Question

why do farmers use manures and fertilizers in the crop feild ?????????????? 

Answer 1

farmers use manures and fertilizers in the crop feild to increse fertility of soil.1 fertilizer is an inorganic salt whereas manure is a natural substance obtained by the decomposition of cow dung, human waste and plant residues.
2. fertilizer can be prepared in factories whereas manure is prepared in field.

Answer 2

Farmers use manures and fertilizers in the crop field because Manure is an excellent fertilizer containing nitrogen, phosphorus, potassium and other nutrients. It also adds organic matter to the soil which may improve soil structure, aeration, soil moisture-holding capacity, and water infiltration.  Fertilizers is any material of natural or synthetic origin that is applied to soils or to plant tissues (usually leaves) to supply one or more plant nutrients essential to the growth of plants.