Submitted to: Soil Biology
Publication Type: Book / chapter
Publication Acceptance Date: 6/14/2010
Publication Date: 1/15/2011
Citation: Dao, T.H., Schwartz, R.C. 2011. Manure management effects on phosphorus biotransformations and losses during animal production. In: Bunemann, E.K., Oberson, A., Frossard, E., editors. Phosphorus in Action: Biological processes in soil P cycling. Soil Biology. Berlin, Germany: Springer. p. 407-429. Interpretive Summary: Livestock and poultry can convert crop residues, forages, and grains into high-quality proteins as milk, meat, and eggs that are important to human nutrition and health. In 2007, animal agriculture accounts for over 51% of the U.S. gross agricultural receipts, or about $153.5 billion. Intensification of livestock and poultry production in various regions of the U.S. has drastically changed the natural landscape on millions of hectares of arable lands. One outcome of intensification is the accumulation of animal manure. Oftentimes the quantity of manure generated far exceeding the requirements of crops grown in the region. Under these circumstances, excess nutrients, along with other salts, organic matter, pathogenic organisms, and antibiotics are subject to lost to the atmosphere and surface and ground waters. Nutrients, in particular manure nutrients, continue to be recurrent major problems plaguing efforts in reversing the impairment of aquatic ecosystems such as the Everglades in Florida, the Gulf of Mexico, or the Chesapeake Bay. An accurate description of the inorganic and organic P forms in manure, and their environmental dispersal is critical to the success of restoring impacted ecosystems. Particular attention was given to the composition of manure, and the speciation of P in manure from various animal production systems to identify the likely loss pathways in the associated systems of manure management. Ligand compounds that can exchange place with, and release soluble P forms in manure and soils have a critical role in the break down and turnover of organic P by hydrolases enzymes in manure storage structures and stockpiles, and the solubilization of organic P substrates from animal manure upon contact with the soil. The contribution of biologically mediated processes along with physical and chemical ones must be fully understood to develop management practices to sustainably utilize this non-renewable resource and bionutrients in agricultural byproducts. Lastly, the potential approaches available to mitigate P losses from major modern animal production systems were identified to suggest strategies to alleviate their environmental footprint.
Technical Abstract: The bioactivity of manure P is highly dynamic and dependent on interactions with the reactive soil surface and biologically mediated transformations. Biological tools that combine ligand exchange and enzyme-mediated mineralization of organic P can mimic plants and microorganisms in their ways of acquiring P from their environment. More of this type of methods are direly needed to differentiate various bioactive P pools that contribute to the solution-phase phosphate concentration in animal manures, in manure storage structures, and manure-amended soils, and determine organic nutrient turnover and P environmental dispersal mechanisms. Phosphorus losses from animal production systems can occur via its transport in rainwater or snowmelt running off from animal housings, pens, manure storage areas, and/or leaching from manure-amended fields, pastures, and rangelands to the environment. In most watersheds, off-site P transport is dominated by the runoff-erosion process as where it is conveyed in a dissolved form or in association with suspended sediments. These transport processes interact in a complex way with the timing of manure applications and conservation practices that ultimately determine offsite P export. The management of excess P has centered on five complimentary strategies (i) improving P utilization in rations especially in non-ruminants to decrease excretion, (ii) manure separation technologies to concentrate the P in solids for use offsite, (iii) blending manure with co-amendments to directly reduce P solubility or recover P from the manure, (iv) use of high yielding, hyperaccumulator forages to accelerate P sequestration, and (v) use of conservation and best management practices to reduce risks of offsite transport. In most cases, a combination of these practices can mitigate the potential adverse effects of manure P in animal production systems.