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This study developed an indirect air-cooling combined with evaporative cooling (IAC þ EC) system for temporary storage of fruit and vegetables (FV) to improve the shelf life of fresh produce under hot and humid climatic conditions. The aim of the study was to investigate the effect of IAC þ EC in providing optimum storage environment of temperature and relative humidity (RH) for the tomato fruit compared to storage under ambient conditions. The IAC þ EC system had a 53-m 3 storage chamber able to store 3.8 tons of tomatoes. Solar energy during the day and a battery bank facility at night powered the cooling system. The structure was constructed and assembled at Ukulinga research center in Pietermaritzburg. The performance of the IAC þ EC was evaluated based on the temperature and the RH measured hourly from 05h00-22h00 daily during a period of 28 days. Temperature and RH were measured in the psychometric unit, various positions in the storage chamber and at ambient conditions. There were significant variations (P < 0.001) in temperature and RH between storage and ambient conditions. The temperature inside the storage chamber was on average 7 C-16 C lower while the average RH was 13%-41% higher than ambient conditions. Temperature and RH at the exhaust end of the IAC þ EC storage chamber were 16.40 C and 88.9% compared to 30.9 C and 47.6% under ambient conditions. Such conditions can enhance the shelf life of FV of moderate respiration rates. Inside the storage chamber, temperature was 15.7 C-16.4 C while the RH was 89.6%-93.8% depending on location. The cooler efficiency varied from 88.04% to 95.6%. The IAC þ EC system performed at the same level as evaporative cooling under dry and arid conditions. The results in this study are evidence that IAC þ EC system can provide optimum storage conditions for FV as well as being a low-cost technology utilizable in hot and sub-humid to humid areas in sub-Saharan Africa.

A 53 m 3 solar-powered evaporative cooler for temporary storage of tomato fruit was developed to improve the shelf life of tomatoes under hot and humid climatic conditions. This study investigated the effect of indirect air-cooling combined with evaporative cooling (IAC+EC), maturity stage at harvesting and period of storage on the quality of tomatoes. The effect of total soluble solids, firmness, color, physiological weight loss (PWL), and marketability of tomatoes (star 9037) was investigated by monitoring the storage of green and pink maturity stage harvested fruit over 28 days under both IAC+EC and ambient conditions. The three factors had a significant effect (P < .001) on the overall quality of tomatoes. The tomatoes stored in the IAC+EC system were 18.9% firmer, maintained 10.5% lower concentration of sugars, increased the hue angle by 3%, had 6.31% lower PWL and were 24.8% more marketability than tomatoes stored under ambient conditions. The tomatoes harvested at the green stage were 20.2% firmer, had 6.6% lower total soluble content, increased the hue angle by 4.9%, had a 3.1% lower PWL, and were 11.6% more marketable than the pink harvested tomatoes. This study clearly demonstrated the efficacy of IAC+EC under sub-humid and hot conditions in improving the quality and marketability and increasing the shelf life of tomatoes by reducing the rate of ripening and utilization of sugar. Efectos de la refrigeración indirecta por aire combinada con refrigeración por evaporación directa en la calidad de tomates almacenados RESUMEN Para efectos del presente estudio se fabricó un enfriador por evaporación de 53 m 3 activado mediante energía solar, el cual se destinó al almacenamiento temporal de tomates, mejorando su vida útil en condiciones climáticas cálidas y húmedas. Al respecto, el estudio investigó el efecto del enfriamiento causado por aire indirecto combinado con el enfriamiento causado por evaporación (IAC+EC), la etapa de madurez de los tomates en el momento de la cosecha y el impacto del periodo de almacenamiento sobre la calidad de los tomates. Monitoreando el almacenamiento durante 28 días-bajo IAC+EC y condiciones ambientales-de tomates verdes y rosados cosechados en la etapa de madurez se investigaron: el efecto de los sólidos solubles totales, la firmeza, el color, su pérdida de peso fisiológica y la comerciabilidad de los tomates (star 9037). Se constató que los tres factores tuvieron un efecto significativo (P <.001) en la calidad general de los tomates. Los tomates almacenados en el sistema IAC+EC fueron 18.9% más firmes, exhibieron una concentración de azúcares 10.5% más baja, mostraron un aumento de 3% en el ángulo de tono, una pérdida de peso fisiológica (PWL) 6.31% más baja y eran 24.8% más comercializables que los tomates almacenados bajo condiciones ambientales. Los tomates cosechados en la etapa verde fueron 20.2% más firmes, tuvieron un contenido soluble total 6.6% más bajo, mostraron un aumento de 4.9% en el ángulo de tono, presentaron un PWL 3.1% más bajo y eran 11.6% más comercializabl...

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Remote sensing data play a crucial role in precision agriculture and natural resource monitoring. The use of unmanned aerial vehicles (UAVs) can provide solutions to challenges faced by farmers and natural resource managers due to its high spatial resolution and flexibility compared to satellite remote sensing. This paper presents UAV and spectral datasets collected from different provinces in South Africa, covering different crops at the farm level as well as natural resources. UAV datasets consist of five multispectral bands corrected for atmospheric effects using the PIX4D mapper software to produce surface reflectance images. The spectral datasets are filtered using a Savitzky–Golay filter, corrected for Multiplicative Scatter Correction (MSC). The first and second derivatives and the Continuous Wavelet Transform (CWT) spectra are also calculated. These datasets can provide baseline information for developing solutions for precision agriculture and natural resource challenges. For example, UAV and spectral data of different crop fields captured at spatial and temporal resolutions can contribute towards calibrating satellite images, thus improving the accuracy of the derived satellite products.

This study developed a low cost and affordable to small-scale farmers’ indirect air-cooling combined with evaporative cooling (IAC+EC) system for storage of fruit and vegetables under both arid and hot; and humid and hot climatic conditions. Field heat from freshly harvested produce should be immediately removed through cooling to the desired storage temperature. The aim of this study was to determine the effectiveness of IAC+EC system in terms of the cooling time requirement of the fresh tomato fruit. A fresh tomato cooling experiment to remove field heat during the summer month of September in Pietermaritzburg was conducted for 36 hours where the IAC+EC system was compared to storage under ambient conditions. The results showed that 16 hours was required to reduce the flesh temperature of tomatoes to 16.5oC while the flesh temperature for tomatoes under ambient conditions followed the ambient temperature profile with time of storage. The IAC+EC system reduced and maintained the microenvironment air temperature inside the coolers to 16.50C- 19°C. The ambient temperature varied between 21 and 32°C. The results in this study are evidence that IAC+ EC system can be a choice to farmers, for cooling the fresh by reducing the field temperature after harvest.

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