Phosphorus Mobilisation and Immobilisation Vary in the Root Environment of Different Barley Genotypes with Different Phosphate Sources

ABSTRACT

A method was developed to estimate root efficiency of barley (Hordeum vulgare L.) in making available phosphorus (P) from various unlabelled, sparingly-soluble compounds containing P. The post-treatment method is based on axenic germination on a P-free medium, removing the seedling from the medium and incubating the P substance to be tested in situ in the medium, followed by soluble P determination. Seven lines of landrace barley were tested with 8 day old seedlings. CaHPO₄ was found to be dissolved by five of the lines, while two of them on average immobilized phosphate (dissolved less than in controls without a plant) with significant differences between the lines (p < 0.01). The acidification of the medium by the barley correlated significantly (r_s = 0.727; p < 0.001) with the dissolved level of P from CaHPO₄. On average, FePO₄ was immobilized by all the barley lines though with significant differences (p < 0.01), and showed a significant negative correlation with the acidification of the medium (r_s = −0.306; p = 0.011). One barley line showed wide variation towards FePO₄ having both mobilizing and immobilizing plants in the sample, either meaning a temporary change in capability or genetic heterogeneity within the line. The immobilization of FePO₄ is in accordance with the observed accumulation of FePO₄ in soils also frequently sown with barley. P of Siilinjärvi Apatite was immobilized by all the barley lines without significant differences, but showed a minor negative correlation between P dissolving and acidification (r_s = −0.168; p = 0.108). These results corroborate the poor capability of apatite dust to serve as a source of P for barley observed in published field trials in organic farming, and cast doubts on the usefulness of apatite as a direct fertilizer of slowly soluble P for barley. The polymorphic properties of the landrace barleys with regard to P acquisition are considered against the prescribed fire practices on soil preceding sowing and use of top mulch of manure on sown barley fields in the past. The introduced post-treatment method revealed several statistically significant differences. It can be applied to other sources of P avoiding the use of labelled compounds and as a cheap test extended to various substances, which can then be studied as to their changes by roots of different species.