Antonio José Steidle Neto

Transpiração e temperatura foliar da cana-de-açúcar sob diferentes valores de potencial matricial

The objective of this study was to evaluate the diurnal behaviour of transpiration and leaf temperature of sugarcane (cv. RB867515) under different water matrix potential in the cultivation substrate and greenhouse meteorological conditions. The water stress effect on transpiration and leaf temperature was determined after irrigation suspension, when three measurement campaigns were initiated at 122; 150 and 185 days after planting (DAP) until the matrix water potential in the substrate (Ψ) reached -1,500 kPa, approximately. Under the absence of water stress (Ψ>-50 kPa), plant transpiration reached the maximum value between 10:00 AM and 13:00 PM, near to 60; 70 e 100 gplant-1h-1, for 122; 150 and 185 DAP, respectively. Under severe water stress (Ψ<-1,100 kPa), there was daily transpiration reduction of approximately 73%, compared to measurements performed without water stress and under similar meteorological conditions. Under the absence of water stress and overcast sky conditions, the average value of the difference between leaf temperature and air temperature was -2.9 oC. In contrast, under severe water stress and high values of global solar radiation, the leaf temperature was found to be 6.6 oC above the air temperature.

Razão entre radiação fotossinteticamente ativa e radiação global no cultivo do tomateiro em casa-de-vegetação

It was proposed in this study to determine and analyze variations in the ratio between photosynthetically active radiation (PAR) and global solar radiation (GR) during the growth season of tomato (Lycopersicon esculentum Mill., cv. Duradoro) crop in sand substract under protected cultivation. Measurements of GR and PAR were conducted inside of a single layer polyethylene greenhouse during the dry season in Vicosa, Minas Gerais, Brazil. Simultaneously, the GR was measured in an automatic weather station. The PAR/GR ratio decreased from 1.691 to 1.574 mol MJ-1, from the first to the ninth week after transplanting, and was relatively constant, oscillating between 1.571 and 1.587 from the ninth to the thirteenth week. Thereafter, when clear sky conditions changed to cloudy days, the PAR/GR ratio increased considerably (1.93 e 2.07 mol MJ-1), reaching values near to those determined in other Brazilian locations. Based on results it is possible to affirm that little effect of leaf expansion on multiple reflections of solar radiation inside the greenhouse occurred, but a remarkable influence of the clouds in the PAR/GR ratio was verified.

Determinação do tempo térmico para o desenvolvimento de mudas de eucalipto na fase de enraizamento

The genus Eucalyptus is important in commercial forest plantations due to its rapid growth and ability to adapt to Brazilian climatic conditions. Among the most important stages for production of eucalyptus seedlings, through vegetative propagation, rooting is highlighted due to its requirements for water, nutrients and management which may compromise the quality of seedlings growing demand in Brazilian silviculture. This study aimed to determine the thermal sum to the rooting of clonal cuttings of eucalyptus (Eucalyptus grandis x E. urophylla) and generate equations to estimate the biomass accumulation in the same stage of production, based on the concept of degree-days (thermal time). The study was conducted in an acclimatized greenhouse in the Seedling Nursery of the Department of Forestry, Universidade Federal de Vicosa, Minas Gerais State, Brazil. At the start of rooting, the mean fresh weight of seedlings was 0.76 ± 0.17 g and the dry biomass was 0.17 ± 0.04 g. At the end of rooting, the means of fresh and dry biomass of seedlings were 1.49 ± 0.43 g and 0.21 ± 0.06 g, respectively. For rooting of eucalyptus seedlings 316.42 degree-days were necessary.

Non-destructive prediction of pigment content in lettuce based on visible-NIR spectroscopy.

BACKGROUND Lettuce (Lactuca sativa L.) is one of the most important salad vegetables in the world, with a number of head shapes, leaf types and colors. The lettuce pigments play important physiological functions, such as photosynthetic processes and light stress defense, but they also benefit human health because of their antioxidant action and anticarcinogenic properties. In this study three lettuce cultivars were grown under different farming systems, and partial least squares models were built to predict the leaf chlorophyll, carotenoid and anthocyanin content. RESULTS The three proposed models resulted in high coefficients of determination and variable importance for the projection values, as well as low estimative errors for calibration and external validation datasets. These results confirmed that it is possible to accurately predict chlorophyll, carotenoid and anthocyanin content of green and red lettuces, grown in different farming systems, based on the spectral reflectance from 500 to 1000 nm. CONCLUSION The proposed models were adequate for estimating lettuce pigments in a quick and non-destructive way, representing an alternative to conventional measurement methods. Prediction accuracies were improved by using the detrending, smoothing and first derivative pretreatments to the original spectral signatures prior to estimating lettuce chlorophyll, carotenoid and anthocyanin content, respectively.

Determinação do fluxo de seiva na cana-de-açúcar pelo método do balanço de energia caulinar

Sap flow measurements are important not only in the agrometeorology field, but also in studies of physiological nature to identify vascular diseases and researches concerned with quantification of water movement in soil-plant-atmosphere system. This study was carried out to evaluate the performance of the energy balance method, implemented by insertion of a miniresistor in the stem center of sugarcane plants, in order to determine the sap flow under distinct environment conditions, utilizing gravimetric measurements as comparative standard. The experiment was conducted in a non-environment controlled greenhouse, located at the Federal University of Vicosa, Vicosa-MG. Based on the mean bias error (MBE), it was verified that the energy balance method presented satisfactory results to determine sugarcane transpiration, both in cloudy and partly cloudy sky conditions, underestimating gravimetric values by only 3.0 and 6.5 gplant-1h-1, respectively. In percentage terms, these values correspond to 4 and 5% of the maximum sugarcane transpiration.

Performance evaluation of an automatic system for tomato fertigation control in substrate.

Este trabalho teve por objetivo avaliar o desempenho de um sistema de controle automatico de fertirrigacao para a producao do tomateiro em substrato de areia, comparativamente ao sistema de controle convencional quanto a reducao de solucao nutritiva. No metodo de controle automatico, os eventos de fertirrigacao foram estabelecidos em funcao das condicoes meteorologicas do ambiente de cultivo e do estadio de desenvolvimento da cultura. Para isso, o modelo de Penman-Monteith foi utilizado como suporte para a tomada de decisao sobre a frequencia adequada para aplicacao da solucao nutritiva. No sistema de controle convencional, os intervalos entre as fertirrigacoes permaneceram fixos durante todo o ciclo do tomateiro. Os resultados demonstraram que o sistema de controle automatico atendeu plenamente as necessidades hidricas da cultura, sem comprometer a producao do tomateiro, proporcionando reducoes expressivas no consumo de solucao nutritiva. Por outro lado, o sistema de controle convencional realizou numero excessivo de fertirrigacoes, principalmente durante o estadio inicial de desenvolvimento do tomateiro e nos dias caracterizados por elevada nebulosidade. No estadio inicial de crescimento, verificou-se que os volumes totais de solucao nutritiva, aplicados ao tomateiro pelo sistema convencional, excederam as necessidades hidricas da cultura em 1,31 e 1,39 L planta-1 em dias tipicos com ceu claro e nublado, respectivamente.

Thermistor based system for grain aeration monitoring and control

A low cost aeration control system (AERSY) was proposed and evaluated.The AERSY system was efficient in maintaining safe grain storage conditions.The system is suitable for use mainly in small and medium silos.The system can be adapted for use in greater storage facilities. Aeration is a popular tool, used to modify the grain bulk microclimate and to control the product quality. The aeration controllers are designed to provide automatic starting and stopping of aeration fans based on a selected strategy. However, most of the already proposed automatic controllers are unviable for small and medium farmers due to the high capital costs associated with them. In this work a low cost aeration controller is proposed, which should be easily adopted for small and medium farmers located in different regions of the world. The proposed controller is called AERSY and is based on the AERO control strategy joined to a low cost data acquisition system with thermistors. AERSY was tested, presenting reliable operation. The aeration control strategy was also efficient in maintaining safe storage conditions during the studied period, but the simulation procedures can be improved regarding the grain moisture content estimations. When comparing the capital costs for installation, AERSY was 44% cheaper than an aeration control system with the same features, but based on thermocouples. The system was found to be suitable for use mainly in small and medium silos (up to 8000m3) but it can be adapted for use in larger storage facilities.

Reference evapotranspiration estimates based on minimum meteorological variable requirements of historical weather data

Reference evapotranspiration (ET0) is critical for agricultural and urban planning, irrigation scheduling, regional water balance studies, and agroclimatological zoning. The objective of this study was to estimate ET0 based on methods with minimum meteorological variable requirements and on empirical models to predict solar radiation. These alternative methods were compared to the FAO Penman-Monteith method by using more than 80 yr of historical weather data. Alternative methods were adapted from the standard FAO Penman-Monteith or Priestley-Taylor methods, which allow estimating ET0 when fewer meteorological variables are available. The Hargreaves-Samani method was also analyzed. The mean absolute error, index of agreement, correlation coefficient, and confidence index were used to compare the alternative methods. Results showed that alternative methods based on the maximum and minimum temperatures, sunshine hours, and/ or wind speed are appropriate for estimating ET0 in the region under study.

Monitoramento remoto de temperaturautilizando o sistema 1-wireTM:avaliação da transmissão de dados

Resumen pt: Em unidades industriais de producao e processamento de proteinas de origem animal e vegetal, assim como em outros setores em que o acompanhamento da tem...