Effects of different land use systems in carbon, nitrogen and phosphorus cycles: comparison between slash-and-burn and chop-and-mulch systems.
Roberta
de Fátima Rodrigues
Coelho, Bolsista DTI CNPQ/LBA, robpantoja@hotmail.com
André Luiz
Cote
Roman, Bolsista Programa SHIFT, coteroman@yahoo.com.br
Cláudio José
Reis de Carvalho, Embrapa Amazônia Oriental, carvalho.bel@terra.com.br
Ricardo
de O.
Figueiredo, Embrapa Amazônia Oriental, ricardo@cpatu.embrapa.br
(Presenting)
Tatiana
Deane de Abreu
Sá, Embrapa Amazônia Oriental, tatiana@cpatu.embrapa.br
Danielle
Santos
Fontenelle, Bolsista ITI, CNPQ/LBA, dfagro@hotmail.com
In the traditional system of small-scale agriculture in Eastern Amazonia, land preparation prior to cropping is done by slashing and burning the fallow vegetation, to have access to nutrients, mainly phosphorus (P), from the ashes. With the intensification of land use the fallow period has been shortened, affecting consequently the biogeochemical functions of secondary vegetation, leading to its degradation. The alternative system, chop-and-mulch of the fallow vegetation, associated to the improvement of the fallow vegetation by planting fast growing leguminous trees, appears as an option to shorten the fallow period, increasing carbon accumulation (including soil organic matter) and nutrient cycling, while keeping the fallow vegetation roots which act as a barrier to nutrient leaching. The consequences of burning to biogeochemical processes have been reasonably studied, but little is known about the impact on carbon and nutrients accumulation derived from the mulch, and on the mineralization or fixation promoted by the soil biota. To study these processes two plots (2 ha each) were set up with the following treatments: i) traditional slash-and-burn system; ii) alternative chop-and-mulch system (with fertilizer application). In both maize and cassava were cropped followed by a fallow phase (improved by planting two leguminous tree species in the alternative system). We are evaluating: microbial biomass, C and N, activity of enzymes associated to N and P mineralization, organic carbon accumulation and soil organic matter, NH4+, NO3- and P availability, and organic P species, as well as vesicular arbuscular mychorrhizas (VAM) activity. Two years after land preparation, the results show that the measured variables in the alternative system seem to be closer to what is found in the original secondary vegetation.