Burning sugarcane leaves and tops on standing mature crops has been practiced for centuries in Brazil, in order to facilitate the harvest, transportation and processing of sugarcane stalks. ...Currently, due to economic, environmental and legal reasons, the unburned harvest, with residues left on the soil, has been increasingly adopted. There is little information, though, about the effects of the addition of sugarcane trash on the soil carbon dynamics of the sugarcane crop. The objective of this study was to evaluate the effect of trash management on carbon dynamics of the sugarcane crop. The study area is located in the São Martinho farm, in Pradópolis, São Paulo, in Southeastern Brazil. Two chronosequences were studied, in plots where sugarcane had been replanted 2, 6 and 8 years before the soil samplings, with and without pre-harvest burning. An area of native vegetation adjacent to the sugarcane fields was also sampled, as a reference. The soil in the area is classified as a clayey Oxisol. The soil samples were analyzed for bulk density, sand, silt and clay content, total carbon, carbon in the particulate organic matter and microbial biomass carbon. The soil microbial biomass carbon and the particulate organic matter carbon were more sensitive to residue management changes than total carbon. The area with the longest period of adoption of the unburned management, 8 years, had higher contents of total carbon (30% higher), microbial biomass carbon (by a factor of 2.5), and particulate organic matter carbon (by a factor of 3.8) than the area where the residues were burned. The total carbon stocks were also higher in the unburned treatment, markedly in the area with 8 years of green cane management.
Increasing demand for biofuel has intensified land-use change (LUC) for sugarcane (Saccharum officinarum) expansion in Brazil. Assessments of soil quality (SQ) response to this LUC are essential for ...quantifying and monitoring sustainability of sugarcane production over time. Since there is not a universal methodology for assessing SQ, we conducted a field-study at three sites within the largest sugarcane-producing region of Brazil to develop a SQ index (SQI). The most common LUC scenario (i.e., native vegetation to pasture to sugarcane) was evaluated using six SQI strategies with varying complexities. Thirty eight soil indicators were included in the total dataset. Two minimum datasets were selected: one using principal component analysis (7 indicators) and the other based on expert opinion (5 indicators). Non-linear scoring curves were used to interpret the indicator values. Weighted and non-weighted additive methods were used to combine individual indicator scores into an overall SQI. Long-term conversion from native vegetation to extensive pasture significantly decreased overall SQ. In contrast, conversion from pasture to sugarcane had no significant impact on overall SQ at the regional scale, but site-specific responses were found. In general, sugarcane production improved chemical attributes (i.e., higher macronutrient levels and lower soil acidity); however it has negative effects on physical and biological attributes (i.e., higher soil compaction and structural degradation as well as lower soil organic carbon (SOC), abundance and diversity of macrofauna and microbial activity). Overall, we found that simple, user-friendly strategies were as effective as more complex ones for identifying SQ changes. Therefore, as a protocol for SQ assessments in Brazilian sugarcane areas, we recommend using a small number of indicators (e.g., pH, P, K, Visual Evaluation of Soil Structure -VESS scores and SOC concentration) and proportional weighting to reflect chemical, physical and biological processes within the soil. Our SQ evaluations also suggest that current approaches for expanding Brazilian sugarcane production by converting degraded pasture land to cropland can be a sustainable strategy for meeting increasing biofuel demand. However, management practices that alleviate negative impacts on soil physical and biological indicators must be prioritized within sugarcane producing areas to prevent unintentional SQ degradation over time.
Soil tillage and other methods of soil management may influence CO2 emissions because they accelerate the mineralization of organic carbon in the soil. This study aimed to quantify the CO2 emissions ...under conventional tillage (CT), minimum tillage (MT) and reduced tillage (RT) during the renovation of sugarcane fields in southern Brazil. The experiment was performed on an Oxisol in the sugarcane-planting area with mechanical harvesting. An undisturbed or no-till (NT) plot was left as a control treatment. The CO2 emissions results indicated a significant interaction (p < 0.001) between tillage method and time after tillage. By quantifying the accumulated emissions over the 44 days after soil tillage, we observed that tillage-induced emissions were higher after the CT system than the RT and MT systems, reaching 350.09 g m−2 of CO2 in CT, and 51.7 and 5.5 g m−2 of CO2 in RT and MT respectively. The amount of C lost in the form of CO2 due to soil tillage practices was significant and comparable to the estimated value of potential annual C accumulation resulting from changes in the harvesting system in Brazil from burning of plant residues to the adoption of green cane harvesting. The CO2 emissions in the CT system could respond to a loss of 80% of the potential soil C accumulated over one year as result of the adoption of mechanized sugarcane harvesting. Meanwhile, soil tillage during the renewal of the sugar plantation using RT and MT methods would result in low impact, with losses of 12% and 2% of the C that could potentially be accumulated during a one year period.
Agricultural management practices that promote net carbon (C) accumulation in the soil have been considered as an important potential mitigation option to combat global warming. The change in the ...sugarcane harvesting system, to one which incorporates C into the soil from crop residues, is the focus of this work. The main objective was to assess and discuss the changes in soil organic C stocks caused by the conversion of burnt to unburnt sugarcane harvesting systems in Brazil, when considering the main soils and climates associated with this crop. For this purpose, a dataset was obtained from a literature review of soils under sugarcane in Brazil. Although not necessarily from experimental studies, only paired comparisons were examined, and for each site the dominant soil type, topography and climate were similar. The results show a mean annual C accumulation rate of 1.5 Mg ha⁻¹ year⁻¹ for the surface to 30-cm depth (0.73 and 2.04 Mg ha⁻¹ year⁻¹ for sandy and clay soils, respectively) caused by the conversion from a burnt to an unburnt sugarcane harvesting system. The findings suggest that soil should be included in future studies related to life cycle assessment and C footprint of Brazilian sugarcane ethanol.
The introduction of crop management practices after conversion of Amazon Cerrado into cropland influences soil C stocks and has direct and indirect consequences on greenhouse gases (GHG) emissions. ...The aim of this study was to quantify soil C sequestration, through the evaluation of the changes in C stocks, as well as the GHG fluxes (N
2O and CH
4) during the process of conversion of Cerrado into agricultural land in the southwestern Amazon region, comparing no-tillage (NT) and conventional tillage (CT) systems. We collected samples from soils and made gas flux measurements in July 2004 (the dry season) and in January 2005 (the wet season) at six areas: Cerrado, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT), in each case after a 2-year period of rice under CT. Soil samples were analyzed in both seasons for total organic C and bulk density. The soil C stocks, corrected for a mass of soil equivalent to the 0–30-cm layer under Cerrado, indicated that soils under NT had generally higher C storage compared to native Cerrado and CT soils. The annual C accumulation rate in the conversion of rice under CT into soybean under NT was 0.38
Mg
ha
−1
year
−1. Although CO
2 emissions were not used in the C sequestration estimates to avoid double counting, we did include the fluxes of this gas in our discussion. In the wet season, CO
2 emissions were twice as high as in the dry season and the highest N
2O emissions occurred under the NT system. There were no CH
4 emissions to the atmosphere (negative fluxes) and there were no significant seasonal variations. When N
2O and CH
4 emissions in C-equivalent were subtracted (assuming that the measurements made on 4 days were representative of the whole year), the soil C sequestration rate of the conversion of rice under CT into soybean under NT was 0.23
Mg
ha
−1
year
−1. Although there were positive soil C sequestration rates, our results do not present data regarding the full C balance in soil management changes in the Amazon Cerrado.
•We compute rates of soil C accumulation under no-tillage management.•We compare both the synchronic and diachronic approach.•More moderate rates of soil C accumulation were observed ...diachronically.•Results suggest that diachronic approach might be more conservative.
No-tillage (NT) practices with crop residue mulching are seen as an effective way to accumulate soil carbon (C). The rate of soil C accumulation can be determined by measuring soil C stocks over time (diachronic approach) or along a chronosequence that substitutes spatial history differences for time differences (synchronic approach). The objective of this communication is to compare the diachronic and synchronic approaches for determining the rates of soil C storage under NT in the Cerrado region of Brazil. In 2003 and 2007, soil C stocks (0–20cm) were determined in three NT fields with 5, 9 and 17 years of NT adoption in 2007 (NT-5, NT-9 and NT-17, respectively), one conventionally tilled field (CT, 30 years of tillage in 2007) and one native Cerrado plot (CE) in Rio Verde (Goiás state, Brazil). Soil C accumulation rates were calculated following both the synchronic and diachronic approach. Results from the synchronic approach showed that 30 years of cropping under CT depleted the soil C stock to 34.4MgCha−1, which is a decrease of about 27% of the original levels observed under the native vegetation (CE, 47.1 and 47.3MgCha−1, respectively, in 2003 and 2007). Instead, NT adoption had been accumulating soil C through the evaluated years. Soil C stocks measured under NT areas in 2003 and 2007 were 29.9 and 31.3MgCha−1 (NT-5), 33.4 and 34.4MgCha−1 (NT-9) and 45.8 and 46.4MgCha−1 (NT-17), respectively. Much more moderate rates of soil C accumulation were observed diachronically (0.12–0.28MgCha−1year−1) than with the synchronic approach (1.33 and 1.27MgCha−1year−1 in 2003 and 2007, respectively). Soil C stocks under CE between 2003 and 2007 (in the diachronic approach) did not change, indicating that diachronic measurements were accurate. Thus, it appears to be very difficult to eliminate all non-wanted sources of soil C variation (i.e. soil texture, land-use history) analysing the soil C accumulation in a chronosequence (synchronic approach). In spite of a time span of years between sampling dates, our results suggest the need for using the diachronic approach when assessing soil C changes under altering land-use or management patterns. Increasing the number of diachronic assessments may also help the parameterization of process-oriented models for exploring the effects of no-tillage systems on soil C storage rates more accurately.
Land use changes (LUC) from pasture to sugarcane (Saccharum spp.) crop are expected to add 6.4Mha of new sugarcane land by 2021 in the Brazilian Cerrado and Atlantic Forest biomes. We assessed the ...effects of these LUC on the abundance and community structure of animals that inhabit soils belowground through a field survey using chronosequences of land uses comprising native vegetation, pasture, and sugarcane along a 1000-km-long transect across these two major tropical biomes in Brazil. Macrofauna community composition differed among land uses. While most groups were associated with samples taken in native vegetation, high abundance of termites and earthworms appeared associated with pasture soils. Linear mixed effects analysis showed that LUC affected total abundance (X2(1)=6.79, p=0.03) and taxa richness (X2(1)=6.08, p=0.04) of soil macrofauna. Abundance increased from 411±70individualsm−2 in native vegetation to 1111±202individualsm−2 in pasture, but decreased sharply to 106±24individualsm−2 in sugarcane soils. Diversity decreased 24% from native vegetation to pasture, and 39% from pasture to sugarcane. Thus, a reduction of ~90% in soil macrofauna abundance, besides a loss of ~40% in the diversity of macrofauna groups, can be expected when sugarcane crops replace pasture in Brazilian tropical soils. In general, higher abundances of major macrofauna groups (ants, coleopterans, earthworms, and termites) were associated with higher acidity and low contents of macronutrients and organic matter in soil. This study draws attention for a significant biodiversity loss belowground due to tropical LUC in sugarcane expansion areas. Given that many groups of soil macrofauna are recognized as key mediators of ecosystem processes such as soil aggregation, nutrients cycling and soil carbon storage, our results warrant further efforts to understand the impacts of altering belowground biodiversity and composition on soil functioning and agriculture performance across LUC in the tropics.
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•We examined the soil macrofaunal community responses to sugarcane expansion from pasturelands.•Macrofaunal abundance decreases 89% and diversity of macrofauna groups deceases 39% when sugarcane replaces pasture.•Termites and earthworms largely dominate the macrofaunal community in PA soils.•Ants and coleopteran insects become the most abundant groups when land use is changed to SC.•This study draws attention for a significant biodiversity loss belowground due to bioenergy crop expansion in the tropics.
Currently there is a trend for the expansion of the area cropped with sugarcane (Saccharum officinarum L.), driven by an increase in the world demand for biofuels, due to economical, environmental, ...and geopolitical issues. Although sugarcane is traditionally harvested by burning dried leaves and tops, the unburned, mechanized harvest has been progressively adopted. The use of process based models is useful in understanding the effects of plant litter in soil C dynamics. The objective of this work was to use the CENTURY model in evaluating the effect of sugarcane residue management in the temporal dynamics of soil C. The approach taken in this work was to parameterize the CENTURY model for the sugarcane crop, to simulate the temporal dynamics of soil C, validating the model through field experiment data, and finally to make predictions in the long term regarding soil C. The main focus of this work was the comparison of soil C stocks between the burned and unburned litter management systems, but the effect of mineral fertilizer and organic residue applications were also evaluated. The simulations were performed with data from experiments with different durations, from 1 to 60 yr, in Goiana and Timbaúba, Pernambuco, and Pradópolis, São Paulo, all in Brazil; and Mount Edgecombe, Kwazulu-Natal, South Africa. It was possible to simulate the temporal dynamics of soil C (R2 = 0.89). The predictions made with the model revealed that there is, in the long term, a trend for higher soil C stocks with the unburned management. This increase is conditioned by factors such as climate, soil texture, time of adoption of the unburned system, and N fertilizer management.
Since 2000, the southwestern Brazilian Amazon has undergone a rapid transformation from natural vegetation and pastures to row-crop agricultural with the potential to affect regional biogeochemistry. ...The goals of this research are to assess wavelet algorithms applied to MODIS time series to determine expansion of row-crops and intensification of the number of crops grown. MODIS provides data from February 2000 to present, a period of agricultural expansion and intensification in the southwestern Brazilian Amazon. We have selected a study area near Comodoro, Mato Grosso because of the rapid growth of row-crop agriculture and availability of ground truth data of agricultural land-use history. We used a 90% power wavelet transform to create a wavelet-smoothed time series for five years of MODIS EVI data. From this wavelet-smoothed time series we determine characteristic phenology of single and double crops. We estimate that over 3200 km
2 were converted from native vegetation and pasture to row-crop agriculture from 2000 to 2005 in our study area encompassing 40,000 km
2. We observe an increase of 2000 km
2 of agricultural intensification, where areas of single crops were converted to double crops during the study period.
Brazilian farms produce 15% of the world׳s beef, and consequently they are important sources of greenhouse gases (GHG). The beef sector faces the challenge to meet the increasing demand without ...further increase of GHG emissions. To reduce the pressure on forests it is essential that farmers are provided with sustainable options of intensification of pasture growth and cattle production. The improvement of the whole-farm beef production system is essential to reduce emissions from all relevant sources, like land use, land use change and livestock. The main objective was to quantify the GHG gas emissions of different beef production systems in Brazil. Therefore we developed a whole farm model that allowed us to calculate GHG emissions from all-important sources (only “on-farm” i.e., not considering emissions from the production of fertilizer, lime or other inputs) for a beef production system in Brazil. We studied the effects of intensification in several steps, starting with a baseline extensive system, followed by four steps of intensification. The main differences between the scenarios are related to pasture management, i.e. continuous or rotational grazing, pasture condition, stocking rate, use of lime and fertilizer, and irrigation; and animal performance, i.e. calving interval, age at first calving, conception rate, total life time until slaughter, and genetic improvement. Compared to the baseline extensive scenario, the total pasture area decreased up to 92% in the most intensified system, while beef production nearly doubled. Intensification increased the number of calves, steers and heifers decreased the total production cycle time and the slaughter age of the steers. Overall, the emission of kgCO2eqkgcarcass−1 was lower with increasing intensification, with an average of 41kgCO2eqkgcarcass−1. The emissions of CH4 decreased, while the emissions of N2O and CO2 increased due to nitrogen fertilizer and lime application. The intensification of beef production, through improved pasture and herd management, reduced the GHG emissions per kg of beef from 2% to 57%. The complete cycle of beef production in intensified systems required less time (years) and area (ha), and may thus help to alleviate the pressure on forests.
•The intensification of beef production reduces the GHG emissions per unit of beef•Results showed that the decrease in CH4 emission outweighs the increase of N2O and CO2 from application of nitrogen fertilizer and lime.•The beef production in intensified systems required less time and area.•The intensification steps simulated in this study can be considered as combined sets of mitigation options.
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