Download
1 / 65
650 likes | 665 Views
The effect of intensive agriculture. soil properties in relation to crop growth. soil erosion. chemical control of pests and weeds. chemical fertilizer. General condersation of soil properties in relation to crop growth. 1. Introduction
E N D
The effect of intensive agriculture
soil properties in relation to crop growth soil erosion chemical control of pests and weeds chemical fertilizer
General condersation of soil properties in relation to crop growth
1.Introduction ~ According to the depth at which it is found , soil is classified topsoil and subsoil . a. Topsoil ~It is the surface layer of soil and is only about a few centimeters deep . ~It contains humus and many mineral salts which are require for crop growth . b. Subsoil ~It is composed of large soil particles and stones . ~It is less fertile .
2.Components of soil a. soil particles ~ They bind with many ions are important for crop growth. Type of soil particles Average diameter(mm) Gravel larger than 2 Coarse sand 2.0 - 0.2 Fine sand 0.2 - 0.02 Silt 0.2 - 0.002 Clay smaller than 2
b. Mineral Salts ~ Many salts are the essential nutrients for healthy plant growth . ~ They affect the pH value of soil which affects plants growth . ~ Most crops grow best in the slightly acidic soil (pH6-6.5). c. Soil water ~ Soil water is absorbed by the root hairs of the crops to support their life .
d. Soil air ~ The oxygen in soil air supports the aerobic respiration of the roots of crops . ~ In water-logged soil there is a shortage of oxygen that : I. hinders the healthy growth of roots . II. slow down the decomposition of humus to form mineral salts . III. enhances the undesirable activities of the denitrifying bacteria that remove the useful nitrates from soil .
e. Humus I. Introduction ~ Humus is the dark brown finely divided organic matter on the surface of top soil. ~ They derive from the excretory wastes and dead remains of living organisms . II. Importance of humus 1. Humus is decomposed by bacteria into nitrates and other mineral salt which are essential for healthy growth of plants .
2. Humus improve the texture of soil : a. It sticks the fine particles of clay soil into larger aggregates so that the aeration and drainage of the soil are improved . b. It sticks the loosely packed sand particles of sandy soil closer together so that the retentivity of the soil is improved . 3. Humus acts as a sponge at the surface of the soil to : a. absorb water . b. reduce the evaporation of water from soil and thus reduce the danger of soil particles to be blown away by wind.
F. Micro-organisms i. Beneficial bacteria The saprophytic bacteria(decomposer) decompose the excretory products and the dead remains into humus which further broken down into soluble salt such as ammonium compounds and nitrates . ii. Harmful bacteria The denitrifying bacteria change the useful nitrates into gaseous nitrogen which cannot be used by plants.
3. Comparison between Sandy soil and clay soil.
Sandy soil clay soil 1.size of soil particles large small 2.air space(aeration) large small 3.drainage(permeability) rapid slow a.mineral content low,mineral salt high, mineral salt easily leached out strongly attached b.fertility Infertile soil Fertile soil 4.Retentivity Poor , dry soil Good,wet soil 5.Capillarity Low High , easily get water from water-table at greater depth .
6. Soil texture large soil particles small soil particles are are loosely packed strongly stuck together by together,they eroded the surface tension of the by wind easily water film covering their surface .When dry they form hard clods which hinder root growth and animal movement . 7.Activity of Low, low humus High , high humus content micro-organism content 8.a)specific heat Low High b)Temp. change High,temperature Low,temperature is extremes rather constant c)Thermal cond. Warm Cold in wet clay
9.Relative weight Light as the soil is dry Heavy as the soil is wet and has large air space and has small air space 10. Digging and Easy, dry particles are Difficult , wet particles ploughing easily separated . strongly stick together ~Neither sandy soil nor clay soil is an ideal soil for cultivation. ~The loam soil is the most productive soil in agriculture since it has properties intermediately between that of the sandy and clay soil .
4. Improvement of sandy and clay soil A. sandy soil ~ Though a sandy soil is well aerated , its rapid drainage causes the low retention water(dry) and the serious leaching of mineral salts(infertile) . It can be improved by adding : I. Clay to make a loam with greater retention of water and mineral slats. II. Humus 1. To increase the fertility of the soil . 2. To reduce evaporation and to protect it from the leaching action of heavy rain .
B. clay soil ~ A clay soil is easily water logged and difficult to dig and plough . It can be improved by : I. Adding slaked lime which joins the small clay particles into bigger aggregates (soil crumbs) to promote aeration and drainage . II. Adding humus to improve texture , aeration and drainage III. Building drainage channels ~ to improve drainage and aeration ~ to prevent water logging .
Soil erosion as a consequence of agricultural practice
Soil erosion Definition : soil erosion is the removal of the top-soil by the wearing action of rain and wind . Reason : a. Deforestation b. Over-grazing c. Poor farming methods
A. Deforestation : • The removal of trees exposes the top-soil which is then no longer protected by the leafy canopy of the forest . • The thin layer of top-soil will be easily washed away by heavy rain .
B. over-grazing • Too large a population of animals rearing on a piece of grassland will quickly turn it into barren land because of over-grazing .
C. Poor farming methods • After harvesting several crops without adding humus will greatly reduce the retentivity of soil so that the soil will dry up quickly and easily be blown away . • The soil structure is deteriorated by using chemical fertilizer instead of natural fertilizers . It is because chemical fertilizer contain no humus . • Long time agriculture can bring out the nutrient from soil .
Erosion and soil loss is the end member of a variety of physical, vegetative and nutrient factors that lead to soil degradation . • Using heavy machinery on soil rapidly compacts it into a hard layer which can hardly absorb any water . Eventually the soil become dry and easily be blown away . • Soil fertility is a complex issue and nutrient loss is not necessarily nor always a consequence of erosion.
Soil conservation • Soil conservation is to take steps to prevent soil erosion . A. Crop rotation i. Definition Crop rotation is growing of different crops on a field from year to year to prevent the soil from lacking of one particular type of material due to the withdrawal by one type of crop .
ii . method 1st and 2nd year : ~ Crop with a high nutritional demand can be followed by the crop which have lower nutritional demands . ~ long-rooted plants crop can be followed by short-rooted crops so that the minerals are removal from different soil level .
3rd year : ~ Leguminous plant(e.g. pea or bean) can be grown . ~ Their root nodules contain nitrogen-fixing bacteria which change the atmospheric nitrogen content to soil. ~ When the residues of these leguminous plants are ploughed in , they increase the nitrogen content of the soil . Wheat Barley Oat Pea / bean (high nutritional ( low nutritional ( increase nitrogen demand ; deep- demands ; short- content of soil ; rooted ) rooted ) leguminous plants) [1st year] [2nd year] [3rd year]
iii . Advantages of crop rotation i. Several crops can be obtained from a single field, i.e. maximum use of land . ii. Depletion of a particular type of minerals is avoided . iii. The nutrients content of the field can be increased by growing leguminous plants . iv. The spread of certain pests and crop diseases can be prevented .
B. Other methods ~ Steep slope are grown with tree to provide canopy to protect the top-soil from washing away by heavy rain . ~ Adequate number of animals is reared on the grassland to avoid the over-grazing of grasses . ~ Gypsum can reduce erosion on heavy clay soils by improving soil structure and increasing water infiltration.
~Lime and other calcium sources. Agricultural lime, chemically described as the oxide, hydroxide, or carbonate of calcium and/or magnesium, is used to correct soil pH.
disease pest can cause of plants brown stink bug yellow striped armyworm
wolly cupgrassowen disease of plants
reasons pest • Use of pesticide to the kill the pest . • Common weed control practices : herbicide (weed -killer)applications and cultivation . weeds
effects • Herbicides kill the weeds which are unwanted plants that compete with the crops for the nutrients , sunlight , water and space in the fields .
advantage • Reduce the disease of plants . • Control of pest and weeds helps to increase crop production . • provide a favor condition for the plant growth.
Pesticides kill the pests which are animals (insect) that consume the crops in the fields . • The amount aphid and thrips populations decreased . • Prevent the pest population from reduces yield.
effects disadvantage • cause crop and environmental damage. • Cause environmental contamination, and adverse side effects . • Some weed control may tie up soil nitrogen . • Pesticide contain toxic substance .
disadvantage • Pesticides , particular DDT , is very poisonous and cannot be easily degraded by natural process . • The toxic chemicals such as pesticide and herbicide may be leached into the river . It can toxic to human by pass through the food chain . It would also kill the aquatic animals and plants . • It also cause water pollution .
As a result ,The application of DDT has the following side effects : A. universal poison . B. Accumulation of DDT concentration along food chain. C. Development of resistant population of pests .
A. universal poison : DDT is non-selective poison that kills not only the pest ,but also the organism in the field . i.e. animals .
B. Accumulation of DDT concentration along food chain . ~ DDT sprayed into crop fields may be absorbed by the surrounding plants . Though the initial concentration in plant is very small , DDT will be accumulated in the herbivores when they eat the contaminated plants . ~ when secondary consumer eat the contaminated herbivores, they also accumulate DDT to a higher concentration . ~ So that DDT is concentrated along the food chain to higher levels in the final predators . As a result , predators are eliminated .
