AP BIOLOGY

Detailed explanation-1: -Peas or beans can be used as a summer nitrogen-fixing cover crop or harvested for food. Both ways, they enrich the soil with plant-suitable N.

Detailed explanation-2: -The use of legumes, such as soybeans or alfalfa, can also be a valuable practice in the overall nitrogen management program of a crop rotation. Their use is valuable because they can add nitrogen to the soil for subsequent crops.

Detailed explanation-3: -Grain legumes such as soybean and peanut use most of their fixed nitrogen for themselves. Forage legumes, such as alfalfa and clovers, are the best crops for companion planting as they can fix substantial amounts of surplus nitrogen under the right conditions.

Detailed explanation-4: -Nitrification. In nitrification, a host of soil bacteria participate in turning ammonia into nitrate – the form of nitrogen that can be used by plants and animals.

Detailed explanation-5: -Nitrogen is produced in nodules that form on the roots of legumes, which contain Rhizobium bacteria. The bacteria take nitrogen from the air and convert it into a form the plants can use. When legumes are pulled up in the fall, excess nitrogen from the nodules is left in the soil.