It is important to know the mechanisms for forage development, especially those related to the tolerance of potentially toxic elements, when considering their use in phytoremediation in heavy metal contaminated areas. In this study, we evaluated plant growth, concentration, and the availability of cadmium (Cd) for forage grasses (Panicum maximum Jacq. cv. Aruana and cv. Tanzânia; Brachiaria decumbens cv. Basilisk; Brachiaria brizantha cv. Xaraés and cv. Marandu) cultivated in Cd contaminated soils. The experiments were performed under greenhouse conditions over a 90-day evaluation period, and the Cd rates were 2, 4, and 12 mg/kg of soil. The relative growth rate of the forage grasses decreased as Cd rates increased, and the following descending order of susceptibility was observed: Marandu > Xaraés > Aruana > Tanzânia > Basilisk, with regard to phytotoxicity in these plants. The forage Cd concentration increased in line with increases in the Cd rates. Cd contents extracted by Mehlich-1 and by diethylenetriaminepentaacetic acid presented high positive correlation with forage relative growth. The forage plants did not block Cd entry into the food chain because they were not capable of limiting Cd absorption.
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 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.
ABSTRACT:The goal of this study was to evaluate the nitrogen fertilization as deep litter for pigs in order to produce biomass and accumulate nutrients by the corn. A deep litter made of rice husk as organic compound, from a commercial pig farm during finishing phase, was used. After three consecutive batches of pigs, the deep litter was subjected to a maturation period of 50 days, and samples of this material were taken for analysis of agronomic value. The experimental design was completely randomized with five replicates. The treatments consisted of doses of 0, 75, 150 and 300mg dm -3 of N of deep litter, as well as an additional treatment with ammonium sulfate, with a dosage of 150mg dm -3 of N. After 45 days, corn plants were harvested in order to evaluate the total dry weight and nutrient concentrations of their aerial parts. Dry matter increases were found with more application of deep litter. Regarding control fertilization, the use of increasing dosages of deep litter allowed accumulation of K, reduced the availability of P, Ca, Mg, Zn and B and did not alter the concentrations of N, Cu, Fe and Mn.
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