Maurício Roberto Cherubin

Soil carbon, nitrogen and phosphorus changes under sugarcane expansion in Brazil

Historical data of land use change (LUC) indicated that the sugarcane expansion has mainly displaced pasture areas in Central-Southern Brazil, globally the largest producer, and that those pastures were prior established over native forests in the Cerrado biome. We sampled 3 chronosequences of land use comprising native vegetation (NV), pasture (PA), and sugarcane crop (SC) in the sugarcane expansion region to assess the effects of LUC on soil carbon, nitrogen, and labile phosphorus pools. Thirty years after conversion of NV to PA, we found significant losses of original soil organic matter (SOM) from NV, while insufficient new organic matter was introduced from tropical grasses into soil to offset the losses, reflecting in a net C emission of 0.4 Mg ha(-1)yr(-1). These findings added to decreases in (15)N signal indicated that labile portions of SOM are preserved under PA. Afterwards, in the firsts five years after LUC from PA to SC, sparse variations were found in SOM levels. After more than 20 years of sugarcane crop, however, there were losses of 40 and 35% of C and N stocks, respectively, resulting in a rate of C emission of 1.3 Mg ha(-1)yr(-1) totally caused by the respiration of SOM from C4-cycle plants. In addition, conversion of pastures to sugarcane mostly increased (15)N signal, indicating an accumulation of more recalcitrant SOM under sugarcane. The microbe- and plant-available P showed site-specific responses to LUC as a function of different P-input managements, with the biological pool mostly accounting for more than 50% of the labile P in both anthropic land uses. With the projections of 6.4 Mha of land required by 2021 for sugarcane expansion in Brazil to achieve ethanols demand, this explanatory approach to the responses of SOM to LUC will contribute for an accurate assessment of the CO₂ balance of sugarcane ethanol.

Loss of soil (macro)fauna due to the expansion of Brazilian sugarcane acreage

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 (X(2)(1)=6.79, p=0.03) and taxa richness (X(2)(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.

Soil Quality Indexing Strategies for Evaluating Sugarcane Expansion in Brazil

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.

RESISTÊNCIA À PENETRAÇÃO, EFICIÊNCIA DE ESCARIFICADORES MECÂNICOS E PRODUTIVIDADE DA SOJA EM LATOSSOLO ARGILOSO MANEJADO SOB PLANTIO DIRETO DE LONGA DURAÇÃO

Frequently, soil compaction limits the yield of grain crops in mechanized lands, and its spatial distribution in the cropland is usually regionalized. In an area managed under long-term no-tillage, we investigated the relationship between soil penetration resistance (PR) and soybean yield, the effectiveness of types of chisel plows, and their effect on soybean yield. The soil from the plateau region of the state of Rio Grande do Sul, Brazil, was classified as a clayey Oxisol. The climate is subtropical (Cfa - Koppen classification), with annual rainfall of 1,750 mm and mean annual temperature of 18.7 oC. A completely randomized block experimental design was used with four treatments and two replications. The treatments, arranged in parallel strips of 100 × 20 m, were: a) site-specific chisel plow with variable depth according to soil penetration resistance (PR) (ESEV); b) conventional chisel plow (EC) with fixed depth; c) site-specific chisel plow with fixed depth (ESEF); d) control - without chisel plowing (SE). To evaluate PR, a digital penetrometer with georeferenced readings with a 50 × 50 m grid was used, with two evaluation periods. Soybean grain yield was obtained through a combine equipped with a yield sensor and GPS satellite receiver. A mean value of 1.4 MPa was observed for RP after cover crop management practices and a mean value of 2.1 after harvest. The RP reading after cover crop management and soybean grain yield exhibited poor correlation (r2 = -0.297; p<0.05). The PR values of 3.0 and 5.0 MPa resulted in decreases of approximately 10 and 38 % of soybean grain yields, respectively. Chisel plowing, regardless of the piece type of equipment used, did not increase soybean yield compared to the control without soil tillage. This result was attributed to the frequent rainfall and good physical and hydraulic conditions of long-term no-till.

Eficiência de malhas amostrais utilizadas na caracterização da variabilidade espacial de fósforo e potássio

The objective of the research was to evaluate the efficiency of the sampling grids, used in areas managed with precision agriculture, for the characterization of spatial variability levels of phosphorus (P) and potassium (K). The study was conducted in 30 agricultural areas, located in Rio Grande do Sul state, presenting soils classified as Oxisols. The sizes of the sampling grids studied were: 100x100m (10 areas), 142x142m (10 areas) and 173x173m (10 areas).Were analyzed the levels of P and K, in depth of sampling from 0.00-0.10m. The data were subjected to descriptive statistical analysis and geostatistical analysis. In, general, the areas showed average levels of P and K suitable for crops development. However, were observed subareas with low levels of P, justifying fertilization on site-specific. Based on geostatistical parameters, sizes of the sampling grids used are efficient to capture the different scales of spatial variability of P and K, however, it is indicated smaller sampling grids to consider the spatial variability over short distances.

Sampling grids used to characterise the spatial variability of pH, Ca, Mg and V% in Oxisols

Knowledge of spatial variability is an important factor to be considered in planning a program of soil sampling and crop management under precision agriculture (PA). In this context, the aim of this work was to evaluate the efficiency of the dimensions of sampling grids used in the state of Rio Grande do Sul (RS), Brazil to characterise the spatial variability of the attributes pHwater, base saturation (V%), calcium (Ca) and magnesium (Mg) levels. The study was carried out on 30 agricultural sites located in the northern region of RS, having soils classified as Oxisols and managed using the tools of PA. The dimensions of the grids under study were: 100 x 100 m (10 areas), 142 x 142 m (10 areas) and 173 x 173 m (10 areas). Soil was collected at a depth of 0.00 to 0.10 m. The data for pHwater, V%, Ca and Mg were subjected to exploratory statistical analysis and to geostatistical analysis by means of semivariograms. The areas showed high Ca (>4.0 cmolc dm-3) and Mg (>1.0 cmolc dm-3) levels and localised problems of soil acidity (pHwater <5.5 or V<65%), justifying the carrying out of liming at specific sites. For the geostatistical procedures, the sample grids used at the sites of the Oxisols managed under PA in RS are not efficient in capturing the scales of spatial variability of the attributes pHwater, V%, Ca and Mg, which could compromise the accuracy of corrective prescriptions for specific sites.

Changes in a Rhodic Hapludox under no-tillage and urban waste compost in the northwest of Rio Grande do Sul, Brazil

The use of urban waste compost as nutrient source in agriculture has been a subject of investigation in Brazil and elsewhere, although the effects on soil physical and chemical properties and processes are still poorly known. The aim of this study was to evaluate the effect of application of urban waste compost and mineral fertilizer on soil aggregate stability and organic carbon and total nitrogen content of a Rhodic Hapludox under no-tillage in the northwestern region of Rio Grande do Sul, Brazil, in the 2009/2010 and 2010/2011 growing seasons. The experiment was arranged in a 2 × 6 (seasons and fertilization) factorial in a randomized complete block design with four replications. The factor time consisted of two growing seasons (sunflower in 2009/10 and maize in 2010/11) and the factor fertilization of five rates of urban waste compost (0, 25, 50, 75 and 100 m3 ha-1), and mineral fertilizer. Soil samples were collected from the 0.0-0.10 m layer to determine aggregate stability (mean weight and geometric diameter), soil organic carbon (SOC) and total nitrogen (TN). Rates of up to 75 m3 ha-1 of urban waste compost, after two years of application to no-tillage maize and sunflower, improved aggregation compared to mineral fertilization in a Rhodic Hapludox. After the second crop, the SOC and TN contents increased linearly with the levels of urban waste compost.

Sugar cane straw left in the field during harvest: decomposition dynamics and composition changes

The understanding of sugar cane straw decomposition dynamics is essential for defining a sustainable rate of straw removal for bioenergy production without jeopardising soil functioning and other ecosystem services. Thus, we conducted a field study in south-east Brazil over 360 days to evaluate sugar cane straw decomposition and changes in its composition as affected by increasing initial straw amounts and management practices. The sugar cane straw amounts tested were: (1) 3.5 Mg ha–1 (i.e. 75% removal); (2) 7.0 Mg ha–1 (i.e. 50% removal); (3) 14.0 Mg ha–1 (i.e. no removal); and (4) 21.0 Mg ha–1 (i.e. no removal plus 50% of the extra straw left on the field). In addition, two management practices were studied for the reference straw amount (14 Mg ha–1), namely straw incorporation into the soil and irrigation with vinasse. The findings showed that dry mass (DM) loss increased logarithmically as a function of the initial amount left on the soil surface. An exponential curve efficiently described straw DM and C losses, in which more readily decomposable compounds are preferably consumed, leaving compounds that are more recalcitrant in the late stages of decomposition. After 1 year of decomposition, net straw C and N losses reached approximately 70% and 23% respectively for the highest initial straw amounts. Straw incorporation in the soil significantly accelerated the decomposition process (i.e. 86% DM loss after 1 year) compared with maintenance of straw on the soil surface (65% DM loss after 1 year), whereas irrigation with vinasse had little effect on decomposition (60% DM loss after 1 year). We conclude that straw decomposition data are an essential starting point for a better understanding of the environmental effects caused by straw removal and other management practices in sugar cane fields. This information can be used in models and integrated assessments towards a more sustainable sugar cane straw management for bioenergy production.

Assessing the greenhouse gas emissions of Brazilian soybean biodiesel production.

Soybean biodiesel (B100) has been playing an important role in Brazilian energy matrix towards the national bio-based economy. Greenhouse gas (GHG) emissions is the most widely used indicator for assessing the environmental sustainability of biodiesels and received particular attention among decision makers in business and politics, as well as consumers. Former studies have been mainly focused on the GHG emissions from the soybean cultivation, excluding other stages of the biodiesel production. Here, we present a holistic view of the total GHG emissions in four life cycle stages for soybean biodiesel. The aim of this study was to assess the GHG emissions of Brazilian soybean biodiesel production system with an integrated life cycle approach of four stages: agriculture, extraction, production and distribution. Allocation of mass and energy was applied and special attention was paid to the integrated and non-integrated industrial production chain. The results indicated that the largest source of GHG emissions, among four life cycle stages, is the agricultural stage (42–51%) for B100 produced in integrated systems and the production stage (46–52%) for B100 produced in non-integrated systems. Integration of industrial units resulted in significant reduction in life cycle GHG emissions. Without the consideration of LUC and assuming biogenic CO2 emissions is carbon neutral in our study, the calculated life cycle GHG emissions for domestic soybean biodiesel varied from 23.1 to 25.8 gCO2eq. MJ-1 B100 and those for soybean biodiesel exported to EU ranged from 26.5 to 29.2 gCO2eq. MJ-1 B100, which represent reductions by 65% up to 72% (depending on the delivery route) of GHG emissions compared with the EU benchmark for diesel fuel. Our findings from a life cycle perspective contributed to identify the major GHG sources in Brazilian soybean biodiesel production system and they can be used to guide mitigation priority for policy and decision-making. Projected scenarios in this study would be taken as references for accounting the environmental sustainability of soybean biodiesel within a domestic and global level.

Phytosociological variability of weeds in soybean field

Understanding spatial distribution of weeds in the crop enables to perform localized herbicide applications, increasing the technical and economic efficiency of operations and reducing environmental impacts. This work aimed to characterize the spatial and phytosociological variability of weeds occurring in soybean commercial field. It was conducted in an agricultural area located at the municipality of Boa Vista das Missoes - RS, during the 2010/2011 harvest season. The area, that had been managed under no-tillage with soybean monoculture (summer) for five years, was divided in regular squares of 50 x 50 m (0.25 ha), totalizing 356 points. For species identification, 0.5 x 0.5 m sample squares were used. During the survey, 1,739 individuals were identified, distributed in 19 species of 13 families. The weed species Cardiospermum halicacabum, Digitaria horizontalis, Urochloa plantaginea and Raphanus raphanistrum showed the highest population variation in the area; however, only C. halicacabum, U. plantaginea and R. raphanistrum stood out based on the Importance Index Value (IVI). Localized management strategies considering the spatial variability of weed species placed in the Magnoliopsidas and Liliopsidas group show a high potential for use in soybean crop. The results show that the sampling method through regular grid was capable of characterizing the occurrence, population density and spatial variability of weed species in soybean crop.