Characteristics and composition of agro-ecosystems

I. Knowledge Structure

II. Teaching Objectives

1. Characteristics of agroecosystems (D: application).

2. Concepts and principles of ecological agriculture (D: application).

3. achievements of ecological agriculture in China (A: know).

III. Key points and difficulties

The concept and principles of eco-agriculture are the key points of this section.

IV. Reference Answers

Review Questions II. 1. (√); 2. (×).

III. 2. Eco-agriculture can realize the multilevel utilization of matter and energy, reduce the consumption of resources and energy, and reduce pollution; eco-agriculture promotes biological control, which can reduce pesticide pollution. It can be seen that eco-agriculture is an important way to realize sustainable development.

3. The number of food chains in agroecosystems and the number of trophic levels in the food chain are not the more the better, but need to be reasonably designed according to the local natural reality. In a certain agro-ecosystem, there is a certain limit to the amount of organic matter produced by the producers. If there are too many food chains in the ecosystem, it will be difficult for the number of organisms in each food chain to reach a certain scale, and this will affect the economic benefits. If there are too many trophic levels in the food chain, according to the principle of energy flow in the ecosystem, the organisms in the higher trophic levels will get very little energy, and the number of organisms in that trophic level will be very small accordingly, which will also not get a high economic efficiency.

Sidebar Reflection Question In addition to fertilizers, seeds, and energy, there are many other substances that humans input into agroecosystems from the outside world, such as farm machinery, plastic film, irrigation pipes, and so on.

Preventing plastic film from polluting farmland, in addition to regular recycling and centralized treatment of used plastic film, people are also researching various effective ways, such as making plastic film contain more biodegradable components such as starch; letting living organisms produce plastics by means of bioengineering, so that the plastics can be decomposed by microorganisms in nature; cultivating engineering bacteria by means of bioengineering that can rapidly decompose plastics; and so on.

V. References

Basic contents of China's eco-agriculture construction The basic contents of China's eco-agriculture construction include the following aspects.

First, making full use of solar energy and striving to realize the material transformation of agricultural production. That is to say, utilizing the photosynthesis of green plants, continuously improving the conversion rate of solar energy, accelerating the process of logistics and energy flow in the movement of the ecosystem, in order to continuously improve agricultural productivity.

Secondly, to improve the utilization rate of bio-energy and waste recycling transformation. The waste referred to here mainly refers to crop residues, human and animal feces, weeds, vegetable scraps and so on. For these wastes, the traditional treatment is directly burned or as fertilizer directly fertilizer, which is actually a waste. If the crop stalks are used to develop animal husbandry, livestock manure biogas system, both for the rural areas to provide feed and energy, but also for agricultural production to increase the source of fertilizer.

Third, the development of rural energy. To solve the rural energy problem should be adapted to local conditions, take a variety of ways, in addition to the use of power supply, coal supply and other ways, but also to build biogas digesters, the promotion of wood-saving stoves, the use of wind, water, solar energy, geothermal energy, etc., to change the practice of relying on the cutting down of trees to solve the problem of fuel for cooking.

Fourth, protect, rationally utilize and multiply natural resources. It is necessary to protect forests, control soil erosion, protect soil, and protect various biological populations.

Fifthly, pollution should be prevented and controlled so that agricultural production has a favorable ecological environment.

Sixth, to establish a self-purification system for the agricultural environment, the main measures include expanding the area covered by green vegetation, building large-scale oxidation ponds, protecting natural enemies and other beneficial wildlife, and promoting biological control.

Design approach of eco-agriculture construction The design and layout of eco-agriculture can be carried out in terms of eco-agriculture's planar design, vertical design, time design and food chain design.

The planar design of eco-agriculture refers to the determination of various types of crops and the proportion and distribution of various agricultural industries in a certain area, which is usually referred to as agricultural zoning or agricultural planning layout.

The vertical design of eco-agriculture refers to the use of ecological principles, a variety of different biological populations combined into a reasonable composite production system, to achieve the fullest and most rational use of environmental resources. Vertical structure includes aboveground and underground parts. The aboveground part includes the hierarchical distribution of stems and leaves of the composite group as well as the spatial configuration of different biological populations at different levels, with the purpose of being able to maximize the use of light, heat, water, gas, and so on. The underground part refers to the distribution of the root system of the composite group at different levels in the soil, and the reasonable underground vertical design can effectively utilize the water and mineral elements in the soil at different levels.

The time design of eco-agriculture is to design a production pattern that effectively utilizes agricultural resources according to the time rhythms of various agricultural resources, so that the resource conversion rate can reach the highest. The temporal design of eco-agriculture includes the design of population nesting (e.g., nesting), the design of seedling transplantation, and the regulation-type design that changes the growing period of crops.

The food chain design of eco-agriculture refers to the rational design of the food chain structure in the agro-ecosystem according to the local actuality and ecological principles, in order to realize the multi-level utilization of material and energy and improve the efficiency of agricultural production. One of the focuses of food chain design is to introduce or add new links to the original food chain. For example, introducing predatory animals to control the number of harmful insects, adding new production links to convert organic matter that people cannot directly utilize into agricultural by-products that can be directly utilized, and so on.

Insects to cure insects China is the world's earliest use of natural enemies to control pests, as early as around 300 AD, China carried out biological control work. In China's Jin Dynasty and Tang Dynasty books, recorded in the vicinity of Guangzhou, the use of "yellow ants" to control citrus pests. After the founding of New China, China's research and practice in the use of natural enemies to control pests has made rapid development, resulting in a number of effective modes of pest control.

There are many kinds of practices of using natural enemy insects to control pests in China, such as the use of red-eyed wasp to control corn borer, the use of seven-star ladybug beetle to control cotton aphids, the use of red ants to control sugar cane borer, and so on.

Since 1951, China's Guangdong Province, the use of red-eye wasp control of sugarcane stem borer research, after the test, in 1958 in Shunde established China's first red-eye wasp station in Zhanjiang, Shunde and other places in the nearly 7,000 hm2 of sugarcane field control of sugarcane stem borer, and achieved obvious results. Then this technology was popularized in Guangxi, Fujian, Sichuan, Hunan and other provinces and regions. 1972, Guangdong Province released ruddy-eyed wasps on a large scale to control the rice leaf borer, and achieved very good results. Dasha District, Sihui County, Guangdong Province, applied the Australian red-eye wasp to control the rice leaf borer, and the released area increased from 8 hm2 in 1973 to 396 hm2 in 1976, and 67% to 83% of the eggs of the rice leaf borer were parasitized. The use of pine caterpillar red-eye wasp control of corn borer in Northeast and North China has also been successful, basically replacing chemical control, thus effectively preventing pesticide pollution.

Bacteria for insects Bacteria for insects is an important part of biological control. China is currently used for biological control of bacterial agents are mainly Bacillus thuringiensis type of bacillus, bacillus stem borer, bacillus pine caterpillar, bacillus Wuhan and so on. Sihui County, Guangdong Province, the application of bacillus stem borer control of rice leaf borer and rice borer larvae, the killing effect reached 70% to 90%.

China also widely used white fungus control of corn borer, soybean heartworm, pine caterpillar and other pests. For example, Changtu County, Liaoning Province, used the white fungus to control the corn borer in 1983, applying an area of 50,000 hm2, and increasing the yield of corn by 1.45×107 kg.

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Agro-ecosystem

China, as a big agricultural country, has made remarkable achievements in agriculture. However, China's agriculture is also facing many problems, such as large population and little land, declining soil fertility and environmental pollution. To solve these problems, it is necessary to seriously study the characteristics of the agricultural ecosystem and vigorously develop ecological agriculture.

Features of agro-ecosystem

Agro-ecosystem is an ecosystem in which human beings, according to their own needs, regulate the interactions between agricultural biotic populations and the abiotic environment by certain means, and carry out the production of agricultural products through the reasonable energy transformation and material circulation. It has many different characteristics compared with the natural ecosystem.

In the agricultural ecosystem, the role of man is very prominent. Which crops to plant and which poultry and livestock to raise are all decided by people. People are also constantly engaged in activities such as feeding, seeding, fertilizing, irrigating, weeding, pest control, and harvesting, and only in this way can the agroecosystem evolve in a direction that is beneficial to human beings (as shown in the figure). The main components of agro-ecosystems are artificially grown organisms with poor resilience (ability to resist adverse environments). Except for the dominant species that are planted and raised according to people's wishes, other species are usually suppressed or excluded, resulting in a greatly reduced variety of organisms and a simple trophic structure. As a result, agro-ecosystems have a relatively low stability of resistance and are vulnerable to droughts and floods, as well as to pests and diseases, and need to be regulated by human management.

What are some of the other human inputs to agroecosystems from the outside world?

The material cycling process of agroecosystems is significantly different from that of natural ecosystems. The organic matter produced by natural ecosystems is basically kept within the system, and the cycling of many mineral elements can be kept in dynamic balance within the system, basically realizing self-sufficiency. Agricultural by-products produced by agroecosystems are often exported outside the agroecosystem in large quantities, so large quantities of substances, such as fertilizers and seeds, must be imported on a regular basis in order for the material cycle of agroecosystems to proceed normally. In addition, modern agriculture consumes large amounts of energy such as oil and electricity.

With the high degree of industrial development, the tools of agricultural production in developed countries such as the United States have been mechanized, electrified and automated, agricultural production technology has become increasingly advanced, and the ability of human beings to regulate the agro-ecosystem has been greatly enhanced, with a rapid increase in the yield of agricultural products. As such agriculture needs to be provided by industry with a large amount of material and energy, such as agricultural machinery, fertilizers, pesticides, plastic film, electricity, fuel, etc., and most of these substances and energy are related to fossil energy sources such as petroleum, and therefore also known as petroleum agriculture. Petroleum agriculture greatly improves the yield of agricultural products on the one hand, but on the other hand, it consumes a lot of resources and energy and causes environmental pollution.

How to prevent white pollution caused by plastic films?

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China's agriculture is in the process of transforming from traditional agriculture to modern agriculture, the tools of agricultural production are being gradually mechanized, and there are more and more inputs of chemical fertilizers, pesticides, plastic films, electricity, and fuel oil, which are increasing the yield of agricultural products. However, the massive use of chemical fertilizers has led to problems such as water pollution, eutrophication, and soil sclerosis; the irrational use of pesticides has led to the contamination of soil, water, and agricultural products, and pests have become resistant to drugs and are once again rampant; and the massive use of plastic films has led to white pollution, which destroys the structure of the soil and reduces the yields of agricultural crops. From the early 1980s, China began to explore the road of sustainable development of agriculture suitable for our national conditions, which is currently being promoted nationwide ecological agriculture.

The concept and principle of ecological agriculture ecological agriculture

refers to the use of ecological principles, under the guidance of the idea of coordinated development of the environment and the economy, the application of modern science and technology to establish a multi-level, multi-functional integrated agricultural production system.

The basic principles of ecology are the main theoretical basis for the development of eco-agriculture. We know that the multi-level utilization of energy and material recycling in the ecosystem is a basic principle of ecology. The food chain is the main channel of the ecosystem's energy flow and material circulation, which is both a chain of energy conversion and a chain of material transfer, as well as a value-added chain from the economic point of view. Therefore, by following this principle, the food chain can be reasonably designed so that the substances and energy in the ecosystem can be utilized at multiple levels, so that the organic waste produced during the production of one product can be used as an input for the production of another, that is, the waste can be resourced, so as to improve the efficiency of energy conversion and reduce environmental pollution. For example, the Nanjing Guquan Eco-Farm rationally combines the production processes of raising pigs, fish, biogas engineering, ducks, earthworms, mushrooms and fruit trees to form a virtuous cycle system (see figure). The farm uses chicken manure as part of the pig's feed, pig manure is put into the biogas digester as the fermentation raw material for biogas, the output biogas is used for cooking and lighting, the methane liquid and digestate are used to feed fish, cultivate edible mushrooms, raise earthworms and as fertilizer for the orchard; the fish ponds are used for the ducks to raise

Red-eyed wasps are a kind of parasitic insect. After the female wasp finds the host egg, she stabs the ovipositor into the host egg to lay eggs, and her larvae eat the material in the host egg to grow up, causing the host egg to die. The hosts of the red-eyed wasp are sugarcane borer, rice borer, cotton bollworm, pine caterpillar and other agricultural and forestry pests.

For activity sites, duck manure down the pond as fish bait; pond mud as orchard fertilizer; orchard farming earthworms; pig manure, chicken manure, mushroom residue as earthworm bait; earthworms improve orchard soil, earthworm manure to provide fertilizer for the orchard, earthworms as chicken feed. The production of various agricultural products in the farm is coordinated and mutually beneficial, realizing the multi-level utilization of energy and material, showing obvious superiority.

There is a relationship of interdependence and mutual constraint between various organisms in an ecosystem. In the agricultural ecosystem, people can utilize the relationship between biological populations to artificially regulate biological populations. Increasing the population of natural enemies of harmful organisms in the ecosystem can reduce the harm of harmful organisms. For example, a place in Guangdong Province, China, utilizes the release of red-eyed wasps to control the rice leaf borer, basically replacing chemical control, thus preventing the pollution of pesticides.

China's ecological agriculture achievements

China's government attaches great importance to the construction of eco-agriculture. 1984 China's government put forward: "We should seriously protect the ecological environment, and actively promote eco-agriculture, to prevent the pollution and destruction of the agricultural environment". 1992, the State Council listed the development of eco-agriculture as one of the ten major measures for China's environment and development. In 1992, the State Council listed the development of eco-agriculture as one of China's top ten countermeasures for environment and development, and the development of eco-agriculture has become an important measure in China's implementation of sustainable development strategy. Since 1984, seven ecological agriculture construction units in China have been awarded the title of "Global Top 500" in environmental protection. By the end of 1995, there were 50 pilot counties at the national level and nearly 100 at the provincial level, and significant economic, ecological and social benefits had been achieved. According to the survey of ecological agriculture pilots in some areas of China, after carrying out the construction of ecological agriculture, the growth of total food production is generally more than 15%, and the local ecological environment has also been improved. At present, China's eco-agriculture is gradually transformed from the pilot stage to the regular development stage, genetic engineering and fermentation engineering and other biotechnology will be widely used in eco-agriculture. Eco-agriculture in China has a broad prospect for development.