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Estimates of above-ground biomass and nutrient accumulation in Mimosa scabrella fallows in Southern Brazil

by Somarriba, E; Kass, D.
Publisher: 2001ISSN: 0167-4366.Subject(s): MIMOSA SCABRELLA | CULTIVO MIXTO | PHASEOLUS VULGARIS | ZEA MAYS | AGROFORESTERIA | REGENERACION NATURAL | BARBECHO | ACLAREO | CONTENIDO DE MATERIA SECA | AGROFORESTERIA | AGRICULTURA TRADICIONAL | NUTRIENTES | SUELO | SIMULACION | BRASIL | MIMOSA SCABRELLA | MIXED CROPPING | PHASEOLUS VULGARIS | ZEA MAYS | AGROFORESTRY | NATURAL REGENERATION | FALLOW | THINNING | DRY MATTER CONTENT | AGROFORESTRY | TRADITIONAL FARMING | NUTRIENTS | SOIL | SIMULATION | BRAZIL | MIMOSA SCABRELLA | CULTURE EN MELANGE | PHASEOLUS VULGARIS | ZEA MAYS | AGROFORESTERIE | REGENERATION NATURELLE | JACHERE | ECLAIRCISSAGE | TENEUR EN MATIERE SECHE | AGROFORESTERIE | AGRICULTURE TRADITIONNELLE | SUBSTANCE NUTRITIVE | SOL | SIMULATION | BRESIL | IMPROVED FALLOW | NUTRIENT CONCENTRATIONS | ABOVEGROUND BIOMASS | SELF-THINNING | TREE INVENTORY | STAND AGE | SEQUENTIAL SYSTEMOnline Resources: En In: Agroforestry Systems (Países Bajos) v. 51(2) p. 77-84Summary: Naturally regenerated stands of bracatinga (Mimosa scabrella Bentham) are harvested for firewood after six to eight years of unregulated growth, debris burnt and the area planted to one cycle of intercropped maize (Zea mays L.) and beans (Phaseolus vulgaris L.). Burning breaks dormancy of bracatinga seed (> 80 percent germination) marking the onset of a new fallow-crop cycle. This production system has been practiced for nearly 100 years in Southern Brazil, covering some 60,000 ha in 3,000 small farms. An estimation of above-ground biomass and nutrient accumulation was made using literature data on stand age, population numbers, tree sizes, tree biomass partitioning and concentration of major nutrients in tree tissues. A simple simulation model, used to quantify above-ground nutrient pathways and their temporal dynamics, confirmed that six to eight years is the optimal rotation length. Biomass and nutrients deposited onto the soil, peak at stand age six years, which may result in significant soil fertility improvement prior to crop planting. At year six, estimated total above-ground biomass amounts to 83 Mg ha-1Summary: 44 Mg ha-1Summary: available as firewood and 39 Mg ha-1Summary: to be returned to the soil. Roughly half the amount of nutrients fixed in the above-ground bracatinga biomass would be exported in firewood and subsequent grain crops.
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Naturally regenerated stands of bracatinga (Mimosa scabrella Bentham) are harvested for firewood after six to eight years of unregulated growth, debris burnt and the area planted to one cycle of intercropped maize (Zea mays L.) and beans (Phaseolus vulgaris L.). Burning breaks dormancy of bracatinga seed (> 80 percent germination) marking the onset of a new fallow-crop cycle. This production system has been practiced for nearly 100 years in Southern Brazil, covering some 60,000 ha in 3,000 small farms. An estimation of above-ground biomass and nutrient accumulation was made using literature data on stand age, population numbers, tree sizes, tree biomass partitioning and concentration of major nutrients in tree tissues. A simple simulation model, used to quantify above-ground nutrient pathways and their temporal dynamics, confirmed that six to eight years is the optimal rotation length. Biomass and nutrients deposited onto the soil, peak at stand age six years, which may result in significant soil fertility improvement prior to crop planting. At year six, estimated total above-ground biomass amounts to 83 Mg ha-1

44 Mg ha-1

available as firewood and 39 Mg ha-1

to be returned to the soil. Roughly half the amount of nutrients fixed in the above-ground bracatinga biomass would be exported in firewood and subsequent grain crops.

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