Shifting cultivation (Jhum) practices in Nagaland have led to:

Increased soil fertility
Soil erosion and degradation
Improved soil structure
Reduced soil biodiversity

The correct answer is: b) Soil erosion and degradation.

Shifting cultivation (Jhum) is a traditional agricultural practice in which land is cleared and cultivated for a few years, then left fallow for several years to allow the land to recover. This practice has been used in Nagaland for centuries, and it has had a significant impact on the soil.

One of the main problems with shifting cultivation is that it leads to soil erosion. When the land is cleared, the topsoil is exposed to the elements and can be easily washed away by rain or blown away by wind. This can lead to a loss of nutrients and organic matter, which can make the soil less fertile.

Shifting cultivation can also lead to soil degradation. When the land is left fallow, it is not properly managed, which can lead to the growth of weeds and the accumulation of organic matter. This can make the soil less productive and can also increase the risk of soil erosion.

In conclusion, shifting cultivation has led to soil erosion and degradation in Nagaland. This has had a negative impact on the environment and the people who live there.

Here is a brief explanation of each option:

a) Increased soil fertility: This is not the correct answer because shifting cultivation leads to soil erosion and degradation, which can make the soil less fertile.

b) Soil erosion and degradation: This is the correct answer because shifting cultivation involves clearing the land, which exposes the topsoil to the elements and can lead to soil erosion. When the land is left fallow, it is not properly managed, which can lead to the growth of weeds and the accumulation of organic matter. This can make the soil less productive and can also increase the risk of soil erosion.

c) Improved soil structure: This is not the correct answer because shifting cultivation leads to soil erosion and degradation, which can damage the soil structure.

d) Reduced soil biodiversity: This is not the correct answer because shifting cultivation does not necessarily lead to a reduction in soil biodiversity. However, it can lead to a change in the types of plants and animals that live in the soil.