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

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.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

Burning crop residues under no-till in semi-arid land, Northern Spain - effects on soil organic matter, aggregation, and earthwor populations.

Stubble burning has traditionally been used in semi-arid land for pest and weed control, and to remove the excess of crop residues before seeding in no-tillage systems. We compared differences in soil properties in a long-term (10 years) tillage trial on a carbonated soil in semi-arid north-east Spain under no-tillage with stubble returned and stubble burnt, with the conventional tillage system (mouldboard plough, stubble returned) as a reference. Differences in total soil organic C and C in particulate organic matter, mineralisation potential, soil physical properties (bulk density, penetration resistance, and aggregate size distribution and stability), and earthworm populations were quantified. The effect of stubble burning was absent or insignificant compared with that of tillage in most of the parameters studied. The most significant effect of stubble burning was the change in soil organic matter quality in the topsoil and penetration resistance. No-till plus stubble burning stocked an amount of organic C in the soil similar to no-till without burning, but the particulate organic matter content and mineralisation potential were smaller. Earthworm activity was similar under the 2 no-till systems, although a trend towards bigger earthworms with increasing penetration resistance was observed under the system with burning. Our results indicate that the role of burnt plant residues and earthworms in organic matter accumulation and soil aggregation in Mediterranean carbonated soils under no tillage is of major importance, meriting further attention and research

Soil water retention as affected by tillage and residue management in semiarid Spain

Conservation tillage preserves soil water and this has been the main reason for its rapid dissemination in rainfed agriculture in semiarid climates. We determined the effects of conservation versus conventional tillage on available soil water capacity (AWC) and related properties at the end of 5 years of management on a clay loam calcic soil (Calcic Haploxerept) in semiarid northern Spain. No-tillage with (NTSB) and without stubble burning (NT), reduced chisel-plough tillage (RT) and conventional tillage with mouldboard plough (MT) were compared in rainfed barley monoculture. Bulk density (¿b), organic matter content (OM), soil water retention (SWR) at matric potentials of 0 to -1500 kPa, and soil water content (SWC) were determined in the driest year of the 5-year study period. Soil OM in the upper 0.15 m was significantly higher (13%) under NTSB, NT and RT than under MT. Soil ¿b in the upper 0.15 m under NT and NTSB was greater than under RT and MT, but at a depth of 0.15–0.30 m was greater under RT than under the other treatments. Reorganisation of pore sizes due to tillage treatments affected AWC. Under RT and MT the largest percentage of the total soil porosity was occupied by pores >9 µm (equivalent pore diameter), in accordance with lower ¿b. Available water capacity was greater with NT than with RT and MT. Higher SWC under conservation tillage systems (NT, NTSB and RT) than under MT was attributed mainly to greater AWC and to the mulching effect of crop residues. Crop yield in the driest year of the 5-year period was lowest under MT whereas no differences among treatments were found over the 5-year period. Stubble burning did not affect AWC nor barley yield. Tillage had a greater impact on soil properties and on crop yield than crop residue management

Micromorphological analysis on the influence of the soil mineral composition on short-term aggregation in semi-arid Mediterranean soils

Aggregation in soils is the result of the interaction of the soil organic components and soil minerals. The reactivity of the mineral phase is acknowledged to interfere with aggregates formation and stabilization, but its influence on aggregation in semi-arid Mediterranean soils remains mostly unknown. In this study, we used micromorphological analysis of aggregates formed in a 28-d incubation in two agricultural soils differing only in the composition of the mineral phase in the upper Ap horizon (a carbonate-depleted Palexeralf with 21.5% clay, and a contiguous carbonate-rich Typic Calcixerept with 20.9% clay before decarbonation which was reduced to 10.4% upon decarbonation). The two soils belong to the same agricultural field and have had similar management for decades. Soil samples were completely disaggregated into their fractions 2 mm) formed during the incubation were separated at days 3, 7, 14, 21 and 28 and used to prepare thin sections. Macroaggregates were more abundant at day 3, and then decreased in number in the two soils, which indicates a dependency between organic matter decomposition and stable macroaggregates formation. They contained a greater proportion of smaller aggregates in the decarbonated soil. Micromorphological analysis revealed significant differences in the fabric and physical characteristics of these macroaggregates, in which bonds among primary particles were observed to be led by clays in the Palexeralf while the coarse fraction appeared embedded in a micromass with crystallitic b-fabric corresponding to carbonates in the Calcixerept. This resulted in a more compact fabric and less porosity in macroaggregates in the Calcixerept. Image analysis of thin sections was used to quantify and characterize the pore system of macroaggregates. Porosity (pores > 20 ìm) was more than double (36.9% for 15.6%) within macroaggregates in the decarbonated soil, with more elongated pores. Although in both soils most pores were 20 to 150 ìm in equivalent diameter, some porosity > 150 ìm was observed only in macroaggregates from the decarbonated soil. These observations allow hypothesizing that the mechanisms responsible for aggregates stabilization and/or formation are different in the two soils, and that they result in different physical characteristics of soil aggregates. The implications of such differences on air and water flow rates within aggregates, and thus on the soil microbial activity and organic matter decomposition, as well as on soil erodibility, need to be studied and accounted for when evaluating the effect of soil management and other practices on soil quality in semi-arid Mediterranean agrosystems.La formacion de agregados en el suelo es el resultado de la interaccion entre los componentes organicos y minerales del suelo. Sin embargo, aunque es sabido que la naturaleza de la fraccion mineral puede interferir en la agregacion, su influencia en suelos semiaridos en regiones de clima mediterraneo es aun poco conocida. En este estudio se utilizaron tecnicas de analisis micromorfologico para estudiar agregados formados en una incubacion de 28 dias de muestras del horizonte superficial Ap de dos suelos cultivados contiguos que difieren unicamente en su mineralogia (un Palexeralf descarbonatado con 21,5% de arcilla y un Typic Calcixerept rico en carbonatos con 20,9% de arcilla antes de la descarbonatacion, que se reduce a 10,4% tras la eliminacion de los carbonatos). Los dos suelos pertenecen al mismo campo de cultivo, por lo que han tenido un manejo similar durante decadas. En los dos suelos, se desagregaron completamente muestras frescas de suelo, para obtener las fracciones 2 mm) formados durante la incubacion se cuantificaron y separaron los dias 3, 7, 14, 21 y 28, y se utilizaron para la preparacion de laminas delgadas. Estos macroagregados fueron, en los dos suelos, mas abundantes el dia 3 y su numero decrecio con el tiempo de incubacion, lo que indica una dependencia entre su formacion y la descomposicion de la materia organica en los dos suelos. Estos macroagregados presentaron una mayor proporcion de agregados estables pequenos en su interior en el suelo sin carbonatos. El analisis micromorfologico de las laminas delgadas revelo diferencias significativas en la fabrica y las caracteristicas fisicas de estos agregados, en los que la union entre particulas primarias corresponde a la arcilla en el Palexeralf, mientras los elementos gruesos aparecen embebidos en una micromasa con fabrica de birefringencia cristalitica, correspondiente a la presencia de carbonatos en el Calcixerept. Como resultado, los agregados de este ultimo suelo fueron mas compactos y con menor porosidad. La cuantificacion y caracterizacion de la porosidad de los agregados se realizo mediante analisis de imagen. La porosidad (> 20 �Êm) fue mayor (36,9% frente a 15,6%) en los macroagregados del suelo sin carbonatos, con una proporcion mayor de poros elongados. Aunque en los dos suelos, la mayor parte de los poros de los macroagregados presentaron un diametro medio equivalente entre 20 y 150 �Êm, en este suelo se observaron algunos poros mayores de 150 �Êm. Estas observaciones permiten suponer que los mecanismos responsables de la formacion y/o estabilizacion de los macroagregados en los dos suelos podrian ser diferentes, resultando en las diferentes caracteristicas fisicas observadas en los agregados. Las consecuencias de estas diferencias en las tasas de flujo de agua y gases dentro de los agregados, y por lo tanto en la actividad biologica y la dinamica de la materia organica asi como en la erosionabilidad del suelo, necesitan ser estudiadas y consideradas en la evaluacion del efecto que el manejo del suelo y otras practicas pueden tener en su calidad en las regiones semiaridas mediterraneas