Bay Journal

Call for complete ban on land application of manure is unfounded

  • By Chase Tanner on December 01, 2009

The October issue featured another commentary, on what the author, a professor, likes to call "animal waste disposal" and is another opportunity to advance the debate and bring us closer to real progress on the ground and in the water. (See "When it comes to animal waste disposal, cheap is costly," October 2009.)

In his opening paragraphs, the author concedes that grazing cattle can have a positive environmental impact, and that the pollution problems associated with agriculture stem from the concentration of large numbers of animals in a small area.

Yet he continues to call for a complete ban on the land application of manure, a move that would be just as detrimental to a cattleman with animal numbers in balance with the land base as to a crop farmer with access to a surplus of poultry litter. Further, it would result in an increase, not a decrease, in leaching and runoff from farm fields where manure is used scientifically and responsibly to build organic soil matter and improve soil health.

Let's take a closer look at the use of manure as a fertilizer.

The author asserts that the nutrients in "animal waste" are in organic forms that must be decomposed by microbes to be available for plant growth, and that is at least partially correct.

Sometimes a little knowledge is a dangerous thing.

Actually, manure contains both inorganic and organic forms of nitrogen. Both must be accounted for when calculating plant-available nitrogen to determine application rates.

It is only the inorganic portion that is available immediately after land application, not the 60 percent of the total nitrogen (for poultry manure) that is cited. The 60 percent figure comes from a first-year mineralization factor (This ranges from 10 percent for composted sludge to 60 percent for caged layers.) and is a prediction of how much of the organic nitrogen will gradually become available during the course of that first growing season in which the manure was applied.

Because the organic nitrogen that is unavailable to plants is also unavailable for leaching, it is not susceptible to being washed out of the soil before crop uptake as chemical fertilizers are.

In other words, manure is the slow, or time-release fertilizer that the author of the commentary wishes that chemists would invent. (They already have, but it's not as good as nature's original.)

The author then mistakenly suggests that the other 40 percent of the nitrogen is headed straight to the Bay. In fact, it is a percentage of the organic nitrogen, and will remain in the field to be mineralized in subsequent years, then become available for crop uptake.

We use the second-, third- and fourth-year mineralization factors to calculate nitrogen credits from past manure applications and reduce the nitrogen rates for crops accordingly.

For sludge, the use of which I oppose for other reasons, we are required, in Maryland at least, to calculate nitrogen contributions for 10 years.

As I explained in my previous response, (See "Throwing away manure is like throwing away money" July-August 2009.) the primary inefficiency concern with organic fertilizer sources is the oversupply of phosphorus.

This problem is overcome by treating phosphorus as the limiting nutrient in determining rates and using either legumes in the crop rotation or chemical fertilizer to supply the remainder of the nitrogen requirement.

It is true that microbial decomposition can continue after the main crop has finished growing, but it is also true that there will be excess nutrients remaining in the soil from chemical fertilization. That's why grass or wooded buffers and cover crops are important elements of nutrient management regardless of the fertilizer source.

Post-growing season nutrient transport does not occur instantaneously at the end of summer crop growth. It requires water movement and occurs primarily from January through March. If an aggressive winter annual is established by mid-autumn, it will do an excellent job of capturing and sequestering these potential pollutants.

As a grass-based livestock produer, I use manure to grow summer and winter annuals that will fill in the production slumps in my perennial pastures. In early September, I can cut a summer pasture with a disk and seed it to cool-season grass and clover.

The annual, though thinned out, will continued to grow and take up the last of those spring-applied nutrients until frost, even as the new seeding is putting its roots down and taking over. Not much potential for leaching runoff there.

Erosion, the other mechanism for nutrient loss, applies just as much to chemically fertilized fields as it does to organically fertilized ones. It is addressed by choosing crops, tillage and timing and application methods for nutrients that are appropriate to the soil type and field topography.

Perhaps the most curious and convoluted argument that I have ever heard against fertilization with manure is the author's assertion that farmers in a society that does a poor job of recycling aluminum shouldn't be worrying about recycling nutrients. By that logic, we shouldn't be allowing schools or businesses to recycle paper, either.

I for the record, do recycle aluminum. Also steel, paper, plastic, glass and used motor oil.

Two of manure's macronutrients-phosphorus and potassium-are just as nonrenewable as aluminum. All three are mined, and the author fails to address the environmental impacts of mining, manufacturing and transporting chemical fertilizers.

Are there times and places where manure is applied when it should be not? Yes, there are.

Do we need alternative options for this resource in areas of concentrated animal populations? We do.

But farmers are not the profit-driven environmental villains that the author portrays. The points I offer for consideration in this or my previous commentary, are not "manufactured excuses to justify anything. They are facts of soil science and agronomy.

If the Bay Journal's readers were also reading farm periodicals, they would find-along with countless stories of conservation initiatives-that across the board, farmers large and small, conventional and unconventional, share an interest in farm-produced energy ranging from solar and wind installations to methane digesters and home-brewed biodiesel.

If he would drop the anti-agriculture stance and put his efforts into crusading for his energy vision, which is good, instead of against a fertilization practice which is also good, the author wouldn't have so much resistance to worry about.

I don't know of anybody in the agricultural community who opposes the use of poultry manure, sewage sludge or any other biomass as a source of energy. So why can't we quit arguing and start burning?

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About Chase Tanner

Chase Tanner is a dairy grazier and Maryland certified nutrient management consultant.

Read more articles by Chase Tanner

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