As the winter cropping season progresses, some fortunate growers may be considering in-crop nitrogen (N) applications.
At the 2016 GRDC research updates, CSIRO researcher and mixed farmer John Angus discussed when and how to review N nutrition during the season. Once a cereal crop has emerged, the key times to review N status and requirements are at stem elongation and approaching booting, when demand for N is greatest. Around 60% of total N uptake occurs in this period, which is why N application during tillering can produce very effective yield increases.
There are a variety of calculation tools available to help growers estimate crop N needs. Equii’s Wayne Pluske outlines how to fine tune mid-season nitrogen requirements, and suggests growers use tools such as Yield Prophet to help make N decisions. GRDC also commissioned Dr Murray Unkovich from the University of Adelaide to conduct a review of nitrogen decision support tools. Other helpful mid-season topdressing tactics and tools that growers can directly apply include deep soil N testing and inclusion of N rich strips in their crops.
If in-crop N application is deemed worthwhile, IPNI’s Rob Norton has shown that getting the timing right for topdressing N fertiliser is more important for N use efficiency than the form of fertiliser used. Applying N early (up to stem elongation) generally has a bigger impact on yield. Late applications of N (at or even after head emergence) can be used to increase crop protein levels.
Field experiments generally show that granular urea, urea solutions and UAN perform equally well in supplying N when used in-crop. However, soil moisture, crop growing conditions and seasonal conditions are critical when topdressing N in-crop, as discussed in three reasons why topdressing nitrogen can fail and the good, the bad and the ugly of topdressing opportunities.