It's walnut harvest time at the Vink Brothers' farm on Banta Road, and on Wednesday Pete Vink supervised another shipment of fresh walnuts.
The next step after the harvest is to prune all of the trees in the orchard, then he and his brother Bart have to get rid of all the twigs and branches they've cut down.
One typical way is to burn it, but Vink said he gave that up years ago. He now shreds branches and mixes them back into the soil.
"It's something everyone has to go through, and it's good for your soil," he said. "It's a good thing, but it's more costly."
Local farmer Keith Robertson also stopped burning waste long ago and uses it as mulch or plows it back into the fields.
"We got a little funding from the government to get a chipper for our prunings," he said. "Every time we prune we try to chip it all."
Robertson said his chipper, an inexpensive model, hooks up to a tractor, which pulls it between the trees and leaves behind a blanket of mulch.
That puts the local farmers a step ahead of the San Joaquin Valley Air Pollution Control District, which has told farmers in June that they are not allowed to burn most agricultural waste anymore.
If they have a permit, farmers can still burn branches from vineyards and some trees, such as walnut, almond, pecan, apple and pear trees, for the next five years. But just about everything else can't be burned anymore.
The California Air Resources Board lists waste fires as a major producer of carbon monoxide and "particulate matter," dust and smoke that can be deeply inhaled.
The new rule also is a source of frustration for farmers who see yet another layer of regulation put on their business.
"We're being blamed for a lot of pollution where we clean the air better than anyone else," said local farmer Jim McLeod, referring to the respiration of trees, which consume carbon dioxide and produce oxygen.
"The fallacy of the whole thing is we take a lot more carbon dioxide out of the air than we put into it by far," he said. "All these rules and regulations, they cost us money."
Farm waste can also end up as fuel for the Tracy Biomass Plant on Schulte Road west of town. Mark Kehoe, director of environmental safety for GWF Energy, owner of the plant, said wood chips from orchards, such as fields of trees pulled out this week on Banta Road, make up about half of what the plant burns. Kehoe said the plant does not typically take pruned branches, straw or other farm waste.
Anthony Presto, spokesman for the air district's Modesto office, said this is the time of year when the new rule counts.
Before this year farmers were allowed to burn waste year-round if they did it on a "burn day" when there wasn't heavy smog in the air.
Typically the ideal conditions would be in fall and winter right after trees were pruned.
"When there were decent conditions everyone would burn at the same time and there was a great deal of smoke," he said.
Contact reporter Bob Brownne at email@example.com.