Applied and Environmental Soil Science

High Andean Páramos are very fragile neotropical ecosystems. Moreover, biodiversity in these areas is threatened by the anthropic activities of agriculture, cattle raising, and mining and has been little studied. Changes associated with potato farming and livestock grazing on microorganisms of Páramo soil of the Nevados National Natural Park (Nevados NNP) were assessed by (1) determination of physical and chemical properties (physicochemical matrix) and enzymatic activities associated (enzymatic activity matrix) with different biogeochemical cycles (C, N, and P); (2) microbial community functional diversity via evaluation of functional groups associated with carbon, nitrogen, and phosphorus cycles using cultivation-dependent techniques (arable functional group matrix and most probable number matrix); and (3) microbial diversity using cultivation-independent techniques that employ the hypervariable V5–V6 region of the 16S rRNA gene and pyrosequencing (16S-454 genus matrix and 16S-454 OTU matrix). Four of the six evaluated matrices (physicochemical, enzymatic activities, most probable number, and arable functional groups) revealed significant differences according to land use. The strategy adopted by the arable functional group matrix, in which the diversity of nitrogen fixation, phosphate solubilization, and cellulolytic compounds was evaluated, showed the most significant impacts of the different factors (land use, season, and elevation), especially those caused by potato cultivation and livestock. These results indicate that the initial impacts of potato farming and livestock grazing on the microbial community in El Bosque Village are better detected by functional diversity analysis than by molecular analysis of the 16S rRNA gene V5–V6 variable region. The results may have been caused by the type of molecular marker used in the analyses and the type of agricultural practices used by peasant farmers, which affect the functional diversity of the soil community. Among these practices are the maintenance of fallow periods greater than 7 years between each potato crop and the small proportion of cattle in relation to the total land area of the village. As the findings can be interpreted as an indicator of the early impacts of potato cultivation and livestock on microbial diversity, the effects of implementing community management plans, applying agroecological models, retaining biocultural memory, and changing agrarian structure are relevant for mitigating future changes.

Several indices can be used to assess the impact of short-term conservation agriculture strategies on improving soil organic carbon (SOC). To find out how the SOC pools and the carbon lability influence the carbon management index (CMI) in response to different agricultural practices in a warm semiarid region, the carbon lability index (LI) and the carbon pool index (CPI) were measured under the interactive effect of different fertilizer applications and crop residue management (hereafter referred to as “farming strategies”) in combination with four crop rotation systems in Ahvaz, Khuzestan, Iran, over four growing seasons from 2018 to 2020. The farming strategies were as follows: (1) using the standard rate of inorganic fertilizer used in the region and removing crop residues from the soil (SIF_no-CR); (2) applying the standard rate of organic fertilizers used in the region and returning 30% of crop residues to the soil (SOF_30% CR); and (3) integrating the use of inorganic and organic fertilizers and returning 15% of crop residues to the soil (IOF_15% CR). The crop rotation systems were fallow-wheat (F-W), corn-wheat (C-W), sesame-wheat (S-W), and mung bean-wheat (B-W). No statistically significant difference was observed between the different farming strategies and rotation systems with respect to LI after two years of the experiment. The highest (1.26) and lowest (1.06) CPIs were observed for SOF_30% CR and SIF_no-CR, respectively. The magnitude of the CMI values followed the order SOF_30% CR (121) > IOF_15% CR (107) ≥ SIF_no-CR (106). B-W and F-W had the highest and lowest CPI with values of 1.29 and 1.01, respectively. No statistically significant difference was found for the different crop rotation systems. Given the low impact of the common farming practices in the region, e.g., SIF_no-CR and F-W, on CPI and CMI at 24 months, our results showed that farming strategies with manure application and crop residue management and summer wheat-based rotation systems appear to be more appropriate farming strategies to improve CMI in arable land.

Litterfall is one of the major inputs for soil nutrients. Understanding the connection of litterfall and soil organic carbon (SOC) as the part of ecological processes is a key step towards carbon sequestration as a climate change mitigation strategy. Yet, it remains inadequate to support by empirical pieces of evidence particularly in tropical ecosystems. In this study, litter traps were used to monitor the monthly organic carbon deposition over a year through litterfall, and soil samples were collected vertically up to 30 cm depth to define the SOC depth distribution in three different land use types located at Wondo Genet district, southern Ethiopia. The results were interpreted by deploying both the carbon stratification ratio (CSR) and carbon flow balance ratio (CFBR) as ecological indicators. The results revealed that both the annual litterfall amount and associated organic carbon input in plantation forest (958.4 ± 112 g·m⁻²·yr⁻¹; 391.4 ± 112 g·C·m⁻²·yr⁻¹) were higher than those in the homegarden (183.5.4 ± 26 g·m⁻²·yr⁻¹; 67.4 ± 10 g·C·m⁻²·yr⁻¹), conceivably due to few litter contributors (trees) present in the homegarden. The CSR of the homegarden (1.3 ± 0.01) was found between the ratio obtained for crop (1.2 ± 0.01) and plantation forest (1.4 ± 0.01), indicating that it is definitely a combination of pure plantation forest and crop system. The CFBR was higher in plantation forest (3.4 yr⁻¹) than in soil of homegarden (0.77 yr⁻¹), implying the net accumulation of soil carbon over time in the latter system. Hence, homegardens could be considered as a system of climate-smart practice with multiple-biogeochemistry pathways, which simultaneously address the social-absolute needs. Given the current tendency of transforming homegarden agroforestry to monoculture types owing to economical drivers, such indicators can dictate of making rational decisions related to land use planning and soil fertility management.

Background. In recent decades, the microbial and plant-derived urease have been used for sand stabilization by the calcium carbonate precipitation method, especially with Sporosarcina pasteurii. However, calcium carbonate precipitation using plant-derived urease has received less attention. Purchasing the extracted and purified commercially available plant-derived urease for the sand improvement is costly. The plant-derived urease-containing crude extract (enzyme substance) is cheaper than purified (commercial) urease. In the present study, the feasibility of sand improvement by enzyme-induced calcium carbonate precipitation method was investigated with urease-containing crude extract (extracted from soybean). Methods. The distilled water, instead of phosphate buffer, was used to provide the main enzyme extraction medium. Also, the effects of temperature, time, and dilution on the activity of the urease-containing crude extract by the electrical conductivity meter were investigated. Results. The results showed that the extraction temperature had a significant effect on the behavior of the enzymes, and according to the results, the temperature range between 19 and 25°C is suitable for the enzyme extraction. The four-layer surface percolation method was used to improve the sand, and 0.75 equimolar (eqM) concentration of urea-CaCl₂ cementation solution is suitable for sand improvement using the UCE extracted from soybean seed. Conclusion. Silica sand was successfully improved by the EICP method using the four-layer surface percolation method, and significant unconfined compressive strength and elasticity modulus were obtained. XRD and XRF analysis also confirmed the successful precipitation of calcium carbonate between the sand particles.

The culture of Pseudomonas mendocina H-3 was selected as the microorganism for oil destruction, and its effect on oil-contaminated soil from the Zhanazhol deposit in West Kazakhstan was studied. After conducting model laboratory experiments, field experiments were carried out. Six and twelve months after the treatment of the oil-contaminated field with microorganisms, the amount of oil fractions in the soil decreased noticeably, while the content of asphaltenes remained constant. Analyses show that the composition of the oil fraction changes—the concentration of paraffin-naphthenic—polycycloaromatic components decreases, whereas the relative amount of mono- and bicycloaromatic hydrocarbons increases. The results of the efficiency assessment showed that the use of Pseudomonas mendocina H-3 cell suspension in natural conditions leads to a decrease in the content of hydrocarbons in the soil from 55 to 70%. The lower efficiency of bioremediation with cell cultures in field experiments (on average, 61%) compared with laboratory model studies (reduction of oil content to 79%) is apparently associated with climatic conditions.

Rice husk biochar (RHB) is a potential source of available silicon in paddy soil and an ecologically responsive soil amendment for sustainable rice production. The study tested the influence of RHB application methods on rice growth, rice yield, and silicon dynamics in sandy loam soil in a pot experiment. RHB was applied at 5 tons ha⁻¹ as a localized-spot-application (LSA) or top-mixed-application (TMA) with the soil at the upper 7 cm or whole-mixed-application (WMA) within 20 cm of the soil column and at 10 tons ha⁻¹ in the TMA and WMA methods and was compared with a control (CTRL) without biochar. Seedlings of the Koshihikari rice variety were transplanted in each pot, and all treatments were replicated thrice. Compared to the CTRL, the LSA and TMA methods did not influence the mean porewater silicon concentration at the vegetative and reproductive stages. However, the WMA method applied at 5 tons ha⁻¹ increased () the mean porewater silicon concentration by 12.3 and 39.5% at the vegetative and reproductive stages, respectively, while at 10 tons ha⁻¹, the respective increase was by 26.1 and 32.7%. All biochar application methods at the 5 tons ha⁻¹ rate increased the rice grain yield () by 21.2% (LSA), 11.3% (TMA), and 47.2% (WMA) compared to the CTRL. Conversely, at 10 tons ha⁻¹, the yield was reduced by 18% in the TMA method, attributable to the immobilization of nitrogen and adsorption of nutrients to biochar surfaces. Our results proved that the choice of biochar application method and rate of application significantly influenced the dissolution of silicon in the porewater, leading to a higher silicon uptake and consequently a higher grain yield. This study provides valuable insights for agricultural practices aiming to enhance silicon dynamics in paddy soil and sustainable rice yield using RHB.