Recovery of soil and fertiliser nitrogen in irrigated cotton in Australia

John Smith, Mike Bell - NSW Department of Primary Industries, The University of Queensland, School of Agriculture and Food Sciences

Type: Conference Paper
Knowledge level: Advanced

Farm Table says:

Lint yield of irrigated cotton is typically responsive to the application of fertiliser nitrogen (N). However, this research shows that the applications of high rates of fertiliser N that exceed crop requirements is not beneficial

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.

Final comment

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.

2016 - Australia - John Smith, Mike Bell - NSW Department of Primary Industries, The University of Queensland, School of Agriculture and Food Sciences
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