Hail Nets Research Articles

Tuning the Proportional-Integral-Derivative Control Parameters of Unmanned Aerial Vehicles Using Artificial Neural Networks for Point-to-Point Trajectory Approach.

Nowadays, trajectory control is a significant issue for unmanned micro aerial vehicles (MAVs) due to large disturbances such as wind and storms. Trajectory control is typically implemented using a proportional-integral-derivative (PID) controller. In order to achieve high accuracy in trajectory tracking, it is essential to set the PID gain parameters to optimum values. For this reason, separate gain values are set for roll, pitch and yaw movements before autonomous flight in quadrotor systems. Traditionally, this adjustment is performed manually or automatically in autotune mode. Given the constraints of narrow orchard corridors, the use of manual or autotune mode is neither practical nor effective, as the quadrotor system has to fly in narrow apple orchard corridors covered with hail nets. These reasons require the development of an innovative solution specific to quadrotor vehicles designed for constrained areas such as apple orchards. This paper recognizes the need for effective trajectory control in quadrotors and proposes a novel neural network-based approach to tuning the optimal PID control parameters. This new approach not only improves trajectory control efficiency but also addresses the unique challenges posed by environments with constrained locational characteristics. Flight simulations using the proposed neural network models have demonstrated successful trajectory tracking performance and highlighted the superiority of the feed-forward back propagation network (FFBPN), especially in latitude tracking within 7.52745 × 10-5 RMSE trajectory error. Simulation results support the high performance of the proposed approach for the development of automatic flight capabilities in challenging environments.

Design and evaluation of an agrivoltaic system for a pear orchard

Agrivoltaic systems are mostly deployed on arable farm land. An interesting application of agrivoltaics for permanent farming such as pear orchards, is in replacing the protective function of hail nets by semi-transparent PV modules. In this study, a theoretical framework is used to design the optimal agrivoltaic lay-out regarding the levelized cost of electricity, electricity generation and incident irradiance. This incident irradiance is modelled using a 3D light simulation tool, capable of including the light distribution within the canopy walls. Given the practical constraints (orientation, planting distance, maximum wind load, protection function), present in an existing pear orchard, a double-inclined PV structure with a PV module transparency level of 40% was used. This system was constructed in Bierbeek, Belgium. Results of the first year of operation are presented and the models used are validated. It is concluded that this application is promising, with positive effects of the climatological conditions, robust energy generation and a minimum loss of 16% on pear yield. Nevertheless, at this moment, the system is financially unviable and a long-term analysis of the shading effect on crop yield and quality is needed before the large-scale deployment of this technology.

Effects of Four Photo-Selective Colored Hail Nets on an Apple in Loess Plateau, China

Hail, known as an agricultural meteorological disaster, can substantially constrain the growth of the apple industry. Presently, apple orchards use a variety of colored (photo-selective) hail nets as a preventative measure. However, it is unclear which color proves most effective for apple orchards. This study provides a systematic investigation of the impact of four photo-selective colored hail nets (white, blue, black, and green; with white being the control) on the microenvironment of apple orchards, fruit tree development, fruit quality, and yield over a two-year period (2020–2021). Different photo-selective nets do not evidently alter the intensity of light, although the nets’ shading effects decrease in the order from black to green to blue. Among them, blue nets increased the proportion of blue light, while green nets enhanced the proportion of green light. On the other hand, black, green, and blue nets diminished the proportion of red and far-red light. Such photo-selective nets effectively lowered soil temperature but did not have an impact on relative humidity and air temperature. Encasing apple trees with blue nets promoted growth, increasing shoot length, thickness, leaf area, and water content, while simultaneously decreasing leaf thickness. Black nets had comparable effects, although the impacts of green nets were inconsistent. Different photo-selective nets did not significantly influence the leaf shape index or overall chlorophyll content. However, black and green nets reduced the chlorophyll a/b ratio, while blue nets slightly boosted this ratio. Additionally, blue nets proved beneficial for apple trees’ photosynthesis. With the employment of a principal component analysis and comprehensive evaluation, this study concludes that blue nets offer the most favorable environmental conditions for apple growth while protecting apple orchards against hail, compared to black, white, and green nets.

Advances in the Sustainable Use of Plastics in Horticulture—Perspectives, Innovations, Opportunities, and Limitations

The use of plastics in horticulture is reviewed with respect to its sustainability based on the traditional criteria of triple Rs (reduce, reuse, and recycling) plus a re-place strategy, taking into account possible alternatives. Hail (and insect) nets made of HD-PE, with their long-term use mostly on apple and polytunnels of LD-PE for cherry and strawberry as well as solarisation mulches (reuse), were found to be relatively sustainable solutions for their needs and are currently without alternatives. In contrast, standard black mulch, with its largest share among horticultural plastics, had the widest range of sustainable alternatives, ranging from biodegradable to spray mulch; few sustainable alternatives are available for fleeces and reflective mulches. For the third sustainable option, pilot recycling schemes were examined, such as PolieCoTM (Italy), MAPLATM (Spain), and ERDETM (Germany); they collect 30–50% of the agricultural plastics used in their respective areas, with a successful retrieval growth rate of ca. 20% per year in the case of ERDETM. For the fourth new R option (replace), future sustainability perspectives for the predominant black mulch are research into and development of better, biodegradable, non-fossilbased plastics, sprayable mulch; microbes for the digestion of deployed polyolefins and, for a certain limited range (on shade tolerant crops or in high-light intensity environment), hail nets and polytunnels that are equipped/substituted by/with solar panels (“agri pv”) for the concomitant sustainable production of green renewable energy.

Insect Pollinator Monitoring in and around a Netted Plot of Apple Trees—Biosafety Implications for Genetically Engineered Fruit Trees

The complete netting of orchards is one strategy to protect fruit trees from pest and pathogen damage by reducing insect movement. When the cultivated trees were derived from genetic engineering (GE), reduced pollinator movement may also reduce outcrossing to cultivated or wild non-GE trees. We report on a field study over four years in a plot of apple tress supplied with insect side nets and covered with hail nets that were closed from shortly before flowering to harvest. A reduced number of arthropods in general, and large bees in particular, were recorded inside the netted plot compared with outside. However, wild bees colonized the plot before the net was closed and built up populations inside. An additional experiment demonstrated that small bees were able to cross the hail net. While the nets were effective in excluding large bees as active pollen vectors, the proportion of small bees acting as such remained unquantified. Furthermore, a companion study showed occasional cross-pollination events through the netting. For the field release of GE apple trees, acceptable levels of outcrossing thus need to be defined.

Influence of the environmental conditions under hail nets on the irrigation and fertilization efficiency in ‘Golden Delicious’ apple trees on replant soils

ISHS IX International Symposium on Irrigation of Horticultural Crops Influence of the environmental conditions under hail nets on the irrigation and fertilization efficiency in ‘Golden Delicious’ apple trees on replant soils

Post-Harvest Quality Evaluation of "Soreli" Kiwifruit at Two Ripening °Brix Values from Vineyards of Different Age Under Hail Nets.

The application of anti-hail nets is a practice that has been employed for a long time on different fruit and vegetable cultivations and in different fields of the world. In this work, we checked the effects of shading with white anti-hail nets on the post-harvest quality of “Soreli” kiwifruit collected at two different °Brix (7–8 and 8–9) from vineyards of two different ages (8 and 9 years) and stored at 1 °C for 90 days. It was observed that during the storage, the firmness and color parameters (L*, a*, b*, and Chroma) and the SSC content were generally higher in kiwifruit samples harvested in open field than in those under the nets. Regarding the bioactive compounds, the open field samples showed higher values in total flavonoids content during storage, and the content of carotenoids and chlorophylls in fruits grown in open fields was higher from 30–45 days up to the end of the storage. In contrast, the polyphenols and ascorbic acid values of fruits in open fields and under the nets showed a similar evolution of the values from 45 to 60 days. In general, the early and late harvest time based on the °Brix values and the different ages of the kiwifruit plants under the nets did not affect the quality parameters.

Effects of hail nets and reflective ground covers on microclimate and evapotranspiration demand in an apple orchard

Effects of hail nets and reflective ground covers on microclimate and evapotranspiration demand in an apple orchard

Spatial and Temporal Enhancement of Colour Development in Apples Subjected to Reflective Material in the Southern Hemisphere

(1) Background: Climate change associated with a warm autumn often hampers the development of colouration of many fruits including late ripening apple varieties in New Zealand. (2) Objective: This study will provide detailed information on the possibility of enhancing colouration of apples under the diffuse light conditions in autumn in the southern hemisphere (SH). The aim is to obtain a larger proportion of fruit meeting the (red) colour market specifications, especially within the first picks, and to identify both the side of the fruit and its position within the tall trees canopy (3.5 m) as affected by reflective mulch on the ground spread at and over different times. (3) Material and methods: Reflective white textile mulch (Extenday®) was spread in the grassed alleyways 4 weeks or 2 weeks before the anticipated harvest in April on cv. Fuji and Pacific Rose apple trees without hail nets in the Northern Part of the South Island (41° S) of NZ. Fruit colour (blush) was determined by scoring and colourimeter during fruit maturation and at harvest, and fruit quality was determined at harvest by standard methods. (4) Results: (a) In cv. Pacific Rose apple, the reflective mulch increased the scored blush value from 1.5 (<50% blush) to 3.9 (ca. 75% blush) before the first pick, whereas the control fruit (without ExtendayR) reached a final score value of only 3.0. (b) Fruit colour improved after one week of exposure to reflective mulch in the SH. (c) The scored blush on fruit near the trunk with reflective mulch doubled (Pacific Rose) or tripled (Fuji) at harvest in comparison with trees with grass alleyways (control). (d) Two and four weeks of reflective mulch enhanced colouration of the down facing side for fruit of both cultivars, especially for fruit from the inside of the canopy near the tree trunk. However, reflective mulch significantly improved blush by 20% on fruit from the periphery of the canopies of the tall trees in both cultivars without significantly affecting fruit firmness, soluble solids, starch breakdown or ripeness. (5) Conclusions: The results from ca. 2000 colour measurements showed that the short exposure of at least two weeks of reflective mulch was sufficient for enhancing colouration for outside, inside and down facing sides of the fruit of both cultivars. As a result of this surprisingly short and efficient exposure time for these tall trees (3.5 m), the reflective mulch increased the portion of fruit harvested in the first pick by 8% (Fuji) and by 27% (Pacific Rose) with improved fruit storability or export quality and thereby increased financial returns to the grower in the SH.

Innovative Strategies for the Use of Reflective Foils for Fruit Colouration to Reduce Plastic Use in Orchards

(1) Background: Plastic in fruit orchards represents an environmental issue due to large CO2eq emissions associated with its production from fossil fuel and disposal (often incineration). (2) Materials and methods: Apple cv. “Braeburn Hillwell” trees on M9 rootstocks under a hail net were used at Campus Klein-Altendorf (CKA), Germany (50 °N) in 2018. In order to reduce the use of plastics to improve the red colouration of fruit particularly under hail nets, three alternatives to the current use of reflective mulch in each alleyway between the tree rows were explored, with uncovered grass alleyways as control. About 2800 colour measurements were done in the four weeks prior to harvest on 720 attached fruit below and above 1 m height in the field, and ca. 6900 additional colour measurements were conducted at harvest. (3) Results: The underlying regulatory mechanisms contrasted between the diffusive reflection of the white woven ground cover (such as LumilysTM or ExtendayTM) in the alleyways and aluminium foil under the trees with regular (straight) light reflection. Good fruit colouring and a plastic reduction were achieved (a) through spreading the white woven ground cover in every other row, and (b) through substituting the white ground cover with aluminium foil (80% recycled). Both methods can reduce greenhouse gas (GHG) emissions (75–110 kg CO2eq/ha for the first option a). (4) Conclusion: Plastic use in fruit orchards can be reduced by multiple use of the material in the same or several years, spreading it in every other row or substituting it by another reflective material, a relevant step towards an environment-friendly sustainable horticulture.

Approaches to Reduce Food Losses in German Fruit and Vegetable Production

Food losses occur in all agricultural value chains, but are especially high in the fruit and vegetable sector. This study quantifies losses of selected fruits (strawberries, apples) and vegetables (lettuce, carrots), identifies the main reasons for food losses, and assesses effective measures for the reduction of these losses. Data were collected in structured interviews with value chain actors from production to food retail and validated in regional expert workshops. Results show that in average years, about 25% of the analysed vegetables are lost at farm level. The range of fruit losses differs widely, from 15% to 20% for strawberries and only 6% to 16% for apples. Weather is a major factor for crop losses, since it can strongly affect product appearance and hence marketability in the food retail sector. There is a lack of alternative market channels for products, which do not meet the high-quality standards for fresh products in the retail sector. Effective measures to reduce food losses are protected cultivation in greenhouses or under hail nets, continuous cooling systems, improved packaging and training of staff. More cooperation and coordination between producers, wholesalers and retailers could also increase the share of marketable products.

Different Methods of Thinning Influenced by Variety and Hail Nets in Apple Orchards

Looking at the effects of thinning on apple quality, the purpose of this study was to investigate the fallouts of thinning methods in different varieties and under hail nets. The experiment was developed in Bavendorf, South Germany. The ‘Pinova’and ‘Braeburn’ apple trees were covered with two types of hail net: white, black and without nets. The following thinners were tested: Mechanical thinning (MT) with the ‘Darwin machine’; chemical thinning with Metamitron (CT-Metamitron) or 6-benzyladenine (CT-BA) and hand thinning (HT). The evaluations were: fruit set, time taken for HT, photosynthesis measurements, fruit retention, yield, fruit quality, and thinning efficacy value. The CT-BA treatment required the highest number of hours to perform HT for both varieties and hail nets. Comparing the varieties, the Pinova demonstrated less efficiency for thinning treatments, hence more hours were needed to thin by hand. Photosynthesis measurements were clearly different between CT-Metamitron versus CT-BA and MT curves, where CT-Metamitron remained in effect for 11 days after the treatment. The HT treatment had the highest value for thinning efficacy with 93% and the MT treatment achieved 74% followed by CT-Metamitron with 64% and CT-BA with 54%. Overall the Braeburn variety is easier to thin than the Pinova variety and the black hail nets showed negative effects on color value.

Modern training systems for forcing sweet cherries – slender spindle or hedgerow for protected growing?

Recent climate change requires crop protection against heavy rain and hail, but also offers new opportunities for horticultural production. While polytunnels and hail nets protect the crops against adverse weather, crops can be forced and harvested, irrespective of the weather. Moreover, the modified microclimate may increase yield as well as the fruit quality. In sweet cherry, growing trees in a closed polytunnel forces the ripeness and reduces fruit cracking. This environmental-friendly approach without fossil fuel enables customers to purchase domestic products with good taste, firmness and carbon footprint as well as good returns to the grower before the field season starts. One objective of the study was to determine the influence of the modified microclimate on flowering and harvest date. Another objective was to compare different planting systems and pruning measures with regard to yield and the efficiency on small cultivation areas. In 2008-2009, three early cherry cultivars ‘Samba’, ‘Bellise’ and ‘Rita’ on dwarfing rootstock GiSelA 3 were grown at Campus Klein-Altendorf (latitude 50.5°N), University of Bonn, Germany. Each research block consisted of 2 single row beddings with a slender crown (system 1: 2.70×2.00 m; system 2: 1.75×2.9 m) and a hedgerow ((2.4×2.0 m)×1.5 m). Half of the trees were grown without cover as control. The pruning of the beddings was made by hand and that of the hedgerow mechanically. The harvest date was advanced by 7-19 days; yield was 7-12 t ha(‑1) in system 1 (1027 trees ha‑1), 8-12 t ha(‑1) in system 2 (706 trees ha‑1) and 13-18 t ha(‑1) in the hedgerow (2000 trees ha‑1). In consequence, the small planting density enables a proper yield on small areas. The use of mechanical thinning signified a substantial time and workload savings.

Hail nets do not affect the efficacy of metamitron for chemical thinning of apple trees

ABSTRACTHail nets reduce photosynthetically active radiation (PAR) and alter the environment under the netting in apple orchards. Thus, we investigated the effect of nets on the efficacy of metamitron, a short-term photosynthesis inhibitor used for fruit thinning. The objective of this study was to evaluate the effect of the netting and metamitron on thinning efficacy, yield, fruit quality and chlorophyll fluorescence in three apple (Malus domestica Borkh.) cultivars. One or two metamitron applications at different doses or rates were applied the tree under different coloured nets. The reduction of PAR was highest with black nets (19%-22%), followed by green (13%-15%) and white nets (6%-11%). There were no significant differences (P> 0.05) in fruit weight or size with or without nets. Double applications of metamitron increased average fruit fresh weight and reduced the fruit set over four experiments. In contrast, single applications were less effective. In two experiments, thinning was associated with lower yields. However, there was no effect in the other two experiments. The double treatments tended to increase the percentage of the crop with fruit larger than 70 mm in diameter. All thinning strategies showed similar inhibition in fluorescence, with the only observed significant differences between treatments occurring when using a single or double application. The results show that netting does not affect the response to thinning with metamitron.

Effect of hail nets and fertilization management on the nutritional status, growth and production of apple trees

Fertilization is a way to feed the fruit trees promoting their growth, production and fruit quality. However, many factors are involved in the process from uptake to allocation and utilization of the nutrients by leaves and fruits. In this study, the effect of different environment under grey hail nets in combination with various fertilization and irrigation management on growth, production, fruit weight and nutritional status of ´Golden Delicious´ apple trees was assessed. Three years old ´Golden Delicious´ trees were grown as modified slender spindle in Holovousy (Czech Republic) on replant soils under drip irrigation. The trees were fertilized through fertigation combined with foliar treatments. The grey hail nets influenced the microclimate of the covered orchard and was linked with significant decrease of the total growth and production of the covered trees limiting the efficiency of the fertilization management on replant soils. This effect may be further connected with limited uptake of N and P into leaves and fruits, altering their partitioning between leaves and fruits during the growing season. Apart from fertilization and irrigation management, the effect of hail nets positively affected the uptake of micronutrients Fe, Mn and Zn. The elements content of fruits is related to the final fruit size and the total fruit set, where the later effect may have a higher impact.

Efficient farming options for German apple growers under risk – a stochastic dominance approach

For a sustainable economic performance of apple production, the determination of efficient farming options considering production risk is crucial. Relying on a permanent crop, apple producers are less flexible to react upon disturbances. Based on data of 134 apple producers operating in the two main production areas in Germany, we compare and determine efficient production options. Furthermore, appropriate risk management instruments (RMIs) are identified using stochastic dominance criteria. In addition, we use Stochastic Efficiency with Respect to a Function to evaluate farming options for defined ranges of relative risk aversion. The results indicate that Red Prince is the most efficient variety in the north and subsidized hail insurance with frost irrigation is superior to frost irrigation as single RMI. In the south Braeburn should be chosen by rational decision makers, but the tested insurance solutions are not as efficient as the common practice of producing apple under hail nets.

Microclimate alterations caused by agricultural hail net coverage and effects on apple tree yield in subtropical climate of Southern Brazil

ABSTRACT The use of hail net coverage on plants is an effective measure to mitigate damage caused by hailstorms. In southern Brazil, areas with apple orchards under hail net coverage have increased in recent years. However, little is known about the possible effects on the microclimate and, consequently, on plant growth, crop yield and fruit quality. The hypothesis of this study was that hail net promotes microclimate and yield changes in apple orchards. The objective was to characterize the microclimate and production of apple trees cultivated under hail nets and to consequently generate numeric parameters that can be used in the management of apple orchards and in crop modeling. The study was conducted in commercial orchards growing under hail net and open sky. Continuous measurements of photosynthetically active radiation (PAR), air temperature and humidity, wind speed and rainfall were performed. Production was assessed based on the number and weight of fruits per plant. The hail nets reduced PAR by 32.8% and the wind speed by 30%. In contrast, coverage did not alter the air temperature, humidity or rainfall. The yield of apples tends to be higher under hail net and this is more pronounced when one hailstorm event occur. These results are important for researchers, and apple farmers to establish criteria for decision making regarding the implementation of hail net coverage and to develop appropriate management systems for protecting orchards to ensure and improve fruit production. Overall, the effects of long-term micrometeorological factors are essential to perform modeling of agricultural production.

Hail nets enhance disruption of sexual communication by synthetic pheromone in codling moth

Hail nets enhance disruption of sexual communication by synthetic pheromone in codling moth

Alternate bearing in fruit tree crops: past, present and future

Alternate bearing, i.e., year-to-year alternation between large and small yields of fruit tree crops worldwide, is often caused by abiotic stress such as late frost at flowering. Economic losses for apple due to alternate bearing were calculated at between ½ and 5 mil US$ year-1 depending on growing region. We recorded the number of flower clusters over three years (autumn 2009 to May 2011) and yield of 2,086 trees of alternate-susceptible 'Elstar' apple on M.9 trees with and without hail nets (for light deprivation) resulting in a data set of 16,000 points. We calculated 'biennial bearing index' (BBI), the ratio of differences in tree yields to cumulative tree yield, and graphed to data to show the tree-to-tree alternation. A Pearson correlation between yield in year x and year x+1 and flower clusters in year x, gave an intersect of 91-106 flower clusters, whereas the mean yield in year x and year x+1, resulted in a range of 72-133 flower clusters, or 9.6 kg tree-1, as a thinning target for sustainable cultivation of 'Elstar' in a pedestrian orchard at 50°N or larger yields with taller trees at a lower latitude. The interaction between the crop levels on the spur and on the whole tree showed that if the tree crop level was low, the tree provided adequate resources for flower bud development in spurs carrying 1 or 2 fruit. Conversely, to obtain good return bloom on normal-to-heavily cropping trees required having good numbers of non-fruiting (also called “resting”) spurs. A scheme for the underlying regulatory mechanisms was developed, which includes light deprivation and subsequent lack of flower initiation, polar basipetal GA7 transport, cytokinin synthesis in the root and level in the xylem and phloem. Countermeasures include early chemical or mechanical thinning of young trees before reaching full crop load and early in terms of the flowering stage.

Comparative study of the effects of black or white hail nets on the fruit quality of ‘Golden Delicious’ apples

Introduction. The use of hail nets to protect apples during development and maturation on the tree is very common in Mexico. This practice can cause changes in fruit quality and aroma composition. The effects of the hail net color on the quality and aroma volatile production of apple cultivated in Chihuahua, Mexico, were evaluated. Materials and methods. ‘Golden Delicious’ apple trees were covered with white or black hail nets. Apple samples were harvested weekly from August to early October, and analyzed for weight, axial and equatorial diameters, color (°Hue), firmness, total soluble solids (TSS), acidity, ethylene production (EC), and aroma volatile composition. The photosynthetically available radiation (PAR) was measured every ten days under each hail net and outside. Results and discussion. Apple quality was affected by hail net color. Black hail nets delayed maturation and quality development of apples by one week when compared with white hail nets. The PAR values were 18% lower under black nets than under white nets. Quality parameters at commercial harvest (162 days after full bloom) showed that white-net apples presented 7% lower firmness, 11.1% less acidity, 8.3% higher TSS and a more developed yellow color, when compared with black-net apples. In addition, white-net apples presented higher contents of the main aroma compounds (in μg L-1 ) 1-hexanol (8.09 vs. 4.38), 2-methyl-1-butanol (6.24 vs. 2.65), and 2-methyl-butyl acetate (0.47 vs. 0.16). At the same maturity stage (beginning of the climacteric rise), no difference was found between white- and black-net apples in TSS, acidity, firmness and aromatic compounds. Conclusion. Hail net functionality goes beyond protecting orchards from hail damage; hail net color affects the apple maturation rate, quality and aroma volatile production.