Well-drained, fertile loamy soil is most suitable for yam cultivation because yams need a soil that supplies water and nutrients while still allowing air to reach the developing roots and tubers. Loam has a balanced texture, so it holds enough moisture for steady growth but does not stay saturated. That is important because yam tubers enlarge underground and can rot or develop poorly in soils that are too wet, too dense, or too low in fertility.

In practical terms, loamy soil is easier to till, mound, and plant, and it lets tubers expand with less physical resistance. Heavy clay can become compacted and restrict tuber growth, while excessively sandy or saline soils often lack the structure and fertility needed for strong production. Farmers usually see better sprouting, healthier vines, and better-shaped tubers when yams are grown in loose, fertile, well-drained loam, so option C is the best answer.

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The optimal soil pH range for yam cultivation is 5.5 to 6.5 because yams generally grow best in slightly acidic soils. In this range, the soil makes key nutrients more available to the plant, which supports good root development, vigorous vine growth, and later tuber bulking. A suitable pH also helps the crop use fertilizer efficiently during its long growing season.

Extremely acidic or alkaline soils make production harder. Very low pH can damage roots and increase toxicity problems, while high pH can reduce the availability of important nutrients such as phosphorus, iron, and zinc. In practice, farmers often test pH before planting and improve the soil with lime, compost, or other amendments if needed. Because slightly acidic conditions are most favorable for yam growth, 5.5 to 6.5 is the best answer.

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Mounding, or making yam heaps, is the traditional soil preparation technique most specifically associated with yam cultivation in West Africa. The reason is agronomic as well as practical: yams form large underground tubers, and those tubers need loose, deep, well-aerated soil to expand properly. A mound creates that environment by concentrating friable soil around each plant.

Raised mounds also improve drainage, which helps prevent rot in planted setts and developing tubers, especially during rainy periods. Farmers benefit in other ways too: mounds make planting, weeding, and locating tubers at harvest easier, and they help keep growth concentrated around each planting spot. While modern systems may use ridges or mechanized tillage, the classic traditional technique for yam fields in West Africa is mound making, so option B is the correct answer.

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For good yam production, the soil should be tilled to about 25-30 cm or more because yams need a deep, loose soil profile for rooting and tuber expansion. A yam tuber is a large underground storage organ, so shallow tillage is often not enough. If compact soil remains just below the surface, it can restrict root growth, distort tuber shape, and reduce final yield.

Deep tillage also improves drainage and soil aeration, both of which help protect planted setts and developing tubers from rot. In practice, farmers preparing land for mounds or ridges get better results when the underlying soil has been loosened well below the surface. That gives the crop more room to develop and makes harvest easier. Because of these agronomic and practical benefits, 25-30 cm or more is the correct answer.

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The practice that is NOT recommended in soil preparation for yams is compacting the soil firmly. Yams develop large underground tubers, so they need a loose, well-aerated soil structure that roots can penetrate and tubers can expand through. Compacted soil reduces pore space, limits air movement, slows drainage, and creates physical resistance that can lead to poor growth or malformed tubers.

The other options all support successful yam production. Organic matter improves soil fertility and structure, good drainage helps prevent rot, and breaking up clods while removing stones makes the soil easier for tubers to grow through. In other words, yam preparation aims to loosen and improve the soil, not press it down. Because compaction works against those goals, option C is the correct answer.

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Mounds play an important role in traditional yam cultivation because they provide good drainage and a loose soil volume for tuber expansion. Yam tubers develop underground and can become large, so they need a deep, friable rooting environment. A mound creates that by lifting and loosening the planting zone, which supports better root establishment and allows the tuber to enlarge more freely.

Mounds are especially helpful in areas with heavy rainfall because raised soil drains faster than flat, compacted ground. That lowers the risk of sett rot and other moisture-related problems. From a farmer’s perspective, mounds also make planting and harvesting easier by clearly defining each planting spot. Their main function, however, is improving the physical growing environment for the yam tuber. That is why option A is the correct answer.

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The best answer is between 2% and 5% soil organic matter because this moderate range supports the kind of soil conditions yams need: good structure, reliable moisture retention, and improved nutrient supply. Organic matter helps create a crumbly, well-aerated soil, which is valuable for both root growth and tuber expansion. It also supports beneficial soil biology over the crop’s long growing season.

Too little organic matter, such as less than 1%, usually means poorer fertility and weaker soil structure. Extremely high percentages are not typical field targets for yam cultivation and are less realistic as a general recommendation. In practice, farmers improve organic matter gradually with compost, manure, mulch, and rotations, especially with legumes. Because yams benefit most from a moderate, well-managed level of organic matter, 2% to 5% is the correct answer.

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Crop rotation with legumes is the practice that best helps maintain soil fertility in yam production systems. Legumes are valuable because they support the soil in several ways: they can contribute nitrogen through biological fixation, add organic residues, improve soil cover, and help maintain better structure. Since yams are heavy feeders and occupy the field for a long period, rotating them with a restorative crop is a smart management strategy.

Rotation also reduces the buildup of pests, diseases, and weeds that often occurs under continuous monocropping. By contrast, removing all residues, avoiding organic inputs, or planting yams repeatedly on the same land tends to lower soil quality over time. In practical farming, a yam-legume sequence is one of the most useful ways to keep the system productive and sustainable. That is why option D is the correct answer.

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Contour ridging is a traditional soil conservation technique often paired with yam cultivation in tropical regions because it helps control erosion on sloping land. When ridges follow the natural contour of the slope, they slow runoff, reduce the loss of topsoil, and improve water infiltration. That is especially important in the tropics, where heavy rains can quickly wash away loosened soil.

This matters for yam cultivation because yam fields are often heavily prepared with mounds or ridges, and the crop depends on good topsoil structure for tuber development. If rain erodes that soil, both current yield and long-term fertility suffer. In practical terms, contour ridging protects the field while still fitting traditional cultivation methods. Because it conserves soil and supports yam production under tropical rainfall conditions, option A is the correct answer.

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When selecting a site for yam cultivation, waterlogged areas with poor drainage should be avoided. Yams need a well-drained root zone because the planted setts and developing tubers require oxygen as well as moisture. In saturated soil, air spaces fill with water, roots function poorly, and rots become much more likely. This can lead to weak establishment, low yields, and damaged or unmarketable tubers.

From a practical farming perspective, poorly drained land often causes trouble from the beginning of the season to harvest. Setts may decay after planting, vines may grow weakly, and tubers may rot underground. By contrast, loamy soils and fields following legumes are usually positive features, not negatives. Since drainage is one of the most important requirements for successful yam production, option C is the correct answer.

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