1、X1 土壤侵蚀和农业要 点概 述 农业活动对全球的许多生态系统产生了较大影响，同时引起了很多生态问题。农业对生态的影响主要有四个方面：（ i） 控制害虫的后果（ U），（ ii） 生物多样性的减少（ V3），（ iii） 土壤侵蚀和（ iv） 营养物、水和能量利用的影响。后两项内容将在这一章进行讨论。农业机械化Agricultural practices have a considerable impact on many ecosystems globally, and give rise to a variety of ecological problems. Four key areas
2、 in which agriculture impacts upon ecology are (i) the consequences of pest control (Section U), (ii) reduction in biodiversity (Topic V3), (iii) soil erosion, and (iv) the effects of nutrient, water and energy use. These last two subjects are covered in the section.Key NotesOverview X1 SOIL EROSION
3、G AND AGRICULTURE土壤侵蚀的原因土壤侵蚀和拙劣的农事活动造成的土壤肥力下降是严重的世界性问题。大规模去除植被，大面积没有屏障来减慢水运动的土地使用，不适宜的耕作技术，所有这些都造成了土壤侵蚀。土壤侵蚀的代价大多数现代农业系统建立在短期经济效益的基础上，由于土壤侵蚀发生非常缓慢，所以短期内似乎没有什么严重后果。土壤侵蚀减少土壤中有机质和养分，降低土壤保水能力，限制扎根深度，从而影响土地的生产力。每年因风蚀和水蚀而损失四百万吨表土，价值约 100亿英镑。过去 50年中，世界 30%的农田因土壤侵蚀而损失，与此同时，由于人口增长，食物需求量也在增加。土壤侵蚀不仅减少土壤生物生产力，而
4、且会带来洪灾。Soil erosion and the loss of soil fertility as a result of poor farming practices are serious problems worldwide. The removal of vegetation cover from soils, the use of large fields without boundaries to slow water movement and inappropriate ploughing techniques all fuel soil erosion.The caus
5、es of soil erosion Most modern agricultural systems are based on short- term economic gain and as soil erosion usually occurs very gradually it may not appear serious over the short term. Erosion reduces productivity of the land by depleting it of organic matter and nutrients. Reducing its water-hol
6、ding capacity and limiting rooting depth. As much as 4billion tons of top soil, valued at 10 billion is lost annually from wind and water erosion. As much as 30% of the worlds farmland has been lost to soil erosion in the past 50 years; whilst food demand increases due to human population growth. So
7、il erosion not only reduces the biological productivity of soils, but also may cause flooding. The costs of soil erosion土壤保护的措施有些方法能用来减少土壤侵蚀。以适当的角度耕作坡田（等高耕作），顺着等高线而不是顺着斜坡开沟。同时，在土壤裸露地区种植谷物（覆盖作物）能够防止水土侵蚀。免耕农业只需要挖一些窄的裂沟，而不需要对土壤进行耕作。这些办法，配合植物轮作，能够减少土壤损失和保持土壤肥力。但是，这些措施的实施进程很慢。相关主题 土壤形成、性质和分类（ G3） 初级和次级生产
8、力（ P2） 食物链（ P3） 杀虫剂和问题（U2） 生物资源和基因库（ V3） 养分、水和能量利用（ X2）A number of methods can be employed to reduce soil erosion. By ploughing a field at right angles (contour ploughing) to the slope, furrows follow the contours of the land rather than the slope, Also, planting crops on areas of bare field (cover
9、crops) helps to prevent soil erosion. No-till farming consists of planting a narrow slit trench without ploughing the soil. These systems. Along with crop rotation, can all be used to reduce soil loss and maintain fertility. However, progress has been slow in establishing these practices.Soil conser
10、vation practicesRelated topicsSoil formation, properties and Pesticides and problems (U2)classification (G3) Biological resources and genePrimary and secondary production banks (V3)Food chains (P3) Nutrient, water and energy use (X2)X2 养分、水和能量利用要 点增加农业生产力向土壤和作物直接施用无机肥料是增加作物产量的一个简单途径。每公顷平均产量由 1950年年
11、1.1t上升到1986年的 2.3t。 如果要在 2000年维持 1987年消费水平，平均粮食产量至少要增加 25%，然而，由施肥而增加的产量正逐年下降， 20年前，向美国土地上施肥 1t可使作物增产 1520t， 今天用同样多的肥料只能增产 610t。The direct application of inorganic nutrients to crops or soils is a simple route to increase crops or soil is a simple route to increase crop yield. Average yield per hecta
12、re has increased from 1.1 tons in 1950 to 2.3 tons in 1986. To maintain 1987 consumption levels in the year 2000 will require at 25% increase in average grain yields. However, there are diminishing returns of fertilizer application; one ton of fertilizer added to US soil 20 years ago increased the w
13、orld grain harvest by 15 to 20 tons today the same amount of fertilizer would result in only a 6- to 10-ton increase.Key NotesIncreasing agricultural productivityX2 NUTRIENT, WATER AND ENERGY USE肥料对磷循环的影响每年至少有 13106t的磷作为肥料撒向农田，此外还有2106t用作家庭洗涤剂。由于农业系统输入大量的磷和氮，世界上许多湖泊为浮游生物的高度生长提供了理想的条件。在这样富营养化的条件下，湖水因浮游植物（尤其是蓝藻类）的高密度生长而变得混浊，大型水生植物生长受到抑制，同时，大量浮游植物的分解会降低溶氧浓度，引起鱼和无脊椎动物的死亡。农业活动对氮循环的影响砍伐森林，垦荒农田通常导致溪流中氮含量增加，以及进入大气而损失的 N2O量的增加。种植豆科植物，利用根瘤中的固氮菌，有助于氮的固定。氮肥（每年多于 50106t） 非常重要。因为撒在田里的肥料中有相当一部分经过各种途径进入河流和湖泊，导致富营养化。
