Few responses to potassium fertilization
Positive wheat and malt barley response under irrigation, but drought masked the benefits under dryland.
September 6, 2023 By Bruce Barker
Potassium (K) fertilizer is often sold as cheap insurance against lodging, and to help promote plumper malt barley seed – a desirable trait for maltsters. Research in Saskatchewan looked into whether these, and other benefits like higher yield and better test weight, are real, even though most soils in Saskatchewan have high soil test K fertility.
“The idea behind this project, brought forward by Sask Wheat and Sask Barley, was to look into whether potassium fertilizer has a clear role and provides yield responses in wheat and barley production,” says Gursahib Singh, research director with the Irrigation Crop Diversification Corp. in Outlook, Sask.
Much of the research on K fertility on the Prairies is old, dating back to the 1950s and 1960s. Westco Fertilizer research between 1989 to 1998 in 124 trials across the Prairies found a barley response to seed-placed K fertilizer in two of five years, and one in five years in wheat. But new, higher yielding varieties might respond differently.
An Agricultural Demonstration of Practices and Technologies (ADOPT) program trial, funded by the Saskatchewan Ministry of Agriculture, was conducted over two years at Agri-Arm research sites across Saskatchewan at Outlook, Yorkton, Redvers, Indian Head, Prince Albert and Swift Current in 2021. Because of the 2021 drought, the trials were repeated at Outlook, Redvers, Yorkton and Swift Current in 2022.
Soil test K levels ranged from a low of 60 ppm at Prince Albert to a high of 587 at Indian Head, and most sites were well above 150 to 200 ppm. Multiply ppm by a factor of two to get kg K2O/ha. For example, at Outlook in 2021, the soil test level was 190 ppm, or 380 kg K2O/ha.
Eight different K fertilizer treatments (0-0-60 KCl) were applied, with different rates and placement:
- 0 kg K2O/ha
- 10 kg K2O/ha seed placed (9lbs/ac)
- 20 kg K2O/ha seed placed (18 lbs/ac)
- 30 kg K2O/ha seed placed (27 lbs/ac)
- 10 kg K2O/ha side band (9 lbs/ac)
- 20 kg K2O/ha side band (18 lbs/ac)
- 30 kg K2O/ha side band (27 lbs/ac)
- 20 K2O seed + 40 K2O band (18 lbs/ac + 36 lbs/ac)
Nitrogen fertilizer was applied at 1.25 times the recommended soil test level to try to push for lodging conditions. The treatments were applied to malt barley and spring wheat – the varieties varying by location.
Effects measured included days to maturity, plant height, lodging, disease, yield, protein, test weight, Thousand Kernel Weight (gm/1,000 seeds) and percentage of plump and thin seeds.
Minimal wheat response to K fertilizer
Singh says that across all sites, there was little to no effect on wheat for most of the parameters measured. This was in part due to the historic drought in 2021 and lingering effects in 2022.
“If the background fertilizer levels are high, that tends to eliminate a response to fertilizer, and that’s what we saw in our study as well,” says Singh. “Those sites with really high soil test levels didn’t show any response.”
Under dryland conditions, the adverse environmental conditions negatively affected wheat growth, and likely had an impact on K fertilizer response. Across all 10 site-years, only ICDC in 2022 showed a wheat yield response under irrigation. At ICDC 2022, the control had the lowest yield of 72 bushels per acre
(4,842 kg/ha), and all other rates and sideband treatments were statistically similar and higher with an average yield of 81 bu/ac (5,447 kg/ha).
“There wasn’t any difference between the K rates or placement,” says Singh.
However, even under irrigation, yields were lower than normal years without a drought. Typically, yields under irrigation at ICDC range from 89.2 to 92.2 bu/ac range (6,000-6,200 kg/ha), compared to the average yield over the two years of 65.6 bu/ac (4,412 kg/ha).
Malt barley responses
Similar to wheat, malt barley on dryland did not respond to K fertilization, again, mostly due to the poor growing conditions. No differences in lodging were observed, even under irrigation. However, there were some differences in yield and grain quality under irrigation at Outlook.
At Outlook, all fertilizer treatments resulted in higher yield compared to the control. The K fertilizer treatments were statistically higher averaging 102 bu/ac compared to the control at 88 bu/ac (4,734 kg/ha) in 2021. In 2022, K fertilizer treatments averaged 118 bu/ac (6,348 kg/ha), and were statistically higher than the control at 104 bu/ac (5,595 kg/ha). The statistically highest yield was Treatment 8 with the split-applied application. The mean yield response to K fertilizer was 17 per cent. When K was seed-placed, yield was highest with the 10 kg K2O/ha rate and declined with additional seed-placed K rates.
“This suggests that although K fertilizer was beneficial, the higher rates may have caused some seedling damage from fertilizer salt, particularly in the dry seed bed conditions prevalent in 2021,” says Singh. “Once fertilizer K was positioned away from the seed, in a side-band application, all treatment rates produced statistically higher grain yield compared to the control treatment.”
Because of the drought, protein content at all sites except Outlook were too high for malt acceptance. At Outlook, all treatments easily fell below the preferred 11 to 12 per cent protein content, with none of the treatments greater than 9.2 per cent. There was a trend at Outlook for lower protein content with the addition of K fertilizer compared to the control, partially due to the dilution effect from having higher grain yield.
“Generally, it appears that at ICDC the 10 kg K2O/ha rate provided optimal barley yield, aligning with the conventional soil test K fertilizer recommendation for this location, says Singh.
For other quality components of grain test weight, TKW and plump seed, very little response was observed, even under irrigation. However, at Indian Head, some K additions did tend to increase the percentage plump seed fraction, though results were variable both within K rates and between K fertilizer positional placement.
Overall, the demonstration trials did show that at high yielding sites K fertilization can provide a yield response in wheat and yield and quality response in malt barley. However, the impact of the adverse growing conditions means the lack of K fertilizer responses under dryland conditions cannot be positively determined.