cycles, the removal of agriculturally usable nutrients
Essential Nutrients for Plants
from the “waste stream” makes sense and helps de-
Element
Common
Source
Available Form
velop more environmentally sound nutrient flows.
Needed in large amounts
• Promote consumption of locally produced
Carbon
CO2
atmosphere
foods by supporting local markets as well as return-
Oxygen
O
ing local food wastes to farmland. When people
2, H2O
atmosphere and soil pores
Hydrogen
H
purchase locally produced foods, there are more
2O
water in soil pores
–
+
possibilities for true nutrient cycling to occur. Some
Nitrogen
NO3 , NH4
soil
–
–2
community-supported agriculture (CSA) farms,
Phosphorus
H2PO4 , HPO4
soil
where subscriptions for produce are paid before
Potassium
K+
soil
the start of the growing season, encourage their
Calcium
Ca+2
soil
members to return produce waste to the farm for
Magnesium
Mg+2
soil
–2
composting, completing a true cycle.
Sulfur
SO4
soil
• Reduce exports of nutrients in farm products
Needed in small amounts
by adding animal enterprises to crop farms. The best
Iron
Fe+2, Fe+3
soil
way to reduce nutrient exports per acre, as well as to
Manganese
Mn+2
soil
make more use of forage legumes in rotations, is to
Copper
Cu+, Cu+2
soil
add an animal (especially a ruminant) enterprise to a
Zinc
Zn+2
soil
crop farm. Compared with selling crops, feeding crops
Boron
H3BO3
soil
to animals and exporting animal products result in
Molybdenum
MoO –2
4
soil
far fewer nutrients leaving the farm. (Keep in mind
Chlorine
Cl–
soil
that, on the other hand, raising animals with mainly
Cobalt
Co+2
soil
purchased feed overloads a farm with nutrients.)
Nickel
Ni+2
soil
• Bring animal densities in line with the land
Notes:
base of the farm. This can be accomplished by
1. Sodium (Na) is considered an essential element for some plants.
2. Although selenium (Se) is not considered an essential element for
renting or purchasing more land—to grow a higher
plants, it is essential for animals and so the Se content of plants is
percentage of animal feeds and for manure applica-
important for animal nutrition. On the other hand, plants growing on
high-Se soils (such as locoweed, asters, and saltbushes) accumulate
tion—or by limiting animal numbers.
enough Se to become toxic to grazing animals.
3. Silica (Si) is considered essential for the normal growth and health of rice.
better match between the timing of nutrient avail-
nutrIent MAnAGeMent GoALs
ability and crop needs.
• Satisfy crop nutrient requirements for yield and quality.
• Minimize pest pressure caused by excess N fertilizer
• Tap local nutrient sources by seeking local
or deficiency of nutrients.
sources of organic materials, such as leaves or grass
• Minimize the environmental and economic costs of
clippings from towns, aquatic weeds harvested from
supplying nutrients.
lakes, produce waste from markets and restaurants,
• Use local sources of nutrients whenever possible.
food processing wastes, and clean sewage sludges (see
• Get full nutrient value from fertility sources.
discussion on sewage sludge in chapter 9). Although
—MODIFIED FROM OMAFRA (1997)
some of these do not contribute to true nutrient
206
Building SoilS for Better CropS: SuStainaBle Soil ManageMent