Agriculture Reference
In-Depth Information
were nutrient surpluses generated by both systems, they were one-tenth
as high for phosphorus and potassium, and one-third as high for nitrogen
on organic dairies. The need for nitrogen fertilization can be reduced by
including nitrogen-fi xing legumes, but bloat-causing legumes such as the
Trifolium
(true) clovers are limited to no more than 50% of mixtures. Ben-
brook [9] estimated that in 2008, due to the organic dairy industry alone,
40 million pounds of synthetic nitrogen was not applied to land designated
for certifi ed organic use. Integrating livestock and cropping enterprises
on a single farm not only spreads economic risk, but can improve the ef-
fi ciency of nutrient cycling. Mixed crop-livestock systems such as dairies
that grow their own conserved feed for winter, have been shown to mini-
mize inputs due to synergies between components, specifi cally fertilizer,
putting them at lower risk for nitrogen pollution than other systems [30].
It is well accepted that legume-based systems can reduce nitrogen losses
associated with cropping [31] and grazing [32]; therefore, organic produc-
ers utilizing mixtures of grass and legume forage species are able to take
advantage of naturally occurring nitrogen fi xation.
4.2.2 SOIL ORGANIC MATTER
A number of soil factors can influence forage plant growth and nutrient
acquisition, which becomes more critical as the proportion of forages in
a ruminant's diet increases. If soil bulk density is excessive, plant root
growth will be negatively affected, and if soil becomes dry, the dissolution
and movement of nutrient ions in the soil solution will be restricted. The
pH of the soil can also affect the availability of nutrients, some to toxic
levels when soils become very acidic, and the proliferation of soil mi-
crobes, including those involved with legumes in nitrogen fixation. While
high plant productivity can be achieved on unhealthy soils through the
additional of high levels of fertilizer, long-term soil health is a goal of or-
ganic agricultural systems because these ―conventionalǁ options are not
available in organic systems [31].
A healthy soil is a soil with an optimal pH, aeration, and nutrient- and
water-holding capacity considering the parent material, plant community
and climate under which it was formed. A healthy agricultural soil is one
