Growth and phosphorus uptake of maize cultivated alone, in mixed culture with other crops or after incorporation of their residues

Intercropping or rotating of P-efficient crop species Which mobilize sparingly soluble P by their root exudates can have beneficial effects on growth and P uptake of P-inefficient species. We aimed at studying the effect of intercropping or incorporating of crop residues of P-efficient crops on the components of maize P-uptake, i.e. the root-system size and P influx (P-uptake rate per unit root length). This was studied in 3 pot experiments in a low-P sandy soil. In the first experiment, maize was intercropped with white lupine, sugar beet or oilseed rape, and with groundnut in the second experiment. In the third experiment, maize was grown after incorporating the crop residues of white lupine, sugar beet or oilseed rape. Maize growth and yield was strongly inhibited when intercropped with white lupine, sugar beet or oilseed rape, probably because of competition for nutrients. But with groundnut as the accompanying species, maize yield was increased by a factor of 3, mainly because of an enhanced P influx. Crop residues of oilseed rape and sugar beet increased the yield of maize by factors 2 and 1.6, respectively, because of a 3 and 2 times higher P uptake as compared to maize grown after maize without incorporation of crop residue. The reason for the higher maize P-uptake after oilseed rape was an 11 times higher P influx as compared to maize without crop residues, and after sugar beet residues because of an enhanced root growth and a 4 times higher P influx. Lupine residues did not improve maize growth, mainly because of a low P influx, which was even less than that of maize grown without crop residues. The soil solution P concentration and calcium acetate lactate-extractable P (CAL P) measured in this study did not reflect the P availability as indicated by the plants (P uptake, P influx). This indicates that other mechanisms such as P mobilization in the rhizosphere by root exudates or cell-wall components were responsible for the increased P availability. These mechanisms need further investigation.