RESUMO
In a previous study we demonstrated that Zinnia hybrida 'Profusion White' can be effective in the remediation of oil-contaminated soil. However, the rates of removal of total petroleum hydrocarbons (TPH) were greatest in soils containing 9000 mg/kg TPH and less in soils with higher concentrations of TPH. This study was conducted to investigate the effects of basal fertilizer rates and perlite amendments on the growth of zinnia and its remediation capacity in soils with TPH concentrations of 26,000 mg/kg. METHODOLOGY: Soils were prepared with or without TPH at an initial concentration of 26,194 mg/kg, and then each of these soils was amended with either a basal fertilizer rate with or without 20% perlite, or twice the basal fertilizer rate with or without 20% perlite. Pots were prepared with the following treatments in these soils: contaminated soil planted with zinnia (planted-contaminated), uncontaminated soil planted with zinnia (planted-uncontaminated), and contaminated soil not planted with zinnia (unplanted-contaminated). Plant growth, soil dehydrogenase activity (DHA), and TPH concentrations were analyzed at 30 and 60 days after sowing. RESULTS: Plant growth in oil-contaminated and uncontaminated soils was superior in pots with twice the basal fertilizer and with perlite. The DHA values in the planted-uncontaminated treatments were significantly lower than those in the planted-contaminated and unplanted-contaminated treatments. However, the effects of basal fertilizer amount and perlite on the DHA values of the soils were small. The TPH concentrations in the planted-contaminated soils were significantly lower than those in the unplanted-contaminated soils after 30 and 60 days. Furthermore, the TPH concentrations in the planted-contaminated soils were lowest in pots with twice the basal fertilizer and with perlite. CONCLUSIONS: These results show how phytoremediation of soils with high levels of oil contamination by Z. hybrida 'Profusion White' can be practically enhanced by amending the soil with perlite and higher basal fertilizer rates.
RESUMO
Improvement of phosphorus circulation in the soil is necessary to enhance phosphorus availability to plants. Phosphorus circulation activity is an index of soil's ability to supply soluble phosphorus from organic phosphorus in the soil solution. To understand the relationship among phosphorus circulation activity; bacterial biomass; pH; and Fe, Al, and Ca concentrations (described as mineral concentration in this paper) in agricultural soil, 232 soil samples from various agricultural fields were collected and analyzed. A weak relationship between phosphorus circulation activity and bacterial biomass was observed in all soil samples (R² = 0.25), and this relationship became significantly stronger at near-neutral pH (6.0-7.3; R² = 0.67). No relationship between phosphorus circulation activity and bacterial biomass was observed at acidic (pH < 6.0) or alkaline (pH > 7.3) pH. A negative correlation between Fe and Al concentrations and phosphorus circulation activity was observed at acidic pH (R² = 0.72 and 0.73, respectively), as well as for Ca at alkaline pH (R² = 0.64). Therefore, bacterial biomass, pH, and mineral concentration should be considered together for activation of phosphorus circulation activity in the soil. A relationship model was proposed based on the effects of bacterial biomass and mineral concentration on phosphorus circulation activity. The suitable conditions of bacterial biomass, pH, and mineral concentration for phosphorus circulation activity could be estimated from the relationship model.