With the help of DNA sequencing, Canadian researchers are linking soil microbial communities to soil health and potato yields. This research is the first stage in eventually developing a tool to diagnose the health of potato fields and to help identify management practices to improve tuber yields and quality.
Brenda Shanahan, Member of Parliament for Châteauguay—Lacolle, on behalf of Minister of Agriculture and Agri Food Lawrence MacAulay, has announced a repayable contribution of $470,000 to help a Quebec company, Logiag Inc., commercialize a laser-based soil analysis system that replaces the more traditional chemical analyses.
Studies have shown adding biochar to soil can improve soil fertility, increase nutrient utilization in plants, improve soil water-holding capacity, increase crop yield and reduce emission of greenhouse gases.
However, if you are a potato farmer, your joy may be short-lived. According to research from Aarhus University in Denmark, biochar and potatoes do not go together very well, especially if you’re aiming to save water.
Caixia Liu, a PhD student in the university’s department of agroecology, investigated the effects of adding biochar produced from wood on potato growth, yield, nutrient uptake and water utilization when three other factors were also taken into consideration: irrigation methods; phosphorous fertilization; and inoculation with a certain class of beneficial fungi. Liu’s aim was to investigate the interactions between biochar and the fungi on the growth of potatoes.
Biochar and AM-fungi do not go well together
Potatoes are rather sensitive to drought and phosphorous deficiency because of their relatively small root system. It would be easy to merely irrigate and fertilize in plentiful amounts, but since both phosphorous and water are limited resources, it is important to use them optimally.
Earlier studies at Aarhus University have shown water can be saved by irrigating alternately on each side of the potato ridge and letting the other side remain dry – the so-called alternating partial root zone drying irrigation method.
It is also possible to save phosphorous. In the course of her PhD studies, Liu found inoculation of potatoes with the beneficial arbuscular mycorrhizal fungi (AM fungi) can improve potatoes' utilization of phosphorous, make utilization of water more efficient, and increase potato yield in crops that are stressed due to drought or phosphorous deficiency.
The question was what would happen when biochar and inoculation with AM fungi are combined. Would there be a double win? The answer was no.
Liu conducted a series of studies with various combinations of irrigation (either full irrigation or alternating partial root zone dehydration), phosphorous fertilization (none or 0.11 milligrams of phosphorus per gram of soil, or mg P/g soil), inoculation with AM fungi (inoculation or no inoculation) and addition of biochar (addition or no addition).
Biochar inhibited the growth of potatoes
If the crop is irrigated fully, the soil is given no phosphorous at all, and the potatoes are not inoculated with AM fungi, then addition of biochar can increase potato yield. This was the only case in which this was true; in all other instances, addition of biochar to the soil had the opposite effect.
The negative effect on potato growth was especially pronounced when phosphorous was added, alternating partial root zone drying irrigation was used, and the potatoes were inoculated with AM fungi. Addition of biochar inhibited the growth and vigour of young potato plants. Some of the young potato plants even died.
“I would recommend that the farmer refrains from adding biochar produced on the basis of wood to an AM system, where the soil has been fertilized with phosphorous or if the soil is prone to drought. Biochar remains in the soil for a long time so there is no going back,” Liu said, in a press release.
Due to hot, dry conditions, farmers in Norfolk County, Ont., have used irrigation in an effort to save the crop. But with less than half an inch of rain in eight weeks, irrigation has been no use, and the local yield could be down by 50 per cent. | READ MORE
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.
A New Brunswick researcher says that despite the common perception that water and wind are responsible for erosion, tillage erosion is actually the leading cause of soil degradation in most cultivated fields in Canada.
Li Sheng, a hydrology/croplands and water management expert with Agriculture and Agri-Food Canada, has been analyzing the causes of erosion in order to develop management recommendations.
His message is surprisingly positive.
“Our perception is that soil erosion is really bad in Eastern and Atlantic Canada, but it’s actually getting much better,” he says. “People are more aware of erosion, and a lot of structures have been put in place to reduce it. However, in critical times, you’ll still see a lot of erosion happening and erosion remains the number one cause of soil degradation in many fields.”
For the past few years, Sheng has led a research team conducting several studies in erosion. One study comparing water, wind and tillage erosion, conducted in partnership with David Lobb, a University of Manitoba soil researcher, found that wind erosion is much less severe than water erosion in Eastern Canada. While it is more damaging in Western Canada, wind erosion in most fields is still not at the same level as water or tillage erosion.
The most worrying aspect of erosion on the East Coast, says Sheng, is the combined effect of water and tillage erosion.
These days, Sheng’s team is testing the hypothesis that water and tillage erosion work together to create a more severe problem – that tillage erosion actually offers a mechanism for soil to leave the field by water erosion.
“If you have gullies going down the field, cutting through the soil to the edge of the field, if you till the field and fill those gullies in, in the next major rainfall event, all of this loose soil will be washed away,” he explains. “We are thinking that in Eastern Canada this is probably one of the major mechanisms of the transportation of sediments going out of the field.”
In the summer of 2015, Sheng and his team set up multiple research sites on Prince Edward Island and in New Brunswick. A gauging station on the edge of the field will measure sediment and take water samples. The research team also put cameras and erosion pins at different points in the fields to analyze surface changes due to erosion.
The study will run three years to allow the researchers time to collect solid data during potato rotation schedules.
Maintaining erosion structures
Sheng’s team has developed a list of best management practices to help growers minimize erosion. Conservation tillage and mulching are both key strategies, along with erosion management structures such as terracing and grassed waterways.
The latter might not be commonly used in Western Canada, but Sheng says it’s difficult to find potato fields on the East Coast that do not employ them.
The problem is a lack of maintenance.
“A lot of these structures are not very well maintained – there’s certain maintenance that has to be done to keep them functioning,” Sheng says.
Diversion terraces (sometimes called contour terraces) are one good example. On hilly land, diversion terraces break up long, sloping fields into smaller sections with shorter slopes, to slow down and divert runoff. “The longer the slope, the higher the water erosion, and the greater potential for eroded soil to be carried away by that high-power runoff,” he says. Terracing can vastly mitigate this problem. But growers should ensure they use terraces to their maximum potential – and don’t cut corners.
“Above the terrace berm, where the water comes down, there is supposed to be a one- to three-metre-wide channel, or runoff ditches, to allow runoff to flow at a non-erosive speed and sediments to deposit. However, many farmers will farm right to the edge of the berm, because allowing it means a loss of acreage and total production,” Sheng says.
Sometimes farmers are slow to clear out runoff ditches, but once filled, they lose their function. Runoff during heavy rainfall events can cut across the terraces.
Another example is the use of grassed waterways as informal roadways for field access, Sheng says. Grassed waterways are used as roadways “by maybe 90 per cent of farmers,” resulting in severe soil compaction, which can lead to reduced water infiltration and reduced function of grassed waterways on erosion control.
But the number one cause of soil erosion in many fields – tillage erosion – is the problem growers should focus on addressing.
“Some farmers do recreational tillage – when they have some free time, they like to go out in the field and do additional tillage that is not needed,” Sheng says. But growers should reduce disturbance to the soil as much as possible, which means eliminating unnecessary tillage, and any other unnecessary disturbances during seeding or harvesting.
“Reduce the frequency of tillage, the intensity of tillage, and the variability of tillage – the speed and depth,” he says. “Keep it as uniform as you can. Controlling speed and depth across the landscape will reduce tillage erosion.”
Most of all, growers should take a “landscape perspective” to erosion control, Sheng says, considering the entire system rather than individual fields and strategically employing best practices.
A study completed last year by Agriculture and Agri-Food Canada scientist Li Sheng shows spring run-off is only part of the soil loss problem.. Photo courtesy of AAFC.
June 12, 2015, Fredericton, NB – Soil erosion is the leading cause of soil degradation in potato producing areas of New Brunswick. But even if this is the time of year when farmers discover erosion in their fields due to spring run-off, a study completed last year shows this is only part of the soil loss problem.
May 6, 2015, Fredericton, NB – Agriculture and Agri-Food Canada (AAFC) has joined forces with McCain Foods Canada and the province’s potato growers in a major project to improve potato yields in New Brunswick by improving soil health.
In September 2011, wheat phases [except the second one of 5CONS, P-W-SB-W-B], as well as the oat phase from the six-year rotation (6CONS) were sampled (0-7.5 cm) to explore rotation and management practices effects on soil aggregates and organic matter. Photo courtesy of Drusilla Pearson.
A 12-year irrigated rotation study near Vauxhall, Alta., which set out to examine the impact of rotation length and conventional (CONV) and conservation (CONS) management practices for potatoes, sugar beets, beans and soft wheat, has concluded that growing crops without conservation management practices may result in reduced yields and diminished soil quality.
The study, led by Agriculture and Agri-Food Canada (AAFC) researcher Frank Larney, was initiated in 2000 after meetings with various key players in Alberta, including the Alberta Pulse Growers, the Potato Growers of Alberta and Rogers Sugar/Lantic Inc., along with growers from around the province.
“We had buy-in from growers very early on. We used those meetings to plan the experiment and come up with the crops we wanted to include, [as well as the] sequence we wanted to grow them in,” says Larney.
The CONS rotations used in the study were built around four specific management practices: direct seeding and reduced tillage where possible; fall-seeded cover cropping (fall rye); feedlot manure compost applications; and where beans occurred in the rotation, solid-seeding narrow-row beans versus seeding conventional wide-row beans.
Six rotations were used in the study (see Table 1) with each of the 26 phases appearing each year, and replicated four times in total.
Larney explains that CONS practices were chosen with direct input from growers and were thus highly practical in nature. For example, the compost practice was chosen because, he says, “a lot of irrigated land is closely associated with the feedlot industry in southern Alberta, so the use of composted manure to replace some of the chemical fertilizer inputs seemed obvious.”
Additionally, Larney and his team chose to use narrow-row solid-seeding management for beans because, when the study began, only a single Alberta grower was using the technique. Estimates revealed at the Irrigated Crop Production Update meeting in Lethbridge in late January show that in 2013, 15 per cent of bean growers were solid-seeding in narrow rows. “It’s a management practice that’s set up to protect soil quality and reduce the risk of erosion,” says Larney.
The researchers chose to include rye as a fall-seeded cover crop because there was interest from growers.
Yields increase using CONS
The study’s results show that growing potatoes in rotation (potatoes-beans-wheat) without the use of CONS practices is not recommended due to declines in yield of between 12 and 18 per cent over the long term. Overall, CONS practices increased potato yield by seven per cent, with this number increasing for rotations longer than four years. CONS practices also improved soil quality parameters such as organic carbon, microbial biomass and soil aggregate stability.
Larney says that once the rotation plots had been established, many researchers used the study to investigate a variety of research concerns. Populations of weeds, insects and nematodes, respectively, were measured over time, and soil microbiologists examined microbiological indicators of soil quality. “I also did some measurements on various soil quality indicators, like soil organic matter, and looked at effects of rotations on nitrogen and phosphorus in the soil profile,” says Larney.
Key among the findings was the positive impact of CONS practices on soil health. “The soil microbiology indicators were quite consistent,” says Larney. “All but one of 10 indicators showed positive effects of CONS on biological indicators of soil health.”
The chief indicator of soil quality is soil organic carbon. The study was set up to compare CONV and CONS practices in three-year rotations, as well as CONV and CONS practices in four-year rotations. In the three-year rotation comparison, there was a 17 per cent increase in soil organic carbon in the top 30 centimetres of soil at the end of 12 years.
In the four-year rotation comparison, there was a 23 per cent increase in soil organic carbon in the top 30 centimetres of soil after 12 years. “The main driver of those increases was the compost application, because that’s how we were putting carbon back into the soil,” says Larney.
Overall, the study highlights the importance of maintaining good management practices in order to protect soil health in the long-term – a lesson that is already well understood by Prairie growers, according to Larney. “Soil organic matter content can decline, and if there’s no effort made to replenish that by adding manure or compost or reducing tillage or growing cover crops, you can run into problems with reduced soil organic matter, which, in turn, leads to problems with soil erosion, or general soil degradation.”
Growers face frequent temptation to tighten up rotations, but if organic matter is not returned to the soil, soil quality will decline, and this will ultimately impact yields. “Farmers should be aware of their soil organic matter levels,” says Larney. “They can test soil organic matter or carbon, and if these levels look like they’re low, growers can look at using compost as a way of increasing them.
“You have to balance the economic returns with the environmental effects that you want. You want to keep your soil in good condition and productive.”
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