These high-throughput spectroscopic techniques are also more economical and have the potential to give estimations of multiple soil properties, therefore allowing a higher density of soil sampling in large field surveys, or within fields, and facilitating a precision agriculture approach. Mid-infrared spectroscopy has proved successful at determining multiple soil properties, including texture 13, 14, 15, 16, 17, 18. Overtones and combinations of these fundamental frequencies occur in the NIR region, making quantification in the NIR region more difficult 13. Fundamental molecular frequencies occur in the MIRS region between 600–4000 cm −1, such as C-H and C-N bonds in organic materials and Si–O bonds in minerals. Mid-infrared spectroscopy is sensitive to both organic and inorganic phases, so is ideal for soils. Unlike the afore mentioned techniques, infrared analyses the chemistry of soil constituents. Other more high-throughput spectroscopic methods, in addition to LDA, include X-ray attenuation 12, Coulter/electrical sensing zone method, and infrared spectroscopy with visible (vis), near-infrared (NIR) and mid-infrared (MIRS) radiation. This has also been observed with the LDA technique 7, 11.Īnother disadvantage of gravitational-sedimentation techniques is that they are extremely time-consuming. In the sieve-pipette method, the clay fractions ( 2% SOM, clay will be under-estimated using the sieve-pipette method because of aggregation 5 or the hydrometer method 10. Thus, knowing the texture of a soil is essential to understanding how well it functions for crop production and other soil functions.Ĭonventional measurements of soil texture use the sieve-pipette and hydrometer 1 techniques, which are gravitational-sedimentation methods and make granulometric measurements of grain size. Clay particles have high cation exchange capacity which affects nutrient availability to crops. Soil texture, describing the relative proportion of sand, silt and clay in the mineral phase of soils is a major determinant of its water storage capacity and permeability, aeration, bulk density, aggregate stability and carbon storage capacity. It was concluded that in typical agricultural soils with < 5% OC and < 60% clay content, both techniques could be used for cheap, fast and reliable estimates of soil texture. Unlike granulometric measurements of texture such as the LDA, MIRS analysis is not subject to the limitations imposed by the shape and density of particles. In soils with OC removed, the MIRS prediction of clay content improved, indicating interference between over-lapping spectral regions for organic and mineral constituents. The LDA over-estimated clay by ~ 60% (calibration set R 2 = 0.36), indicating that the widely used clay threshold of 5% OC the LDA under-estimated (R 2 = < 0.1) and MIRS over-estimated (R 2 = 0.34) clay content. The MIRS over-estimated clay at low clay content and under-estimated at high clay content (calibration set R 2 = 0.83). The MIRS predictions of clay content were much better than the LDA measurements, but both techniques gave good measurements of sand content. It has used soils with a broad range of organic carbon (OC) contents to investigate whether, as in other techniques, clay-OC aggregation affects the estimation of clay with MIRS. To our knowledge this comparison between LDA and MIRS has not been made previously. Royal Society of Chemistry members receive a discount of 15% for this course (membership number required).Spectroscopic methods for the determination of soil texture are faster and cheaper than the standard methods, but how do the results compare? To address this question, laser diffraction analysis (LDA) and mid-infrared spectroscopy (MIRS) analysis have been compared to conventional sieve-pipette measurements of texture in diverse European and Kenyan soils. Scheduled course price: £110 + VAT per delegate Delegates are able to ask live questions either by using their microphone or by typing into the chat boxes. This course is taught live in a virtual classroom and offers a fully interactive experience, with instrument parts and consumables to see. You will learn about the components of Laser Diffraction Analysis instrumentation, the purpose and principles of data analysis and the different sampling techniques that can be used. This live and interactive online course explains the principles of these techniques, along with some of the industries which use them and their applications. The course is also ideal for analysts or technicians looking for a refresher in these techniques. This course provides an introduction to Laser Diffraction Analysis (LDA), aimed at complete beginners.
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