The correct answer is A. Una, Hamirpur.
Soil in Una and Hamirpur districts is particularly deficient in nitrogen. This is because the soil in these districts is mostly sandy and loamy, which does not retain nitrogen well. Additionally, the climate in these districts is dry, which also contributes to nitrogen deficiency.
Nitrogen is an essential nutrient for plants, and its deficiency can lead to a number of problems, including stunted growth, yellowing leaves, and reduced yields. To address this issue, farmers in Una and Hamirpur districts often apply nitrogenous fertilizers to their crops. However, this can be expensive and may not always be effective.
One way to improve the nitrogen content of the soil in Una and Hamirpur districts is to plant nitrogen-fixing crops. These are crops that can take nitrogen from the air and convert it into a form that plants can use. Some examples of nitrogen-fixing crops include legumes, such as beans and peas.
Another way to improve the nitrogen content of the soil is to add organic matter, such as compost or manure. Organic matter helps to improve the structure of the soil and makes it more able to retain nitrogen.
By taking these steps, farmers in Una and Hamirpur districts can help to improve the nitrogen content of the soil and boost the yields of their crops.
Option B, Kullu and Kangra, is incorrect because the soil in these districts is mostly alluvial, which is a type of soil that is rich in nutrients.
Option C, Chamba and Dalhousie, is incorrect because the soil in these districts is mostly hilly, which means that it is not as fertile as the soil in other parts of the state.
Option D, Solan and Nahan, is incorrect because the soil in these districts is mostly loamy, which is a type of soil that is not as rich in nutrients as other types of soil.