Mohr: Long-Term Residual Effects of Alternative Nitrogen Management Practices in Canola Production Systems
Date: December 2016
Term: 4 years
Status: Completed
Researcher(s): Ramona Mohr and Cynthia Grant, AAFC-Brandon Research and Development Centre
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Nitrogen (N) fertilizer is one of the key inputs in most annual crop production systems, however, N fertilization strategies and decisions may also have longer-term implications for N dynamics in cropping systems. Therefore, upon completion of a four-year N management study in wheat and canola, researchers initiated a follow-up study to determine the effect of previous N management on plant-available N levels in the next two growing seasons. The results demonstrate that preceding crop productivity and N management have the potential to impact N availability in the cropping system in subsequent years, and therefore should be considered when making N management decisions.
Nitrogen (N) fertilizer is one of the key inputs in most annual crop production systems. While research has typically focused on the effect of N management in the year of implementation, N fertilization strategies and decisions may also have longer-term implications for N dynamics in cropping. Understanding the cumulative effect of N management practices applied over time may help to identify risks and benefits associated with specific management decisions. In addition, information regarding N availability following a poor- versus high-yielding crop may provide some insights into possible N management strategies to address these situations.
In a previous four-year study conducted near Brandon, MB from 2010 through 2013, researchers determined the effect of N management on crop yield, and on N input and removal, in a 2-year canola/spring wheat rotation. Various N management practices were studied, with treatments ranging from control plots receiving no N fertilizer to treatments receiving 150% of soil test N recommendations in 1 of 4 years. In 2013, the final year of the management study, poor emergence resulted in negligible canola yields regardless of treatment, while spring wheat yielded well overall averaging about 3700 kg/ha. This situation presented a unique opportunity to compare the effects on N availability of growing a poor- versus high-yielding crop.
The objective of the follow-up research study conducted in 2014 and 2015 was to determine the effect of previous N management on plant-available N levels in two subsequent growing seasons. Researchers were also able to compare effects of preceding crop productivity by comparing N availability following the poor-yielding canola versus high-yielding wheat crops grown in 2013. In 2014 and 2015, wheat receiving no N fertilizer was established across the entire experimental site of the previous canola-wheat rotation. In both years of the study various measures were collected, including plant stand, grain and straw yield and N concentration, protein, test and seed weight. Soil samples were collected periodically over the course of the study including fall samples at 0-15, 15-30 and 30-60 cm. While this study was conducted in Manitoba, results are expected to apply to similar ecozones in Saskatchewan.
The study results showed evidence of residual effects of preceding crop productivity and preceding N management in both 2014 and 2015. In 2014, higher grain yield and increased N availability were evident following the poorly-yielding 2013 canola crop compared to the high-yielding 2013 wheat crop. This was likely due at least in part to lower N demand and removal by the 2013 canola crop. On average, those treatments that included a 1 in 4 year application of the 150% N rate resulted in increased crop N uptake, fall soil nitrate content, and available N supply compared to those treatments that included a 1 in 4 year application of 0 N. Effects of preceding treatments appeared to diminish somewhat by 2015; however, fall soil nitrate content and available N supply followed a similar trend as in 2014.
These findings demonstrate that preceding crop productivity and N management have the potential to impact N availability in the cropping system in subsequent years, and therefore should be considered when making N management decisions. Observed differences in soil nitrate levels suggest that soil testing may provide information regarding residual N effects and therefore may be a helpful tool for growers when making fertilizer decisions.