Relationships among main soil properties and three N availability indices.

A biological (aerobic incubation for 3 and 6 weeks) and a chemical method [successive extractions with cold 0.1 (H1-N) and 0.5 M HCl (H2-N)] were applied to 21 soils to determine: a) the potentially mineralizable-N; b) the most useful soil variables for predicting soil N availability; and c) their usefulness for predicting N uptake by a greenhouse wheat crop. At t=3, both net N mineralized (NNM) and net N mineralization rate (NNMR) were correlated: a) positively with SOM- and CEC-related variables; and b) positively with soil δ 15N and negatively with soil pH, suggesting that Nmineralization, dominated by nitrification, is associated with NO3 --N losses and soil acidification. At t=6, all previously discussed variables were important for NNM, but not for NNMR, mainly controlled by the available-P content. The importance of H1-N increased with N2-inputs and decreased with NO3 - losses and soil-N. Relationships of H1-N and H2-N with soil CEC and texture showed the strong relations among nutrients content, biological activity and N mineralization, as well as the recalcitrance of clay-bounded SOM. Soil total-N correlations with wheat-N in absolute amount (positive) and as percentage of soil-N (negative) showed an important supply of available-N by N-rich soils, despite their slow N turnover. The best regression models for wheat-N always included 1-2 main available nutrients. The percentage of soil N exported to plant biomass was negatively correlated with noncrystalline Al compounds and soil δ 15N. Mineralized-N and wheat-N pools did not share many correlations with soil properties and seemed to come from different sources; consequently, the former pool, which only explained a quarter of wheat-N variance, was not more useful than soil total-N for predicting it. Only a positive correlation with soil total-N was shared by wheat-N and hydrolysable-N, highlighting that the latter N pools are mainly unrelated. Nevertheless, half of wheat-N variation was explained by its negative relationship with the percentage of soil-N as (H1+H2)-N; a possible explanation is that chemically labile N is also biologically labile, being cumulated because of a limiting factor for microbial N mineralization or plant growth and emerging as a good predictor for wheat-N uptake.Peer reviewe

Bioavailability of macro‐ and micro‐nutrients chemically extracted in acidic soils for wheat

[Background] Chemical methods allowing a single soil extraction followed by multi‐elemental simultaneous measurement by ICP‐OES are increasingly used to predict plant uptake; however, calibration results against crop response are scarce and contradictory.[Aims] Our aims were to evaluate the efficacy of five extractants to predict nutrient uptake by a greenhouse wheat crop, as well as the influence of soil properties on nutrient concentrations in soil extracts and wheat plants.[Methods] Unlike other calibration studies, we monitored the pre‐seeding to post‐harvesting changes in soil available Ca, K, Mg, Cu, Fe, Mn, Zn, and Al. We extracted 14 acidic soils (C content: 47–114 g kg−1) with two traditional (AA: ammonium acetate; DTPA: diethylenetriamine‐pentaacetic acid) and three multi‐element extractants (AB‐DTPA: ammonium bicarbonate‐DTPA; Mehlich‐3; AA‐DTPA: ammonium acetate‐DTPA).[Results] Relationships between bioavailable and chemically extractable elements were strong for K (R2 = 0.776 to R2 = 0.882; p < 0.001) and Zn (R2 = 0.663 to R2 = 0.721; p < 0.001), especially for AB‐DTPA and AA‐DTPA. Multiple regressions including also soil properties can predict wheat‐Ca (Feoxihydroxides, clay and CaAB‐DTPA; R2 = 0.656; p < 0.001) and wheat‐Cu [Aloxihydroxides and either CuAB‐DTPA (R2 = 0.515; p < 0.01) or CuAA‐DTPA (R2 = 0.472; p < 0.01)]. Pre‐seeding to post‐harvesting changes in KAA‐DTPA and KAB‐DTPA were strongly related with K uptake by wheat (R2 = 0.927 and R2 = 0.949, respectively; p < 0.001); similarly, for wheat‐Zn the best relationships were with ZnMehlich‐3 and ZnAA‐DTPA (R2 = 0.654 and R2 = 0.757, respectively; p < 0.001).[Conclusion] Consequently, chemical extractants alone can adequately predict K and Zn bio‐availability, and combined with some soil properties can predict wheat uptake of Ca and Cu, but not that of other nutrients.This research was supported by the Spanish Ministry of Education and Science through the project number AGL2005‐05726‐C02‐01. The participation of S. García‐Marco and A. Couto‐Vázquez in this research was supported by a postdoctoral and predoctoral CSIC I3P contracts, respectively.Peer reviewe

Soil N biochemical diversity and numerical taxonomy as tools in the pedogenetic study of a fossil profile

Distribution and diversity of the soil biochemical N fractions were studied in a fossil profile, a Podzol (IIA1 and IIBhs horizons) buried under a Cambisol (IA1 and IB horizons), to elucidate the genesis and evolution of the profile. The buried IIA1 horizon showed the lowest N biochemical diversity, which suggested a strong change in the pedogenetic conditions, probably not related to climate since another nearby Podzol was not affected. Soil numerical classification showed that the Cambisol is atypical, its two horizons being similar to the underlying podzolic IIBhs horizon in its physical and chemical characteristics. Based on biochemical N fractions, the IA1 and IB horizons were grouped with horizons from Cambisols and with podzolic horizons, respectively. The distribution of the organic N forms in the fossil Podzol was similar to that of a nearby recent Podzol in the Bhs horizon but not in the A1 horizon. The organic N of the fossil IIA1 horizon showed characteristics, such as extremely low content of α-amino acid N and high content of non-hydrolyzable N, similar to those of burned soils from the same region. Moreover, the presence of charcoal and the very low total N content in the IIA1 horizon suggest that a wildfire could have affected the A1 horizon of the original Podzol and the surrounding podzolic area, promoting soil erosion and thus the fossilization of the studied Podzol by podzolic colluvial sediments eroded from the upper part of the slope. The similarity of the biochemical N fractions distribution for the upper IA1 horizon with that of corresponding horizons from Cambisols suggests that currently pedogenetic processes are promoting the formation of a Cambisol in the podzolic sediments that fossilized the Podzol.Peer reviewe

A strategy to improve the detection of drug-induced hepatotoxicity Una estrategia para mejorar la detección de hepatotoxicidad por medicamentos

Aims: to report a new strategy for the detection of hepatotoxic adverse drug reactions (ADRs) in hospitalized patients improving the results obtained with other methods. Design: the model is based on the identification of a single alert signal in various target clinical departments over a 12-month period. Each patient was later interviewed following a set protocol. The main results analyzed were the drugs suspected of ADR; causal relationship between suspected drugs and ADRs; ADR severity, and incidence of hepatotoxic ADR/100,000 inhabitants. Subjects: population served by a university-affiliated urban teaching hospital (519,381 inhabitants). Results: The overall ratio of confirmed/suspected ADRs was high (35/80). The most commonly reported drug was amoxicillin-clavulanic acid (4 cases). With regard to causality, 2 suspected cases were classified as definite and 14 as probable. The distribution according to the severity of hepatotoxicity was 6 severe and 29 mild cases. The incidence of hepatotoxic ADRs/100,000 inhabitants as revealed by our method was much higher versus voluntary report (6.74 and 1.79, respectively). Conclusions: our method has proven effective for improving the detection of hepatotoxic ADRs, and may be extended to other types of adverse reactions.<br>Objetivos: comunicar una nueva estrategia para la detección de reacciones hepatotóxicas por medicamentos que mejora los resultados obtenidos con otros métodos utilizados. Diseño: el modelo se basa en la identificación de una señal de alerta simple en los pacientes de varios servicios diana, durante 12 meses. Cada paciente fue posteriormente entrevistado siguiendo un protocolo específico. Se analizaron: los fármacos sospechosos de producir hepatotoxicidad, la relación de causalidad entre el fármaco sospechoso y la hepatotoxicidad, la gravedad y la incidencia de hepatotoxicidad medicamentosa/100.000 habitantes. Pacientes: la población del área de influencia de nuestro hospital (519.381 habitantes). Resultados: se encontraron 80 sospechas de reacciones hepatotóxicas a medicamentos. La relación de reacciones confirmadas/sospechadas fue de 35/80. El fármaco imputado con mayor frecuencia fue amoxicilina/clavulánico (4 casos). En relación al grado de imputabilidad, 2 sospechas fueron calificadas como definitivas y 14 como probables. Según la gravedad, se encontraron 6 reacciones graves y 29 leves. La incidencia de reacciones hepatotóxicas por medicamentos/100.000 habitantes (6,74) fue mucho mayor que las obtenidas con otros métodos. Conclusiones: la aplicación de este método mejora la detección de reacciones hepatotóxicas por medicamentos y podría ser empleado en otros tipos de reacciones adversas

Successional dynamics of soil characteristics in a long fallow agricultural system of the high tropical Andes

To detect soil changes related to vegetation and fertility restoration in a long fallow agricultural system of the Venezuelan Andes, 32 soil (A horizon, 0–15 cm depth) and litter characteristics were studied in plots at different stages of the fallow-cultivation cycle. Four sectors of the valley were sampled, each one including seven plots: recently ploughed after a long fallow period; 1 and 2 years under potato crop; 1, 4–5 and 8 years in fallow and natural vegetation. Each sector had similar topography, parent material and exposure to reduce the spatial heterogeneity that can hinder the synchronic analysis of the succession. Data of each sector were standardized before the statistics comparisons. Although all soils were acidic, those involved in the cropping cycle, or with only 1 year of fallow, had a significantly lower pH than the others, indicating that soil cultivation triggered off acidifying processes intense enough to overcome the strong buffering indices of the soils. These acidifying processes, facilitated by the acidity generating ions that widely dominate the desaturated CEC, are surely due to the stimulation of litter and soil organic matter mineralization after ploughing the soil and also to the N fertilization of the cultivated soils. The high soil contents of exchangeable Al3+ and free Al oxides suggest that Al plays an important role in SOM stabilization, lowering its mineralization. No successional increase of any main plant nutrient was found in soil or litter. Moreover, soil available P and litter-P contents are higher during the cultivation phase and at the beginning of the succession, probably as a consequence of fertilization. Water holding capacity was similar for all soils, indicating that this long fallow agriculture system does not change the water storage capability of the soil, an important aspect for the role of the páramo in the regional water balance. The main characteristics of soils and litters, including their δ 13C values, were useless to monitor soil changes during cultivation and fallowing. Nevertheless, the δ 15N values of SOM decreased steadily along the crop-fallow chronosequence, while those of litterfall were rather constant from recently ploughed to 1 year fallow soils, decreasing suddenly on medium fallow plots and again on the virgin páramo. Together, the δ 15N values of soil- and litter-N grouped the soils following the crop-fallow chronosequence, suggesting that a change from ‘open’ to ‘closed’ N cycling is the characteristic that better discriminates the soils along the succession.This research was framed within the INCO-DC programme of the European Union through the contract number ERBIC18CT98-0263 and was also supported by CYTED (project XII.4). The isotopic ratio mass spectrometer was partly financed by the European Regional Development Fund (EU).Peer reviewe