Lynton Land's solution of eliminating animal waste on fields in his commentary, "Reduce nutrient pollution where it will be most meaningful: animal waste," [September 2010] plays fast and loose with basic facts concerning manure and nutrient use. His solution is unsustainable and would do tremendous harm to the Bay and our world.
Let me begin with the first erroneous assumption that fertilizer is less of a threat to the environment because it is more "plant available." A portion of animal manure in the urea/ammonia form is chemically identical to fertilizer. This amount varies 50-75 percent depending on the animal species and how the manure is handled. The remaining nitrogen is in the organic form, which is a controlled-release nitrogen - the solution suggested at the end of the article.
The biological processes that work on manure are no different than the processes that impact fertilizer. The only difference is that the nitrogen in the organic matter portion of manure is available over years rather than weeks. However, the in-season soil and tissue tests, along with the end-of-season stalk tests, allow us to manage manure-based nitrogen as well or better than fertilizer nitrogen.
The most unsustainable part of not land-applying manure is the massive amounts of commercial fertilizers that will need to be imported from Russia, Trinidad and other fertilizer-exporting countries.
Commercial fertilizer requires fossil fuels as its major input. Nitrogen is made from natural gas. Phosphorus is mostly mined from the earth. Both of these processes have major detrimental environmental consequences. Granted, they don't take place in the Bay watershed, but they do occur in somebody's watershed.
In addition to the manufacturing processes, the carbon footprint of shipping these bulky, explosive products from other parts of the world through our ports to distribution centers and then out to the remotest parts of our watershed where crops are grown consumes millions of gallons of fuel. That fuel consumption itself puts nitrogen and other compounds into our airshed.
Now add to that the fuel required to move and transform manure from the countryside to a place where it can somehow be rendered safe would also require tremendous amounts of fossil fuel. The carbon footprint and the environmental footprint of replacing manure with fertilizer is unacceptably high.
We often fail to realize that there is a nutrient cycle just like there is a water cycle. Water evaporates, falls as rain, replenishes our streams and groundwater, is used by humans and animals, and then evaporates. The cycle continues.
The nutrient cycle operates in a similar way. Plants take up nutrients. Some of those nutrients return to the soil, others are consumed by animals and humans. The animals and humans use what they need to survive and recycle the rest back to the soil to repeat the cycle.
That has been the cycle since the dawn of time until 80 years ago. At that time, we began to flush our nutrients out to sea and synthesize other nutrients from fossil fuels to replace them. This has created an unmanageable situation much like our desert cities have done with their water supply. This has resulted in excess nutrients piling up in our bays and estuaries.
Human and animal waste can only go to one of three places: our rivers, our land or our air. We should recognize the dangers of putting it in water. Putting it in the air is expensive, sometimes fuel intensive and has its own environmental consequences. Putting it on to the land where it can be recycled requires management, but is by far the best solution.
Sewage sludge, unfortunately, is often contaminated by industrial waste and is more of a challenge. However, the highest end use for animal manure is and will always be as a plant nutrient source.
Let's use our existing and developing technology to its greatest extent and use manure for its highest environmental useâ€¦as a crop nutrient.