Soil - Agroecology: The Ecology of Sustainable Food Systems - page 109

after three years, probably because the lower C/N ratio of
the incorporated organic matter caused more rapid micro-
bial breakdown.
A more recent innovation in the cover-cropping
approach is the use of a living mulch, where a noncrop
species is planted between the rows of the crop during the
cropping cycle. Living mulches have become especially
popular in vineyard, orchard, and tree crop systems.
Research has focused on ways of minimizing negative
interactions between cover crop and crop species, espe-
cially living mulches in annual crops. Studies are also
finding that living mulches can provide and conserve
nitrogen for grain crops, reduce soil erosion, reduce weed
pressure, and increase soil organic matter content
(Hartwig and Ammon, 2002).

nutrients for crop growth (Seiter and Horwath, 2004).
Dairies and feedlot operations produce large amounts
of animal wastes that are converted to a useful resource
when returned to fields, but as we have already noted in
Chapter 1, there are many problems involved in contain-
ing, storing, transporting, and applying such large quan-
tities of animal manures. Small, integrated farm operations
can more easily use animal manures that accumulate in
stables or pens for intensive vegetable production or use
on other crops (Chapter 19). The use of silkworm drop-
pings in Chinese agriculture is yet another example of the
use of animal manures.
At any scale, the direct application of animal manures
can have many drawbacks, however. Smell and flies are
often associated with direct manure application. Nitrogen
loss through ammonification can be quite high. Runoff of
nitrates and other soluble materials can be a problem.
And once fresh manures are incorporated into the soil,
there often is a waiting period for decomposition and
stabilization before planting can take place. To avoid these
problems, current organic certification standards in the
U.S. require that fresh or raw animal manures be com-
posted under specific conditions before they are applied
(Figure 8.6).

Manure

It is a long-standing practice, both in conventional and in
alternative farming systems, to add animal manures to the
soil to improve organic matter content. The application of
animal manure is an important tool for an integrated
nutrient management strategy because applications can
simultaneously increase soil organic matter and supply

FIGURE 8.6 Manure spreader used on a dairy farm near Cody, Wyoming. Aged manure is returned to fields in which feed is
grown for the farm's dairy cows.