The effect of increasing rates of superphosphate manufactured from Kola apatite, marketed in Hungary in the early 90s, and basic rock phosphate from Algeria on the Cd, Cr, Sr, Mn, Ni, Al, Co and Mo concentrations in the grain and by-products of spring barley was investigated in a pot experiment involving three acidic soils from Hungary and one each from Slovakia, Romania and Algeria. The rock phosphate used in the pot experiment contained three times as much Cd and twice as much Cr as is currently permitted in Hungary. Nevertheless, neither of these elements could be detected in the grain yield of barley. The chromium content in the by-products was also below the detection limit in all the treatments on less acidic soils. Even on extremely acidic soils there was only a detectable concentration of chromium in treatments where the development of spring barley was severely retarded. Cadmium, however, was detectable in the by-products on all the soils, in a concentration that depended primarily on the properties of the initial soils and the rock phosphate rates applied. Cobalt could not be detected in the grain yield on any of the soils, and nickel only on extremely acidic brown forest soil with alternating thin layers of clay in treatments where the underdeveloped plants produced a very low grain yield. In the by-products nickel, like chromium, was only present in detectable quantities in the underdeveloped plants growing on extremely acidic soils. On the latter soils cobalt was detected in the by-products in all the treatments, but in healthy plants its concentration was an order of magnitude lower than in retarded plants. Molybdenum was only detected in the grain yield of spring barley on weakly acidic soils, but was present in the by-products on all soils in treatments where healthy plants of spring barley developed. Manganese, aluminium and strontium were found in detectable quantities in plants in all the treatments on all the soils. On the majority of soils the concentration in the by-products was an order of magnitude higher than in the grain. Naturally the plant concentrations of the various elements were influenced by the quantities introduced into the soil with the P fertilizer (Sr, Cd) and by the extent to which the pH changed as the result of the P fertilizer (Cr, Co, Ni, Mo, Cd, Mn and Al). The Ni, Co, Cr, Al and Mn concentrations of the retarded plants growing on extremely acidic soils was several times higher than that of healthy plants (Treatments 9-12). On such soils the rates of basic rock phosphate applied in these treatments served not only as P fertilizer but also as liming agents, exerting a favourable effect by reducing the acidity of the soil and thus the availability of the potentially toxic elements. In agreement with observations found in the literature, the results of the pot experiment on spring barley indicated that heavy metals and potentially toxic elements were accumulated in the vegetative organs of barley, rather than in the grain yield. On soils where the lower pH caused by P treatment increased the availability of potentially toxic elements, plant concentrations were higher, emergence was poor, the plants were retarded and no grain yield was produced. These results provide an indication of the processes to be expected when soils become more acidic.
Effect of Carbon, Nitrogen Sources and Abiotic Stress on Phosphate Solubilization by Bacterial Strains Isolated from a Moroccan Rock Phosphate Deposit
