Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

Background and aims: Alternate wetting and drying (AWD) saves water in paddy rice production but could influence soil physical conditions and root growth. This study investigated the interaction between contrasting rice genotypes, soil structure and mechanical impedance influenced by hydraulic stresses typical of AWD. Methods: Contrasting rice genotypes, IR64 and deeper- rooting Black Gora were grown in various soil conditions for 2 weeks. For the AWD treatments the soil was either maintained in a puddled state, equilibrated to −5 kPa (WET), or dried to −50 kPa and then rewetted at thewater potential of −5 kPa (DRY-WET). There was an additional manipulated macropore structure treatment, i.e. the soil was broken into aggregates, packed into cores and equilibrated to −5 kPa (REPACKED). A flooded treatment (puddled soil remained flooded until harvest) was set as a control (FLOODED). Soil bulk density, penetration resistance and X-ray Computed Tomography (CT) derived macropore structure were measured. Total root length, root surface area, root volume, average diameter, and tip number were determined by WinRhizo. Results: AWD induced formation of macropores and slightly increased soil mechanical impedance. The total root length of the AWD and REPACKED treatments were 1.7–2.2 and 3.5–4.2 times greater than that of the FLOODED treatment. There was no significant difference between WET and DRY-WET treatments. The differences between genotypes were minimal. Conclusions: AWD influenced soil physical properties and some root characteristics of rice seedlings, but drying soil initially to −50 kPa versus −5 kPa had no impact. Macropores formed intentionally from repacking caused a large change in root characteristics

Control biológico de la exposición laboral a citostáticos en personal sanitario: Ensayo de mutagenicidad urinaria

El objetivo del estudio ha sido la evaluación de la exposición ocupacional a citostáticos de 13 individuos del servicio de farmacia y oncología de un hospital mediante un ensayo de control biológico. Como grupo control del estudio participaron once trabajadores del área administrativa del mismo hospital. En el grupo expuesto se diferenció entre exposición directa, producida por la preparación y/o administración de estas sustancias, y exposición indirecta, derivada del aseo de enfermos, obtención de muestras biológicas en pacientes de quimioterapia y la manipulación de residuos. En este último caso, la posible exposición se puede producir tanto con la propia sustancia, como con sus correspondiente metabolitos. Se obtuvieron muestras de orina de 24 horas tras tres días consecutivos de trabajo, que se analizaron mediante el ensayo de mutagenicidad urinaria test de Ames con las cepas TA98 y TA100 de Salmonella typhimurium sin y con activación metabólica S9. No se han obtenido diferencias significativas en la actividad mutagénica en orina de la población expuesta comparada con la población control. Este mismo resultado se ha obtenido al comparar los dos grupos de exposición, directa e indirecta. Únicamente se ha detectado excreción de mutágenos en la orina de los individuos fumadores con la cepa TA98 activación metabólica. En un 20% del total de la población estudiada no se han obtenido resultados al provocar su orina toxicidad para Salmonella typhimurium

An automated disc infiltrometer for infiltration rate measurements using a microflowmeter

This work presents a new design of disc infiltrometer, which, associated with a microflowmeter (MF) and a solenoid valve set, makes it possible to automate the infiltration rate (Q) measurements at different soil pressure heads ( ). The MF consists of a 13Ð8-cm long and 1Ð5 mm i.d. pipe, with a pressure transducer connecting the two ends of the MF, inserted in a water-flow pipe that connects the Mariotte tube and the water-supply reservoir of the disc infiltrometer. Water flow is calculated from the head losses in the MF. Changes in ψ in the bubble tower, automatically affected when the infiltration rate reaches steady state, are controlled by a datalogger connected to four solenoid valves. The new design was tested in laboratory and field conditions, and the results showed that the MF allows the soil water infiltration rates to be correctly estimated for different soil characteristics. The solenoid valve set plus datalogger system satisfactorily monitored the changes in and allowed the measurement time to be optimized

Root Growth of Barley as Affected by Tillage Systems and Nitrogen Fertilization in a Semiarid Mediterranean Agroecosystem

6 Pag., 2 Tabl, 6 Fig.Conservation tillage systems are being widely adopted in the Mediterranean region. A long-term field experiment was established in 1996 comparing three N fertilization levels (zero, 0 kg ha−1; medium, 60 kg ha−1; and high, 120 kg ha−1), under three tillage systems (conventional tillage, CT; minimum tillage, MT; and no-tillage, NT) in a semiarid Mediterranean agroecosystem annually cropped with winter barley (Hordeum vulgare, L., cultivar Hispanic), to study the response of root growth. During four consecutive growing seasons, from 2005 to 2009, root length density (RLD) and soil water content were evaluated. Penetration resistance (PR) and soil bulk density were only evaluated in the fourth and last year of this experiment. In dry years, root growth was similar under NT and MT systems but highly reduced under CT due to reduced water availability, which, in the surface 25 cm of soil was 7% and 18% lower than under MT and NT systems, respectively. However, in a wet year (i.e., 2009), RLD was double under CT than under NT due to reduced soil strength. PR at 5 to 15 cm soil depth under NT was 1MPa greater than under MT or CT. Root growth was not affected by N fertilization, in contrast to the response of grain yield that showed a significant interaction between N fertilization and tillage system. In spite of moderate soil compaction, which may reduce root growth in wet years, long-term NT adoption does not reduce grain yields for monoculture of barley under semiarid Mediterranean conditions.This work was supported with by the Comision Interministerial de Ciencia y Tecnologia of Spain (Grants AGL 2004-07763-C02-02 and AGL2007-66320-CO2-02/AGR). The doctoral studies of F.J. Morell were funded by the Spanish Ministry of Science and Innovation.Peer reviewe

Densidade crítica ao crescimento de plantas considerando água disponível e resistência à penetração de um Argissolo Vermelho distrófico arênico Bulk density critical to the growth of plants considering available water and soil resistance to penetration of a Paleudalf

O estabelecimento de culturas está associado a condições restritivas impostas pelo tipo e pelo manejo de solo. O objetivo deste estudo foi avaliar o intervalo de densidade crítica de um Argissolo Vermelho distrófico arênico, considerando a disponibilidade de água para as culturas e os valores restritivos de resistência à penetração (1,5; 2,0; 2,5; 3,0 e 3,5MPa). A amostragem de um Argissolo Vermelho distrófico arênico sob plantio direto desde 1989, com estrutura de solo preservada, foi feita nas camadas de 0,00 a 0,10 m e 0,10 a 0,20m. As amostras (oito repetições) foram saturadas em água, equilibradas em diferentes potenciais (-0,001; -0,004; -0,006; -0,033; -0,07 e -0,1MPa) e dois grupos de amostras foram secadas em laboratório, por um período de 7 e 9 dias, perfazendo um total de 128 amostras. Após atingir o equilíbrio, foi avaliada a resistência à penetração e a densidade do solo. Um incremento na resistência à penetração possibilitou maiores intervalos de densidade adequados ao desenvolvimento das plantas, i.e., quando considerada uma resistência à penetração de 2MPa, o intervalo de densidade adequado foi de 1,44Mg m-3 a 1,76Mg m-3 e, para uma resistência de 3MPa, o intervalo foi de 1,53 a 1,88Mg m-3. Valores superiores e inferiores ao intervalo de densidade obtidos são críticos ao desenvolvimento de culturas, considerando a resistência à penetração e a disponibilidade de água.<br>Crop establishment is linked to restrictive conditions imposed by soil type and soil management. This study aimed at evaluating the interval of bulk density critical for a Paleudalf, considering water availability to the crops and restrictive values to the root resistance to penetration (1.5; 2.0; 2.5; 3.0 e 3.5MPa). Soil samples, from a Paleudalf under no-tillage since 1989, with preserved structure were collected in the layers of 0.00 to 0.10m and 0.10 to 0.20m depth. The samples (eight replicates) were saturated in water and balanced different potentials (- 0.001; -0.004; -0.006; -0.033; -0.07 and -0.1MPa), plus 2 groups of soil samples were dried in the laboratory for a period of 7 and 9 days, being a total of 128 samples used in this study. After reaching the balance, the soil resistance to penetration and bulk density were evaluated. An increase in the resistance to penetration allows for large intervals of bulk density no restrictive to the plant development. For instance, when considered a resistance to penetration of 2MPa, the adequate interval of bulk density was 1.44Mg m-3 to 1.76Mg m-3, and for a resistance to penetration of 3MPa the interval was 1.53 to 1.88Mg m-3. Bulk density smaller or larger than interval obtained are critical to the development of plants, considering soil resistance to penetration and water availability