Finding a LIBS method for improved plant nutrition in grape production

December 1, 2021

Assessing plant nutrients, quickly and in the vineyard, would improve fertilization decisions for the table grape industry all over the world.

Introduction

SciAps handheld LIBS instruments are being used in Germany to investigate critical elemental in-field analysis in agricultural soil with no sample preparation, even for challenging key indicators like carbon and phosphorus. Now, researchers in Italy are experimenting to see whether these analyzers can inform leaf testing to advance more efficient and sustainable nutrition management for the popular table grape industry.“There is a considerable interest by several leading companies in the table grape industry all over the world in plant nutrient assessment with in-situ fast methods,” says Dr. Giorgio S. Senesi, a researcher at the Institute for Plasma Science and Technology, Bari seat, within the National Research Council of Italy. SciAps has lent Senesi a Z-300 LIBS for the effort through its Academic Loaner program. SciAps is the only handheld analyzer with enough laser power to perform the required analysis.“The specific instrumentation from SciAps is working well,” Senesi says. “I have tested other instruments and also bench top LIBS set-ups. Actually, it is hard to get a nice emission spectroscopic signal for some elements, especially in the UV region of the spectrum. But the SciAps LIBS can. It makes me think that we would be able to obtain trustable quantitative results, which will be helpful for the aim of the study and possibly in the near future for the industry.”The estimated total world production for grapes is 79 million metric tons, up 6.5 percent between 2017 and 2018, and 36 percent of that production is dedicated to table grapes, according to the most recent numbers available from the Food and Agriculture Organization Corporate Statistical Database. A LIBS nutrient management application could span the globe—China is the largest exporter of grapes, followed by Italy, Chile, Peru, and the United States.

Method

Historically, using the foliar diagnostic method, mass spectroscopy techniques analyze the chemical composition of a leaf after sample digestion with respect to the dominant nutritive mineral entities at the time of sampling, especially for nitrogen, phosphorous, potassium, magnesium, and sulfur. But this method is destructive, and the sample is sent to a third-party laboratory for analysis, which can take time for the results and interpretation. These delays are in contrast with the need to immediately optimize the nutrient elements during fertilization.

In this study, the aim was to carry out parallel analysis with two handheld field instruments. “At this point we are interested in the calibration of hLIBS and pXRF analysis of table grape fresh leaves with reference to conventional analysis — sample digestion with ICP analysis — to try to set up a reliable method and a protocol,” Senesi says. The ICP is the reference standard technique, and that is the one they will use to build calibration curves to obtain quantitative analysis with LIBS data.“As LIBS is able to acquire a multi-spectral range, we can observe the relations between elements. The interactions and the balances between the different nutrients may be much more important to plant growth and nutritional health than the concentration of each single nutrient. This could also be the key for further understanding of the complexities of plant nutrition, which involves a wide range of macronutrients such as nitrogen, phosphorus, potassium, magnesium, calcium, and micronutrients such as manganese, sulfur, boron, iron, copper, and zinc. These are all elements that can be detected by LIBS,” Senesi says.

Preliminary data

Senesi recently concluded a preliminary set of analysis on ten different varieties of fresh grape leaves. “Working with fresh samples is quite challenging because of the effects of the moisture content on the properties of laser induced plasma and on the stability of the spectral signal intensities. Most of the research work until now has used pelletized leaf samples, which consist of dried leaf samples ground and pressed for better homogeneity. In the studies performed previously by other research groups, the standard deviation is much lower for the pelletized dried leaves than fresh leaves. But the objective of this study was to find a method and a protocol allowing the use of handheld LIBS in-situ with high analysis speed for a preliminary diagnosis.”

Expanding applications with handheld LIBS

Dr. Senesi, a geologist by training, has been using LIBS technology since 2007 in his studies of low temperature plasmas, and in recent years has been using handheld LIBS technology (developed by SciAps in 2015) in the field for his work at the Institute for Plasma Science and Technology. Limited size and weight are crucial features for applications that require high portability and fast analysis outside the laboratory, so a challenge for such instrumentation is the high level of technological performance required.“When I met LIBS, I understood I should attempt to introduce the technique in other scientific fields, such as geology and the environment,” Senesi says. “It is important to note that LIBS technique does not produce any chemical waste. Many standardized techniques use dilution with chemical reagents to get answers.”Most experiments are conducted in collaboration with Micro X-Ray Labs, in particular with Prof. Roberto Terzano and Dr. Matteo Spagnuolo of the Department of Soil, Plant and Food Sciences, University of Bari, Italy, and coordinator of the Technical Scientific Committee of the Italian Table Grape Commission.“I like to call myself a freelance researcher, so I am always looking for any kind of collaboration, especially about environmental issues,” says Senesi, who has collaborated with Dr. Russell Harmon and Dr. Richard Hark, other Academic Loaner participants, in the past. “Now, more than ever, we have to be respectful to the environment and the changes on our planet.”[/text_output][line id="" class="" style=""][text_output]How can we support your creativity with our Academic Loaner Program? We frequently loan handheld analyzers for a few weeks or a month to academic researchers, so that they can perform a study or field analysis. Reach out to us at academic@sciaps.com with a brief description of what you want to measure.SciAps handheld instruments are great for short-term lab work with students or research in the field, and those projects are great for SciAps, too — our partners are always coming up with novel applications for the instruments and giving us invaluable feedback.LIBS is often a preferred technique, especially for students, since operators do not have to deal with the regulatory complexities of X-ray fluorescence analyzers. And our accompanying Profile Builder software for PC and tablet provides operators complete freedom to add powerful bench top functionality for field and lab work.

Dr. Giorgio S. Senesi, Institute for Plasma Science and Technology at the National Research Council of Italy