The Characteristical Analysis Of Energy Conversion And Elemental Cycling In Agricultural Ecological System Of Guang'an City

Energy flow and substance cycle is the significant reflect of function of agricultural ecosystem. The research object is focused on the area of Guang'an city, using the dynamic data of land utilization between 1993-2005 and Social Economy, combining the peasant survey, using the assistance of Ecological Theory and Geographic information systems, to analyze the farm subsystem,forest farm subsystem,animal husbandry subsystem,fisheries subsystem,peasant subsystem and energy flow characteristics of watershed ecosystem in the Guang'an city in last decade. The main results as follows:1. Energy-input structure of farm subsystem of Guang'an city changes greatly in the last decade. In the process of total energy-input increasing, percentage of industry auxiliary energy input has been increasing. The utilization rate of fertilizer and machine is increasing quickly. With the increase of indurstry auxiliary energy, the dependency of farm system on the external increases more and more. The change of totall benefit cost ratios and economy benefit cost ratios is the trend of upward. Inorganic auxiliary energy plays an important role in impoving productivity of farm, but the influence of organic auxiliary energy has been strengthening. The output direction and flow quantity of farm energy varies with the plant structure and peasant's consume structure. The proportion of energy outputed into peasant is descended year by year, the proportion into energy flow outside increasing year by year, but the proportion into animal husbandry and the proportion left in the farm system inside are stable. 2. There is high utility rate of luminous energy in the forest land, which makes the fixed solar energy increasing in the flow and improves the stability of flow. As the forest land is the main exporter of firewood, the output of economy forest is the energy exporting into the outside of flow. The output of economy forest reduced at recent years, which made the potential energy exporting into flow outside reduced accordingly. The relation of forest land outputable energy and area is closely. Through analyzing the year increment, the forest farm subsystem accumulates more energy, but only average 11% output to the outside of the subsystem, the majority leaving in the system. Analysing by economy, wood accumulating is the potential energy exportable in the forest farm subsystem and the economic benefit accumulated is more significant along with the increasing of tree age. Analying by ecology, forest can clear air,improve the living environment and adjust the climate condition of plant system, which are irreplaceable.3. Benefit cost ratios of animal husbandry is increasing gradually, reaching 0.57 by 2001. The energy put into animal industry which is increasing gradually varies with the scale of animal husbandry, but the percent conversion of animal industry subsystem is low. Constitute of livestock influence the energy percent conversion directly, so one efficient method to improve the benefit cost ratios of animal husbandry is to adjust the constitute of livestock.Fisheries is also the subsystem of Guang'an agricultural system. However, thanks to the restrict of technology and environment, the fisheries develop slowly and the percent conversion of fesheries system energy is lower than animal husbandry, so the more reasonable management and feed input are really necessary to improve the percent conversion of energy and economic benefit of fesheries.4. In peasant subsystem, the foodstuff consume energy from farm land has been going down gradually recentlly, accordingly the foodstuffs energy inputed from flow outside increases. The energy consume on the animal husbandry is in the slow updown. The labor outputing structure shows that the energy exporting to the farm land take a large proportion by average 43%. The change trend of energy exporting to the animal husbandry is parallel to energy change of animal husbandry which take 13% of totall exporting energy. The change extent of labor exporting to the forest land is small. In the past decade, the labor exporting structure has changed, part released from farm land to the outside flow.5. Along with increasing of flow artificial assistant energy invent, the utility rate of luminous energy of flow increases from 0.35% to 0.43%. The flow economic structure analysis shows that the change width of flow structure index of variability is large in the past years of controling when the industry is in the process of adjusting. In the recent years, the change width of flow structure index of variability decreased, which reflects that the adjust of flow production structure is more reasonable and has more resistance capability and any persistence, the flow ecological system in the positive cycle way of development.6. In the past decade, the nutrient from organic fertilizer and chemical fertilizer has been increasing in the farm land subsystem, the input quantity of nutrient substance N,P and K from fertilizer respectively reach average 567.05 kg/hm~2,205.12 kg/hm~2,215.75 kg/hm~2. But the synchronous nutrient substance N,P and K from farm land is average 231.67 kg/hm~2,105.40 kg/hm~2,296.72 kg/hm~2. The N is surplus a lot, the P followed, the K lost. The plent of surplus nutrients flow into environment in the production by various way.