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What is Sustainable?
(Page 3 of 4)
By Ed Perkins

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 close connection.

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 reduced.

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 wagons" rolled 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.