Search

Copyright of Revista Caatinga is the property of Revista Caatinga and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Important among global issues is the trilemma of abrupt climate change, food insecurity, and environmental degradation. Despite the increasing use of fossil fuel, about one third of global C emissions come from tropical deforestation and indiscriminate use of agricultural practices. Global food insecurity, affecting one in seven persons, aggravates environmental degradation. The importance of judicious land use and soil sustainability in addressing the trilemma cannot be overemphasized. While intensifying agronomic production on existing land, it is also essential to identify suitable eco-regions for bringing new land under production. Based on 35-years of data from Brazil, we report that C emissions from agroecosystems are 4 to 5.5 times greater by bringing new land under production in Amazon than in the Cerrado for pastures and cropland production, respectively. The data presented indicate that agricultural intensification is feasible in the Cerrado, and the forest in Rondônia and Mato Grosso states must be protected and restored for nature conservancy. Now is the time to think beyond COP 21—Paris 2015 and take concrete actions to address these issues of global significance. [ABSTRACT FROM AUTHOR]

In Brazil, sugarcane expansion for ethanol production has been predominantly on areas previously used as pasture. Losses of C and N induced by land use change raise controversies about the environmental suitability of biofuel production. Therefore, we conducted a field study within the largest sugarcane-producing region of Brazil to evaluate the effects of the primary land use change (LUC) sequence in sugarcane expansion areas (i.e., native vegetation to pasture to sugarcane), on C and N dynamics in the top 1 m soil layer. The LUC sequences caused substantial but varying changes in soil C and N stocks in areas undergoing expansion of sugarcane in south-central Brazil. The increase of C stocks in areas converted from pasture to sugarcane cultivation was 1.97 Mg ha −1 yr −1 , in contrast to conversion of native vegetation to pasture, which decreased soil C stocks by 1.01 Mg ha −1 yr −1 for 0–1.0 m soil layer. The use of 13 C measurements to partition soil C sources showed that the greater C stocks in sugarcane areas compared to pasture was due to retention of the native-C stocks and increased accrual of modern-C comparing to pasture. Finally, the inclusion of deeper soil layers, at least down to 1.0 m depth, is essential to assess the impacts of LUC on C balances in agricultural areas. [ABSTRACT FROM AUTHOR]

Southern Amazonia harbors the largest agricultural frontier worldwide, where native vegetation has been converted to agriculture. Land use change in this region compromises deforestation as well as changes in agricultural management intensity (e.g. liming, fertilization, and number of crops) that shapes plant cover and soil chemistry. Our objective was to investigate the effects of these changes on soil bacterial community structure (i.e. community composition based on T-RFLP profiles of 16S rRNA and abundance of functional groups related to C and N cycling). Two representative agricultural regions within the biomes rainforest and Cerrado were chosen, each spanning land uses from native vegetation to pasture and soybean fields, and three replicated sites sampled for each land use type/region. Soil chemical alterations concurrent with land use changes to agriculture included increases in soil pH, Ca, Mg, P, K, and N concentrations, and easily decomposable litter. These alterations influenced bacterial community structure by changing both, community composition and functional gene abundance, findings supported by redundancy analysis and principal components analysis. Confirming one of our working hypotheses, based on the 16S rRNA gene, bacterial richness did not decrease from pristine vegetation to agricultural uses, but its composition shifted with land use change. In addition, a change in the abundance of microbial functional groups related to the production of the greenhouse gases N 2 O (denitrifiers, nosZ ), and CH 4 (methanogens, mcrA and methanotrophs, pmoA ) reflected the influence of land use change in samples from both biomes. In accordance with our second hypothesis, the management intensive soybean soils exhibited the most distinct chemical (higher pH and nutrient levels) and microbiological profiles, including a significant decrease of the functional genes tested. In conclusion, our results identify land use intensity (namely its alterations in soil pH, C, litter degradability, pesticides and nutrient levels) as the driver for soil bacterial community structure (T-RFLP composition of 16S rRNA genes and functional gene abundance) in the studied samples. These formed a gradient of land use change consequences from native vegetation, to pasture and then to the soybean areas, which presented the most distinct chemical and bacterial profiles. [ABSTRACT FROM AUTHOR]

Highlights: [•] IPCC-based soil carbon stock methodology verified for Amazon and Cerrado biomes. [•] Meta-analysis of SOC change promotes adoption of no-tillage practices. [•] Clay content shown to influence SOC changes. [•] Conservation systems have potential for sequestering SOC in the Cerrado biome. [•] IPCC-based approach shown to be more robust and a sensitive way to evaluate SOC changes. [Copyright &y& Elsevier]

Abstract: Changes in land use can result in either sources or sinks of atmospheric carbon (C), depending on management practices. In Brazil, significant changes in land use result from the conversion of native vegetation to pasture and agriculture, conversion of pasture to agriculture and, more recently, the conversion of pasture and agriculture to integrated crop-livestock systems (ICL). The ICL system proposes a diversity of activities that include the strategic incorporation of pastures to agriculture so as to benefit both. In agricultural areas, for example, the implementation of ICL requires the production of quality forage for animals between crops as well as the production of straw to facilitate the sustainability of the no-tillage (NT) management system. The objective of this study was to evaluate the modifications in soil C stocks resulting from the main processes involved in the changes of land use in Amazonia and Cerrado biomes. For comparison purposes, areas under native vegetation, pastures, crop succession and ICL under different edapho-climatic conditions in Amazonia and Cerrado biomes were evaluated. This study demonstrated that the conversion of native vegetation to pasture can cause the soil to function either as a source or a sink of atmospheric CO2, depending on the land management applied. Non-degraded pasture under fertile soil showed a mean accumulation rate of 0.46gha−1 year−1. Carbon losses from pastures implemented in naturally low fertile soil ranged from 0.15 to 1.53Mgha−1 year−1, respectively, for non-degraded and degraded pasture. The conversion of native vegetation to agriculture in areas under the ICL system, even when cultivated under NT, resulted in C losses of 1.31 in six years and of 0.69Mgha−1 in 21 years. The conversion of a non-degraded pasture to cropland (soybean/sorghum) released, in average, 1.44 Mg of C ha−1year−1to the atmosphere. The ICL system in agricultural areas has shown evidences that it always functions as a sink of C with accumulation rates ranging from 0.82 to 2.58Mgha−1 year−1. The ICL produces soil C accumulation and, as a consequence, reduces atmospheric CO2 in areas formerly cultivated under crop succession. However, the magnitude of C accumulation in soil depends on factors such as the types of crops, the edapho-climatic conditions and the amount of time the area is under ICL. [Copyright &y& Elsevier]