Explanation:

Let’s break down those options:

- Soil erosion: Sure, it’s a big problem. When topsoil washes or blows away, nutrients go with it. That’s a definite loss for fertility.

- Land degradation : This is the big umbrella. It covers loss of nutrients and fertility from not just erosion, but also overuse, chemical contamination, and poor farming. Everything that makes soil less productive falls under this—so this is the best answer to explain widespread nutrient loss.

- Water logging: Too much water chokes roots and ruins crops, but it mainly reduces productivity, not so much nutrient loss. It’s bad, but not the main culprit here.

- Air Pollution: This can harm crops, but it doesn’t really cause the soil itself to lose nutrients or fertility in a big way.

So, land degradation is spot-on—everything else is a piece of the puzzle, but not the whole story.