Jesús D. Gómez

Summary Biochar ( BC ) amendment to soils is a proposed strategy to improve soil fertility and mitigate climate change. However, before this can become a recommended management practice, a better understanding of the impacts of BC on the soil biota is needed. We determined the effect of addition rates (0, 1, 5, 10 and 20% by mass) of a fast‐pyrolysis wood‐derived BC on the extraction efficiency ( EE ), abundance and temporal dynamics of phospholipid fatty acids ( PLFAs , microbial community biomarkers) in four temperate soils during a 1‐year incubation. Additionally, the effects on microbial mineralization/incorporation of BC‐C were determined by measuring CO 2 efflux and the BC contribution to CO 2 and PLFA‐C using the natural 13 C abundance difference between BC and soils. Biochar addition proportionally increased microbial abundance in all soils and altered the community composition, particularly at the greatest addition rate, towards a more gram‐negative bacteria‐dominated (relative to fungi and gram‐positive) community. Though chemically recalcitrant, the BC served as a substrate for microbial activity, more so at large addition rates and in soil with little organic matter. Microbial utilization of BC‐C for growth could only partially explain the observed increase in microbial biomass, suggesting that other, potentially abiotic, mechanisms were involved. The strong decrease in PLFA EE (−77%) in all soils with biochar addition emphasizes the need to measure and correct for EE when using PLFA biomarkers to estimate soil microbial responses to BC additions. Overall, our study provides support for BC use as a soil amendment that potentially stimulates microbial activity and growth.

Spatial interpolation, temperature modeling, terrain analysis, lapse rate, geographic information systems

The purpose of this study was to analyze the influence of wind erosion on the productivity of citric crops over gypsiric Fluvisols in Gador area (Almeria, SE Spain) by blowing air through a wind tunnel. Wind erosion varies considerably depending on time since the last tillage. This is because a physical crust forms after tilling which protects the soil from wind. Crust formation in the study area is strongly favored by dew, which causes them to form in around a week. The repeated measurements ANOVA, as a nonparametric alternative to the ANOVA, using the Geiiser method and the Friedman test shows significant differences (P ≤ 0.05) in the fractions of very fine sand and coarse silt, which confirmed that very fine sand and coarse silt are the fractions most susceptible to loss from wind. The same statistical analysis for fertility showed smaller differences in organic carbon and K2O content, while N and P2O5 increased. Nutrients lost from wind imply an additional fertilization cost for a crop to be economically feasible. The cost of this restoration of nutrients lost from the soil because of wind erosion was based on experimental data taken in crusted soil and immediately after tilling. Losses in organic matter (O.M.), N, P2O5 and K2O were estimated based on the cost of fertilizers most commonly used in the area.

Se estudió la distribución de la biomasa de raíces finas, medias y gruesas, la concentración carbono orgánico del suelo (COS), la densidad aparente (Da), los almacenes de COS, en los primeros 90 cm de profundidad en tres bosques con predominio de encino (Quercus sp.) ubicados en la zona centro de México (Morelos). La edad estimada de los árboles de los tres bosques fue (a) ≈ 40 años o maduro, ≈ 20 años o medio y ≈ 10 años o joven. En general, la concentración de COS y los almacenes de COS decrecieron a medida que lo hacía la profundidad del suelo, en tanto que la Da aumentaba. Más de la mitad del COS almacenado se encontró en los primeros 30 cm del perfil. La biomasa de raíces finas presentó un patrón de disminución exponencial con la profundidad, mientras que la biomasa de las raíces medias y gruesas tuvo un patrón irregular, pero siempre con tendencia a disminuir a medida que lo hacía la profundidad. En los bosques de las tres edades indicadas, la biomasa de raíces finas, medias y gruesas presentó mayor correlación con la Da que con los almacenes de carbono orgánico del suelo. Los coeficientes de ajustes (R2) de los modelos de regresión lineal que relacionan Da con el contenido de COS se ubicaron entre 0.61 y 0.72.

The estimation of biomass in seasonally tropical dry forests requires basic information that for some species is scarce. To help solve this deficit, we generated allometric equations for five species of tropical dry forest (TDF). Equations for each tree species studied, for two groups of species, and all species together are reported. The equations were of the power type, based on diameter at breast height (dbh). The allometric model of each species included was fitted resulting in high values of the coefficient of determination using only the vari­able dbh. The allometric equations for each of the five forest species differed from each other (p < 0.05). Species grouped according to similar specific wood density showed a better fit of the model (p < 0.05), particularly those with high values for this parameter, than when considering only one species. The biomass of all species was predicted correctly by using only the measures of the basal area. However, the coefficient of determination increased, and the estimated error decreased, when the specific wood density was added to the model. Finally, the best fit of the model is attained by adding the tree height to the equation. The last two characteristics, however, were not significant when determining the individual models for each species.