BLE 211 Principles of Agriculture and Forestry Lecture

BLE 211: Principles of Agriculture and Forestry Lecture 3

Factors Influencing Agriculture ® Factors affecting the environment of plants include: ® Above ground including ® ® ® Radiation energy - light, day length, spectral composition, intensity Temperature - seasonal and daily fluctuation gradients between depths, incidence of frost Humidity - (vapour pressure) Clouds mist and fog Rainfall Composition of the atmosphere - carbon dioxide pollution, ozone

Factors Influencing Agriculture ® Below ground including ® ® Composition of soil atmosphere CO 2/O 2 ratio Nutrients - concentration, balance, availability Soil reaction – p. H Depth and character of soil - air, water, growth of plant roots.

Above Ground Climate: In the tropical environment, temperature and rainfall are the most important determinants of crops to be grown. ® As temperatures are high all the year round, they are not limiting to plant growth but determine what plants will be grown. ® Variation in duration of rainfall is a limiting factor in plant growth except in equatorial rain forests where high rainfall contributes to luxuriant and varied plant growth. ® Rainfall however is a critical factor deciding the types of crops grown and the seasonal activities of crop husbandry ®

Influence of Rainfall on Agriculture ® Supplies essential water for the growth and development of all crops and natural vegetation. ® Heavy and frequent rainfall may be a disadvantage by: ® Increasing the leaching of nutrients or ® carrying away soil and applied fertilisers in surface run-off or ® interfering with farming operations.

Influence of Rainfall on Agriculture Occurrence of dry seasons limits the production of many crops to the wet part of the year. ® Thus the rainfall regime is the most important climatic factor influencing agriculture, having the biggest effect in determining the potential of any area, the crops which can be grown, the farming system and the sequence and timing of farming operations. ®

Important aspects of rainfall ® most important aspects of rainfall: ® ® ® Amount Duration Intensity

Rainfall Amount ® Total rainfall may be adequate, but poor distribution or low reliability in any one month may increase the chances of failure or reduce yields. ® Distribution and reliability of the rainfall within the season is important in indicating the possibility of growing certain crops in an area.

Rainfall Duration ® Heavy downpour received within a short duration e. g. within a few hours is destructive as it causes flash floods. ® The floods cause Soil erosion through run-off ® Destruction of crops ® Destruction of the infrastructure ® ® Choosing crops, sowing rates and cultural methods best suited to the rainfall regime is difficult because the start, duration and total amount as well as the distribution all vary from year to year.

Rainfall Intensity ® In most parts of the tropics a large proportion of the rainfalls in heavy showers and storms of high intensity. ® The battering of the soil surface by the raindrops of high intensity storms breaks up the soil aggregates, or crumbs, and the resulting very fine particles block the soil pores, causing the soil surface to become sealed or "capped“.

Rainfall Intensity ® Capping results in: ® Reduced infiltration of rainwater. ® Increase in run-off and erosion. ® Reduced proportion of rainfall that percolates into the soil and becomes effective for crop production is reduced. ® To make the best use of rainfall there is need to ensure that as much of it as possible infiltrates into the soil.

Means of Aiding Rainfall Infiltration Protection of the soil from direct raindrop impact by keeping it covered by a crop canopy or mulch ® Ridging or tie - ridging to hold rainwater on the surface of sloping land give it times to infiltrate into the soil ® Creating a semi-stable structure by bush fallowing or growing a restorative crop for several seasons. ®

Effects of Rainfall Agricuture Where rainfall is scarce like in the deserts or ASALs, vegetation is scanty with more bare ground than plant cover. ® As rainfall increases towards the equator, the savanna vegetation characterised by trees and grasses emerges. ® At the equatorial region where rainfall is high all the year round, trees are the most dominant with mixed tree stands and luxuriant vegetative growth. ®

Effects of Rainfall Agriculture ® Low rainfall causes: Plant wilting ® Yellowing ® Pest infestation ® ® High rainfall causes Leaching ® Soil erosion through run-off ® Yellowing ® Disease epidemics ®

Influence of Temperature on Agriculture ® Low temperature not normally a limiting factor to crop growth and production in the tropics except where it is markedly reduced by altitude. ® In Kenya there is a sharp contrast between the tropical crop production of areas at or near sea level and the extensive semi-temperate farming of the highlands above 2000 m.

Influence of Temperature on Agriculture ® In highlands, 2000 m above sea level, crop production is based mainly on wheat, barley, oats and pyrethrum. ® Livestock production is based on natural grasslands or some pastures. ® In the lowlands, up to 1, 500 m, crops grown include sorghum, millets, cassava and cotton. Temperatures at the higher altitudes are often below the optimum for the growth of these crops.

Effects of High Temperatures ® High temperatures and low humidity cause: Death of maize tassels by desiccation ® Boll shedding of cotton ® Premature fruit drop of certain fruit trees. ® Scorching (local killing some areas of the bark) e. g in tea and pinneapples. , ® ® When exposed to intensive radiation, the surface temperatures of some soils may considerably exceed air temperature and become hot enough to inhibit or retard germination and early growth of some crops.

Effects of High Temperatures ® Lack of low temperatures or winter chilling for some crops may cause: Irregular flowering ® Shedding of flower buds ® Failure of certain crop plants to reach full development before the buds open ® ® Fruit crops requiring chilling include apple, pear, plum, peach, apricot, almond, olive, pecan, grape and strawberry, Pyrethrum requires low temperatures to initiate flower development.

Influence of Humidity on Agriculture ® This is the amount of vapor in the atmosphere otherwise known as the vapour pressure. ® Water loss or transpiration from plant surfaces occurs when the vapour pressure in the leaf cells is greater than the atmospheric vapour pressure. This is when humidity is low. ® Transpiration is vital to plant growth as it ensures that a continual stream of nutrients enters the plant from the soil and also cools the leaves.

Effects of Humidity ® High humidity over long periods, combined with high temperatures favours rapid development of fungal diseases of crops (e. g. coffee Berry Disease of coffee) and of mould on stored produce. ® Drying of crops, such as grains, pulses, coffee and cocoa, to low enough moisture content for storage is often hindered or rendered difficult in humid conditions unless special equipment is used.

Influence of Wind on Agriculture Wind is air in motion It affects the rate of evaporation as it brings fresh unsaturated air which absorbs any available moisture. ® It also helps in the dispersal of seed and pollination. ® ® Light seeds are dispersed by wind to new areas greatle enhancing crop distribution Wind enhances cross-pollination of some crops thus leading to higher crop productivity. The magnitude and extent of this effect depends on the air, the height and roughness of the crop and the amount and persistence of the wind. ® The effect is particularly noticeable in irrigated crops in arid areas. ®

Effects of Wind When wind, which has passed over hot, dry land areas reaches, cropped land, the energy in the wind increases the water loss from the plants and the resulting growth and yield moisture stress may lead to reduced growth and yield. ® Moderate to strong, hot, dry winds blowing persistently from desert areas at certain seasons may have desiccating effects over very large areas. ® Strong winds carry away fertile top soils leading to loss of vital plant nutrients. ® Very strong winds destroy both crops and trees that may have week root system ®

Radiation Energy ® If water and nutrients are not limiting, the input of solar/radiation energy sets the ultimate limit to crop production. ® The energy for photosynthesis and transpiration is derived from the incident short-wave solar radiation absorbed by the plant. ® Certain aspects of the development of many plants, especially flowering, are affected by day-length.

Radiation Energy ® With respect to flowering behaviour species fall into three broad classes: Short-day plants: Do not flower if the daily period of illumination or photoperiod, exceeds a certain critical length (normally 13 hours). ® Long-day plants: Flower only when the daily photoperiod exceeds some critical duration (normally 13 hours). ® Day-neutral or photo-insensitive plants: flower readily over a wide range of day-lengths. ®

Effects of Radiation Energy ® Higher amount of incoming radiation will increase amount of biomass produced through increased photosynthesis rate ® However, under water/rainfall limited conditions increased solar radiation intensifies evapo-transpiration leading water stress and to decline of yields ® Higher radiation energy increases atmospheric temperatures which may lead to the wilting of crops.

Influence of Vegetation on Agriculture Nature of vegetation is controlled by climate, soil and topography (principal physical factors determining agricultural potential). ® Some types of vegetation possess features of direct agricultural significance. For example, some kinds of forests or woodlands are much more difficult to clear. ® The extent to which vegetation is a useful indicator of agricultural potential varies in different places. ®

Influence of Vegetation on Agriculture ® Though the nature of vegetation is largely determined by soil, climate and topography, there is an interrelation between all four factors forming one integrated ecosystem. ® For example, the vegetation itself influences the formation and nature of soil by: The organic matter it deposits on death or defoliation and ® The degree to which the living cover affords protection to the soil from the climate in moderating soil temperature and breaking the battering effect of rainfall. ®

Influence of Vegetation Agriculture ® The degree to which vegetation reflects soil type is variable. ® Same type of vegetation may occur on several soils, or different types of vegetation may occur on the same soil. ® The factors that affect climate interplay to form natural vegetation of different types. ® The most important way in which climate, soil and topography affect vegetation is by their influence on the moisture available to plants either through the rainfall and moisture stored in the soil or the losses from surface run-off, subsoil drainage and evaporation.

Effects of Vegetation ® Tree vegetation act as a wind breaker thus preventing soil erosion from occurring. ® Ground cover vegetation protects the soil from the effects of direct sunlight and well as from the pounding effects of heavy rains. ® Leaf fall from vegetations acts as a means of adding and maintaining soil fertility. ® Heavy natural vegetation plays a major role in modifying the microclimate of an area especially in improving the hydrological cycle.

Influence of Soils on Agriculture ® Provide anchorage for crops. ® Provides the source of nutrients and moisture for crop growth. ® Value of a soil for agriculture depends on: Nutrient content in the soil ® Nutrient holding capacity of the soil ® Nutrient availability ® Soil acidity and alkalinity (soil p. H) as it affects availability of nutrients. ® Physical properties of soil: Texture, structure, depth, nature of profile ® Water holding capacity. ® Stability to erosion ®

Influence of Soils on Agriculture ® Texture affects the drainage system of the soils. ® Poorly drained clay soils cause water logging that leads to wilting and yellowing of crops. ® Well drained loamy soils are suitable for production of most crops. ® Sandy soils have poor water retention capacity thus not suitable for crop production.

Soil Fertility ® Is the ability of soil to provide physical conditions favourable to root growth and supply enough water and nutrients to enable a crop to make the best use of other environmental features of a site. ® May also be defined as the availability of nutrients in a soil to the plants growing on it. ® Soil fertility indicates the capacity of a soil to produce crops at a satisfactory level over a period of time. ® Depends on the availability of major nutrients (Nitrogen, Phosphorus and potassium, NPK). Micronutrient deficiencies usually localized.

Chief Factors Contributing to Soil Fertility ® Physical characteristics of soil: texture, structure, depth and nature of the profile. ® Availability of major and micro-nutrients ® Soil reaction (Soil PH) and ® Microorganism presence ® Parent material ® Man’s activities ® Organic matter content

Depth and Nature of Profile Deep soils are of importance in areas with seasonal and unreliable rainfall as only a deep soil can hold an appreciable amount of water to supply crops in a dry spell and enable the uptake of nutrients that are dissolved in the water. ® Features of the nature, sequence, position and thickness of the soil determine the water holding capacity of the soil. ® Very shallow soils are generally ® ® ® Unproductive since they provide little root room for crop anchorage and extraction of nutrients and water. Are usually water logged or hold too little moisture.

Soil Texture ® Influences the aggregate stability, permeability to air and water, drainage characteristics, water-holding capacity, ease of cultivation and nutrient status of the soil. ® Fine sandy soils form aggregates which combine with water easily on wetting to form an impervious surface cap and thus are poorly drained and difficult to manage ® Silty Soils form unstable aggregates. As the pores between the fine particles are narrow, they have a high water-holding capacity but tend to suffer from impeded drainage thus impeding the availability of some nutrients by leaching them.

Soil Structure ® Determines suitability of soil for root growth. ® Roots can only ramify freely through the soil if there are pores and channels of a certain minimum size into which they can grow. In order that carbon dioxide is removed and oxygen replaced by diffusion in the soil, there must be a continuous system of air-filled pores extending from the soil surface throughout the root zone. ® The supply of water is also effected through the pores ® A productive soil must have a fairly even distribution of pore sizes capable of holding water available to crops. ®

Soil Reaction (p. H) ® Refers to level of alkalinity or acidity of the soil. ® High soil p. H (alkaline) renders certain nutrients unavailable e. g. zinc and iron ® High p. H favours the prevalence of fungi in the soil. ® Low p. H increases availability of iron to toxc levels ® Very acidic soils inhibit nitrogen fixing microorganism activity.

Microoganism ® Their movement and burrowing enhances aeration of the soil. ® They aid the decomposition of organic matter thus releasing nutrients into the soil. ® Some are involved in the nitrogen fixing activity in the root nodules of leguminous plants: Rhizobium ® Others (Azotobacter) convert free nitrogen into nitrates for absorption by plants.

Parent Material ® Soil is formed through the weathering of parent rocks. ® The breaking down of the parent material provides nutrients for the plants. ® Soils developed from limestone are usually fine-texture and are higher in organic matter than those from coarse-textured material. ® Sandstones high in quartz often give rise to sandy soils that are poor in nutrients and readily become acidic. ® Soils derived from fine materials such as volcanic ash, are very rich in nutrients.

Man’s activities ® Man’s agricultural activities such as bush clearing and crop cultivation ® Interrupt organic matter accumulation, ® Result in nutrient removal and ® Enhance surface run-off ® Alter microbiological systems ® All these may directly or indirectly affect soil fertility.

Organic Matter ® Organic mater added to well-aerated moist tropical soils decomposes to release nutrients especially nitrogen to the soil. ® Decomposition also leads to formation of the humus which contains ® Nitrogen, phosphorus, and sulphur that were present in the original plant residues. ® Humus is not a stable product and its continuous slow decomposition by soil microorganisms gradually releases these nutrients in a form available to plants

Influence of socio-economic factors on agriculture ® Factors ® Social include: structures and customs ® Land Tenure and inheritance ® Population Pressure ® Human Health and Nutrition ® Technology/Farm Equipment and requisites ® Government Support and Finance

Social Structures and Customs ® The rate of adoption of agricultural technologies is affected by the social systems of a community. ® In most social systems, there is an informal hierarchy which determines who interacts with whom and under what circumstances. ® This influences the readiness of an individual to adopt an innovation.

Land Tenure and Inheritance ® Land tenure determines the security that a farmer has to invest in the various improvements of the agricultural production system. ® Lack of secure land tenure leads to: Lack of improvement or maintenance of the productive capacity of the soil. ® Low yields. ® ® Inheritance laws lead to fragmentation of land into uneconomic units ® Also leads to scattering of plots of land for the offspring.

Population pressure ® Influence is in the following ways: Provision of labour for agricultural production. ® Fragmentation of land ® Improved technology to cope with production of food for the population. ® ® Human Health and Nutrition Affects the ability of the farmer and his/her family to provide labour for the various farm operations. ® Healthy and well-fed labourers are more productive than malnourished labour with bad health. ®

Farm Equipment and Machinery ® Level of mechanization will affect the level of productivity of a farm through: ® Increasing efficiency through timely field operations ® Reducing drudgery in farm work ® Increasing the farm output per humanlabour ® Reducing spoilage, waste and other losses of agricultural produce

Farm Equipment and Machinery Preservation and proper processing of farm produce ® Maximizing yields by improved farm operations ® Facilitating the production of more or additional food produce ® Improving water supplies and water control systems ® Reclamation of abandoned land ® Developing new land for agriculture by clearing obstructions or by drainage of waterlogged land, leveling or other reclamation operations ®

Government Support and Finance ® Governments may provide incentives through various forms of financial assistance, subsidy and credit schemes. ® Subsidies give financial assistance to farmers, but unlike credits, are not repayable.

Government Support and Finance ® They may take the form of ® Regular allowances paid by government to farmers or farmers’ cooperative societies to help them meet part of the expenditure on specified commodities. ® Inputs such as improved seedlings, new varieties, livestock, fertilizers or pesticides, at low level so that more farmers can afford to buy them. ® Commercial banks and other special banks such as the Agricultural finance corporation and cooperative Bank in Kenya, grant loans for farming projects.