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Sugarcane straw is a potential feedstock to increase bioenergy production. However, leaving straw on the soil surface is important to sustaining soil organic matter (SOM). We conducted a field experiment to evaluate the impacts of two years of straw removal on SOM in a sugarcane area--on an Eutric Nitisol in south-eastern Brazil--with low straw production (7 Mg [ha.sup.-1]). The experiment was a randomised complete block design (four blocks) with four rates of straw removal: (i) no removal, (ii) medium removal, (iii) high removal and (iv) total removal. We evaluated straw decomposition, soil carbon (C) and nitrogen (N) stock (0-30 cm), labile C, and microbial biomass C and N (0-10 cm). Increases in the straw removal rates reduced decomposition, with 30-42% of the initial straw amount remaining on the soil after one year (first year) and 33-38% remaining at the end of the second year. During the first year, no effect was found on soil C (8 kg [m.sup.-2]) and N (0.7 kg [m.sup.-2]) stocks; however, during the second year, total straw removal reduced soil C stock by 10% (0-30 cm) compared with no straw removal. Straw removal rates negatively affected the labile C (6-10% and 20-25%, first and second year respectively) and microbial C (correspondingly 10-15% and 21-27%). Microbial N was not altered in the first year, but decreased 26% due to straw maintenance (no removal) during the second year. Total straw removal decreased the C management index (CMI) by 15% (first year) compared with no straw removal. However, during the second year, all rates of straw removal decreased the CMI: by 15% for medium, 22% for high and 26% for total removal. Our findings indicate that any straw removal in areas with low straw production negatively affects SOM, initially through reduction in labile C pools. Although slight impacts on soil C and N stock were detected, reduction in straw-derived inputs stimulates microbial utilisation of soil C pools, and consequently reduces SOM over time. Keywords: carbon cycling, carbon mineralisation, crop residues, decomposition, soil organic carbon., Introduction Soils play a fundamental role in a large number of ecosystem services (Adhikari and Hartemink 2016; Pereira et at. 2018). The ability of soils to provide these services is [...]

Sugarcane straw is a potential feedstock to increase bioenergy production. However, leaving straw on the soil surface is important to sustaining soil organic matter (SOM). We conducted a field experiment to evaluate the impacts of two years of straw removal on SOM in a sugarcane area--on an Eutric Nitisol in south-eastern Brazil--with low straw production (7 Mg [ha.sup.-1]). The experiment was a randomised complete block design (four blocks) with four rates of straw removal: (i) no removal, (ii) medium removal, (iii) high removal and (iv) total removal. We evaluated straw decomposition, soil carbon (C) and nitrogen (N) stock (0-30 cm), labile C, and microbial biomass C and N (0-10 cm). Increases in the straw removal rates reduced decomposition, with 30-42% of the initial straw amount remaining on the soil after one year (first year) and 33-38% remaining at the end of the second year. During the first year, no effect was found on soil C (8 kg [m.sup.-2]) and N (0.7 kg [m.sup.-2]) stocks; however, during the second year, total straw removal reduced soil C stock by 10% (0-30 cm) compared with no straw removal. Straw removal rates negatively affected the labile C (6-10% and 20-25%, first and second year respectively) and microbial C (correspondingly 10-15% and 21-27%). Microbial N was not altered in the first year, but decreased 26% due to straw maintenance (no removal) during the second year. Total straw removal decreased the C management index (CMI) by 15% (first year) compared with no straw removal. However, during the second year, all rates of straw removal decreased the CMI: by 15% for medium, 22% for high and 26% for total removal. Our findings indicate that any straw removal in areas with low straw production negatively affects SOM, initially through reduction in labile C pools. Although slight impacts on soil C and N stock were detected, reduction in straw-derived inputs stimulates microbial utilisation of soil C pools, and consequently reduces SOM over time. Keywords: carbon cycling, carbon mineralisation, crop residues, decomposition, soil organic carbon. Received 11 January 2020, accepted 8 September 2020, published online 14 October 2020, Introduction Soils play a fundamental role in a large number of ecosystem services (Adhikari and Hartemink 2016; Pereira et ul. 2018). The ability of soils to provide these services is [...]

Abstract. Brazilian bioenergy production based on sugarcane is globally known as a sustainable energy matrix. In order to supply the growing demand for biofuels, the sugarcane area expanded by 46% [...]

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.sup.-1] (i.e. 75% removal); (2) 7.0 Mg [ha.sup.-1] (i.e. 50% removal); (3) 14.0 Mgha-1 (i.e. no removal); and (4) 21.0 Mg [ha.sup.-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.sup.-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. Additional keywords: bioelectricity, C and N dynamics, cellulosic ethanol, crop residues., Introduction Global demand for bioenergies has increased significantly in recent years in response to international agreements for the mitigation of greenhouse gas (GHG) emissions, which arc the main drivers of [...]

The Brazilian Amazon is one of the most rapidly developing agricultural areas in the world and represents a potentially large future source of greenhouse gases from land clearing and subsequent agricultural management. In an integrated approach, we estimate the greenhouse gas dynamics of natural ecosystems and agricultural ecosystems after clearing in the context of a future climate. We examine scenarios of deforestation and postclearing land use to estimate the future (20062050) impacts on carbon dioxide (C[O.sub.2]), methane (C[H.sub.4]), and nitrous oxide ([N.sub.2]O) emissions from the agricultural frontier state of Mato Grosso, using a process-based biogeochemistry model, the Terrestrial Ecosystems Model (TEM). We estimate a net emission of greenhouse gases from Mato Grosso, ranging from 2.8 to 15.9 Pg C[O.sub.2]-equivalents (C[O.sub.2]-e) from 2006 to 2050. Deforestation is the largest source of greenhouse gas emissions over this period, but land uses following clearing account for a substantial portion (24-49%) of the net greenhouse gas budget. Due to land-cover and land-use change, there is a small foregone carbon sequestration of 0.2-0.4 Pg C[O.sub.2]-e by natural forests and cerrado between 2006 and 2050. Both deforestation and future land-use management play important roles in the net greenhouse gas emissions of this frontier, suggesting that both should be considered in emissions policies. We find that avoided deforestation remains the best strategy for minimizing future greenhouse gas emissions from Mato Grosso. carbon | soy | scenarios | ecosystems modeling | conservation policy doi/ 10.1073/pnas.1000780107

There is growing interest in sugarcane straw removal from the field to use as raw material for bioenergy production. In contrast, sugarcane straw removal may have negative implications for many soil ecosystem services and subsequent plant growth. A two-year experiment was conducted at Bom Retiro and Univalem mills within the dry and wet seasons for assessing the impact of straw rates removal on plant production. The experimental design was randomized blocks with five treatments proportional to 0, 25, 50, 75 and 100% of straw removal. Plant parameters evaluated included: tillering, phytomass accumulation, stalk yield and stalk industrial quality. Straw removal increased plant tillering at Bom Retiro mill in both seasons and within dry season at Univalem mill, however the plant population at the end of each ratoon cycle was not affected by straw management. Phytomass yield across each ratoon cycle was fit to a sigmoidal model (R 2 ≥ 0.92, p < 0.05). Time necessary for plant completes its lag-phase is higher at the treatments applied in the dry season, whereas there was no time-pattern for plants to complete the linear and stationary growth phases. Moderate amounts of straw: 4–9 Mg ha −1 (dry base) on soil surface enhanced stalk yield. Different rates of straw removal did not affect stalk industrial quality. Overall, partial straw removal, at least in the short-term, could be a win–win situation, sustaining sugarcane yields and providing feedstock for bioelectricity cogeneration and/or 2G-ethanol production. [ABSTRACT FROM AUTHOR]