農(nóng)業(yè)生態(tài)系統(tǒng)-資料下載頁
2025-01-01 03:03本頁面
【正文】 fixation. ?Anthropogenic nitrogen fixation is extremely energy intensive, thus affecting the carbon cycle through fossil fuel use. ?Nitrates escaping into groundwater have serious health effects (blue babies) ?Nitrogen is the most limiting nutrient in most agroecosystems. ?Runoff of N and P into streams causes eutrophication. Fertilization by N, P, and K causes higher yields, but when plants are removed, many cations (esp. Ca and Mg) are removed. This increases the acidity of the soil. SOIL EROSION ?Exposing bare soil to the elements and decreasing infiltration rates causes wind and water erosion. Conservation Reserve Programs, lowtill techniques, increasing anic matter, and planting of hedgerows have decreased this problem. MONOCULTURES ?Planting crops in monocultures encourages pests, diseases, and crop failure. Polycultures allow plementarity, and are making a eback. GENETIC EROSION The geic diversity of domestic animals and crop plants is being depleted. Genes for resistance to stress and disease are lost. ENERGETICS Most mechanized agriculture has more energy input than output. The nation is on a pesticide treadmill because pests bee resistant to the effects of pesticides, requiring farms to adopt new and more potent poisons, to which pests eventually bee resistant. There is no end to this toxic spiral. Resistance cannot be avoided。 it is a natural part of the evolutionary process. When a group of pests is exposed to a toxic chemical, some of them survive. These hardy few reproduce and their offspring inherit genes resistant to this particular chemical. Excessive use of a pesticide speeds up the process by which pests develop resistance. More than 500 insects have now developed resistance to one or more pesticides。 so have 270 species of weeds and 150 plant diseases. 謝謝觀看 /歡迎下載 BY FAITH I MEAN A VISION OF GOOD ONE CHERISHES AND THE ENTHUSIASM THAT PUSHES ONE TO SEEK ITS FULFILLMENT REGARDLESS OF OBSTACLES. BY FAITH I BY FAITH
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