Agriculture Reference
In-Depth Information
These manures are typically transported by truck
and directly land applied, stacked for storage, or
composted. Slurry manure is typically generated
where little bedding is added to the excreted
manure/urine. The simplest manure collection
arrangement is slotted or perforated flooring over
a collection tank. Slurry manure can also be col-
lected using scrapers or vacuums. Slurry is usu-
ally pumped and stored or treated, in some cases it
is directly land applied. Liquid manures generally
result from the addition of washwater or rainwa-
ter to manure. Flush systems are common where
manure is flushed from the confinement building
using either fresh or recycled water. Runoff from
lot surfaces can be treated and stored in holding
ponds. In most cases, the liquid is blended with
clean water and used as irrigation water.
The characteristics of the manures col-
lected in these systems will vary with species
and production system and determine the
nutrient value of the manure, the potential for
gaseous emissions, the potential for energy
generation, and the extent of treatment/pro-
cessing needed to transform the manure into
value added products. Tables 7.1 and 7.2 pro-
vide some manure characteristics as excreted
by livestock and poultry, while Table 7.3 pro-
vides 'as removed' manure characteristics for
the main livestock and poultry groups. It is
important to remember that these values can
change greatly based on animal feeding (see
Chapter 6, this volume) and manure handling
and storage. As demonstrated in these tables,
manures contain valuable nutrients that can
be recycled in the crop-animal system and sol-
ids that can be converted to energy and other
valuable manure by-products.
longer term, manure can substantially augment
soil organic matter and soil structural properties
that stabilize aggregates, increase water-holding
capacity and improve rainfall infiltration. Despite
these benefits, land application of manure can
result in adverse impacts, many of little immedi-
ate concern to crop production, which compli-
cate land application and must be considered in
devising sustainable manure management strat-
egies. Westerman and Bicudo (2005) listed eight
challenges for integration of manures into agri-
cultural production, which included:
•
Regional imbalances of nutrients (e.g. not
enough land on the farm to apply nutrients
produced by animals on the farm);
•
Imbalances of nutrients in manure com-
pared with crop needs;
•
The relatively low nutrient concentration
compared with chemical fertilizers;
•
The variability in nutrient content, difficulty
in quickly determining nutrient content,
and predicting the availability of nutrients
to growing crops;
•
The often bulky nature of manures making it
more difficult to haul and spread consistently;
•
Possible transfer of weed seed;
•
Satisfying environmental regulations on
application amounts, application timing,
and application methods; and
•
Possible environmental concerns, such as
emission of ammonia (NH
3
) and green-
house gases (GHG), odour, pathogens and
pharmaceutically active compounds (PAC).
Given these concerns and the growing
regulatory and paperwork burden of land-
applying manure in many areas of the developed
world, manure's value can readily turn from an
agronomic resource to a perceived liability
(Kleinman
et al
., 2012). Manure's bulky nature,
heterogeneous nutrient forms, concentrations
and ratios and adverse qualities (e.g. weed seed,
odour, pathogens) make manures imperfect fer-
tilizer substitutes. As a result, pound for pound,
manure nutrients are more costly to transport
than commercial fertilizers, often making the
economic value of manure greatest near the
point of generation, i.e. the livestock barn.
Land application of manure for crop produc-
tion involves an array of potential environmental
and human health concerns, the latter of which
are discussed in greater detail below. Sustainable
Land Application of Manures for
Crop Production
Land application of manure to support on- and
off-farm crop production is common worldwide
and a fundamental attribute of sustainable
manure management systems. The positive
contributions of manure to soil fertility and soil
tilth are well established (e.g. Williams and
Cook, 1961; Bationo and Mokwunye, 1991).
Crop response to recent application of manure is
generally positive, with yields stimulated by
macro- and micronutrients in manure. Over the
