For this, animal manures or dried blood are often added.

To think of animal manure as pollution rather than fertility is a relatively new (and industrial) idea.

An example of this would be the use of animal manure.

There has even been a study on using certain animal manure, like chickens, to decrease pest population.

Otherwise the animal manures can burn plants if used fresh due to the high urine-salt content.

This system utilized fertilizer in the form of animal manure.

Farms are sources of pathogens from animal manure, insecticides and crops.

The Greeks did not use animal manure, possibly due to the low number of cattle.

My second question is this: nitrate in groundwater can come from sources other than animal manure.

A third was of a man whose head was a pile of animal manure.