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Sugarcane straw is a crop residue that has a dual purpose and can be maintained on the fields or used to produce bioenergy. The straw retention in the field provides multiple ecosystem services, and the complex interactions between straw and yield responses are hard to predict by local studies. The aim of this study was to investigate the straw removal effects on sugarcane yield in south-central Brazil. To achieve the objective, a set of 21 field studies was conducted in contrasting edaphoclimatic conditions. In addition, data of seven studies from the literature were included to build a more robust dataset. Since straw removal treatments were not homogeneous in all experiments, they were grouped as follows: NR, no removal (baseline treatment); LR, low removal; MR, moderate removal; and TR, total removal. To facilitate the data analysis, the experiments were gathered in four macroregions: southern Goias, western Sao Paulo, central-eastern Sao Paulo, and northeastern Sao Paulo. The site location was the most effective individual factor to explain the straw removal effects on sugarcane yields. Compared with NR treatment, the average yield losses induced by LR, MR, and TR were 2, 10, and 13 Mg ha−1 in southern Goias and 2, 4, and 6 Mg ha−1 in western Sao Paulo states, respectively. In other regions, no clear pattern was observed, and only site-specific effects were observed. Straw removal affected sugarcane yields in all soil types, but higher responses were observed under best conditions for sugarcane growth (i.e., clayey soils in southern Goias). Our findings indicated harvesting season has a relevant role on determining yield responses to straw removal and younger ratoons are more responsive to straw removal. Conclusions from this study suggest straw removal recommendations cannot be designed based on isolated factors but require holistic and integrated knowledge to ensure that the straw amount left on field is enough to sustain multiple soil ecosystem services and crop yields.

Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments. Made available in DSpace on 2019-05-15T00:32:22Z (GMT). No. of bitstreams: 1 CNPASA2019sa.pdf: 842784 bytes, checksum: d219add8dd86dd7f87953f3e2e34b6fe (MD5) Previous issue date: 2019

Sugarcane straw removal is a promising strategy to increase bioenergy production in Brazil. However, if straw removal is not properly managed, it may lead to soil health degradation, thus threatening sustainability of the entire bioenergy production system. In this context, a comprehensive assessment was conducted in 12 field experiments located in central-southern Brazil, the world’s largest sugarcane-producing region, to investigate the impacts of straw removal scenarios on soil health, using the Soil Management Assessment Framework (SMAF). Two groups of experiments were arranged in this study, consisting of three (no–NR; moderate–MR; and total removal–TR) and four straw removal treatments (NR; low–LR; high–HR; and TR). Soil samples were collected (0–10 and 10−20 cm) to evaluate a selected set of soil health indicators (i.e., pH, available phosphorus, exchangeable potassium, bulk density and soil organic carbon). Indicators were individually scored and then integrated into an overall Soil Health Index (SHI) and its chemical, physical, and biological components. Datasets were analyzed by site, experiment groups and soil texture (clayey and sandy soils) and the relationships among straw removal, soil health, and sugarcane yield were also investigated. Our findings showed that soil health responses to straw removal were properly detected by SMAF scoring curves. Based on SHI, sandy and clayey soils were functioning at 41–56% and 67–86% of their full potential, respectively. Soil health degradation was mostly induced by TR and HR, while LR and MR resulted in minimal detrimental effects on a short-term basis compared with NR. However, sandy soils were more prone to soil health degradation, indicating that straw removal should be avoided on those soils. For clayey soils, decline in soil health was driven by physical degradation. Healthier soils were associated with higher sugarcane stalk yields, and physical degradation was the main driver for crop yield losses. Conclusions drawn from this study suggest that comprehensive soil health assessments by integrating chemical, physical and biological indicators are fundamental to design more sustainable straw management and bioenergy production systems in Brazil.

One of the steps needed to achieve sustainable bioenergy is to reduce our reliance on synthetic nitrogen (N). Despite the fact that legume cover crops have the potential to increase soil quality and sugarcane (Saccharum spp.) yield, much information is still needed to determine amount of N available from cover crops to sequential ratoon cycles. This study was designed to assess the impacts of sunn hemp (Crotalaria spectabilis) cover crop on soil N dynamics and sugarcane ratoon response to N fertilization during two harvest seasons across three contrasting soil and climatic conditions in southern Brazil. The treatments consisted of cover crop and fallow established prior to sugarcane replanting; in addition to three N-fertilizer rates 60, 120 and 180 kg N ha−1 and a 0-N control applied during the first and second ratoons. Although there was increased sugarcane yield (8–13 Mg ha−1 in first ratoon and 10–16 Mg ha−1 in second ratoon) in plots planted with cover crop, it was not possible to detect significant increases in soil inorganic N, microbial biomass C and Illinois Soil N Test content under cover crop compared with fallow. Cover crop with sunn hemp increased the accumulated two-year yields by 14–25 Mg ha−1 at all sites and NUE (Mg stalks kg−1 N) across all N rates at two sites. Our findings support the conclusion that cover crop did not change the N requirement of succeeding ratoon crops but increases the yield, thereby improving NUE in sugarcane systems.

Sugarcane straw is a crop residue known as the main input of carbon (C) to the soil, but its removal represents a valuable asset for bioenergy purposes, which may adversely affect soil organic C (SOC) stocks. Most studies related to this issue is limited to site-specific conditions and comprehensive studies in a wide range of soils and climate regions are scarce. This study was designed to evaluate temporal SOC stocks changes induced by sugarcane cultivation and straw management in the southern-central of Brazil. Ten field experiments were arranged in a randomized block design with four replications, including four straw removal rates: total (TR), high (HR), low (LR) and no removal (NR). Soil samples were collected to a 30-cm depth at the beginning of the trial establishment and after four consecutive years. The dataset suggested that 19% and 25% of the C added via straw were accumulated into the soil of the sandy and clayey areas, respectively. This study showed strong SOC depletion in sandy soils at rates of 1.4, 1.5, 1.9 and 2.3 Mg ha-1 year-1 under NR, LR, HR and TR, respectively. In contrast, clayey soils exhibited SOC accumulation over time, even removing all the straw from the soil surface. Based on SOC changes, these findings provide a robust scientific basis to support policy and management decisions for straw-derived bioenergy, showing that the removal of sugarcane straw may be potentially advantageous in clayey soils but should be avoided in sandy soils of tropical regions in Brazil.

Sugarcane production for biorenewables demands substantial inputs of nitrogen (N) fertilizer that can lead to environmental consequences, and no clear effect has been reported on soil organic carbon (SOC) and N stocks. The use of a previous legume crops cultivation to add N to soil is a promising strategy to reduce the dependence in synthetic N fertilizer, having an international appeal for sustainable production of bioenergy crops. This study investigates a four-year impact of N fertilization on SOC and N stocks and sugarcane ratoon yields in a sandy and clayey soils, while considering the effects of a legume cover crop cultivated during the renovation period on decreasing N fertilizer requirements. Treatments with N fertilizer rates were arranged in a randomized block design after plant-cane harvest: 60, 120, 180 kg N ha−1 and control (without N) in two paired areas previously managed with Crotalaria spectabilis and bare fallow. Soil samples for SOC and N stocks were quantified at the beginning of the trial, and measured again along with microbiological attributes after four consecutive years, while sugarcane yield was assessed annually. SOC and N stocks were unaffected by N fertilizer rates, whereas the cultivation of cover crop increased soil N storage and microbial biomass carbon. There was limited responsiveness of sugarcane ratoons to additional N supplied by inorganic fertilizer under cover crop, whereas positive responses occurred under bare fallow. Considering the average of four-harvest yields, cover crop increased sugarcane yield by 9 % (5 Mg ha−1) at sandy soil and 15 % (16 Mg ha−1) at clayey soil relative to bare fallow. Cover crop provided an annual N fertilizer replacement of 9 and 15 kg ha−1 in the sandy and clayey soils. The long-lasting historical effect of cover crop in increasing sugarcane yield per area without the need for extra N from fertilizer opens a new possibility to increase the sustainability and alleviate associated greenhouse gas emissions of sugarcane fields by allowing savings in synthetic N fertilizer.

Current knowledge indicates that sugarcane straw is a short-term sink of fertilizer nitrogen (N) due to N immobilization during the decomposition process. This study aimed to determine whether sugarcane straw removal from the field benefits the N-fertilizer recovery by plant (NRP), and if legume cultivation will further improve NRP. Half of a field was planted with sunn hemp (Crotalaria spectabilis) and half was left fallow. In the second ratoon, treatments with 0, 50, and 100% of sugarcane straw maintenance levels were installed, receiving 120 kg ha−1 N over straw. A microplot of ammonium nitrate labeled with 1.99% atoms 15N was included. NRP was quantified at 92, 164, and 264 days after fertilization (DAF). At harvest (264 DAF), soil samples and straw ( 4 mm fractions) were collected to determine N-fertilizer recovery in the soil (NRS) and in the straw (NRSt). Maintaining 50 and 100% of straw improved NRP over the sugarcane cycle. NRP was not improved by crop rotation cultivation and NRS averaged 50% in the entire soil profile. NRSt at harvest averaged 1–3% in the 50% and 100% straw levels. Contrary to the current view, N-fertilizer immobilization in the straw was negligible and keeping straw could improve NRP. The findings indicate that increasing N rates in green cane trash blanket system to compensate for the N-fertilizer immobilization is not necessary, and that straw removal for bioenergy production will change the short-term demand for N-fertilizer.

Planting cover crops as a strategy to enhance soil quality has been long adopted in several agroecosystem worldwide. Among the cover crops, some legume species are must chosen due to their abilities to fix atmospheric nitrogen (N) into the soil, which increases soil N availability for the cash crop planted subsequently. Our hypothesis was that planting a legume within the sugarcane (Saccharum spp.) renewal period can be adopted as a strategy to supply the N required for the sugarcane at planting. The hypothesis was tested through an experiment set up within Southeast Brazil into two adjacent areas: in an area sunn hemp (Crotalaria junceae L.) was planted within the sugarcane renewal period (rotation system), whereas the another area was left in fallow (fallow system). Five N-fertilizer rates: 0, 130, 260, 390, and 520 kg N ha-1 were arranged in a randomized block design with four replications within both systems. The N amounts were divided throughout the plant cane, first and second ratoons cycles. Plant parameters evaluated included: tillering, stalk yield and stalk industrial quality. The N content on leaves as well as the inorganic N dynamic on soil were also evaluated. Overall, sunn hemp cropped within the sugarcane renewal period potentially replaces 60 kg ha-1 of N at sugarcane planting. Moreover, the rotation system enhanced stalk yield in 20 Mg ha-1 over both ratoon cycles, whereas the N amount required for each Mg of stalk harvested is reduced by 12.5%, indicating augmented the nitrogen recovering (NUE). The sucrose content and sugar yield are both enhanced under rotation system. However, soil N inorganic dynamic, the N content on leaves and amounts removed on plant components were little sensitive to the rotation system. Our findings highlight the rotation system as a feasible alternative to replace part of the N required by the sugarcane, which improves the NUE for the crop. Conclusions from this study indicate that legume rotation system adoption increases the sustainability of bioenergy from sugarcane by reducing the dependency on synthetic N fertilizers.

A adoção da rotação de culturas com leguminosas em áreas de implantação e reforma de canaviais é uma estratégia promissora para recuperação e manutenção da fertilidade do solo, e tem potencial no aproveitamento do N para as soqueiras. A análise mais detalhada do comportamento do N no solo durante o ano agrícola e dos parâmetros de produção em locais que possuem solo e clima contrastantes, permitem aprimorar o manejo da adubação nitrogenada da cana-de-açúcar. As hipóteses deste trabalho são (1) a rotação de culturas irá aumentar a disponibilidade de N no solo, a qual suprirá parte da demanda do N das soqueiras subsequentes e (2) a rotação de culturas promoverá redução da resposta das soqueiras à adubação nitrogenada. Objetivou-se avaliar o efeito da rotação de culturas nas transformações do N no solo (N mineral, N-ISNT e N e C da biomassa microbiana) e na produtividade da primeira soqueira. Os experimentos foram instalados em quatro regiões representativas de cultivo de cana-de-açúcar na região Centro Sul do Brasil: Quatá/SP (Local A); Iracemápolis/SP (Local B); Chapadão do Céu/GO (Local C) e Quirinópolis/GO (Local D). Em cada local, foi instalado um experimento em esquema de parcelas subdivididas no delineamento blocos ao acaso com quatro repetições, em áreas submetidas (com rotação) ou não (sem rotação) ao plantio de leguminosa do gênero crotalária. Após a colheita da cana planta, foram implantados os seguintes tratamentos: 60, 120 e 180 kg ha-1 de N e um controle (sem N), aplicados superficialmente sobre a palhada. Foram realizadas três amostragens para determinação do conteúdo de N mineral, N-ISNT e C e N da biomassa microbiana. Entre 150 a 180 dias após a colheita da cana-planta, foram realizadas avaliações de perfilhamento e índice SPAD. Na colheita, avaliou-se matéria seca da parte aérea, produtividade e atributos tecnológicos. Os resultados demonstraram que a mineralização dos resíduos da crotalária influenciaram a dinâmica do C e N e os reservatórios de N no perfil do solo ao longo do ciclo da primeira soqueira, com destaque para o solo de textura média (Local A). Apesar da rotação de culturas ter modificado o conteúdo de N mineral, N-ISNT, e aumentado o perfilhamento e índice SPAD no local A, somente nos solos argilosos (Locais C e D), a rotação aumentou a produtividade da soqueira. A hipótese de que a rotação de culturas reduz a demanda de fertilizantes nitrogenados não foi aceita; houve resposta à adubação nitrogenada nos quatro locais, independentemente da rotação de culturas. Porém, a rotação demonstrou potencial em aumentar a produção de biomassa com manutenção da dose de N. Esta pesquisa demonstrou a viabilidade de rotação de culturas em solos argilosos com elevado conteúdo de C e N total, com potencial de aumentar a produtividade do canavial, porém sem reduzir a demanda de adubação nitrogenada. The adoption of crop rotation with sugarcane is a promising strategy for the recovery and maintenance of soil fertility, and it shows potential in the use of N to the sugarcane ratoon. A more detailed analysis of the transformations N in soil during the agricultural year and production parameters in sites that have contrasting soil texture and climate, allows to improve management of N fertilization for sugarcane. The hypothesis of this work are (1) crop rotation will increase soil N availability, which will satisfy part of N requirements of sugarcane ratoon and (2) crop rotation will reduce the sugarcane ratoon response to N fertilization. The objective was to evaluate the effects of sunn hemp rotation in the transformations of N in soil (mineral N content, ISNT-N and microbial biomass C and N) and sugarcane ratoon yield. The field trials were installed in four representative regions of cultivation of sugarcane in Brazil: Quatá/SP (Site A); Iracemápolis/SP (Site B); Chapadão do Céu/GO (Site C) e Quirinópolis/GO (Site D). At each site, a field trial was installed in split plot in a randomized block experimental design with four replications, in areas sowed (rotation) and not sowed (no rotation) with sunn hemp. After the harvest of cane-plant, the following treatments were applied: 60, 120 and 180 kg ha-1 of N and a control (without N) over the straw. Three sampling were performed to determine the soil inorganic N content, ISNT-N, C and N of microbial biomass. Between 150 to 180 days after the harvest of the cane-plant, tillering was counted and SPAD index was measured. At harvest of the sugarcane ratoon, biometric parameters, yield and quality parameters were evaluated. The results showed that mineralization of residues of sunn hemp influenced the dynamics of C and N and N content in the soil profile throughout the cycle of the sugarcane ratoon, with emphasis on medium-textured soil (Site A). Despite crop rotation has modified mineral N stocks, ISNT-N, and increased tillering and SPAD index in site A, crop rotation only increased the sugarcane ratoon yield on clay soils (Sites C and D). The hypothesis that crop rotation reduces N-fertilizer requirement was not accepted; there was response to N fertilization in four sites, regardless of crop rotation. However, the rotation showed potential in increase biomass production with maintenance of N rate. This research demonstrated the viability of crop rotation in clay soils with high total C and N content, with potential to increase sugarcane yield, but without reducing N-fertilizer requirement.

N Fertilizer recommendations must be improved to optimize N use efficiency (NUE) for bioenergy crops. A study was conducted to test the hypothesis that sites varying in historical usage of by-product differ in soil N-supplying power and sugarcane (Saccharum spp.) responsiveness to N fertilization. Our aim was to quantify soil N availability and N fertilizer rates, sources, and application timings for their effects on sugarcane yield and NUE. Three N response trials, each involving 0 to 200 kg N ha−1, were conducted in the state of São Paulo, Brazil, at sites varying historically in the usage of vinasse. Before fertilizer application and at harvest, soil inorganic N content was quantified and potential N mineralization estimated by the Illinois Soil Nitrogen Test (ISNT); stalk yield and sugar content were measured at harvest and used to estimate NUE. Sugarcane showed significant response to N fertilization only at the sites with no history of vinasse usage. Reducing the N rate from 120 to 80 kg N ha−1 showed limited potential for lowering yield (~ 1 %), while increasing the NUE by 54 %, which was far better than the 14 % increase achieved by modifying the N source or application timing. Monitoring inorganic N and ISNT levels over time to estimate soil N-supplying power has potential for predicting the responsiveness of sugarcane to N fertilization; however, ISNT interpretations must consider factors that impede mineralization or crop N utilization, such as soil acidity or a limitation on the availability of Ca or P. Soil N testing can help optimize NUE for sustainable bioenergy production.