Juliane Seeger

Lysimeter studies in East Germany concerning the influence of set aside of intensively farmed land on the seepage water quality

Abstract Since 1990, the five new federal states of Germany have experienced a fundamental structural change in agriculture. As much as 10% of the 6.2 million hectares of the previously intensively farmed agricultural areas were abruptly set aside. In the spring of 1991, a lysimeter test, designed in 1983 to maximize yields, was adapted to these new agricultural conditions. The purpose of the test was to investigate the impact of the structural changes on water balance and budget of materials. Leaching of relevant cations (Ca 2+ , Mg 2+ , Na + , and K + ) and anions (total PO 4 3− , NO 3 − , Cl − , and SO 4 2− ) contained in the seepage water as well as the resulting pH-values were determined for various types of set aside. The reference treatment consisted of intensively farmed lysimeters following the principles of BMP (best management practices). The tests covered a period of three years. The studies proved that restricting agricultural usage on areas previously farmed heavily, by converting them into permanent or rotation fallow, will result in measurable changes of seepage water recharge and quality within less than one year. The permanent fallow showed large leaching losses of the measured cations even three years after set aside. In contrast, the leaching of the measured anions NO 3 − , SO 4 2− and Cl − decreased significantly compared with the initial level. If cation leaching decreases from lack of additional supply, a shift of the pH into the acid range is to be expected. A one year set aside in the form of a rotation fallow is connected with increased leaching of nitrate. Compared with intensively farmed agricultural land, nitrate leaching in the year of set aside is increased by approximately 55% and in the year of resuming intensive agricultural production by 30%.

Assessing the impact of agricultural land use changes on water quality

To study and predict environmental impacts of land use changes on water quality we conducted different types of lysimeter experiments. All of them are linked to representative experimental catchment areas in the field. This allows the verification and extrapolation of lysimeter results. The objective of this paper is to discuss a strategy for using and scaling-up of lysimeter results to a field and catchment scale. It will be shown that the N-loss determined with lysimeters falls within the variation of N-balance based model calculations, and also within ground water recharge rates calculated with models commonly used in hydrology. Extrapolation of lysimeter data to a catchment with similar soils provides a reliable basis for estimating the N-leaching caused by a change in agricultural land use. On the basis of the N-loss from the soil and the N-load of the stream, the calculations show that an increase in the proportion of one year rotation fallow from 10 to 25% results in nearly a 10% increase in the N-load of the stream. However, from the point of view of protecting drinking water quality, rotation fallow for one year is not recommended because of the resulting intensified leaching of nitrates.

Analysis of the effect of meteorological factors on dewfall.

To get an insight into when dewfall will occur and how much to expect we carried out extensive calculations with the energy balance equation for a crop surface to 1) identify the meteorological factors which determine dewfall, 2) establish the relationship between dewfall and each of them, and 3) analyse how these relationships are influenced by changes in these factors. The meteorological factors which determine dewfall were found to be air temperature (T(a)), cloud cover (N), wind speed (u), soil heat flux (G), and relative humidity (h(r)). Net radiation is also a relevant factor. We did not consider it explicitly, but indirectly through the effect of temperature on the night-time radiation balance. The temperature of the surface (T(s)) where dew forms on is also important. However, it is not a meteorological factor, but determined by the aforementioned parameters. All other conditions being equal our study revealed that dewfall increases linearly with decreasing N or G, and with increasing h(r). The effect of T(a) and u on dewfall is non-linear: dewfall initially increases with increasing T(a) or u, and then decreases. All five meteorological factors can lead to variations in dewfall between 0 and 25 W m(-2) over the range of their values we studied. The magnitude of the variation due to one factor depends on the value of the others. Dewfall is highest at N=0, G=0, and h(r)=1. Ta at which dewfall is highest depends on u and vice versa. The change in dewfall for a unit change in N, G or h(r) is not affected by the value of N, G or h(r), but increases as T(a) or u increase. The change in dewfall for a unit change in Ta or u depends on the value of the other four meteorological factors.

Estimating the effects of set‐aside on water quality: scaling‐up of lysimeter studies

Since 1990, agriculture in the five new federal states of Germany has experienced a fundamental structural change. As much as 10 per cent of the 6·2 million ha of previously intensively farmed agricultural land were set-aside abruptly. In the spring of 1991, a lysimeter trial (filled with soils common in the catchment area of the Elbe River), was set up to investigate the impact of set-aside on the water and solute balance. The studies proved that restricting agricultural use in areas previously farmed intensively by converting them into permanent or rotation fallow will result in measurable changes in deep percolation (ground-water recharge) and water quality in less than one year. The results of the lysimeter studies were extrapolated to calculate the effects of set-aside in a catchment area (about 2 500 ha) with similar meteorological and soil conditions. The calculations showed that increasing the area under rotation fallow from 8 to 15 per cent increases the nitrogen load of the stream draining the catchment by about 5 per cent. Copyright

Strategies to mitigate diffuse phosphorus pollution during rewetting of fen peat soils

The cultivation of fen peat soils (Eutric Histosols) for agricultural purposes, started in Europe about 250 years ago, resulting in decreased soil fertility, increased oxidation of peat and corresponding greenhouse gas fluxes to the atmosphere, nutrient transfer to aquatic ecosystems and losses in total area of the former native wetlands. To prevent these negative environmental effects set-aside programs and rewetting measures were promoted in recent years. Literature results and practical experiences showed that large scale rewetting of intensively used agricultural Histosols may result in mobilisation of phosphorus (P), its transport to adjacent surface waters and an accelerated eutrophication. The paper summarises results from an international European Community sponsored research project and demonstrates how results obtained at different scales and from different scientific disciplines were compiled to derive a strategy to carry out rewetting measures. Based on this findings a simple decision support system (DSS) for a hydrologically sensitive area in the Droemling catchment in north-eastern Germany was developed and since 2005 practically used to prevent freshwater resources from non point P pollution.

Lysimeter- und Kleineinzugsgebietsuntersuchungen zum Einfluß von Landnutzungsänderungen auf die Wasserqualität

Seit Beginn der 90iger Jahre finden in der Landwirtschaft der neuen Bundeslander verstarkt Landnutzungsanderungen statt (vorrangig Extensivierungen und Flachenstillegungen). Zur Aufklarung der damit verbundenen Auswirkungen auf die Veranderung der Wasserbeschaffenheit, vor allem auf die Nahrstoffe Stickstoff (N) und Phosphor (P), werden seit einigen Jahren Untersuchungen in unterschiedlichen Skalenbereichen (UFZLysimeterstation Falkenberg — Mikroskala; Kleineinzugsgebiet „Schaugraben“ — Mesoskala) durchgefuhrt. Aus den seit 1993 durchgefuhrten Emissions- und Immissionsbetrachtungen ist ersichtlich, das erhebliche Unterschiede zwischen dem N-Eintrag aus der Bodenzone und dem N-Austrag aus dem Kleineinzugsgebiet zu verzeichnen sind (Differenz zwischen 29 und 54%). Aufgrund stark verringerter Stoffkonzentrationen im Oberflachenwasser des Schaugrabens im Versuchsjahr 1997 gegenuber den zu Beginn der Messungen 1993 festgestellten Werten soll versucht werden, die Frage zu beantworten, inwieweit dieses Ergebnis bereits auf die zwischenzeitlich erfolgten Landnutzungsanderungen zuruckzufuhren ist oder ob andere Ursachen hierfur verantwortlich sind.

Langjährige lysimeterversuchsergeb‐nisse über den einfluss einer gestaffelten mineraldüngung auf den nährstoffaustrag

Zur Untersuchung der Zusammenhange zwischen dem Niveau der mineralischen Dungung und dem sik‐kerwassergebundenen Nahrstoffaustrag ist 1985 ein kombinierter mehrfaktorieller Lysimeterversuch mit den Teilgliedern Mineraldungung, Nutzung und Bodenart angelegt worden. Als Ergebnis der achtjahrigen Auswertung konnte sowohl eine signifikante Reduzierung der Abflusbildung als auch eine signifikante Ertragszunahme mit steigendem Mineraldungeraufwand belegt werden. Bei dem aus Sicht der Trinkwasserversorgung besonders interessierenden Kriterium Stickstoff bzw. Nitrat wurde die geringste Auswaschung von durchschnittlich 6 kg N/ha·a auf dem lehmigen Sandboden bei Graslandnutzung und die hochste von 24 kg N/haa auf dem Sandboden mit Ackernutzung festgestellt. Die erwartete Verminderung des Austrages von Stickstoff, Phosphor und Kalium bei einer um 50% reduzierten Mineraldungung konnte im untersuchten Applikationsspektrum nicht statistisch nachgewiesen werden. Eine deutliche Reduzierung der Nahrstoffbelastung der Wass...