In Season Prediction of Nitrogen Use Efficiency and Grain Protein in Winter Wheat (Triticum Aestivum L.)
Abstract
The algorithm currently used at Oklahoma State University for mid-season fertilizer nitrogen (N) recommendations utilizes an assumed nitrogen use efficiency (NUE) of 0.5. The recommended N rate is calculated by subtracting N uptake without additional N from N uptake with additional N and dividing the difference by the NUE. Refining the estimation of NUE would allow more precise N fertilizer recommendations. Also, many winter wheat producers in Oklahoma have at some point encountered protein related deductions at the elevator. Knowing protein levels mid-season would allow farmers to make fertilizer adjustments in time to achieve optimal yield and protein levels. The objective of this study was to evaluate the use of Normalized Difference Vegetation Index (NDVI) and SPAD chlorophyll meter readings to predict NUE and grain protein in winter wheat. In addition yield, NUE, grain protein, and N uptake were evaluated as a function of rate and timing of N application. Preplant treatments ranged from 28 kg ha-^1 to 224 kg ha-^1. Selected treatments also included topdress rates of 28, 56, 84, 112, and 140 kg N ha^-1. GreenSeeker and SPAD readings were collected at Feekes (F) 3, 4, 5, and 7. Over two cropping seasons it was noted that NDVI did not reliably predict NUE. GreenSeeker NDVI readings collected at Hennessey gave the best correlation with grain protein (in 2010, r^2= 0.32, 0.47; F4, F5, respectively and in 2011, r^2= 0.31, 0.33, 0.66; F3, F5, F7, respectively). In general grain yield and grain protein increased with increasing N rates, and NUE decreased with increasing N rates; a phenomenon most clearly observed at Hennessey. The results of this study suggest that the environment has to be accounted for to improve the prediction of grain protein and NUE.
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- OSU Theses [15752]