Automatic Recovery Estimation of Degraded Soils by Artificial Neural Networks in Function of Chemical and Physical Attributes in Brazilian Savannah Soil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq: 309380/2017-0The Oxisols is predominant in 54% of Brazilian territories and characterized by high weathering, relatively low chemical properties, and adequate structure. This study aimed to analyze the Oxisols through an Artificial Neural Network (ANN) with the purpose of estimating its recovery in function to soil chemical and physical attributes. The chemical attributes considered were: pH, cation exchange capacity (CEC), base saturation (V%), phosphorus (P), magnesium (Mg2+), and potassium (K+) and for the physical attributes, bulk density, soil porosity and soil resistance to penetration. The ANN used in this study is the Multilayer Perceptron (MLP), composed of three layers, input, intermediate and the output and with backpropagation training algorithm (supervised training). The intermediate layer is composed by 10 neurons and the layer of exit by 1 neuron, which has a function of informing the levels of chemical recovery (high, medium and low chemical attributes of the soil) and soil physics (recovered, partially recovered or not recovered). From the results obtained by ANN showed that the network reached an adequate training, with low mean square error (MSE). Therefore, ANN is a powerful and automatic alternative for the recovery estimation of degraded soils

Impact of organic inputs on wettability characteristics and structural stability in silty vineyard topsoil

International audienceOrganic inputs were used for 10 years on a French vineyard topsoil to improve structural stability and thus to protect against erosion. The three types of organic inputs (mulches) included: conifer compost, CC (100 m3 ha-1 every 3 years); conifer bark, CB (300 m3 ha-1 every 5 years); and cereal straw, S (10 t ha-1 every 2 years). The other two types of organic inputs were cover crops of clover (C) and fescue (F). The impacts of these organic inputs on soil organic carbon (SOC) content, wettability (capillary rise and X-ray photoelectron spectroscopy (XPS)) and structural stability were studied. The SOC content was twice as large in the CC, C and F topsoils (SOC content of 2.56-3.24%) as in the reference (R) topsoil (SOC content of 1.39%). Both apparent contact angle (theta) and surface OH:C mass ratio indicated that the R and S topsoils were hydrophilic (theta of 27.4-33.4 degrees, surface OH:C ratio of 3.20-4.41), whereas the CB, C and F topsoils were partially hydrophobic (theta of 69.1-79.8 degrees, surface OH:C ratio of 1.36-2.86), and the CC topsoil had intermediate values (theta of 46.9 degrees, surface OH:C ratio of 2.43-2.81). Moreover, the greater the theta value, the smaller the water sorptivity value and the greater the proportion of water-stable aggregates, Ag(w). The increase in SOC content had beneficial effects on Ag(w), particularly for the partially hydrophobic C and F topsoils (Ag(w) of 22.3-44.5%) against the hydrophilic R and S topsoils (Ag(w) of 8.2-12.7%). Development of hydrophobicity, correlated with the decrease in the surface OH:C ratio and the increase in the C-O, C-N proportion on surface C, should be attributed to humified organic matter or/and to plant and microbial polysaccharides. As the XPS and aggregate stability data describe soil physical processes at small scales (nm to mm), we suggest an experimental and modelling framework for upscaling these results for practical improvement and management of vineyard soils

Urban soils as hot spots of anthropogenic carbon accumulation: Review of stocks, mechanisms and driving factors

Urban soils and cultural layers may accumulate C over centuries and consequently large C stocks may be sequestered beneath cities. Processes and mechanisms leading to high C accumulation in urban soils remain unknown. Data on soil organic carbon (SOC), soil inorganic carbon (SIC), black (pyrogenic) carbon (BC), and nitrogen contents and stocks in urban soils were collected from 100 peer-reviewed papers. The database (770 data points for SOC, SIC, and BC stocks from 116 cities worldwide) was analysed considering the effects of climate and urban-specific factors (city size, age, and functional zoning) on C stocks. The processes of C accumulation specific for urban soils were analysed, and C sequestration rates were assessed. For the wide range of climatic conditions, total C content in urban soils was 1.5–3 times higher, and C accumulation was much deeper compared with natural soils, resulting in 3–5 times larger total C stocks. Urban SOC stocks increased with latitude, whereas SIC stocks were less affected by climate. City size and age were the main factors explaining intercity differences in C stocks. The intracity variability of C and N stocks was dominated by functional zoning: Large SOC and N stocks in residential areas and large SIC and BC stocks in industrial zones and roadsides were consistent across all climates and for cities of various sizes and ages. Substantial amounts of SOC, SIC, and N are sequestered in the subsoils, cultural layers, and sealed soils, underlining the importance of these hidden stocks for C assessments. Long-term С input from outside the cities and associated C accumulation coincided with upward soil growth of ~50 cm per century, and continuous accumulation of 15–30 kg C/m2 per century in urban soils and cultural layers. We conclude that, despite the relatively small area of cities, urban soils are hot spots of long-term soil C sequestration worldwide, and the importance of urban soils will increase in future with global urbanization