Soil Fertility and Sustainability
It is no mystery where the plant nutrients are
coming from in the present agricultural system. Chemically synthesized
fertilizers provide two thirds of all nitrogen, phosphorus and potassium
required by U.S. crops. Over 160 pounds of fertilizer per person
is being used and the amount has doubled in the last twenty years.
The nitrogen in chemical fertilizer is produced
using natural gas and a lot of energy. It is the same process
used to make explosives. After
World War II plants which made explosives were converted to making nitrogen
fertilizer. The Oklahoma City bombing is a grim reminder of this
The phosphorus comes from rock phosphate deposits
which is then treated with acid to make it more soluble. Untreated
rock phosphate is used as an organic fertilizer.
Is this system sustainable? Estimates are that
the natural gas supply in the U.S. will last around 50 years. For rock
phosphate the estimates are 100-200 years. So it is not sustainable
for the measure of time.
Another measure of sustainability is what environmental
damage is done. Nitrates
contaminate ground water. One study found four times more nitrate
ground water pollution in farm land compared to forest land. Phosphorus
pollution in rivers and lakes causes algae blooms and fish kills. So
it is not sustainable for the measure of environmental damage.
How will soil fertility be maintained in a sustainable agriculture system?
REDUCE WASTE. It is estimated that in the Midwest a third of the
nitrogen fertilizer is wasted and that 5-10% of all chemical nitrogen
is lost to the atmosphere when applied. Studies done by members
of Innovative Farmers of Ohio have shown that by fine tuning fertilizer
applications using mid-season nitrate tissue tests waste can be greatly
USE ALL ORGANIC WASTES. JB King in the classic
book, Farmers of Forty Centuries, told how the Chinese maintained soil
fertility by extensive use of all organic wastes, including human. The "honey
through the streets at night collecting "night soil" to the
taken directly to the farm. Not very hygienic by today's standards
but it kept their fields fertilized.
Any sustainable farming system would require nutrient cycling of all
organic matter at both the farm and regional level.
Could farm animal manure replace all the chemical
fertilizer used today? Long
term studies done on corn at Morrow Experiential Station in Illinois
since 1888 and on wheat at Rothammsted in England since 1852 show that
manure can maintain soil fertility and crop yields.
But would there be enough if all farms were to
depend on manure. One
study found that in 1987 174 million tons of manure were produced and
that this provided 6% of the nitrogen, 18% of the phosphorus and 36%
of the potassium required by all crops grown at that time. Clearly
manure could not provide all crop nutrient needs alone.
The present system has removed farm animals from
the land which produces their feed. Large factory farm confinement
operations concentrate animals and their manure in a small area causing
health and pollution problems. With the manure concentrated in
a few places it is difficult to redistribute it to fertilize enough farms. This
system has turned valuable fertilizer into a waste disposal problem.
Farm animals need to be returned to the farms where their manure can
fertilize the crops.
Sewage sludge is another organic waste that should
be used in a sustainable system. An average of 70 pounds per person per year is produced. It
contains around 3% of the nitrogen, 9% of the phosphorus and .7% of the
potassium required in any year. Of course the problem is toxics
in the sludge. Toxic products should be eliminated from the waste
stream so that sludge can be safely returned to the land.
Garbage should also be returned to the land. Over 4 pounds
are produced per person per day and 80% of it is organic. All organic
garbage should be composted and returned to the soil.
On farm crop residues are usually being returned to the soil and provide
significant amounts of fertility - 24% of the nitrogen, 13% of the phosphorus
and 36% of the potassium by one estimate.
But even if all organic wastes were being returned to the soil other
sources of crop nutrients would be needed.