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Soil water repellency (WR) is a widespread phenomenon caused by aggregated organic matter (OM) and layers of hydrophobic organic substances coating the surface of soil particles. These substances have a very low surface free energy, reducing a soil's water attraction.There is focus on WR due to its effects on germination, root growth, liquid-vapour dynamics, surface erosion and leaching of chemicals through fingered flow paths. However, common techniques for measuring WR are time-consuming and expensive. Meanwhile, it is well established that visible near infrared (vis-NIR) spectroscopy is a reliable method for determining soil OM. Potentially it could therefore provide fast measurements of WR through autocorrelation with OM. The aim of this study was to test the feasibility of vis-NIR spectroscopy for estimating the WR of soils with a small gradient in soil organic carbon (SOC) and texture, and to evaluate the effect of soil pretreatment on the predictive ability of WR models. A total of 87 soil samples from an agricultural coarse sandy field in Denmark were analysed for SOC, particle size fractions, water content and WR. Soil samples were scanned with a vis-NIR sensor (350-2500 nm) after air-and oven-drying at 60°C and 105°C. WR, expressed as liquid surface tension (mN m −1 ), was determined using the molarity of ethanol droplet test. Partial least squares regression models of SOC, texture and water content showed no predictive ability (r 2 values between 0.10 and 0.51). However, successful models (r 2 = 0.85) were generated for WR. The majority of bands important in the vis-NIR region of WR models were related to different components of OM indicating that, across the investigated field, WR was related to specific hydrophobic components of soil OM rather than to the total amount of carbon. A lower prediction error of the WR model for soils dried at 105°C (1.93 mN m −1 ) than at 60°C (2.52 mN m −1 ) can be explained by a lower range of WR values for the soils dried at 105°C. Moreover, a higher temperature reduced the number of absorption bands related to OM, indicating a degradation of hydrocarbon groups and a more hydrophobic character of the soil.

The gas diffusion coefficient, air permeability, and their interrelations with air-filled porosity are essential for characterization of diffusive and convective transport of gases in soils. Variations in soil bulk density can affect water retention, air-filled pore space, and pore-network connectivity and tortuosity and, thereby, control gas diffusion and air permeability. Considering 86 undisturbed core samples with variable bulk densities that were extracted on a 15 by 15 m grid from the top layer of a sandy field, the effects of soil bulk density on gas transport parameters and the soil water characteristic were investigated. Interactions with soil organic matter, sand, and clay fractions were also examined. To evaluate bulk density effects, two constitutive parameters were derived from each of the three measured relationships. The Campbell pore-size distribution index (b) and the air-entry matric potential (y ae ) were derived from the soil water characteristic; the diffusive percolation threshold (e DPT ), the air-filled porosity where gas diffusivity ceases to almost zero because of interconnected water films creating isolated-inactive air content, and a pore-network connectivity index (A 2 ) were derived from the gas diffusivity curve, and the analogous parameters convective percolation threshold (e CPT ) and convective pore-network connectivity index (B 2 ) from the air permeability curve. All six parameters showed significant negative correlations with bulk density. To further account for the effects of both bulk density and macroporosity in parametric gas transport models, a diffusive-analog macroporosity-dependent model (DAMP) for gas diffusivity and a generalized Kawamoto et al. model (GK) for air permeability, which yielded improved predictive capabilities when compared with previous models, were developed. Both new models apply a reference point of prediction at −100 cm H 2 O matric potential (macroporosity drained), corresponding to the point where analysis of pore-network tortuosity (T) and equivalent pore diameter for gas transport (d g ) showed diminishing effects of water blockage on gas transport in the sandy soil.

Biochar is a carbon-rich organic material, obtained by the thermochemical conversion of biomass in an oxygen-limited environment, used as a soil amendment to stimulate soil fertility and improve soil quality. There is a clear need in developing countries for access to low cost, low technology options for biochar production, for example, top-lit updraft (TLUD) stoves, which are popular and spread worldwide. However, TLUD biochars are inevitably very variable in their properties for a variety of reasons. We present laboratory triplicate tests carried out on TLUD biochars obtained from waste pinewood and a Guadua bamboo. Analyzed properties include specific surface area (A-BET), porosity, skeletal density, hydrophobicity, proximal and elemental composition, cation exchange capacity (CEC), relative liming capacity and pH. SEM images of the bamboo and wood biochars are compared. The biochars were mixed with composted human excreta at 5% and 10% biochar content, and available water content (AWC) was analyzed. Operating temperatures in the TLUD were recorded, showing different behaviors among the feedstocks during the process. Differences in operating temperatures during charring of the bamboo samples seem to have led to differences in A-BET, hydrophobicity and CEC, following unprecedented trends. For the mixtures of the biochars with compost, at 5% biochar no significant differences were observed for AWC. However, in the 10% biochar mixtures, bamboo biochar showed an unexpectedly high AWC. Overall, variations of chemical and physical properties between bamboo biochars were greater, while pinewood biochars showed similar properties, consistent with more homogeneous charring temperatures.

Soil degradation and water stress in Costa Rica challenge the production of highly sensitive crops. This work is aimed at evaluating the physical and chemical changes in sandy loam (SL) and a silt loam (SiL) soil when amended with bamboo biochar while estimating the enhancement of tomato productivity. Biochar, obtained from Guadua Angustifolia bamboo feedstock, was mixed into sieved bulk soil substrate from the topsoil, from Andosol and Umbrisol groups, at application rates of 1, 2.5, and 5% (dry mass). Physicochemical and morphological properties of biochar such as pH, hydrophobicity, scanning electron microscopy images, helium picnometry, specific surface area by the Brunauer–Emmett–Teller (BET) method, CHNS, and ash content were determined. Soil hydrophobicity, acidity, electrical conductivity, cation exchange capacity and water retention, available water content, and air capacity were analyzed for the amended soils. Tomato yield was quantified after a harvest period of two months. The admixture of biochar did not significantly increase soil cation exchange capacity but increased water retention in the range of available water content. Class A (>200 g) tomato yield increased 350% in the SL and 151% in the SiL. Class B (100–200 g) tomato yields increased 27% in the SL but decreased about 30% in the SiL. Tomato yield response seems attributable to variation of water retention capacity, available water content, and air capacity. These results support the use of adapted water management strategies for tomato production based on soil physical changes of biochar.

El principal objetivo de este estudio fue analizar el flujo de agua por redistribución a través de los horizontes de perfiles de suelos volcánicos en la Zona No Saturada (ZNS), una vez que ha finalizado la infiltración de agua por lluvia. A partir de monolitos experimentales, se monitorearon los contenidos volumétricos de agua en perfiles a diferentes profundidades para entender la dinámica de flujo temporal a lo largo de un perfil. Se evaluaron en laboratorio las propiedades físicas e hidráulicas de los horizontes como: textura, granulometría, materia orgánica, densidad aparente, densidad real, porosidad, conductividad hidráulica y retención de humedad. Se encontró que las propiedades físicas e hidráulicas de los horizontes ayudan a explicar el comportamiento del agua en profundidad. Los aportes de agua por redistribución en profundidad, debido a flujo vertical, fueron encontrados mediante el análisis de los contenidos volumétricos de agua. Estos aportes se evidenciaron por los incrementos en los contenidos volumétricos durante el desarrollo del experimento. Se pudo observar cómo cambió el flujo por redistribución en los perfiles de un horizonte, al mostrar de esa forma la variación de las propiedades de los horizontes en profundidad. Una vez establecidos los flujos por redistribución de agua, se caracterizaron los tipos de flujos de agua que se dieron lugar en los perfiles de los monolitos para establecer cuál es la dinámica del frente de humedecimiento en profundidad y como avanza este durante el desarrollo del experimento. Los resultados mostraron que en los monolitos se presentan el flujo de pistón, el flujo preferencial y el flujo dual o combinado producto de la combinación de ambos.

El desarrollo tecnológico de los vehículos aéreos no tripulados, VANT´s da acceso a nuevas aplicaciones en múltiples campos de la ciencia y la ingeniería. El uso de sensores remotos, el análisis satelital, la medición de datos en el sitio han sido las principales herramientas empleadas para la monitorización y el estudio de los recursos naturales. Los VANT´s son una tecnología de bajo costo capaz de recolectar información de manera rápida y precisa, con alta resolución espacial. El objetivo del presente trabajo fue realizar una revisión de las características principales y las aplicaciones de los vehículos aéreos no tripulados en el manejo de los recursos naturales, principalmente en la región latinoamericana. En este trabajo se describen los tipos de drones existentes, sus ventajas, desventajas y los diferentes tipos de sensores que se pueden adaptar. Además, se revisaron trabajos sobre VANTS realizados en Brasil, Perú y Colombia como una guía para América Latina. Se muestra una   serie de posibles arreglos entre VANTS y sensores remotos., Próximamente, estos arreglos tendrán un amplio potencial de incrementar la eficiencia de adquisición de datos, incrementando su aplicabilidad en el campo del estudio de los recursos naturales. El futuro del uso de este tipo de tecnologías parece apuntar a una mayor automatización en la captura de datos, mejoras en el rendimiento de los tiempos de vuelo y sistemas automatizados con algoritmos complejos capaces de ofrecer información en tiempo real.

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