For general farms that keep livestock as well as plant field and/or row crops manure isn't a problem, it's an asset that can be recycled to the fields to great benefit. It's more common to specialize, to either keep livestock or plant crops but not both, and confinement feeding has largely replaced free range finishing.

Manure has become more of a problem than an asset. One way to deal with it is to install systems that process the manure to yield methane fuel. But is this a smart thing to do? Some say not.

TALK of reducing our dependence on foreign oil through alternative energy sources like biomass is everywhere these days — even on our president's lips. As a livestock farmer and environmental lawyer, I've paid particular attention to discussion about using manure as "green power." The idea sounds appealing, but power from manure turns out to be a poor source of energy. Unlike solar or wind, it can create more environmental problems than it solves. And it ends up subsidizing large agribusiness. That's why energy from manure should really be considered a form of "brown power." . .

Government officials tout such projects as energy generation that benefits both nature and agriculture, and are pouring public funds into them. Few seem to question whether the projects make economic or environmental sense. And there are plenty of questions that need to be addressed. For starters, manure simply does not contain enough energy to produce cost-effective power. Studies show that manure power projects are probably not viable without large public subsidies and are likely to remain so. An analysis by researchers at the University of Minnesota's Applied Economics Department found that methane digesters are dependent on big subsidies to break even. Electrical rates would have to double to pay the full cost of digesters, says Jeff Lorimor, an Iowa State University agricultural engineering professor. Electricity from manure-burning incinerators is also much more expensive than other power, requiring federal and state subsidies to make it competitive with other sources, according to the Institute for Local Self-Reliance. . .

Even manure power projects' immediate environmental benefits are dubious. Digesters, for example, don't make the manure disappear; instead, a manure slurry (which is sometimes larger than the original volume of manure) is left over and still has to be stored somewhere. Moreover, the slurry contains most of manure's original pollutants, researchers note. In other words, what comes out of a digester may be a bigger problem than what went in.

Methane digesters also fail to abate most environmental damage caused by concentrated animal operations, according to the Sierra Club. Farms with digesters still generally use large manure storage ponds, the main source of pollution problems. Incinerators, meanwhile, destroy the valuable components of manure and raise the specter of air emissions. While it's a nuisance on factory farms, manure as it is used on traditional farms greatly benefits soil fertility and tilth, increasing water-holding capacity, reducing wind erosion, improving aeration and promoting beneficial organisms. But many of these benefits are lost in burning. "Incineration destroys the nitrogen and organic material content of manure," reports the Institute for Local Self-Reliance. The institute has calculated that "an electricity plant that burns 500,000 tons of manure in effect destroys $3 million in nitrogen."

Ouch. It seems that manure energy systems are pataphysical devices that accomplish little but do it in convoluted ways, and are only attractive because of the subsidies. Not all agree of course. The UN FAO is a booster but emphasizes the value of the slurry.

Economic evaluation studies have shown the importance of using the digested slurry after the anaerobic digestion process, as well as the biogas. . . The economic importance of the digested slurry is becoming more acceptable in recent years in the Developing Countries as well, and this concept is presented in many publications of China, India and other countries. What follows is a summary of some of the commoner uses of the digested slurry, and the main research done in this topic, with the economic emphasis on its uses.

The slurry discharged from a digester contains 1 - 12% solids and consists of refractory organics, new cells formed during digestion, and ash. The slurry can be used in its liquid or solid fractions, dried or as total slurry.

Components of slurry which provide fertilizer and soil conditioner properties are soluble nutrients and trace elements, insoluble nutrients, and the organics present in the solids (humic materials). The components of a specific digested material are similar in content, despite other differences, to the raw material used for the digestion process, and must be examined according to the original materials uses and value.

Like the NYT article the FAO report considers the value of the nitrogen in manure and notes that digesters don't destroy the nitrogen the way burning does. But it goes into more detail about how much nitrogen there is and what it takes to benefit from it. In an earlier post, Horse Puckey, I poo-pooed the idea.

Manure isn't a useful source of nitrogen for crops. There is a small amount of nitrogen in it, but little of that small amount is in a mineralized, plant available, form. Worse, it is already spoken for by the bacteria that have the job of decomposing the manure - composting it in effect - to recycle it back to soil. Putting manure on your fields reduces available nitrogen and retards plant growth. There is a small net benefit after time has passed and all the workers have done their jobs to release and reform the organic nitrogen, but it is a mistake to equate manure with fertilizer.

The FAO report dances around the subject a bit but when you read between the lines it is in substantial agreement. Yet fields do improve from manure. They aren't sure why.

The nitrogen present in inorganic fertilizers is assumed to be potentially 100% available to plant=. For comparative purposes, the availability of nitrogen in organic manures i" assumed to range from 25% (e.g. Idnani and Varadarajan 1974) to 100%. Both inorganic fertilizers and organic manures often contain plant nutrients in addition to nitrogen, and organic manures provide important soil conditioning factors. . .

The application of digested sludge over a period of years has led to a continuous increase in crop production (Marchaim 1983 and others). This may be due to the effect of slow release nitrogen compounds and improved soil structure.

The vast majority of nitrogen in manure is in the form of organic proteins and amino acids. Plants can't use these molecules as nitrogen sources, they need mineral nitrogen, either nitrate or ammonium. It is misleading to even mention the organic nitrogen since it takes mineral nitrogen to convert organic nitrogen to mineral form. There is some mineral nitrogen in fresh manure, very fresh manure, but it soon evaporates since it is in the form of urea which bacteria rapidly convert to ammonia gas, which escapes into the air.

But fields do improve. The other nutrients such as phosphorous and potassium in manure have real value, and more importantly the organic matter in manure helps keep mineral nitrogen from leaching out of the root zone by increasing soils tilth and its ability to hold water. The problem is that soil bacteria convert everything to nitrate, NO3, which is repelled by clay colloids and organic matter since they have the same polarity. Ammonium has the opposite polarity and sticks, but bacteria quickly convert it to nitrate. Since the nitrates remain dissolved in soil moisture it is easily available to plants, but also can wash away. Soil that holds water better retards leaching. In time bacteria will convert the proteins and amino acids of organic matter to ammonium, and then nitrate, which can be used by plants. It's not much but it's time release so to speak and so is less subject to leaching.

Too much manure, too often, kills soil. It has salts in it that accumulate over time and slowly creates an environment hostile to plants. This is less of a problem with high rain fall to leach the salts out, but it leaches the nitrogen and phosphorous too. There's no way to win with manure.

If only there was some magic way to hold nitrates in soil so that they didn't leach away. But wait - isn't that what bio-char can do?

Applying the knowledge of terra preta to contemporary soil management also can reduce environmental pollution by decreasing the amount of fertilizer needed, because the bio-char helps retain nitrogen in the soil as well as higher levels of plant-available phosphorus, calcium, sulfur and organic matter.

There's even a scheme to produce nitrogen enriched bio-char as a combined soil amendment and fertilizer. The nitrogen won't leach out since it requires enzymes produced by bacteria to free it from the bio-char, but the bacteria get their nourishment from plant root hairs. The nitrogen is only freed when there are plants to use it.

It's complicated, especially when you add nitrogen fixing bacteria and denitrifying bacteria into the cycle. Some bacteria turn atmospheric nitrogen into mineral forms that plants can use, and others do the reverse. It's easy to see why soil tests can be misleading - available nitrogen is continuously changing and if time passes between the soil test and soil amendment conditions will have changed too. Plus, adding mineral nitrogen to soil can cause a bacterial bloom and speed up the decomposition of organic matter, changing the whole equation.

There's an old saying that the best fertilizer is a farmer's footprints. Continuous monitoring and insightful response by someone intimately familiar with the terrain can at least partially compensate for the dynamic nature of soil nutrient levels. We may soon have sensor networks that help with this chore and allow a skilled farmer to manage more land, but for now someone just has to pay attention, in person, and understand what he sees as well as know how to respond.