The lack of information about the effects of cultivars, crop age and climate on the sugarcane (Saccharum ssp.) crop yield and quality has been the primary factor impacting the sugar-ethanol sector in Brazil. One of the processes about which we do not have a satisfactory understanding is sugarcane ripening and the effects of cultivars, crop age and climate on that. Sugarcane ripening is the process of sucrose accumulation in stalks, which is heavily infl uenced by several factors, mainly by climatic conditions such as air temperature and water defi cits. Because it is a complex process, studies of the variables involved in sugarcane ripening can provide important information, resulting in a better use of commercial cultivars, bringing advantages to growers, processing units, breeding programs and scientifi c community. In this review, we discuss the available knowledge of the interaction between climate conditions and sugarcane ripening, under the infl uence of genotypic characteristics and crop age. In several studies, the main conclusion is that sugarcane ripening depends on a complex combination of climate variables, the genetic potential of cultivars and crop management. Soil moisture and air temperature are the primary variables involved in sugarcane ripening, and their combination stimulates the intensity of the process. In addition, the need for studies integrating the effects of climate on plant physiological processes and on the use of chemical agents to stimulate sugarcane ripening is highlighted.

The effect of weather variables on sugarcane ripening is a process still not completely understood, despite its huge impact on the quality of raw material for the sugar energy industry. The aim of the present study was to evaluate the influence of weather variables on sugarcane ripening in southern Brazil, propose empirical models for estimating total recoverable sugar (TRS) content, and evaluate the performance of these models with experimental and commercial independent data from different regions. A field experiment was carried out in Piracicaba, in the state of São Paulo, Brazil, considering eight sugarcane cultivars planted monthly, from March to October 2002. In 2003, at the harvest, 12 months later, samples were collected to evaluate TRS (kg t(-1)). TRS and weather variables (air temperature, solar radiation, relative humidity, and rainfall) were analyzed using descriptive and multivariate statistical analysis to understand their interactions. From these correlations, variables were selected to generate empirical models for estimating TRS, according to the cultivar groups and their ripening characteristics (early, mid, and late). These models were evaluated by residual analysis and regression analysis with independent experimental data from two other locations in the same years and with independent commercial data from six different locations from 2005 to 2010. The best performances were found with exponential models which considered cumulative rainfall during the 120 days before harvest as an independent variable (R (2) adj ranging from 0.92 to 0.95). Independent evaluations revealed that our models were capable of estimating TRS with reasonable to high precision (R (2) adj ranging from 0.66 to 0.99) and accuracy (D index ranging from 0.90 to 0.99), and with low mean absolute percentage errors (MAPE ≤ 5 %), even in regions with different climatic conditions.

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RESUMO -A presente pesquisa foi realizada com o objetivo de avaliar o efeito da época de semeadura sobre os períodos de interferência das plantas daninhas na cultura do amendoimrasteiro (Arachis hypogaea cv. IAC Runner 886). Dois experimentos foram instalados em épocas diferentes -início de novembro e de dezembro de 2005 -em áreas vizinhas e provenientes de reforma de canavial, no município de Jaboticabal, SP, num solo de textura média. O delineamento experimental foi de blocos ao acaso, com os tratamentos constituídos por períodos crescentes de convivência ou de controle das plantas daninhas com as plantas de amendoim. As plantas daninhas que se destacaram em importância relativa, na primeira e segunda épocas, foram Ipomoea triloba, Digitaria nuda, Hyptis lophanta e Sida spp. A comunidade infestante e a cultura foram influenciadas pela época de semeadura, modificando suas relações de interferência. Os valores de acúmulo de massa seca da parte aérea das plantas daninhas na segunda época superaram em 23,7% os encontrados na primeira época durante todo o ciclo de desenvolvimento da cultura, refletindo, principalmente, em redução de produtividade de vagens de amendoim. Admitindo 5% de tolerâ ncia na redução da produtividade de vagens, verificou-se que o período anterior à interferência (PAI) na primeira época foi de 28 dias após a emergência (DAE), e o período total de interferência (PTPI), de 78 DAE, com redução de produtividade de 53,5%. Na segunda época, os efeitos da convivência da comunidade infestante com a cultura foram mais drásticos, pois afetaram com maior intensidade a produtividade da cultura, reduzindo-a em 86%, com PAI de 33 DAE e PTPI de 93 DAE. Quando no limpo, durante todo o ciclo da cultura, o amendoim semeado mais cedo (início de novembro) apresentou produtividade de vagens maior, superando em 23,7% o semeado um mês mais tarde. Palavras-chave:Arachis hypogaea, competição, controle. November and December 2005, at ABSTRACT -This research was conducted to determine the effect of sowing time on weed interference periods in peanut crop (Arachis hypogaea cv. IAC Runner 886). Two experiments were set at different times, early

a b s t r a c tIrrigation increases sugarcane yield, especially in areas under restricted rainfall conditions. However, few studies have been carried out on the environmental impacts of this activity, mainly regarding greenhouse gas (GHG) emissions. Therefore, the aim of this study was to estimate the environmental impacts of sugarcane irrigation, contemplating GHG emissions at different production scenarios. For that, biomass production was simulated under rainfed conditions and different irrigation systems, comparing six Brazilian regions (Ribeirão Preto e SP; Araçatuba e SP; Paracatu e MG; Itumbiara e GO; Paranaíba e MS; and Petrolina e PE). After gathered, GHG emission estimates of each scenario were confronted with sugarcane production data. The results were expressed in "carbon (C) footprint" (kg CO 2 eq t À1 ). For all evaluated regions, irrigation intensifies and encumbers environmentally the agricultural practices by increasing GHG emissions (~7447.0 kg CO 2 eq ha À1 yr À1 ) compared with rainfed condition (~2154.6 kg CO 2 eq ha À1 yr À1 ). Irrigation systems require a large amount of electric power, diesel and other inputs such as synthetic nitrogen fertilizers. Surprisingly, this situation can change substantially if C footprint is considered. We observed that irrigated areas had a decrease C footprint of up to 59% (33.0 kg CO 2 eq t À1 ) against rainfed ones, as observed in Petrolina scenario. In other regions, C footprint reductions ranged from 23% (7.1 kg CO 2 eq t À1 ) in Ribeirão Preto to 37% (13.9 kg CO 2 eq t À1 ) in Paracatu. Thus, irrigated agriculture impact could be explored in terms of C footprint, which depends on regional biomass production as well as irrigation system efficiency towards a better water use.

Sugarcane ripening is a process controlled by cultivar characteristics and the interaction of genotypes with local climate. The objective of this study was to characterise the temporal variation of sugarcane ripening by assessing the multivariate structure contained in sugarcane quality data, and by correlating the results with local climatic conditions. Eight sugarcane cultivars were evaluated from March to October in Piracicaba, São Paulo State, Brazil. Characteristics related to the quality of raw sugarcane juice were submitted to statistical analysis by ANOVA, hierarchical and non-hierarchical (k-means) clustering methods, and principal components, in order to classify the cultivars into groups for each month of sampling. The ANOVA showed a clear difference (P < 0.001) among harvesting months for all sugarcane quality variables, which was reinforced by the cluster analysis for the whole dataset that selected groups according to the month of harvest. By analysing the quality variables by months, patterns of similarity among sugarcane cultivars were identified, which allowed three ripening groups to be established: early, middle and late. As the harvesting season progressed, the variations within each group, as well as among groups, were explained mainly by local soil-water availability conditions. The early ripening cultivars showed polarisable sugar (Pol) values >13% in early May, whereas these values were reached by the middle cultivars in July, and the late ones in August–September. However, the differences among groups tended to decrease through the harvest season, as expressed by the Euclidean distance, which decreased from 5.62 in March to 1.82 in September, when the water deficit reached the maximum accumulated value, totalling >130 mm. The non-hierarchical analyses (k-means) and principal components methods agreed, resulting in the identification of the same three main cultivar groups. The approach proposed for cultivar classification in this study is more complete than the usual analysis of Pol variation over time, since it allowed all of the variability contained in the sugarcane quality dataset to be analysed in an integrated way, providing a better understanding of the differences observed in the ripening of different cultivars.

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RESUMOO conhecimento científico sobre a biologia de plantas daninhas contribui para a implantação de adequadas estratégias de manejo e controle. Este trabalho foi desenvolvido com o objetivo de avaliar a germinação de sementes de ervaquente (Spermacoce latifolia Aubl.), importante planta infestante em áreas de reflorestamento. As sementes foram submetidas à superação de dormência, em que foram avaliados a escarificação mecânica, tratamento químico (H 2 SO 4 e KNO 3 ) e térmico, além da testemunha. Foram avaliados ainda a temperatura (10, 15, 20, 25, 30 e 35°C), filtros de luz (ausência, vermelha, verde, amarela, vermelha distante, azul, laranja e transparente) e disponibilidade de água (0,0, -0,2, -0,4, -0,6, -0,8 e -1,0 MPa) na germinação e vigor das sementes. Os tratamentos foram arranjados em delineamento experimental inteiramente casualizado com quatro repetições, sendo a parcela experimental constituída por caixas plásticas tipo gerbox, com 50 sementes. A escarificação mecânica (lixa) foi o método que proporcionou melhor quebra de dormência, indicando que as sementes de S. latifolia possuem impermeabilidade do tegumento à água. As sementes apresentaram maiores percentagens de germinação em condições de leve restrição hídrica (-0,2 MPa) e a temperatura ótima foi de 25°C. A luz de cor azul reduziu a porcentagem de germinação. Palavras-chave:Escarificação, estresse hídrico, qualidade de luz, temperatura. Dormancy break and influence of environmental factors on the germination of Spermacoce latifolia seeds ABSTRACTUnderstanding basic information on weed biology contributes to the implementation of appropriate management and control strategies. Thus, this work was developed to evaluate the germination of Spermacoce latifolia Aubl. seeds, an important weed in reforestation areas. The seeds were subjected to dormancy break treatments, in which the mechanical scarification, chemical treatment (H2SO 4 and KNO 3 ), heat treatment, and control, were evaluated. Three more tests were done determinate the effects of temperature (10, 15, 20, 25, 30 and 35°C), light filters (absence of light and red, green, yellow, distant red, blue, orange and clear light) and water availability (0.0, -0.2, -0.4, -0.6, -0.8 and -1.0 MPa) on the seeds germination and vigor. The treatments were arranged in a completely randomized design with four replications, and the experimental plot was constituted by gerbox plastic boxes with 50 seeds. The mechanical scarification (sanding) provided the best dormancy break, indicating that Spermacoce latifolia seeds have tegument water impermeability. The seeds showed higher germination percentage under conditions of mild water stress (-0.2 MPa) and the optimal temperature was 25°C. The blue light reduced seed germination.