Abstract
Canola has a high nitrogen requirement and optimal nitrogen (N) management in environments with variable rainfall is a challenge. This study investigated the impact of timing of N as a single or split application at different growth stages on seed yield, N uptake and water-use efficiency in canola. Nitrogen rates of 100 and 200 kg ha−1 were applied after sowing when two leaves were unfolded or equally split between the rosette, green bud and first flower stages. The experiments were conducted at two sites with contrasting rainfall and a supplementary irrigation treatment at the low rainfall site, generating a third environment. Nitrogen application increased seed yield by up to 20% at a high rainfall site and by up to 77% at a medium rainfall site, but the timing of N did not significantly affect the yield response to N. Seed yield was closely associated with total dry matter production and seed m−2. N-use efficiency was influenced more by N recovery and uptake efficiency, rather than physiological efficiency, which highlights the importance of soil moisture availability and the ability of the crop to exploit soil water and N reserves. The results suggest that better use of subsoil moisture by overcoming some of the subsoil constraints may be an avenue for further improvements in yield and nitrogen-use efficiency (NUE) of canola in this environment.
Highlights
The introduction of hybrid cultivars with high early vigor, better weed control and increased use of nitrogen (N) fertilizers has improved canola (Brassica napus L.) production in Australia [1].Annual production reached 3.9 Mt in 2017–2018 from approximately 1.8 Mt in 2008–2009 [2].there is still a large gap between actual and attainable yields [1,3,4,5]
Oil content was lower in the split application of 200 kg N ha−1 than the single N application of the same amount under rainfed conditions whereas no such reduction of oil content was observed in the irrigated crop (Table 2)
This study revealed that the rate of N application was more critical to yield than the timing of N
Summary
The introduction of hybrid cultivars with high early vigor, better weed control and increased use of nitrogen (N) fertilizers has improved canola (Brassica napus L.) production in Australia [1].Annual production reached 3.9 Mt in 2017–2018 from approximately 1.8 Mt in 2008–2009 [2].there is still a large gap between actual and attainable yields [1,3,4,5]. The introduction of hybrid cultivars with high early vigor, better weed control and increased use of nitrogen (N) fertilizers has improved canola (Brassica napus L.) production in Australia [1]. In farming systems of southern Australian canola was grown after legume-based pastures to use high-mineral nitrogen (N) in the soil and to break the cereal root disease cycle. With the intensification of the cropping system and increased popularity of canola, canola is grown most often in continuous cropping systems where it is often grown after cereals in soils with low N status and where high rates of N are required to achieve high yields. In the Mediterranean environment of South Australia, water and N availability are the most critical factors for sustaining crop productivity [5,7,8,9], but often water-use efficiency (WUE) and nitrogen-use efficiency (NUE) are low
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