Farm Table says:
What is the problem?
Nitrogen nutrition is an important determinant of the growth and yield of irrigated cotton and recently there has been increasing focus on the use of N within the Australian cotton industry.
Growers continue to use high rates of fertiliser N with the aim of achieving higher lint yields despite N
representing one of the highest components of crop variable costs under their control.
This research was the first in a planned series of experiments to assess the impact of irrigation method on
crop N recovery within N fertiliser rate experiments.
What did the research involve?
Nitrogen recovery efficiency was determined in four field experiments conducted during the 2014/15 cotton
season on the Darling Downs region of Southern Queensland, Australia.
Two field sites were established in each of two irrigation systems, overhead and flood-furrow, although only three field sites were used in the analysis due to the impact of disease at one of the overhead irrigation sites.
At each site, eight N fertiliser treatments were applied approximately 10 weeks prior to sowing the cotton,
with plots 8 rows wide (1 m row spacing) and 20 metres long.
What were the key findings?
This work is consistent with other studies within the Australian cotton industry in that adequate levels of N
uptake to achieve maximum lint yield can be achieved from lower levels of N fertiliser application than are
currently being applied commercially.
The application of large amounts of fertiliser N to cotton crops to increase total N supply results in a significant reduction in nitrogen recovery efficiency (NRE), compared to when total N supply was sufficient to achieve maximum lint yield.
Improving low NRE across the industry by manipulating the applied N rate to reflect both starting soil N and likely crop requirement is a significant opportunity for the industry, but one that has to be balanced against the financial risk of lower lint yields.