Complete contact of Brassica roots with phosphorus fertilizer in a phosphorus-deficient soil

Abstract

The preferential development of Brassica lateral roots for phosphorus (P) to forage for P fertilizer was observed by using alginate gel beads in which powdery dicalcium phosphate dihydrate (DCPD) was suspended (DCPD gel bead). The DCPD gel beads enabled to detect the characteristic root growth around them because of their larger diameter (1.5 cm) than that of standard fertilizer particles. The thin Brassica lateral roots completely encircled the DCPD gel beads and no soil area remained between the roots and the DCPD gel beads. This morphological plasticity of Brassica roots is highly suitable for improving the P recovery rate because even a few mm of soil with a high P retention capacity between a plant root and P fertilizer reduces the P recovery rate. The P recovery rate in the Brassica shoots exceeded 0.05 and the ratio of the shoot dry weight in the plot treated with DCPD gel beads to that in the control plot exceeded 10. Thus, the Brassica plants showed both a high P recovery rate and satisfactory growth in the P-deficient soil compared with other tested plants due to the complete contact between their roots and the DCPD gel beads. The preferential root proliferation for P was also observed in Fagopyrum esculentum Moench as well as Brassica plants among the 20 tested plants.