Effects of in-season fertilizer strategies on the yield and nitrogen use efficiency of irrigated corn
Date
2016
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Inefficient use of nitrogen (N) fertilizer in agronomic crop production can lead
to water quality concerns and reduced yields for growers. Nitrogen left in the soil after
crop harvest is subject to leaching losses to groundwater or gaseous losses to the
atmosphere. Split additions of N via sidedressing or fertigation can better time N
applications with corn N uptake and improve N use efficiency (NUE). Irrigation can
also stabilize yields and raise NUE at decade time scales. The objectives of this study
were to 1) quantify the effect of N rate and timing under central pivot irrigation on
grain yield and N use efficiency in Delaware using a plot study and 2) investigate the
impact of irrigation on yield and NUE in Delaware using historical yield data.
A plot study was completed by establishing irrigated corn on well-drained soil
which received zero N (control) or 6.72 Mg ha-1 poultry litter, 34 kg ha-1 starter N at
planting, and 0, 82, 140, or 198 kg ha-1 of in-season N (applied at sidedress at V5 or
via fertigation at V5, V8, V11, and V13). Grain yield was determined for each
treatment at harvest using a weigh wagon. Pre-plant soil, post-harvest grain, residue,
and in-season soil samples were collected and analyzed to allow calculation of NUE
by several methods. Nitrogen application rate affected yields and NUE more than N
timing and application when in-season N was applied. Yields of irrigated corn were
statistically similar at N rates exceeding 82 kg ha-1; average yields over the study
period were 17 Mg ha-1. Partial factor productivity of nitrogen was above 60 kg kg-1
for corn at all N rates except the highest rate. Total aboveground biomass for irrigated
corn treatments receiving supplemental N generally contained more N in plant tissue
(values ranged from 214 to 254 kg ha-1) than Chesapeake Bay Model Scenario Builder
(SB) maximum uptake estimates of 218 kg ha-1. Mass balance estimates of NUE
indicated that 13 to 49% of available N applied to plots could not be unaccounted for
in plant tissue or soils. The mass balance approach illustrated a trend for increasing
unaccounted for N with increasing N rate but, this was only significant in 2014.
Leachate concentrations of NO3-N at 60 cm depth were highest in plots receiving
supplemental N, with mean concentrations of 7 and 22 mg L-1 NO3-N in 2014 and
2015, respectively.
Currently, irrigated land receives an interim credit of 4% reduction in total N
in the Chesapeake Bay Model. This reduction is modeled like a filter, where irrigated
corn would release 4% less N than comparable rainfed fields. Historical data from
University of Delaware corn hybrid variety trials were analyzed to evaluate effects of
irrigation on corn yields and NUE over time. Historical yield data and calculated NUE
(from variety trials and UD field plot studies) were compared to values in the literature
and those used by the Chesapeake Bay Program. In the last two decades, hybrid
variety trials met and exceeded the 12.5 Mg ha-1 yield maximum value used in the
Chesapeake Bay Model SB. Rainfed plots were 80 and 85% as efficient as irrigated
plots in converting applied N to grain yield over the 35 year history of UD corn
variety trials. A scenario indicated that irrigated corn could consume 1,030 Mg more
N annually than rainfed plots if they were fertilized based on UD N rates for a realistic
irrigated yield goal.
Based on results of a two-year plot study at UD Warrington Irrigation Farm
and analysis of 35 years of yield data from UD variety trials, we make the following
preliminary recommendations: 1) lower UD N rate recommendations for high yielding
irrigated corn by 15 % to account for increased NUE of irrigated corn and 2) Evaluate
if irrigation’s NUE would be more appropriately modeled as a separate crop category
or, as a BMP. Future research should focus providing data to further refine these
recommendations by quantifying NUE at a regional scale. On-farm strip trials could
be conducted by UD researchers with a common protocol at multiple locations to
evaluate how NUE and yields are affected by irrigation and N management. In
addition, we also recommend collection and analysis of leachate and groundwater
samples as part of these strip trials to determine risk of N losses at different locations
under various soil and management conditions.