Guiding fall fertilization of cool‐season turfgrass lawns with NDVI sufficiency index

Abstract

Fall N fertilizers are applied to turfgrass at predetermined rates instead of being based on plant-N status. Normalized difference vegetative index (NDVI) and the sufficiency index (SI) concept are used to assess plant-N status in some agronomic crops but has not been evaluated for turfgrass. This study was conducted across 3 yr in Connecticut to determine fall and spring NDVI SI values in a mixed species, cool-season lawn. Field experiments were set out with varying fall N rates with NDVI measured weekly in October and November, and in late April. Quadratic and Linear-Response and Plateau (LRP) models were significant (P < .0001) for all fall and spring SI values in response to fall N rates. Fall SI was maximized between 140 and 155 kg N ha −1 for the quadratic model and plateaued between 79 and 102 kg N ha −1 for the LRP model. Spring SI was maximized at 189 and plateaued at ≥116 kg N ha −1 for quadratic and LRP models, respectively. In relation to commonly recommended fall N rates of 24.5, 49, and 98 kg N ha −1 , the models suggest that no supplemental N is needed when SI is ≥92, ≥95, and ≥99% of the N-rich reference in the fall, respectively. Late April SI >89% of spring N-rich reference would indicate that excess fertilizer was applied the previous fall at rates >49 kg N h −1. The NDVI SI can provide site-specific fall N fertilization guidance of cool-season turfgrass lawns.

Evaluating Decision Support Tools for Precision Nitrogen Management on Creeping Bentgrass Putting Greens

“…Vegetation indices such as NDRE and NDVI have been evaluated as methods to guide N fertilization or quantify turfgrass response to fertilization (Kruse et al, 2006 ; Bremer et al, 2011a ; Lee et al, 2011 ; López-Bellido et al, 2012 ; Inguagiato and Guillard, 2016 ; Guillard et al, 2021 ). Our study demonstrated that there was a weak correlation between creeping bentgrass clipping yield and NDRE.…”

“…Interestingly, we observed a weak positive correlation between daily clipping yield and NDRE when the N rate was based on the PACE Turf GP model (relatively higher N), whereas the correlation became negative once the N application rates were lower (experience-based, ML-RF model, and NDRE-based methods). Studies have concluded that NDRE has much stronger correlations with some turfgrass growth characteristics such as turfgrass biomass (Marín et al, 2020 ) and turfgrass N status (Guillard et al, 2021 ). These studies applied a wider range of N rates which resulted in large variation in turfgrass growth.…”

“…NDRE is designed for crops with relatively high canopy density because the red edge band is able to penetrate deeper through the plant canopy. To calibrate the sensor and use spectral reflectance to guide N fertilization, the spectral reflectance readings from the turfgrass area are compared with the readings from reference strips, and then, fertilizer decisions are made according to the relationship between the two readings (Blackmer and Schepers, 1995 ; Raun et al, 2008 ; Samborski et al, 2009 ; Holland and Schepers, 2013 ; Guillard et al, 2021 ). One of the types of reference strips for spectral reflectance is called the virtual reference concept (Holland and Schepers, 2013 ).…”

A review of precision management for golf course turfgrass

“…New research should develop models and decision support systems to determine correct product and application rates for desired function and aesthetic goals similar to how precision agriculture research has focused on developing models and tools for farmers. Guillard et al (2021) developed fall-applied prescription N application models for lawn-height turfgrass in the Northeast United States, providing a PTM method for lawncare providers and homeowners to apply N more precisely to meet the turfgrass N needs. Straw et al (2020) developed a method to create SSMUs from time domain reflectometry soil volumetric water content data.…”

Reduced creeping bentgrass fairway reflectance following synthetic colorant application

“…Deployment of multispectral radiometry by researchers to characterize turfgrass canopy color, density, nitrogen (N) status, and/or a/biotic stress is increasing (Caturegli et al, 2020;Guillard et al, 2016Guillard et al, , 2020Pruyne et al, 2019Pruyne et al, , 2020Zhu et al, 2016). Justifications for adoption include rapid and repeatable measures of canopy reflectance by any number of operators.…”