The appearance of online map services and frameworks (e.g., KML, QGIS) has increased the possibilities to easily, quickly and—in many cases—cost-effectively publish spatial data stored in databases. The aim of this study is to present the geovisualization of spatial databases of a Hungarian settlement on the web, using the open source webGIS system and Google application programming interfaces (APIs). The interactive point and interpolated distribution maps available online provide a detailed picture of the level of contamination, the spatial distribution of the ground water supply of the investigated settlement, and the changes which have occurred following the establishment of the sewage system. In the case of PO43− we determined that in the year before the sewage system was constructed, most of the area of the settlement could be considered contaminated, with the highest level of contamination measured in the central area of the settlement. Five years after the construction of the sewage system, the ratio of the contaminated areas had significantly decreased. In the case of NO3− we found a high level of contamination before the construction of the sewage system with a concentration increase in a North–West direction. After the establishment of the sewage system, the increase in concentration was the most intense in the central parts of the settlement, while the characteristic spatial distribution could no longer be observed. The geovisualization techniques developed are able to provide information about the different spatial data for users in a visual way, and also help to understand better the spatial information using a cognitive approach. The advantage of interactive web maps created with the technologies applied over traditional static maps is a new approach, which allows the user to manipulate the temporal and spatial data directly in the most appropriate way.

In our study we attempt to demonstrate the effects of uninsulated sewage tanks, which are the most important sources of contamination in settlements without sewage systems, on groundwater quality. We compared the results of measurements carried out before and one and a half years after the construction of the sewage system. We established 3 m deep monitoring wells within a 25 m radius of a sewage tank, which were then sampled, and the level of groundwater was recorded. The 3D model constructed on the basis of the saturated zone shows that the effluent wastewater formed a groundwater level dome with a height of more than 1 m. After the sewage tank was taken out of use the difference between the highest and lowest groundwater levels decreased to a few centimetres. In our study we investigated the spatial distribution of NH4+(ammonium). Using the 3D model we were able to precisely determine the volume of water bodies with different levels of contamination. In an approximately 25 m3water body, in the immediate environment of a sewage tank in use we detected NH4+at a concentration which was characteristic of undiluted wastewater (>90 mg·dm−3). After the sewage tank was taken out of use, the concentration in its immediate environment decreased by more than 50%, although almost everywhere in the modelled area concentrations were measured above the limit value. Based on the above, we can conclude that the cleaning process has started, but the complete decontamination of the groundwater will take several years.

In this study the effects of nitrogen effluent from a permeable constructed sewage tank on groundwater quality were investigated. Sampling took place before and 1.5 years after the closure. Using a 3D hydrogeological model, the spatial distribution of dissolved inorganic nitrogen (DIN), comprising the species NH4+, NO2- and NO3-, was modelled in the saturated zone and the amounts and changes in the ratio of NH4-N, NO2-N, NO3-N were determined. The first part of our general hypothesis, that the groundwater was heavily contaminated in the area surrounding the sewage tank, was clearly verified, since every investigated nitrogen compound exceeded the contamination limit values; but the second part of our hypothesis, that the degree of contamination would significantly decrease after the sewage tank was taken out of use has not been confirmed, since the amount of nitrogen present in inorganic forms increased in the modelled zone. The increase in DIN and the relatively high concentration of NH4+ (35 mg/L) in the immediate vicinity of the tank can be explained by the fact that organic matter (OM) accumulated over the decades provided a constant supply of inorganic nitrogen forms.

In 2013 and 2014, the N, P and K contents of the aboveground phytomass and grain yield of maize hybrids (P 9494, SY Afinity) were examined, as well as the different amounts of N, P and K (kg ha -1 ) uptake at different nutrient levels (control, N 90 + PK, N 150 + PK), on calcareous chernozem soil in Eastern Hungary (47°33' N, 21°27' E). Our experimental findings proved that as a result of fertilization, the macronutrient (N, P, K) content of the maize hybrids significantly increased in both years in the vegetative and generative plant parts. In the control, the maize hybrids gave high yields (from 10.2 to 11.3 t ha -1 in 2013, and 11.3-14.6 t ha -1 in 2014), and the surpluses due to fertilization varied between 3.2 and 5.0 t ha -1 (2013) and 2.9 and 3.1 t ha -1 (2014). The experimental results proved that fertiliser dosage, genotype and crop year each influenced the NPK utilisation of the fertiliser applied. With increasing doses of fertiliser, NPK utilization deteriorated. In both years, the SY Afinity gave a better N-utilization than the P 9494 hybrid. P-and K-utilization were significantly affected by the year. N-utilization varied from 49.8 to 97.6%, P-utilization varied from 17.1

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