Predicting Glyphosate Sorption Across New Zealand Pastoral Soils Using Basic Soil Properties or Vis–NIR Spectroscopy

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Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient in Roundup, which is frequently used around the world. It is a non-selective herbicide with carboxyl, amino, and phosphonate functional groups, and it has a strong affinity to clay, and aluminum and iron oxides. Sorption plays a major role for the risk of pesticide leaching. The sorption coefficient of glyphosate (Kd, gly), and hence its mobility, vary greatly among different soil types. Determining Kd,gly is laborious and requires the use of wet chemistry. In this study we aim to estimate Kd, gly using i) basic soil properties, and ii) visible near-infrared spectroscopy (vis–NIR). The latter method is fast, requires no chemicals, and several soil properties can be estimated from the same spectrum. The data set included 68 topsoil samples collected across the South Island of New Zealand, with clay and organic carbon (OC) contents ranging from 0.001 to 0.520 kg kg-1 and 0.021 to 0.217 kg kg-1, respectively. The Kd,gly was determined with batch equilibration experiments and ranged from 13 to 3810 L kg-1. The vis–NIR spectra were obtained on air-dried soil samples using a DS2500 spectrometer (Foss, Denmark), with a spectral range of 400 – 2500 nm. Multiple linear regression was used to correlate aluminum, pH and oxalate extractable phosphorous to Kd,gly, which resulted in an R2 of 0.89 and an RMSE of 259.6 L kg-1. Further, interval partial least squares regression (iPLS) with ten-fold cross-validation was used to correlate vis–NIR spectra to Kd,gly, for which we obtained an R2 of 0.91 and an RMSECV of 228.34 L kg-1. Thus, these preliminary results show that both basic soil properties and vis–NIR spectra can describe the variation in Kd,gly across these samples with high accuracy, and that glyphosate sorption to a soil can be determined within seconds.
Original languageEnglish
Publication year2019
Publication statusPublished - 2019
Event2018 - 2019 SSSA International Soils Meeting : SOILS ACROSS LATITUDES - Sheraton San Diego Hotel & Marina, San Diego, United States
Duration: 6 Jan 20199 Jan 2019
https://www.sacmeetings.org/

Conference

Conference2018 - 2019 SSSA International Soils Meeting
Location Sheraton San Diego Hotel & Marina
CountryUnited States
CitySan Diego
Period06/01/201909/01/2019
Internet address

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