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III. Factors Affecting Phosphorus Composition in Organic Wastes
Farm Gate Phosphorus Balances for Selected European Pig and Dairy Farmsa (in kg P haÀ1)
Net stock exchangel
Animals and animal products
G. S. TOOR ET AL.
Adapted from De Clerq et al. (2001).
Farm with no agricultural land and 2000 fattening pigs, with 2.5 cycles per year.
Means of 13 farms with total area of 79 ha (7 ha of grassland, 1 ha of fodder, 57 ha of cereals, 9 ha of oilseed rape and field pea, 4 ha of fallow). Eight of
the pig farms produced piglets at an average of 22 piglets per sow per year and housed an average of 387 sows. The remaining five farms housed 216 sows
with a mean annual production of 3988 pigs.
Farm with 14 ha of rainfed barley and 1018 pigs in a 5 month cycle.
Farm with 27 ha of wheat, 22 ha of maize, and 220 sows. Farm sold 3920 fattening pigs in 1999. Farm exports 1250 m3 of slurry per year to neighboring
farms due to animal waste management constraints.
Farm with 73 ha of arable cropland and 2300 fattening pigs per year.
Farm with 33 ha of grassland, no arable crops, and 39 dairy cows.
Means of 26 farms with total area of 85 ha (27 ha of grassland, 26 ha of fodder, 23 ha of cereals, 7 ha of beet, 2 ha of fallow) and 128 dairy cows.
Farm with 10 ha of grassland/fodder maize/potato rotation and 23 dairy cows.
Farm with total area of 58 ha (27 ha of grassland, 13 ha of wheat and maize, 15 ha of forage maize, 2 ha of set aside) and 42 dairy cows.
Farm with 48 ha of arable cropland, 42 dairy cows, 15 heifers, and 40–60 beef cattle.
Mainly due to changes in stocks of fodder and slurry between two consecutive years.
CHARACTERIZATION OF P IN ORGANIC WASTES
G. S. TOOR ET AL.
Phytic Acid (Inositol Hexaphosphate) Content in Some FeedstuVsa
Low phytic acid cornb
Total P (%)
Phytic acid (%)
as % of total P
Adapted from Lott et al. (2000).
Adapted from Raboy et al. (2000) Raboy and Gerbasi (1996).
Addition of mineral P (calcium phosphates) is necessary in the diets of
nonruminants (poultry, swine) because these animals lack the inherent phytase enzyme in the digestive tract (Bedford, 2000) and cannot digest phytic
acid present in the diets. The majority of organic P (61–70%) in feed grains,
such as maize, sorghum, and soybean meal, which are commonly fed to
poultry and swine consist of phytic acid (Table V) (Lott, 1984; Nelson et al.,
1968). Phytic acid may bind with diVerent minerals, such as Ca, Fe, Zn
(Sandberg et al., 1993), and proteins (Thompson, 1993), in the animal
digestive tract due to presence of strong negative charges on its surface
(Dao, 2003). This may result in reduced uptake of these minerals thereby
causing nutrient deficiency problems such as anemia and osteoporosis
(Oatway et al., 2001). The development of corn cultivars with lower concentrations of phytic acid should help to increase utilization of feed P by
animals and may provide another alternative to reduce P excretion in
manures. For example, Raboy et al. (1984, 2000) and Raboy and Gerbasi
(1996) have developed low phytic acid corn that has similar total P levels to
nonmutant hybrids but lower levels of phytic acid (37% of total P) and
higher levels of inorganic P (63% of total P) (Table V).
Klopfenstein et al. (2002) suggested that using the latest advances in diet
management, such as adding phytase, feeding closer to animal requirement,
using higher bioavailability feed ingredients, adding vitamin D3 metabolites,
and choosing low phytic acid ingredients could result in a 40% reduction in
total P in poultry waste. Studies by Angel et al. (2005), Applegate et al.
(2003), Maguire et al. (2004), and Toor et al. (2005c) have confirmed these
observations that feeding P to requirement, including high available P corn
(or low phytic acid corn) in diets, and supplementing diets with phytase can
reduce total P excretion in poultry litters and swine manures by 40%.
Similarly, P excretion in finished pigs manure can be reduced by 30–40%
with dietary P management (Baxter et al., 2003; Pierce et al., 1997). Overall, these studies have concluded that the reduction of P overfeeding and
CHARACTERIZATION OF P IN ORGANIC WASTES
supplementation of phytase is a sound management practice that should be
recommended to reduce total P excretion in the manures.
Excess P is often added to dairy diets due to the common supposition that
P helps to maintain a better reproduction rate. This belief is largely based on
a study conducted by Hignett and Hignett (1951) in the United Kingdom,
where diets contained 0.10–0.25% P prior to P supplementation, however, most present day dairy diets contain greater than 0.30% P without
P supplementation and sometimes as high as 0.40 to 0.45% P. The National
Research Council’s current recommendation (National Research Council,
2001) as well as a number of other studies (Dou et al., 2002, 2003; Karn,
2001; Valk et al., 2000; Wu et al., 2001) propose that the P content in diets
can be safely reduced to between 0.32 and 0.38%. These studies have shown
that reduction of P in dairy diets will lead to reductions in P in manures. Dou
et al. (2002) analyzed fecal samples and reported that increasing dietary
P levels led to a higher concentration of total P in feces. Toor et al. (2005d)
sampled 40 dairy farms in Mid‐Atlantic United States and calculated that
there will be about 40% more P to manage each year on dairy farms using
high‐P diets (mean of 21 farms: 5.1 g total dietary P kgÀ1) than on farms
feeding low‐P diets (mean of 19 dairy farms: 3.6 g total dietary P kgÀ1).
In summary, the modification of dairy and poultry diets by reducing
P concentration in diets and adding phytase and using low phytic acid
foodstuffs in poultry and swine diets can result in manures with approximately 40% less total P. Therefore, with the advent of the new century, we
have new feeding management strategies for dairy, poultry, and swine that
may result in manures with diVerent chemical composition.
B. ORGANIC WASTES HANDLING EFFECTS
Prior to land application or other oV‐farm usage of organic wastes, they
must be removed from animal houses and municipal treatment plants and
transported to a storage facility or directly spread on land. Major waste
handling and treatment factors that influence the amount and forms of P in
manures are: type and amount of bedding material (e.g., straw, saw dust, wood
shavings, paper and sand, nonlegume hay, alfalfa), addition of feed additives (e.
g., phytase enzyme in poultry and swine diets) and manure amendments (e.g.,
aluminum sulfate in poultry litter), manure accumulation time, amount of
water used to flush the house (e.g., in dairy parlors, typically 145–300 liter
water is used per cow per day), and storage time prior to land application.
G. S. TOOR ET AL.
The following sections describe the major treatment and storage practices
Organic waste treatments consist of physical and chemical to biological
processes, which are often needed to reduce the volumes of waste, destroy
pathogens, control odors, and improve palatability. These treatments
can also modify the physical, chemical, and biological characteristics of
wastes, resulting in heterogeneity in P speciation from one production site
to another. The following section summarizes the common treatments.
a. Physical Treatment Physical treatment of wastes involves solid–liquid separation by sedimentation or screening and is mostly used for dairy
and swine manures and biosolids. The separated solids can then be composted, reused as bedding, or feed, or pelletilized, or directly applied to soil
as an amendment. The liquids can be used to flush the animal house to
remove manure before using to supply plant nutrients. The major advantage
of this process is lower transport costs due to reduction in waste volume,
which can be of significant concern in large animal production facilities.
Other alternative methods of manure use, primarily for poultry litter and
biosolids, include drying, incineration, and pyrolysis. A detailed discussion
of physical treatment processes for wastes has been provided by Moore
(1993) and Day and Funk (1998).
b. Chemical Treatment Organic wastes can be treated with chemicals
to precipitate particulates and colloidal matter, to control pH and odor, and
to enhance biological treatment. The most commonly used coagulants in
wastewater are aluminum sulfate, ferric sulfate or chloride, and lime. Some
polyelectrolytes and polymers have also been used in biosolids and manures
(Dao and Daniel, 2002; Dao et al., 2001). In poultry houses, sodium bisulfite
is used for NH3 control, litter acidification, and for pathogen reduction
(Salmonella and Campylobacter) (Moore et al., 1996; Yang et al., 1998).
Another common chemical additive used today in poultry houses is aluminum sulfate (alum), which reduces soluble inorganic P concentrations and
NH3 emissions (Moore et al., 2000; Sims and Luka‐McCaVerty, 2002).
Usage of alum and aluminum chloride to reduce soluble inorganic P in
swine manure has also been documented (Smith et al., 2001).
c. Biological Treatment Biological treatment can significantly reduce
the solids content of waste by the action of biological organisms in the
presence (aerobic) or absence (anaerobic) of oxygen, thus changing the
physical and chemical properties of the waste. Wastes are composed of