Questions 10-18
Some people are concerned that our soils arc becoming depleted of trace minerals by continuous agricultural use and hence that foocte are becoming depleted in vital minerals.
This is a complex issue about which not a great deal is known, but the lack of evidence of
Line mineral deficiencies in our population speaks to the adequacy of our soils. Furthermore,
5 soils are replenished in trace minerals by rainwater and especially by irrigation water that
is obtained from rivers or wells that draw water from other soil or rock formations far
away from the farm,
On the other hand, agricultural practices that remove the total crop from the field year
after year with no replenishment of trace minerals can over time result in a crop poor in
10 these minerals. Of course, the fanner could supply chemical fertilizer to the fields* but
with most fertilizers this practice would replenish only potassium, phosphates, and nitrogen. Rotating a "green manure" crop such as clover, which is plowed under after the end of the
growing season, would renew only nitrogen in the soil, not trace elements. There is a
growing realization, therefore, (hat so-called organic farming makes good commercial
15 sense and would help minimize mineral depletion: Organic fanning essentially refers to farming that does not depend on chemical fertilizers; rather, soils are invigorated by
applying manure and by plowing in crop wastes, such as corn stalks and bean vines, and compost. These techniques return organic material and trace minerals back to the soils and
are to be commended. However, for maximum yields, a chemical fertilizer may be required
20 in addition to manure and plant waste.
Some critics of modern farming methods fear that the hardier varieties of fruits and
vegetables that have been developed to make shipment easier have resulted in loss of
vitamin content. This concern is unfounded because the creation of vitamins by plants is
an automatic biological process. Any variety of plant will make the full complement
of vitamins it needs, regardless of species.
【題組】14. Which of the following does the passage identify as examples of plant waste products?
(A) Potassium and phosphates
(B) Clover
(C) Trace elements
(D) Com stalks and bean vines
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