Cultivars of canola respond similarly to applied nitrogen in n-deficient soils of south Western Australia

ABSTRACT

Six cultivars of canola (Brassica napus L.) were grown with six levels of applied nitrogen (N) fertilizer (urea 46% N) at six locations in south Western Australia (SWA) during 2010 and 2011. The aim of the experiment was to determine if the seed yield (SY) increase (response) of the canola and associated herbicide technologies were different to applied N. Open pollinated (OP) and hybrid cultivars of associated herbicide technologies (Triazine Tolerant, TT; Roundup Ready, RR; Clearfield, CL) were used. Varieties had large SY differences with no N applied. Generally, RR hybrid of 2011 tended to have the highest SY, except for Katanning 2011 where several varieties obtained the same SY. The average amount of N required for 90% of the maximum SY was 113 kg N ha⁻¹ and economic breakeven N rates were less than or equal to 100 kg applied N ha⁻¹. The average rate of return on investment in fertilizer N was $1.60.

In four out of six experiments RR hybrids had the highest oil concentration with no applied N. N decreased the oil concentration in all canola types, except at Gibson 2010. At Gibson in 2010, N application increased the oil concentration to about 100 kg N ha⁻¹ with further additions of N decreasing the oil concentration. There was a linear relationship where N application decreased the oil concentration and increased protein concentration of the seed. In this study, the summation of oil percentage and protein concentration in the seed was on average 65%, with RR hybrids producing 67%.

In most aspects, RR hybrids outperformed RR, OP and other canola types; however, hybrid TT and hybrid CL canola did not consistently outperform their OP counterpart. We suggest that current N fertilizer recommendation models are useful for all canola types currently grown in SWA; however, adjustments should be made to take into account the higher SY and oil concentration potential of RR hybrids compared to TT canola at every rate of applied N.

Keywords:

• canola
• nitrogen
• nitrogen use efficiency
• oil concentration
• protein concentration

Acknowledgments

We thank the farmers and managers of various Research Farms of the Department of Agriculture and Food for the use of land, land preparation and harvesting of the crop. Technical assistance was provided by Pam Burgess, Chris Matthews, Vince Lambert, Trevor Bell and Colin Norwood. Plant and soil analyses were provided by chemists of the CSBP Laboratories, Bibra Lake (WA). CBH (WA) measured concentration of nitrogen and oil in grain.

Funding

The funds were provided by the Government of Western Australia.