Soil Management Handbook - Ministry of Agriculture and Lands

5. Animal Manure Management
The purpose of this section is to describe manure
management options that are environmentally sound
and which comply with existing environmental laws,
i.e., the Code of Agricultural Practice for Waste
Management. There is a series of environmental
guidelines that were written to support the Code, and
other legislation, and to provide industry with various
options for managing their farms in an
environmentally sound manner. A copy of the Code
and commodity oriented guidelines are available from
the Resource Management Branch, BCMAFF,
Abbotsford. Animal manures are a valuable source of
plant nutrients and organic matter and contain a vast
array of organisms that add to the biological activity
of soils. However, if not managed with sufficient
care, manures can be major sources of pollution and
contribute to contamination of surface and ground
waters.
5.1 Managing Manures for Crop Production
Management is the key to using manures to promote
crop production and soil improvement while
minimizing any hazard to the environment.
Management means application of manures at rates
and times of year that:
• are compatible with the nutrient requirements and
growing characteristics of the crop;
• take into account soil characteristics, drainage
and the slope of the land; and
• recognize the presence of surface and ground
waters.
Table 18 provides a general indication of the nutrient
contents of various manures. Note that the moisture
content of manures varies considerably. These values
must be adjusted accordingly before they can be used
as a guide to adjust fertilization rates.
5.2 Factors Affecting Contamination from
Manures
5.2.1 Soil Characteristics
The proportion of sand, silt, clay and organic matter
in a soil determine the water and nutrient-holding
capacity. In general, soils with a high clay and/or
organic matter content have a relatively high capacity
to hold water and nutrients in the root zone. Sandy
soils, on the other hand, have a low capacity.
Therefore, the leaching of nutrients from sandy soils
is greater rate than from fine-textured soils or soils
with a high level of organic matter.
5.2.2 Drainage
When poorly drained soils become saturated,
precipitation can no longer enter the soil and,
therefore, water accumulates on the soil surface and
eventually runs off into adjacent ditches or other
water courses. When this happens, materials, such as
manures, that have been applied to the soil surface are
removed with the water.
5.2.3 Slope
If water does not infiltrate into soils on sloping land, it
must run off. If such lands also become saturated,
runoff is even greater.
5.2.4 Nitrates in the Root Zone
The nitrate form of nitrogen is of major concern in the
region due to its potential to contaminate drinking
water and increase the nutrient content of lakes and
streams. Nitrate is also the dominant form of plant
available nitrogen found in agricultural soils. When
nitrate-nitrogen (NO3-N) in the root zone is exposed
to excessive rainfall or irrigation, it can leach into
ground water. Unlike coastal regions of B.C., NO3-N
leaching in the interior is commonly associated with
over use of fertilizers, manures in conjunction with
irrigation and porous soils. Where soils are over
ground waters used for drinking or adjacent to surface
waters, the nitrate has a high potential of contributing
to water contamination.
Excessive levels of root zone nitrates are found in
soils where the spring application rates of manure and
fertilizer have been high in relation to the ability of
the crop to use the nitrogen, or in soils where there
has been a fall application of manure after harvest.
Soil Management Handbook – Okanagan-Similkameen Valleys 79