TITLE:
The Effects of Stabilized Urea and Split-Applied Nitrogen on Sunflower Yield and Oil Content
AUTHORS:
Christopher J. Graham, Jac J. Varco
KEYWORDS:
Nitrogen Uptake, Urease Inhibitor, Isotopic Nitrogen, Nitrogen Use Efficiency
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.8,
July
10,
2017
ABSTRACT: Sunflower
is an efficient nitrogen (N) accumulator due to its aggressive taproot and
extensive root system. While N rate studies in sunflower have shown a yield
response, the response is often highly variable and difficult to predict in
many instances. Additionally, since most sunflower production is intended for
the oil market, surplus nitrogen tends to decrease oil content. Therefore, it
is critical to hone nitrogen rates to maximize both yield and oil production
and to incorporate alternative approaches to fertilizer application, which
includes timing and method of application. The objective of the present study
was to assess the efficacy of a split-application of N at either the V4 or R1
growth stage to increase yield and/or oil content in sunflower. A second
objective was to examine whether a urease inhibitor could be used to retain
soil N longer and achieve a similar effect as a split-application. Studies were
conducted at two locations over two growing seasons in South Dakota, USA. A
target rate of 90 kg·ha-1 was
applied as urea-ammonium nitrate (UAN) either as an at-planting application or
split-applied. Overall, N additions did significantly increase yield over a
control. On average, the urease inhibitor tended to increase grain yields over
split-applying N at either growth stage, however, there was no statistical
effect on either grain yield or oil content. Based on 15N
analysis, approximately 27% of the N in the grain was derived from the UAN
fertilizer, which indicates a relatively large reliance upon soil N for grain N
content. The addition of a urease inhibitor significantly increased average
fertilizer uptake by nearly 6% to 32.7%.