By Julienne Isaacs
Bernie Zebarth is leading a four-year project that will study large-scale compost application on potato fields in New Brunswick, and the resulting effects on yield and soil health. Photo courtesy of Bernie Zebarth.
In 2013, eastern Canadian potato growers were concerned: they were not seeing the yield increases experienced by growers throughout the rest of North America. Manitoba has seen an average yield increase of 4.4 hundredweight per acre (cwt/acre) each year. By contrast, New Brunswick sits at an average yield increase of 1.4 cwt/acre, and P.E.I. at 1.1 cwt/acre.
One possible culprit for stagnating yields is declining soil health in the eastern provinces. “With sloping land and intensive tillage, you have a lot of issues with soil erosion,” says Bernie Zebarth, a researcher with Agriculture and Agri-Food Canada (AAFC) based in Fredericton. “We also have a short rotation for potato, so we’re not getting much organic matter back to the soil. Our concern is that the declining soil health is limiting yield.”
New Brunswick’s processing potato industry is crucial; the province exports most of its product for french fries, and without increasing productivity it loses competitive advantage.
Industry asked for help, and in 2014, Zebarth took the science lead on a four-year industry-led project that will study large-scale application of compost on fields across New Brunswick, and the resulting effects on potato yield and soil health. Potatoes New Brunswick is leading the project, with McCain Foods Canada heading up the on-farm trials. The project will also study a variety of compost products in experimental plots at the AAFC Fredericton Research and Development Centre.
“We want to see the implications of adding compost to the soil, in terms of yield and tuber quality,” Zebarth says. “How much of a yield difference is there? Will it be cost-effective? How will it fit into growers’ practices? What soil quality parameters does it improve? We want to be able to know which index is the best to use to assess soil health. Can we suppress soil-borne diseases? Will compost fit into New Brunswick potato production?”
The study is part of a larger three-year study that aims to identify areas in New Brunswick, Manitoba and P.E.I. potato fields that have a yield limitation, identify the source of the limitation, and identify mitigation practices to overcome that limitation.
Zebarth says his team is hoping to assess whether adding compost to the soil will help accomplish in a short time what improved rotations might accomplish over a much longer period.
“Because we don’t irrigate, I’m thinking that when it comes to soil health and soil quality, what we’re really after is improvement of the soil’s physical properties, such as water holding capacity and tilth. Any field with a problem with physical properties could benefit from compost.”
The field-scale trials led by McCain in commercial fields for the project involve paired treatment strips in growers’ fields – one treated with compost, one untreated. They are evaluating yield and tuber quality, as well as soil water content and other physical properties of the soil.
Meanwhile, with help from Dalhousie masters student Carolyn Wilson, Zebarth is analyzing five different compost products, assessing their impact on tuber yield and quality, soil quality and on soil-borne diseases like common scab.
The compost being used in the field trials is a wood shaving litter with poultry droppings, which reuses wastes from agriculture and forestry to build soil organic matter. The other composts being analyzed at the Fredericton Research and Development Centre include a forestry residue compost, a source-separated organics compost, a poultry manure-bark compost and a marine-based compost.
The third component of the study is based in the lab, where, along with AAFC researcher Claudia Goyer, Zebarth is using next-generation sequencing to characterize the microbial life in soil samples.
It’s too soon to talk about results. Zebarth is optimistic that compost can help improve soils over time, but he cautions that compost is a “probabilistic” solution. “We’re thinking about compost almost like you look at a capital investment,” he says. “It’s not like a nutrient application, but an infrastructure improvement, where you get payback over the next five to 10 years.”
In some fields, growers may only need to apply compost to certain parts of the field that have soil physical problems. As cost has traditionally been a prohibiting factor for growers hoping to use compost, Zebarth’s team is hoping the study might help them identify a particular compost product that can be scaled up to reduce the costs.
There’s no silver bullet when it comes to soil health, but compost is what Zebarth calls “one tool in the tool box” for improving the soil – and ramping up productivity – over time.