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Summary Band 36

Wolf, Andreas: Water Protecting Agriculture Subject to Typical Arable Soils and Field Crops in a Water Reservation Area Northwest of Cologne. Bonner Bodenkundl. Abh. 36 (2001), 161 pp.

 

In the catchment area of the water extraction system „Weiler and Langel/Worringen“ of the GEW Köln AG, the nitrate levels increased in the ground water rapidly in the 1970`s. The concern was that either the supply systems would have to be closed or expensive processing steps would have to be undertaken. For these reasons, a study in water protecting agriculture has been developed combining the „Arbeitskreis Ackerbau und Wasser im linksrheinischen Kölner Norden e. V.“. After selecting agricultural steps, which show potential decreases in nitrate and pesticide output levels, their effectivness on ground water was studied within a framework of field tests.

Typical soils of the test area, the widespread Luvisols, two Cambisols and two Arenosols were selected for the field tests. The latter ones have the tendency to leach nitrates and pesticides, which are unfavourable characteristics (lower field capacity and higher water conductivity). This manifests in ground water as a high nitrate level. After forming two test groups with three different soils, two crop rotations with four variants each were observed for a period of three years. Simultanously to the field tests, in which nitrate and pesticides were detected in the soils, ground water and in the crops (sugar beets and grain), the development in the respective water quality parameters was measured.

The results were as followed:
The sandy soils, which were studied, did not only show a worse nitrate saving level but also a lower nutrient utilisation level. This was shown in lower yields and a higher Nmin-level after harvesting. According to N-fertiliser prognosis, an increase in N-fertiliser is normally recommended for sandy soils. This defined increase from the agricultural viewpoint is paradox to water protection. This is because porous soils with a low potential for production receive higher fertilizer values. Different harvest times as well as the timing and intensity of soil tillage have an important influence in the winter nitrate levels. The reduction of soil tillage in order to decrease N-seepage is, nevertheless, tied to optimal weather conditions which can not be controlled by the farmers.

The investigated mulch seeding procedure led to an increase in available N for the intermediate crops, a higher N-assimilation through the intermediate crops and a lower Nmin-level in late autumn. The mulch-seeded beets extracted more nitrogen from the soil than the variants with conventional intermediate crops and the nitrate level could be reduced by as much as 64 %. The ground water in the Water Reserve Weiler is well protected against contamination from pesticides (0.27 % positive).
However the only surface water, the Pulheimer Pond, was more polluted till 1993 (7.68 % positive). A waste water treatment plant exit drain in which the polluted water, containing pesticide residues and cleaning water for the farm machinery, was identified as the main source of contamination. Based on the acquired results, a replacement of chemical pesticides with mechanical processes of weed control in the test area is neither necessary from the viewpoint of water supply and distribution nor feasible under the current agrarpolitic conditions.

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