The odd one out is A. Manure. Manure is a substance that is used to fertilize soil. It is made from animal waste, plant waste, or compost. The other options are all elements that are essential for plant growth. Nitrogen is the most abundant element in the atmosphere. Ammonia is a gas that is produced when nitrogen and hydrogen combine. Urea is a solid that is produced when ammonia and carbon dioxide combine. Potash is a mineral that is rich in potassium. Potassium is an essential element for plant growth. It helps plants to produce proteins and carbohydrates. It also helps plants to regulate water and nutrient uptake.
Manure is not an element. It is a substance that is made from animal waste, plant waste, or compost. It is used to fertilize soil.