R. Schulin

Estimating unsaturated soil hydraulic parameters using ant colony optimization

Abstract Although models are now routinely used for addressing environmental problems, both in research and management applications, the problem of obtaining the required parameters remains a major challenge. An attractive procedure for obtaining model parameters in recent years has been through inverse modeling. This approach involves obtaining easily measurable variables (model output), and using this information to estimate a set of unknown model parameters. Inverse procedures usually require optimization of an objective function. In this study we emulate the behavior of a colony of ants to achieve this optimization. The method uses the fact that ants are capable of finding the shortest path from a food source to their nest by depositing a trail of pheromone during their walk. Results obtained with the ant colony parameter optimization method are very promising; in eight different applications we were able to estimate the `true parameters to within a few percent. One such study is reported in this paper plus an application to estimating hydraulic parameters in a lysimeter experiment. Despite the encouraging results obtained thus far, further improvements could still be made in the parameterization of the ant colony optimization for application to estimation of unsaturated flow and transport parameters.

Simulating unsaturated flow and transport in a macroporous soil to tile drains subject to an entrance head: model development and preliminary evaluation

Abstract Accurate prediction of water flow and chemical transport in agricultural soil profiles requires the use of a simulation model that considers the most important physical, hydrological and chemical processes. Two important flow-related processes in tile-drained field systems are macropore flow and water discharge from the tile drains. To better account for these two processes, we extended an existing two-dimensional model (SWMS_2D) by adding a macropore flow component as well as a Hooghoudt type boundary condition that considers the presence of an entrance head at the tile drain. The macropore component is necessary to account for water and solutes short-circuiting the soil matrix, while the drainage entrance head is needed to account for the contraction of streamlines around the drains, a feature that causes delayed discharge. The applicability of the new model to a landfill problem was examined. The simulation results, which included water flow and solute transport, compared well with other models.

Solubilization and Plant Uptake of Zinc and Cadmium from Soils Treated with Elemental Sulfur

ABSTRACT In growth chamber experiments we studied the potential use of elemental sulfur (S8) as an acidifying agent to enhance the uptake of Cd and Zn from three different polluted soils by candidate phytoremediation plants (Brassica juncea, Helianthus annuus, Salix viminalis). Two of the three soils were calcareous, the other slightly acidic. One of the calcareous soils had been contaminated by dust emissions from a nearby brass smelter. The pollution of the other two soils had resulted from sewage sludge applications. Sulfur was added to soils in quantities of 20 to 400 mmol sulfur kg-1 soil. Plants were grown under fluorescent light in 1.5 l (

Modelling regional-scale mass balances of phosphorus, cadmium and zinc fluxes on arable and dairy farms

OS 13 cm) pots for 28 d. Within 700 h soil pH decreased significantly in all soils, depending on S8 dosage. In the acid soil, pH decreased from pH 6.5 to about 4 at the highest treatment level, while pH in one of the calcareous soils dropped even below pH 4. The effect was smaller in the second calcareous soil. NaNO3-extractable Cd and Zn increased up to 26-and 13-fold, respectively, in the acid soil, while in the calcareous soils, maximum increases were 9-and 11-fold, respectively. Increased NaNO3-extractable concentrations translated well into shoot concentrations (dry matter) in plants. Shoot Zn concentrations in H. annuus, for example, increased from 930 in the controls to 4300 mg kg-1 in the highest S8 treatment. However, effects observed in the plants were generally smaller than in the soils. In addition, in some variants growth was negatively affected, resulting in reduced metal removal from the soils.

Modelling heavy metal and phosphorus balances for farming systems

Abstract Accumulation of heavy metals in agricultural soils may cause serious problems for soil quality, groundwater and food chains. Based on the databases of the Swiss agricultural statistics and on data from experimental farms, we modelled regional-scale mass balances of phosphorus (P), cadmium (Cd) and zinc (Zn) and their uncertainties for a large number of arable and dairy farms in the northwest of Switzerland using the model PROTERRA-S. Large differences in P fertilization characteristics between these farm types were found. Crop demand for P on arable farms were primarily met through additions of inorganic fertilizers and sewage sludge, while on dairy farms the largest P input was provided by animal manure. Average model calculations predicted an enrichment between 0.8 and 1.9 g ha −1 per year for Cd and between 76 and 525 g ha −1 per year for Zn for soils of arable and dairy farms, respectively. Hence, according to our analyses, current agricultural land use is not sustainable in terms of soil quality standards. Predicted accumulation of Cd in soil was larger for arable crops than for grassland, while the opposite was true for Zn. Analyzing scenarios of changes in P fertilization management showed that Cd and Zn enrichment in soil was more sensitive to decreasing net P inputs to arable farms than to dairy farms. When uncertainty of input data was taken into account, large variances of the calculated accumulation rates were found. Coefficient of variation of the net fluxes ranged between 56 and 162% for Cd, and between 46 and 82% for Zn, and distribution functions of the net fluxes indicated that in some soils, particularly under grassland, also a depletion of Zn and Cd may occur. Hypothetical steady-state soil concentrations of Cd were estimated to exceed average soil threshold concentration on arable farms, while steady-state Zn concentrations in soils of dairy farms were on average below the corresponding threshold value. However, if the uncertainty of these Zn estimates was considered, a significant part of the distribution exceeded the threshold value. The results of our study demonstrate that information on variation in element balances is beneficial. Average flux balances alone do not provide sufficient information for an adequate assessment of sustainable land use.

Agricultural zinc fluxes into soils and crops of central Iran at regional scale

Accounting for agricultural activities such as P fertilization in regional models of heavy metal accumulation provides suitable sustainable management strategies to reduce nutrient surpluses and metal inputs in agricultural soils. Using the balance model PROTERRA-S, we assessed the phosphorus (P), cadmium (Cd) and zinc (Zn) flux balances in agricultural soils of a rural region in Switzerland for different farm types and crop types. The P requirements of crops on arable farms were mainly supplied by commercial fertilizers and sewage sludge, while on animal husbandry farms P fertilizer demands were met by animal manure alone. Metal accumulation in soil was very different between the balance units. Estimated net Cd fluxes ranged between 1.0 and 2.3 g ha−1 yr−1 for arable farm types, 0.6 and 2.0 g ha−1 yr−1 for dairy and mixed farm types, and 9.1 and 17.8 g ha−1 yr−1 for animal husbandry farm types. Largest net Zn fluxes of 17.9–39.8 kg ha−1 yr−1 were estimated for animal husbandry farms, whereas for arable farm types net Zn fluxes of 101–260 g ha−1 yr−1 and for dairy and mixed farm types of 349–3360 g ha−1 yr−1 were found. The results indicate that P management is a primary factor determining the variation of these net Cd and net Zn fluxes. The latter were highly sensitive to the Zn/P concentration ratio in animal manure, atmospheric deposition and crop concentrations. Variation of net Cd fluxes resulted mainly from uncertainty in crop concentrations, atmospheric deposition, leaching parameters and uncertainty in Cd/P concentration ratio of commercial fertilizers. In addition, element balances were sensitive to empirical assumptions on fertilization strategy of farmers, such as the partitioning of manure between balance units.

A stochastic empirical model for regional heavy-metal balances in agroecosystems.

Mass flux assessment can provide information that is essential for a sustainable management of elements in agricultural soils. In this article, we present an assessment of regional-scale averages of zinc (Zn) fluxes into agricultural soils and crops of central Iran for the period 1997–2011, using available databases such as regional agricultural statistics. The basic units of the balances were 15 townships of the provinces Qom, Isfahan and Fars. Averaged over the entire study region, the net Zn input into arable soil resulting from all fertilizer inputs – Zn removal with harvested crops was 1515 g ha−1 yr−1 across the entire region, with a range of 438–3009 g ha−1 yr−1 among townships. Estimated average Zn inputs with manure, mineral fertilizers, sewage sludge and compost were 1254, 531, 19 and 7 g ha−1 yr−1, respectively. The input-to-output ratio of these fluxes ranged from 1.8 to 12.9 among townships and averaged 6.1 for the entire study area. Considering that outputs other than with crop harvests are minor, Zn stocks are rapidly building up in the soils of the study region. Uncertainties in the manure and crop removal data were the main sources of estimation uncertainty in this study.