Constantinos Kittas’s research while affiliated with University of Thessaly and other places

Over the last decade, the total population of the sub-Saharan region of Africa has been increasing rapidly at a rate of more than 3% annually, with urbanization expected to be approximately 40% of the total population by 2050. Parallel growth has not been achieved in the agricultural sector in West Africa, with vegetable production and consumption being amongst the lowest in the world. This has aggravated the already food insecurity and malnutrition situation in the region. In this context, and within the framework of their agricultural development policies, 10 countries of West Africa (Burkina Faso; Cabo Verde; Côte d’Ivoire; Guinée; Guinée Bissau; Mali; Mauritanie; Niger; Sénégal; Chad), established the “African Network for Horticultural Development “RADHORT” (Réseau Africain pour le Développement de l’Horticulture), in order to cooperate for the diversification and intensification of horticulture in the region. The countries of RADHORT cover different climate zones ranging from the arid climate (desert), to the Sahelian zone (semi-arid), to the dry tropical zone (with long dry season and short rainy season), and to the wet tropical zone (humid zone with bimodal rainfall). Temperatures and global radiation are very suitable for vegetable production in tropical countries throughout the year, but open air cultivation can be severely hampered by high temperatures, winds, heavy rainfall, while being exposed to pest and disease infestation. Sheltered cultivation will help to moderate negative effects of climate factors on the crop, improve water productivity and the efficiency of eco-friendly pest and disease management. The paper analyses and discusses different technical options of sheltered cultivation to be tested in RADHORT countries, as a means to enhance horticulture crops productivity and quality for meeting the growing demand of an expanding rural and urban population.

BACKGROUND The use of water containing calcium bicarbonate (Ca(HCO3)2) at excessively high concentrations in closed hydroponic crops can cause calcium ion (Ca²⁺) accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca²⁺ concentrations that do not harm the crop and to simulate the pattern of Ca²⁺ accumulation when the Ca²⁺ concentration in the irrigation water, and concomitantly in the replenishment nutrient solution (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L⁻¹ Ca²⁺ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. RESULTS At 1.5 mmol L⁻¹ Ca²⁺, no Ca²⁺ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L⁻¹ in the irrigation water, the Ca²⁺ concentration in the recirculating NS, increased by the latter cropping stages to 17, 28 and 37 mmol L⁻¹, corresponding to 6.4, 9.0 and 10.8 dS m⁻¹. The accumulation of Ca²⁺ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca²⁺, sulphate ion (SO4²⁻) and magnesium ion (Mg²⁺), but this was not the case for nitrogen (N) or potassium ion (K⁺). Growth, yield and plant water uptake were restricted at moderate (3.0 and 4.5 mmol L⁻¹) and high (6.0 mmol L⁻¹) external Ca²⁺ levels. CONCLUSION In soilless pepper crops with zero discharge of fertigation effluents, the Ca²⁺ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L⁻¹ to avoid yield restrictions due to salinity. © 2021 Society of Chemical Industry

Investigation of the combined addition of attapulgite clay and benzoic acid in fattening pig diets seems to be reasonable both from a pig performance and environmental point of view. In this research, an in situ experimental procedure was performed in order to investigate the effect of supplementing the conventional diet (CNVD) supplied to the fattening pigs of a commercial pig farm in Greece (based on maize, barley, wheat bran and soybean meal) with 0.4% w/w attapulgite and 0.5% w/w benzoic acid at the expense of maize (ATTBAD diet) on their feed efficiency and growth performance. The results suggested a significant increase (p≤0.05) in the total weight gain and the slaughter live-weight and a significant decrease (p≤0.05) in the feed intake and feed conversion ratio per fattening pig when supplied the ATTBAD. These results were further used as an input to a ‘cradle-to-farm-gate’ environmental Life Cycle Assessment. The functional unit (FU) was 1 kg of sold pig live-weight and the environmental impact categories (EICs) assessed were climate change (CC) and CC from direct land use change, acidification, eutrophication, land use, water use and fossil energy use. The indicators for all EICs were connected with lower potential estimates per FU in the ATTBAD system, suggesting an improvement of the environmental performance when the ATTBAD is supplied to the fattening pigs of the farm. The improvement of intestinal functionality and enzyme activity, an increase in digesta retention time and a drop of digesta pH in the gastrointestinal tract were indicated as possible causes for the improvement in the growth performance of the fattening pigs when supplied the ATTBAD diet, which however need to be confirmed with further research. The contribution analysis highlighted the importance of the decreased feed intake and the increased total weight gain of the fatteners on the improved environmental performance of the ATTBAD system. The reasonable differences between the indicator estimates of this study and relevant literature, the fair data quality which characterizes the compiled life cycle inventory and the results of the performed Monte Carlo simulation, are considered as a good indication of the validity of the received results and further support the argument of the ATTBAD system's improved environmental performance. Therefore, the use of the ATTBAD instead of the CNVD could potentially offer environmental benefits to the studied supply chain.

Two experiments were conducted in different cropping seasons under Mediterranean climatic conditions to investigate the impact of two cooling systems (fan-pad evaporative as opposed to fan ventilation) on greenhouse microclimate and soilless cucumber growth. The second objective of the experiment was to determine the most appropriate irrigation regime (between 0.24 and 0.32 L m −2) in relation to crop water uptake and greenhouse fertigation effluents. The use of a fan ventilation system enhanced the vapor pressure deficit; thus, the crop transpiration improved by 60% in relation to the transpiration rates of plants grown under the fan-pad system. Higher transpiration rates alleviated the heat load as the external-inside greenhouse air differences declined from 6.2 • C to 3 • C. The leaf-air temperature differential indicated that plants were not facing any water stress conditions for both cooling systems tested; however, fan ventilation reduced drainage emissions outflows (95% decrease) compared with evaporative cooling. Results also demonstrated that an irrigation regime of 0.24 L m −2 can be applied successfully in soilless cucumber crops, keeping the drainage to a minimum (20% of the nutrient solution supply). These results suggest that fan ventilation cooling system in conjugation with an appropriate irrigation regime prevents overheating and minimizes the nutrient and water losses in spring-grown soilless cucumber crops in Mediterranean greenhouses without compromising yield.

Precision agricultural greenhouse systems indicate considerable scope for improvement of irrigation management practices, since growers typically irrigate crops based on their personal experience. Soil-based greenhouse crop irrigation management requires estimation on a daily basis, whereas soilless systems must be estimated on an hourly or even shorter interval schedule. Historically, irrigation scheduling methods have been based on soil or substrate monitoring, dependent on climate or time with each having both strengths and weaknesses. Recently, plant-based monitoring or plant reflectance-derived indices have been developed, yet their potential is limited for estimating the irrigation rate in order to apply proper irrigation scheduling. Optimization of irrigation practices imposes different irrigation approaches, based on prevailing greenhouse environments, considering plant-water-soil relationships. This article presents a comprehensive review of the literature, which deals with irrigation scheduling approaches applied for soil and soilless greenhouse production systems. Irrigation decisions are categorized according to whether or not an automatic irrigation control has the ability to support a feedback irrigation decision system. The need for further development of neural networks systems is required.

Water and nitrogen deficit stress are some of the most important growth limiting factors in crop production. Several methods have been used to quantify the impact of water and nitrogen deficit stress on plant physiology. However, by performing machine learning with hyperspectral sensor data, crop physiology management systems are integrated into real artificial intelligence systems, providing richer recommendations and insights into implementing appropriate irrigation and environment control management strategies. In this study, the Classification Tree model was used to group complex hyperspectral datasets in order to provide remote visual results about plant water and nitrogen deficit stress. Soilless tomato crops are grown under varying water and nitrogen regimes. The model that we developed was trained using 75% of the total sample dataset, while the rest (25%) of the data were used to validate the model. The results showed that the combination of MSAVI, mrNDVI, and PRI had the potential to determine water and nitrogen deficit stress with 89.6% and 91.4% classification accuracy values for the training and testing samples, respectively. The results of the current study are promising for developing control strategies for sustainable greenhouse production.

The aim of this study was to examine climate conditions, air quality, potential heat stress and their relations in a sheep barn under Greek hot weather conditions. Hourly averaged values of temperature, relative humidity, wind speed, and coarse and fine airborne Particulate Matter (PM) concentration recorded inside and outside a naturally ventilated sheep barn during July, August and September of 2015 were used. Indoors potential heat-stress levels were assessed by means of the Temperature Humidity Index (THI). Descriptive statistics were presented and relations between the environmental parameters and the THI values were investigated. The results showed that inside the sheep barn, THI was positively correlated (p < 0.0001) with wind speed and negatively correlated with relative humidity. Additionally, inside the sheep barn, the concentration of coarse PM was positively and negatively correlated (p < 0.0001) with temperature and relative humidity, respectively, whereas the opposite was observed for the concentration of fine PM. Measures that could be applied to alleviate animals' heat-stress were proposed.

The microclimate and cucumber crop response in a screenhouse and in an evaporatively cooled greenhouse were studied in Oman during winter/spring and spring/summer cultivation periods. Measurements were carried out in two similarly shaped structures: (1) a greenhouse equipped with a pad-and-fan system for evaporative cooling of the greenhouse environment and (2) a screenhouse with no cooling system. Analysis of the spring/summer period climate data showed that the evaporative cooling in the greenhouse reduced the mean air temperature by about 4.5°C compared to outside and maintained the leaf temperature close to the greenhouse air temperature. The 24 h mean leaf and air temperatures in the greenhouse reached 25.8°C ±1.3°C and 25.9°C ±0.8°C, respectively. On the other hand, the 24 h mean leaf and air temperatures in the screenhouse were higher by 1.0°C and 1.3°C, respectively, compared to outside. The 24 h mean leaf and air temperatures in the screenhouse reached 32.8°C ±1.2°C and 31.8°C ±1.5°C, respectively. Furthermore, the evaporative cooling in the greenhouse maintained the 24 h mean air vapor pressure deficit (VPD) values at levels lower than 1.1 kPa, while the 24 h mean air VPD in the screenhouse reached values up to 4.5 kPa. These differences resulted in a 50% decrease in crop fruit yield during the spring/summer period. The radiation and water use efficiency (WUE) values observed in the two structures were similar during the winter/spring period but were higher in the greenhouse during the spring/summer period. However, for the greenhouse, when the water evaporated in the wet pad was also considered, the overall WUE was at the same level in both structures during summer. Furthermore, the evaporative cooling applied in the greenhouse enhanced the mean values of fruit quality characteristics measured during the spring/summer, such as fruit dry matter content (5.6%), fruit firmness (5.0 kg cm ⁻² ), and chroma (18.6), compared to that of the screenhouse (5.0%, 4.9 kg cm ⁻² and 16.3, respectively), but did not significantly affect other fruit quality characteristics, such as mean fruit weight (128 g for greenhouse and 123 g for screenhouse), total soluble solids content (3.9 °Brix for both structures), and juice pH (5.7 for greenhouse and 5.6 for screenhouse). Overall, it can be concluded that under the weather conditions of Oman, although greenhouses are still needed during spring/summer, screenhouses can be used during winter without jeopardizing crop production quantity and quality. Keywords: Evaporative cooling, Evapotranspiration, Radiation use efficiency, Water user efficiency. Total water use efficiency, Climate.