http://orcid.org/0000-0002-1206-1105
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ABSTRACT
The use of optical sensors to detect nitrogen (N) deficiencies and determine in-season fertilizer recommendations has grown. Nitrogen responses are difficult to detect early in the growing season. The objective of this experiment was to determine if different N sources could deliver early season detection of N deficiencies. Four N fertilizer sources were applied at rates of 90 and 180 kg N ha−1 across three site-years. A Greenseeker and SPAD sensor were used to measure in-season fertilizer response index (RI). When differences in sensor RI values between N rates were present, they did not occur until the V9/10 growth stage. No specific N source provided superior results that led to a reliable, early season detection of N deficiency. Reliable differences in response index values could be detected beyond the V7/V8 growth stages. For earlier detection of N responsiveness, and potential N deficiency, other management strategies should be investigated.
Abbreviations
| AS | = | ammonium sulfate |
| CN | = | calcium nitrate |
| GBAOS | = | ground-based active optical sensors |
| GDD | = | growing degree day |
| N | = | nitrogen |
| NUE | = | nitrogen use efficiency |
| NDVI | = | normalized difference vegetation index |
| RI | = | response index |
| UAN | = | urea ammonium nitrate |
Conflict of interest
The mention of any trademarked products or equipment utilized in this experiment was for research purposes only and does not act as an endorsement by Oklahoma State University. The authors and Oklahoma State University have no direct financial relation with any of the named manufacturers, thus the authors declare there is no conflict of interest regarding the publication of this manuscript.
Acknowledgments
The authors would like to thank the Oklahoma Soil Fertility Research and Education Advisory Board for funding of this research project and their continued financial support of soil fertility and sensor-based nutrient management research at Oklahoma State University.