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February 4, 2020
Put delicately, there are massive mounds of manure --- prolific piles of poop --- that are all part of acclaimed recycling efforts going on at Green Valley Pecan Company, thousands of acres of former Southern Arizona cotton farmland converted into one of the world’s largest irrigated pecan orchards.
What started as a small family farm now encompasses multi-state operations employing more than 300 employees and producing enough in-shell Wichita and Western Schley pecans to circle the Earth…twice.
Despite the pace of production, attention is also paid to environmental considerations, specifically recycling and that brings us to a 17-acre repository for bovine byproduct that functions as an extremely large composting process that recycles pecan leaves, twigs, shells, and a whole lot of excrement.
“We get a lot of our manure from Shamrock Dairy as well as area feed yards and stockyards,” says third-generation farm manager Rich Walden. (The nearly 100- year-old dairy maintains a herd of 10,000 cows, all eating and excreting). “They’ve got so much product, they’re more than happy to get rid of it if we’ll pick it up. And we do so on a daily basis.
“Some other orchard operations may compost, but probably not to the extent we do. We have the capability of producing upwards of 30,000 tons of compost each year and we use it all on the farm as nutrition input for our 115,000 trees.”
Sustainable Conservation’s Ryan Flaherty, speaking to the issue of Compost: Enhancing the Value of Manure, notes: “Composting dairy waste as a strategy for reducing farming’s climate impacts in many ways that make good business sense.”
That group has been working with California dairies for over 15 years and reports that, “We identify compost as a low-tech, economically-viable option for dairies to export excess manure resources. Composting dairy manure creates a high-quality soil amendment, kills pathogens, reduces nitrates that threaten water quality, and produces a more compact product that can boost soil health.”
The microorganisms responsible for composting are indigenous to manures which are staged in windrow piles, commonly 4-6 feet tall and 10-12 feet wide, usually dictated by the length of the pad and the size of the turning implement.
Water management is required because 40-65 percent of the pore space in composting materials need the moisture. “We have one well dedicated to compost and water our piles using a center pivot sprinkler which we re-tasked from previous hay, corn, and alfalfa projects,” Walden says. “It’s much easier than taking a water truck up and down each aisle and refilling it over and over again.”
PROCESS IS SIMPLE
The composting process itself is relatively simple --- mix manure and moisture with air and let bacteria break down the material. The Natural Resources Conservation Service recommends: “Heat the pile to between 145-160 degrees, add water, and turn periodically to cover all the manure in the pile.”
“It takes us about 90 days to make compost to the grade level we need. It’s not as finely filtered as what you’d find in a florist shop, because we don’t mind if some small sticks remain as they work their way into the soil and aerate it.”
Here’s the Green Valley Pecan Plan for composting: Pruners go down the rows (36 trees per acre at this site, 54 per acre in a newer orchard in nearby San Simon), topping out at a height of 40 feet.
“Every time we prune, the smaller stuff just gets whisked into the ground and becomes organic matter. At harvest, when we do 100 acres in a day, a tractor with finger drums rakes everything into a row that is picked up with nuts going to a cleaning plant and everything else, the leaves and sticks, gets ground up for composting.”
Dairy manure represents about 60 percent of the compost pile with the remainder made up of plant trash, prunings, and broken branches. Once ground and logistically sited for regular sprinkler moisture, the piles are turned regularly through a drum mechanism with 72 teeth that rotates the pile and mixes the moisture in what is called an PFRP or Process to Further Reduce Pathogens.
“Different bugs do most of the work for us,” Walden says. “There are three different kinds starting with the kind you’ll find in home composters that work up to about 110 degrees. Then the 110-135 degree bugs take over and do the majority of the breaking down before the 135-165 degree bugs finish the job.”
Once temperatures get into the 180-185 degree range, the possibility arises of a chemical reaction that could end up in spontaneous combustion.
“For us, the process takes a couple of weeks, 130 degrees or so for 15 days during which we turn the mixture five times. By then, the compost is considered organic because the pathogens can’t stand that level of heat. Once it’s processed, we stage it on the farm and let it continue to cure, improving with age until we use it for compost in our organic orchards in place of commercial fertilizer.”
Once that part of the environmental footprint is accounted for, attention is turned to the processing plant where shells are cracked and nuts removed. What to do with the broken shells?
“We only use about 15-20 percent of nuts that couldn’t be processed for some reason as bulk material for our compost pile because the shells don’t really absorb the moisture --- so we found another use for them,” says Bruce Caris, Chief Operating Officer.
The remaining hulls --- upwards of 30 yards a week --- are transported to Frito Lay Potato Chip company in nearby Casa Grande where they become part of the agricultural waste used to keep a 60,000 lb/hr biomass boiler burning in order to turn 500,000 potatoes a day into potato chips --- and generate nearly zero waste going to the landfill.
So there’s a recycled dairy cow product up front that is given a second use, then turned into a product with a second life, and the cracked shells find a recycling mission --- a win-win-win.
“As a corporate citizen, it’s the right thing for us to do as it helps mitigate our environmental footprint. “We’re also making something that improves the soil faster and is safer to use,” says Walden.
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