Photo By Brandon Thibodeaux for The New York Times
Day and night, 24/7, a huge contraption prowls the grounds at Frank Volleman’s dairy in Central Texas. It has a 3,000-gallon tank with a heavy-duty vacuum pump and hoses... and underneath, adjustable blades that scrape the surface as it passes along.
In function it is something like a Zamboni used to smooth ice, but one that has crossed over to the "dark side". This is no hockey rink, and it’s not loose ice being scraped up. It’s cow manure.
Lots of cow manure. A typical lactating Holstein produces about 150 pounds of waste — by weight, about 2/3 wet feces, 1/3 urine — each day. Mr. Volleman has 3,000 lactating Holsteins and another 1,000 that are temporarily “dry.” Do the math: his Wildcat Dairy produces about 200 million pounds of manure every year!
Mr. Volleman, who came to Texas from his native Luxembourg 16 years ago, takes pride in his operation which produces about 25,000 gallons of milk a day. “It’s all about keeping it clean, keeping it comfortable and producing high quality milk,” he said, adding that what is good for his cows is good for him. “They’re writing my paycheck.”
Dairies differ from feedlots, poultry operations and hog farms in how they handle manure. At a feedlot, for example, manure is often collected only once every six months, after the thousands of fattened cattle have been shipped out. (Can't you just imagine how our foods get contaminated?) Dairy operators seem like neatniks by comparison, but even among dairies, manure management varies according to location, climate, regulations and other factors.
At a large operation like Mr. Volleman’s, it is the inexorability of excrement, as much as the sheer volume, that defines the waste-handling process. A cow’s digestive system, with its series of four stomachs, is built to handle lots of roughage. And you cannot turn it off.
So among the 40 employees at Wildcat Dairy are some whose main task is to handle the manure, 24 hours a day. They collect it from the huge open-sided barns, which house up to 1,200 cows each. The animals bed down in sand, but there are concrete alleys running the length of each barn for food, and others for excrement.
While the cows are at the rotary parlor — the stainless-steel merry-go-round of milking stalls that the Holsteins ride every eight hours around the clock — a worker on a tractor tows the tank-pump contraption up those manure alleys. The worker hops off the tractor as needed to rake solids in the bedding area into the alleys for collection.
When the tank is about half full, the worker drives it to a nearby patch of dirt, opens a valve and spreads — sprays, really — the manure out to dry. Twice a week, the solids are scraped into windrows and then spread on fields as fertilizer.
Even dried, manure contains a lot of water, so it is not economical to truck it very far — beyond about 10 miles, it is cheaper for a farmer to buy inorganic fertilizer. Some dairy producers compost their manure, making it more valuable as fertilizer, but composting costs time and money.
Mr. Volleman’s manure is spread only on his fields and those of nearby farmers. “We bring the manure to their fields, they spread it out to grow crops, we bring the crops back to feed the cows,” he said. “So it’s kind of a circle — a closed circle.”
When manure is mismanaged, the nutrients in it can foul streams, lakes and aquifers; the pathogens in it can contaminate food products; and the gases it produces, including ammonia, methane and bad-smelling volatile compounds, can upset the neighbors and pollute the atmosphere.
Even with best practices, manure can cause environmental headaches. So researchers are working on ways to improve manure handling, to modify the nutrients in it and to develop alternative uses.
Some dairy producers do compost their manure, making it more valuable as fertilizer, but composting costs time and money. One problem, said Robert T. Burns, a professor in the department of agricultural and biosystems engineering at Iowa State University, is that manure typically has more phosphorous than needed. “Manure is an unbalanced fertilizer from the plant’s view,” Dr. Burns said.
Diet modification can help, to some extent. Phosphorous is added to dairy feed as a supplement, and research has shown that it tends to be added in excess, said William P. Weiss, a professor in the animal sciences department at Ohio State University.
Nitrogen, on the other hand, comes from protein, and a lactating cow needs to consume a lot of protein. “Decrease it a bit, and then milk production falls off,” Dr. Weiss said.
With nitrogen, the problem is usually not that there is too much, but that much of it is eventually lost from the manure in the form of gaseous ammonia. The bacteria in feces contain an enzyme, urease, that breaks down the urea in urine into carbon dioxide and ammonia. As with phosphorous, diet can affect the amount of nitrogen retained in the manure.
As corn-based ethanol production has increased in the United States, many dairies and feedlots now give their animals a large amount of so-called distillers’ grains, the waste corn after fermentation, which is plentiful and cheap. (...and I wonder if there's still any nutrition in the grains after distilling?)
A recent study of feedlots in the Texas Panhandle, by scientists with the United States Department of Agriculture, showed that feeding a diet high in distillers’ grains produced significantly higher ammonia emissions from the manure.
There are several options in handling manure, but they are expensive. Even in a good economy, a dairy producer may be reluctant to add costs. And the industry is currently suffering — milk prices are low, producers are losing money and some are going out of business. “Given these times,” Dr. Mukhtar said, “there is really not a whole lot of incentive to do all that.”