Blackshaw: Fertilizer N Efficiency and Utilization of Crops and Weeds in a Canola-Barley Rotation

Date: March 2010
Term: n/a
Status: Completed
Researcher(s): Bob Blackshaw, Agriculture and Agri-Food Canada (AAFC), Lethbridge; Xiving Hao, K. Neil Harker, John T. O'Donovan, Eric Johnson and Cecil L. Vera (AAFC)
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Nitrogen fertilizer is a major input cost in canola (Brassica napus L.) production and farmers are interested in improving nitrogen use efficiencies. A multi-site study in western Canada was conducted to determine the merits of polymer-coated urea (ESN) compared with urea on weed management and yield of hybrid and open-pollinated (OP) canola. Overall, the study results indicated that using ESN may reduce crop-weed competition for soil N, and can result in increased yield and may be advantageous in some situations. The study also showed that switching from urea to ESN could reduce N2O emissions, but the benefits were affected by crop, weed management and local weather conditions.

Nitrogen fertilizer is a major input cost in canola (Brassica napus) production and farmers are interested in improving nitrogen use efficiencies. As nitrogen fertilizer costs have increased markedly in recent years, any increase in N use efficiency will reduce costs and increase farm profits. A multi-site study in western Canada was conducted to determine the merits of polymer-coated urea (ESN) compared with urea on weed management and yield of hybrid and open-pollinated (OP) canola. Previous research has documented that many agricultural weeds successfully capture N fertilizer that would otherwise be used by the crop. Therefore, researchers question whether agronomic systems can be developed to reduce N losses to weeds and maximize N utilization by crops, and reduce environmental impacts, such as greenhouse gases, in production systems.

In this study, researchers wanted to determine if high yielding canola hybrids require greater amounts of N fertilizer than open-pollinated (OP) cultivars; and if polymer-coated urea fertilizer (ESN) could result in greater amounts of available N late in the growing season, which may increase crop yield or quality. They also looked at whether competitive cultivars of canola and/or the use of ESN could reduce the amount of N captured by weeds and reduce the overall level of weed competition; and if competitive cultivars and/or slow release N fertilizer were utilized in a multi-year approach, if the amounts of herbicide used could be reduced. And finally, they wanted to determine if emissions of the greenhouse gas nitrous oxide (N2O) could be reduced by using coated urea fertilizer or growing more productive cultivars that have a greater N demand. Information gained in this study will be utilized to develop improved fertilization strategies for canola production on the semi-arid Canadian prairies.

The study was conducted over four years, and included three Alberta sites, Lethbridge, Lacombe and Beaverlodge and two locations in Saskatchewan, Melfort and Scott. Canola was grown in rotation with barley in a no-till system and both crops were present each year. Fertilizer and herbicide rate treatments were applied to the same plots in four consecutive years to determine annual and cumulative effects. Treatments included a hybrid and OP canola cultivar (both Liberty Link), ESN and urea, 100 and 150% of soil test N fertilizer rates, and 50 and 100% of registered in-crop herbicide rates.

The study showed that hybrid compared with OP canola reduced weed tissue N concentration in 40% of the cases and reduced weed biomass in 80% of the cases. Additionally, weed tissue N concentration was lower with ESN than with urea in 70% of the cases, indicating that weed competition for soil N might be reduced if ESN were utilized. Canola yield was greater with hybrid than with OP cultivars in 15 of 20 site- years. Both hybrid and OP cultivars expressed a positive yield response to the 150% N fertilizer rate in the majority of site years, indicating that there may be merit in farmers fertilizing at higher N rates. Canola yield was similar with ESN and urea in 14 of 20 site- years. ESN compared with urea increased canola yield in 4 site-years and in one additional site-year with hybrid but not OP canola, indicating that ESN may be advantageous in some situations. Canola seed oil concentration was similar with ESN and urea in 19 of 20 site-years.

The investigation on the effect of ESN and weed management on soil N2O emissions at the three Alberta sites showed that N2O emissions were generally low during the growing season (averaging 0.70 kg N ha-1 yr-1 and ranging from 0.08 to 6.85 kg N ha-1 yr-1). Weed management had no effect on N2O emissions. N2O emissions in barley over three years were 34% lower with ESN than with urea. N2O emissions in canola over three years were also lower with ESN, being 17% less than emissions with urea. N2O emissions from canola fields at Lethbridge and Lacombe were similar but were 81% higher at Beaverlodge with the 150% ESN rate in all three years. This result may be due to lower N demand by a less vigorous canola crop at Beaverlodge. Applying ESN at 150% of the soil test N rate resulted in similar N2O emissions as applying urea at the 100% N rate, further evidence that N2O emissions can be reduced with ESN use.

Scientific Publications

Blackshaw, R.E., Hao, X., Brandt, R.N., Clayton, G.W., Harker, K.N., O’Donovan, J.T., Johnson, E.N. and Vera, C.L. 2010. Canola response to ESN and urea in a four- year no-till cropping system. Agron. J. (in press).

Blackshaw, R.E., Hao, X., Clayton, G.W., Harker, K.N., O’Donovan, J.T., Johnson, E.N. and Vera, C.L. 2010. Barley response to ESN applied in a four-year zero-tillage study. Can. J. Plant Sci. (submitted).

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