Leandro Paulino

Greenhouse Gas (CO2 AND N2O) Emissions from Soils: A Review

En actividades agricolas los principales gases de efecto invernadero (GHG) son los relacionados con los ciclos globales de C y N. El impacto de la agricultura sobre las emisiones GHG se ha convertido en una cuestion clave, especialmente si se considera que los ciclos naturales C y N se ven influidos por el desarrollo agricola. Esta revision se centra en emisiones de CO2 y N2O del suelo en los ecosistemas terrestres, con enfasis en agro-ecosistemas de Chile y similares alrededor del mundo. Se analiza la influencia del uso del suelo y las practicas de manejo del cultivo sobre emisiones de CO2 y N2O, se discuten medidas de mitigacion para reducir estas emisiones. Un mayor conocimiento sobre los procesos biologicos que promueven las emisiones GHG del suelo permitira la creacion de oportunidades para el desarrollo agricola en condiciones ambientalmente amigables, donde el suelo puede actuar como un reservorio y/o emisor de GHG, dependiendo del balance de entradas y salidas.

Plant extracts from the Mediterranean zone of Chile potentially affect soil microbial activity related to N transformations: A laboratory experiment

Abstract Available soil N can be lost through ammonia volatilization, nitrate leaching to surface and ground waters, and nitrous oxide emission under intensive systems of agricultural production. Research has shown that phenolic compounds isolated from certain plants influence N cycling in soils, which results in a decrease of N losses and represents a key issue for environmental protection worldwide. In this study, water-soluble and ethanol-soluble compounds were extracted from the leaves, bark and roots of certain tree and shrub species in the Mediterranean zone of Chile, with the aim of measuring their effects on N transformation, soil respiration, soil microbial biomass and urease activity. The studied species were Acacia caven Mol, Quillaja saponaria Mol., Bacharis linearis (Ruiz & Pav.) Pers. and Pinus radiata D. Don. Plant extracts were applied to soil (Haploxeralf) fertilized with urea. The extracts obtained from the roots of A. caven in water, bark of A. caven in ethanol, bark of P. radiata in ethanol, leaves of P. radiata in water and roots of B. linearis in water showed a reduction in the soil nitrification rate. The bark of A. caven in ethanol and bark of P. radiata in ethanol extracts showed a reduction in urease activity. In conclusion, only the bark of P. radiata in ethanol extract affected all the biological parameters considered, reducing soil nitrification, urease activity, microbial biomass and carbon dioxide emissions from the soil, these being attributed to high levels of phenolic content in the extract. However, further research is necessary to explain the mechanisms involved.

CO2 and N2O emissions from an Andisol in Chile under a no-till system using non-fixed closed chambers

Chile has different types of soil and climate conditions that favor a wide range of agricultural activities that can generate potential atmospheric contamination like greenhouse gases (GHG). Nevertheless, the contribution of agricultural soils to atmospheric emissions has yet to be measured in Chile. The aim of this study was to assess seasonal variability of CO2 and N2O effluxes in situ from a volcanic ash-derived soil under different agronomic management practices. Gas samples were obtained from headspaces of non-fixed closed chambers in an annual crop rotation under a no-till system in an Andisol in southern Chile (36° S). Two N-sources (NH4+ and NO3-) and ammonium fertilization plus two lime doses (0.5 and 1 Mg ha-1) were considered for soil treatments Effluxes of CO2 and N2O were determined periodically for 1 yr, and soil variables, such as temperature, water, and mineral N content, were recorded. Results showed that CO2 effluxes respond to a seasonal pattern. No effect was evidenced when considering crop management practices with a maximum of 53.2 ± 8.5 kg CO2-C ha-1 d-1 in the wet fall period and a minimum of 9.7 ± 2.1 kg CO2-C ha-1 d-1 for summer, fall dry period, and winter. N2O efflux was highly variable throughout the year and showed no influence of treatments or season variability with a mean of 0.95 kg N2O-N ha-1 yr-1. Soil mineral N variations are not related to GHG effluxes as a single variable. Results indicate that an Andisol under a no-till system in southern Chile has a low N2O emission potential, and higher CO2 emissions are mainly produced in wet seasons (wet fall and/or spring).

Water and temperature dynamics of Aquands under different uses in southern Chile

Aquands are soils derived from holocenic volcanic ashes located in southern Chile. Due to the presence of very high levels of organic matter (30 %), these soils present a high total porosity (80 %) but at the same time, a limited water storage capacity due to their shallow soil depths. The aim of this work was to analyze the influence of land use change of a Duric Histic Placaquand (Nadi) soil on soil physical properties and their consequences on water and temperature dynamics. The volumetric water content (qField) and soil temperature (T) were registered at different depths in a Nadi soil under a secondary native forest (sNF) and naturalized grassland (NG). Undisturbed soil samples were collected to analyze the water retention curve, saturated (Ks) and unsaturated (Ku) hydraulic conductivity and water repellency. The dynamics of rainfall and water table depth (WT) were registered using a rain gauge and groundwater wells. The land use change of a Nadi soil from sNF to NG induced soil structural changes in the first 15 cm of soil reducing the amount of macropores under NG and affecting the hydraulic conductivity function as well as qField and T dynamics, i.e. while the WT in winter reached the soil surface in the NG, under sNF the air-filled pores were still present. Similarly, the T gradients increased as qField decreased, being more intensive under NG. A nonhomogeneous soil wetting and water infiltration was assessed, which can be related to an increased spatial water repellency, soil hydraulic properties and rainfalls.

Retención de nutrientes en una microcuenca con bajos niveles de contaminación antropogénica

SUMMARY Streamside native forests filter nutrients and sediments from extra-riparian environments. Most related studies have been carried out in environments chronically polluted by nutrients, making it difficult to assess whether the detected patterns would hold in less polluted areas, such as Chile. However, there are no studies about Chilean natural streamside vegetation ability to filter nutrients and sediment. We hypothesized that southern Chilean streamside forests efficiently retain nutrients due to their, previously documented, tight nitrogen cycle especially in terms of fixation, mineralization and plant uptake, in addition to the high phosphorus adsorption by volcanic soils and high cation retention due to the expected higher cationic exchange capacity (CEC) in floodplains. We studied a fluvial terrace with grasslands covering the uplands, a forest on a slope, and a floodplain with native trees adjacent to a creek. We laid out nine parallel transects in the aforementioned environments and installed five wells in each transect. We extracted and analyzed groundwater three times a year, finding that the nitrate concentration decreased in the transect from the grassland to the floodplain forest. Ammonium, calcium, potassium, and electrical conductivity increased in the same transect, but these variables were always higher than those in the stream. Moreover, soil chemical determinations showed that ammonium, basic cations, aluminum, aluminum saturation and organic matter increased significantly in the floodplain soil compared to the grassland soil. The CEC was marginally different in the studied transects. We conclude that native forest ecosystems constitute effective filters for the studied nutrients, highlighting the associated soils role.

Dairy slurry application to grasslands and groundwater quality in a volcanic soil

Research in volcanic-ash soils has shown that they largely capture the dairy slurry following application to land; however, their hydrological properties would favor nutrient leaching. Our objective was to evaluate the contribution of biogeochemical and hydrological controls on the pollution of groundwater by cattle slurry applied to a permanent grassland growing on a volcanic soil. We sampled groundwater chemistry since 10 months before the fertilization (three samplings), and 16 months after, with samplings 1-2 months after the fertigation. Following fertilization, ammonium, exchangeable potassium, and magnesium soil concentrations increased in the fertilized plots compared to the control plots. In contrast, no effect of slurry on groundwater quality was detected, with the exception of dissolved organic nitrogen, a main component of dairy slurry that increased in the groundwater below the fertilized plots. Despite the fact that biogeochemical controls predominate, hydrological aspects would be important when rainfall is high, evapotranspiration is low, groundwater table level is high, and water movement in the saturated zone increases. We concluded that the application of slurry to pastures under rates comparable to a high fertilization in the short term, does not generally impact the groundwater quality in volcanic ash-derived soils.