Abstract: The effect of physical-chemical slurry treatment on the mobility and transformation of nitrogen and organic matter from pig slurry after soil application is evaluated. Two different pig slurries (one treated by stripping with air at pH=9 and another non-treated) were applied at the top of a soil column, containing approximately 100 kg of soil. Effluents were monitored measuring concentration values of ammonia, nitrites, nitrates and total organic carbon (TOC). The breakthrough curves were modelled using STANMOD and HYDRUS 1D codes. Low concentrations of ammonia were detected in the effluent recovered at the bottom of the soil profile for both types of slurry. Nitrate concentration in effluent was lower and more homogenous over time when applying stripping treated pig slurry. In N modelling, adsorption of ammonia by soil proved an important process, nitrite and nitrate adsorption being less significant, although not negligible. Transformation from ammonia to nitrite controls the kinetics of the nitrification process. Total organic carbon in the column effluent was higher in the experiment using treated pig slurry, which can be attributed to organic matter solubilisation in the stripping treatment process.
Abstract: Arsenic accumulation in vegetables for direct human consumption represents a concern for food safety purposes. This potential problem can be of economic importance particularly in much appreciated, high-quality horticultural products. In this work, a greenhouse set of experiments were conducted to evaluate possible phytotoxic effects and arsenic accumulation in the production of curly endives with arsenic contaminated water.Two concentration levels (0.5 mg/L and 1.0 mg/L) and two arsenic species (As+3 and As+5) were considered. Dry mass production tended to be reduced as As+3 concentration increased in irrigation water. However, As+5 treatments did not show significant dry mass production differences with a blank (control experiment). As accumulation in plant increased with As concentration in irrigation waters, following a linear trend. Nevertheless, the increase of accumulated As was not statistically significant for As+5 at 0.5 mg/L. Calculated biological absorption coefficients resulted in higher than previous values reported in the literature, which was attributed here to the source of arsenic (irrigation water). Considering field values for As+5/As+3 ratio and averaged concentrations in water, the obtained results support that there is not a short-or medium-term risk to food safety in the curly endive crop in the region of Castilla y León (Spain).
Abstract: The rate of volatilisation of the formulated herbicide triallate was investigated in a wind tunnel under controlled wind-speed conditions. An experimental set-up is described which allows the monitoring of wind speed (w.s.), soil-water content, and the temperature of air and soil. A system controlling soil-water content is also described. The influence of air velocity and soil texture was investigated measuring the cumulative volatilisation losses of triallate from soil. The herbicide volatilisation losses after application ranged from 40% at 3 m/s to 53% at 9 m/s for loam soil and from 60% at 3 m/s to 73% at 9 m/s for sandy soil.
Abstract: The sorption at 25 °C of the acidic herbicides tribenuron-methyl, chlorsulfuron, and imazamethabenz-methyl on three soils (clay content percentages ranging from 7.2 to 54.6, pH values ranging from 6.5 to 7.6, and organic matter percentages <1.5) was studied. Only imazamethabenz-methyl presented significant sorption in these soils. Sorption isotherms of imazamethabenz-methyl were well correlated to the Freundlich model, although linearity can be reasonably assumed. Desorption studies of this herbicide presented remarkable hysteresis and nonlinearity. Chlorsulfuron sorption was low, and tribenuron-methyl presented negligible or negative adsorption. The effect of the soil/solution ratio employed in batch experiments on the estimated distribution coefficient of the three herbicides was also investigated. By changing the soil/solution ratio from 1:3 to 1:1, an increase in the distribution coefficient of imazamethabenz-methyl and chlorsulfuron was observed. On the other hand, the distribution coefficient of tribenuron-methyl decreased within the same range of soil/solution ratios. Results indicate that these herbicides, but especially chlorsulfuron and tribenuron-methyl, could be mobile in the soils studied. The effect of the soil/solution ratio or hysteresis in desorption seems to be more important than the isotherm nonlinearity in modeling the transport of these hebicides in soil.
Abstract: We developed a computationally efficient model for estimating the transient soil temperature distributions resulting from a heat source at a fixed depth beneath a greenhouse. The model was developed for use as a submodel of the air-soil systems in greenhouses where the soil is used as a heat storage medium, with a network of buried pipes acting as a heat exchanger. The model assumes soil thermal properties are spatially and temporally constant and that energy transfer between the greenhouse and soil is primarily a result of net radiation and sensible heat transfer. First-order energy transfer terms are also used to account for lateral energy exchanges with the surrounding soil and the heat source is included as a plane at a fixed depth. This was achieved by obtaining a Green's function solution in the Laplace domain and performing a numerical inversion with a fast Fourier-transform algorithm, which requires very little computational time. Model parameters are optimized using a Simplex algorithm during a 3-d simulation to show the ability of the method to describe the greenhouse soil temperature. This method provides a reasonable description of the heat flux under these conditions.
