Technical Abstract: Sustainable agriculture systems often use green- or animal-manure as a nitrogen source. The addition of these materials also has positive impacts on soil phosphorus (P) availability. This study was conducted to investigate the effects of animal- and legume-based cropping systems on the chemistry of organic matter and soil P. Two cropping systems, Potato Ecosystem (ECO) located in Presque Isle, ME and Grass Fertility (GF) located in Stillwater, ME, received animal manure. Two others, Liebman Rotation (LER) in Stillwater, Maine and Porter Rotation (PR) in Presque Isle, ME, were primarily legume-based rotations. The dissolved organic matter (DOM) concentration was higher (p < 0.10) in the treatment that received animal manure than those which only received legume residue. The E2/E3 spectrophotometric test indicated that the DOM extracted from the ECO manure-treated plots was more humified than that from the ECO control plots. There were no significant differences between the amended and control treatments in Olsen P or total P for all the tested cropping systems. The two cropping systems that received animal manure (ECO and GF) had higher concentrations of water soluble P (p < 0.10). There was a positive, linear relationship between DOM and water-soluble P concentrations across soils. A simulation model was used to study how changes in P soil chemistry may affect P uptake by crops. The model showed that predicted P uptake was greater for the animal manure-based ECO and GF systems, but not for the legume based LER and PR systems (p < 0.05). This study shows that cropping systems that include animal manure may increase soil P availability.