Animals in Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 280

TA B L E 1 9 . 1
Benefits of Integrating Livestock into a Crop Production Agroecosystem

Aspect of Integrated System Ecological Effects Agricultural Benefits

Including grazed forages in crop rotation,
especially perennial species

Higher diversity
Greater soil microbial activity
Maintenance of soil coverage
Less frequent disturbance; pioneer
(weedy) species not encouraged
Provision of habitat for natural pest
control agents

Soil organic matter allowed to increase
Soil not exposed to erosion
Reduction in weed pressure
Improved performance of subsequent crops
Elimination or reduction of need for biocides
Better retention of soil nutrients

Feeding marketed livestock on feedstuffs
produced in the same system

Cyclical (vs. linear) nutrient flows
Less nutrient export

Reduction in dependence on purchased inputs
Enterprise diversification
Opportunities for productive use of crop wastes

Using livestock manure as a nutrient source
instead of inorganic fertilizer

Improvement of soil structure
Higher soil biodiversity and microbial
activity
Better nitrogen cycling

Reduction in dependence on purchased inputs
Improvement of soil organic matter content
Higher crop yields

Using livestock for vegetation and weed
management

Mimics natural-system role of herbivores Elimination or reduction of need for biocides

Reduction in manual human labor

barley straw serve as supplemental feed for a range of
animals in many agroecosystems around the world, with
the greatest energy efficiency achieved when the site of
straw production is as close as possible to the consuming
animals. Allowing the animals to directly graze the straw
remaining in the field is probably the most efficient
method, although straw can be cut and hauled to a storage
area in order to feed the animals when they are confined.
In California, where intensive vegetable production is
so common, many crops produce residues that are used to
supplement animal grazing or forage, such as culled Brus-
sels sprouts, waste tomatoes, and carrot pulp after juice
extraction. Pigs are excellent transformers of food and
crop waste in many rural small-farm systems in the devel-
oping world. Since the animals in this case are not actually
in the fields where the vegetable crops are raised, the
manure the animals produce must be returned to the crop
fields.

manure and urine produced in large-scale livestock con-
finement systems have already been discussed in Chapter
1. Integrated livestock-cropping systems — in which for-
age is grown on the farm, fields are rotated between grazed
forage and crops, and crop residues are incorporated into
animal feed — can greatly increase the efficiency of
manure and compost management. A study carried out in
Denmark (Dalgaard et al., 2002) showed that a farm con-
verted to mixed dairy and pig production, using an array
of grain crops for harvest and grass and legume forage
species for animal feed, could obtain total self sufficiency
in animal fodder while reducing nitrogen contamination
of local ground water systems to very low levels as
compared to conventional systems and organic livestock
operations more dependent on imported feed.

Improving Soil Health

The key component of a healthy soil is soil organic matter.
Many factors, organisms, and interactions drive organic
matter quantity and quality, with soil health manifested in
tilth, structure, water holding capacity, and resistance to
both compaction and erosion. Long-term cultivation gen-
erally leads to the breakdown of soil organic matter, with
accompanying degradation of the indicators of soil health.
However, bringing livestock into the cropping system in
the form of a rotated grazed forage not only reduces the
need for cultivation, but it also adds nutrient- and energy-
rich organic matter. Soil microbial activity increases, soil
structure improves, and nutrient retention and availability
favor better crop development. In some regions, especially
the Midwestern areas of the U.S. and Canada, the inclu-
sion of a perennial forage in cropping system rotations,
with its accompanying respite from the negative impacts

Returning Nutrients to the Soil in Manure
and Compost

Plants contain nutrients that they have taken up from the
soil, and through their consumption in plant biomass,
digestion, and deposition as manure, the nutrients are
cycled back to the soil. Depending on the farming system,
the manure can be collected, composted, and applied at
any location on the farm where it is needed most. Return-
ing manure to the soil is an important way to put both
nutrients and organic matter back into the soil ecosystem
(Chapter 8), as well as to reduce the need to import these
materials from outside the farm operation.
The ecological and economic efficiencies of trying to
import to cropping systems the massive amounts of