Agriculture Reference
In-Depth Information
As a fourth manure-handling option,
equipment was added to the manure applicator
to inject the manure below the soil surface.
Subsurface injection can reduce gaseous emissions
and the surface runoff of nutrients (Rotz
et al
.,
2011c). Use of this practice on this farm reduced
field emission of ammonia by 97%, which
reduced the total farm emission by about 50%
(Table 10.2). Nitrate leaching and denitrifica-
tion losses were increased though, so the total
loss of reactive N was reduced about 20%.
Placing the manure below the surface reduced P
runoff by 16%. Greenhouse gas emissions and
the carbon footprint were not affected by this
added operation, but the energy use was
increased slightly due to the additional time and
power needed to inject the manure. With the
cropping strategy used on this farm (abundance
of N available through legume fixation by the
lucerne), there was little economic benefit
received through more efficient N use. The
increased cost of the injection equipment and
the added fuel and labour required reduced farm
profit an additional US$32 per cow.
As illustrated through these simulations,
changes in manure-handling practices can be
made to reduce nutrient, particularly N, loss to
the environment. Reduced ammonia emissions
can be beneficial in improving air quality, but if
changes in the cropping strategy are not made to
improve the utilization of the retained N, greater
losses through nitrate leaching and denitrifica-
tion will occur. Changes in manure-handling
practices often come at a cost to the producer,
reducing farm profit. Therefore, there is little
incentive for producers to make these changes
unless they are reimbursed through increased
prices or other societal payments.
rates. For the final 4 months, growing cattle were
finished on a high grain diet. Throughout the
year, cows and replacement heifers were main-
tained on pasture and harvested forage with
most of the manure deposited directly on pasture
land. During the finishing period, cattle were
maintained in a bedded barn with that manure
applied to cropland in the spring and autumn.
For the first cropping option, the land base
consisted of 80 ha of perennial grassland and
50 ha of maize. The maize land was tilled with a
mouldboard plough followed by a series of con-
ventional tillage operations to prepare the soil
for planting. About two-thirds of the maize was
harvested and fed as maize silage. Controlled
grazing was not used, which affected both yield
and nutritive content of the pasture forage.
Animals maintained on pasture obtained about
60% of their feed from grazing with the remain-
der from maize silage. With this tillage practice
on this sloping terrain, the erosion of sediment
and loss of sediment-bound P were very high
(Table 10.3).
As a second option, a no-till strategy was
used for establishing maize, i.e. all maize was
planted using a zone till planter with no other
tillage operations. All other aspects of the farm
remained the same except for increased use of
pesticides for weed and insect control. The
reduced tillage provided a large decrease in ero-
sion and P runoff with very minor effects on N
losses and greenhouse gas emissions (Table
10.3). With fewer tillage operations, energy use
in the production system was reduced 3% and
this provided a very small reduction in the car-
bon footprint. The reduced cost for tillage opera-
tions was partially offset by increased pesticide
costs leaving an increase in annual farm profit
of US$37 per cow.
For a third option, a winter cover crop was
used following maize silage harvest. Annual rye
was established soon after harvest in late sum-
mer to maintain ground cover over the winter.
In the spring, the crop was killed prior to spring
planting of maize. During the spring and sum-
mer, degradation of the crop residue returned
nutrients back to the soil for use by the growing
maize crop. The additional soil cover reduced the
erosion of sediment an additional 30%, and the
cover crop uptake and turnover of N reduced
nitrate leaching by 10% (Table 10.3). Gaseous
emissions were not affected by this change in
Crop management
To illustrate the effects of crop management,
a beef farm was simulated in southern
Pennsylvania. The herd consisted of 150 Angus
cows and their offspring including 40 replace-
ment heifers and 100 growing cattle. The land
base was 130 ha of loam soil with a sloping
terrain. Calves were weaned at 7 months of age
and maintained as stocker cattle for 5 months.
During these periods, animals were fed pasture
or other forage to maintain appropriate growth
