Carlos Gregorio Hernández Díaz-Ambrona

Cereal–legume rotations in a Mediterranean environment: biomass and yield production

Abstract The effects of various crop rotations on the biomass and yield of barley (Hordeum vulgare L.), faba bean (Vicia faba L.), and pea (Pisum sativum L.) grown under Mediterranean conditions were studied during three growing seasons in the semiarid Spanish Central Plateau. The treatments comprised six crop sequences: barley monoculture, fallow–barley (currently used in the area), faba bean–barley, pea–barley, fallow–barley–faba bean, and fallow–barley–pea. The fallow was of 16-month duration. The site is representative of cultivated areas of the Plateau, and the soil has a loam texture. Results concentrate on barley as the main crop. Season distribution of rainfall restricted the effectiveness of the management practices and in consequence there were few differences between rotations. Barley had greater biomass and yield after fallow than after other crops but significant differences were dependent on year. Legumes, an alternative to fallow, increased land use, permitted alternative weed control measures, and reduced the need for fertiliser. The intensification of the fallow–barley cropping system is best achieved by reducing the frequency of fallow and including other crops of relatively small biomass production, thereby minimising the impact on yield of the succeeding barley crop.

Faba bean canopy modelling with a parametric open L-system: a comparison with the Monsi and Saeki model

Abstract A three-dimensional (3D) model of canopy growth for faba bean (Vicia faba L.) based on the aggregation of simulated single plants, spatially distributed at a certain density, is presented. The plants are considered individual geometric objects that can be characterised with a Lindenmayer system (L-system). Plant growth was described with recursive algorithms coupled to traditional growth functions obtained from greenhouse experiments. A basic type of plant with three stems was first built with a deterministic L-system, then stochastic functions allowed for the representation of the plasticity of the legume under field conditions. The canopy model was validated with data from field experiments. Simulation of leaf area index and light interception were comparable to those obtained from traditional crop models such as CERES, CropSyst, etc. that consider the Monsi and Saekis model. This 3D model, displaying growth and structures of a single plant and of a canopy, can become the basis for modelling the environment of individual organs of a faba bean plant. Decreasing the thermal time step would allow for daily or smaller time steps and for the inclusion of functions describing diurnal patterns of physiological processes.

Contribution of crop model structure, parameters and climate projections to uncertainty in climate change impact assessments

Climate change impact assessments are plagued with uncertainties from many sources, such as climate projections or the inadequacies in structure and parameters of the impact model. Previous studies tried to account for the uncertainty from one or two of these. Here, we developed a triple-ensemble probabilistic assessment using seven crop models, multiple sets of model parameters and eight contrasting climate projections together to comprehensively account for uncertainties from these three important sources. We demonstrated the approach in assessing climate change impact on barley growth and yield at Jokioinen, Finland in the Boreal climatic zone and Lleida, Spain in the Mediterranean climatic zone, for the 2050s. We further quantified and compared the contribution of crop model structure, crop model parameters and climate projections to the total variance of ensemble output using Analysis of Variance (ANOVA). Based on the triple-ensemble probabilistic assessment, the median of simulated yield change was -4% and +16%, and the probability of decreasing yield was 63% and 31% in the 2050s, at Jokioinen and Lleida, respectively, relative to 1981-2010. The contribution of crop model structure to the total variance of ensemble output was larger than that from downscaled climate projections and model parameters. The relative contribution of crop model parameters and downscaled climate projections to the total variance of ensemble output varied greatly among the seven crop models and between the two sites. The contribution of downscaled climate projections was on average larger than that of crop model parameters. This information on the uncertainty from different sources can be quite useful for model users to decide where to put the most effort when preparing or choosing models or parameters for impact analyses. We concluded that the triple-ensemble probabilistic approach that accounts for the uncertainties from multiple important sources provide more comprehensive information for quantifying uncertainties in climate change impact assessments as compared to the conventional approaches that are deterministic or only account for the uncertainties from one or two of the uncertainty sources.

Participatory evaluation of food and nutritional security through sustainability indicators in a highland peasant system in Guatemala

ABSTRACT Food and Nutritional Security (FNS) is still an outstanding problem, and rural areas of Guatemala demonstrate this by an increase in the undernourished population from 1.4 million in 1991 to 2.5 million in 2014. Some FNS programs were developed in the past, and our research evaluates the following: (1) the critical points perceived by farmers related to the sustainability of their systems, (2) the performance of FNS program through a set of 7 indicators, and (3) how the FNS levels are related to sustainability indicators among hamlets. We used mixed methods (participatory rural appraisals and 64 semi-structured household surveys) across six hamlets. The most robust 15 indicators were selected through correlation analysis. Two series of five least squares regression models determined that the critical points had significant impacts on economic disparities but failed to explain malnutrition levels. Consequently, we compared two contrasting hamlets according to their energy and protein supply. The results showed that FNS is linked to sustainability as the more self-reliant and equitable community exhibited higher food security. However, FNS depends upon a complex array of self-sufficiency strategies that remain linked to individual household idiosyncrasies.