Pig manure is an excellent fertilizer and rich source of organic carbon and nitrogen compounds such organic nitrogen (O-N) (95% of total nitrogen) that is plant-unavailable-nitrogen (PUN) and mineralized nitrogen (about 1% of total nitrogen) such as ammonium (NH4+) and nitrate (NO3) that are plant-available-nitrogen (PAN). In addition, manure also contains two forms of estrogens: (i) poorly estrogenic thus essentially nontoxic conjugated estrogens (cEs) such as estrone (cE1), estradiol (cE2) and estriol (cE3); and (ii) highly estrogenic and toxic free estrogens (fEs) such as fE2, fE1 and fE3. This study showed that aerobic processing reduced concentrations of total carbon (TC), O-N, PAN and NH4+/NH3 ratio, transiently hydrolyzed cEs (cE2 > cE1 > cE3) into corresponding fEs, transiently increased estrogenic activity and potential toxicity, and rapidly degraded fEs (fE2, fE1 > fE3), thus reducing the estrogenic activity in manure. Unlike aerobic processing, anaerobic processing stabilized and increased PAN and NH4+/NH3 ratio, thus increasing the manure’s fertilizer value. However, anaerobic processing, relative to aerobic processing, poorly hydrolyzed cEs (reducing transient toxicity and increasing reserve toxicity potential) and poorly degraded fEs (increasing toxicity) in manure. Thus, aerobic and anaerobic environments have distinct effects on manures’ PAN and estrogenic activity, presenting an interesting dilemma: anaerobic incubation that increases manures’ PAN does not effectively degrade estrogens, while aerobic incubation that effectively degrades estrogens (after transiently increasing their estrogenic activity) also decreases PAN, thus making manure less profitable. New techniques are need to fully use manure as organic fertilizer.
Bibliographical noteFunding Information:
This project was partially funded by grants from the National Pork Producers, Consortium for Water Quality and the University of Minnesota, Graduate School—faculty seed grant. Technical support was provided by Gupta Shveta, Gupta Arun and Jiang Yin.
© 2015 by the authors; licensee MDPI, Basel, Switzerland.
- Organic nitrogen
- Plant available nitrogen