Plastic nets in agriculture ; a general review of types and applications

At the moment, there are a large number of agricultural net types on the market characterized by different structural features such as type of material, type and dimensions of threads, texture, mesh size, porosity / solidity and weight; by radiometric properties like color, transmissivity/reflectivity/shading factor; by physical properties like air permeability and several mechanical characteristics such as tensile stress, strength, elongation at break, and durability. Protection from hail, wind, snow, or strong rainfall in fruit-farming and ornamentals, shading nets for greenhouses and nets moderately modifying the microenvironment for a crop are the most common applications. A systematic review of the current state-of-the-art of structural parameters, standard and regulations, most common agricultural net applications, and their supporting structures has been developed by means of a literature study, technical investigations, concerning characteristics and use of nets. As a result, the survey highlighted that in many cases different, not even similar, net types were adopted for the same application and the same cultivations by various growers. Results show that neither growers nor net producers have clear ideas about the relationship between the net typology optimization for a specific application and the construction parameters of the net. The choice often depends on empirical or economic criteria and not on scientific considerations. Moreover, it appears that scientifically justified technical requirements for nets used in specific agricultural applications have not been established yet

Performance evaluation using timed coloured Petri nets

Colored Petri nets are Petri nets in which attributes are associated with individual tokens. These attributes are called colors. The set of colors is finite. Colors can be modified during transition firings, and the same transition can perform different transformations for tokens of different colors. Colors can thus distinguish tokens, and this allows one to fold similar subnets of a net into a single subnet, reducing the model complexity. In timed colored nets. the transitions fire in real-time, i.e., there is a firing-time associated with each color and each transition of a net. A state description of timed nets is proposed which represents the behavior of a timed colored net by a probabilistic state graph. Performance analysis of timed colored nets is based on stationary probabilities of state

Red and blue netting alters leaf morphological and physiological characteristics in apple trees

There is little information about the role of red and blue light on leaf morphology and physiology in fruit trees, and more studies have been developed in herbaceous plants grown under controlled light conditions. The objective of this research was to evaluate the effect of red and blue screens on morpho-anatomy and gas exchange in apple leaves grown under ambient sunlight conditions. Apple trees cv. Fuji were covered by 40% red and blue nets, leaving trees with 20% white net as control. Light relations (photosynthetic photon flux density, PPFD; red to far-red light ratio, R/FR and blue to red light ratio, B/R), morpho-anatomical features of the leaf (palisade to spongy mesophyll ratio, P/S, and stomata density, SD) and leaf gas exchange (net photosynthesis rate, An; stomatal conductance, gs; transpiration rate, E; and intrinsic water use efficiency, IWUE) were evaluated. Red and blue nets reduced 27% PPFD, reducing by 20% SD and 25% P/S compared to control, but without negative effects on An and gs . Blue net increased gs 21%, leading to the highest E and lowest IWUE by increment of B/R light proportion. These findings demonstrate the potential use of red and blue nets for differential modulation of apple leaf gas exchange through sunlight management under field conditions

Influence of Different Netting Structures on Codling Moth and Apple Fruit Damages in Northwest Croatia

During the vegetation season of 2015 exclusion nets were set up in IPM apple orchard in Krapina (Croatia) to test their effectiveness in preventing the attack of codling moth to apple fruits. Nets were the same in mesh size (2.4 x 4.8 mm) but different in color (white, red, yellow) in order to examine their effect on vegetative growth and quality of apples. To assess the presence of pest, weekly sampling of codling moth on pheromone traps in protected and unprotected (control) net rows was conducted. Single row netting structures resulted in a highly significant reduction of codling moth catches on pheromone traps in comparison to the unprotected control in the experimental orchard. The percentage of codling moth infested fruits during the harvest time was considerably lower, in the protected net rows in comparison with unprotected rows. The lowest percentage of damaged fruits was recorded under the red net (0.96%), followed by white net (1.04%) and yellow net (2.86%). Percentage of damaged fruits in unprotected row amounted to 11.39%. Considering the fact that the mean net efficiency amounted to almost 90%, these results confirm the effectiveness of netting structures in the protection of apple fruits from CM damages

Photoselective Shade Netting in a Sweet Pepper Crop Accelerates Ripening Period and Enhances the Overall Fruits Quality and Yield

Photoselective nets are used to protect horticultural plants from sunburn and prolong the cropping period in conditions of excess light. In this work, we studied the influence of four photoselective shading nets (Pearl 30, Red 30, Silver 30, Red 40), a standard blackcolored net (Black 35), and a control (no cover) on the evolution of color during the ripening of two types of pepper, namely, Lamuyo and California. For this purpose, the evolution of the colors of the fruit was followed from the beginning of their formation until the harvest, and was correlated with the total radiation and the temperature. The plant material used were peppers of the California type -cultivars Bendigo and Cayetano- and of the Lamuyo type, cultivars Alcudia and Pompeo. The results showed that the rate of change of the pepper coloration depended on the net used in the greenhouse. The speed of the change in color from green to red was more dependent on the cultivar and the total radiation, as conditioned by the different photoselective nets, than on the type of pepper. The greatest differences were between the control (without a net) and the black net, the increase in the red color of the peppers being faster in the former. Radiation values below 75 W m-2 or greater than 110 W m-2 negatively affected the yield. The temperature below the net was not affected significantly by the type of net, and thus its effect on the different cultivars was similar

Modification of sunlight radiation through colored photo-selective nets affects anthocyanin profile in Vaccinium spp. berries

<p>Objectives In recent years, the interest on the effects of the specific wavelengths of the light spectrum on growth and metabolism of plants has been increasing markedly. The present study covers the effect of modified sunlight conditions on the accumulation of anthocyanin pigments in two Vaccinium species: the European wild bilberry (V. myrtillus L.) and the cultivated highbush blueberry (V. corymbosum L.). <p>Methods The two Vaccinium species were grown in the same test field in the Alps of Trentino (Northern Italy) under modified light environment. The modification of sunlight radiation was carried out in field, through the use of colored photo-selective nets throughout the berry ripening during two consecutive growing seasons. The anthocyanin profile was then assessed in berries at ripeness. <p>Results The results indicated that the light responses of the two Vaccinium species studied were different. Although both studied species are shade-adapted plants, 90% shading of sunlight radiation was beneficial only for bilberry plants, which accumulated the highest content of anthocyanins in both seasons. The same condition, instead, was not favorable for blueberries, whose maturation was delayed for at least two weeks, and anthocyanin accumulation was significantly decreased compared to berries grown under sunlight conditions. Moreover, the growing season had strong influence on the anthocyanin accumulation in both species, in relation to temperature flow and sunlight spectra composition during the berry ripening period. <p>Conclusions Our results suggest that the use of colored photo-selective nets may be a complementary agricultural practice for cultivation of Vaccinium species. However, further studies are needed to analyze the effect of the light spectra modifications to other nutritional properties, and to elucidate the molecular mechanisms behind the detected differences between the two relative Vaccinium species

Matrix-geometric solution of infinite stochastic Petri nets

We characterize a class of stochastic Petri nets that can be solved using matrix geometric techniques. Advantages of such on approach are that very efficient mathematical technique become available for practical usage, as well as that the problem of large state spaces can be circumvented. We first characterize the class of stochastic Petri nets of interest by formally defining a number of constraints that have to be fulfilled. We then discuss the matrix geometric solution technique that can be employed and present some boundary conditions on tool support. We illustrate the practical usage of the class of stochastic Petri nets with two examples: a queueing system with delayed service and a model of connection management in ATM network

Plants of Achillea millefolium L. grown under colored shading nets have altered secondary metabolism

Here we evaluate the effect of quality and quantity of light on growth and secondary metabolism of Achillea millefolium L. plants. Plants were cultivated under either full light or colored shading nets (blue, red or black). Analyzes were performed after eight weeks of shading and two and four weeks after the removal of the nets. Plants grown under nets presented lower dry weight of leaves and flowers. In addition, the synthesis of phenols and flavonoids decreased in leaves and flowers of shaded plants. On the other hand, the blue net increased the content of essential oil yield in leaves. The concentration of the majority of the compounds analyzed in the essential oil increased when using the black net. Farnesol and chamazulene were the most plenteous compounds in the oil of leaves and flowers in all conditions. Overall, these results indicate that different compounds respond differently to specific light lengths in A. millefolium plants. Thus, the photoselective treatments should be directed to the production of the target metabolite.(Plantas de Achillea millefolium L. crescidas sob sombreamento com malhas coloridas possuem alterações no metabolismo secundário). O efeito da qualidade e quantidade de luz no crescimento e metabolismo secundário foram avaliados em plantas de Achillea millefolium L.. As plantas foram cultivadas sob luz plena ou sob redes coloridas (azul, vermelho e preto) e avaliadas após oito semanas de sombreamento e após duas e quatro semanas da retirada das redes. Plantas sombreadas apresentaram menores valores de matéria seca de folhas e flores. Além disso, a síntese de fenóis e flavonóides diminuiu em folhas e flores de plantas sombreadas. Por outro lado, a rede azul aumentou o teor de óleo essencial nas folhas. A concentração da maioria dos compostos analisados no óleo essencial das plantas aumentou quando se utilizou a rede preta. Farnesol e chamazuleno foram os compostos mais abundantes no óleo essencial de folhas e flores em todas as condições. De forma geral, esses resultados demonstram como os compostos secundários respondem diferentemente à qualidade da luz em plantas de A. millefolium. Assim, os tratamentos fotosseletivos devem ser direcionados para a produção do metabólito de interesse