Definición de un Modelo Edafogeomorfológico para la Identificación de Necesidades de Manejo y Recuperación de Suelos a Nivel Local. Caso Cuenca Cañada La Gorda, Machiques Colón, Estado Zulia, Venezuela.

El objetivo de este trabajo es generar un modelo Edafogeomorfológico útil en la identificación de necesidades de manejo de suelos, se realizó un estudio en el área de la cuenca Cañada La Gorda Machiques-Colón, estado Zulia, Venezuela, caracterizada por un clima tropical de condición subhúmeda, con duración del periodo de crecimiento (DPC) de 230 días, régimen de humedad Ustic y de temperatura Isohipertémico. Se empleó el enfoque de la ecuación factorial de formación de suelos para el análisis y descripción biofísica de los factores a lo largo de una carena. El relieve caracterizado a partir de fotografías aéreas, imágenes de satélites y de chequeos sistemático mediante transectos en el sentido del flujo del escurrimiento; la vegetación a través del uso de la tierra, la cobertura vegetal, la identificación de las especies dominantes a partir de sus nombres vernáculos y la definición de indicadores de vegetales (Iv). Los suelos fueron descritos y clasificados según la Taxonomía de suelos y valorados mediante el modelo paramétricode Riquier et al. (1970) para determinar el índice de productividad (Ip). Se caracterizaron dos paisajes gemorfológicos: Colinar (C) y Valle (V), seis posiciones geomorfológicas entre ambos paisajes definidas por la sucesión de relieves en el sentido de la pendiente: Tope de colina-loma (TC), mesa conservada (MC), vertientes de mesa alta (VA), media (VM), baja (VB) y valle intracolinar (VI); e igual número de perfiles de suelos representativos, los cuales mostraron edafogénesis muy avanzada con Ip inferiores a 8% en todas las posiciones, exceptuando la VB, con una productividad de 13%. El uso de la tierra es a base de pastoreo semi-intensivo de plantas forrajeras introducidas. Las formaciones vegetales predominante fueron los matorrales y arbustales dispersos, acompañados con restos de una selva tropófila fuertemente afectada por la extracción forestal y la conversión en áreas de pastoreo. Se identificaron 8 Iv, asociados fuertemente con condiciones de físicas e hidrológicas del suelo. El alto impacto de las actividades humanas sobre el suelo y vegetación, expresado a través de los procesos de erosión activa, la ausencia de áreas boscosas y la baja productividad de los sistemas de ganadería reportada para la zona, señalan la necesidad de reorientación del uso actual de la tierra, para lo cual se plantean alternativas como la incorporación de bosques protectores y sistemas agrosilvopastoriles In order to generate an Edaphogeomorphological model to be used for the identification of management requirements of soils, a study was carried out in the area of the Cañada La Gorda watershed, Machiques Colon, Zulia State with a tropical climate, subsumid conditions with a growing period of 230 days, an Ustic soil moisture and Isohypertermic regimes. The soils factorial equation approach was used for the analisis and description of the factors of soil formation throughout a soil catena. Relief was characterized through aerial photographs, satellite images and systematic checks of transects drawn in the sense of surface runoff and also taking into account geomorphological features. Vegetation cover and land use were described and vegetation components were indified by its local names to defined vegetations indicators (VI) for the local conditions. Soils were described and classified according to soil taxonomy and valued by means of a parametric model proposed by Riquier et al, (1970) for determining the productivity index (PI). Two geomorphological landscapes were defined: Hilly and Valley with six positions within the landscapes: hilltop (round or elongated), preserved tableland summit, slopes of high, medium and low tableland and valleys between hills. Representative soils of each position were studied showing a highly advanced degree of edaphogenesis with PI values below 8% in all positions except the valleys with a PI of 13%. Land use type is based on semi intensive pasturing of introduced forage species, with a vegetation of brushwood and scattered shrubs, with some trees relicts of woods affected by timber extraction and turn to grassland Eight VI were identified, highly associated to local physical and hidrological soil conditions. The enormous impact of human activity on soils and vegetation as shown by active erosion processes and absence of wooded areas and the low productivity of livestock systems reported for the area, indicates the necessity of a reorientation of the present land use introducing alternatives like the incorporation of protective woods and agrosilvopastoral management systems.

Effects of forage type on diversity in bacterial pellets isolated from liquid and solid phases of the rumen content in sheep and goats.

Two sheep and two goats, fitted with a ruminal cannula, received two diets composed of 30% concentrate and 70% of either alfalfa hay (AL) or grass hay (GR) as forage in a two-period crossover design. Solid and liquid phases of the rumen were sampled from each animal immediately before feeding and 4 h post-feeding. Pellets containing solid associated bacteria (SAB) and liquid associated bacteria (LAB) were isolated from the corresponding ruminal phase and composited by time to obtain 2 pellets per animal (one SAB and one LAB) before DNA extraction. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S ribosomal DNA was used to analyze bacterial diversity. A total of 78 and 77 bands were detected in the DGGE gel from sheep and goats samples, respectively. There were 18 bands only found in the pellets from sheep fed AL-fed sheep and 7 found exclusively in samples from sheep fed the GR diet. In goats, 21 bands were found only in animals fed the AL diet and 17 were found exclusively in GR-fed ones. In all animals, feeding AL diet tended (P < 0.10) to promote greater NB and SI in LAB and SAB pellets compared with the GR diet. The dendrogram generated by the cluster analysis showed that in both animal species all samples can be included in two major clusters. The four SAB pellets within each animal species clustered together and the four LAB pellets grouped in a different cluster. Moreover, SAB and LAB clusters contained two clear subclusters according to forage type. Results show that in all animals bacterial diversity was more markedly affected by the ruminal phase (solid vs. liquid) than by the type of forage in the diet.

The contribution of two common shrub species to aboveground and belowgraound carbon pool in Iberian Dehesas

Shrubs play an important role in water-limited agro-silvo-pastoral systems by providing shelter and forage for livestock, for erosion control, to maintain biodiversity, diversifying the landscape, and above all, facilitating the regeneration of trees. Furthermore, the carbon sink capacity of shrubs could also help to mitigate the effects of climate change since they constitute a high proportion of total plant biomass. The contribution of two common extensive native shrub species (Cistus ladanifer L. and Retama sphaerocarpa (L.) Boiss.) to the carbon pool of Iberian dehesas (Mediterranean agro-silvo-pastoral systems) is analyzed through biomass models developed at both individual (biovolume depending) and community level (height and cover depending). The total amount of carbon stored in these shrubs, including above- and belowground biomass, ranges from 1.8 to 11.2 Mg C ha_1 (mean 6.8 Mg C ha_1) for communities of C. ladanifer and from 2.6 to 8.6 Mg C ha_1 (mean 4.5 Mg C ha_1) for R. sphaerocarpa. These quantities account for over 20e30% of the total plant biomass in the system. The potential for carbon sequestration of these shrubs in the studied system ranges 0.10e1.32 Mg C ha_1 year_1 and 0.25e1.25 Mg C ha_1 year_1 for the C. ladanifer and R. sphaerocarpa communities’ respectively

Changes in rumen microbes in sheep in response to dietary forage quality and relationships with fermentation characteristics

An in vitro experiment was carried out using the Hohenheim gas production technique to evaluate 24-h gas production, apparently and truly degraded dry matter (DM), partitioning factor (PF), short chain fatty acids, crude protein (CP) and carbohydrate (CHO) fractionation of grass and multipurpose tree species (MPTS) foliage diets. Four grasses and three MPTS were used to formulate 12 diets of equal mixtures (0.5:0.5 on DM basis) of each grass with each MPTS. In vitro gas production was terminated after 24 h for each diet. True DM degradability was measured from incubated samples and combined with gas volume to estimate PF. Diets had greater (P<0.001) CP (102–183 g/kg DM) content than sole grasses (66–131 g/kg DM) and lower (P<0.001) concentrations of fibre fractions. Contrary to in vitro apparently degraded DM, in vitro truly degraded DM coefficient was greater (P<0.001) in diets (0.63–0.77) than in sole grasses (0.48–0.68). The PF was on average higher in diets than in sole grasses. The proportion of potentially degradable CP fractions (A1, B1, B2 and B3, based on the Cornell Net Carbohydrate and Protein System) in the diets ranged from 971 to 989 g/kg CP. Crude protein fractions, A and B2 were greater in diets but B1 and B3 fractions were less in diets than in sole grasses. A similar trend was also observed in the CHO fractions. Results showed that the nutritive value of the four grasses was improved when MPTS leaves were incorporated into the diet and this could ensure higher productivity of the animals.

Quantitative characterization of five cover crop species

The introduction of cover crops in the intercrop period may provide a broad range of ecosystem services derived from the multiple functions they can perform, such as erosion control, recycling of nutrients or forage source. However, the achievement of these services in a particular agrosystem is not always required at the same time or to the same degree. Thus, species selection and definition of targeted objectives is critical when growing cover crops. The goal of the current work was to describe the traits that determine the suitability of five species (barley, rye, triticale, mustard and vetch) for cover cropping. A field trial was established during two seasons (October to April) in Madrid (central Spain). Ground cover and biomass were monitored at regular intervals during each growing season. A Gompertz model characterized ground cover until the decay observed after frosts, while biomass was fitted to Gompertz, logistic and linear-exponential equations. At the end of the experiment, carbon (C), nitrogen (N), and fibre (neutral detergent, acid and lignin) contents, and the N fixed by the legume were determined. The grasses reached the highest ground cover (83–99%) and biomass (1226–1928 g/m2) at the end of the experiment. With the highest C:N ratio (27–39) and dietary fibre (527–600 mg/g) and the lowest residue quality (~680 mg/g), grasses were suitable for erosion control, catch crop and fodder. The vetch presented the lowest N uptake (2·4 and 0·7 g N/m2) due to N fixation (9·8 and 1·6 g N/m2) and low biomass accumulation. The mustard presented high N uptake in the warm year and could act as a catch crop, but low fodder capability in both years. The thermal time before reaching 30% ground cover was a good indicator of early coverage species. Variable quantification allowed finding variability among the species and provided information for further decisions involving cover crop selection and management.