You’ve cleaned out the sprayer, now what do you do with the rinse water?
“The common dilemma is what to do with the dilute rinsing,” research scientist Tom Wolf told attendees at the recent Canadian Association of Agriculture Retailers conference. “This is a difficult problem.”
But the Agriculture Canada scientist thinks he’s found an answer.
Biobeds are in wide use in Europe and Wolf, who discovered them on a trip to Sweden, has been testing their efficacy at the Bayer Crop Research Farm.
“A biobed is essentially a pit that has been dug into the ground and filled with something called a biomix,” he said. “It becomes a place to park a sprayer or to dispose of rinsing solution.”
Biomix consists of two parts straw, one part soil and one part compost, blended together and left to sit for about six weeks to allow the material to settle, then placed in a pit.
Not surprising, the biomix quickly goes mouldy – and that’s a good thing. The biomix has a type of white mould with a microbial enzyme that breaks down pesticides
European studies of pesticide breakdown have been very encouraging.
“Of the 1,100 pesticide samples they took, they found the concentrations of pesticides in these samples were reduced by 10,000-to 100,000-fold, a significant reduction,” said Wolf. “About 80 per cent of the leaching they found had virtually no detectable trace of the pesticides left.”
NINETY-NINE PER CENT DECLINE
Wolf’s team started its research by comparing the breakdown of 2,4-D in soil versus a biobed.
“Over about 10 weeks we saw the percentage of 2,4-D in the soil decline by about 99 per cent,” he said. “In a biobed that had seen no 2,4-D previously, the same degradation occurred in three weeks.”
In a biobed that had seen 2,4-D previously but no longer contained any residue, the breakdown occurred in two weeks. Microbial activity increases as the temperature increases. A temperature between 15 C to 20 C is sufficient for microbial activity.
Wolf’s research team found biobeds work well for diluted chemicals, but doesn’t recommend using them for undiluted chemicals.
“The intent of the biobed is really to dispose of diluted waste,” Wolf said. “We’re talking about a practice where you empty your sprayer and spray it in the field and do a first rinse in the field as well and spray that out. Then you bring the sprayer to the farmyard for proper decontamination and then you would put the dilute waste that contains less than one per cent active ingredient into the biobed.”
Wolf’s team built biobeds by lining a peat gravel pit and using biomix made from forage straw and composted animal manure. The biomix sat for about six weeks, and generated heat as it decomposed. The team then dug a hole three metres by three metres, with sloped walls. The hole was lined with a liner, placed in weeping tile with a lysimeter and filled with biomix. Both pits were covered with grass, as the Swedish research indicated a grass layer was important for maintaining healthy microbial activity and preventing water evaporation. They also built one biobed that was four metres by six metres and another above ground.
Wolf said biobeds are easy to construct and above-ground biobeds could be easy to move and manipulate. A biobed can be built for about $2,000. Each year, the biomix will shrink slightly as straw decomposes so may have to be amended, but the mix only needs to be changed every five to eight years, said Wolf.
Wolf plans to conduct further research but is clearly sold on the technology.
“We have a vision for the future and that vision is a biobed on every farm,” he said.
– TOM WOLF, AAFC