Should nitrogen rates be increased on blocks that produce very high yields?

  • High-performing sites are those blocks that perform well above the district yield potential (DYP) (Table 1) on a consistent basis.
  • In some cases, zones within a block may be high-performing rather than the whole block.
  • It is more likely for these sites to achieve high yields in the plant and early ratoon crops.
  • Record yields are substantially higher than the district yield potential in all regions (Table 1).
  • These are an indicator of what has been achieved under ideal conditions at a small number of sites, although average yields on these blocks are likely to be significantly lower.

 

Table 1. District yield potentials and record yields

  • High-performing sites generally have few soil constraints, are well managed and perform well when environmental conditions are favourable.
  • Due to the high yield, nitrogen use efficiency on these blocks may be better than poorer performing blocks on a farm or within a region. However, it is also important to optimise inputs on these sites to maximise profitability and minimise off-site effects.
  • Evidence suggests that the SIX EASY STEPS recommended nitrogen rate based on the district yield potential is unlikely to limit productivity at these sites.
  • There is a poor relationship between yield and optimum N rate (Thorburn et al. 2018) in sugarcane.
  • An assumption that big crops require higher nitrogen application rates than smaller crops may not be correct. Application of additional nitrogen will increase input costs and may not result in improved productivity, profitability or nitrogen use efficiency.
  • A risk associated with increasing nitrogen application rates on these sites is the potential to increase lodging and suckering and lowering CCS.

For these high-performing sites, the SIX EASY STEPS recommended rate should be applied unless evidence is available to support an increased nitrogen rate.

 

  • Reef regulations currently require productivity data that shows performance above the district yield potential in 3 of the last 15 years (refer to “Farming in Reef catchments – Prescribed methodology for sugarcane cultivation”).
  • From an agronomic perspective, a grower should determine whether there is a productivity and economic response to applying additional nitrogen fertiliser on these blocks or zones.
  • Ideally an on-farm trial comparing the SIX EASY STEPS recommended nitrogen rate to a higher rate should be conducted over several seasons.
  • This evaluation process needs to comply with reef regulations and a higher rate may need to be offset elsewhere on the block/farm.
  • A guideline for conducting on-farm trials is included in the SIX EASY STEPS toolbox.
  • Leaf testing also provides a valuable method for checking on the adequacy of nutrient inputs.

Disclaimer:

Papers published from the Australian Society of Sugar Cane Technologists annual conference are also available at www.assct.com.au

 

Version: April 2020

 

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