Pedo-Transfer Functions for Estimating Soil Bulk Density in Central Amazonia

Abstract

Under field conditions in the Amazon forest, soil bulk density is difficult to measure. Rigorous methodological criteria must be applied to obtain reliable inventories of C stocks and soil nutrients, making this process expensive and sometimes unfeasible. This study aimed to generate models to estimate soil bulk density based on parameters that can be easily and reliably measured in the field and that are available in many soil-related inventories. Stepwise regression models to predict bulk density were developed using data on soil C content, clay content and pH in water from 140 permanent plots in terra firme (upland) forests near Manaus, Amazonas State, Brazil. The model results were interpreted according to the coefficient of determination (R²) and Akaike information criterion (AIC) and were validated with a dataset consisting of 125 plots different from those used to generate the models. The model with best performance in estimating soil bulk density under the conditions of this study included clay content and pH in water as independent variables and had R² = 0.73 and AIC = -250.29. The performance of this model for predicting soil density was compared with that of models from the literature. The results showed that the locally calibrated equation was the most accurate for estimating soil bulk density for upland forests in the Manaus region.

The use of Pedotransfer functions and the estimation of carbon stock in the Central Amazon region

“…The Bernoux et al (1998) model presented the highest RMSPE value and our model the lowest (Table 5). Barros and Fearnside (2015) also developed PTFs for Oxisols in the Central Amazon region and compared the performance of their model with those presented by authors reported in this work (Benites et al, 2007;Bernoux et al, 1998;Tomasella and Hodnett, 1998). The authors found that the application of these three PTFs overestimate soil bulk density, which is in agreement with our findings.…”

“…The authors found that the application of these three PTFs overestimate soil bulk density, which is in agreement with our findings. However, we highlight that the soil bulk density determined by Barros and Fearnside (2015) is significantly lower than what we found in the region of the Urucu River (average and median values of 0.66 and 0.62, respectively). This can explain why even the model developed by Tomasella and Hodnett (1998) also overestimated soil bulk density in the Oxisols evaluated by Barros and Fearnside (2015).…”

“…However, we highlight that the soil bulk density determined by Barros and Fearnside (2015) is significantly lower than what we found in the region of the Urucu River (average and median values of 0.66 and 0.62, respectively). This can explain why even the model developed by Tomasella and Hodnett (1998) also overestimated soil bulk density in the Oxisols evaluated by Barros and Fearnside (2015). Therefore, the model developed using local data of the study site to predict D b outperformed the three others, both in terms of accuracy and precision.…”

“…The D b strongly correlates with SOM content and soil texture (Adams, 1973;Manrique and Jones, 1991). Barros and Fearnside (2015), working with oxisoils, also in the Central Amazon region, found that the clay content accounts for about 70 % of the variation in soil bulk density. However, the importance of each variable depends on the study site.…”

Hydrologic Response to Land Use Change in a Large Basin in Eastern Amazon

“…In general, the soils are highly weathered, deep, clayey, and porous [51,52]. Using mean texture values from the literature [52][53][54][55][56][57][58], the main soil parameters such as bulk density, available water capacity, and saturated hydraulic conductivity were estimated using pedotransfer functions developed for Amazonian soils [51,[59][60][61][62].…”