In soil conservation, the method in which different crops are grown in alternate rows or strips and are sown at different times to reduce soil erosion and protect the soil from being washed away by rain is called what?

Introduction / Context:
Soil erosion by water is a major agricultural problem, especially on sloping land or in areas with heavy rainfall. To reduce erosion, farmers and conservationists use several soil conservation techniques. One of these methods involves planting different crops in alternating rows or strips and staggering their sowing times so that the soil surface is always well protected by vegetation. This question asks you to identify the correct name of that method from among several commonly mentioned soil conservation practices.

Given Data / Assumptions:

• The method uses different crops grown in alternate rows or strips.
• Crops may be sown at different times to ensure continuous cover and reduce rain impact.
• The main goal is to protect the soil from being washed away by rain water.
• Other methods like mulching, rock dams and terrace farming are also known soil conservation techniques but have different characteristics.

Concept / Approach:
Strip cropping is a soil conservation method in which different crops are grown in long, narrow strips across the slope of the land. Often, erosion resistant crops such as grasses or legumes alternate with erosion prone crops such as maize or cotton. When rain falls, the strips of dense vegetation slow down water flow and trap soil, reducing erosion. By sowing different crops at different times, farmers maintain continuous cover on some strips even when other strips are bare or newly planted. Mulching involves covering the soil with plant residues or plastic, rock dams slow water flow in gullies and terrace farming converts steep slopes into steps. None of these other methods match the description of alternating rows of different crops as clearly as strip cropping does.

Step-by-Step Solution:
Step 1: Focus on the key description in the question: different crops grown in alternate rows and sown at different times to protect soil from rain wash. Step 2: Recall that strip cropping specifically involves growing crops in alternate strips across the slope to check soil erosion. Step 3: Consider mulching, which uses straw, leaves or other materials spread on soil, but does not necessarily involve alternating crops. Step 4: Recognise that rock dams are small stone barriers placed in channels to reduce water speed, and terrace farming shapes the land into stepped fields, both very different from alternating crop strips. Step 5: Match the described method to strip cropping and choose the option that explicitly mentions alternate rows of different crops as the correct answer.

Verification / Alternative check:
Agriculture and soil science textbooks describe strip cropping as growing two or more crops in strips on the same field, often oriented at right angles to the direction of wind or water flow. Illustrations show alternating strips of tall and short crops, or of cereals and grasses, which break the force of wind or water and reduce erosion. In contrast, mulching is shown as a blanket of residue on soil, rock dams are structures in gullies and terrace farming involves cutting broad steps into hillsides. These descriptions confirm that the technique of alternating different crops in rows and sowing them at different times to reduce rain wash is called strip cropping.

Why Other Options Are Wrong:
Option a, mulching, protects soil by covering it with organic or synthetic materials, but it does not involve growing different crops in alternate strips.

Option c, rock dam, involves placing rocks in drainage channels to slow water, which is a structural measure rather than a cropping pattern.

Option d, terrace farming, reduces erosion by modifying the shape of hilly land into flat steps, not by alternating crop rows on the same slope.

Common Pitfalls:
Learners sometimes confuse strip cropping with terrace farming because both are associated with soil conservation on slopes. Another common mistake is to choose mulching whenever they see the word protect soil without checking the specific method described. To avoid these errors, focus on whether the technique involves changing the cropping pattern or changing the physical shape of the land or covering the soil with mulch. The description of alternating crops in rows matches strip cropping, making it the correct choice for this question.

Final Answer:
The soil conservation method described is called Strip cropping, where different crops are grown in alternate rows or strips.