Unheated Greenhouse Research Articles

Effect of Cutting Size and Basal Heat on Rooting of Micromeria fruticulosa Stem Cuttings

Micromeria fruticulosa (Bertol.) Grande is a small pulviniform shrub, belonging to the Labiates, and characterized by twisted stems and pink-purple flowers. Endemic to Campania and Sicily (Italy), M. fruticulosa grows from sea level to 600 m altitude. This specie might be considered an excellent native plant for landscape purposes in Mediterranean areas because of its long flowering period, extending from November to June, and its tolerance to heat and drought. The exploitation of wild plants for ornamental purposes implies knowledge on the factors influencing the propagation methods. Root development of stem cuttings of M. fruticulosa was investigated in relation to basal heat and cutting size. Softwood terminal cuttings of a clone grown in Sicily were trimmed to two sizes: short (3 cm) or long (6 cm) length. Propagation was performed in unheated greenhouse covered with clear polyethylene and external 70% shade-cloth. To verify the rooting response to basal heat, half of the cuttings were placed on a basal heated bench (22 ± 2 °C constant temperature) while the remaining were placed on an unheated bench. Acclimatized rooted cuttings were thereafter transplanted into each plastic pot (diameter 16 cm). Plants were thereafter transplanted in the open field and were evaluated for their ornamental value. Basal heat promoted earlier rooting and positively affected adventitious root formation. Six cm long cuttings exposed to basal heat exhibited the best development in terms of number and length of adventitious roots. Flowering plants derived from 6 cm long cuttings exposed to basal heat showed the highest number of flowering branches and flowers per plant.

Microclimate and agronomical effects of internal impermeable screens in an unheated Mediterranean greenhouse

In unheated greenhouses in mild-winter areas, low-cost, fixed, water-impermeable plastic screens are frequently installed in winter cycles of the vegetable crops more sensitive to fungal diseases. They are used to prevent rain and condensation falling on the crop and to improve the greenhouse air temperature. Two experiments were carried out to quantify how fixed and movable impermeable screens affect microclimate and crop behaviour in an unheated greenhouse in a mild-winter area. The fixed screen improved the night-time temperature and humidity of the air below the screen, and reduced the water condensation on its inner plastic surface or the proliferation of fungal diseases, but did not completely prevent it. Compared to the greenhouse without screen, the movable screen, usually unfolded at night, increased the night-time temperature of the air and the crop, reduced the night-time relative humidity of the air below the screen, prevented the water condensation on the screen or the crop, accelerated melon crop development, and significantly increased early marketable yield of melon fruits and their quality, but it did not substantially affect the substrate temperature, or the total marketable yield of melon fruits. In the comparison of the greenhouse with fixed versus movable screen, no substantial differences were found for a winter cucumber cycle in night-time temperature and relative humidity of the air below the screens, in shoot biomass or in fresh weight of total and marketable cucumber fruits. This can be mainly attributed to the small differences between both treatments in the shortwave radiation reaching the crop.

Productivity of a building-integrated roof top greenhouse in a Mediterranean climate

Urban Agriculture (UA) is an emerging field of agricultural production aimed to improve food security and the resilience of cities and to improve the environmental, social, and economic sustainability of urban areas. One of the options of UA are roof top greenhouses (RTGs), which are greenhouses built on the roof of a building, typically fitted with soilless culture systems. Further benefits can be achieved if the greenhouse and building are integrated, so that they exchange and optimise energy, water and CO2 flows. Integration is possible if the RTG and the building can exchange air and can collect rain water or use properly treated grey water for irrigation. Such type of integrated RTG is referred to as i-RTG. Both the environmental profile and the social value of i-RTGs have been studied, but information on their productivity is rather scarce. As the economic viability of i-RTGs is given by the value of all services provided, including the yield, the productivity of such systems needs to be maximised. This study attempts this, through the analysis (and discussion) of an i-RTG built in a Mediterranean climate (Barcelona area, Spain), producing beef type tomatoes (“Coeur de boeuf” cultivar).The experimental study showed that the i-RTG had poor light transmission. As a consequence, yield was low and the radiation use efficiency (RUE), referred to the outside radiation, was lower than in standard production (unheated greenhouses) in the same region. Nevertheless, RUE referred to the radiation above crop canopy, was similar in the i-RTG and standard greenhouses. Compared to conventional greenhouses in the area, which are generally unheated, a strong asset of the i-RTG was its improved (night-time) temperature regime, thanks to the thermal connection to the building. This advantage translates into energy savings referred to greenhouses on the ground, in case such greenhouses were heated.In order to discuss possible improvements, we adapted an existing greenhouse tomato production model to simulate this particular type of system. After validation, we quantify and discuss the yield rise that could be achieved by improving transparency of the RTG and by increasing CO2 concentration through daytime connection to the building. We show that there is potential to more than double the yield in comparison with the measured crop yield in the i-RTG. Last but not least, we discuss the option of switching to a cropping pattern more adequate for this growing system, that is: to extend the cropping cycle during the winter months, which is not possible in unheated greenhouses in the area.To our knowledge, this work is the very first attempt to evaluate productivity of roof top greenhouses in mild winter regions and quantify options for improving their agronomic performance.

Evaluation of the SALTMED model for tomato crop production in unheated greenhouses

The SALTMED model is one of the few available generic models that can be used to simulate crop growth with an integrated approach considering water, crop, soil and field management. It is a physically based model using the well-known water and solute transport, evapotranspiration, and water uptake equations. The possibility of using models able to simulate crop growth with this integrated approach can be very useful for farmers as a decision support tool, helping with decisions such as: what crop/variety to use, when to plant and harvest, when and how much to irrigate, what yield to expect under a specific irrigation system or strategy, when using a certain water quality, and also to allow increasing water use efficiency and crops productivity. The SALTMED model has been calibrated and validated for several field crops, in several parts of the world, including field tomato. However, the greenhouse environment has specific conditions that are not always easy to simulate with generic crop growth models. The objective of this work was to evaluate SALTMED model for a tomato crop grown in unheated greenhouse conditions. Climatic data and crop parameters were recorded during two years, in two greenhouses with different ventilation management, and three different sets of data were used to calibrate and to validate the model. The results showed that the model can accurately simulate soil grown tomato crop yield under Mediterranean unheated greenhouse conditions.

Improvement of greenhouse climate control in Mediterranean conditions: a case study from Turkey

In Turkey, protected cultivation includes the production in greenhouses and under low plastic tunnels. The total area reached 64 912 ha in 2014, of which 76% is greenhouses. As in the other Mediterranean countries, protected cultivation is mainly located where the climatic conditions are favourable for production without any additional heating. However, in the last decade high tech greenhouses have been introduced particularly in order to use renewable alternative energy for greenhouse heating. In this research a greenhouse climate and crop yield model was used in order to evaluate possible improvements under simple structures and high tech greenhouses, applying different climate control strategies in different locations of Turkey. The results showed that significant yield increase could be provided by increasing the heating set-point to 13°C in unheated low tech greenhouses. Also evaporative cooling systems could be used for early planting dates for high tech greenhouses. It was concluded that greenhouse climate and crop yield model could be used as a tool to estimate the improvements of climate control strategies on yield.

Interaction effect of planting date and foliar application on some vegetative growth characters and yield of broccoli (Brassica olerasea var italica) grown under unheated plastic tunnel

This study was conducted during autumn season of 2016 at Grdarasharesearch field, Agriculture College, Salahaddin University-Erbil, 434 meters abovesea level to determine the effect of planting date and foliar application on the yieldand some vegetative growth characters of broccoli. Seeds of Agassi F1 Hybridbroccoli cultivar were planted in the beginning of August 2016 then the seedlingswere transplanted to unheated greenhouse in two different periods of time, the firstwas on 20th October and the second one was 20 days after the first transplantingdates which was on 10th November 2016. Foliar fertilizer PRO.SOL (10+20+30)was also used with three levels (75g PRO.SOL/100 L water), (150g PRO.SOL /100L water), (225g PRO.SOL /100 L water including control (0 g PRO.SOL/100 Lwater (spray with distilled water with factorial RCBD design). The result indicatedthat planting date significantly influenced some vegetative growth characters ofbroccoli and higher result was recorded for the total yield for seedlings transplantedin November. The average weight of main and secondary heads compared to thecontrol, the main heads of the seedlings transplanted on 20th October producedhighest yield while lateral heads recorded lower weight in compare to thosetransplanted on 10th November. However, the yield of the main heads recorded abetter result for those grown in November. Foliar application had also significantlyaffected both yield and vegetative growth of broccoli. Seedlings sprayed with150g/100 L water recorded the highest yield and vegetative growth. The interactionof foliar and time had a significant effect of the total yield and some vegetativegrowth at both times. The best result recorded at both times (October andNovember) and sprayed with 150g of PRO.SOL/100 L water compare to thecontrol (0 g PRO.SOL/100 L water) and the other foliar application levels.

Numerical prediction of thermal environment and energy consumption of three different greenhouses under hot and semi-arid climate

The evaluation of the thermal performance of a greenhouse requires an understanding of the energy exchanges between its components. In recent years, Computational Fluid Dynamics (CFD) proved to be efficient to predict the microclimate inside greenhouses, but few CFD works analyzed hot and arid climatic conditions. The aim of the present study is to investigate the impact of such specific conditions prevailing in the southern Mediterranean basin considering three different unheated greenhouses equipped with rows of canopy (tunnel, Venlo and plastic vertical wall greenhouse). 2D simulations were conducted in order to estimate the influence of the greenhouse geometry and cover material on the energy balance, focusing in particular on the heat losses. To establish the boundary conditions and validate the model, experiments were launched inside the greenhouses. Simulations were conducted for two contrasted conditions: the nocturnal period when the energy performance of each type of greenhouse was investigated, and the diurnal period for which a solar day was simulated taking account of natural ventilation. A good agreement was found with experiments concerning the temperature profiles and the energy losses. The predicted stable flow patterns slightly differed from one greenhouse to another for each condition: during the night they all disclosed two convective loops sweeping the floor, rising along the middle of the greenhouse, cooling down along the roof and moving down along the sidewalls of the greenhouse, while during the day flow patterns were strongly impacted by the vent openings. The obtained values (temperature and velocity) were coherent with results found in the literature for different greenhouse types and sizes. The developed tool offers potential applications in research on greenhouse climate to assess different cover material performances. It could also be used to investigate the energy consumption and partition for different greenhouse shapes, different crop densities different growth stages.

Quantitative Analysis of Greenhouse Kohlrabi (<i>Brassica oleracea var. gongylodes </i>L.) Growing

This study were carried out to of different sowing time in order to determine the effects on plant growth of kohlrabi cultivation under Samsun condaitions during the autumn growing periods in unheated greenhouse. Four different seed sowing times (1st September, 15th September 1st October, 15th October), two different kohlrabi cultivars (Kolibri F1 and Korist F1) and two mulch applications (mulch covered and uncovered) were used in this study.The plant growth parameters analyzed (total plant dry weight, leaf area ratio, specific leaf area, net assimilation rate and relative growth rate) were found statistically significant (p<0.05). The highest total plant dry weight (114.1 g) was obtained from mulch application and 1st September seed sowing time. The highest leaf area ratio value were obtained in both mulch application the Kolibri F1 variety grown on October 15th. The highest net assimilation rate (0.65 g cm-2 day-1*1000) and relative growth rate (0.0090 g g day-1) were obtained from mulch covered plants grown in Kolibri varieties during September 1st. As a result, in this study higher dry matter accumulation was achieved by 1st September seed sowing times in vegetable growing in the last season in the greenhouse. In this way, the plants have successfully grown up and increased their productivity by entering the winter months, when the temperature and light intensity are decreasing.

EFFECT OF SPRAYS NUMBER AND FOLIAR MICRONITE 35 ON GROWTH AND YIELD OF PEPPER UNDER UNHEATED GREEN HOUSE

This research was conducted during the season of 2014 - 2015 inside unheated green house to investigate the effect of sprays number and different concentrations of micronite 35 (0.0, 1.0, 2.0, 2.5 and 3.0 cm3 .l-1) and their interaction on growth and yield of Pepper var. California Wonder with using (RCBD) with three replicates. Results showed that the sprays number and the concentrations of micronite 35 and their interaction had a significant effect on all the characteristics that studied. The interaction of three sprays with 3 cm3 .l-1 of micronite 35 gave the highest average of plant height (103.12cm), branches number.plant-1 (11.61), leaves number.plant-1 (107.41) leaf area.plant-1,(121.31dc2) flowers number (80.96) and set of flowers percentage (92.403). Results also gave the highest average of fruits number.plant-1, fruit long, fruit weight, yield-1. plant, early yield, and yield /greenhouse that were (38.81, 11.63cm, 80.99gm, 3.143kg, 0.229ton, 6.034ton) respectively. While the average was 10.86 fruits number.plant-1, 5.08cm fruit long, 30.71g. fruit weight, 0.333 kg. yield. Plant-1, 0.136ton early yield and 0.639ton yield.greenhouse-1 respectively at compared with control treatment.

Modelling changes to an unheated greenhouse in the Canadian subarctic to lengthen the growing season

In remote communities in Northern Canada, food is delivered by aircraft and as a result is very expensive. Food self-sufficiency would make these communities more sustainable and resilient, but the climate is not suitable for outdoor gardens. The Iqaluit Community Greenhouse (ICG) Society purchased and, for three months in a year, operates a co-operative greenhouse that allows the growing of leafy greens. Modifications to conventional greenhouse designs, such as insulation on the north walls and roof, night covers, and adding thermal mass and a vestibule, have been shown to extend the growing season in unheated greenhouses in similar cold climate areas. A computer simulation of the ICG was constructed using TRNSYS in order to quantify the effects of different greenhouse modifications on the growing season.

Short evaluation of eggplant production and variety usage in Romania – short overview and perspectives

Abstract Eggplant (Solanum melongena L.) became wide-spread after the First World War in Romania. The most important growing areas of this plant are located in the southern, south-eastern, and south-western parts of Romania and are usually cultivated on open fields as well as in unheated greenhouses. In the past, only Romanian OP varieties were grown. Over the past ten years, requirements of eggplant varieties have increasingly shifted towards productivity, uniformity, and high tolerance to stress factors, diseases, and pests. Therefore, the cultivation of hybrids and the disappearance of Romanian OP cultivars have intensified. Due to monoculture practice, the soil was attacked by pathogens in many areas. As a result, grafting became necessary to be put into practice. Consumption of eggplants is about 4.5 kg per person per year in Romania and they are consumed in many different ways such as baked, grilled, or as a special cream. Agrosel SRL has gained a significant role in supplying the Romanian vegetable seed market over the past twenty years and has started its own hybrid programme to renew eggplant production in Romania.

Irrigation scheduling and water use efficiency of cucumber grown as a spring-summer cycle crop in solar greenhouse

This 3-year study aimed to determine the most appropriate irrigation application and water use efficiency programs based on Class A Pan evaporation for mini (Lebanese) type cucumber plants grown as a first crop under protected conditions in a solar greenhouse. Research was carried out in an unheated solar greenhouse constructed on the lands of Ataturk Soil Water and Agricultural Meteorology Research Institute in Kirklareli, Northwestern Turkey. In order to prevent excessive increase in temperature within the protective structure, the semicircular shaped unheated greenhouse with sidewall ventilation was screened with 75% green-coloured shading net. The experimental layout of the study was a split-plot design with 3 replications. Two irrigation intervals (D1–2days and D2–4days) and four different plant–pan coefficients (0.75, 1.00, 1.25 and 1.50) were applied to main and subplots in the experiment. It was determined that cucumber yields increased with the increase in the irrigation water amount and reached averages of 128.2 and 126.5tonha−1 with use of highest plant pan coefficients of 1.50 and 1.25 vs. 90.7 and 90.9tonha−1 under the lowest Ecp coefficient of 0.75. The highest irrigation water use efficiency (IWUE) and water use efficiency (WUE) values of about 56kgha−1m−3 and 42kgha−1m−3 were obtained from the conditions with least applied irrigation water amounts. The average seasonal value of the yield response factor (ky) estimated on the basis of data from the 3-year study was determined as 0.75.

Effects of Substrate Type on Plant Growth and Nitrogen and Nitrate Concentration in Spinach

The effects of three commercial substrates (a mixture of forest residues, composted grape husks, and white peat, black peat and coir) on plant growth and nitrogen (N) and nitrate (NO3) concentration and content were evaluated in spinach (Spinacia oleracea L. cv. Tapir). Spinach seedlings were transplanted at 45 days after emergence into Styrofoam boxes filled with the substrates and were grown during winter and early spring in an unheated greenhouse with no supplemental lighting. Each planting box was irrigated daily by drip and fertilized with a complete nutrient solution. The NO3 content of the drainage water was lower in coir than in the other substrates. However, shoot NO3 concentration was not affected by substrate type, while yield and total shoot N and NO3 content were greater when plants were grown in peat than in the mixed substrate or the coir. Leaf chlorophyll meter readings provided a good indication of the amount of N in the plants and increased linearly with total shoot N.

Approaches for evaluation of resistance to European canker (Neonectria ditissima) in apple

European canker is caused by the fungus Neonectria ditissima (Neonectria galligena, formerly Nectria galligena). The disease causes significant losses to apple production in Sweden and many other countries with a temperate wet climate. Application of fungicides and good horticultural practices do not prevent canker damage in nurseries and orchards. Disease outbreaks damage and even completely destroy trees. To date, complete resistance to N. ditissima is not known in apple, but cultivars differ considerably in their level of partial resistance. To be able to conduct breeding for resistance to European canker, reliable plant tests are urgently needed. Differences in resistance to N. ditissima (colonization rate; CR) in apple cultivars were evaluated by wound inoculations with a standardized number of conidia on cut shoots from mature trees placed in a climate chamber and on potted trees in an unheated greenhouse. Infection percentage (Inf%) was assessed by 'natural' inoculations in leaf scars under high infection pressure in the field. All the experiments were carried out over 2 years. Lengths of lesions were measured at regular time intervals on five occasions for shoots and seven occasions for trees. Considerable differences in CR and Inf% were found among the cultivars. The relative levels of resistance obtained are consistent with previous reports for most cultivars. Assessment of CR (area under curve) and Inf% thus proved to be useful tools for evaluation of resistance to European canker. Also, some potentially new sources of resistance were identified.

Performance of three numerical models to assess winter chill for fruit trees—a case study using cherry as model crop in Germany

The Meckenheim fruit growing region in Western Germany may be affected as a consequence of climate change by lack of chilling, i.e. a cold period in the winter required for tree species to flower in the subsequent spring. As sweet cherry requires high chill, 160 potted trees of three sweet cherry cultivars with threefold different chilling requirements were cultivated in a large experiment over 4 years, either in the orchard or in an unheated greenhouse (simulated climate change). The orchard temperatures in the warmer winter (6.0 °C) exceeded those in the unheated greenhouse (4.7 °C) in the cold winter. Chilling computations for this region showed that cherry trees of low chill cultivar ‘6000CZ’ required 22.3–26.6 chill portions (CP), medium chill cv. ‘Brooks’ about 37.9–54.4 CP and the high chill cv. ‘Schneiders spate Knorpelkirsche’ about 54.4–79.3 CP for a natural flowering. Cherry trees cv. ‘6000CZ’ receiving <300 CH, cv. ‘Brooks’ <500 CH and cv. ‘Schneiders spate Knorpelkirsche’ <700 CH were unable to flower, equivalent of 50 % of the assumed chilling optimum of the respective cultivar. Maximum chill accumulation in this region is currently achieved, so that warmer winters may reduce the available chill. The beginning of leaf drop was identified as a suitable initiation point for computing chill accumulation. Overall, the work has shown that environmental change has an effect on chilling availability in Meckenheim and possibly other fruit growing regions along 50°N. The insights gained ultimately highlight the need for cross-sectoral, adaptive management practices that jointly target a sustainable regional development.

Lamb’s lettuce mineral content in floating system

In recent times lamb's lettuce become a very interesting leafy vegetables to consumers because of its rich mineral and chemical composition. Due to a market demand for this valuable leafy vegetable throughout year, it is necessary to research other production technologies (such as floating system) beside conventional one. The aim of this research was to determine the influence of two different nutrient solutions on yield, dry matter, mineral and nitrate content of lamb's lettuce. The experiment was laid out according to the randomized block scheme with three replications in floating hydroponic system in unheated greenhouse. In the first pool nutrient solution was prepared according to Pimpini and in the second pool according to Johnson with a smaller concentration of potassium nitrate. Sowing of lamb's lettuce, cultivar 'Juwabel' was conducted on March 17 in polystyrene trays, filled with inert substrate. Nutrient solution prepared according to Johnson resulted with higher values of yield (1.26 kg m-2), dry matter (12.95%), phosphorus [47.92 mg 100 g-1 fresh weight (fw)], magnesium (53.1 mg 100 g-1 fw) and calcium (116.6 mg 100 g-1 fw). Also, smaller values of potentially harmful nitrate were measured (1425 mg kg-1 NO3 fw) compared to lamb's lettuce grown in Pimpini's nutrient solution (1881 mg kg-1 NO3 fw). Due to higher yield, dry matter and concentrations of the most observed minerals as well as smaller amounts of nitrate, nutrient solution according to Johnson can be proposed for growing of lamb's lettuce in floating system.

EFFECT OF GREENHOUSE NIGHT HEATING BY SOLAR ENERGY SYSTEM AND ORGANIC FERTILIZER ON THE PRODUCTIVITY OF TOMATO

The aim of this experimental work was to investigate the effect of utilizing different rates of dried biogas digester residue as organic fertilizer and solar energy for heating greenhouse on growth, development, productivity, and fruit quality of tomato hybrid (Agiad 7) during winter of two following growing seasons (2013 and 2014). Two similar gable-even-span greenhouses were functioned at EL-Sabahia Horticultural Research Station. The seedlings of tomato hybrid Agiad 7 were planted on the 1st week of December during the two growing seasons under two different greenhouse microclimates. The first greenhouse (GH1) was equipped with a complete heating system utilizing the solar energy, while, the second greenhouse (GH2) was mechanically ventilated during daylight without heating system. Referring to the effect of the solar heating system on the greenhouse microclimate, the obtained results revealed that, the maximum and minimum indoor air temperatures of greenhouse (GH1) were (24.3 and 11.6), (26.0 and 12.1), (28.1 and 15.2), (28.6 and 16.3) and (30.6 and 17.1) oC during the experimental period (from December to April), respectively. On the other hand, the maximum and minimum indoor air temperatures of the greenhouse (GH2) were (25.3 and 6.0), (26.8 and 6.3), (28.0 and 10.8), (29.8 and 13.4) and (32.6 and 15.3) oC during the same period, respectively. Referring to the effect of organic fertilizer rates on the tomato plant vegetative growth, showed that increasing the organic fertilizer rate significantly increased all the studied characters; plant length, leaf area, number of leaves per plant, dry weight and stem diameter in both seasons whereas, the fresh weight increase was not significant in 2014 season. The data also, showed that plants fertilized with 30 m3/fed from dried biogas residue gave the best vegetative growth characteristics; plant height, leaf area, fresh, dry weight per plant and stem diameter as compared with other used organic levels in both seasons. Early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan were significantly increased by increasing the organic fertilizer rate in both 2013 and 2014 seasons. For the heated greenhouse (GH1), the percentages increase in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan were 28.64, 13.04, 6.89, 20.84 and 20.84%, respectively for dried biogas residue of 30 m3/fed over those of farm yard manure, respectively in 2013 season. For the unheated greenhouse (GH2), the percentages increase in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan over those of farm yard manure were 13.18, 16.29, 8.30, 25.52 and 25.52%, respectively for 30 m3/fed dried biogas residues in same season. Whereas, in the second season 2014, for the heated greenhouse (GH1), the percentages increase in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan over those of farm yard manure were 24.87, 11.18, 6.89, 18.86 and 18.86%, respectively for 30 m3/fed dried biogas residue, respectively. For the unheated greenhouse (GH2), the percentages increase in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan over those of farm yard manure were 17.18, 16.29, 5.87, 22.84 and 22.84%, respectively for 30 m3/fed dried biogas residues in same season. Concerning effect of the microclimatic conditions of (GH1) it was at and around the optimal level for the tomato crop, resulting in increase the tomato growth, development, and productivity. The percentages increase for greenhouse GH1 over GH2 greenhouse in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan were 21.32, 17.42, 12.87, 32.28 and 32.28%, respectively, in 2013 season while, they were 16.06, 15.33, 10.14, 27.08 and 27.08%, respectively in 2014 season.

Current situation and future trends of greenhouse vegetable production in Croatia

Croatia belongs to the Mediterranean countries that are considered to be very favorable for such cultivation. With a convenient location, the large fluctuations in the price of seasonal crops are noticed, which indicates the existence of a market for the off-season production, and possibility to decrease an import of crops that can be produced in Croatia. To overcome the fact of growing imports of fresh and processed vegetables, The Operational Program for the Development of Vegetable Production was accepted, with the aim to increase the area under greenhouses, to achieve self-sufficient and continuous production of vegetables for the Croatian market and exports. Beside increasing of greenhouse area and applying new technologies (i.e. soilless culture), there is a need to increase and organize wholesales markets and storage capacities, and to introduce new standards of market quality. Croatian Chamber of Agriculture in 2011 estimated that the vegetables is produced on 72, 433 ha or 5% of the total arable land with an annual production of about 450 thousand tons. Greenhouse vegetable production represents approximately 3% of total production. In 2013, Agricultural Advisory Service determined by field research there is about 432 ha of heated and unheated greenhouse for soil production and about 60 ha of soilless culture. The off-season production when prices are much higher is certainly one of the reasons that should motivate producers to consider starting production in greenhouses. However, it requires heated greenhouses with climate control and year-round hydroponic production, which mean additional costs for producers.

Comparison of Seed Longevity for Thirty Forest, Grassland and Weed Species of the Central European Flora: Results of a Seed Burial Experiment

ABSTRACT We compared seed longevity of herbaceous species in three habitat types differing in stability. We hypothesized that seed longevity is the lowest for forest species (living in stable habitat), the highest for weeds, while species of xerothermic grasslands take an intermediate value. Ten species were selected from each of the three habitats with balanced representation of plant families among habitats. Seeds of the 30 species were deep buried at 65 cm depth, then replicates recovered after 1, 2, 3, 4 and 6 years, and germinated in an unheated greenhouse. Weeds expressed the highest germination rate (36.1% in average) exceeding forest (14.4%) and grassland species (10.2%) which did not differ significantly. The number of species with transient, short-term persistent and long-term persistent seed bank, respectively, was 1, 7 and 2 for grasslands; 1, 3 and 6 for forests; and 0, 1 and 9 for weeds. As expected, weeds possessed the highest seed longevity. Contrary to our assumption, low seed longevity w...

Supercooling Points of Murgantia histrionica (Hemiptera: Pentatomidae) and Field Mortality in the Mid-Atlantic United States Following Lethal Low Temperatures.

The harlequin bug, Murgantia histrionica (Hahn), is a serious pest of brassicaceous vegetables in southern North America. While this insect is limited in its northern range of North America, presumably by severe cold winter temperatures, specific information on its cold hardiness remains unknown. We determined the supercooling points (SCPs) for Maryland and Virginia adult populations and found no significant difference among these populations. SCPs were similar for adults ([Formula: see text] = -10.35 °C; [Formula: see text] 2.54) and early and late instar ([Formula: see text] = -11.00 °C; [Formula: see text] 4.92) and between adult males and females. However, SCPs for first instars ([Formula: see text] = -21.56 °C; [Formula: see text]1.47) and eggs ([Formula: see text] = -23.24 °C; [Formula: see text]1.00) were significantly lower. We also evaluated field survival of overwintering harlequin bug adults during extreme cold episodes of January 2014 and January 2015, which produced widespread air temperatures lower than -15 °C and subfreezing soil temperatures in the Mid-Atlantic Region. After the 48-h episode in 2014, bug mortality in exposed field sites averaged 88%, compared to <5% mortality of bugs sheltered in an unheated greenhouse (recorded minimum temperature 4.4 °C). After the 2015 episode, ∼80% of adults that were established in the field the previous November and then sheltered in an unheated garage during the episode, died, in contrast to 96% mortality in exposed field sites. Our results provide new information on M. histrionica overwintering biology, and thermal limitations to its distribution, which leads to improved predictive capabilities to forecast pest severity.