Pedogenic, mineralogical and land-use controls on organic carbon stabilization in two contrasting soils

UPNa. Departamento de Ciencias del Medio Natural. Área de Edafología y Química AgrícolaOrgano-mineral complexation in soils is strongly controlled by pedogenesis, but the mechanisms controlling it and its interaction with cultivation are not yet well understood. We compared the mineralogy and quality of organic carbon (C) among organo-mineral fractions from two soils with contrasting pedogenic origin. Sequential density fractionation (SDF; using 1.6, 1.8, 2.1, 2.4 and 2.6 g mL(-1) sodium polytungstate solutions) followed by thermal analysis was applied to a Chernozem from Ellerslie, Alberta, and a Luvisol from Breton, Alberta, each under native and cultivated land uses. Similar clay mineralogy suggested that pedogenic controls on organic C stabilization were related to long-term vegetation cover. In addition to large differences in total organic C quantities, bulk soil and isolated fractions showed significant differences in organic C quality. Samples under native vegetation revealed greater organo-mineral complexation at Ellerslie compared with Breton, as expressed by less solubilisation, more organic C recovered in intermediate-density fractions, and exothermic differential scanning calorimetry peak signals associated with more stable forms of organic C. Long-term cultivation resulted in an overall shift to more stable organo-mineral complexes. The proportion of soil C in the 2.1-2.4 g mL(-1) fraction increased under cultivation from 21 to 32% in Breton samples, and from 6 to 16% in Ellerslie samples. The quality of inherited pedogenic soil organic C stored in a soil thus appears to determine its response to long-term cultivation

Effects of innovative long-term soil and crop management on topsoil properties of a mediterranean soil based on detailed water retention curves

The effectiveness of conservation agriculture (CA) and other soil management strategies implying a reduction of tillage has been shown to be site-dependent (crop, clime and soil), and thus any new soil and crop management should be rigorously evaluated before its implementation. Moreover, farmers are normally reluctant to abandon conventional practices if this means putting their production at risk. This study evaluates an innovative soil and crop management (including no-tillage, cover crops and organic amendments) as an alternative to conventional management for rainfed cereal cropping in a calcareous soil in a semi-arid Mediterranean climatic zone of Navarra (Spain), based on the analysis of soil water retention curves (SWRCs) and soil structure. The study was carried out in a small agricultural area in the municipality of Garínoain (Navarre, Spain) devoted to rainfed cereal cropping. No other agricultural area in the whole region of Navarre exists where soil and crop management as proposed herein is practiced. Climate is temperate Mediterranean, and the dominant soil is Fluventic Haploxerept. Within the study area there is a subarea devoted to the proposed soil and crop management (OPM treatment), while there is another subarea where the soil and crop management is conventional in the zone (CM treatment). OPM includes no-tillage (18 years continuous) after conventional tillage, crop rotation, use of cover crops and occasional application of organic amendments. CM involves continuous conventional tillage (chisel plow), mineral fertilization, no cover crops and a lower diversity of crops in the rotation. Undisturbed soil samples from the topsoil and disturbed samples from the tilled layer were collected for both systems. The undisturbed samples were used to obtain the detailed SWRCs in the low suction range using a HYPROP©device. From the SWRCs, different approaches found in the literature to evaluate soil physical quality were calculated. The pore-size distribution was also estimated from the SWRCs. Disturbed samples were used in the laboratory to assess soil structure by means of an aggregate-size fractionation and to perform complementary analysis from which other indicators related to soil functioning and agricultural sustainability were obtained. The approaches evaluated did not show clear differences between treatments. However, the differences in soil quality between the two forms of management were better observed in the pore size distributions and by the analysis of the size distribution and stability of soil aggregates. There was an overabundance of macropores under CM, while the amount of mesopores (available water) and micropores were similar in both treatments. Likewise, more stable macroaggregates were observed in OPM than in CM, as well as more organic C storage, greater microbial activity, and biomass. The proposed management system is providing good results regarding soil physical quality and contributing also to the enhancement of biodiversity, as well as to the improvement in water-use efficiency. Finally, our findings suggest that the adoption of the proposed practice would not result in a loss in yields compared to conventional management.This study was partially supported by the Ministerio de Economía y Competitividad (Government of Spain) via research project CGL2015-64284-C2-1-R and PID2020-112908RB-I00 funded by 568 MCIN/AEI/10.13039/501100011033/FEDER “Una manera de hacer Europa”

Evaluación de la calidad del suelo tras la implantación de cubiertas permanentes en viñedos de zonas semiáridas. Materia orgánica y propiedades físicas y biológicas del suelo

El establecimiento de cubiertas vegetales permanentes (PGC) en viñedos de zonas semiáridas, con manejo tradicional de suelo desnudo mediante laboreo y aplicación de herbicidas, es controvertido, porque tiene ventajas agronómicas y ambientales, pero puede inducir cambios negativos en la calidad física del suelo. Los objetivos de este trabajo fueron: (i) avanzar en el conocimiento del efecto de la implantación de PGC en la calidad física y biológica del suelo, e (ii) identificar los indicadores de calidad del suelo más apropiados para suelos calizos de viñedo en una zona semiárida. Se determinaron propiedades físicas y biológicas clave en un Calcisol Cámbico con PGC de diferente edad (1 y 5 años), con un control manejado convencionalmente. El análisis de correlaciones mostró una relación directa entre la estabilidad estructural (WSA), la capacidad de retención de agua útil (AWC), la biomasa microbiana y las actividades enzimáticas del suelo bajo PGC. El contenido de C orgánico total (SOC) y lábil (POM-C) estuvo también correlacionado con los parámetros microbianos. Los indicadores de calidad del suelo más sensibles se identificaron mediante análisis factorial por componentes principales (PCA). La actividad de lombrices, AWC, WSA, SOC y POM-C mostraron el mayor peso en los dos factores obtenidos con PCA, por lo que estas propiedades pueden considerarse indicadores adecuados de la calidad del suelo en este agrosistema. Estos resultados indican que tanto los atributos físicos como biológicos del suelo son diferentes bajo PGC, y necesitan ser evaluados al estudiar las consecuencias de su introducción en suelos de viñedo.Changing from conventional vineyard soil management, which includes keeping bare soil through intense tilling and herbicides, to permanent grass cover (PGC) is controversial in semi-arid land because it has agronomic and environmental advantages but it can also induce negative changes in the soil physical status. The objectives of this work were (i) gaining knowledge on the effect of PGC on the soil physical and biological quality, and (ii) identifying the most suitable soil quality indicators for vineyard calcareous soils in semi-arid land. Key soil physical., organic and biological characteristics were determined in a Cambic Calcisol with different time under PGC (1 and 5 years), and in a conventionally managed control. Correlation analysis showed a direct positive relationship between greater aggregate stability (WSA), soil-available water capacity (AWC), microbial biomass and enzymatic activity in the topsoil under PGC. Total and labile organic C concentrations (SOC and POM-C) were also correlated to microbial parameters. Factor analysis of the studied soil attributes using principal component analysis (PCA) was done to identify the most sensitive soil quality indicators. Earthworm activity, AWC, WSA, SOC and POM-C were the soil attributes with greater loadings in the two factors determined by PCA, which means that these properties can be considered adequate soil quality indicators in this agrosystem. These results indicate that both soil physical and biological attributes are different under PGC than in conventionally-managed soils, and need therefore to be evaluated when assessing the consequences of PGC on vineyard soil quality