Manure as a Fertilizer:
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.
Manure is a source of many nutrients including: nitrogen, phosphorus, potassium and many others. However, nitrogen is often the main nutrient of concern for most crops. Potassium deficiency is usually quite localized within a field and would not be corrected with common rates of manure.
Other Benefits of Manure:
The use of manure helps to maintain the organic matter content of the soil which can improve soil structure and water infiltration. However, manure is quickly decomposed under warm, moist soil conditions. With the manure rates used for most crops, organic matter content in soil is only temporarily increased.
and so farmers use it