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.

O objetivo deste trabalho foi avaliar a variação diurna da transpiração e da temperatura foliar da cana-de-açúcar, cv. RB867515, sob diferentes potenciais matriciais de água no substrato de cultivo e as condições meteorológicas em ambiente protegido. O efeito do estresse hídrico na transpiração e temperatura foliar foi determinado a partir da suspensão da irrigação, quando foram realizadas três campanhas de medições, iniciadas aos 122; 150 e 185 dias após o plantio (DAP) até que o potencial matricial de água no substrato (Ψ) alcançasse -1.500 kPa, aproximadamente. Sob ausência de estresse hídrico (Ψ>-50 kPa), a transpiração das plantas atingiu o valor máximo entre 10 e 13 h, próximo de 60; 70 e 100 g planta-1 h-1 para 122; 150 e 185 DAP, respectivamente. Sob condições de estresse hídrico severo (Ψ<-1.100 kPa), houve redução na transpiração diária de aproximadamente 73%, comparativamente às medições realizadas sem estresse e sob condições meteorológicas similares. Em condições de ausência de estresse hídrico e de céu nublado, o valor médio da diferença entre a temperatura foliar e a temperatura do ar foi de -2,9 ºC. Em contraste, sob condições de estresse hídrico severo e valores elevados de radiação solar global, a temperatura foliar chegou a ser 6,6 ºC superior à temperatura do ar.

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.

Unsuitable postharvest management is one of the most serious problems that floriculture has to face. An option for reducing postharvest losses is to use automatic systems for flower sorting and classification, which yield consistent results, reduce costs and speed up these tasks. The objective of this work was show the potential of spectral reflectance to distinguish different postharvest development stages of calla lily flowers, Zantedeschia aethiopica (L.) Spreng., aiming the use of this technology within automatic systems for flower classification. The measuring equipment was a spectrometer connected to a portable computer and configured for reflectance data acquisition in the 400 to 1000 nm range. Based on the results, it was verified a differentiation between the spectral reflectance curves of calla lily flowers, with gradual decreases on the measured values according to the increase of the senescence stages. Thus, the spectral reflectance has potential to be used in the development of automatic systems for postharvest classification of calla lily flowers.

El manejo poscosecha inadecuado es uno de los problemas más serios que la floricultura tiene que enfrentar. Una opción para reducir las pérdidas poscosecha es emplear sistemas automáticos para ordenar y clasificar las flores, los cuales permiten resultados consistentes, reducen gastos y aceleran estas tareas. El objetivo de este trabajo fue demostrar el potencial de la reflectancia espectral para discriminar las diferentes fases de desarrollo poscosecha de flores de cala (Zantedeschia aethiopica [L.] Spreng.), visando el uso de esta tecnología en sistemas automáticos para la clasificación de flores. El equipo de medición fue un espectrómetro conectado a un computador portátil y configurado para la adquisición de datos de reflectancia comprendidos en la región espectral de 400 a 1000 nm. Con base en los resultados, se constató una diferencia entre las curvas de reflectancia espectral, con reducciones graduales en los valores medidos de acuerdo con el aumento de la senescencia. Por tanto, la reflectancia espectral tiene potencial para ser empleada en el desarrollo de sistemas automáticos para clasificación poscosecha de flores de cala.