Abstract
In Brazil, about 80% of the 60 million hectares of pasture are in some state of degradation. Among the causes of this degradation is the lack of investment in liming and fertilization at the time of planting. Phosphorus is especially critical because it stimulates root growth in the establishment phase of forage growth. The objective of the study was to evaluate different sources of phosphorus in the formation of Marandu and Xaraes forages. An experimental design of randomized blocks in a factorial arrangement, 2 x 4, with 5 repetitions was used. Treatments consisted of two cultivars of Urochloa brizantha: Marandu and Xaraes and three sources of phosphorus: triple superphosphate (41% P2O5), natural reactive phosphate (28% P2O5) and organic mineral (4- 14-8) plus the absence of phosphate fertilizer (control). Plant height, stem diameter, chlorophyll A and B content and fresh and dry matter mass were evaluated 60 days after germination. Leaf content was also examined for the following mineral nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn). The Marandu cultivar was superior to the Xaraes cultivar in terms of height. Among the sources of phosphorus examined, there were no significant differences among organic mineral, triple superphosphate and reactive phosphate, for any of the characteristics considered. All the sources, however, differed from the control. The maximum extraction of soil macronutrients by Urochloa brizantha was, in descending order: the macronutrients K>N>Ca>Mg>P>S and micronutrients Mn>Fe>Zn>Cu. These nutrients, thus, needed to be replaced as they were removed through grazing, to replenish the soil. The sources of phosphorus evaluated were not associated with differences in the leaf contents of Cu, Zn and S. The leaf content of the Xaraes cultivar had higher values of N, P, K, Ca, Mg, S, Mn and Zn in relation to Marandu. Key words: Forage, degraded area, mineral nutrients, fertilization.
Highlights
The Brazilian cattle industry plays an important role in the national economy
The maximum concentration of mineral nutrients in the fresh forage was observed in the following order (K> N> Ca> Mg> P> S) at 60 days after germination
Similar reductions were observed by Costa et al (2010). These results demonstrate the need to replace the micro-nutrients in the soil as forage plants are grazed
Summary
The Brazilian cattle industry plays an important role in the national economy. Almost 20% of the total land area is used for pasture. Cattle production has been characterized by years of exploitation. Pastures are usually of low soil fertility and mineral nutrients extracted by the animals are not restored, leading to degradation. Dias-Filho (2012) mentioned that one of the main causes of grassland degradation is the absence of periodic restoration of soil fertility. Pasture degradation is associated with reduced animal carrying capacity and reduced productivity of meat and milk
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