Background 

Potash (KCl; 0-0-60) fertilizer is the most economical and widely used source of potassium (K) and chloride (Cl) for crop nutrition. However, the link between KCl fertilization, crop yield, and disease incidence has not been investigated for chickpea, durum wheat, and mustard crops grown in the drier regions of the Canadian Prairies that encompass the brown soil climatic zone.  

Prior research has shown that K may play an essential role in a crop’s ability to mitigate drought, salinity, metal toxicity, high or low temperatures, and other abiotic stresses (Wang et al., 2013). In addition, starter K’s potential for yield response has been documented in several crops, including barley (Karamanos et al., 2003), and a few studies have observed responses to starter K despite high levels of soil test extractable, exchangeable K.  

Investigations by multiple researchers have linked Cl to direct effects on tissue water balance, charge-balancing functions, photosynthetic performance, nitrogen (N) use efficiency, lodging prevention, and disease suppression. It has also been linked to increased yield in canary seed grown in some Southern Saskatchewan soils (May et al., 2012) as well as to a reduction in root and shoot diseases incidences in some cereal crops grown in the Pacific Northwest region of the United States (Christensen & Brett, 1985; Christensen & Hart, 2008; Freeman et al., 2006). However, the contributions of Cl supplied through KCl fertilization have yet to be investigated in chickpea, durum wheat, and mustard grown on the Prairies.  

The potential benefit of adding phosphorus (P) and copper (Cu) fertilizers to pulse crops under root disease stress has also recently been suggested (Holzapfel, 2016; Rahman & Schoenau, 2020). 

To make site-specific recommendations regarding which crops would likely respond well to KCl fertilization, how soil and environmental conditions affect benefit from fertilization, and how interactions with other nutrients may factor in, it is important to understand how the different soil and environmental conditions in southern Saskatchewan’s typical undulating kettle and knob topography affect the response of chickpea, durum wheat, and mustard to KCl fertilization at the landscape scale. 

Design of Experiment 

A two-year field study was conducted in two undulating agricultural fields located near the town of Central Butte in South-Central Saskatchewan in 2022 and 2023. In addition, controlled-environment growth chamber experiments were conducted using three different soils with contrasting properties (Chaplin, Elstow, and Swinton soil associations) taken from across the brown soil zone of Saskatchewan. The goals of this study were to:  

This research was conducted in a region where the soil test results often indicate high soil potassium concentrations and supply rates.  The field study aimed to explore the potential benefits of KCl application in spring at the time of seeding at low rates as a “starter” in enhancing crop yields, maintaining soil fertility, and mitigating plant disease, despite the presence of adequate K according to soil analysis of spring samples. Previous research has occasionally reported positive outcomes from KCl fertilization in other crops with sufficient soil test K.  

Study fields consisted of moderately rolling knob and kettle morainal topography and included an upslope eroded knoll position and an adjacent depression landscape position. These fields had no record of previous KCl applications, and air temperature and rainfall were monitored throughout the growing seasons.  

The field trial was structured as a randomized complete block design, and treatments were replicated four times in both study years.  

Starter KCl was banded at 40 kilograms per hectare (kg/ha) on 1 x 4 metre (m) treatment plots. The control received no KCl. Chickpea plots were side-banded during seeding with ammonium sulphate, monoammonium phosphate (MAP), and copper sulphate (CuSO4) as basal applications at recommended rates in all treatments. In contrast, mustard and durum wheat plots were side-banded with urea, ammonium sulphate, MAP, and CuSO4.In both study years, Kabuli chickpeas (var. CDC Leader) were seeded in mid-May at a rate of 200 kg/ha, and mustard (var. AAFC Hybrid Brown) at 6.7 kg/ha. Durum wheat (var. CDC Precision) at 140 kg/ha using a small plot four-row seeder with openers on 10-inch spacings that provided a 1-inch side-banded spread.  

Chickpeas received a seed-placed granular inoculant at double the recommended rate and a fungicidal seed treatment. Weeds were controlled pre- and post-planting using a combination of mechanical methods and registered herbicides that were applied according to label recommendations. Grasshoppers were controlled in July and August of each study year, as needed, with registered pesticides applied according to label recommendations. 

Surface (0-15 cm) and subsurface (15-30 and 30-60 cm) soil samples were collected prior to seeding and post-harvest in both study years.   

Also in both study years, a visual assessment was performed in July on above-ground biomass and root samples for disease (Fig. 1). Above-ground biomass was then harvested during the second week of August for each crop and tests were performed to determine grain and straw yield, K and Cl concentration and uptake, disease ratings, and fall soil levels of K and Cl after harvest.  

Figure 1. Crop disease assessments are being conducted during the 2023 growing season. 

Additional field studies were conducted in 2023 and 2024 to determine if prior-year KCl fertilization had any residual effect on hard red spring wheat (var. CDC Hughes) yield the following year. 

Controlled-Environment Growth Chamber 

Controlled-environment growth chamber studies examined the effect of starter KCl, MAP, and CuSO4, applied alone and in combination, on early crop growth as well as on root and shoot disease incidence in chickpea, durum wheat, and mustard crops grown in three different soils (Chaplin, Elstow, and Swinton soil associations) collected from fields in South-Central Saskatchewan. 

Seven different fertilizer treatments were applied to the three crops, including a control. All treatments for mustard and durum wheat included a basal application of urea and ammonium sulphate at a rate of 125kg N/ha and 25kg S/ha. Chickpeas were inoculated with a commercial rhizobium and received only ammonium sulphate in the basal application.  

The seven treatments applied to the crops were: 

  1. Control (no KCl, no MAP, no CuSO4) 
  2. 40 kg/ha of KCl alone 
  3. 40 kg/ha of MAP alone 
  4. 5 kg/ha of Cu supplied as CuSO4 (20kg/ha of CuSO4) alone 
  5. KCl + MAP 
  6. KCl + Cu 
  7. KCl + MAP + Cu 

Plants were grown for one month in the phytotron following germination. The same varieties from the field trials were used, and chickpea seeds were treated with a registered fungicide.  

The treatment pots were placed in a controlled-environment growth chamber using a completely randomized design (Figure 2). After approximately one month, the above-ground plant material was harvested for biomass determination and nutrient analysis.  

Figure 2. Controlled-environment growth chamber pot study of the chickpea, durum wheat, and mustard grown in the Swinton soil over approximately one month. 

The three crops were visually inspected, and above-ground tissue was rated for disease incidence prior to harvesting the pots. A root disease assessment was performed post-harvest.  

Measured parameters included: shoot biomass for all three crops, root biomass for mustard and durum wheat, K, P, Cl, and Cu tissue concentration, and shoot and root disease incidence ratings. Effects were examined separately in all soil and crop types.  

Results 

During the two-year field study, growing season conditions were hotter and drier than usual. The KCl fertilization provided no significant yield benefit at either topographic position for the chickpea, durum wheat, and mustard crops, and there were no significant reductions in disease incidence, consistent with the soil analyses showing high available K concentrations and supply rates. In one field season (2023) at one site, the chickpeas did show a small but statistically significant reduction in root rot incidence from KCl application, but this did not translate into a significant yield benefit.   

The primary factor influencing crop yield was landscape position. Due to the higher inherent soil fertility and greater available moisture, crop yield was much higher and nutrient removal was greater in the depression site compared to the drier upslope eroded knoll site. This highlights the need to consider differences in crop removal across the landscape in a variable rate fertilization program that is intended to replace or build soil K and Cl fertility over several years. 

Crop and straw tissue analysis revealed no significant increases in K or Cl concentration in the chickpea, durum wheat, or mustard from the KCl application. Most of the K and Cl uptake in the above-ground biomass was in the straw portion rather than the grain, with about 30% of the above-ground K and Cl contained and removed in the grain of the chickpea and only about 10% in the grain of the durum wheat and mustard. The occurrence of most of the K and Cl in the straw compared to the grain, especially for durum wheat and mustard, indicates that harvesting the straw along with the grain would significantly accelerate soil K and Cl fertility depletion over time. 

The field studies added in 2023 and 2024 determined that prior K treatment did not significantly impact subsequent hard red spring wheat yield at either landscape position in either additional year.  

Controlled-Environment Growth Chamber Results 

Under controlled environment conditions, significant early-season growth responses to fertilization were sometimes observed despite the high extractable K concentrations and K supply rates and P and Cu levels that were above sufficiency in all three soils. However, they varied by soil association and crop type. For instance, increases were seen in early-season biomass in mustard grown in sandy Chaplin, durum wheat grown in loamy Elstow and chickpea grown in Swinton association soils.  

Chickpea biomass values were influenced by the presence of the Chickpea Health Issue in the growth chamber, which reduced overall biomass values in the Swinton soil and, to a lesser extent, in the Chaplin soil. There was no observed effect from fertilization on the severity of Chickpea Health Issue or any other disease.  

Overall, chickpea, durum wheat, and mustard responses to KCl fertilization alone on these high K soils were small under the ideal conditions that were present in the growth chamber and aligned with the lack of response to KCl fertilization seen in the more adverse conditions that prevailed during the field study. 

Where benefits from fertilization were observed, the most significant increases appeared to be the result of an additive fertilizer effect. For example, applying all three fertilizers (KCl, MAP, Cu) together in the Elstow soil association resulted in the most significant increase in early-season biomass compared to the unfertilized control.  

Recommendations 

Applying additional starter KCl for chickpea, durum wheat, and mustard crops grown under the conditions of the field study—dry, low disease pressure, and high inherent soil test K and Cl levels—offers no significant yield advantage for producers in the brown soil zone.  

However, regular removal of straw from these crops along with grain will contribute to fertility depletion over the long term since the K and Cl were found to mainly reside in the straw and should be monitored and accounted for in order to maintain soil supplies. Higher yields and associated K and Cl removal in harvested grain in the depressions highlight the need to consider differences in crop removal across the landscape in a variable rate fertilization program that is intended to replace or build soil K and Cl fertility over several years. 

Early-season growth responses sometimes observed when KCl was applied in combination with P and Cu fertilizer in the growth chamber point to the need to ensure balanced fertility to obtain the most benefit from all nutrients applied. 

Also note that KCl, CuSO4, or MAP fertilization was ineffective for mitigating the Chickpea Health Issue in this study, the cause of which remains unidentified.  

Future Research 

Additional research would be desirable under wetter conditions to evaluate the effects of KCl fertilization on yield response and disease incidence, where pathogen presence is higher and disease pressure is more severe than what was observed in this study.  

Further field research should also be conducted on crops to understand better the collective impact of the combined use of KCl, MAP, and CuSO4 fertilization on yield, nutrient uptake, and disease.  

Additional research is also needed to identify the cause of the Chickpea Health Issue to determine whether alternative nutrient management strategies have the potential to mitigate its severity effectively. 

Acknowledgements 

Project Lead: Dr. Jeff Schoenau, Professor and Ministry of Agriculture Strategic Research Program (SRP) Chair in Soil Nutrient Management, University of Saskatchewan 
Graduate Student: Tristan Chambers, Department of Soil Science, University of Saskatchewan 
Research Associate: Dr. Ryan Hangs, Postdoctoral Fellow, Department of Soil Science, University of Saskatchewan 
Collaborators and Co-Investigators: Dr. Michelle Hubbard, Research Scientist, Agriculture and Agri-Food Canada; Dr. Randy Kutcher, Plant Pathologist, Department of Plant Sciences, University of Saskatchewan 

Project Funding 

Saskatchewan Pulse Growers (SPG), Saskatchewan Wheat Development Commission (Sask Wheat), Alberta Wheat Commission (Alberta Grains), Mustard 21 Canada, Ministry of Agriculture, and the Sustainable Canadian Agriculture Partnership.