Phosphatversorgung von Sommerweizen (Triticum aestivum L.) in Mischkultur mit Weißer Lupine (Lupinus albus L.)

Phosphorus nutrition of spring wheat (Triticum aestivum L.) in mixed culture with white lupin (Lupinus albus L.). Spring wheat (Triticum aestivum L. ?Schirokko”?) and white lupin (Lupinus albus L.) were grown in mixed culture in Mitscherlich pots with 20 kg of soil in a green house. The soil used was a B_t of a Parabraunerde-Pseudogley from loess low in available P and limed from pH 4.6 to pH 6.5. Phosphorus was added as phosphate rock. In half of the pots cylinders of stainless steel screen prevented intertwining of the roots of the plant species. Independent of P addition, white lupin had higher dry matter production and P uptake than wheat, even although wheat had thinner roots and higher root densities than lupin, factors which favour the utilization of soil and fertilizer P. The higher P efficiency of white lupin was due to higher P uptake rates per unit root length mainly through mobilization of P especially in the rhizosphere of the proteoid roots. When the roots of the two species were allowed to intertwine, shoot dry matter production of wheat was nearly double because of improved tillering. Higher P concentrations and a more than 2-fold higher P uptake indicated that the increase in dry matter production of wheat was due to improved P nutrition. Nitrogen concentrations, however, remained unaffected at sufficient levels. An increased P uptake rate per unit root length was responsible for the better utilization of P by wheat, rather than the increase in total root length, due to the extended root volume. White lupin was able to mobilize P in the rhizosphere in excess of its own requirements. Thus mobilized P may be available to less P-efficient plants grown in mixed culture.