Soil Erosion and Degradation World Desertification Soil erosion

• Soil Erosion and Degradation(土壤沖蝕 和退化)—兼論沙漠化、鹽化和浸水 World Desertification(沙漠化) Soil erosion and degradation affect crop yield and farming success. A. Preserving the world’s topsoil is of great importance in feeding the world’s masses. B. A 1992 joint UN and World Resources Institute report estimated that topsoil is eroding faster than it is replenished on 38% of the world’s cropland. Worldwide erosion causes $375 billion per year. C. Loss of crop productivity can result from repeated irrigation, which produces salt buildup and water logging of plant crops. Moderate Severe Very Severe

• Causes of Desertification(沙漠化) Ø Overgrazing(過度放牧) Ø Deforestation(砍伐森林) Ø Erosion(侵蝕) Ø Salinization(鹽化) Ø Soil Compaction(土壤密實) Ø Natural Climate Change(自然氣候變遷)

Causes Overgrazing Consequences Deforestation Worsening drought(嚴重乾旱 ) Erosion Famine(飢荒) Salinization Economic losses(經濟損失) Soil compaction Natural climate change Lower living Standards(生活 水準降低) Environmental Refugees(環境難 民增多)

• Causes of Soil Erosion(土壤沖蝕原因) Soil erosion and degradation affect crop yield and farming success. n A. Preserving the world’s topsoil is of great importance in feeding the world’s masses. n Land degradation occurs when the future ability of the land to support crops, livestock, or wild species is decreased. n Water, wind, and people cause soil erosion; soil components are moved from one place to another. n Depletion of plant nutrients in topsoil, through farming, logging, construction, overgrazing, and burning vegetation, leads to loss of soil fertility. n

土壤沖蝕原因 n Eroded soil becomes sediment in surface waters where it pollutes water, kills fish, and clogs irrigation ditches, channels, reservoirs, and lakes. n Soil is a renewable resource unless eroded faster than it can form.

土壤沖蝕原因 n B. n n n A 1992 joint UN and World Resources Institute report estimated that topsoil is eroding faster than it is replenished on 38% of the world’s cropland. Worldwide erosion causes $375 billion per year. Soil erosion in the U. S. is being slowed through planting crops without disturbing the soil and government-sponsored soil conservation programs. The Dust Bowl of the 1930 s resulted in Congress passing the Soil Erosion Act in 1935 and established the Soil Conservation Service (a part of the USDA). Desertification occurs when production falls by 10% or more though a combination of natural causes (drought) and human activities. It may be moderate, severe, or very severe; only in extreme cases does it lead to a desert. Prolonged droughts can’t be controlled, but the consequences can be reduced by reducing overgrazing, deforestation, and destructive forms of planting, irrigation, and mining. Restoration of these areas includes planting trees and grasses to anchor soil and hold water.

• Global Soil Erosion (全球性土壤沖蝕 ) Areas of serious concern Areas of some concern Stable or nonvegetative areas

• Soil Degradation(退化) on Irrigated (灌溉)Land Ø Salinization (鹽化) Ø Waterlogging (浸水) Evaporation Transpiration Evaporation Waterlogging Less permeable clay layer

土壤鹽化和浸水 n C. Loss of crop productivity can result from repeated n n irrigation, which produces salt buildup and water logging of plant crops. 1. Forty percent of the world’s food is produced on twenty percent of the cropland that is irrigated. 2. Salts left behind when irrigation water is not absorbed into the soil can be left in the topsoil. This is called salinization. 3. Salinization has reduced yields on 20% of the world’s cropland. 4. Waterlogging occurs when saline water (from irrigation) envelops the deep roots of plants. This saline water accumulates underground and raises the water table.

• Reducing and Cleaning Up Salinization Ø Reduce irrigation Ø Switch to salt-tolerant crops Ø Flush soils(沖洗土壤) Ø Not growing crops for 2 -5 years Ø Install underground drainage(排水系統)

• Soil Salinization土壤鹽化(解決方案) Solutions Soil Salinization Prevention 防治 Cleanup 清理 Reduce irrigation 減少含鹽灌溉用 水 Flushing soil (expensive and wastes water) 洗鹽，但昂貴 Switch to salttolerant crops (such as barley, cotton, sugar beet) 改重耐鹽作物如： 大麥等 Not growing crops for 2 -5 years 休耕達 2 -5年 Installing underground drainage systems (expensive) 設置地下排水系統-貴

• Soil Conservation (土壤保持水土保持要項) A. Soil conservation seeks ways to reduce soil erosion and restore soil fertility(恢復肥力). To reduce soil erosion, farmers must eliminate plowing and tilling and keep the soil covered with vegetation. 1. Conventional-tillage farming(傳統式耕作經營) means plowing in the fall and leaving the soil bare all winter, making it vulnerable to wind and erosion. 2. Conservation-tillage farming(保育式耕作經營) disturbs the soil as little as possible while planting. 3. Minimum-tillage farming allows the soil to rest over the winter. The subsurface soil is broken up and loosened but the topsoil is not turned. 4. No-till farming uses special machines to inject seeds, fertilizers, and herbicides into thin slits in the unplowed soil and, then, cover the slits. 5. About 45% of U. S. farmers used conservation tillage in 2003. The USDA estimates that using it on 80% of cropland would reduce soil erosion by 50% or more.

Trade-Offs Figure 14 -13 Conservation Tillage保育式耕作經營 Disadvantages Advantages Page 284 Reduces erosion Saves fuel Can increase Herbicide(除草劑) use for some crops Cuts costs Holds more soil water Reduces soil Compaction 減緩密實化 Allows several crops per season Does not reduce crop yields Reduces CO 2 release from soil Leaves stalks(葉柄) that can harbor(庇護) crop pests(害蟲) and fungous diseases (真 菌) and increase pesticide use(增用殺蟲 劑) Requires investment in expensive equipment (增加投資設 備)

土壤保持-續 2 B. Additional methods to reduce soil erosion include: 1. Terracing converts the land into a series of broad, nearly level terraces that run across the contour of the land. This method holds water for crops and reduces runoff. (保水並減低逕流) 2. Contour farming plows and plants crops in rows across the slope of the land, not up and down. Each row acts as a small dam(小水堤). 3. Strip cropping(條栽) plants alternating strips of a row crop (corn/cotton) with another crop that completely covers the soil (grass/legume豆 科作物). Runoff is caught by the cover crop覆蓋

土壤保持-續 3 1. Terracing(梯田) 2. Contour farming plows and plants crops 等高線栽培

土壤保持-續4 4. Plant cover crops like rye(黑麥) or alfalfa(苜蓿) after harvest. 5. Leave crop residues on the land after harvest. 6. Alley cropping/agroforestry plants several crops together in strips/alleys between trees or shrubs 灌木, which may provide fruit or fuelwood. n a. The shade of the trees/shrubs reduces evaporation and helps retain soil moisture. n b. Fruit, fuelwood, and trimming can be used as mulch. 7. Windbreaks or shelterbelts of trees reduce wind erosion, help retain soil moisture, provide fuelwood, and support bird and insect habitats.

土壤保持- 續 5 6. Alley cropping(畦作 ) 7. Windbreaks(防風林)

• Soil Restoration(土壤復育) Ø Organic fertilizer(有機肥料) Ø Animal manure(動物糞肥) Ø Green manure(綠肥作物) Ø Compost(堆肥) Ø Crop rotation(輪作) Ø Commercial inorganic fertilizer(無機化肥)

土壤復育-續1 Soil fertility can be maintained best through soil conservation. The next best thing is to restore some of the nutrients by the use of fertilizer. n 1. Organic fertilizer can be used to restore lost plant nutrients. a. Animal manure improves soil structure, adds nitrogen, and stimulates soil bacteria and fungi. b. The U. S. Department of Agriculture researchers are evaluating the value of burnt chicken wastes that are rich in phosphorus as an organic fertilizer. c. Green manure plows freshly cut or growing green vegetation into the soil to increase organic matter and humus. d. Microorganisms in the soil break down organic matter in leaves, food wastes, paper, and wood to form compost.

土壤復育-續2 n 2. Crop rotation plants different crops to replenish the soil, especially if a previous crop has depleted the soil of certain nutrients. n 3. Inorganic fertilizers, used with organic fertilizers, can restore soil fertility. n Commercial inorganic fertilizers contain nitrogen, phosphorus, and potassium. n There advantages and disadvantages to the use of inorganic fertilizers.

Trade-Offs Inorganic Commercial Fertilizers Advantages Disadvantages Easy to transport Do not add humus to soil Easy to store Reduce organic matter in soil Easy to apply Reduce ability of soil to hold water Inexpensive to produce Lower oxygen content of soil Help feed one of every three people in the world Without commercial inorganic fertilizers, world food output could drop by 40% Require large amounts of energy to produce, transport, and apply Release the greenhouse gas nitrous oxide (N 2 O) Runoff can overfertilize nearby lakes and kill fish

報告完畢，謝謝各位 資料來源： 1. Miller G. Tyler JR. Living in the Environment-Principles Connections and Solutions 13 th ed. California: Brooks/Cole 2004 2. 法規: 山坡地保育利用條例、國土復育策略方案暨行動計畫、海 埔地開發管理辦法、海岸法草案 3. 邱文彥，與海爭地──海埔地開發的省思與前瞻 http: //210. 60. 226. 25/science/content/1993/00090285/0009. htm