The correct answer is option 2, which states that alluvial soils are poor in nitrogen and humus. Alluvial soils are formed by the deposition of sediments carried by rivers or streams over long periods of time. They are known for their fertility and are often used for crop cultivation. However, they do lack certain elements necessary for plant growth. Nitrogen is an essential nutrient for plants and is responsible for their overall growth and development. Humus, on the other hand, is organic matter that contributes to soil fertility and helps retain moisture. Both nitrogen and humus are important for healthy crop growth, and their absence in alluvial soils can limit the productivity of crops grown in these soils. It is necessary to supplement these nutrients through fertilization in order to optimize crop yields.