Search

Agricultural activities in the state of Rio Grande do Sul (RS), southern Brazil, have traditionally been quite intensive and led to decreased overall soil quality, and to depletion of soil organic matter and nutrients. There have been attempts at restoring soil quality by using integrated crop–livestock systems (ICLS). ICLS in association with no-tillage (NT) potentially increase soil organic matter content and nutrient supplies. The aim of this work was to assess the influence of grazing intensity in three different treatments [viz., intensive grazing (IG), moderate grazing (MG) and no grazing (NG)] on the mineralogy of an Oxisol in an integrated soybean–cattle beef production system in southern Brazil by using various types of methods and tests. Mineralogical XRD analyses of the clay fraction (< 2 μm) showed it to consist mainly of kaolinite and 2:1 clay minerals of the hydroxy-interlayered mineral (HIM) type. The reflections for 2:1 clay minerals under the IG treatment were better defined than those for the minerals under NG, which suggests the prevalence of HIMs. The 2:1 clay minerals in the IG group exhibited expandable layers. Splitting the clay fraction into three subfractions according to size (< 0.05 μm, 0.05–0.1 μm and 0.1–2 μm) exposed considerable alterations. Thus, hydroxy-aluminum interlayered vermiculite (HIV-Al) was present irrespective of treatment. Also, the HIV-Al reflection was better defined under IG and MG than under NG, which suggests strong aluminization of 2:1 clay minerals. Chemical analyses revealed a decrease in total organic carbon (TOC) with increasing depth in all treatments. The decrease was especially marked under NG by effect of the absence of animals favoring accumulation of plant shoots. pH water was higher under IG as a result of the removal of aluminum from the soil solution increased aluminization of 2:1 clay minerals. K concentrations in solution were low under IG as a result of the formation of HIMs and/or swelling layers with exchangeable K; by contrast, solution K levels under NG where high owing to the absence of HIMs. The presence of animals, which increases K availability through animal wastes, may have resulted in competition between exchangeable K + and Al 3 + to form HIMs. Without splitting the clay fraction it would have been impossible to confirm the mineralogical alteration in 2:1 phyllosilicates due to the impact of ICLS systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Integrated crop–livestock systems in the Brazilian subtropics are highly diverse. [•] Livestock reduce the vulnerability of crops in rain-fed systems. [•] Crops in rotation with livestock may produce more. [•] Livestock improve many physical, chemical and biological attributes of soil. [•] Integrating crops and livestock is a unique approach to ecological intensification. [ABSTRACT FROM AUTHOR]

In this paper we calculated soil carbon stocks in Brazil studying 17 paired sites where soil stocks were determined in native vegetation, pastures and crop-livestock systems (CPS), and in other regional samplings encompassing more than 100 pasture soils, from 6.58 to 31.53° S, involving three major Brazilian biomes: Cerrado, Atlantic Forest, and the Pampa. The average native vegetation soil carbon stocks at 10, 30 and 60 cm soil depth were equal to approximately 29, 64, and 92Mgha-1, respectively. In the paired sites, carbon losses of 7.5Mgha-1 and 11.6Mgha-1 in CPS systems were observed at 10 cm and 30 cm soil depths, respectively. In pasture soils, carbon losses were similar and equal to 7.5Mgha-1 and 11.0Mgha-1 at 10 cm and 30 cm soil depths, respectively. Differences at 60 cm soil depth were not significantly different between land uses. The average soil δ13C under native vegetation at 10 and 30 cm depth were equal to -25.4‰ and -24.0 ‰, increasing to -19.6‰ and -17.7‰ in CPS, and to -18.9 ‰, and -18.3‰ in pasture soils, respectively; indicating an increasing contribution of C4 carbon in these agrosystems. In the regional survey of pasture soils, the soil carbon stock at 30 cm was equal to approximately 51Mg ha-1, with an average δ13C value of -19.6 ‰. Key controllers of soil carbon stock in pasture sites were sand content and mean annual temperature. Collectively, both could explain approximately half of the variance of soil carbon stocks. When pasture soil carbon stocks were compared with the average soil carbon stocks of native vegetation estimated for Brazilian biomes and soil types by Bernoux et al. (2002) there was a carbon gain of 6.7Mgha-1, which is equivalent to a carbon gain of 15% compared to the carbon soil stock of the native vegetation. The findings of this study are consistent with differences found between regional comparisons like our pasture sites and plot-level paired study sites in estimating soil carbon stocks changes due to land use changes. [ABSTRACT FROM AUTHOR]

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]

Forest corridors are often considered the main instrument with which to offset the effects of habitat loss and fragmentation. Brazilian forestry legislation requires that all riparian zones on private landholdings be maintained as permanent reserves and sets fixed minimum widths of riparian forest buffers to be retained alongside rivers and perennial streams. We investigated the effects of corridor width and degradation status of 37 riparian forest sites (including 24 corridors connected to large source-forest patches, 8 unconnected forest corridors, and 5 control riparian zones embedded within continuous forest patches) on bird and mammal species richness in a hyper-fragmented forest landscape surrounding Alta Floresta, Mato Grosso, Brazil. We used point-count and track-sampling methodology, coupled with an intensive forest-quality assessment that combined satellite imagery and ground truthed data. Vertebrate use of corridors was highly species-specific, but broad trends emerged depending on species life histories and their sensitivity to disturbance. Narrow and/or highly disturbed riparian corridors retained only a depauperate vertebrate assemblage that was typical of deforested habitats, whereas wide, well-preserved corridors retained a nearly complete species assemblage. Restriction of livestock movement along riparian buffers and their exclusion from key areas alongside deforested streams would permit corridor regeneration and facilitate restoration of connectivity. [ABSTRACT FROM AUTHOR]