Understanding the impacts of land-use change on landscape-hydrological dynamics is one of the main challenges in the Northern Brazilian Cerrado biome, where the Amazon agricultural frontier is located. Motivated by the gap in literature assessing these impacts, we characterized the soil hydro-physical properties and quantified surface water fluxes from catchments under contrasting land-use in this region. We used data from field measurements in two headwater micro-catchments with similar physical characteristics and different land use, i.e. cerrado sensu stricto vegetation and pasture for extensive cattle ranching. We determined hydraulic and physical properties of the soils, applied ground-based remote sensing techniques to estimate evapotranspiration, and monitored streamflow from October 2012 to September 2014. Our results show significant differences in soil hydro-physical properties between the catchments, with greater bulk density and smaller total porosity in the pasture catchment. We found that evapotranspiration is smaller in the pasture (639 ± 31% mm yr^-1) than in the cerrado catchment (1,004 ± 24% mm yr^-1), and that streamflow from the pasture catchment is greater with runoff coefficients of 0.40 for the pasture and 0.27 for the cerrado catchment. Overall, our results confirm that conversion of cerrado vegetation to pasture causes soil hydro-physical properties deterioration, reduction in evapotranspiration reduction, and increased streamflow.

Arenosols in the Brazilian Cerrado are increasingly being used for agricultural production, particularly maize. These sandy soils are characterized by low soil organic matter, low available nutrients, and poor water-holding capacity. For this reason, adding biochar as a soil amendment could lead to improved water and nutrient retention. A greenhouse experiment was carried out using twelve biochars derived from four feedstocks (cotton husks, swine manure, eucalyptus sawmill residue, sugarcane filtercake) pyrolized at 400, 500 and 600 °C and applied at 5% w/w. The biochars’ effect on maize biomass was examined, along with their contribution to soil physical properties including water retention, electrical conductivity (EC), and grain size distribution. After six weeks, maize plants in soils with eucalyptus and particularly filtercake biochar had higher biomass compared to those in soils with cotton and swine manure biochars. The latter’s low biomass was likely related to excessive salinity. In general, our biochars showed potential for increasing θ in sandy soils compared to the soil alone. Filtercake and eucalyptus biochars may improve soil aeration and water infiltration, while applying cotton and swine manure biochars at levels <5% to avoid high salinity could contribute to improved soil water retention in Cerrado Arenosols.

The experiment was conducted in a greenhouse located at the Federal University of Mato Grosso, Cuiaba-MT, from March to May 2012. The objective was to assess the effects of different rates of nickel application with and without liming on maize growth and micronutrient levels. The study was a randomized block design in a 2 x 5 factorial arrangement with four replicates, for a total of 40 plots, including with and without liming and five rates of nickel application, on a clayey Red Yellow Latosol (Oxisol, USDA classification and Ferralsol, FAO classification). Both lime and nickel applications influenced plant growth, reducing plant development with increased nickel application without liming. It was also observed that both lime and nickel applications altered micronutrient levels in the maize plants, independent of which part of the plant was evaluated. Nickel played an antagonistic role with manganese and zinc and a synergistic role with copper and iron.

Despite occupying a large area of the globe and being the next agricultural frontier, sandy soils are seldom explored in scientific studies. Considering the high capacity of remote sensing in soil characterization, this work aimed to: (i) characterize sandy soils’ profiles from proximal sensing; (ii) assess the ability of visible, near, and short-wave infrared (Vis-NIR-SWIR) as well as mid-infrared (MIR) spectroscopy to distinguish soil classes of highly sandy content; (iii) quantify physical and chemical attributes of sandy soil profiles from Vis-NIR-SWIR and MIR spectroscopy as well as X-ray fluorescence (pXRF). Samples were described and collected from 29 sandy soil profiles. The 127 samples went under Vis-NIR-SWIR and MIR spectroscopy, X-ray fluorescence, and chemical and physical analyses. The spectra were analyzed based on “Morphological Interpretation of Reflectance Spectrum” (MIRS), Principal Components Analysis (PCA), and cluster methodology to characterize soils. The integration of different information obtained by remote sensors, such as Vis-NIR-SWIR, MIR, and Portable X-ray Fluorescence (pXRF), allows for pedologically complex characterizations and conclusions in a short period and with low investment in analysis and reagents. The application of MIRS concepts in the VNS spectra of sandy soils showed high potential for distinguishing pedological classes of sandy soils. The MIR spectra did not show distinct patterns in the general shapes of the curves and reflectance intensities between sandy soil classes. However, even so, this region showed potential for identifying mineralogical constitution, texture, and OM contents, assuming high importance for the complementation of soil pedometric characterizations using VNS spectroscopy. The VNS and MIR data, combined or isolated, showed excellent predictive performance for the estimation of sandy soil attributes (R² > 0.8). Sandy soil color indices, which are very important for soil classification, can be predicted with excellent accuracy (R² from 0.74 to 0.99) using VNS spectroscopy or the combination of VNS + MIR.

This study evaluated biochar influence on water retention in sandy soils with different source materials. Samples from Horizon A of six profiles of Neossolos Quartzarênicos (Salto das Nuvens, Utiariti, Pantanal, Coberturas Detrito Lateríticas Ferruginosas, Botucatu e Bauru formations), collected in different regions of the state of Mato Grosso, Brazil, were used to determine the hydro-physical characteristics with the addition of biochar. The biochars assessed were produced from two sources of raw material (sugarcane filter cake and cotton husks) under pyrolysis at a temperature of 400 °C. Retention curves for soils with and without biochar, the field capacity, permanent wilting point, available water in the soil, total porosity, macroporosity, and microporosity were determined. The results evidenced that the application of biochar increases the microporosity (86.7% with cotton husks biochar and 67.9% with filter cake biochar) and reduces the microporosity of sandy soils (38.2% with cotton husks biochar and 36.0% with filter cake biochar); also, there was a higher increase in water availability with biochar from cotton husks (57.1%). There was an increase in soil microporosity and a reduction in macroporosity due to the influence of biochar addition in the sandy soils from the Salto das Nuvens, Utiariti, Pantanal e Coberturas Detrito Lateríticas ferruginosas, with no changes in the Botucatu and Bauru Formations. Biochar increases water retention in sandy soils; however, this does not occur for all geological formations studied.