Internal N efficiency
(IE) is defined as the amount of grain dry matter (GDM) produced per unit of N
in the above ground plant at physiological maturity (PMN). Currently, a static
value of IE (48 kg GDM kg<sup>-1 </sup>N) is used to define the optimal PMN in
yield goal-based N recommendations used in 30 U.S. states and several N
recommendation models. To evaluate the accuracy and variability of this value
of IE at the economic optimum N rate (IE<sub>E</sub>), experiments were
conducted at 47 sites located in eight states over a three year period
(2014-2016). To establish IE<sub>E</sub>, N treatments ranged from 0 to 315 kg
N ha<sup>-1</sup> in 45 kg N ha<sup>-1</sup> increments, applied either
at-planting or split with 45 kg N ha<sup>-1</sup> at-planting and the remainder
at the V9±1 V-stage. Average IE<sub>E</sub> across all
site-years was 53 kg GDM kg<sup>-1</sup> N with 79% of the observations between
46 and 60 kg GDM kg<sup>-1</sup> N, higher than the currently accepted value of
IE. Half of the time the timing of N application affected IE<sub>E</sub>, with
greater IE<sub>E</sub> with split N in 70% of these instances due to lower PMN
arising from reduced stover dry matter. In most cases the timing of N did not
affect IE<sub>E</sub>. Across all site-years, GDM at the EONR or EONR were unrelated
to IE<sub>E</sub>. Plant N content at VT of the non-fertilized and 45 kg N ha<sup>-1</sup>
at planting treatments were single variables most highly correlated with IE<sub>E</sub>
(<i>p</i> ≤ 0.10, r = -0.42 and -0.50, respectively). These
variables reflected the amount of residual or available N retained in the plant
and/or SDM at the optimal N rate. Other factors such as plant available water
content at various depths and crop reflectance at the V9 leaf stage
(sufficiency and simple ratio indices for both NDVI and NDRE at 0 and 45 kg N
ha<sup>-1</sup>) were negatively related to IE<sub>E</sub> across all site-years,
but only weakly. Predictive models for IE<sub>E</sub> at planting and prior to
sidedressing accounted for < 50% of the variation in IE<sub>E</sub>.
Internal N efficiency varied considerably, but was difficult to predict, thus
contributing to the inaccuracy of the yield-goal based N recommendations.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/7773974 |
| Date | 10 June 2019 |
| Creators | Matthew E. Shafer (5930849) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Factors_Affecting_Internal_Nitrogen_Efficiency_of_Corn/7773974 |
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