Final answer:
Manure is a natural form of fertilizer that supplies essential nutrients to plants, improving soil fertility and quality. Synthetic fertilizers are also used to increase crop yields, but organic farming usually avoids them to maintain environmental balance.
Step-by-step explanation:
A natural form of fertilizer would be manure. Fertilizers are materials, whether natural or synthetic, that are applied to soil or plant tissues to supply essential nutrients for plant growth. Natural fertilizers such as manure have been used traditionally to improve soil fertility. Commercial fertilizers, which can be high in nutrients like nitrogen and phosphorus, are also used to increase crop yields. However, organic agriculture often prohibits synthetic fertilizers in favor of natural ones, as they can contribute to improved soil quality, biodiversity, and natural biogeochemical cycles.
The application of nitrogen and phosphorus is critical because they are key nutrients needed by plants to produce organic compounds and are often limiting factors for plant growth. However, it's important to note that excess amounts of these nutrients can lead to ecological disturbances such as eutrophication of water bodies.
Nitrogen in the air is not easily accessible to plants due to the strong bond between nitrogen atoms, hence the process of nitrogen fixation is necessary to convert it into a form that plants can use. Manure contains not only nitrogen and other nutrients but also organic matter that can enhance soil structure and fertility.