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Potash fertilizer use in Prairie dry regions

Improving crop resilience, yield and disease resistance in chickpea, mustard and durum in the Brown soil zone.

March 16, 2024  By Donna Fleury


KCL field study low-slope site in farm field plots in south-central Saskatchewan, June 2023. Photo Courtesy of Jeff Schoenau, USask.

Crops such as durum wheat, mustard and chickpeas are commonly grown in the Brown soil zone areas. Although potash fertilizer has been shown to improve plant resistance to stresses such as diseases, drought and cold, and help optimize yields for crops such as barley and wheat, little information is available about the potential of potash fertilizer in these drier region crops. Researchers in Saskatchewan have a project underway to learn more.

“We are investigating the response of crops normally grown in the drier region of the Prairies to the addition of starter potassium chloride (KCl) on yield and disease incidence,” says Jeff Schoenau, professor of Soil Science and Saskatchewan Ministry of Agriculture chair in soil nutrient management, Department of Soil Science at the University of Saskatchewan (USask). “In this project, we are examining the extent to which potash fertilizer applied at seeding may benefit durum wheat, chickpea and mustard yield. We are also exploring how this fertilizer impacts crop health by supplying ample soil K and Cl, which are important in early nutrition, standability, drought tolerance and disease resistance. Along with field trials, we also have controlled environment studies with the same crops.”

Schoenau is leading the project in collaboration with graduate student Tristan Chambers and research associate Ryan Hangs, as well as Michelle Hubbard, research scientist with Agriculture and Agri-Food Canada (AAFC), and Randy Kutcher, professor in the Department of Plant Science at USask.

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Field trials were conducted in southern Saskatchewan over two crop seasons in 2022 and 2023. Three crops – durum, mustard and chickpea – were grown in both field trials and under controlled environment conditions on two soils: a sandier soil of Chaplin association and a second slightly heavier silty loam textured Swinton association soil. The project also compared the response to KCl at two landscape positions in farm fields in south-central Saskatchewan: a higher slope (knoll) position and a lower slope (depression). A starter application of potash was applied by side-banding at seeding at a single rate of 40 kg/ha of 0-0-60. In 2024, spring wheat will be seeded across the two field trial sites to evaluate whether there are any residual effects from the potash application.

“We included two different slope locations to better understand how crops respond at different landscape positions,” explains Schoenau. “The landscape dependency and interaction of soil and environmental conditions on crop response become important when considering site-specific precision fertilizer program recommendations. The knolls tend to be drier, higher pH and often sandier soils. The lower depressional areas tend to be the wetter part of the landscape, with lower pH, soils that are more highly leached and potentially more susceptible to disease. From past research, we know these can be the most deficient parts of the field where chloride, which is highly mobile in the soil with water, may be leached below the root zone in spring as a result of the accumulation of snowmelt runoff in the low spots.”

During the two field seasons of the study, the conditions in southern Saskatchewan were very dry. Schoenau notes that the precipitation, particularly in June and July, was well below normal.

“The conditions were an extension of three years of drought that really started in 2021. These dry conditions very much muted the treatment responses in the field trials. In terms of yields of the three crops, the results showed no significant response to the addition of the starter potash in either slope position. However, in 2023 there was a trend of a positive response in durum to the potash treatment in the upper slope position. We could visually see the response at mid-season, however, the final grain yield results were not statistically significant. The drier study conditions also meant there was little in the way of either root or foliar diseases. Although root rot incidence was very low in general, one trial did show a small but statistically significant reduction in root rot in chickpea with potash grown on the upper slope or knoll landscape position.”

The uptake of KCl by the crops and yield were also evaluated in the study. The available soil supply of potassium and chloride was quite high in these sites at the start of the project. The results showed that the lower slope sites not only outyielded the drier upslope sites but also had a much greater uptake of potassium and chloride in the plant materials. Much of the potassium those crops took up and especially the chloride remains behind in the straw. Therefore, if the straw was removed out of those fields along with the grain, the export or removal of potassium and chloride through harvest is much greater. This is something that needs to be taken into consideration in managing potassium and chloride fertility over several years if straw is being removed from the field along with the grain. Also, under typically wet spring conditions with a lot of snowmelt runoff, chloride can potentially be leached out of the soil profile because it is mobile. However, under the dry study conditions, the results did not show any evidence of that.

“Our study also included similar controlled environment trials including all three crops and soils with a range of clay contents from southern Saskatchewan,” explains Schoenau. “For the controlled environment, the objective was to evaluate the early-season response to the starter potash application by measuring the shoot biomass produced after one month of growth. The trials also included applications of potash, monoammonium phosphate and copper sulfate alone and in combination, along with a no-fertilizer check. The results showed there can be an impact of early nutrition, with some trials showing a significant positive yield response in the first month of growth. For mustard grown on the sandy soil, there was a significant positive response to fertilization, with higher early-season biomass yields for the fertilizers alone and in the combinations. This is consistent with what we might expect with a sandier textured soil. Similar to the field trials, there were no significant incidences of either root or leaf diseases in the controlled experiments.”

Schoenau adds, that one interesting observation in the controlled environment experiments was the appearance of the emerging chickpea health issue that has been showing up in some chickpea fields in southern Saskatchewan over the past three or four years.

Schoenau is part of a team led by Michelle Hubbard at AAFC to try and determine the cause of the issue, whether it is disease, fertility, herbicide injury or some other factors. Symptoms observed were bleaching and chlorosis extending from the leaf tips and necrosis and wilting, primarily of the mid-to-upper branches and leaflets; however, symptoms are variable, and so far, no specific cause has been identified.

Researchers in Saskatchewan have a project underway to learn more about the use of potash fertilizer in drier regions.
Photo courtesy of constantgardener/iStock/Getty Images Plus.

“In our controlled environment trials, the symptoms occurred across all of the chickpea treatments, including fertilized treatments and the unfertilized control,” says Schoenau. “Therefore, the issue does not seem to be related to a lack of fertility in the nutrients tested, although we still don’t know the cause. Hopefully, the continued research efforts will help solve this puzzle.”

As part of nutrient management planning, a soil assessment is the first good indicator of whether there is the potential for a response to potash. Although not the case in this study, if fields show low supplies of available potassium and low chloride, then a potash application could be considered. Sandier textured soils can also be more prone to lower supplies of nutrients.

It’s also important to be aware of environmental conditions, such as in a spring with a lot of runoff water from snowmelt or rainfall resulting in water leaching through the soil profile. This can result in reduced chloride levels. Because chloride is also a mobile nutrient element, it is a good strategy to soil test to a 60-cm depth.

“Although our field study was conducted in some very dry conditions over the two years, drier than normal even for southern Saskatchewan, we did learn about crop responses under those conditions,” says Schoenau. “We did see a trend in the one year for a positive early-season response with the durum crop to the potash application in the field on the upper slope position. It will also be interesting to see if there are any residual effects in the following spring wheat crop in 2024. Although the dry study conditions limited the development of root or foliar diseases in the field, good nutrition overall can help a crop be more resilient.

“Fertilizer alone won’t solve disease problems; however, a well-nourished crop with good nutrition is generally better able to fend off diseases. Crops such as chickpea, mustard and durum grown in the drier regions of the Prairies could see crop health and yield benefits from a starter potash fertilizer application, depending on soil nutrient availability and environmental conditions.” 

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