As we saw in the last lecture, a major cause of climate change is the rapid rise in the level of carbon dioxide in the atmosphere over the last century. If we could reduce the amount of CO2, perhaps the rate of climate change could also be slowed down. One potential method involves enhancing the role of the soil that plants grow in, with regard to absorbing CO2. Rattan Lal, a soil scientist from Ohio Stage University, in the USA, claims that the world’s agricultural soils could potentially absorb 13 per cent of the carbon dioxide in the atmosphere – the equivalent of the amount released in the last 3o years. And research is going on into how this might be achieved.
Lal first came to the idea that soil might be valuable in this way not through an interest in climate change, but rather out of concern for the land itself and the people dependent on it. Carbon-rich soil is dark, crumbly and fertile, and retains some water. But erosion can occur if soil is dry 【Q31】, which is a likely effect if it contains inadequate amounts of carbon. Erosion is of course bad for people trying to grow crops or breed animals on that terrain. In the 1970s and ‘80s, Lal was studying soils in Africa so devoid of organic matter that the ground had become extremely hard 【Q32】, like cement. There he met a pioneer in the study of global warming, who suggested that carbon from the soil had moved into the atmosphere. This is now looking increasingly likely.
Let me explain. For millions of years, carbon dioxide levels in the atmosphere have been regulated, in part, by a natural partnership between plants and microbes – tiny organisms in the soil. Plants absorb CO2 from the air and transform it into sugars and other carbon-based substance 【Q33】. While a proportion of these carbon products remain in the plant, some transfer from the roots to fungi and soil microbes 【Q34】, which store the carbon in the soil.
The invention of agriculture some 10,000 years ago disrupted these ancient soil-building processes and led to the loss of carbon from the soil. When humans started draining the natural topsoil, and ploughing it up for planting, they exposed the buried carbon to oxygen. This created carbon dioxide and released it into the air. And in some places, grazing by domesticated animals has removed all vegetation, releasing carbon into the air. Tons of carbon have been stripped from the world’s soils – where it’s needed – and pumped into the atmosphere.
So what can be done? Researchers are now coming up with evidence that even modest changes to farming can significantly help to reduce the amount of carbon in the atmosphere.
Some growers have already started using an approach known as regenerative agriculture. This aims to boost the fertility of soil and keep it moist through established practices 【Q35】. These include keeping fields planted all year round, and increasing the variety of plants being grown 【Q36】. Strategies like these can significantly increase the amount of carbon stored in the soil, so agricultural researchers are now building a case for their use in combating climate change.
One American investigation into the potential for storing CO2 on agricultural lands is taking place in California. Soil scientist Whendee Silver of the University of California, Berkeley, is conducting a first-of-its-kind study on a large cattle farm in the state 【Q37】. She and her students are testing the effects on carbon storage of the compost that is created from waste – both agricultural, including manure and cornstalks, and waste produced in gardens 【Q38】, such as leaves, branches, and lawn trimmings.
In Australia, soil ecologist Christine Jones is testing another promising soil-enrichment strategy. Jones and 12 farmers are working to build up soil carbon by cultivating grasses that stay green all year round 【Q39】. Like composting, the approach has already been proved experimentally; Jones now hopes to show that it can be applied on working farms and that the resulting carbon capture can be accurately measured.
It’s hoped in the future that projects such as these will demonstrate the role that farmers and other land managers can play in reducing the harmful effects of greenhouse gases. For example, in countries like the United States, where most farming operations use large applications of fertiliser, changing such long-standing habits will require a change of system. Rattan Lal argues that farmers should receive payment not just for the corn or beef they produce but also for the carbon they can store in their soil. 【Q40】
Another study being carried out …
Complete the notes below.
Write ONE WORD ONLY for each answer.
听前预测：定位词 erosion、soil；提示词 is。此处应填形容词。
题目解析：本题的定位词出现在转折词 but 之后，并且定位词和考点在同一个句子中。 “But erosion can occur if soil is dry, which is a likely effect if it contains inadequate amounts of carbon.”（如果土壤变得干燥，就会发生侵蚀，当然如果土壤含碳量低就很可能发生这样的结果。），所以答案为 dry。
听前预测：定位词 Lal、soil、Africa；提示词 was、very。此处应填形容词。
题目解析：本题的定位词出现在主句中“In the 1970s and ’80s, Lal was studying soils in Africa”，然后“so devoid of organic matter that the ground had become extremely hard”，这里 had become 同义替换了 was，extremely 同义替换了 very，从而得到答案 hard。
听前预测：定位词 plants、CO2、air、carbon-based substances；提示词 turn。此处应填名词。
题目解析：本题应该先关注小标题 soil and carbon，这两个单词的信息点比较分散，但是还是可以定位到“For millions of years, carbon dioxide levels in the atmosphere have been regulated, …tiny organisms in the soil.”，本题定位词和答案出现在小标题后面的句子中“Plants absorb CO2 from the air and transform it into sugars and other carbon-based substances”，这里 transform into 是 turn 的同义替换，因此答案为 sugar(s)。
听前预测：定位词 some CO2、plants、microbes；提示词 moves from。此处应填名词。
题目解析：本题的定位词 some CO2 在原文被拆分成前后两个定位信息点 carbon products 和 some，“While a proportion of these carbon products remain in the plant, some transfer from the roots to fungi and soil microbes”，transfer from 同义替换了 moves from，plants 被同义替换为 fungi，因此答案应该是这两个替换词中间的单词 roots。
听前预测：定位词 soil；提示词 remains、fertile。此处应填形容词。
题目解析：提示词 fertile 和空白处的形容词都是修饰定位词 soil 的，在听力原文中 fertile 发生词性变换并被提前，“This aims to boost the fertility of soil and keep it moist through established practices”，并且提示词 remains 被 keep 同义替换，因此得到答案 moist，也可填其同义词 damp 或 wet。
听前预测：定位词 plants；提示词 year-round planting、increasing。此处应填名词。
题目解析：本题的定位词和提示词一同出现“These include keeping fields planted all year round, and increasing the variety of plants being grown”，其中提示词 year-round planting 被同义替换为 keeping fields planted all year round，但 increasing 并没有被替换，所以答案定位在提示词和定位词中间的 variety。
听前预测：定位词 California study、farm；提示词 big。此处应填名词。
题目解析：本题的小标题紧接着 36 题出现“Strategies like these can significantly increase… is taking place in California”，然后定位词和提示词一起出现“Soil scientist…is conducting a first-of-its-kind study on a large cattle farm in the state”。这里 large 替换了 big，从而得到答案 cattle。
听前预测：定位词 compost、waste、agriculture；提示词 made from。此处应填名词或动名词。
题目解析：本题的定位词和提示词一起出现“She and her students are testing the effects on carbon storage of the compost that is created from waste—both agricultural, including manure and cornstalks, and waste produced in gardens…”， 这 里 made from 被 is created from 所替换，而且这里是并列结构“from waste—both agricultural…and waste produced in gardens”，因此答案为 gardens，也可填其同义词 gardening。
听前预测：定位词 Australia study、soil carbon；提示词 increase、using。此处应填名词。
题目解析：小标题在 38 题后出现“In Australia, soil ecologist…”，接着提示词及定位词出现 “Jones and 12 farmers are working to build up soil carbon by cultivating grasses that stay green all year round”，这里 build up 同义替换了 increase，cultivating 同义替换了 using，所以答案为 grasses。
听前预测：定位词 farmers、carbon storage；提示词 giving。此处应填名词。
题目解析：先定位小标题下第 1 句话里的提示词 reducing 和 fertilizer 还有定位词 farming， “It’s hoped in the future…can play in reducing the harmful effects…. For example…where most farming operations use large applications of fertiliser…”， 接着定位词 farmers 出现“farmers should receive payment not just for the corn or beef they produce, but also for the carbon they can store in their soil”，这里 receive 同义替换了 giving，听力原文的意思是农民不仅要得到玉米或牛肉的钱，还应得到存储在土壤里的碳的钱，而题目的主语是 future developments，它的意思是未来的发展还应在碳的存储方面给农民钱，所以尽管 receive 和 giving 意思相反，在这个 语境下它们是同义替换，因此答案为 payment(s)，也可填它的同义词 money。