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The objective of this work was to describe the diurnal and seasonal evolution of incidence of global irradiance (IG), photosynthetically active irradiance (IPAR), and luminance in aboveground forest nurseries under different shading screens. Radiometric fractions were evaluated and statistical equations were obtained based on the external incidence. Instantaneous measurements of IG, IPAR, and luminance in the exterior and interior of nurseries (East-West direction), solstices (22/12/2018 and 22/06/2019) and equinoxes (21/03/2019 and 21/09/2019), and local zenithal culminations (18/02/2019 and 20/10/2019) were evaluated between 7:00 and 17:00 h. Estimates were evaluated and the data were grouped into two databases composed of 70% and 30%, respectively, to generate and validate regressions for each variable. The statistical performance of regressions was evaluated using the following statistical indicators: coefficient of determination (R2), mean square error (MSE), root mean square error (RMSE), and Willmott index (d). IG, IPAR, and luminance presented similar dynamics of diurnal and seasonal evolution under the shading screens for external conditions, and the transmissivity was affected by the environmental conditions (water seasonality and solar declination) and intrinsic characteristics of the shading screens (porosity and color). The transmission and absorption of IG, IPAR, and luminance were affected by color and porosity of the shading screens, whereas the reflection was affected only by the color. The agreement indexes (d) were higher than 0.9975 and 0.9973 for black screen and photoselective screen, respectively, and were considered as good, indicating that the equations generated good estimates of IG, IPAR, and luminance for application in different regions. The choice of shading screens for crops are dependent on spectral composition requirements and IPAR transmissivity of each species., Radiação solar incidente sob diferentes telas de sombreamentos em clima tropical: evolução diurna e estimativas RESUMO: O uso de telas foto-seletivas melhora a produtividade e qualidade das plantas, e é necessário compreender a dinâmica da transmissividade da radiação solar sob esses microambientes para subsidiar projetos de produção agrícolas e florestais. Nesse sentido, o objetivo foi descrever a evolução diurna e sazonal das irradiâncias global (IG), fotossintéticamente ativa (IPAR) e luminância incidentes em viveiros florestais suspensos sob diferentes telas de sombreamento. Além disso foram avaliadas as frações radiométricas e obtidas equações estatísticas de estimativas baseadas na incidência externa. As medidas instantâneas de IG, IPAR e luminância ocorreram no exterior e interior dos viveiros (alinhados no sentido Leste-Oeste), nos solstícios (22/12/2018 e 22/06/2019), equinócios (21/03/2019 e 21/09/2019) e nas culminações zenitais locais (18/02/2019 e 20/10/2019), entre às 7h00min e 17h00min. Para avaliação das estimativas, os dados foram agrupados em duas bases, compostas por 70 e 30% para geração e validação das regressões, para cada variável, respectivamente. Para avaliação do desempenho estatístico das regressões foram empregados os indicativos estatísticos: coeficiente de determinação (R2), erro absoluto médio (MBE), raiz quadrada do erro quadrático médio (RMSE) e índice de Willmott (d). IG, IPAR e luminância apresentaram dinâmicas semelhantes na evolução diurna e sazonal sob as telas de sombreamento em relação as condições externas, sendo a transmissividade influenciados por condições ambientais (sazonalidade hídrica e declinação solar) e intrínsecas a tela (porosidade e cor). A transmissão e absorção de IG, IPAR e luminância foram afetadas pela cor e porosidade líquida, enquanto que a reflexão apenas pela cor. Os valores do índice de Willmott foram superiores a 0,9975 e 0,9973 para as telas pretas e foto-seletivas, respectivamente, sendo considerado como ótimos, indicando que as equações ajustadas permitem boas estimativas de IG, IPAR e luminância para aplicação em diferentes regiões. A escolha da tela de sombreamento para o cultivo de plantas fica dependente das necessidades de composição espectral e transmissividade da IPAR de cada espécie. Palavras-chave: propriedades radiométricas de telas foto-seletivas; radiação fotossinteticamente ativa; irradiâncias; luminância; indicadores estatísticos. ABSTRACT: The use of photoselective screens improves plant productivity and quality, and it is necessary to understand the dynamics of solar radiation transmissivity under these microenvironments to subsidize agricultural and forestry production projects. Therefore, the objective of this work was to describe the diurnal and seasonal evolution of incidence of global irradiance (IG), photosynthetically active irradiance (IPAR), and luminance in aboveground forest nurseries under different shading screens. Radiometric fractions were evaluated and statistical equations were obtained based on the external incidence. Instantaneous measurements of IG, IPAR, and luminance in the exterior and interior of nurseries (East-West direction), solstices (12/22/2018 and 06/20/2019) and equinoxes (03/21/2019 and 09/21/2019), and local zenithal culminations (02/18/2019 and 10/20/2019) were evaluated between 7h00min and 17h00min. Estimates were evaluated and the data were grouped into two databases composed of 70% and 30%, respectively, to generate and validate regressions for each variable. The statistical performance of regressions was evaluated using the following statistical indicators: coefficient of determination (R2), mean square error (MSE), root mean square error (RMSE), and Willmott index (d). IG, IPAR, and luminance presented similar dynamics of diurnal and seasonal evolution under the shading screens for external conditions, and the transmissivity was affected by the environmental conditions (water seasonality and solar declination) and intrinsic characteristics of the shading screens (porosity and color). The transmission and absorption of IG, IPAR, and luminance were affected by color and porosity of the shading screens, whereas the reflection was affected only by the color. The values of Willmott index were higher than 0.9975 and 0.9973 for black screen and photoselective screen, respectively, and were considered as good, indicating that the equations generated good estimates of IG, IPAR, and luminance for application in different regions. The choice of shading screens for crops are dependent on spectral composition requirements and IPAR transmissivity of each species. Keywords: radiometric properties of photoselective screens; photosynthetically active radiation; irradiance; luminance; statistical indicators.

The whole construction parameters of the net, combined with the shape of the structure, the position of the sun and the sky conditions affect the radiometric performance of the permeable covering system. The radiometric properties of the permeable membrane influence the quality of the agricultural production and the aesthetic characteristics of the netting system. Moreover, the colour of the material and the light reflection- especially of the wavelengths visible for the human eye (VIS, 380-760nm)- is an interesting criterion to determine the aesthetic value of the net structure and its environmental impact. In order to investigate the influence of the threads colour on the radiometric properties of the net, a set of field tests were performed by means of a spectroradiometer in combination with an experimental setup 120x120x50cm covered with membranes formed by threads with different colour. A second set of experiments were performed, on the same kind of nets, in laboratory by means of a combination of a large integrating sphere and a small one: the transmissivity from a direct (tauDIR) and diffuse ((tauDIF) source and the reflectivity from diffuse source (?) of 50x50cm samples were measured in the PAR range. The evaluation of the transmissivity values shows that the colour of a net influence spectral distribution of the radiation passing through the net absorbing their complementary colours. The transmissivity of black nets is almost constant in the visible range and the reduction of the incoming radiation is proportional to the solidity of the net. In the PAR range transparent and black nets doesn?t cause an alteration of the spectrum of solar radiation and transmittance is almost constant with a slight growth in nets having lower porosity.

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.

Nets are commonly used for agricultural applications. However, only little is known about the radiometric properties of net types and how to influence them. In order to investigate the influence of net construction parameters on their radiometric properties, a set of radiometric tests were performed on 45 types of agricultural nets. Laboratory tests on large size net samples was performed using a large and a small integrating sphere. Open field radiometric test were carried out by means of an experimental set up (120x120x50 cm) and a full scale shade house. Small differences (less than 5%) occurred between laboratory and open field tests. Results highlighted that the porosity and the mesh size, combined with the colour and secondarily, with the fabric and the kind of threads of the net influenced the shading performance of the net. The colour influenced the spectral distribution of the radiation passing through the net absorbing its complementary colours. Since nets are three-dimensional structures the transmissivity of direct light under different angles of incident of solar radiation changes when installed in the warp or weft direction. Transmissivity could be considered one of the main parameters involved in the agronomic performances of the netting system.

An innovative biodegradable coating that can be sprayed was developed and tested as suitable alternative to low density polyethylene (LDPE) films for soil mulching in horticulture. A mulch was created by spraying onto the soil a sodium alginate water-based solution that, at the end of the cultivation cycle, could be tilled into the soil to be biodegraded. The mechanical and radiometric properties, the functionality of the spray coating, and its biodegradation were assessed by means of laboratory measurements and cultivation field tests. In the field, during the cultivation of strawberries, the spray coating was compared with a LDPE mulching film and a straw mulch. The mechanical properties of the coating degraded when exposed in the field, but the coating kept its mulching effect for 6 months. The radiometric properties varied without regular trends, but the coating maintained its capacity to suppress weeds. The biodegradation tests showed that the spray coating samples biodegraded by 65% after 6 months into the soil.

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.

The performance, the degradability in soil and the environmental impact of biodegradable starch-based soil mulching and low tunnel films were assessed by means of field and laboratory tests. The lifetime of the biodegradable mulches was 9 months and of the biodegradable low-tunnel films 6 months. The radiometric properties of the biodegradable films influenced positively the microclimate: air temperature under the biodegradable low tunnel films was 2 °C higher than under the low density polyethylene films, resulting in an up to 20% higher yield of strawberries. At the end of the cultivation period, the biodegradable mulches were broken up and buried in the field soil together with the plant residues. One year after burial, less than 4% of the initial weight of the biodegradable film was found in the soil. According to ecotoxicity tests, the kinetic luminescent bacteria test with Vibrio fischeri and the Enchytraeus albidus ISO/CD 16387 reproduction potential, there was no evidence of ecotoxicity in the soil during the biodegradation process. Furthermore, there was no change in the diversity of ammonia-oxidizing bacteria in the soil determined on the basis of the appearance of amoA gene diversity in denaturing gradient gel electrophoresis.

Biodegradable starch-based extruded mulching films and biodegradable sprayable water-born polysaccharides based coatings were prepared within two European Projects as an alternative to soil mulching films made of synthetic petrochemical polymers. The biodegradable mulches, both films and coatings, had appropriate mechanical and physical properties to assure their functionality throughout the crop cycle in relation to the cultivation needs, the geographical region, and the season. The useful lifetime of the biodegradable films and coatings was fully comparable with the low density polyethylene films currently in use: the biodegradable films lasted up to 9 months, the biodegradable coatings up to 6 months. They satisfy the mulching task of weed control during the crop cycle reducing solar PAR radiation reaching the mulched soil and creating a physical barrier preventing airborne weed seeds.

To cover agricultural structures for protecting plants from high solar radiation in hot and sunny regions different types of shading nets are used. In summer, the amount of photosynthetically active radiation (PAR) transmitted through these nets usually fulfils plant growth requirements. However, their applicability in winter is still unknown. So far, the choice of nets has mostly been empirical, because technical data such as the radiometric properties that are used to characterize the different types of nets are not available. This paper presents a simple method for measuring the radiometric properties related to global and diffuse PAR of seven types of shading nets including nets with colours and shading rates that are commonly used in hot regions. A shading system was developed to simulate the diffuse PAR under cloudy conditions. The results show that under clear sunny and cloudy conditions the radiometric properties depended on both net porosity and colour. Net reflectance strongly depended on net colour. Net transmittance and absorptance depended primarily on colour and secondarily on porosity. The radiometric properties of nets under global and diffuse PAR conditions tended to be similar to those of translucent materials so that a plastic net can be considered as translucent material when investigating the equivalent optical parameters (refractive index and absorption coefficient). This can help to predict the radiometric properties of the net without the need of measurements. Under the sunny conditions of winter seasons, the structures covered with the tested nets are suitable for growing crops that can grow at PAR less than 150 W m −2 . However, under cloudy conditions very few plants will grow that can grow at PAR less than 30 W m −2 .

Biodegradable starch-based extruded mulching films and biodegradable sprayable water-born polysaccharides based coatings were prepared within two European Projects as an alternative to soil mulching films made of synthetic petrochemical polymers. The biodegradable mulches, both films and coatings, had appropriate mechanical and physical properties to assure their functionality throughout the crop cycle in relation to the cultivation needs, the geographical region, and the season. The useful lifetime of the biodegradable films and coatings was fully comparable with the low density polyethylene films currently in use: the biodegradable films lasted up to 9 months, the biodegradable coatings up to 6 months. They satisfy the mulching task of weed control during the crop cycle reducing solar PAR radiation reaching the mulched soil and creating a physical barrier preventing airborne weed seeds.