Describe crop-field as an ecosystem. (3 marks type)
Answers
An ecosystem is a natural system that is formed by dynamic interactions between biotic and non-biotic elements in a defined area. Biotic elements include plants, insects (pests, natural enemies, decomposers), microbes and other living organisms, and non-biotic elements comprise weather components such as temperature, relative humidity, wind, sunshine, rain and soil. Each element has its special characteristics and role in the system that, as a function of time and place, will influence the distribution and population of living organisms. The term ecosystem also involves nutrient and energy flows within the system.
A crop agroecosystem is characterized by a much simpler composition with regard to the number of species residing in the system and the relative simplicity of energy flows compared with a natural, stable ecosystem. Therefore, the agroecosystem needs energy input to maintain its balance. The wet paddy ecosystem, for example, although an artificial system, has a rather complex composition of biotic and non-biotic elements, providing it with relative stability. Injudicious use of pesticides, however, disturbs this balance due to the killing of natural enemies and other organisms in the rice field.
Stability of the agroecosystem is the founding concept for integrated crop management ("ICM"). By maintaining stability, pest populations can be kept at manageable levels.
The following important points need to be remembered:
Each ecosystem is dynamic with respect to numbers, position, role and intensity of each element within that transform and develop continuously. They form a living, ever-changing system.
Each ecosystem contains a hierarchical structure. For example: plants are producers of vegetable food which will be used to feed herbivores. The herbivores (including pests) eat the plants using various modes of attack. The herbivores, in turn, serve as food for the carnivores (including the natural enemies), which again may be eaten by other carnivores. Finally, all organisms serve as food for the decomposers. In the agroecosystem, if no natural enemies exist, the pests will multiply unlimitedly and destroy the crop. But if the crop is finished, the pests will die of starvation. Many natural enemies are not choosy about their food and will eat other organisms, such as decomposers or plankton eaters, when there are no pests. Hence, they form an important protection mechanism in the field.
All elements of the agroecosystem are strongly linked and disturbance of one element disturbs the whole balance. Therefore, the task of farmers is to maintain the natural balance among elements in the agroecosystem, ensuring a good environment for the crop to grow well.
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