Cycling of N and P in Grass-Alone (\u3ci\u3eBrachiaria\u3c/i\u3e) and Mixed Grass/Legume (\u3ci\u3eBrachiaria/ Desmodium ovalifolium\u3c/i\u3e) Grazed Pastures in the Atlantic Forest Region of Brazil

There are estimated to be \u3e 80 M ha of Brachiaria pastures in the tropical regions of Brazil. When continuously grazed with only modest fertiliser inputs (and no N) these pastures can maintain reasonable cattle weight gains (\u3e 200 kg LWG/ha per year). However, without fertiliser and when overgrazed, LWGs fall rapidly to low levels. Recent studies have shown that N and P deficiency are the most important factors limiting productivity. The objective of this study was to study fluxes of N and P in the pasture system in order to understand resilience to poor management and minimum nutrient requirements to guarantee their sustainability

Carbon Accumulation in Soils under \u3ci\u3eBrachiaria\u3c/i\u3e Pastures in the Atlantic Forest Region of the South of Bahia, Brazil

The objective of this study was to investigate the change in carbon stocks in soil following deforestation of the Atlantic forest in the South of Bahia State (Brazil) and replacement with productive pastures of Brachiaria humidicola either in monoculture or with the introduction of the forage legume Desmodium ovalifolium. Carbon stocks in the 0-30 cm layer were 44.5 Mg ha-1 under the original forest and found to be approximately 42 Mg ha-1 C 10 years later. At this time pastures of B. humidicola with or without the presence of D. ovalifolium were formed and grazed continuously for a further nine years until 1997. To 30 cm depth, C stocks increased during this time to 49.3 Mg ha-1 in the grass-only pasture and 52.4 Mg ha-1 in the mixed pasture which suggests that the presence of the legume enhanced C accumulation under the Brachiaria pastures. Analysis of the 13C abundance of samples taken to 100 cm depth in 1997 revealed that there was significant accumulation of organic matter derived from the Brachiaria to a depth of 50 cm in the soil and this material was of high C:N ratio (22-27)

Forage Legume Presence and Grazing Intensity Effect on Nitrogen Dynamics in \u3ci\u3eBrachiaria\u3c/i\u3e Pastures in the South of Bahia, Brazil

The objective of this study performed in the Atlantic forest region of the South of Bahia (Brazil) was to examine the influence of the presence of the forage legume Desmodium ovalifolium in pastures of Brachiaria humidicola on the nitrogen recycled through plant litter over stocking rates of 2, 3 and 4 head ha-1. The results demonstrated that the presence of the D. ovalifolium in the pasture significantly increased the protein content of the associated Brachiaria grass, and the rate and quantity of N recycled through the litter pathway. While had no significant increase in animal weight gain due this legume, the increase in N recycled through the litter pathway should provide an increase in the sustainability of pasture production, especially at the lower stocking rate where the grazing pressure was lower and the proportion of legume was higher

Avaliação do impacto da introdução de leguminosas forrageiras na produção e sustentabilidade de pastagens de Brachiaria através de estudos do ciclo de N.

Região de mata atlântica, sul da Bahia. Região de cerrado.bitstream/CNPAB-2010/27262/1/doc067.pd

The effect of the presence of a forage legume on nitrogen and carbon levels in soils under Brachiaria pastures in the Atlantic forest region of the South of Bahia, Brazil

The impact of forest clearance, and its replacement by Brachiaria pastures, on soil carbon reserves has been studied at many sites in the Brazilian Amazonia, but to date there appear to be no reports of similar studies undertaken in the Atlantic forest region of Brazil. In this study performed in the extreme south of Bahia, the changes in C and N content of the soil were evaluated from the time of establishment of grass-only B. humidicola and mixed B. humidicola/Desmodium ovalifolium pastures through 9 years of grazing in comparison with the C and N contents of the adjacent secondary forest. The decline in the content of soil C derived from the forest (C3) vegetation and the accumulation of that derived from the Brachiaria (C4) were followed by determining the 13C natural abundance of the soil organic matter (SOM). The pastures were established in 1987, 10 years after deforestation, and it was estimated that until 1994 there was a loss in forest-derived C in the top 30 cm of soil of approximately 20% (9.1 Mg C ha−1). After the establishment of the pastures, C derived from Brachiaria accumulated steadily such that at the final sampling (1997) it was estimated 13.9 Mg ha−1 was derived from this source under the grass-only pasture (0–30 cm). Samples taken from all pastures and the forest in 1997 to a depth of 100 cm showed that below 40 cm depth there was no significant contribution of the Brachiaria-derived C and that total C reserves under the grass/legume and the grass-only pastures were slightly higher than under the forest (not significant at P=0.05). The more detailed sampling under the pastures showed that to a depth of 30 cm there was significantly (P<0.05) more C under the mixed pasture than the grass-only pasture. It was estimated that from the time of establishment the apparent rate of C accumulation (0–100 cm depth) under the grass/legume pastures (1.17 Mg ha−1 yr−1) was almost double that under the grass-only pastures (0.66 Mg ha−1 yr−1). The data indicated that newly incorporated SOM derived from the Brachiaria had a considerably higher C:N ratio than that present under the forest