Jaume Boixadera

Hydromorphic and clay-related processes in soils from the Llanos de Moxos (northern Bolivia)

Abstract The Llanos de Moxos is one of the largest wetlands in the world (more than 100,000 km2) due to seasonal floods. The soil parent materials are fine Quaternary sediments brought by tributaries of the Amazon River. Forests cover some areas, although the dominant vegetation is a pastured savannah and backswamps. At present, the main land use is a very extensive rangeland, and slash and burn agriculture in minor areas. We have studied 15 profiles from several sample areas between Trinidad and San Ignacio. Field and laboratory studies have been carried out in order to elucidate the soil-forming processes taking place and to gain basic knowledge for a sustainable land management. Coarser soils are located near the present river system or in former riverbank areas, often under forest; textures here are loam or silty loam, silty clay loam being dominant. Finer soils may have up to 85% clay and are usually under savannah cover. Illite is the dominant clay mineral in all soils, followed by smectite and kaolinite; vermiculite is absent. Quartz is present in a very significant amount in the clay fraction of all studied soils. Goethite and lepidocrocite are present in all soils, lepidocrocite being a good indicator of poor drainage conditions. Soils are mainly acid, but there are soils with calcium carbonate accumulation in the subsoil, or even saline soils (salitrales). Soils are flooded for a significant period (3–6 months) and bypass flow is very active. Hydromorphic processes are always present and morphologies include hard and soft iron–manganese concretions with diffuse boundaries within peds, impregnative Fe coatings and Fe depletion hypocoatings along pore walls. The micromorphological study shows different degrees of hydromorphism, some of them associated to the present pore system and some with a palaeo character, often disturbed by active slickensides. Microsparite nodules are also present in some low-lying soils. The soils present several morphological features related to the mobility of the fine fraction that can be related to drainage conditions, as recent clay coatings, clay and silt infillings and coatings and clay-depleted hypocoatings. The most clayey soils show striated b-fabrics and frequent slickensides, and some others point to ferrolysis as iron-depleted hypocoatings and low crystallinity clay coatings along pores, although this is not supported by mineralogical data. A moderate cation supply probably prevents strong acidification.

Pig slurry and mineral fertilization strategies' effects on soil quality: Macroaggregate stability and organic matter fractions

Applying pig slurry to the land as fertilizer at appropriate agronomic rates is important to close nutrient cycles and optimize the value of organic matter. However a long-term discussion has taken place about its effects on soil quality. In the north-east of Spain, eight fertilization strategies were evaluated on the soil quality parameters aggregate stability, soil organic matter (SOM) physical fractions and soil microbial biomass (SMB). Six strategies used different pig slurries (PS) which provided organic matter from 1.7 to 2.6 t ha(-1)yr(-1), the rest (mineral N fertilization and a control) did not. Pig slurries were applied at sowing and/or at cereal tillering, as sidedressing. Field experiments were maintained for an 8-year period, in a silty loam soil devoted to a rainfed winter cereal. Soil samples were taken once, before the last sidedressing in 2011. Aggregate stability was quantified using the standard water-stable aggregate method but including a modification which meant that pre-wetting was avoided (WSA(MOD)). When using the WSA(MOD) method, we found a tendency for the percentage of water-stable aggregates to increase due to PS application (differences of up to 74% in the increment) and it was more marked the nearer they were measured to the application time (3 months vs. 12 months). The strategies which include PS show a positive effect on the SOM amount, mainly in the 0.05-0.2 mm light fraction, which increased by up to 34% with every 10 t ha(-1) organic C applied, and on SMB (up to 53% increment). There is a positive and significant linear relationship (p < 0.05, R(2) = 0.75) between the SOM light fraction (%) and the water-stable aggregates soil content (%, WSA(MOD)). Thus, the introduction of PS in fertilization strategies improves soil quality parameters. However, the soil quality benefits need to be balanced with any other potential environmental impact.

Long term application of dairy cattle manure and pig slurry to winter cereals improves soil quality

Organic fertilizers (manures and slurries) applied repeatedly over many cropping seasons favourably influence nutrient recycling, maintenance of soil organic matter (SOM), and improve soil quality parameters such as soil aggregation and porosity. These aspects are particularly relevant in Mediterranean environments characterized by low SOM. This study was set up in a subhumid Mediterranean area where two different trials, devoted to winter cereals, were fertilized with dairy cattle manure (DCM) or pig slurry (PS) for a period of 12xa0years. One objective of this research was to evaluate the impacts of these fertilization practices on aggregate stability and SOM fractions, when compared with a mineral N fertilizer and a control (no-N) treatment. Porosity and pore shape were also studied in PS plots. The use of DCM significantly increased water stable aggregates by up to 16.4–18.0xa0%. Slurry addition did not affect aggregation but it increased the area occupied by pores >65xa0µm. Soil organic carbon (SOC) and light organic fraction (0.05–0.2xa0mm) increased with DCM incorporation but in PS treatments the SOC increment was non-significant. Data from DCM and PS together showed a positive and significant linear relationship between SOC (pxa0<xa00.05, R2xa0=xa00.60), SOC light fraction (pxa0<xa00.01, R2xa0=xa00.75) and SOC light fraction at 0.05–0.2xa0mm size (pxa0<xa00.01, R2xa0=xa00.83), with water-stable aggregate. The use of animal residues (DCM or PS), applied according to an N criterion, increased available phosphorus and potassium soil content while improving yields. The enrichment of soil nutrients with DCM and PS use requires further research in order to avoid potential environmental impacts.

Benchmark soils on alluvial, fluvial and fluvio-glacial formations of the upper-Segre valley

La cabecera del rio Segre, en sus tramos Pirenaicos, ofrece una variedad de formaciones geomorfologicas que permiten estudiar cronosecuencias de suelos. El objetivo de este trabajo es ampliar el conocimiento sobre las principales caracteristicas y los procesos de formacion de algunos suelos desarrollados sobre materiales fluvio-glaciales, aluviales y de terrazas Pleistocenas y Holocenas relacionados con el rio Segre, ya sean silicicos o carbonaticos. Ello permitira identificar los procesos formadores del suelo propios de ambientes mediterraneos, como redistribucion de carbonatos, formacion y movilizacion de arcillas y rubefaccion, y relacionarlos con el material parental y la edad. Se clasificaron cinco perfiles en materiales con edades desde el Pleistoceno Inferior al Holoceno, de acuerdo con Soil Taxonomy /WRB. El perfil de Montferrer (Palexeralf Calcico /Calcic Cutanic Luvisol (cromic)) es un suelo profundo, descarbonatado en parte, con acumulacion de carbonato de calcio en profundidad superpuesto a rasgos glaciales. El perfil Torre del Remei (Paleustalf tipico /Cutanic Luvisol) esta desarrollado sobre morrenas silicicas y muestra formacion e iluviacion de arcilla extrema. Los perfiles de Alp (Haplustalf tipico /Cutanic Luvisol) y Tartera (Calciustept petrico /Petric Calcisol) son suelos desarrollados sobre abanicos aluviales con una fuente de carbonato de calcio. El primero esta descarbonatado, mientras que el ultimo esta rubefactado en la parte superior y muestra cemento geopetal de carbonatos con morfologia de espeleotemas con superposicion de iluviacion de arcilla. El perfil mas joven (Abellerols, Calciustept tipico /Typic Calcisol) esta descarbonatado solo en parte y muestra acumulacion de calcita en profundidad. Los resultados indican que el desarrollo del suelo se determina por la edad de las superficies y la fuente de calcita, ya sea en el material parental o a traves de escorrentia. La iluviacion de arcilla es extrema en ausencia de carbonatos. Las morfologias especiales de cemento geopetal de carbonato son indicadores de las condiciones ambientales. La coexistencia de los revestimientos de arcilla y calcita secundaria puede ser explicada por recarbonatacion o por diferenciacion espacial de los ambientes de suelos en el perfil. Una de las implicaciones de esta investigacion es la inconsistencia del uso de indices de desarrollo del suelo basados en indicadores morfologicos cuando los suelos estan formados sobre materiales parentales diferentes y estan sujetos a dinamicas geomorfologicas distintas.

Investigation of Water Dynamics and the effect of Evapotranspiration on grain Yield of rainfed wheat and barley under a mediterranean environment: A modelling approach

Agro-hydrological models have increasingly become useful and powerful tools in optimizing water and fertilizer application, and in studying the environmental consequences. Accurate prediction of water dynamics in such models is essential for models to produce reasonable results. In this study, detailed simulations were performed for water dynamics of rainfed winter wheat and barley grown under a Mediterranean climate over a 10-year period. The model employed (Yang et al., 2009. J. Hydrol., 370, 177-190) uses easily available agronomic data, and takes into consideration of all key soil and plant processes in controlling water dynamics in the soil-crop system, including the dynamics of root growth. The water requirement for crop growth was calculated according to the FAO56, and the soil hydraulic properties were estimated using peto-transfer functions (PTFs) based on soil physical properties and soil organic matter content. Results show that the simulated values of soil water content at the depths of 15, 45 and 75 cm agreed with the measurements well with the root of the mean squared errors of 0.027 cm3 cm-3 and the model agreement index of 0.875. The simulated seasonal evapotranspiration (ET) ranged from 208 to 388 mm, and grain yield was found to correlate with the simulated seasonal ET in a linear manner within the studied ET range. The simulated rates of grain yield increase were 17.3 and 23.7 kg ha-l for every mm of water evapotranspired for wheat and barley, respectively. The good agreement of soil water content between measurement and simulation and the simulated relationships between grain yield and seasonal ET supported by the data in the literature indicates that the model performed well in modelling water dynamics for the studied soil-crop system, and therefore has the potential to be applied reliably and widely in precision agriculture. Finally, a two-staged approach using inverse modelling techniques to further improve model performance was discussed.

Soil – landscape relationships in the Empordà basin (Catalonia, NE Iberian Peninsula)

Soils developed in representative landforms, which were previously mapped at a detailed scale in the Emporda Basin, were selected to characterize their main pedogenetic processes and to improve the soil maps through a better understanding of the soil – landscape relationships. This basin is a relatively large region (1,300 km2) in Northeastern Catalonia, where Neogene and Quaternary sediments outcrop. They are alluvial and delta fan deposits that mainly reflect a continental environment. Besides varying degrees of soil rubefaction, we can identify calcium carbonate redistribution, clay illuviation and sodication as the main soil forming processes, together with abrupt textural changes, vertic and redoximorphic features. These processes and features are expressed under different morphologies in the area, depending not only on parent material, landform and age, but also on human action, which allows us to refine the conceptual soil-landscape model. Calcium carbonate redistribution is a key process reflecting both changing general environmental conditions and local chemical soil conditions. The actual soil characteristics and the soil forming processes allow us to propose that (i) aeolian dust inputs in these soils have been low to moderate throughout, and that (ii) the rainfall pattern in the last part of the Holocene was able to remove these dust inputs, but unable to leach carbonates from medium textured, moderately calcareous soils in the area when they are some kilometres from the sea and not directly affected by the dune system.