Nutrient dynamics in soils of Lower Austrian agricultural landscapes

Supported by the Lower Austrian Landscape Fund (LAFO)
Christian Holzinger, B.Sc.¹,
Walter Wenzel, Univ.Prof. Dipl.-Ing. Dr.nat.techn.¹

¹ University of Natural Resources and Applied Life Sciences Vienna, Institute for Soil Research, Konrad Lorenz-Straße 24, A-3430 Tulln an der Donau

The current condition of the investigated arable land classified as good for organic carbon. Only 5% are in the lowest class. The same applies to the C/N ratio, only 9% have a slightly too wide ratio. The pH value divided into 24% in the acidic, 22% in the neutral and 54% in the alkaline range. Phosphorus availability shows an undersupply for almost 50% of the sites, while 32% sufficiently supplied and 20% are oversupplied. For potassium availability, 38% are in the low range, 33% adequately supplied and the remaining 29% in the higher ranges. For the available silicon fraction, a differentiated picture emerges depending on the assumed limit value. While only 12% are below 20 mg/kg (sugar cane), 60% are below 43 mg/kg (rice).

For the current condition of the grassland sites investigated, only the organic carbon and the C/N ratio are in a good range. The majority (69%) of the sites have an acid soil reaction. The proportion of 26% in the strongly acidic range is high. For the plant-available phosphorus is a low supply indicated. 91% are under-supplied, 5% sufficiently supplied and 4% in the high and very high range. Potassium availability is 48% in the undersupplied range, 26% considered adequately supplied and 26% classified as oversupplied. The availability of silicon shows a poor picture (at the assumed limits 60% are < 20 mg/kg and 98% < 43 mg/kg).

The investigation into possible changes in soil parameters over time in arable farming could only detect a significant change for the CN ratio. The available phosphorus decreased slightly (not significantly). The number in the lowest content classes A and B increased, the proportion of sufficiently supplied class C remained stable and the oversupplied classes D and E decreased. The organic carbon content showed a non-significant increase in the median, from 20.5 to 22.9 g/kg.

In grassland, there was a significant increase in soil organic carbon, total nitrogen, CN ratio and a very large increase in available potassium (median almost quadrupled). The pH and the amorphous silicon fraction decreased significantly. The available phosphorus increased slightly (not significantly). Thera are no changes for the potentially available silicon fraction.

When considering changes over time in geographical areas, the values determined for arable land and the main production area " North-Eastern Plain and Hill Country " (HPG 8) and the small production areas "Vienna Soil" and "Baden-Gumpoldskirchen Area" (KPG 809 - 810) could be compared well with that of the ÖPUL evaluation (AGES, 2010).

In the small-scale production areas "Vienna Soil" and "Baden-Gumpoldskirchen Area", the pH values remained largely stable in the carbonate buffer range. The organic carbon content increased somewhat (median 34.2 to 39.5 g/kg), although the increase could not be statistically verified. The total nitrogen contents remained almost constant (3.1 and 3.4 respectively). The proportion of the content classes of plant-available phosphorus decreased into the low - and sufficiently supplied range. For potassium availability, there was a decrease in the under-supplied classes (A and B) and a slight increase in the sufficiently supplied class C, as well as in the higher classes (D and E). The silicon fractions show no significant changes over time. In the main production area "North-Eastern Plain and Hill Country", there was a relevant, statistically at present still scarcely reliable increase of 15% in the median values of the organic carbon content.

The values determined for the main production area "Voralpen" (HPG 2) were far below the values of the ÖPUL evaluation. One reason could be the high number of soils with hydromorphic characteristics in the renewed sampling of the agricultural soil mapping. The water balance and the associated air balance are of immense importance for biogeochemical soil reactions. If there is no relatively homogeneous distribution of important soil characteristics, or also soil types (in Austria according to genetic characteristics), this can also lead to non-comparable soil data. Especially the water balance (and air balance) can be attributed an important role in this respect.

The pH value shows a significant decrease (median from 5.9 to 5.4). Organic carbon (median from 37.6 to 54.6 g/kg) and total nitrogen (median from 4.1 to 5.5 g/kg) have increased significantly. The C/N ratio has improved significantly, and is now in a better range. Phosphorus availability has not improved and the majority of soils are in the undersupplied range (94%).  Potentially plant-available potassium shows a strongly significant increase (median from 21.8 to 84.6 mg/kg), and the distribution in the content classes has improved. For silicon availability, no significant change is shown (median from 14.9 to 15.6 mg/kg). The amorphous silicon fraction shows a significant decrease (median from 2290 to 1980 mg/kg).

The increase in organic carbon content in both land use types (arable land and grassland) assessed positively. The increase in arable land is in line with the results of AGES (2015). It pointed out that the data on organic carbon in particular are preliminary evaluations, as only part of the analytical data is currently available.

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Map with new sampling in Lower Austria

The map shows the locations of the basic programme of soil monitoring activities of the province of Lower Austria in cooperation with the Institute of Soil Research of BOKU at the Tulln site (UFT). Based on the sampling network of the Lower Austrian Soil Condition Inventory (BZI - grey squares), numerous sites in the Pannonian region were initially re-sampled in 2020 to determine changes in soil properties over time. In addition, about 600 soil profile sites of the Austrian Soil Mapping re-sampled in 2016-2020 to further densify the measurement network. Both for the BZI and for the shown soil mapping locations, archive samples hold on behalf of the province of Lower Austria at the BOKU Tulln (UFT) site and analyzed for comparison with the newly taken samples.

The current analysis programme aims at determining the current soil condition and its changes during the last decades with regard to important parameters such as organic carbon (humus), soil acidity (pH), carbonate content, as well as available nutrients (nitrogen, phosphorus, potassium, silicon) and potential pollutants (arsenic, heavy metals).

 The measuring network shown here is supplemented by permanent soil monitoring plots (above all in central settlement areas such as the districts of Tulln and Schwechat) and further investigations at selected sites (organic pollutants; monitoring of soil protection facilities, networking with European monitoring programmes such as LUCAS, etc.). Thus, in accordance with the Lower Austrian Soil Protection Act, soil monitoring is as comprehensive as possible, taking into account new scientific findings.

Download map with new sampling in Lower Austria (pdf)