Soybean response to potassium fertility and fertilizer in Manitoba
Bourns, M. 2020.
Abstract
Production of soybean [Glycine max (L.) Merr], a high potassium (K) consuming crop
(18 - 23 g K2O kg-1 or 1.1 - 1.4 lb K2O bu-1), has rapidly expanded in Manitoba in recent years.
However, there has been little comprehensive historical K fertility research for soybean in the
province. A two-year study was developed to assess the frequency of soybean yield response to
K fertilization and determine the effectiveness of K fertilizer rate and placement combinations
for increasing seed yield. The study included small plot trials, field scale on-farm trials and
paired microplots within each on-farm trial.
Small plot trials were primarily used to determine the efficacy of different K fertilizer
rate and placement combinations (33 or 66 kg K2O ha-1 sidebanded, and 33, 66 or 132 kg K2O
ha-1 broadcast and incorporated) for improving seed yield. Although the potential for K fertilizer
response was present at midseason in some site-years, as indicated by an increase in tissue K
concentration of the whole plant (WP), uppermost mature trifoliate (UMT) leaves and the stem,
there was no significant seed yield response to K fertilization at any small plot site-year.
On-farm trials were used to investigate the frequency of soybean response to K
fertilization across a range of NH4OAc soil test K (STK) concentrations (52 - 451 mg kg-1), and
microplots within on-farm trials were used to investigate the response relationships at a more
detailed scale. Three out of nineteen site-years had significant seed yield responses to K
fertilization at a field-scale; one response was negative and two were positive. In the microplots,
the potential for fertilizer K response was also present in some site-years at midseason with
increases in UMT K concentration. However, the site-years with midseason tissue K responses
did not have significant seed yield differences at maturity. There were two site-years that did
have a significant yield increase with K fertilization in microplots, but these were not site-years where K fertilization increased midseason tissue K concentrations. Consistent with the small plot
and field scale results, there was no significant relationship between STK and relative seed yield
in the microplots.
