Literatura académica sobre el tema "Artificially wetted soil"

This paper focuses on the tensile strength (Q) and porosity of Dystric Cambisol cylinders with and without biochars (0.1% or 5% dose) obtained from wood waste (BC1) and sunflower husks (BC2). The experiments were performed on air-dried and wetted artificial aggregates remolded from unfractionated soil and its selected fractions (1–0.25, 0.25–0.1, 0.1–0.05, and <0.05 mm). The obtained results indicated that the biochar addition reduced the tensile strength of all examined samples, regardless of the type of biomass used in pyrolysis. This effect was more significant with the larger biochar dose of 5%. When cylinders formed from a wetted 1–0.25 mm fraction with 5% BC2, the Q reduction equaled as much as 0.048 MPa. The noted decrease in tensile strength was mainly associated with the formation of macropores in the cylinders (of maximum radii: 4.77 µm BC1 and 5.78 μm BC2). The highest tensile strength was observed in the air-dried samples formed from the largest silica-rich fraction (1–0.25 mm) without biochar (0.078 MPa for the air-dried cylinders and 0.066 MPa for the wetted ones). The higher Q parameter for the air-dried remolded soil aggregates was probably related to the dehydration of soil gels and the thermal transformation of iron and alumina oxides during drying.

Soil solutions were extracted by immiscible liquid displacement with trichlorotrifluoroethane and by centrifuge drainage from surface and subsoil samples having a wide range of chemical and physical properties. Extractions were performed on field-moist samples and on air-dry samples which were re-wetted to different matric suctions and for different lengths of time. The composition of the soil solution obtained was the same with both methods of extraction when samples had been pre-wet to a matric suction of 0-1 bar. Immiscible liquid displacement extracted solution from a krasnozem surface soil at suctions as great as 15 bar; in contrast, centrifuge drainage failed to extract solution from this soil at >3 bar. The concentration of ions in solutions extracted by displacement from soils with increasing matric suction rose to a far greater extent than that anticipated if concentration was the only mechanism operating. In re-wet air-dry samples, major cations and anions were at equilibrium levels in solution after incubation for 1 day; longer incubation times resulted in an artificial elevation of ionic strength through mineralization of organic matter in some surface samples. The levels achieved after 1 day were similar to those present in solutions extracted from field-moist samples.

As plant roots take up water and the soil dries, water depletion is expected to occur in the rhizosphere. However, recent experiments showed that the rhizosphere was wetter than the bulk soil during root water uptake. We hypothesise that the increased water content in the rhizosphere was caused by mucilage exuded by roots. It is probably that the higher water content in the rhizosphere results in higher hydraulic conductivity of the root–soil interface. In this case, mucilage exudation would favour the uptake of water in dry soils. To test this hypothesis, we covered a suction cup, referred to as an artificial root, with mucilage. We placed it in soil with a water content of 0.03 cm3 cm–3, and used the root pressure probe technique to measure the hydraulic conductivity of the root–soil continuum. The results were compared with measurements with roots not covered with mucilage. The root pressure relaxation curves were fitted with a model of root water uptake including rhizosphere dynamics. The results demonstrated that when mucilage is added to the root surface, it keeps the soil near the roots wet and hydraulically well conductive, facilitating the water flow from dry soils towards the root surface. Mucilage exudation seems to be an optimal plant trait that favours the capture of water when water is scarce.

Abstract. Chemical and meteorological parameters measured on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 Atmospheric Research Aircraft during the African Monsoon Multidisciplinary Analysis (AMMA) campaign are presented to show the impact of NOx emissions from recently wetted soils in West Africa. NO emissions from soils have been previously observed in many geographical areas with different types of soil/vegetation cover during small scale studies and have been inferred at large scales from satellite measurements of NOx. This study is the first dedicated to showing the emissions of NOx at an intermediate scale between local surface sites and continental satellite measurements. The measurements reveal pronounced mesoscale variations in NOx concentrations closely linked to spatial patterns of antecedent rainfall. Fluxes required to maintain the NOx concentrations observed by the BAe-146 in a number of cases studies and for a range of assumed OH concentrations (1×106 to 1×107 molecules cm−3) are calculated to be in the range 8.4 to 36.1 ng N m−2 s−1. These values are comparable to the range of fluxes from 0.5 to 28 ng N m−2 s−1 reported from small scale field studies in a variety of non-nutrient rich tropical and sub-tropical locations reported in the review of Davidson and Kingerlee (1997). The fluxes calculated in the present study have been scaled up to cover the area of the Sahel bounded by 10 to 20 N and 10 E to 20 W giving an estimated emission of 0.03 to 0.30 Tg N from this area for July and August 2006. The observed chemical data also suggest that the NOx emitted from soils is taking part in ozone formation as ozone concentrations exhibit similar fine scale structure to the NOx, with enhancements over the wet soils. Such variability can not be explained on the basis of transport from other areas. Delon et al. (2008) is a companion paper to this one which models the impact of soil NOx emissions on the NOx and ozone concentration over West Africa during AMMA. It employs an artificial neural network to define the emissions of NOx from soils, integrated into a coupled chemistry-dynamics model. The results are compared to the observed data presented in this paper. Here we compare fluxes deduced from the observed data with the model-derived values from Delon et al. (2008).