Moses Lake, WA 98837, USA

Green manure as biofumigant, increasing potato soil health

Staff Writer

PASCO — “Trying to do more with less.” That is what Grant Morris, a farming partner at Schneider Farms, north of Pasco, sees as one of the challenges facing farmers.

“We’re asked to raise more food on the same amount of ground with less inputs,” Morris explained. “Every year becomes more competitive. We’re trying to figure it out. It’s something everyone struggles with.”

So how do farmers, in particular, potato farmers increase yields while using less chemicals? That is something that Morris and other potato farmers like him are attempting to figure out.

With potatoes, the goal is to get rotations down to two years. Currently, with the help of fumigants, potato farmers are able to plant potatoes every four to five years on the same piece of ground. Without fumigants, potatoes can only be planted every 12 years on the same land.

With the demand for Washington potatoes being higher than current outputs, farmers are trying new things to increase yields and cut down on the amount of time between rotations.

Schneider Farms has been experimenting with green manure crops. When a crop comes off in July or August, a cover crop, such as mustard or radish, is planted and allowed to grow. Before winter, the cover crop is tilled into the soil where it decomposes. During the decomposition process, it releases a chemical identical to that in fumigants. It also builds up the soil.

“The next year, when we get spuds in there, hopefully there will be better soil,” Morris said. “The plant will be able to defend itself better. At the end of the day, hopefully we’ll have a better yield.”

While Morris is using green manure crops in addition to normal fumigation practices, his farm has seen a decrease in potato rotations.

“Some parts of the farm are down to two year rotations,” Morris said. “We can double crop. In two years, we’re getting three crops off it.”

Morris said that while he and other farmers south of Pasco can double crop, farmers in the Moses Lake, Quincy, Connell and Othello areas are not able to.

“We have to treat the soil and do cover crop amendments,” Morris said. “There are a lot of things guys are doing to support that. Also, there is a two weeks difference on crops. Our crops come off two weeks earlier. It’s not a lot, but it’s enough to get a second crop.”

Further research is needed to help farmers in colder areas cut down their rotations.

“We need more research on this,” Morris said. “Every grower has what they think is working. We need some numbers; we need repetition.”

Among the farmers that incorporate cover crops into the rotations, there are many different variations of what cover crops are used. Schneider Farms uses cover crops such as mustard and radishes or a combination of the two.

“Some guys have 10 to 12 things in there,” Morris said. “We’ve tried a few things ourselves.”

Currently, potato soil health research is still in the beginning stages.

“I think the goal is to tighten up from five years to three years,” Morris said. “That’s a 40 percent increase. I think that’s what we’re shooting for now. Even five to four years, that is an increase. We’re pretty unique down here. If they can replicate that further north in the Basin, we’d be in good shape.”

Morris did note that while they are using cover crops as a biofumigant, they are continuing with their fumigation practices as well. Without traditional fumigation practices, growers run the risk of poor to no yield or a bad quality potato.

“Most growers aren’t taking that risk,” Morris said.

For those growers exporting their potatoes to Japan and Asia who have a higher quality expectation than the United States, they don’t want to risk their crop to experiment with the lack of fumigation.

Schneider Farms does grow a specialty baby potato variety where they don’t use fumigants and grow them back to back. In between crops, they typically will plant a mustard crop to act as the fumigant, just at a lower level. There are also some mustard crops that will bring nematodes to the surface.

“They get a better kill on what’s there,” Morris said. “In some cases, it may be replacing the fumigant. In others, it’s enhancing it.”

Regardless of how cover crops are being used as a fumigant, they are helping to improve soil health. The disadvantage to them is the cost they incur that does not get recouped.

“It’s $200 an acre to raise a cover crop you’re not going to harvest,” Morris said.

While the growers want to see a return for their efforts at the time, Morris thinks that in the long term they will see the return in shorter rotations.

Rachal Pinkerton may be reached via email at