It should be fairly easy to balance inflows and out-
flows on crop farms, at least theoretically. In practice,
under good management, nutrients are depleted a bit
farm-grown crops
by crop growth and removal until soil test levels fall
too low, and then they’re raised again with fertilizers or
fertilizers
crops
crop residues
and lime
leaching,
manures (see chapter 21).
runoff, and
A grass-fed beef operation that uses little to no
volatilization
imported feed should also be able to easily balance
soil
imports and exports because few nutrients leave the
farm (as animals) and few nutrients are brought on to
a) vegetable or agronomic crop farm
the farm (figure 7.2b). Most of the nutrients on this type
of operation complete a true cycle on the farm—they are
pasture
taken up from the soil by plants, which are eaten by the
animals, and most of the nutrients are then returned
lime, small
meat
quantity of
to the soil as manure and urine. The same type of flows
manure
leaching,
fertilizers,
runoff, and
will occur on all integrated crop and livestock farms that
mineral
volatilization
supplements
produce all of their own feed.
soil
A contrasting situation occurs on dairy farms if all of
the forage is produced on the farm but grains and miner-
b) grass-fed beef operation or other type of
als are purchased (figure 7.2c). Many dairy farms in the
integrated crop-livestock farm
northeast U.S. do not have the land base to grow all the
needed feed and tend to emphasize growing forage crops.
farm-grown crops
In this situation, there are more sources of nutrients
coming onto the farm—with concentrates (commonly
milk and
feeds and
meat
mixtures containing corn grain and soy) and minerals
minerals,
crop residues
bedding,
and manure
leaching,
usually comprising a larger source of nutrient inputs
fertilizers
runoff, and
volatilization
than fertilizers. In a study of forty-seven New York state
and lime
dairy farms an average 76% of N came onto the farms as
soil
feeds and 23% as fertilizers. The percentages were pretty
c) dairy farm
much the same for P (73% as feeds and 26% as fertiliz-
ers). Most of the nutrients consumed by animals end up
Figure 7.2. Nutrient flows and cycles on (a) crop farm, (b) grass-fed beef in the manure—from 60% to over 90% of the nitrogen,
or other integrated crop-livestock farm, and (c) dairy farm.
phosphorus, and potassium. Compared with crop farms,
where a high percent of the crop grown is sold, fewer
put it another way, these farms have an inadequate land
nutrients flow from dairy farms per acre. Under this
base to produce all their feed and therefore also have an
situation, nutrients will accumulate on the farm and may
inadequate land base on which to apply their manure
eventually cause environmental harm from excess nitro-
at environmentally safe rates. Animal operations that
gen or phosphorus. This same problem exists for any ani-
import all feeds and have a limited land base to use the
mal farm that imports a high percentage of its feed. To
manure have the greatest potential to accumulate high
71
Building SoilS for Better CropS: SuStainaBle Soil ManageMent