Nanotechnology is a promising field of interdisciplinary research. It opens up a wide array of opportunities in various fields like medicine, pharmaceuticals, electronics and agriculture. The potential uses and benefits of nanotechnology are enormous. The current global population is nearly 7 */billion with 50% living in Asia. A large proportion of those living in developing countries face daily food shortages as a result of environmental impacts or political instability, while in the developed world there is surplus of food. For developing countries, the drive is to develop drought and pest resistant crops, which also maximize yield. The potential of nanotechnology to revolutionise the health care, textile, materials, information and communication technology, and energy sectors has been well publicized. The application of nanotechnology to agriculture and food industries is also getting attention nowadays. Investments in agriculture and food nanotechnologies carry increasing weight because their potential benefits range from improved food quality and safety to reduced agricultural inputs and improved processing and nutrition. While most investment is made primarily in developed countries, research advancements provide glimpses of potential applications in agricultural, food, and water safety that could have significant impacts on rural populations in developing countries. This review is concentrated on modern strategies used for the management of water, pesticides, limitations in the use of chemical pesticides and potential of nano-materials in sustainable agriculture management as modern approaches of nanotechnology. 
 
   
 
 Key words: Agriculture, nanotechnology, nanofertilizer, nanoencapsulation, nanoherbicides.

Nanotechnology in sustainable agriculture: Present concerns and future aspects

The beneficial effects of silicon and its role for plants are well established; however, the advantages of silicon nanoparticles over its bulk material are an area that is less explored. Silicon nanoparticles have distinctive physiological characteristics that allow them to enter plants and influence plant metabolic activities. The mesoporous nature of silicon nanoparticles also makes them good candidates as suitable nanocarriers for different molecules that may help in agriculture. Several studies have shown the importance of silicon nanoparticles in agriculture, but an overview of the related aspects was missing. Therefore, this review brings together the literature on silicon nanoparticles and discusses the impact of silicon nanoparticles on several aspects of agricultural sciences. The review also discusses the future application of silicon nanoparticles in plant growth, plant development, and improvement of plant productivity.

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Application of silicon nanoparticles in agriculture

In plants, pathogen attack can induce an immune response known as systemic acquired resistance that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO2 NPs; food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO2 NP-induced disease resistance are unknown. Here we show that SiO2 NPs, as well as soluble Si(OH)4, can induce systemic acquired resistance in a dose-dependent manner, which involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through the stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in the air spaces in the spongy mesophyll of the leaf. In contrast to the treatment with SiO2 NPs, the induction of systemic acquired resistance by Si(OH)4 was problematic since high Si(OH)4 concentrations caused stress. We conclude that SiO2 NPs have the potential to serve as an inexpensive, highly efficient, safe and sustainable alternative for plant disease protection. New mechanistic insights into nanoparticle–plant interactions show that specifically designed silica nanoparticles have the potential to serve as an inexpensive, highly efficient, safe and tracelessly degradable alternative for pesticides.

Silica nanoparticles enhance disease resistance in Arabidopsis plants

The use of foliar sprays with silicon compounds is relatively new. Initially (in 1990) foliar sprays with silicates were used. In 2003, foliar sprays with (stabilized) silicic acid were introduced, and more recently foliar sprays with silica nanoparticles have also been applied. Foliar sprays with silicates are effective as pesticides, while (stabilized) silicic acid sprays increase growth and yield and decrease biotic and abiotic stresses. The limited data on foliar silica-nano sprays show a tendency to decrease biotic stress and to stimulate a limited increase in growth and yield.

The Effects of Foliar Sprays with Different Silicon Compounds.

Silicon (Si) is considered as a quasiessential element for higher plants as its uptake increases plant growth and resistance against abiotic as well as biotic stresses. Foliar application of fertilizers generally is assumed to be a comparably environment-friendly form of fertilization because only small quantities are needed. The interest in foliar fertilization and the use of Si as a fertilizer in general increased significantly within the last decades, but there are only few publications dealing with the foliar application of Si at all. In the present review, the effects of Si foliar fertilization, including nano-Si fertilizers, on the three most important crops on a global scale, that is, maize, rice, and wheat, are summarized. Additionally, different pathways (i.e., cuticular pathways, stomata, and trichomes) of foliar uptake and functioning of Si foliar fertilizers against biotic (i.e., fungal diseases and harmful insects), as well as abiotic (i.e., water stress, macronutrient imbalance, and heavy metal toxicity) stressors are discussed. Future research should especially focus on (1) the gathering of empirical data from field and greenhouse experiments, (2) the intensification of co-operations between practitioners and scientists, (3) interdisciplinary research, and (4) the analysis of results from multiple studies (meta-analysis, big data) to fully understand effects, uptake, and functioning of Si foliar fertilizers and to evaluate their potential in modern sustainable agriculture concepts.

Experiments, Uptake Mechanisms, and Functioning of Silicon Foliar Fertilization—A Review Focusing on Maize, Rice, and Wheat

The study was conducted throughout the period extended from October, 2014 to January, 2015. The main objective was to study the effect of nano-silica in comparison with Silica & Diazinon as a recommended insecticide, applied as foliar spray on squash plants in the greenhouse and fed to newly hatched larvae of Spodoptera littoralis (Bosid.) for both foliar and semi-synthetic diet applications. Squash leaves were treated with 4 different concentrations 200,300,400, and 500 ppm of the three tested compounds. In bioassays, the neonate, second and fourth instars test larvae were fed on treated leaves and monitored for larval mortality as well as certain biological parameters e.g., larval duration, pupal duration, pupal weight, pupation percentage, the rate of adult emergence and adult longevity in both treatments in comparison with untreated control foliage. Obtained results showed that generally hydrophilic nano-silica caused higher toxic action values than with the other treatments. Mortality rate among larvae in any of the treatments was directly correlated with the increase in concentration. Also, the newly hatched larvae were more susceptible to treatments than the other tested instars, where mortality was 73.07, 79, 72, 87.88 and 89.82% in concentration treatments in their ascending order, in comparison with Diazinon which caused 95.95% mortality. The observed developmental stages among survivals of test insects were also affected by the treatments. This investigation recommends the application of nanosilica at 500 ppm concentration for the suppression of S. littoralis pest.

https://www.entomoljournal.com/archives/2016/vol4issue1/PartC/3-5-118.pdf

Elnagar S

Papers

The silica-nano particles treatment of squash foliage and survival and development of Spodoptera littoralis (Bosid.) larvae