Onward, with Mulch! Effects of Straw Mulch in Organic Potato Production
By Erin Schneider, Hilltop Community Farm, La Valle, WI
With Ruth Genger, UW-Madison
I am in the fields, prepping the soil in anticipation of peppers (potatoes already firmly tucked in), body and broadfork rocking like a metronome tick as if I am slowly learning how to salsa. Step, rock, slide, one, two, three, unearthing the earth worms and turning over the rye and vetch as I move across the soil floor. Whether you mechanically till or manually turn, roll and crimp or no-till, each year, as farmers we scramble to keep the beat and work with the seasonal rhythms to grow food without beating up our soils and bodies along the way. Potato production, as with many annuals and especially root/tuber crops, is hard on the soil. A Canadian study of rotation length in organic potato production systems found that four years of grain/forage rotation were required after a single year of potato production to restore microbial biomass to previous levels. Declining soil organic matter is a serious problem in long-term potato production systems.
Fortunately, there are options and good dance partners to help prop us up and give our bodies and our soils stamina. The longer I farm, the more I discover that mulching is a favored dance partner to support me (and my soil) when growing organic potatoes.
Dancing with mulch
Organic mulch materials include straw, hay, cover crops, woodchips, leaves, marsh grass, other crop residues, and even coffee chaffe – basically what’s most on hand and readily available. Cover crops can also be grown to maturity (flowering), mechanically killed, and left on the soil surface to provide an in-situ organic mulch for no-till planting. Ronald Morse, Professor Emeritus at Virginia Tech, has done extensive research on no till organic potato production. This topic deserves its own blog post, though Dr. Morse summarizes it better than I ever could in his paper, No-Till Production of Irish Potato on Raised Beds.
Beyond weed suppression
Mulches are useful for their role in weed management, moderating soil temperature and conserving soil moisture. But what are the long term effects of mulch in building organic matter, carbon cycling, and supporting the soil microbial community? In potato production system, with extreme disruption of the soil at planting and harvest, can mulch contribute to building or at least retaining soil organic matter? Or does the carbon just return to the atmosphere?
Hay and straw are among the most widely used organic mulches, with the latter being the focus of a research trial that Dr. Ruth Genger and team are working on this year in collaboration with five farms in Wisconsin, Minnesota and Ohio. in previous research station trials, the team has seen good weed control with mulch, and observed increased tuber yields from mulched plots in two out of three years. This year, the focus of the research has broadened to include straw mulch effects on soil carbon and nitrogen, plant nutrition, and greenhouse gas emissions from current and previous straw mulched plots.
I find this fascinating, and not just because I tend to geek out on soil biology, but also, how do you measure emissions from mulch? Collecting the samples is fairly easy, with the help of a video description from Professor Randy Jackson’s lab at UW Department of Agronomy.
Mulch timing, balancing inputs, and the long view
“In every good dance there is a step back too,” poet Robert Sund reminds me. I just discovered that the same is true with mulching. I look at my potato beds, which I covered with straw mulch just after planting a few weeks prior, and realize that the thickness just won’t cut it, with weed seedlings already poking through next to the Austrian Crescents that just emerged. While I only have a few hundred row feet, I can manage the expense, rake back the mulch and start again. But if you’re talking an acre of potatoes (or two or three, or more), multiple attempts at mulching aren’t a great option, and getting the timing and amount right become more important, especially given the vagaries of spring weather and the difficulty of bringing equipment into a wet field. Trials at the West Madison Agricultural Research Station this year will compare the effects of straw mulch applied at potato planting or at plant emergence, versus unmulched plots which are tine weeded and hilled. Labor needs and costs for these activities, as well as for ongoing weed management, will be recorded, and balanced against potato yield and quality.
At present, mulching these potato plots is a task for a large field crew to do by hand. At a small scale, this is manageable, but larger scale application will require mechanization options that could allow mulching to happen in conjunction with other field passes. A creative approach to straw mulch application was taken by on-farm research participants from New Story Farm, who unrolled a round bale over seed potatoes placed on a worked field plot, in comparison to planting in soil and mulching over this with straw. Thanks Stephanie and Dan for the great photos!
Long-term, Genger and team hope this year’s discoveries inform future research that takes a look at the soil microbial make-up and the long-term economics of what it takes, as farmers to grow our own mulch. The prospects of shifting the annual dance from expensive (i.e. cost of mulching inputs, labor/weed management) to wealth generating (less passes with the tiller, increased organic matter, the ability to grow your own etc.): that’s a farmer, researcher, and microbial community I could dance with.
One last turn rock n slide with the broadfork, I stop, look up, gaze honing in on the round bale and the mulching work that lies ahead. But first, just a little nap atop the bale, letting its pliable structure absorb the weight of my body, imagining what a potato (and the soil) might ‘feel’ knowing that it has this much support as it dances from tuber to table. Onward with mulch!
We’d love to hear from you
What are some of your mulching techniques and tips that you would recommend to other farmers?
Do you have experience with growing your own mulch for use in potato production? What worked? What were the challenges?
What practices do you use to build your soil organic matter?
Learn More
Soil Health in Organic Potato Systems
Measurement of Greenhouse Gas Flux from Agricultural Soils Using Static Chambers
Organic mulching materials for weed management.
What is Organic No-Till and is it Practical?
From the blog archives:
Wet Weather Weeds and Early Potatoes – 2014 Post by Ruth Genger
This article was posted in Blog Posts and tagged organic potato, organic weed management, soil carbon, straw mulch.