Cristina Chinchilla-Soto

Introducción: el biocarbón es un material carbonoso obtenido por pirólisis de biomasa en condiciones limitadas de oxígeno, cuyo potencial para aplicaciones agrícolas y ambientales depende directamente de sus propiedades químicas y estructurales. La temperatura de pirólisis y el método de producción influyen en la proporción de grupos funcionales oxigenados, el grado de aromaticidad y el contenido mineral, modificando así su estabilidad y funcionalidad. Objetivo: determinar el efecto de las condiciones de pirólisis sobre las propiedades químicas superficiales de biocarbones derivados de pinzote de palma africana, madera de ciprés y bambú. Métodos: empleamos dos modalidades de producción: una en un horno de campo Kon-Tiki y otra bajo condiciones controladas de laboratorio a cuatro temperaturas: 400 grados Celsius, 500 grados Celsius, 600 grados Celsius y 700 grados Celsius. Caracterizamos los biocarbones mediante análisis proximal, determinación de pH y conductividad eléctrica, análisis elemental de carbono, hidrógeno, nitrógeno, azufre y oxígeno, medición del potencial zeta, titulación de Boehm y espectroscopía infrarroja, utilizando un carbón activado comercial como referencia. Resultados: el aumento de la temperatura redujo la materia volátil e incrementó el carbono fijo y las cenizas. El pH aumentó con la temperatura. El análisis elemental mostró un incremento de carbono hasta el 82% y una disminución de oxígeno e hidrógeno. Las proporciones atómicas entre hidrógeno y carbono orgánico y entre oxígeno y carbono orgánico disminuyeron progresivamente, indicando una alta estabilidad aromática. Se identificó el valor más elevado de nitrógeno en el pinzote de palma en comparación con el bambú y el ciprés, mientras que el azufre se mantuvo en niveles traza o indetectables. Los valores de potencial zeta se hicieron menos negativos con la temperatura debido a la desoxigenación superficial confirmada por espectroscopía infrarroja y titulación de Boehm. Frente al carbón activado, los biocarbones conservaron una mayor densidad de sitios activos. Conclusiones: los biocarbones de laboratorio presentaron propiedades más homogéneas y estabilidad estructural, mientras que los de campo mostraron mayor heterogeneidad química. Los criterios técnicos derivados de este estudio, como el gradiente de grupos funcionales, estabilidad aromática y carga superficial en función de la temperatura y la biomasa, constituyen una base para seleccionar el biocarbón más adecuado según el objetivo agronómico específico en condiciones tropicales.

Introduction. Simulation models are a tool to study crop behavior under different climatic and water conditions and agronomic management practices. Objective. To evaluate the AquaCrop model for estimating yield and water productivity in soybean var. CIGRAS-06. Materials and methods. The study was carried out at the Estación Experimental Agrícola Fabio Baudrit Moreno of the University of Costa Rica, in Alajuela, Costa Rica, from June 6 to October 23, 2018. The AquaCrop v. 7.1 model was used to simulate soybean crop development and yield. Simulated data on canopy cover, biomass production, and yield were compared with experimental data from a plot planted with soybean variety CIGRAS-06. Soil parameters measured in the field and generated with pedotransfer equations were used. Results. Predictions of yield, total biomass, and canopy cover were good (similarity values: d ≥ 0.97), but predictions of leaf coverage during the early crop cycle were susceptible to improvement. Differences between the two types of soil parameters used did not significantly affect the final simulation. Conclusions. AquaCrop successfully simulated soybean yield, biomass, and leaf coverage. Water productivity simulation was higher than values reported in the literature.

RESUMEN. Introducción: El biocarbón es un material carbonoso con potencial para mejorar la fertilidad de los suelos y contribuir a la sostenibilidad agrícola. Sus propiedades fisicoquímicas dependen tanto de la biomasa empleada como de las condiciones de producción. En Costa Rica, cultivos como café y palma africana generan grandes volúmenes de residuos lignocelulósicos con escaso aprovechamiento, lo que representa una oportunidad para su transformación en biocarbón. Objetivo: Evaluar el efecto del tipo de horno en la producción de biocarbón a partir de madera de ciprés (Cupressus sp.), pinzote de palma africana (Elaeis guineensis) y bambú (Guadua angustifolia), sobre las propiedades físicas y químicas. Métodos: Elaboramos biocarbones en un horno abierto de campo tipo “Kon Tiki” y en un horno de laboratorio tipo mufla bajo condiciones controladas. Caracterizamos los materiales mediante análisis proximal, determinación de cenizas, pH y conductividad eléctrica. La capacidad de adsorción la evaluamos mediante las pruebas de azul de metileno y número de yodo, el área superficial y la porosidad total la estimamos con el método BET. Resultados: Observamos diferencias significativas entre los biocarbones según la biomasa y el tipo de horno. Los biocarbones producidos en campo presentaron valores más altos de pH, conductividad eléctrica y cenizas, propiedades asociadas a una mayor capacidad de intercambio catiónico, pero a una menor homogeneidad estructural. En contraste, los biocarbones de laboratorio mostraron mayor contenido de carbono fijo, menor fracción de compuestos volátiles y mejor desarrollo textural, reflejado en áreas superficiales y porosidades totales superiores. El índice de yodo fue consistentemente mayor que la adsorción de azul de metileno, lo que confirma la predominancia de la fracción microporosa. Conclusiones: Tanto la biomasa como el tipo de horno influyen de manera determinante en las propiedades del biocarbón, que condicionan su desempeño como enmienda agrícola.

Introduction. Universities, private companies, non-governmental organizations, and producers’ organizations have conducted research on biochar in Costa Rica in the last 15 years. Objective. To compile observed results in technical documents (bulletins, reports) and scientific documents (scientific papers and theses) related to the use of biochar in Costa Rica. Content. Different furnace designs are presented, with a predominant of the small-scale tin furnace and temperatures between 400 and 600 °C. The raw materials used to produce biochar are wood residues (Gmelina arborea, Cordia alliodora), firewood from coffee and banana agroforestry systems, bamboo, sugarcane stubble, and oil palm stalk. Methodologies have been developed to characterize biochar such as elemental analysis, proximate analysis, and nutrient content. Conclusions. Positive results have been observed in crop development, in acidic soils (doses between 10 and 20 t ha-1) cropped with oil palm and vegetables. No significant increases in crop development were seen with the application of biochar in soils with high cation content (Inceptisols) and volcanic ash derived soils (Andisols) in cocoa, oil palm, and vegetables. Significant improvements in water retention were seen at doses of 30 t ha-1 in sandy soils and a significant decrease in the incidence of Radophulus similis and Fusarium oxysporum in banana was observed, with the addition of biochar + endophytic microorganisms. Biochar production from agricultural byproducts and its use in crops and areas near the production site is recommended to promote the bioeconomy. Future lines of research should include: the improvement of ovens design to work with resistant materials such as oil palm fiber, evaluation of the biochar impact on water, nutrients, and pesticides retention, as well as crop productivity in acid and sandy soils.

Knowledge of the soil carbon stock (SCS) is vital for appropriate farming practices management, ie. tillage and to monitor SCS changes as mitigation strategies of carbon footprint. This study aims to quantify the variability and spatial distribution of the SCS. In an area of 1 ha 45 micro-pit (1 x 0.8 x 1 m) were divided into four strata. Vertical distribution of soil carbon was quantified along with other chemical and physical soil properties that affect rice production in Parrita, Costa Rica. A map of spatial prediction of the distribution and goodness-of-prediction values were calculated to estimate the effectiveness of the SCS prediction when different numbers of sampling points were used 45, 27, 15 and 7 microplots. As accurate measurements, the Mean Absolute Error and the Mean Square Error were calculated. In this study, the SCS was 85.8 (±2.6) Mg C ha-1, into the total profile (0-100 cm), where the first 30 cm represented 46.2%. Prediction of the spatial distribution suggests that in annual agricultural crops, with tillage systems 15 sampling points ha-1 a can effectively estimate the SCS.

In the Yaqui Valley, Mexico, the current and estimated annual growth rate of durum wheat (Triticum turgidum L. subsp. durum) yield is insufficient to satisfy the food demand that the world will be facing by 2050. Furthermore, besides the high doses of fertilizers applied to wheat in this region, nitrogen-use efficiency (NUE) remains low (Bacillus cabrialesii subsp. cabrialesii TE3^T, Priestia megaterium TRQ8, and Bacillus paralicheniformis TRQ65 on grain yield, grain quality, and NUE (measured through ¹⁵N-isotopic techniques) at different stages of development of durum wheat variety CIRNO C2008 under three doses of urea (0, 120, and 240 kg N ha⁻¹) fractionated at 30%, 60%, and 10%. Results showed that yield, quality, and NUE were highly affected by the N doses, while the inoculation of the BC had a lower impact on these parameters. Nevertheless, the inoculation of the BC on wheat had positive effects at the early stages of growth, on plant height (+1.6 cm), root depth (+11.9 cm), and spikes per square meter (+25 spikes m⁻²). Moreover, the addition of the BC improved N acquisition by the plants, at different crop growth stages, compared to uninoculated treatments. Finally, our results indicated that reducing the N dose from 240 kg of N ha⁻¹ to 120 kg of N ha⁻¹ improved the NUE (27.5% vs. 44.3%, respectively) of the crop. Hence, results of this preliminary study showed that the incorporation of bacterial inoculants into the wheat crop requires a simultaneous adequate N management, in order to obtain the desired positive effect on wheat productivity.

Coffee is one of the most commonly traded agricultural commodities globally. It is important for the livelihoods of over 25 million families worldwide, but it is also a crop sensitive to climate change, which has forced producers to implement management practices with effects on carbon balance and water use efficiency (WUE) that are not well understood due to data scarcity. From this perspective, we propose crop canopy coupling to the atmosphere (Ώ) as an index of resilience and stability. We undertook an integrated observational approach for the scaling-up of measurements along the soil–plant–atmosphere continuum at different stages of the coffee crop phenological cycle. Additionally, we develop this perspective under pronounced climatic seasonality and variability, in order to assess carbon balance, WUE, and agroecosystem resilience in a sun-grown coffee field. Further, we devised a field layout that facilitates the measurement of intrinsic, instantaneous, and actual water use efficiency and the assessment of whether coffee fields differ in canopy structure, complexity, and agronomic management and whether they are carbon sources or sinks. Partitioning soil and canopy energy balances and fluxes in a sun-grown coffee field using eco-physiological techniques at the leaf and whole plant levels (i.e., sap flow and gas exchange), as proposed here, will allow the scaling-up to whole fields in the future. Eddy covariance was used to assess real-time surface fluxes of carbon, gross primary productivity (GPP), and evapotranspiration, as well as components of the energy balance and WUE. The preliminary results support the approach used here and suggested that coffee fields are CO₂ sinks throughout the year, especially during fruit development, and that the influence of seasonality drives the surface–atmosphere coupling, which is dominant prior to and during the first half of the rainy season. The estimated WUE showed consistency with independent studies in coffee crops and a marked seasonality driven by the features of the rainy season. A plan for the arborization of the coffee agroecosystem is suggested and the implications for WUE are described. Future comparison of sun- and shade-grown coffee fields and incorporation of other variables (i.e., crop coefficient-KC for different leaf area index (LAI) values) will allow us to better understand the factors controlling WUE in coffee agroecosystems.