No manure is a waste product for crop production. It is extensively utilized in conventional agriculture. Organic production unfortunately uses it inefficiently.

There are some pretty complicated biological processes to explain this but I'll try to keep it short.

First off manure is a not balanced fertilizer. It's got two much of some nutrients and not enough of others . This imbalance causes two issues: it delays the release of nutrients and causes excess unused nutrients to buildup in the soil.

The nutrient composition in manure varies widely as well. There are many variables that can affect this. It's pretty wild when you get the laboratory test back.

Most of the nitrogen in the original food source for the animal is lost by denitrification before the next years crop can utilize it. There flat out is not enough N in the manure to raise our crops without synthetic fertilizer

Application of manure acidifies the soil. Acidic soil locks up nutrient via chemical reactions.

The most efficient and environmentally friendly way to fertilize crops is with a combination manure, compost, synthetic fertilizer and covercrops. The addition of synthetic fertilizers allows farmers to reduce the amount of manure they apply and balance out the nutrients ratios. It also reduces the total need of synthetic fertilizer and increases the soil microbial activity. The covercrops capture and hold nutrients over the winter and minimizing the runoff and inputs for the following year.