Abstract
Determining a precise nitrogen fertilizer requirement for maize in a particular field and year has proven to be a challenge due to the complexity of the nitrogen inputs, transformations and outputs in the nitrogen cycle. Remote sensing of maize nitrogen deficiency may be one way to move nitrogen fertilizer applications closer to the specific nitrogen requirement. Six vegetation indices [normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), red-edge normalized difference vegetation index (RENDVI), triangle greenness index (TGI), normalized area vegetation index (NAVI) and chlorophyll index-green (CIgreen)] were evaluated for their ability to detect nitrogen deficiency and predict grain maize grain yield. Strip trials were established at two locations in Arkansas, USA, with nitrogen rate as the primary treatment. Remote sensing data was collected weekly with an unmanned aerial system (UAS) equipped with a multispectral and thermal sensor. Relationships among index value, nitrogen fertilizer rate and maize growth stage were evaluated. Green NDVI, RENDVI and CIgreen had the strongest relationship with nitrogen fertilizer treatment. Chlorophyll Index-green and GNDVI were the best predictors of maize grain yield early in the growing season when the application of additional nitrogen was still agronomically feasible. However, the logistics of late season nitrogen application must be considered.
Highlights
Intensive maize production often necessitates external nitrogen inputs
The goal of this study was to determine the relationships among nitrogen fertilizer rates, maize grain yield, maize growth stage and an assortment of vegetation indices (TGI, normalized area vegetation index (NAVI), CIgreen, green normalized difference vegetation index (GNDVI), red-edge normalized difference vegetation index (RENDVI) and normalized difference vegetation index (NDVI); Table 1)
20% of maize nitrogen demand is satisfied between vegetative tasseling (VT) and R3 with some uptake extending into later stages (English et al, 2017)
Summary
Intensive maize production often necessitates external nitrogen inputs. Approximately 5.5 Mt of nitrogen was applied to maize (Zea mays L.) in the United States in 2018 (USDAERS, 2019). In Arkansas, as well as many other states, N-rates are established using two factors: maize grain yield goal and soil texture. Maize grown on silty or sandy loam soils with a grain yield goal of 11 t ha−1 will require 247 kg N ha−1 (Espinoza & Ross, 2012; Morris et al, 2018). It is well documented that no-tillage and winter cover crops can significantly alter nitrogen dynamics within an agroecosystem (Doran, 1987; Kaspar et al, 2012; Kuo et al, 2001; Mahal et al, 2018; Tonitto et al, 2006). N-recommendations based on conventional systems may not be applicable under the agricultural practices of no- or minimal tillage, winter cover crops and/or diverse crop rotations
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