A global spectral library to characterize the world's soil

Soil provides ecosystem services, supports human health and habitation, stores carbon and regulates emissions of greenhouse gases. Unprecedented pressures on soil from degradation and urbanization are threatening agro-ecological balances and food security. It is important that we learn more about soil to sustainably manage and preserve it for future generations. To this end, we developed and analyzed a global soil visible-near infrared (vis-NIR) spectral library. It is currently the largest and most diverse database of its kind. We show that the information encoded in the spectra can describe soil composition and be associated to land cover and its global geographic distribution, which acts as a surrogate for global climate variability. We also show the usefulness of the global spectra for predicting soil attributes such as soil organic and inorganic carbon, clay, silt, sand and iron contents, cation exchange capacity, and pH. Using wavelets to treat the spectra, which were recorded in different laboratories using different spectrometers and methods, helped to improve the spectroscopic modelling. We found that modelling a diverse set of spectra with a machine learning algorithm can find the local relationships in the data to produce accurate predictions of soil properties. The spectroscopic models that we derived are parsimonious and robust, and using them we derived a harmonized global soil attribute dataset, which might serve to facilitate research on soil at the global scale. This spectroscopic approach should help to deal with the shortage of data on soil to better understand it and to meet the growing demand for information to assess and monitor soil at scales ranging from regional to global. New contributions to the library are encouraged so that this work and our collaboration might progress to develop a dynamic and easily updatable database with better global coverage. We hope that this work will reinvigorate our community's discussion towards larger, more coordinated collaborations. We also hope that use of the database will deepen our understanding of soil so that we might sustainably manage it and extend the research outcomes of the soil, earth and environmental sciences towards applications that we have not yet dreamed of

Soil sensing: A new paradigm for agriculture

Last century, during the ‘Green Revolution’ the use of synthetic fertilizers contributed to increased agricultural production. However, their use did not reflect local soil and water conditions because recommendations were developed for larger agro-ecological zones. They only focused on increased productivity, neglecting any adverse environmental consequences. Largely, this legacy remains and recommendations are still made using ‘top-down’ procedures based on limited data and generic, empirical relations between soil nutrient contents, fertilization rates and yields. Using soil sensors in agriculture can fundamentally change this approach by allowing innovative ‘bottom-up’ approaches that characterize local soil and environmental conditions in space and time, improving the efficiency of production to maximize farm incomes and minimize environmental side effects. The sensed information can be used to build site-specific databases of relations between soil and plant condition and growth. Recent technological developments in sensing coupled with ongoing advances in information and communication technologies have given ground to a renewed interest in soil sensing and its use in different applications at different spatial scales. Soil sensing can facilitate the measurement and monitoring of the soil's physical and biochemical attributes (e.g. nutrients, water) to better understand their dynamics, their interactions with the environment while considering their large spatial heterogeneity. The new sensing methods can also be used to effectively monitor soil organic carbon and be central to the adoption of best agronomic practices that also allow carbon sequestration and a reduction of greenhouse gas (GHG) emissions. Thus, sensing can help us to better articulate the potential of soil to meet the world's needs for food, fiber, climate adaptation and environmental sustainability allowing the design and implementation of innovative management practices and policy aimed at sustainable development