A method was developed to estimate root efficiency of barley (Hordeum vulgare L.) in making available phosphorus (P) from vatious unlabelled, spatingly-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 oflandrace barley were tested with 8 day old seedlings. CaHPO, 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 con·elated significantly (r = 0.727; p < 0.001) with the dissolved level ofP from CaHP0 4 • On average, FePO, was immobilized by all the barley lines though with significant differences (p < 0.01), and showed a significant negative cotTelation with the acidification of the medium ( r, = -0.306; p = 0.011). One barley line showed wide variation towards FeP0 4 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 FeP0 4 is in accordance with the observed accumulation of FeP0 4 in soils also frequently sown with barley. P of Siilinjarvi Apatite was immobilized by all the barley lines without significant differences, but showed a minor negative con·elation between P dissolving and acidification (r, = -0.168; p = 0.108). These results coiToborate the poor capability of apatite dust to serve as a source of P for barley observed in published field ttials 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 toP 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.

To assess the efficiency of pea roots to mobilize available phosphorus (P) from P compounds we subjected various pea genotypes to a post‐treatment method. Axenic seedlings were raised on P‐deficient semisolid synthetic medium using control blanks without a plant otherwise treated in the same way. AlPO4, CaHPO4, FePO4, apatite and meat‐bone‐meal (MBM) were tested. A genotype was tested from 1‐day through 15‐days of growth. There were differences between the compounds (p < 0.001). P was dissolved from CaHPO4 with apparent maxima at 72‐h intervals and to a significantly lesser extent from MBM. With AlPO4, FePO4 and apatite, the roots did not show a dissolving effect, but, on the contrary, significantly immobilised P. In each case a correlation with an increase in acidity, H+ (p < 0.001) was observed. The correlation was negative in the AlPO4, FePO4 and apatite series. A CaHPO4 treatment combined with apatite or MBM significantly decreased solubility of P from that of CaHPO4 singly. Tests with six additional genotypes showed that all solubilised P from CaHPO4, some to a significant extent from apatite, MBM or slightly from FePO4, but none from AlPO4. The accumulation of nearly water‐insoluble aluminium and iron phosphates in field and virgin soils is partly explainable by the immobilisation through the root action on P, which we have found also with other plant species. The root responses must also have ecophysiological functions distinct from P acquisition.