Geotechnologies on the phosphorus stocks determination in tropical soils: General impacts on society.

Phosphorus (P) is a critical nutrient for primary production in terrestrial and aquatic ecosystems. As P mineral reserves are finite and non-renewable, there is an increasing discussion on its sustainable utilization to safeguard food security for future generations. Understanding the spatial distribution of soil P is central in advancing effective phosphorus management and fostering sustainable agricultural practices. This study aims to digitally map the stocks of available P (AP) and total P (TP) in Brazil at a fine resolution (30 m). Using the Random Forest machine learning algorithm and a database of topsoil (0-20 cm) with 28,572 samples for AP and 3154 for TP, we predicted P stocks based on environmental covariates related to soil formation processes. By dividing Brazil into two sub-regions, representing areas with native coverage and anthropogenic ones, we built independent predictive models for each sub-region. Our results show that Brazil has a TP stock of 531 Tg and an AP stock of 17.4 Tg. The largest soil TP stocks are in the Atlantic Forest biome (73.8 g.m2), likely due to higher organic carbon stocks in this biome. The largest AP stocks were in the Caatinga biome (2.51 g.m2) because of younger soils with low P adsorption capacity. We also found that fertilizer use significantly increased AP stocks in agricultural areas compared to native ones. Our results indicated that AP stocks strongly influenced Brazil's agricultural production, with a correlation coefficient ranging from 0.20 for coffee crops to 0.46 for soybean. The maps generated in this study are expected to contribute to the sustainable use of P in agriculture and environmental systems.

Rhizosphere microbiological processes and eucalypt nutrition: Synthesis and conceptualization.

In this review, we present the state of art regarding rhizosphere effects on eucalypt plantations. It provides a greater understanding of carbon (C) and nitrogen (N) turnover in forest soils. P organic hydrolysis, soil mineral solubilization, indoleacetic acid, gibberellin, resistance factors, and production of siderophores by rhizosphere microbial populations help to explain the tolerance of Eucalyptus plants to biotic and abiotic stresses and the apparent steady-state condition of C and N soil stocks in many planted forests. This work aims to present the main findings on Eucalyptus rhizosphere processes and highlights their importance for trees nutrition, especially for N mineralization triggered by microbial activation or microbial community structure changes regarding the so-called rhizosphere priming effect and N fixation. Furthermore, we present an explanatory conceptual model of the steady-state condition for soil organic matter (SOM) stocks and its relation with fertilization based on a nutrient balance model. This review also considers the main experimental and modeling studies that demonstrate the quantitative importance of rhizosphere processes to Eucalyptus genus and their shortcomings. This provides a framework for process modeling under scenarios of global climate change. A better understanding of rhizosphere microbiological processes may allow improvements in Eucalyptus nutrition and production, as well as in accurate long-term estimates of SOM stocks and C-CO2 exchanges between forest soils and the atmosphere.