Regional environmental controllers influence continental scale soil carbon stocks and future carbon dynamics.

Understanding the influence of environmental factors on soil organic carbon (SOC) is critical for quantifying and reducing the uncertainty in carbon climate feedback projections under changing environmental conditions. We explored the effect of climatic variables, land cover types, topographic attributes, soil types and bedrock geology on SOC stocks of top 1 m depth across conterminous United States (US) ecoregions. Using 4559 soil profile observations and high-resolution data of environmental factors, we identified dominant environmental controllers of SOC stocks in 21 US ecoregions using geographically weighted regression. We used projected climatic data of SSP126 and SSP585 scenarios from GFDL-ESM 4 Earth System Model of Coupled Model Intercomparison Project phase 6 to predict SOC stock changes across continental US between 2030 and 2100. Both baseline and predicted changes in SOC stocks were compared with SOC stocks represented in GFDL-ESM4 projections. Among 56 environmental predictors, we found 12 as dominant controllers across all ecoregions. The adjusted geospatial model with the 12 environmental controllers showed an R2 of 0.48 in testing dataset. Higher precipitation and lower temperatures were associated with higher levels of SOC stocks in majority of ecoregions. Changes in land cover types (vegetation properties) was important in drier ecosystem as North American deserts, whereas soil types and topography were more important in American prairies. Wetlands of the Everglades was highly sensitive to projected temperature changes. The SOC stocks did not change under SSP126 until 2100, however SOC stocks decreased up to 21% under SSP585. Our results, based on environmental controllers of SOC stocks, help to predict impacts of changing environmental conditions on SOC stocks more reliably and may reduce uncertainties found in both, geospatial and Earth System Models. In addition, the description of different environmental controllers for US ecoregions can help to describe the scope and importance of global and local models.

C-offset and crop energy efficiency increase due industrial poultry waste use in long-term no-till soil minimizing environmental pollution.

Brazil is one of the major global poultry producers, and the organic waste generated by the chicken slaughterhouses can potentially be used as a biofertilizer in agriculture. This study was designed to test the hypothesis that continuous use of biofertilizer to the crops, substituting the use of mineral fertilizer promote C-offset for the soil and generate crop energy efficiency for the production system. Thus, the objectives of this study were to evaluate the effects of biofertilizer use alone or in combination with mineral fertilizer on soil organic carbon (SOC) stock, carbon dioxide (CO2) mitigation, C-offset, crop energy efficiency and productivity, and alleviation of environmental pollution. The experiment was established in southern Brazil on a soil under 15 years of continuous no-till (NT). Experimental treatments were as follows: i) Control with no fertilizer application, ii) 100% use of industrial mineral fertilizer (Min-F); iii) 100% use of organic waste originated from poultry slaughterhouses and hereinafter designated biofertilizer (Bio-F), and iv) Mixed fertilizer equivalent to the use of 50% mineral fertilizer + 50% of biofertilizer (Mix-F). Effects of experimental treatments were assessed for the crop sequence based on bean (Phaseolus vulgaris), soybean (Glycine max) and corn (Zea mays) in the summer and wheat (Triticum aestivum) and black oat (Avena strigosaSchreb) in the winter composing two crops per year, as follow: bean/wheat-soybean/black oat-corn/wheat-soybean/black oat-corn/wheat-bean. The continuous use of Bio-F treatment significantly increased the index of crop energy efficiency. It was higher than that of control, and increased it by 25.4 Mg CO2eq ha-1 over that of Min-F treatment because of higher inputs of crop biomass-C into the system. Further, continuous use of Bio-F resulted in a significantly higher CO2eq stock and offset than those for Min-F treatment. A positive relationship between the C-offset and the crop energy efficiency (R2 = 0.71, p < 0.001) indicated that the increase of C-offset was associated with the increase of energy balance and the amount of SOC sequestered. The higher energy efficiency and C-offset by application of Bio-F indicated that the practice of crop bio fertilization with poultry slaughterhouse waste is a viable alternative for recycling and minimizing the environmental impacts.

Molecular Techniques to Study Microbial Wastewater Communities

Abstract wastewater treatment (WT) is of major importance on modern cities, removing wastewater pollutants resultant from anthropogenic activities. The unique abilities of microbes to degrade organic matter, remove nutrients and transform toxic compounds into harmless products make them essential players in waste treatment. The microbial diversity determines the metabolic pathways that may occur in WT and quality of treated wastewater. Therefore, understanding WT microbial community structure, distribution, and metabolic functioning is essential for development and optimization of efficient microbial engineering systems. Since cultivation methods can only detect a small fraction of the microbial diversity, the use of culture-independent molecular methods has circumvented this issue, allowing unprecedented access to genes and genomes used for microbial composition and function evaluation. Traditional approaches like RAPD, DGGE, ARDRA, RISA, SSCP, T-RFLP, and FISH and modern approaches like microarray, qPCR, and metagenomics are essential techniques for identifying and depicting the total microbial community structure and their interaction with environmental and biotic factors. Thus, this review describes traditional and state of the art molecular techniques which provide insights into phylogenetic and functional activities of microbial assemblages in a WT system.

Multiple Effect of Different Plant Growth Promoting Microorganisms on Beans (Phaseolus vulgaris L. ) Crop

Abstract We evaluated the effect of combined Rhizobium tropici, Trichoderma asperellum and plant growth-promoting rhizobacteria (PGPR) in beans crop. The hypothesis that strains of T. asperullum, R. tropici and PGPR combined could improve growth, biomass accumulation and beans yield was tested under greenhouse and field conditions. The treatments consisted of control, mineral nitrogen application and inoculation, isolated and associated with the following microorganisms: Rhizobium tropici, Bacillus subtilis, Trichoderma asperellum and Burkholderia sp. 10N6. Results were evaluated by shoot dry weight (SDW) and root dry weight (RDW), number of nodules and yield components. In greenhouse environment all the microorganisms behaved similarly, and the treatments inoculated with Burkholderia sp. 10N6 (IBu) and R. tropici (IR) stood out regarding the production components. In field conditions the treatments IR and IRTBa presented the highest values of SDW and RDW. Our results suggest that inoculation with R. tropici, T. asperellum and PGPR may promote beans growth and bring benefits to shoot and root accumulation, increase the number of nodules as well as improve yield components, contributing to a sustainable agriculture.

Liming and Nitrogen Fertilization Effects on Soil Microbial Community in Long Term No-till

Abstract Soil management influences organic matter decomposition rates as well soil microbial community functional behavior. No-till (NT) is the most used management system by farmers due to its conservation practices and high productivity. The main objective of this study was to evaluate the impact of surface-applied lime, nitrogen (N) application, and black oat residues on soil microbial community of a Typic Hapludox under continuous NT. Therefore, soil chemical attributes, microbial biomass carbon, basal respiration, metabolic quotient, most probable number of diazotrophs, as well as bacterial functional analysis were performed. The effect of liming and N fertilization amendments inputs were saw in soil respiration and metabolic quotient measurements, showing them to be good indicators of soil quality. Further studies should be carried out in order to molecularly identify microbial communities present in soils with different liming and N fertilization management to evaluate the behavior of specific bacterial taxa under such conditions.

Macroaggregation and soil organic carbon restoration in a highly weathered Brazilian Oxisol after two decades under no-till.

Conclusions based on studies of the impacts of soil organic carbon (SOC) fractions and soil texture on macroaggregation and SOC stabilization in long-term (>20years) no-till (NT) fields remain debatable. This study was based on the hypothesis that the amount and frequency of biomass-C input associated with NT can be a pathway to formation of macroaggregates and to SOC buildup. The objectives were to: 1) assess the macroaggregate distribution (proportional mass, class mass) and the SOC and particulate organic carbon (POC) stocks of extra-large (8-19mm), large (2-8mm) and small (0.25-2mm) macroaggregate size classes managed for two decades by NT, and 2) assess the recovery of SOC stocks in extra-large macroaggregates compared to adjacent native vegetation (Andropogon sp., Aristida sp., Paspalum sp., and Panicum sp.). The crop rotation systems were: soybean (Glycine max L.), maize (Zea mays L.) and beans (Phaseolus vulgaris L.) in summer; and black oat (Avena strigosa Schreb), white oat (Avena sativa), vetch (Vicia sativa L.), black oat.+vetch (Avena strigosa Schreb+vetch) and wheat (Triticum aestivum L.) in winter. The experimental was laid out as 2×2 randomized block factorial with 12 replicates of a NT experiment established in 1997 on two highly weathered Oxisols. The factors comprised of: (a) two soil textural types: clay loam and sandy clay, and (b) two sampling depths: 0-5 and 5-20cm. The three classes of macroaggregates were obtained by wet sieving, and the SOC content was determined by the dry combustion method. The extra-large macroaggregate classes in 0-20cm depth for sandy clay (SdC) and clay loam (CL) Oxisol represented 75.2 and 72.4% of proportional mass, respectively. The SOC and POC stocks among macroaggregate classes in 0-5 and 5-20cm depths decreased in the order: 8-19mm>2-8mm ≈ 0.25-2mm. The SdC plots under soybean/maize at 3:1 ratio recovered 58.3%, while those at 1:1 ratio (high maize frequency) in CL recovered 73.1% of SOC stock in the extra-large macroaggregates compared with the same under native vegetation for 0-20cm depth. Thus, partial restoration of the SOC stock in original extra-large macroaggregate confirms the hypothesis that NT through higher maize cultivation frequency can be a pathway to fomation of macroaggregates and SOC buildup.

Driving factors of soil carbon accumulation in Oxisols in long-term no-till systems of South Brazil.

In a climate change scenario, it is important to understand the factors that lead to changes in a soil carbon (C) sink. It is recognized that such process is highly dependent on climate, soil properties, topography, and vegetation. However, few studies demonstrate how these mechanisms operate in highly weathered Oxisols. Therefore, this study evaluated the driving factors for C recovery and accumulation and its relations with fertility attributes in the soil profile (0 to 1m depth) in no-till (NT) croplands of south Brazil. The adoption of NT in the studied fields started between 1978 (pioneer areas) and 1990 and represent a range of textural and mineralogical characteristics South Brazil main croplands. Soil samples were collected in paired fields of native vegetation and NT (NV vs. long-term NT) to a depth of 1m. The studied NT areas of Rio Grande do Sul State were managed according to the principles of conservation agriculture (minimum soil disturbance, permanent soil cover and diverse crop rotation). The processes that drove SOC recovery in the studied sites were soil fertility management allied with high C input through intense crop rotation. The C recovery was were for areas with the predominance of soybean in the cropping system, higher levels of Al3+ and lower levels of Mg2+ and P. Sites with medium/high cropping intensity, lower levels of Al3+ and higher levels of P, Ca2+, Mg2+, and K+ resulted in higher C recovery.

Why does carbon increase in highly weathered soil under no-till upon lime and gypsum use?

Field experiments have been used to explain how soil organic carbon (SOC) dynamics is affected by lime and gypsum applications, however, how SOC storage occurs is still debatable. We hypothesized that although many studies conclude that Ca-based soil amendments such as lime and gypsum may lead to SOC depletion due to the enhancement of microbial activity, the same does not occur under conservation agriculture conditions. Thus, the objective of this study was to elucidate the effects of lime and gypsum applications on soil microbial activity and SOC stocks in a no-till field and in a laboratory incubation study simulating no-till conditions. The field experiment was established in 1998 in a clayey Oxisol in southern Brazil following a completely randomized blocks design with a split-plot arrangement and three replications. Lime and gypsum were surface applied in 1998 and reapplied in 2013. Undisturbed soil samples were collected before the treatments reapplications, and one year after. The incubation experiment was carried out during 16months using these samples adding crop residues on the soil surface to simulate no-till field conditions. Lime and gypsum applications significantly increased the labile SOC stocks, microbial activity and soil fertility attributes in both field and laboratory experiments. Although the microbial activity was increased, no depletion of SOC stocks was observed in both experiments. Positive correlations were observed between microbial activity increase and SOC gains. Labile SOC and Ca2+ content increase leads to forming complex with mineral soil fractions. Gypsum applications performed a higher influence on labile SOC pools in the field than in the laboratory experiment, which may be related to the presence of active root system in the soil profile. We conclude that incubation experiments using lime and gypsum in undisturbed samples confirm that soil microbial activity increase does not deplete SOC stocks under conservation agriculture.