by Tamara Scully

Technology, along with the increasing use of conservation practices, has enabled farmers to reduce greenhouse gas (GHG) emissions. A new piece of equipment, patented by Dr. Dan Pote at the ARS’s Dale Bumpers Small-Farm Research Center in Arkansas, has added another practical and effective tool to increase crop health and yields while decreasing GHG emissions associated with fertilizer applications.

“A subsurfer is a piece of equipment…if you can imagine a combination between a no-till drill and a manure spreader,” Dr. Phillip Owens, research leader at Dale Bumpers said. A brief video of the subsurfer can be viewed at

The subsurfer has a hopper, where dry chicken litter is loaded. The litter is then pulverized, a slit is opened up in the soil and the litter is dropped in via tubes and then covered with soil, burying it several inches under the soil.

The subsurfer is “a really novel technique for trying to keep litter below ground, and nutrients below ground,” Owens explained during a recent National Center for Applied Technology (NCAT) sustainable agriculture podcast.

Fertilization with Chicken Litter

Arkansas has a lot of commercial poultry houses, and therefore a lot of poultry litter. Chicken litter is utilized as a crop fertilizer, primarily applied to pastures where high-quality forages for grazing or hay are required.

The litter is often surface applied just prior to a rain event. The nitrogen in the litter volatilizes the longer it sits on top of the soil, creating GHG emissions and removing its potential to fertilize the soil. Applying the litter prior to rain or irrigation events prevents nitrogen loss from ammonia volatilization, as the rain serves to incorporate the nitrogen into the soil, as does tilling. Both of those practices can have detrimental effects on the environment, including GHG emissions, runoff and soil disturbance. Phosphorous runoff is also a concern.

“Poultry litter is a great fertilizer source because it’s not just one or two nutrients. It’s got a lot of macro and micro nutrients, and also it’s a natural liming agent,” Dr. Amanda Ashworth, ARS research scientist, said. “The subsurfer can reduce GHG losses from soil applications by about 88%.”

The subsurfer prevents ammonia volatilization of the nitrogen without the soil disturbance from tilling and without concern of timing application with rain events. It can be used in conjunction with dry land farming, supplying fertility directly into the soil, where it remains accessible to plants when the rain does arrive.

The first trials of the subsurfer on pasture forages demonstrated that subsurfer application of chicken litter allowed forages to thrive, outperforming surface applied litter even after several months without rain.

“When you apply the poultry litter, that nitrogen will just off-gas. When it volatilizes, you don’t have access to that nitrogen anymore. If you can keep it below ground, when you eventually get the rains, the nitrogen is there for the plants to access when they have the water to use it,” Owens said. “Even in dry areas, this would be an appropriate technology to capture what’s available of the nutrients, minimize greenhouse gas emissions and boost your yield.”

Ashworth has been conducting research on use of the subsurfer in applying poultry litter to organic edamame and corn crops. The trials included a control plot and litter applied with a subsurfer at distances of five, 10 or 15 inches away from the seeded crop rows in both irrigated and dry land situations.

Corn was found to have the best yield when planted five inches from the buried poultry litter, while edamame was found to perform best at 10 inches away. Increased crop quality, as well as increased yields, over surface applied litter as well as inorganic fertilizer applications were seen. Edamame yields were 67% greater than with other methods.

“It really keeps the nutrients in the soil,” Ashworth said. “There’s a multi-benefit from using poultry litter and from also using it in targeted applications close to where the crops can use [nutrients].”

Next Steps

The patented subsurfer had eight machines manufactured by a small-scale manufacturer before that company was purchased by a large manufacturer who did not wish to continue with its production. A new equipment manufacturer hasn’t been found yet, and is being actively sought.

Aside from not having subsurfers available for purchase, other concerns are the amount of acreage which can be treated per day. A maximum of 30 acres per day makes the subsurfer unsuitable for very large farms, but perfect for small to mid-sized farmers.

The poultry litter must be kept dry in order for the equipment to properly pulverize and spread it. While application directly from the poultry houses would work, farmers wanting to store the litter prior to application would have to find a dry place in order to keep moisture content low.

Organic growers can benefit from utilizing a subsurfer for crop or pasture fertility. One complication might be weed control, if growers are plowing between rows. That would plow up the soil where they litter was buried by the subsurfer, moving the nitrogen back on top of the soil, where it would volatilize.

“It’s difficult to get good fertilizer supplies and application in the organic market,” Owens said. “Poultry litter is approved…it would be okay for the certified organic producers.”

There is potential that the subsurfer could become part of official conservation programs, such as the NRCS, Ashworth said. Preliminary rainfall simulation studies have shown quantifiable increases in water quality in small plots where the subsurfer was used to apply litter when compared to other fertilization methods.

A SARE grant has funded ongoing trials where subsurfer versus top dressed poultry litter is applied to pastures. The research goal is to “identify optimal plant combinations for increasing forage production in organic cropping systems,” Ashworth said.

The need to locate a manufacturer willing to produce this game-changing piece of equipment is the hurdle preventing widespread use of it.