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The application of sewage sludge or biosolids on soils has been widespread in agricultural areas. However, depending on their characteristics, they may cause increase in heavy metal concentration of treated soils. In general, domestic biosolids have lower heavy metal contents than industrial ones. Origin and treatment method of biosolids may markedly influence their characteristics. The legislation that controls the levels of heavy metal contents in biosolids and the maximum concentrations in soils is still controversial. In the long-term, heavy metal behavior after the and of biosolid application is still unknown. In soils, heavy metals may be adsorbed via specific or non-specific adsorption reactions. Iron oxides and organic matter are the most important soil constituents retaining heavy metals. The pH, CEC and the presence of competing ions also affect heavy metal adsorption and speciation in soils. In solution, heavy metals can be present either as free-ions or complexed with organic and inorganic ligands. Generally, free-ions are more relevant in environmental pollution studies since they are readily bioavailable. Some computer models can estimate heavy metal activity in solution and their ionic speciation. Thermodynamic data (thermodynamic stability constant), total metal and ligand concentrations are used by the GEOCHEM-PC program. This program allows studying heavy metal behavior in solution and the effect of changes in the conditions, such as pH and ionic strength and the application of organic and inorganic ligands caused by soil fertilization.

No abstract

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin.

Forage legumes increase nutritive value and provide N to grass‐based grazing systems. Few legumes have a long stand life in the southeastern US, but persistence is documented for rhizoma peanut (RP; Arachis glabrata Benth.). Several RP introductions have been released recently from the University of Florida, but their responses to grazing management have not been evaluated. The objective was to determine productivity, persistence, and nutritive value of three RP cultivars (‘Florigraze’, ‘UF Peace’, and ‘UF Tito’) and the germplasm Ecoturf grazed every 3 or 6 wk to remove 50 or 75% of pre‐grazing canopy height. Herbage accumulation (HA) was not different among RP entries and averaged 8790 and 6210 kg ha‐1 in Years 1 and 2, respectively. Greater HA occurred for the regrowth interval of 6 wk vs. 3 wk in the 50% removal treatment (8040 and 7010 kg ha‐1, respectively), and the response approached significance (P = 0.073) for the 75% treatment (7800 vs. 7140 kg ha‐1, respectively). Treatments had minimal effect on nutritive value, and all entries had crude protein (CP) ≥ 140 g kg‐1 and in vitro digestible organic matter (IVDOM) ≥ 660 g kg‐1. Grass encroachment was greater in Ecoturf and Florigraze when grazed every 3 wk (13 and 24%, respectively) than every 6 wk (7 and 15%, respectively), but regrowth interval did not affect grass percentage in Peace and Tito. New RP cultivars and germplasm had similar HA as Florigraze, but also greater percentage RP and lesser weed frequency than Florigraze, especially under frequent or close grazing.