| Summary: | ABSTRACT Conventional soil analysis produces large amount of residues and demand resources and time consuming. The construction of soil spectral database for estimating soil attributes is the newest alternative on soil mapping. The objective in this study was to build spectral libraries and study the quality of the generated prediction models for soil attributes. It was obtained 7185 soil spectral (400-2500 nm) in laboratory with respective soil analysis. The spectral libraries "general", "regional", and "local" were generated from these spectral readings. The general spectral library contained the full range of data and several states, the regional libraries contained data from geographically close municipalities, and the local libraries contained soil data from a single municipality. In general we observed the sequence of R2 for General (0.85), Regional (0.67 to 0.77) and Local (0.55 to 0.77). In conclusion, the best database was the general one. On the other hand, independent of the size of the database, predictive models based on physical attributes such as sand, clay, and organic matter generate good predictions until an R2 of 0.7. The determination of spectral libraries including highly variable soils formed from different parent materials create worse results for the estimation of chemical attributes and better results for the estimation of the physical ones. The low range of variation in a given attribute was a limiting factor in the generation of effective predictive models. A great spectral library can certainly improve soil quantitative evaluation.
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