Nitrogen fertiliser for canola in low and medium rainfall regions

Mark Seymour and Sally Sprigg

The Department of Agriculture and Food, Western Australia.

The Grains Research and Development Corporation (GRDC) Project: Tactical Break Crop Agronomy (DAW00227)

The Department of Agriculture and Food, Western Australia (DAFWA) have conducted 17 canola nitrogen experiments over three years from 2012 to 2014 in the low to medium rainfall zones in south-west Western Australia. The rates of applied nitrogen were 0, 25, 50, 75 and 100 kg/ha in 10 low rainfall trials and 0, 25, 50, 75 and 150 kg/ha in 8 medium rainfall trials. Nitrogen was either applied as urea (46% N) or foliar N (UAN 42% N) in a single dose or applied over two to four doses/times at seeding, 4 weeks after seeding (WAS), 8WAS and/or 12WAS.

A typical response is shown in Figure 1, where oil% decreased and grain yield increased at Salmon Gums with applied nitrogen in 2013. At Salmon Gums, oil reduced quicker than grain yield increased, resulting in a flat financial response at rates of applied nitrogen above 40 kg/ha. The balance between oil decreasing and seed yield increasing as applied nitrogen increased resulted in no financial gain from applying nitrogen at eight out of the 17 sites having. This highlights the importance of using computer tools such as SYN – Select your Nitrogen (Excel based) and N Broadacre (iOS) which use rotation history and soil test results to determine nitrogen availability from the soil and plant residues, and setting realistic target yields when determining nitrogen application rates.

Supporting your success

Figure 1 Response of canola grain yield (kg/ha), seed oil (%) and gross margin ($/ha) to increasing nitrogen at Salmon Gums in 2013

In low rainfall areas, the yield of canola can be variable. In particular canola yields in very low rainfall seasons drop off dramatically compared to cereals. Therefore growers may wish to delay canola inputs until they are more assured of obtaining an economic return on their investment. A key component of the DAFWA trials was to determine if the timing of nitrogen had any effect on yield or oil, and if growers could delay their nitrogen top-up closer from their typical timing of 6-8 weeks until ~ 12 weeks – around the start of flowering or mid July for April sown crops.

In general for the same total rate of applied nitrogen the time when the nitrogen was applied had very little effect. For example in 14 out of 15 trials, a typical low rainfall nitrogen rate of 25 to 30 kg N/ha applied produced similar yields and oil, whether applied as split applications, top-ups, in one dollop at seeding, 4, 8 or 12 weeks after seeding (see Fig 2).

At higher rates of 50 kg N/ha, more typically used in medium rainfall areas, similar yields (see Fig 3) and oils were produced if the nitrogen was applied in splits or top-ups, but oils decreased if all the nitrogen was applied at 12 weeks - which is not a normal practice.

Whilst DAFWA would still recommend farmers stick with the common strategy of applying nitrogen in the first 8 weeks, the results from this series of experiments provide growers with the confidence to delay their decisions until closer to flowering, if conditions earlier are uncertain.

Figure 2: Seed yield response of canola to 25 or 30 kg N/ha applied at various times in DAFWA trials conducted in low rainfall areas in 2013 and 2014.

Figure 3: Seed yield response of canola to 50 kg N/ha applied at various times in DAFWA trials conducted in medium rainfall areas in 2013 and 2014.

Photo 1: DAFWA canola timing of nitrogen trial at Salmon Gums June 192013. Plot 3007 has already received 25 kg N/ha 4 weeks after sowing (WAS) whilst Plot 3008 will receive the same amount in another month.

Photo 2: DAFWA canola timing of nitrogen trial at Salmon Gums July 15 2013. Plot 3007 has already received 25 kg N/ha 4 weeks after sowing (WAS) whilst Plot 3008 is set to receive the same amount later in the day at 12 weeks after sowing.

Photo 3: Andrew Hall (DAFWA casual) standing in the canola timing of nitrogen trial at Salmon Gums July 25 2013. Plot 3007 received 25 kg N/ha 4 weeks after sowing (WAS) whilst Plot 3008 received the same amount 10 days prior to the photo being taken at 12 weeks after sowing.

Photo 4: Jackie Bucat (DAFWA Development officer) standing in the canola timing of nitrogen trial at Salmon Gums September 19 2013. Plot 1008 received 25 kg N/ha 4 weeks after sowing (WAS) whilst Plot 1009 received the same amount at 12 weeks after sowing.

Photo 5: Chris Matthews (DAFWA Senior Technical Officer) standing in the canola timing of nitrogen trial at Salmon Gums at harvest in 2013. Plot 3007 received 25 kg N/ha 4 weeks after sowing (WAS) whilst Plot 3008 received the same amount at 12 weeks after sowing.

Important disclaimer

The Chief Executive Officer of the Department of Agriculture and Food and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.

Copyright © Western Australian Agriculture Authority, 2014