Below: Onions were mulched with straw or Spent Brewers Grains to a depth of 1 inch. Photos courtesy of Regina Dlugokencky.
Organic vegetable growers are limited to hand weeding, cultivation, and mulching to keep weed pressure to a minimum. Hand weeding is time consuming and thus labor costs are high. Cultivation is limited in long-term effectiveness. Mulching material on Long Island, New York, where I farm, is an expensive option because cereal farming is not done and therefore straw is in short supply.
With the establishment of more than 20 new microbreweries on Long Island (with more poised to open), Spent Brewers Grains—a byproduct in the brewing process—are becoming more abundantly available. A microbrewer brewing a single seven-barrel batch (217 gallons) of beer will consistently produce a large amount of Spent Brewers Grains (which I will hereafter refer to as SBG) — at least 220 pounds per brewing day. Most microbrewers consistently brew more than two batches of beer each week.
I received a SARE grant to investigate the effectiveness of SBG as a low-cost option for suppressing weeds in organic onion and broccoli production. The study was conducted on a small certified organic farm in Huntington, New York. All of the SBG from this year’s study was provided by Blind Bat Brewery in Centerport, New York.Here are the details:
This study compared three treatment types: Straw, Spent Brewers Grains, and Control Plots (no mulch whatsoever) for weed suppression. It evaluated the quality and weight of the two crops (Onions followed by Broccoli), and finally, analyzed results of micro and macronutrients of the three treatments. There were four replications of the three treatment types.
About one month after planting the onions, the total area was mulched with the spent grain and straw (approximately 160 sq. ft. for each treatment) at a 1-inch depth.
Below: Spent Brewers Grains come from the brewery in large plastic trash cans. The grains are wet, dense, and smelly before they are applied.
Application of the SBG mulch for this project was done manually. Spent brewer’s grain is wet (and stinky...especially as it ages) and a bit more difficult to apply than Straw. First-hand experience of using the grain in a previous study provided insight on the difficulty of applying it with a 6” spacing without the grain touching the base of the plants. Since I previously found no negative effects of the SBG being placed right up to the side of plants in non-study situations, I applied the grain without concern about it touching the plants. As a result, it was easier (and faster) to apply than the straw. The plants were growing well after about two weeks and seemed to be thriving in the wet mulch.
Weeding was done at the end of June, and the end of July, with a final weeding done while harvesting onions in August. Weeding and weighing was quite time consuming, since the weed pressure at this site was very high. The weeds in the un-weeded sections were so tall that they had to be cut back earlier in the season to prevent shading out the rows next to them. (Weights of the toppings were added to the final weed weights.)
A significant difference in time spent weeding and weight of weeds was found between the weeded Straw plot and the un-weeded Control plot. There was also a significant difference in time spent weeding and weight of weeds between the weeded Spent Brewer’s Grain plot and the un-weeded control plot, and the least amount of time was spent weeding the straw-mulched plots during the growing season. Quality was not affected by any treatment, and was high for both crops.
The results suggest that maximum control of weeds can be best achieved by mulching, regardless of type of mulch, and weeding combined.
This data suggests that SBG is as effective as Straw as mulch for weed suppression.
In terms of effects of type of mulch on yield, a significant difference in weight was found only between the onions mulched with straw (whether weeded or un-weeded) and those grown in the un-weeded Control Plot. No statistical significance was found in the yield of Broccoli following the onions between the three treatment plots.
Macro and Micro Nutrient analysis revealed a drop in Potassium and Sulfur levels as compared to soil samples at pre-plant, and an increase in Sodium, Calcium, Magnesium, Manganese, and Zinc. Calcium and Magnesium were higher in the Straw and Control plots than in SBG plots, when compared to pre-plant samples, even though these two nutrients are associated with SBG.
The land where I conducted this study had very, very high weed pressure and so results may have been diminished. This scope of this particular study doesn’t go beyond one growing season to evaluate how Spent Brewers Grain affects soil quality. I would hypothesize that the value of SBG is underestimated but would be interested to see if the benefits are longer lived and how they would change over time. I posit that even more benefits of this product are yet to be explored, including investigating the effect of SBG on soil organisms. Anecdotally, I have observed a higher population of earthworms in soil that has been mulched with SBG than soil that has not.
To read the complete report, visit www.sare.org and search for Project Number FNE12-743.
Regina Dlugokencky is the owner of Seedsower Farm in Centerport, New York.