Effects of grazing on soil properties in mediterranean forests (Central-Eastern Spain).

Traditional management practices, such as grazing, can have adverse impact on soils. Despite an extensive body of literature exploring the effects of grazing on soil and plants worldwide, there is a notable lack of research on its impacts in Mediterranean forests within the Iberian Peninsula Furthermore, there is a knowledge gap on the enzymatic activities and basal respiration of soil in forest after grazing. To address these gaps, this study aimed to investigate the impact of grazing on various important physicochemical and biological soil properties along with vegetation richness in a Mediterranean forest located in Castilla-La Mancha (Central Eastern Spain). Relative to undisturbed sites, grazing significantly reduced soil water content (-53%) and available water (-59%). However, soil hydraulic conductivity remained unaffected by animal trampling and the soil water repellency observed in ungrazed sites disappeared. Grazed soils experienced a slight increase in pH (+18%). Among the biochemical properties studied, only dehydrogenase showed a significant increase (+100%) while basal respiration exhibited a notable decrease (-24%). Grazing resulted in a reduction of plant species richness (-34%) indicating a loss of biodiversity in grazed areas. The observed significant alterations in key soil and plant properties due to livestock activity suggest that grazing has the potential to modify the overall soil quality of these sites. Certain variables that exhibited noteworthy differences between grazed and ungrazed sites could serve as indicators of grazing impacts in Mediterranean forests. These indicators may be considered proxies for establishing effective land management strategies to mitigate degradation in the Mediterranean forest ecosystem.

Effects of applying peanut shell and its biochar on the microbial activity and community structure of dryland red soil.

Due to its soil formation process, dryland red soil has certain characteristics that are unfavorable for crop growth, including acidity, fineness, plate structures, and erosivity. The use of large amounts of fertilizer can decrease fertility and biodiversity and increase acidification, thereby seriously restricting the sustainable utilization of dryland red soil resources. Therefore, there is an urgent need for techniques that improve the crop quality and yield in dryland red soil areas. Returning crop waste to fields as fertilizer is a promising approach to sustainable agriculture. In the present study, the effects of applying peanut shell and an associated biochar product to dryland red soil were investigated, with a focus on soil microbial activity and community structure. Field experiments were conducted in Jiangxi Province, southern China, in 2020, in field plots of sweet potato crops. Seven treatments were set up according to the principle of equal carbon return to farmland: Control: (conventional fertilization); S1, S2, S3 (peanut shell application of 3000, 4500 and 6000 kg hm-2, respectively); and BC1, BC2, BC3 (peanut shell biochar application of 1000, 1500 and 2000 kg hm-2, respectively). The application of peanut shell and its biochar improved soil basal respiration, with the greatest increase relative to controls of 161.06% found in treatment S3 at the root harvest stage. The most obvious increase in microbial biomass carbon content due to biochar application was 206.50% in treatment BC2 at the root harvest stage. The application of peanut shell and its biochar increased the phospholipid fatty acid (PLFA) contents of total soil microorganisms and different microbial groups. The maximum increases in the PLFA contents of total soil microorganisms, gram-positive bacteria, and gram-negative bacteria occurred at the early root formation stage in treatment BC2, which were 112.16%, 102.52%, and 115.64%, respectively. Both peanut shell and biochar increased the PLFA contents of soil actinomycetes, arbuscular mycorrhizal fungi (AMF), and other fungi to certain extents. The soil actinomycetes PLFAs increased by 120.08% at the early root formation stage in BC2, while the AMF PLFAs increased by 79.44% at the seedling stage in S2. This study provides theoretical and practical guidance for the comprehensive utilization of peanut shell and the implementation of circular agriculture in dryland red soil regions. It also provides a scientific basis for improving the fertility of dryland red soil.

Earthworms accelerate rice straw decomposition and maintenance of soil organic carbon dynamics in rice agroecosystems.

BACKGROUND: To promote straw degradation, we inoculated returned farmland straw with earthworms (Pheretima guillelmi). Increasing the number of earthworms may generally alter soil organic carbon (SOC) dynamics and the biological activity of agricultural soils. METHODS: We performed soil mesocosm experiments with and without earthworms to assess the decomposition and microbial mineralization of returned straw and soil enzyme activity across different time periods. RESULTS: When earthworms were present in soil, the surface residues were completely consumed during the first four weeks, but when earthworms were absent, most of the residues remained on the soil surface after 18 weeks. On day 28, the SOC content was significantly higher in the treatment where both earthworms and residue had been added. The SOC content was lower in the treatment where earthworms but no residue had been added. The organic carbon content in water-stable macroaggregates showed the same trend. During the first 14 weeks, the soil basal respiration was highest in the treatments with both residues and earthworms. From weeks 14 to 18, basal respiration was highest in the treatments with residues but without earthworms. We found a significant positive correlation between soil basal respiration and soil dissolved organic carbon content. Earthworms increased the activity of protease, invertase, urease and alkaline phosphatase enzymes, but decreased ß-cellobiohydrolase, ß-glucosidase and xylosidase activity, as well as significantly reducing ergosterol content. CONCLUSION: The primary decomposition of exogenous rice residues was mainly performed by earthworms. Over a short period of time, they converted plant carbon into soil carbon and increased SOC. The earthworms played a key role in carbon conversion and stabilization. In the absence of exogenous residues, earthworm activity accelerated the decomposition of original organic carbon in the soil, reduced SOC, and promoted carbon mineralization.

Ecotoxicological characterization of biochars: role of feedstock and pyrolysis temperature.

Seven contrasting feedstocks were subjected to slow pyrolysis at low (300 or 350°C) and high temperature (550 or 600°C), and both biochars and the corresponding feedstocks tested for short-term ecotoxicity using basal soil respiration and collembolan reproduction tests. After a 28-d incubation, soil basal respiration was not inhibited but stimulated by additions of feedstocks and biochars. However, variation in soil respiration was dependent on both feedstock and pyrolysis temperature. In the last case, respiration decreased with pyrolysis temperature (r=-0.78; p<0.0001, n=21) and increased with a higher volatile matter content (r=0.51; p<0.017), these two variables being correlated (r=-0.86, p<0.0001). Collembolan reproduction was generally unaffected by any of the additions, but when inhibited, it was mostly influenced by feedstock, and generally without any influence of charring itself and pyrolysis temperature. Strong inhibition was only observed in uncharred food waste and resulting biochars. Inhibition effects were probably linked to high soluble Na and NH4 concentrations when both feedstocks and biochars were considered, but mostly to soluble Na when only biochars were taken into account. The general lack of toxicity of the set of slow pyrolysis biochars in this study at typical field application rates (≤20 Mg ha(-1)) suggests a low short-term toxicity risk. At higher application rates (20-540 Mg ha(-1)), some biochars affected collembolan reproduction to some extent, but only strongly in the food waste biochars. Such negative impacts were not anticipated by the criteria set in currently available biochar quality standards, pointing out the need to consider ecotoxicological criteria either explicitly or implicitly in biochar characterization schemes or in management recommendations.

Carbono orgânico e biomassa microbiana do solo em plantios de Acacia mangium no Cerrado de Roraima / Soil organic carbon and soil microbial biomass in Acacia mangium plantation in the Savanna of Roraima

O objetivo do estudo foi avaliar os efeitos de plantios de Acacia mangium, localizados no cerrado em Roraima, sobre o carbono orgânico e biomassa microbiana do solo. Foram realizadas amostragens de solo nas profundidades de 0-20 cm e 20-40 cm em dois plantios de A. mangium com cerca de cinco anos de idade, e em duas áreas de Cerrado nativo consideradas referência. Um dos plantios de A. mangium (localizado na Fazenda Cigolina) correspondeu a um plantio homogêneo (espaçamento de 3,6 m entre linhas e 2,0 m entre plantas) enquanto que o outro (localizado no Campo Experimental Água Boa - CEAB) correspondeu a um plantio em faixas com duas linhas de plantio (espaçamento de 6 m entre linhas, 2,5 m entre plantas e cerca de 30 m entre faixas). As amostras de solo foram analisadas quanto ao carbono orgânico, carbono da biomassa microbiana, respiração basal do solo e quociente metabólico, além de atributos químicos de fertilidade. Foi verificado que os plantios de A. mangium não proporcionaram aumentos significativos do carbono orgânico do solo em comparação às áreas de referência. Entretanto, na média geral, esses plantios proporcionaram aumento do carbono da biomassa microbiana do solo e redução do quociente metabólico, indicando a possibilidade de acúmulo de carbono orgânico no solo em longo prazo. Também foi observado que, em comparação ao plantio da fazenda Cigolina e às áreas de referência, o carbono microbiano do solo foi maior e acompanhado de menor quociente metabólico no plantio de A. mangium no CEAB, mostrando que a estrutura de plantio exerceu influência sobre a biomassa microbiana do solo.

The aim of this study was to evaluate the effects of Acacia mangium plantation in the Roraima's Savanna, on soil organic carbon and soil microbial biomass. Soil samplings were collected on the depths of 0-20 cm and 20-40 cm in two Acacia mangium plantation sites, about five years old, and in two sites of native savanna as reference. One of the A. mangium sites (located at Fazenda Cigolina) was composed by a homogeneous plantation (3.6 m between row and 2.0 m between trees) and, the other one (located at Campo Experimental Agua Boa Experimental - CEAB) was composed by a plantation on which the planting distances had strips of two rows 6 meters apart, 2.5 meters between trees and 30 meters between strips). Soil samples were analyzed regarding soil organic carbon, microbial biomass carbon, soil basal respiration and metabolic quotient, besides soil fertility attributes. Results showed that A. mangium plantations did not provide significant increases of organic carbon on the soil comparing with sites used as reference. However, generally, A. mangium plantation increased soil microbial biomass carbon and reduced metabolic quotient, indicating a possibility of soil organic carbon accumulation in long-term. It was also observed that, soil biomass microbial carbon was higher, followed by smaller metabolic quotient at CEAB A. mangium plantation compared with Cigolina and reference sites, showing that planting design exercised influence on soil microbial biomass.