R. Meissner

Influence of different agricultural management systems on nitrogen leaching: results of lysimeter studies

The objective was to estimate the potential risk of N leaching into the groundwater under various types of agriculture by using lysimeter experiments on the nitrogen(N)-cycle of various soil types. Results were obtained with 12 weighable, monolithic lysimeters with a surface area of 1 m2, a total depth of 3 m, and free drainage. Mean annual N-leaching losses of 5 to 44 kg ha—1 and nitrate concentrations of the seepage water (leachate) between 80 and 200 mg l—1 were measured during the period of intensive agricultural use. On fallow land with a well-established grass vegetation, some nitrate was removed by the plants. As a result, the nitrate concentrations in the leachate were reduced significantly. Ecological farming measures generally reduced N leaching losses and kept the N-concentration in the leachate below the German threshold value for drinking water with 50 mg l—1 nitrate. However, ploughing in of clover or leguminous vegetation and the application of farmyard manure in autumn caused the nitrate concentration in the leachate to rise significantly above the mentioned threshold value. Einfluss unterschiedlicher landwirtschaftlicher Nutzungsformen auf den Stickstoffaustrag: Ergebnisse von Lysimeteruntersuchungen Das Ziel der Untersuchungen bestand in der Abschatzung des Stickstoff (N) — Auswaschungspotenzials bei differenzierter Intensitat der ackerbaulichen Nutzung und verschiedenen Bodenformen. Dazu wurden langjahrige Messreihen von 3 m tiefen und 1 m2 grosen, monolithischen Lysimetern ausgewertet. Es wurden bei intensiver landwirtschaftlicher Nutzung im Mittel N-Austrage von 5 bis 44 kg ha—1 a—1 und Nitratgehalte von 80 bis 200 mg l—1 ermittelt. Begrunte Brache mit gut etablierten Grasbestanden war in der Lage, N-Uberschusse festzulegen. Mit den Masnahmen des okologischen Landbaues wurden N-Austrag und Nitratgehalt im Sickerwasser unter den in Deutschland geltenden Grenzwert fur Trinkwasser in Hohe von 50 mg l—1 abgesenkt. Der fur eine bessere Nahrstoffversorgung im okologischen (biologisch-dynamischen) Landbau ubliche Umbruch von Kleegras und Leguminosenbestanden und die Ausbringung von Stalldung bewirkten eine deutliche Erhohung der Nitratgehalte im Sickerwasser uber den bestehenden Nitrat-Grenzwert.

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.

Novel lysimeter techniques — a basis for the improved investigation of water, gas, and solute transport in soils

For many years lysimeters have been proven to be effective tools in assessing and predicting the effects of current land use and future land use changes in catchment areas on both water and solute balances. Although due to the diverse aspects of mass transport modelling, many different types of lysimeters exist, water and solute balances are by no means fully understood, especially in post-mining areas. To tackle this problem, a new piece of equipment has been developed which enables the actual weight of a lysimeter to be precisely measured. The newly designed device, which has been used for one of the experiments described in this paper, permits the weighing of for example a 2 m3 lysimeter vessel with an accuracy down to 30 g. The second newly developed appliance presented here is the GAMS (Gas-Migration-Simulator). Basically comparable to a lysimeter, the difference is that the GAMS allows the detailed investigation of soil-gas migration processes and their dependence on parameters like the diffusion coefficient and the gas permeability of the soil, alterations of the groundwater level and on various external influences such as changes of the actual meteorological conditions. These two newly developed techniques are described in this paper, and their respective suitability is demonstrated on the basis of data sets recorded during initial experiments. Neue Lysimetertechniken — eine Grundlage zur verbesserten Untersuchung des Wasser-, Gas- und Stofftransportes in Boden Lysimeter haben sich als effektives Hilfsmittel zur Bewertung und Voraussage der von gegenwartigen Landnutzungen und kunftigen Landnutzungsanderungen in Einzugsgebieten ausgehenden Wirkungen auf den Wasser- und Stoffhaushalt bewahrt. Obwohl fur die modellhafte Beschreibung von Stoffbilanzen verschiedene Lysimeteranlagen verfugbar sind, konnte der Wasser- und Stoffhaushalt in Bergbaufolgelandschaften bisher nicht vollstandig aufgeklart werden. Zur Losung dieses Problems wurde eine neue Generation von Lysimetern entwickelt, mit denen beispielsweise die Wagung von 2 m3 grosen Bodensaulen mit einer Genauigkeit von 30 g moglich ist. Bei der zweiten hier vorgestellten Neuentwicklung handelt es sich um einen Gas-Migrations-Simulator (GAMS). Der grundsatz-lich mit dem Bauprinzip eines Lysimeters vergleichbare GAMS ermoglicht im Gegensatz zu herkommlichen Lysimetern die detaillierte Untersuchung der Bodengasmigration bzw. der Abhangigkeit dieser Migrationsprozesse von verschiedenen Einflussgrosen. Relevante einflussnehmende Parameter sind beispielsweise der Diffusionskoeffizient und die Gaspermeabilitat des Bodens, Ande-rungen des Grundwasserstandes oder externe Einflusse wie tageszyklische oder langerfristige Schwankungen der meteorologischen Verhaltnisse. Die beiden Neuentwicklungen werden anhand erster Untersuchungsergebnisse beschrieben, und es werden Schlussfolgerungen fur die weitere Arbeit abgeleitet.

N-, P- and DOC-dynamics in soil and groundwater after restoration of intensively cultivated fens

Most fens in Northeast-Germany have been drained since the late 18th century with a consequent increase in intensity of agricultural land use until the early 1990s. This cultivation resulted in severe peat degradation. Nowadays schemes are introduced to restore such degraded wetland sites. However, little is known about the impact of these restoration schemes on nutrient dynamics in soil and water.

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