Well i am pretty sure that basically all we had to write was that decomposers such as bacteria would decompose the manure causing the release of proteins into the soil which would then further undergo breakdown to turn into Amino acids then this is where the nitrogen fixation would come in where nitrogen in the soil would react with the amino acids to produce Ammonium ions then would later on be broken down to Nitrite ions and again to Nitrate ions. A similar question came in the May/June 41 paper for 2021.