The environmental situation and current yield performance of sugar beet production in Germany are described and compared to those in other European regions. A continuous increase in yield performance and enhanced technical quality have been achieved through progress in breeding and improvements in crop management systems. This rise in yield potential has been brought about not by increased production intensity, but by better use of natural resources and production factors. In Germany, legislation rules many environmental aspects of agricultural plant production, and special laws are in force concerning fertilizer use, soil protection, and pesticide use. In sugar beet, nitrogen fertilizer use has decreased greatly and may be reduced further in some regions. A further reduction of potassium and phosphorus fertilizer use does not seem to be appropriate. Conservation tillage contributes to soil protection and is already performed on > 100 000 ha of land growing sugar beet. Strategies of integrated production aim to reduce pesticide use to the bare minimum. Integrated pest management is effective to control insects, nematodes and leaf spot diseases. Pesticide use in sugar beet is dominated by herbicide application. The most promising strategy to reduce the amount of active ingredient seems to be the growing of genetically modified herbicide‐tolerant varieties. Possible directions for future research are discussed, and the prospects for sustainable development, in terms of economic, ecological and social factors, are considered.

Phosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil‐root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al‐P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg−1) in combination with either ammonium or nitrate nitrogen (100 mg N kg−1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model of Barber and Claassen. In the treatments with no and low P supply NH4‐N compared to NO3‐N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH4‐N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO3‐N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH4‐compared to NO3‐N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO3‐N and 72 % in the NH4‐N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%.

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Nt&und NO&chaltc dcs Bodens, eilies Luvihols BUS LdU, bcstimnit. Der pH-Wen des wurzelfcmen Bodens blieh in der Versuchszeit unbccintlullt. wcnn kcin N oder 400 mg N kg-1 mil eincm Nitrifikotionshcninistoff (DCD) eingeniischt wurde. bui gleiclier N-Gnbe ohne DCD nahm er dugcgcn von pH 6.6 auf S.8 irb. Dcr pl-I-Wen clef Rhizosphiire sunk in allen Fiillcn ah und zww vorwiegcnd im Bereich unler I nun Absmd von der WurLelschich!. jcdoch mit Gradienten. die zwischen 2 und 4 mm in dcn Boden hineinreichten. Die stiirkste pH-Absenkung. von pH 6.6 auf 49. trat 11 den Wurzeln von Pflanzcn ein. die sowohl NtIJ-N als auch DCD erhalten hiitten. Rci ihnen war dcr Hauptteil des Minemlstickstoffs in dcr NH4-Fonn verbliehen. In dicsem Falle triit auch gels-SICS Al in dcr BodcnlOsung auf. wie ;in Jer Austauschaziditlt zu erkennen ww. Von der gcsamtcn Aziditgt stamnite bci NH,-DOngung ohne DCD der Hauptteil aus der Nitrifikation und nur ein lileinerer Anteil iiUS der netto-Protonenabgabc der Wurzeln. Die Vcrsauerung dcr Wuncln wurde durch Nitrifikation veningert. wcil dic Nitnttaufnilhme dcr Wurreln der Vcrsuuerung entgegenwirkte. Es wird der Schlull gczogen. dd Nitrifikntionshcnimstoffc zwar den Protoncncintrng in den Boden mindeni. d d sie aber die Bodenversauerung an dcr Wurzcl ventarken und so xu At-Toxizitat an den Pflanzen filhren klinnen.