Johann Fank

Determining water and nitrogen balances for beneficial management practices using lysimeters at Wagna test site (Austria)

The shallow Murtal aquifer south of Graz, Austria, provides easily withdrawable groundwater, which is supplied as drinking water without any chemical treatment. The aquifer is also used intensively by agriculture. Common agricultural management practices are the main source for diffuse nitrogen leaching and high groundwater nitrate concentrations. To safeguard the coexisting use of these two important resources, lysimeters are operated at the agricultural test site Wagna, Austria, and the influence of two beneficial management practices--low nitrogen input and organic farming--on nitrogen leaching towards groundwater is investigated. The technical lysimeter design as presented here consists of: (1) high-resolution weighing cells, (2) a suction controlled lower boundary condition for sucking off seepage water, thus emulating undisturbed field conditions, (3) comparative soil temperature, water content and matrix potential measurements inside and outside the lysimeter at different depths, (4) an installation of the lysimeters directly into test plots and (5) a removable upper lysimeter ring enabling machinery soil tillage. Our results indicate that oasis effects or fringe effects of the lysimeter cylinder on unsaturated water flow did not occur. Another lysimeter cultivated with lawn is operated for observing grass-reference evapotranspiration, which resulted in good agreement with calculated grass-reference evapotranspiration according to the FAO-Penman-Monteith method. We conclude that lysimeters installed at Wagna test site did not show any fringe effects and, thus, are appropriate tools for measuring water balance elements and nitrogen leaching of arable and grass land at point scale. Furthermore, our results for the period of 2005 to 2011 show that beneficial management practices reduced nitrate leaching and, hence, may allow for a sustainable coexistence of drinking water supply and agriculture in the Murtal aquifer.

Performance assessment of nitrate leaching models for highly vulnerable soils used in low-input farming based on lysimeter data

The agricultural sector faces the challenge of ensuring food security without an excessive burden on the environment. Simulation models provide excellent instruments for researchers to gain more insight into relevant processes and best agricultural practices and provide tools for planners for decision making support. The extent to which models are capable of reliable extrapolation and prediction is important for exploring new farming systems or assessing the impacts of future land and climate changes. A performance assessment was conducted by testing six detailed state-of-the-art models for simulation of nitrate leaching (ARMOSA, COUPMODEL, DAISY, EPIC, SIMWASER/STOTRASIM, SWAP/ANIMO) for lysimeter data of the Wagna experimental field station in Eastern Austria, where the soil is highly vulnerable to nitrate leaching. Three consecutive phases were distinguished to gain insight in the predictive power of the models: 1) a blind test for 2005-2008 in which only soil hydraulic characteristics, meteorological data and information about the agricultural management were accessible; 2) a calibration for the same period in which essential information on field observations was additionally available to the modellers; and 3) a validation for 2009-2011 with the corresponding type of data available as for the blind test. A set of statistical metrics (mean absolute error, root mean squared error, index of agreement, model efficiency, root relative squared error, Pearsons linear correlation coefficient) was applied for testing the results and comparing the models. None of the models performed good for all of the statistical metrics. Models designed for nitrate leaching in high-input farming systems had difficulties in accurately predicting leaching in low-input farming systems that are strongly influenced by the retention of nitrogen in catch crops and nitrogen fixation by legumes. An accurate calibration does not guarantee a good predictive power of the model. Nevertheless all models were able to identify years and crops with high- and low-leaching rates.

Modeling coupled unsaturated and saturated nitrate distribution of the aquifer Westliches Leibnitzer Feld, Austria

The aquifer Westliches Leibnitzer Feld, Austria, is a significant resource for regional and supraregional drinking water supply for more than 100,000 inhabitants, but the region also provides excellent agricultural conditions. This dual use implicates conflicts (e.g., non-point source groundwater pollution by nitrogen leaching), which have to be harmonized for a sustainable coexistence. At the aquifer scale, numerical models are state-of-the-art tools to simulate the behavior of groundwater quantity and quality and serve as decision support system for implementing groundwater protecting measures. While fully and iteratively coupled simulation models consider feedback between the saturated and unsaturated zone, sandy soil conditions and groundwater depths beneath the root zone allow the use of a unidirectional sequential coupling of the unsaturated water flow and nitrate transport model SIMWASER/STOTRASIM with FEFLOW for the investigation area. Considering separated inputs of water and nitrogen into groundwater out of surface water bodies, agricultural, residential and forested areas, first simulation results match observed groundwater tables, but underestimate nitrate concentrations in general. Thus, multiple scenarios assuming higher nitrogen inputs at the surface are simulated to converge with measured nitrate concentrations. Preliminary results indicate that N-input into the groundwater is strongly dominated by contributions of agricultural land.

Emerging Measurement Methods for Soil Hydrological Studies

Monitoring and protecting the natural resources of soil and water, and their ecosystems, is intended to ensure the long-term conservation of their functions. To understand the reasons for resource degradation or ecosystem alterations and interactions, knowledge is required of processes and parameters on different scales of landscapes. Soil hydrological studies are an essential part of ecosystem and landscape research. The aim of our study was to develop new research methods and technical equipment to understand and monitor soil hydrological processes. The investigations were carried out on different scales, starting with laboratory and lysimeter measurements, followed by investigations in the field. To measure soil hydrological properties, we developed the Extended Evaporation Method (EEM) and the HYPROP device. In this chapter we report on some innovations in this field. Using new cavitation tensiometers and applying the air-entry pressure of the tensiometer’s porous ceramic cup as the final tension value allowed us to quantify both hydraulic functions close to the wilting point. Additionally, both soil shrinkage dynamics and soil water hysteresis can now be quantified easily and reliably. The experimental setup followed the HYPROP system, which is a commercial device with vertically aligned tensiometers that is optimized to perform evaporation measurements. Depending on the soil and the evaporation rate, the measurement time varied between 2 and at most 10 days. The simultaneous measurement of multiple soil samples was possible with only one balance. Pedotransfer functions (PDFs) were created on the basis of various measured soil water retention and hydraulic conductivity functions. In the next step, a method for quantifying deep seepage and solute leaching under field conditions was developed, tested and applied at more than 40 soil hydrological field plots in Germany. The method is based on tension and soil water content measurements down to a depth of 3 m at arable and grassland sites and a depth of 5 m at forest sites. These data were used to construct a field water retention curve. This pF curve was fitted, the relative hydraulic conductivity function K(θ) was derived and relative deep seepage rates were calculated based on DARCY’s law. To obtain reliable discharge rates, the K function was matched to the water balance. Lysimeter experiments confirmed the validity and reliability of this soil hydrological field method. It works like a virtual lysimeter on sandy to loamy soils which have a deep water table and a zero flux plane above the measurement depth The EEM and the soil hydrological field method have the potential to improve soil hydrological studies, and water and solute transport monitoring systems could be installed in Eurasia.