NATURAL FILTERS for feedlot waste water, duckweed and hyacinths can also be harvested as an alternative source of feed, based on recent research in the Lubbock area.

Weeds Help Treat Feedlot Waste,
Then Provide Feed For Cattle

LUBBOCK — With the total capacity of cattle feedlots in Texas inching closer to eight million head this year and environmental concerns becoming a serious threat, waste treatment and disposal has become an increasingly difficult task.

However, researchers at a demonstration site near Lubbock looking into new and innovative ways of dealing with large amounts of cattle waste may have found an answer to waste disposal. In addition, they may have also found an alternative protein source for livestock feed.

Funded by the Texas State Soil and Water Conservation Board through the U.S. Environmental Protection Agency' s 3 l9(h) program, the project found that growing duckweed or other macrophytes in wastewater holding pits from confined animal feeding operations assists in filtering the waste while serving as an alternative livestock feed.

Dr. Clifford Fedler, Texas Tech professor of civil engineering, said the whole idea of the demonstration stemmed from nonpoint source pollution. It was based on a pond where wastewater flowed by gravity into a lagoon. The wastes were pumped directly from a nearby 1000-head feedlot into a pit in the center of the lagoon, where anaerobic (without oxygen) breakdown of the organic materials takes place.

The pit is designed to protect the solid waste from any oxygenation. The anaerobic pit keeps the pH levels low, enabling the anaerobic microorganisms to digest the waste materials.

Next, the water overflows into the lagoon area surrounding the pit, where aerobic breakdown of the matter further cleans it. This area, known as the facultative pond, produces enzymes that break down the waste's carbon chains, which make up the solid material.

"The pit in the center allows solid material to stay without any turnover or disturbance due to outside weather," Fedler explained. "Then it comes up to the outer portion of the pit, where we use aerobic treatment, which is why it is called an integrated facultative pond. We combine aerobic and anaerobic breakdown in one area."

The overflow then runs into a second pond where knotgrass, duckweed and other species of macrophytes utilize the nutrients for growth. These aquatic plants serve as a filter as they feed off organic matter by utilizing the nitrogen and carbon dioxide.

From there the water can be used in irrigation systems or released to the watershed for replenishment of the Ogallala Aquifer. The plants used in the second pond thrive under the waste conditions. Each plant being grown under the wastewater conditions has been considered as a valuable livestock feeding substitute.

Duckweed, Wolffia, hyacinths and knotgrass have been explored as filtering and feeding options for operations. The different grasses are being looked at to provide alternatives for various producers.

"We are coming up with a lot of different options because each producer has their own idea of how they want something to run," Fedler said. He said the project, which was piloted to demonstrate of a way to reduce feedlot NPS pollution, has shown that the economic liability of wastewater can produce valuable by-products to offset installation costs.

Fedler said aquatic plants break down the organic matter by feeding off of the nitrates and other nutrients. They are also an excellent source of protein for cattle, swine and sheep.

Duckweed, in particular, tested about 30 percent protein as opposed to l0 or 15 percent in normal forage diets, but Fedler said the aquatic plant's protein can be as high as 40 percent.

"When we put duckweed into the cattle diet, they gained as good or better than the cattle on a control diet," said Fedler. He went on to say that the maximum rate of growth appeared when the diet consisted of 11 to 13 percent duckweed.

Although this test alone showed an increase in performance, the most important factor was still to come.

"The interesting thing," Fedler said, "is that when we cut the duckweed out of the rations, the cattle continued to outperform the control group."

According to research, a feedlot should be able to grow enough duckweed to supply each calf 11 to 13 percent of its daily protein requirement to sustain and continue growth.

"With a 30,000 head feedlot at an 80 percent capacity, we can produce enough duckweed just from their waste alone to supply at least 11 percent of their protein in the diet for each animal," Fedler said.

As for harvesting the duckweed, Fedler said putting an auger into the pond will pull up the duckweed. "We put an auger in to grab it, run it through a screen to keep most water out and then it can be put straight into the feed."

Knotgrass, another alternative, is native to the playa areas around Lubbock and Amarillo. It will survive long wetting and drying cycles, meaning it will grow during long periods of drouth or can be submerged in water and continue to thrive after reapplying water. Knotgrass, with a protein content of about 20 to 25 percent, can be harvested just as coastal, alfalfa or any other type of typical hay grass.

Fedler said the project shows that implementing wastewater control systems before regulations become stricter could be advantageous for livestock producers through their byproducts.

Headquartered in Temple, the Texas State Soil and Water Conservation Board oversees the activities of Texas' 216 soil and water conservation districts and is the state's primary agency for dealing with and abating agricultural and silvicultural forms of nonpoint source pollution.