control of soil pH.
Most living organisms do well at a pH around neutral.
Extreme pH inhibit the activities of living organisms.
Can be done by breaking hard layers impeding drainage. Where poor drainage is as a result of poor soil structure and texture, water channels can be used.
The weeds compete with crops for growth resources such as: nutrients, soil moisture, space and sunlight.
Some weeds acts as alternate hosts of crop pests and diseases.
Intercropping and mixed cropping.
Intercropping offers a better ground cover thus smothering weeds and controlling soil erosion. Legumes intercropped with cereals fix nitrogen which is used by the cereal crops.
- Minimum tillage.
Over cultivation destroys the soil structure leading to soil erosion. Therefore unnecessary land operations should be avoided.
- Use of manure.
Supply organic matter, which on decomposition releases nutrients into the soil. This increases the water holding capacity, moderates soil pH and improves soil structure which helps to control soil erosion. ix. Use of organic fertilizer.
Chemical substances which are manufactured to supply specific plant nutrients. Once used they improves the soil fertility.
SOIL FERTILITY: ORGANIC MANURES
Manure are organic substance that are added to the soil to provide one or more plant nutrients. Organic manure supplies organic matter to the soil which after decomposition releases plant nutrients.
Humus. The end product of decomposition. Humus forms part of soil colloids which improves soil chemical properties.
Importance of organic matter in the soil.
- It increases the water holding capacity of the soil, it also increases the infiltration rate due to its colloidal nature.
- It improves soil fertility by releasing a wide range of nutrients into the soil.
- Provides food and shelter for soil micro-organisms responsible for the decomposition of organic matter.
- Improves soil structure. Humus binds soil particles together thus improving the soil structure. Drainage and aeration are also improved.
- It buffers soil pH. That is, it moderates soil pH by avoiding rapid chemical changes.
- Reduces the toxicity of plant poisons that may have built up in the soil as a result of continuous use of pesticides and fungicides. vii. Humus which is mostly dark in colour gives the soil its dark colour. Black colour absorbs heat, thus helps to moderate soil temperatures.
The use of manures, however is limited to small scale due to:
- Have low nutritive value per unit volume thus required in large quantities.
- They are laborious in application and transport. Thus increases cost of production.
- They may spread pests, diseases and weeds. If the materials used to prepare manure is infested.
There is loss of nutrients. If they are poorly stored. Soluble nutrients are easily leached and some are volatilized when exposed to hot sun.
- They may scorch the crops if used when not fully decomposed. The crop does not benefit from them because it releases nutrients which can scorch the crop.
SOIL FERTILITY: ORGANIC MANURES
Types of organic manure.
Manure is classified according to method of preparation and the materials from which it is made.
1) Green manure.
Made of green plants. The plants are grown for the purpose of incorporating into the soil. Leguminous plants are preferred because they fix nitrogen.
Characteristics of plants used as green manure.
- They should be highly vegetative or leafy.
- They should have a fast growth rate.
- They should have a high nitrogen content, thus leguminous plants are preferred.
- The plants must be capable of rotting quickly.
- The plants should be hardy, that is, they should be capable of growing in poor conditions.
Reasons why green manure is not commonly used.
- Most of the crops grown are food crops and it is hard for people to use them as green manure. ii. Green manure crops might use most of the soil moisture and leave very little for the next crop.
- Most of the nutrients are used up by micro-organisms in the process of decomposing the green manure plant. These are released only when the micro-organisms die.
- It takes time for green manure crop to decompose and therefore planting is delayed.
2) Farmyard manure. (FYM)
It is a mixture of animals waste (urine and dung) and crop residues used as animal beddings.
Factors determining the quality of farmyard manure.
- The type of animal used. Dung from fattening animals has higher level of nutrients than from that of dairy animals.Non-ruminats absorb less nutrients from their feeds hence their dung has a higher level of nutrients.
- Type of food eaten: feedstuffs that are highly nutritious results in manure with a higher level of nutrients.
- Type of litter used: wood shavings and sawdust are slow to decompose and contain very little nutrients. Napier grass provides both nitrogen and phosphorus but has low urine absorption capacity. Litter used with a high urine absorption capacity.
- Method of storage: FYM must be stored well in a leak proof and concrete floor to prevent loss of nutrients though leaching and vaporization.
- Age of FYM: well rotten manure is rich in nutrients and it is easy to handle and mix with the soil.
3) Compost manure.
Manure prepared from composted (heaped) organic materials. The compost materials include plant residues and animals waste or plant materials only.
Avoid materials such as synthetic and plant with pests, diseases and weed seeds.
Factors to consider when siting a compost manure site.
- A well-drained place.
This avoids waterlogging which leaches nutrients from the manure.
ii. Direction of prevailing wind.
Should avoid direct drift from the compost manure to the dwelling place. This prevent bad odour being blown to the homestead.
iii.Size of the farm.
The site should be centrally placed to the area of the farm where it is to be used.
The site must be easily accessible to make it easy for transportation of materials needed.
Preparation of compost manure.
There are two methods of preparing compost manure.
1) Indore method (pit method.
Devised at a place called Indore in India. Materials are packed into a pit 1.2M long, 1.2M wide and 1.2M deep.
Materials are put in layers. S Layer one.
Fibrous materials such as maize stalks which forms the foundation of the compost layers.
- Layer two.
Layer of grass, leaves or any type of refuse material.
- Layer three.
Well rotten manure. This provide nutrients to micro-organisms.
- Layer four.
Thin layer of wood ash. This improves the level of potassium and phosphorus in the resulting manure.
- Layer five.
A layer of topsoil. It introduces micro-organisms necessary for decomposition of the organic, materials.
- The above sequence is repeated until the pit is full.
- During the dry season materials should be kept moist by adding water.
- The materials used should be young. However, if old materials are used, nitrogenous fertilizers should be added to raise the level of nitrogen in the manure.
- Materials should not be compacted to increase air supply for fermentation.
- The pit should be covered to prevent entry of too much water causing waterlogging.
- Five pits are dug in a series and materials filled as follows:
- Pit 1, 2, 3 and 4 are filled with fresh materials. After 3 to 4 weeks, materials in pit 4 are transferred to pit 5, materials in pit 3 to 4, in pit 2 to 3 and in pit 1 to 2. The process is repeated until the materials that was first prepared first is well rotten and taken to the filed.
2) Four heap system. (Stack method)
Four heaps are used. The materials on each heap are crop residue, animal waste, old farmyard manure, inorganic fertilisers and top soil
Surface vegetation is cleared and topsoil scraped off the site and the ground is levelled.
Posts are fixed at a distance of 1.2M apart to form corners of the heap. Posts should be 2M high. Wood planks are fixed on the sides and materials arranged
- If four heaps are used, materials are placed in the heaps labelled X. after 3 to 4 weeks, the decomposing materials are transferred to heap Y. after another 3 to 4 weeks the compost materials are transferred to heap Z where it stays for another 3 to four weeks then it is taken to the field.
A long sharp pointed stick is driven into the pile at an angle.
The stick is used for checking temperatures within the heap. If too high water should be added.
SOIL FERTILITY: ORGANIC MANURES