Abstract
Available information of the effects of manganese nutrition on the forage genus Urochloa is scarce. In the context, this study aims to evaluate the tolerance of Urochloa brizantha cv. MG5 to Mn toxicity. The experiment was conducted in a greenhouse at the University of the State of Sao Paulo (UNESP) in the city of Jaboticabal, SP. Plants were cultivated in vases (3.5 L) filled with soil according to a completely randomized experimental design comprising of five levels of Mn (0, 15, 30, 60 and 120 mg?dm?3) and four replications and cut in two periods: one is 42 days after sowing and the other is 30 days after the first one. Samples from both cuts were evaluated as to plant height, number of leaves and tillers, dry weight, Mn content and accumulation, and the green index was determined in the last cut. Manganese addition to soil caused an increase in chlorophyll content at the dosage of 68 mg?dm?3 observed in the second plant cut. Dosages of Mn above 15 mg?dm?3 did not induce increases in nutrient accumulation and in the number of leaves in the first and second cuts of the grass, and tillers in the first cut. The highest concentrations of manganese in the shoots did not produce visual symptoms of damage or a decrease in forage productivity demonstrating that Urochloa brizantha cv. MG5 has high tolerance to manganese toxicity.
Highlights
Forage plants in many cultivated areas in Brazil belong to the genus Urochloa, a good annual producer of biomass irrespective of the different climate conditions prevailing in the country
The experiments in this study were conducted in green houses at the Faculty of Agrarian and Veterinarian Sciences, State University of Sao Paulo (UNESP) in Jaboticabal, SP, Brazil, from August to October, 2011, utilizing the forage plant Urochloa brizantha cv
Soil fertilization with dosages of Mn resulted in an increase of the leaf green color index with quadratic adjustments when determined in plants of the second cut, a maximum value attained when the nutrient dosage was 68 mg·dm−3 (Figure 1(a))
Summary
Forage plants in many cultivated areas in Brazil belong to the genus Urochloa, a good annual producer of biomass irrespective of the different climate conditions prevailing in the country. Forage production in Brazil is limited by low fertility soils and inadequate agricultural practices leading to nutritional imbalance. Increased availability of Al and Mn in the predominantly acid tropical soils, may lead to Mn toxicity as observed in mandaru grass According to van Raij [2] in micronutrient soil fertilization care should be taken to keep Mn concentrations below the level of 1.5 mg·dm−3. Mn as a micronutrient has an important role in processes like ionic absorption, photosynthesis and respiration, hormonal control, protein synthesis, resistance to illness and protection against oxidative stress [3]. Adequate Mn concentrations in Urochloa brizantha plants should be around 40 to 250 mg·kg−1 [4]
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