Ammonium nutrition of higher plants results in rhizosphere acidification due to proton excretion by root cells. The acidification induced by ammonium-fed plants can be exploited to promote a localised metal mobilisation in neutral to alkaline polluted soils and therefore to improve phytoextraction. The effects of ammonium uptake by sunflower (Helianthus annuus L.) plants on the external medium pH, aerial and root growth and tolerance to soluble Cd were studied in hydroponic culture. The ammonium-fed sunflowers induced a strong acidification of the solution and, compared to the nitrate-fed sunflowers, a small modification in mineral nutrition and a different Cd partitioning between root and shoot. Moreover, ammonium nutrition was found to induce a great mobilisation of a sparingly soluble form of cadmium (CdCO 3 ). A pot experiment studied the ability of different ammonium-based fertilisers (ammonium sulphate, ammonium thiosulphate, urea) to modify bulk and rhizo-soil pH, compared to the effect of calcium nitrate and to the unfertilised soil. Furthermore, in order to promote the persistence of ammonium in soil, a combined treatment of ammonium sulphate and DMPP, a nitrification inhibitor, was tested. Soil pH was strongly modified by chemical and biological processes involved in fertiliser transformations. In particular, due to nitrification, all ammonium-based treatments showed a bulk soil acidification of over 1.5 pH units and a relative increase in rhizo-soil pH as a consequence of nitrate uptake. The treatment with DMPP showed an opposite trend with a lower pH in rhizo-soil than in bulk soil. The ability of ammonium-fed plants to mobilise heavy metals from the non-labile pool was studied in another pot experiment using three soils with different properties and at different degree and type of heavy metal contamination. Whatever the soil, the metal concentrations in shoots were higher in plants fed with ammonium (ammonium sulphate plus DMPP treatment). Our results support the hypothesis that ammonium nutrition with nitrification inhibitors is a viable strategy to improve heavy metals phytoextraction while protecting bulk soil from acidification and presumably from metal leaching.
A study was conducted to collect, classify and analyze a large number of compost samples to establish a database for determining the relative quality of different types of composts and their potential use based on their hydrological and physicochemical characteristics. Special attention was devoted to the use of compost for flower growing, which extended the analysis to include substrates, such as peats and organic substrates for pot coltures. Some 64 samples of various composts were collected directly from production plants in northern Italy. Depending on the starting raw materials, compost samples were grouped in six categories: sludge compost; animal manure compost; slaughterhouse waste compost; source separated MSW compost; raw MSW compost and yard waste compost. At the same time, 52 samples chosen from among peats and organic substrates, for professional growers and amateur gardeners, were obtained or bought from greenhouses, garden centres and shops. Hydrological and physicochemical properties of the 116 samples (composts, peats and substrates) were determined including: easily available water (EAW), water buffering capacity, (WBC), air capacity, total porosity, bulk density, real density, pH, specific electrical conductivity, cation exchange capacity, organic carbon and ash
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.