CROP PRODUCTION I
LAND PREPARATION
Land preparation involves all those activities that make land suitable for planting e.g. ploughing, harrowing, ridging and rolling
Seed bed: this is a piece of land prepared ready for planting. To achieve good germination of seeds the following must be achieved:
- Suitable size of clods
- Good depth
- Looseness of soil
- Absence of weeds
Importance/Reasons for land preparation
- To kill weeds
- To incorporate manure and other organic matter in the soil
- To destroy different stages of crop pest such as eggs, larva or adult stages by burying them and exposing them to the heat
- To encourage the penetration of roots in the soil
- To make subsequent operation easy
- To encourage water penetration in the soil
Operations in land preparation
- Land clearing
- Primary cultivation
- Secondary cultivation
- Tertiary operations
- Land clearing
This is the removal of vegetation cover from the surface before land is cultivated. It is done to prepare land for cultivation as well as a method of land reclamation
Conditions that necessitate land clearing
- When opening up virgin land
- Where a stalk growing crop was previously planted
- Where the interval between primary and secondary cultivation is long such that land is reverted back to its original virgin state
- Where land was left fallow for a long time
Methods of land clearing
- Tree felling
- Burning
- Slashing
- Use of chemicals
- a) Tree felling
This involves cutting down trees. Axes, pangas, are used and small power saws where the trees are few. Bulldozers and root rakers are used where trees are on large scale. After cutting down the trees, destumping or removal of stumps and disposal of trash is done.
- b) Burning
Here fire is set on the vegetation cover. It should be done when the speed of wind is low to avoid spread of fire to other fields.
Burning should be discouraged because:
- It destroys organic matter
- kills useful soil micro organisms
- Destroys plants nutrients
- Destroys soil structure
- Fire can spread to an area where it was not intended hence destruction of property ,forests and desirable crop and plant species
- c) Slashing
Small bushes or grasses can be cleared by slashing. Slashers or pangas are used in a small area, while a tractor drawn mower can be used in large areas
- d) Use of chemicals
Chemicals used to kill weeds are called herbicides e.g. Roundup, Atrazine, Gramoxone. They kill weeds faster and more easily.
- Primary cultivation
This is the initial opening of land either after land clearing or following a previous crop.
Primary cultivation should be done well before the onset of rains to give time for all operations to be done in good time.
Importance of primary cultivation
- To remove weeds
- To burry organic matter for easy decomposition
- To facilitate water infiltration and aeration
- To destroy soil borne pests by exposing them to predators and scorching effects of the sun
- To make subsequent operation easier e.g. planting
- Eases the penetration of crop roots
Ways of carrying out primary cultivation
- Hand digging
- Mechanical cultivation
- Use of ox plough
- a) Hand digging
This is mainly the use of simple hand tools such as Jembes, mattocks and fork Jembes to cut and turn the soil slices.
- b) Mechanical cultivation
Where large pieces of land are involved, farmers use tractor mounted implements which include mould board, disc ploughs. Also there is use of sub soilers to break the hard pan.
- c) Use of an ox plough
This is use of ploughs drawn (pulled) by animals such as donkeys, camels, oxen etc. common in areas where such animals are available and the terrain is flat.
Aspects to be considered when carrying out primary cultivation
- i) Time of cultivation
- ii) Depth of cultivation
iii) Choice of implements
- i) Time of cultivation
Land preparation should be done early enough before the onset of rains.
Reasons for early cultivation
- To give weeds and other vegetation enough time to dry up and decompose into organic matter
- To allow carbon dioxide and other gases to diffuse out of the soil while being replaced by oxygen required in seed germination and growth of soil organisms
- Also gives time for subsequent operations to be done giving way for early planting
- ii) Depth of cultivation
Factors that determine the depth of ploughing are:
- The type of crop to be planted: Deep rooted crops require a soil which has been cultivated deeply, because it will facilitate easy root penetration. Shallow rooted crops may not need deep cultivation
- The implements available: There are some implements which cannot cut the soil beyond a certain depth. Such implements can be sharpened or weight be added
- Type of soil: heavy soils are hard particularly when they are dry. Simple implements such as Jembes tend to dig shallowly on such hard soils
iii) Choice of implements
Choice of implements used in primary cultivation is determined by:
- The condition of the land: If the land has a lot of stones and stumps, it would be advisable for one to choose a disc plough which would not break easily when working on such land. A Jembe cannot be used efficiently on land which has a lot of couch grass because it cannot pull all the rhizomes.
- The type of tilth required: very fine tilth requires the use of different types of implements
- The depth of cultivation needed: heavy implements are necessary when deep cultivation is needed and light implements are required when shallow cultivation is necessary
- Secondary cultivation
These are operations which follow the primary cultivation and means seedbed refinement practices before planting, also called harrowing
Importance of secondary cultivation
- To remove any weeds that might have germinated after primary cultivation
- To break the soil clods into small pieces for easy planting
- To level the field on order to achieve a uniform depth of planting
- To incorporate organic matter into the soil in order to encourage decomposition before planting
Factors that determine the number of times of secondary cultivation
- Size of planting materials: Big seeds such as those of groundnuts, maize etc require a fairly rough seedbed, and small seeds such as those of finger millets require fine seedbed
- Slope of the land: When the land is very steep, less cultivation should be done to discourage soil erosion
- The moisture content of the soil: In dry soils less cultivation are preferred so as to conserve the available moisture
- Condition of the soil after primary tillage: where there is plenty of trash, more harrowing operations should be carried out to incorporate most of the trash into the soil
N/B: Implements used for secondary cultivation are: pangas, Jembes, fork Jembes, and garden rakes. Tractor drawn harrows e.g. Discs, spike toothed and spring tine harrows
- Tertiary operations
These are operations carried out to suit production of certain crops. They are carried out after land clearing primary cultivation and secondary tillage. They include:
- Leveling
- Rolling
- Ridging
- a) Leveling
This is the practice of making the soil surface flat and uniform so as to promote easy germination of small seeded crops such as wheat, grasses, and barley. It facilitates uniform germination of seeds.
- b) Rolling
This is done to compact soil which is loose or fine tilth. It is done to prevent small seeds from being carried away by wind and to prevent soil erosion. Also increases seed soil contact. Implements used are: simple hand tools and heavy rollers
- c) Ridging
This is the process of digging soil in a continuous line and heaping it on one side to form a bund ( ridge) and a furrow. The ridges are important for planting root crops like Irish potatoes, cassava etc.
Reasons for ridging
- It improves soil drainage
- Helps in tuber expansion
- Helps in water conservation
- Easy harvesting of root crops.
N/B: Other tillage operations include:
- Sub soiling
- Minimum tillage
- Sub soiling
This is the process of cultivating the soil for the purpose of breaking up the hard pans which might have formed as a result of continuous use of heavy machinery in land preparation. Implements used in sub soiling are:
- Sub soiler
- Chisel ploughs
- Cultivators
Importance of sub soiling
- Helps to break up hard pans
- Helps to facilitate gaseous exchange in the soil
- Also brings to the surface, minerals which might have leached to the deeper layers
N/B: hard pan is an impervious layer of soil found within the sub soil.
- Minimum tillage
This is the application of a combination of farming practices aimed at least disturbance to the soil.
Reasons for carrying out minimum tillage
- To reduce the cost of cultivation or ploughing by reducing the number of operations
- To control soil erosion, mulching and cover cropping greatly reduce chances of soil erosion
- To maintain soil structure, continuous cultivation destroys soil structure hence its avoided
- To conserve moisture, continuous cultivation exposes the soil to the heat of the sun thus enhance evaporation of available moisture
- To prevent disturbance of roots and underground structures for example tubers and bulbs
- To prevent exposure of humus to adverse conditions such as the suns heat that cause volatilization of nitrogen
Ways of achieving minimum tillage
- Application of herbicides in controlling weeds
- Use of mulch on the soil surface. Mulch prevents weeds from growing by smothering them
- Timing cultivation, late weeding of cotton crop, for example often produces a clean seedbed for finger millet to be sown without further cultivation
- Restricting cultivation to the area where seeds are to be planted. Weeds in the rest of the field are controlled by slashing
- Establishment of cover crop on the field
- Uprooting or slashing weeds on perennial crops