Agriculture and its impact on ecosystemA.Agricultural farmland as a unstable ecosystem:An agricultural ecosystem is established and manipulated by human beings in various ways to suit their own purposes, e.g . for food production.This ecosystem is unstable in many aspects:1.Continual removal of soil mineral nutrients due to absorption by crops and weeds. Natural recycling of minerals is hindered as a result of harvesting and subsequent export of biomass from the ecosystem.2.Removal of the original plant vegetation (and also the animal s) inhabiting the area in order to clear up the land for growing crops. This lead to the loss of plant and animal species.3.Monoculture - growing the same o ...view middle of the document...
4.Shift agriculture () and monocultureA patch of land is burnt and cleared to get land for farming. After monoculture (of a single crop species), the soil becomes depleted for a certain type of mineral and become infertile. It is then abandoned and the people move to exploit a new area.The loss of soil by erosion is very serious.C.Other problems created by agriculture1.Excessive use of inorganic fertilizers-Inorganic fertilizers are mainly inorganic compounds of phosphorus and potassium produced industrially or more commonly from rocks.-Nitrogen fertilizer is now obtained entirely by industrial fixation of atmospheric nitrogen as ammoniaAdvantages of using chemical/inorganic fertilizers(i)They are concentrated, easy to handle and apply and is of known mineral content so farmers can decide what sort of fertilizers can be used to meet a particular requirement.(ii)Relatively cheap.(iii)As they are inorganic minerals, so can be readily absorbed by roots rapidly. And increase soil fertility immediately.Disadvantages of using chemical/inorganic fertilizers(i)Their production requires considerable industrial treatment which uses much energy.(ii)Prolonged use of chemical fertilizers trends to make the soil excessively acidic and not suitable for crop growth.(iii)IF WASHED/LEACHED TO NEARBY RIVERS, PONDS, EUTROPICATION AND ALGAL BLOOM MAY OCCUR.2.Problems of pests:-Pests are organisms that consume the agricultural products or degrading their quality.-Can be animals (mostly insects or annelids) or plants (weeds)-They reduce the yield of crops.Chemical controls of pests:Pesticides - chemicals used to eradicate the pests/weeds(i)insecticides - killing insect pests e.g. locusts, earthworm(ii)fungicides - killing the fungal pests(iii)herbicides - killing the weeds.Some pesticides are poisonous to humans and they may be(i)persistent (chemically very stable)(ii)non-biodegradable - cannot be broken down by cellular metabolism(iii)accumulative - cannot be excreted out of the body and therefore will concentrate along the food chain (biomagnification)Harmful effects of chemical control of pests and weeds:(a)Concerning with agricultural industry directly:-resistant species arise soon, especially after the prolonged use of one type of pesticide.-The natural enemy of the pests will be removed directly or indirectly. In their absence, the population size of the pests becomes unchecked and may increase a higher level than before.e.g.Spraying fruit trees with DDT in the 1950's caused red spider mite to become a serious pest because its natural enemy/predators were killed.-The persistent pesticides may affect later crops.-Workers and children living in the farms are under high risk.(b)Contamination of food , water and air during application of pesticides:(c)Causing long and short term dangers to wild life.-herbicides remove certain harmless broad leaf plants as well as the weeds.-Some insecticides are non-selective , thus killing both harmless organisms and pests.e.g...
