Availability and zinc accumulation in forage grasses grown in contaminated soil.

Zinc is an important micronutrient to plant growth, but when present in large quantities it can become a toxic element to plants. This study was aimed to evaluate the growth, concentration, accumulation and availability of Zn to forage grasses (Megathyrsus maximus cvs. Aruana and Tanzania, Urochloa brizantha cvs. Xaraés and Marandu and Urochloa decumbens cv. Basilisk) cultivated in Zn contaminated soils. The experiments were conducted under greenhouse conditions over a 90-day evaluation period, and Zn rates were 0, 100, 300 and 900 mg kg-1 of soil. The Zn rates in soil caused growth reduction in all evaluated forage grasses. The cultivar Aruana was generally more tolerant to Zn, while the Marandu was generally more susceptible to the addition of Zn. The cultivar Aruana proved to be superior to others due to its higher growth and higher critical level toxicity of Zn. None of the forage grasses evaluated can be considered a Zn hyperaccumulator. The extraction order was DTPA at pH 7.3 < Mehlich-1 < USEPA 3051 < USEPA 3052 in the soil independent of forage grasses cultivation. The USEPA 3051 extractor was similar to Mehlich-1 in predicting the availability of Zn in soil.