覆盖作物是帮助农民改善土壤、提高产量的古老方法。现在，它让农民节省了化肥上的开支。
Aref Abdul-Baki等科学家在寻找着新的、更好的覆盖作物。Abdul-Baki是美国农业部农业研究所的一位研究员。他就职于设在马里兰州贝兹维尔的美国可持续农业系统实验室。
Abdul-Baki现已发现了一些覆盖作物，它们能抵御侵袭番茄根部的害虫。
从菽麻，豇豆和龙爪黎豆适宜于温暖、潮湿的地区。夏季，人们耕地时种上覆盖作物。秋季，人们收割地里的覆盖作物，然后再种上番茄。
在气候宜人的地区，如美国的马里兰州和弗吉尼亚州，人们在秋季种植覆盖作物，让其在早春时生长。Abdul-Baki先生告诉我们，毛叶苕子和黑麦是很好的覆盖作物。
为了避免土壤流失，应该先播种后耕地。到了五月，覆盖作物收割后，残余部分留在地面上。同样的方法适用于其它夏季作物，比如，胡椒、甜玉米、绿豆和一些瓜类作物。
收割完覆盖作物之后，土壤里有了一层有机物。它能帮助新作物生长，同时抑制不需要的植物。覆盖作物还能给土壤提供额外的营养，防止土壤干燥和土壤流失。
在炎热干燥的南加利福尼亚等地区，覆盖作物可降低土壤温度，减少水流失和水侵蚀。Lana vetch（译者问题：这玩意儿的中文名是什么？）是一种很好的覆盖作物，一般在秋天种植，这种植物能自己烂掉，然后将种子再撒散到土壤里。
Abdul-Baki先生说，如果农民使用覆盖作物，在种植番茄之前，就不再需要给土壤施甲基溴。甲基溴能杀死多种有机体。但Abdul-Baki先生指出，这种农药也能破坏环境，对人的健康造成威胁。美国政府对甲基溴的使用做了许多限制，许多国家也已商定了取缔甲基溴的协议。
Aref Abdul-Baki说，与未使用覆盖作物的农民相比，用了覆盖作物的农民每公顷土地能出产出数量相同，甚至更多的番茄。
原文
Cover crops are an ancient way to help farmers improve their soil, increase their harvests and, these days, save money on chemicals.
Scientists like Aref Abdul-Baki search for new and better cover crops. Mister Abdul-Baki is with the Agricultural Research Service of the United States Department of Agriculture. He works at the Sustainable Agricultural Systems Laboratory in Beltsville, Maryland.
Mister Abdul-Baki has found some cover crops to resist groundworms that attack the roots of tomatoes.
Sunn hemp, cowpea and velvet bean are good for warm, humid areas. The soil is plowed to plant the cover crops during the summer months. In the fall, the cover crops are turned over in the soil, then the tomatoes are planted.
In states with moderate climates, like Maryland and Virginia, the cover crops are planted in the fall to grow during early spring. Mister Abdul-Baki tells us that good cover crops are hairy vetch and rye.
To avoid soil loss, the seeds are planted without the use of plowing. In May, the cover crops are cut and the remains are left on the surface. The same method can be used for other summer crops like peppers, sweet corn, green beans and some melons.
After the cover crop is cut, the result is a layer of organic material. This will help the new crop grow and suppress unwanted plants. The cover crop provides extra nutrients to the soil. It also keeps the soil from drying out, and helps prevent the loss of soil.
In hot, dry areas, like in Southern California, cover crops help reduce soil temperatures. They also reduce water loss and erosion. Lana vetch is a good cover crop. It is planted in the fall and breaks down without any assistance. It releases its seeds back into the soil.
Mister Abdul-Baki says farmers who use cover crops no longer need to treat their soil with methyl bromide before they plant tomatoes. Methyl bromide kills many kinds of organisms. But Mister Abdul-Baki notes that the poison also damages the environment and is a health danger. The government restricts the use of methyl bromide. And countries have agreed to a treaty to ban it.
Aref Abdul-Baki says farmers who use cover crops produce as many, or more, tomatoes per hectare as compared to no use of cover crops.
PS.感谢爸爸帮我修改这篇译文。
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