To prepare compost, a suitable site needs to be chosen. It should be well-drained and close to the garden or cropping area. The base of the composting area should be concrete and measure 4.0 m long x 1.5 m wide. Instead of concrete, plastic sheeting could be securely pinned to the ground. It is usual to divide the composting area into three equal compartments, each approximately 1.3 m wide and 1.5 m long.
The Phase 3 Section needs a protective cover to prevent loss of nutrients through run-off and leaching. A shed is useful for storing composted material and to protect it from rain.
When construction of the composting area has been completed, all composting materials should be collected and sorted. All bottles, plastic containers, stones and tin cans need to be removed. Plants with hard woody stems are difficult to compost and it is a good idea to remove nut-grass and weed plants with seeds.
The Phase 1 Section is then built up as follows:
• a layer of starter material, consisting of pen manure, is placed on the base to a depth of 10 cm
• a layer of organic matter is loosely arranged on top of the starter and built up to about 25 cm in thickness; both the starter layer and the organic matter need to be loosely arranged to allow air to circulate
• 1.0 kg of sulphate of ammonia is broadcast over the organic matter layer • 0.5 kg of ground limestone is spread evenly on top of this
• alternate layers of starter and organic material (plus the fertiliser and limestone) are stacked until a height of 1.5 m to 2.0 m is reached • the heap is watered and kept loose and moist.
storage shed with compost manure
After 3 to 4 weeks, all the materials in the Phase 1 Section are transferred to the Phase 2 Section, making sure that the undecomposed materials that were at the bottom and sides of the old heap are placed in the middle of the new heap. A suitable moisture level is maintained by watering when necessary. The compost is left in the Phase 2 Section for a further 3 to 4 weeks, after which time it is moved to the Phase 3 Section. The compost is left to decompose here for another 3 to
Section B: Crop Production r
Make a list of the materials which need to be removed from waste before it is composted.
r 4
Explain why fertiliser and limestone are added to the compost heap.
Practical activity:
Prepare some compost following the guidelines given above.
soil erosion ►
Practical activity:
Carry out a demonstration of soil erosion using models which you have made.
r-i
Write a definition of soil erosion.
4 weeks. At the end of this period, the compost is transferred to the storage area and is ready to be used on the garden or cropping area.
During the decomposition of organic material, microbial activity results in high temperatures which destroy parasitic organisms and some of the weed seeds in the plant wastes.
Once the material has been moved out of the Phase 1 Section, a new heap can be built up in this section, following the same sequence. In this way, the farmer has a continuous supply of compost to maintain soil fertility.
The composting process described here is suitable for situations where there is a lot of vegetable waste and the farmer has a large enough area on which to build a site and storage area. Smaller farmers and gardeners may use specially designed plastic bins, which take up less space.
8.11 Soil erosion
Soil erosion is the process by which particles of soil are carried away from one area, by water or wind, and deposited at another area. All soils undergo erosion, but if there has been no clearing or cultivation of the land, the rate of erosion is slow and allows the processes of soil formation to continue. If vegetation cover is removed, as when land is cleared for agriculture, forestry or grazing, then the soil is exposed to wind and water. Soil erosion is speeded up and can become a problem.
Factors that control the amount of soil erosion are: • amount of rainfall
• wind speed and intensity • the type of rock
• the slope of the land
• the amount and type of vegetation cover • the presence of grazing animals.
8.12 Different types of soil erosion
Soil erosion can be entirely due to natural causes or it can result from human activities.
natural soil erosion ► Natural soil erosion occurs in an undisturbed natural environment as a result of: • running water on steep slopes
• running water on sloping areas with loose, friable soil
• landslides of loose, saturated soil, perched on an impervious layer, in hilly or mountainous areas
• strong winds blowing over loose soil in dry, semi-arid or and (desert) areas • sea-waves pounding the land in coastal areas.
accelerated soil erosion ► Accelerated soil erosion occurs as a result of the activities of human beings who disturb the natural environment, creating soil conditions which speed up soil erosion by water and wind.
These activities include:
• burning the vegetation on the land, including 'slash and burn' agriculture -- • overgrazing of pastures by livestock
Name the TWO main types of soil erosion. • deforestation (the cutting and removal of trees) • mining and quarrying operations
• creating bare soil patches on the land by overweeding or brushcutting too closely
List THREE causes of both the types of soil • lack of ground cover, such as a cover crop or a mulch
erosion named in ITO 41. • unsuitable cultural or soil conservation practices on hilly terrain.
°
p 0 1, 1O
splash erosion
water flows downhill soil builds up
sheet erosion
rill erosion on a hillside gully erosion (rills have joined together)
0
a asoil creep ►
saltation ►
Explain how wind can cause erosion.
8.13 The causes of soil erosion
1
Water
In the Caribbean, soil erosion by water is a problem during the rainy season.
Type of erosion Cause Effects
Splash Impact of heavy raindrops. Dislodges soil particles which splash on to young plants; soil particles are carried away by running water.
Sheet Running water dislodges soil particles. Soil particles move downhill as a 'sheet of soil'; soil
gathers at the base of the hill.
Rill Water running down a bare area of sloping
land. Creates many tiny channels, has eroded away. known as rills, where soil
Gully High intensity rainfall and fast-flowing water
on a sloping area of land. Rills and deeper become channels which are called gullies.more eroded. This leads to fewer, wider
Landslide Intensive rainfall on loose soil above a sloping
impervious layer. Loose soil saturated with water.slides away in this situation when it is
Loss of topsoil Running water in hilly or mountainous areas. If soil is not protected by a cover crop, organic matter or
a mulch, topsoil can be lost. Silting up of
water courses
Soil particles carried away by running water. Causes silting up of streams and rivers, eventually leading to flooding of a river basin.
Alluvial soil
deposits Soil slopes particles by streams and rivers.brought down mountainous
Alluvial soil deposits form at the mouths of rivers, on
river banks and on flood plains. Table 8.12 The types, causes and effects of soil erosion by water.
Figure 8.17 Some examples of soil erosion caused by water.
Wind
Wind can also cause soil erosion. Strong winds can cause soil creep, which is the gradual movement of loose soil particles, such as sand, on the soil surface towards the opposite direction from which the wind is blowing.
Saltation of soil particles occurs when strong winds cause loose soil particles to leap suddenly, become airborne for a while and then eventually fall to the ground, forming heaped areas of soil. Where mining, quarrying and land preparation operations are carried out under dry soil conditions, soil particles in suspension are transported by winds and may be deposited many kilometres away.
Soil particles in the atmosphere can cause respiratory problems in people and in farm animals.
Section 8: Crop Production
Burning
burning vegetation ► Burning vegetation as part of land clearing has positive and negative effect Among the positive effects are:
• unwanted material, such as cane-trash, is burnt out, so cane-cutters work more efficiently
• land clearing can be carried out more speedily ` • harmful plants, such as nettles, are destroyed
List TWO advantages and TWO disadvantages of • harmful animals, such as snakes, scorpions, centipedes and the nests of wasps burning vegetation when clearing land for crop are destroyed
production.
• the ashes on the land add potash to the soil
• the soil is sterilised as a result of the intense heat.
However, burning vegetation is not recommended as it creates smoke pollution i the atmosphere. It is recommended instead that harmful plants and crop residue are cut and stacked in an area where they can decompose slowly.
Other negative effects of burning vegetation are:
• the destruction of organic matter which took many years to accumulate • humus in the soil is also destroyed
• soil organisms are killed
• the soil surface becomes bare with no plant cover so it is more exposed to soil erosion
• soil water is lost more rapidly through evaporation • leaching of nutrients can occur more readily.
Animals
Any bare land exposed to heavy rainfall can lose nutrients through leaching an mineral particles from run-off. The effects of animals, through grazing or trampling can leave soil bare and open to erosion, particularly in the rainy season.
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8.14 Soil and water conservation methods
soil conservation ► Soil conservation refers to protecting the soil from erosion and maintaining i fertility. It is of great importance to agriculture in the Caribbean region.