The ravines of the Chambal valley are the standard Indian example of

The correct answer is D, alluvial. A delta is built out of silt that a river carries down and drops where it meets the sea, so deltaic land is alluvial by definition, and the eastern coastal deltas of the Mahanadi, Godavari, Krishna and Kaveri are among the most fertile rice tracts of the country. Option A is wrong because black soil is a residual soil formed in place by the weathering of the Deccan lava and is found on the plateau, not in the deltas, although the same rivers flow across it upstream. Option B is wrong because arid soil belongs to the dry west, chiefly western Rajasthan, where rainfall is low and the soil is sandy and saline. Option C is wrong because forest soil forms on hill slopes and in valleys under a cover of trees, not on a coastal plain.

The correct answer is B, because black soil is poor in phosphoric acid, nitrogen and organic matter, not rich in them. What it is rich in is calcium carbonate, magnesium, potash and lime, and remembering that short list is the safest way to answer any statement question on this soil. Option A is a correct statement, since black soil formed from the weathering of the lava of the Deccan trap and its main belt lies over Maharashtra, Madhya Pradesh, Gujarat and Chhattisgarh. Option C is a correct statement, because the fine clayey texture of the soil lets it hold moisture through the dry months, which is exactly why cotton grows on it without irrigation. Option D is a correct statement, because the soil shrinks in the heat and opens deep cracks that let air into the lower layers, giving it the name self-ploughing soil.

The correct answer is C, sheet erosion. In sheet erosion water spreads over a wide slope and carries away a thin, even film of topsoil, so nothing obvious is left behind to see, and the loss is noticed only years later as falling yields. That invisibility is what makes it the most dangerous form for farmers. Option A is wrong because gully erosion cuts visible channels down a slope, deep enough to stop a plough. Option B is wrong because a landslide is a sudden and highly visible mass movement of rock and soil down a hillside. Option D is wrong because ravines are gullies that have widened and deepened over a large area, producing the badland of the Chambal valley, which is visible even from the air. The order of visibility runs from sheet erosion at the least to landslides at the most.

The correct answer is D, weathering. Weathering is the natural breaking down of rock by temperature, water, wind and living things, and it is the process that makes soil in the first place; it is not a technique that a farmer applies to save soil, so it cannot be a conservation method. Option A is wrong as an answer because intercropping, growing two crops together in alternate rows, keeps the ground covered through the season and reduces the impact of rain on bare soil. Option B is wrong as an answer because mulching covers the bare ground between plants with straw or crop residue, which cuts evaporation and stops the topsoil from being washed or blown away. Option C is wrong as an answer because contour ploughing runs furrows across the slope instead of down it, so each furrow acts as a small barrier to running water.

The correct answer is C, the right mix of minerals and organic matter. Fertility needs mineral nutrients such as nitrogen, phosphorus and potassium from the weathered rock, and organic matter, that is humus from decayed plants and animals, which holds water, feeds soil organisms and releases nutrients slowly. Option A is wrong because an excess of acid lowers the availability of nutrients and harms root growth, which is why lime is added to strongly acidic fields. Option B is wrong because it leaves out organic matter and mentions only inorganic material; a soil of pure mineral grains, such as desert sand, is not fertile however rich its minerals. Option D is wrong because high salt content is the mark of saline or usar land, which is among the least productive soil in the country and has to be reclaimed with gypsum and drainage before it can be cropped.