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

Abstract

ABSTRACTA 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 (rs = 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 (rs = −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 (rs = −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.