Application of nano silica fertilizer in agricultural sustainability (a review)

Silica (Si) is a beneficial element for plants because it has many benefits in increasing plant growth and yields. However, the use of silica as fertilizer is currently still very limited, so the use of fertilizer is a major concern given a large number of uses of silica for plants. Today, recent advances in nanotechnology have opened new avenues for plant improvement, wherein plants can derive benefits associated with Si nanoparticles. Several studies have demonstrated the positive effects produced by the utilization of Si nanoparticles. Nanotechnology is expected to be able to answer the challenges of using environmentally friendly fertilizers and high efficiency of nutrient use. The use of nano fertilizers opens up new approaches to precision farming and sustainable agriculture. This paper will discuss the application of silica nanoparticles in plant growth and plant productivity. Nanosilica fertilizer is one of the promising technologies that can be used for precision and sustainable agriculture.


Introduction
Chemical fertilizers are fertilizers that are widely used by the community because they are easy to obtain and apply.However, current practice cannot meet the growing demand for food without relying on the intensive use of fertilizers.The continuous use of chemical fertilizers certainly causes serious problems with sustainability.Decreasing soil quality, soil pollution, and eutrophication are the impacts of intensive fertilizer use [1].More efficient use of fertilizers is an approach that needs to be taken in increasing food production.
Nanotechnology is a promising technology and has the potential for sustainable development.Nanotechnology uses nanomaterials that are as small as 1-100 nm [2].One of the nano fertilizers currently being developed is nano-silica.The use of silica in several plants has been shown to increase 1230 (2023) 012063 IOP Publishing doi:10.1088/1755-1315/1230/1/012063 2 vegetative growth, increase yields, protect plants against disease, and adapt to environmental stress [3][4][5].
Some of the soils in Indonesia are acidic due to the high level of leaching of alkaline cations.About 102,000,000 ha of acid soils, namely Ultisols, and Oxisols, are dominant besides Spodosols, Entisols, and Inceptisols [6].This type of soil has been used for rice cultivation in Indonesia.Even though Si is a very abundant element in the soil, which ranges from 25-35%, the availability of Si in the soil is low because continuous cultivation without the addition of Si fertilizer can reduce the level of Si in the soil.Currently, the most common form of Si material used as fertilizer is an industrial by-product [7].However, the most effective and efficient way to meet the needs of Si in the soil is by using crop residues such as rice husks and also bagasse which have a high Si content [8].
In rice, Si fertilization increases plant stem wall thickness, and peroxidase activity, thereby increasing plant tolerance to stress and lodging [9].Apart from the direct impact of nano silica as a fertilizer on plant growth, nano silica can also be used as a nano pesticide, and nanoherbicide.
The application of nano-silica in agriculture can also lead to global food security by assisting in the development of superior varieties with high productivity [10].The nanoparticles have agricultural implications and are currently being tested for crops.The use of nano-silica is expected to be a sustainable and environmentally friendly solution.
Currently, researchers have developed research on nano silica in agriculture, given the positive impact that nano silica has.However, there are still many people who do not know about nano-silica.This paper will discuss the definition, role, use, and features of the nanosilica perspective.

Definition of Nanofertilizer
Nano fertilizers based on nanoparticles are available in powder or liquid forms [11].Nano fertilizer can help increase nutrient release and plant uptake [12], increase crop productivity [13][14], inhibits the leaching of nutrients in the soil [15].The precise use of fertilizers is important in the agricultural sector because of the need to increase productivity and reduce excessive fertilization with negative impacts on agricultural ecosystems [16].Currently, nano-fertilizers have been used and developed to increase the efficiency of fertilizer use and reduce environmental impact.
Nano silica is one of the nano fertilizers that is currently being developed and has benefits for several plants.Silica can be applied in the form of nano to reduce the use of excessive doses while maintaining its role.The use of nano fertilizers is very appropriate because nanoparticles have a large surface area [17].However, further studies are needed to understand the effects of nanoparticles on plants [18], because their use in nutrient solutions is limited [19].Nano-fertilizers are more effective than conventional fertilizers in increasing nutrition and protecting plants against environmental stress [20][21][22].Si fertilizers usually have low bioavailability, whereas nano Si fertilizers with smaller or nano-sized particles can be easily absorbed by plants [23].In addition, nanotechnology reduces the excessive use of chemical fertilizers and pesticides.Nano fertilizers are simple, cost-effective, environmentally friendly, do not require a long process of manufacture, and are sustainable [24].

Role of Nano Silica
The application of liquid silica fertilizer increased the accumulation of Si in rice by 47.3% compared to not using Si.The application of nano silica increased the lignin content of the leaves by 112.7% when compared to the control.Silica has the effect of increasing net C assimilation by 1.83% and the rate of transpiration increases by 48.3% [25].Application of nano silica through leaves can increase rice yield parameters in saline-sodic soils, namely seed yield, number of panicles, panicle length, plant height and chlorophyll content [26].
The application of nano-chitosan (NC), nano-silica (NS), and a combination of nano-chitosan and nano-silica through the leaves can significantly improve the function of enzymatic and non-enzymatic antioxidant systems in wheat plants.Plants gave NC, NS, and NC-NS increased proline, amino acids, glycine betaine, and sugar to protect cells against osmotic pressure due to salinity stress [27].
The combination of nano silica fertilizer and N through the leaves can increase growth, yield, and nutrient uptake in 178 cultivars.Application of nano silica 60 g L -1 and 2% N through leaves can sustainably increase productivity [28].The use of nano silica in the form of SiO2 at a dose of 60 mg L - 1 applied through the leaves can increase the growth and yield of cucumber plants [29], increase the absorption of nutrients N, P, K, and withstand salinity stress in wheat at a dose of 600 mg L -1 was applied through the leaves and 80 mg kg -1 through the roots [30].Corn can enlarge the leaf area thereby increasing photosynthetic activity with a dose of 15 kg ha -1 applied directly to the soil [31].
The combination of tree bark fibers for planting rice seedlings and nano silica synergistically increases rice yields, lodging resistance, root characteristics, and photosynthesis [32].In addition, the use of nano-silica fertilizers under drought stress can increase grain yields by 28-32% compared to controls on wheat [33].
In tomatoes (Lycopersicon esculentum), the use of nano-silica can increase germination, germination time, seed vigor index, fresh weight, and dry weight [34].Nano-silica also increased the content of chlorophyll, a, b, and carotenoids at all concentration doses used, namely 400, 2000, and 4000 mg L -1 .However, 400 mg L -1 gives maximum results on photosynthetic pigments compared to the control [35].
High heavy metals can cause the overproduction of ROS in organisms.ROS is a fundamental process in plants and is used to transmit information signals in response to changing environmental conditions.One of the consequences that occur under abiotic stress conditions is the disruption of the balance of ROS and the antioxidant defense system, thus triggering excessive accumulation of ROS and inducing oxidative stress in plants [36][37].Arsenic (As) is a toxic metal that has a negative impact on plant growth by reducing photosynthesis and increasing Reactive Oxygen Species (ROS).The use of nano-silica can prevent damage and increase photosynthesis, as well as increase the activity of antioxidant enzymes to fight the formation of ROS [38].
The application of nano silica increases the fresh and dry weight of basil (Ocimum basilicum) under saline conditions [39].Salinity causes a decrease in germination percentage, root and shoot length, and fresh and dry weight.However, using nano-silica can increase plant growth even under salinity stress [40].In addition, nano-silica also reduces sodium uptake and increases potassium uptake under saline pressure [41].Salinity and drought are major problems and limiting factors for crop production.Therefore, the presence of nano-silica in plants can increase plant growth and potentially overcome the impacts of climate change such as uneven rainfall, and drought [42].
Haghighi & Pessarakli (2013) were the first to report that nano silica can increase plant resistance to stress due to salinity stress.Application of nano silica also increases photosynthesis, water use efficiency, in cherry tomatoes (Solanum lycopersicum) under salinity stress.In addition, administration of nano silica to cucumber seeds can increase germination proportions, germination rate, vigor index, root biomass and plant height under salinity stress [43].The application of nano silica up to a concentration of 200 ppm on cucumbers can increase the K+/Na+ ratio, under the influence of salinity and air deficit.Increasing the concentration of K+ ions in the root tissue together with the uptake of silica in the leaves reduces transpiration levels by regulating the opening of stomata, thus increasing the tolerance of salinity in cucumber plants [44].Here are some applications of nano silica fertilizer on several plants (Table 1

Future Perspectives
Therefore, it is very important to do research and development related to nano fertilizers.Such as improving the synthesis or design of environmentally friendly and sustainable nanomaterials for agriculture, building nanoparticles that can be used as fertilizers and pesticides, so that they are not only for providing nutrition but as plant protection, optimizing the dosage of nano fertilizer for application to various types of plants, developing strategies or common goals among institutions to test nano-products and field applications for broader technology validation and provide education and socialization to the public regarding nano-fertilizers [31].
Nano-silica is one of the nanotechnology products that can increase plant growth and productivity as well as in controlling plant diseases.Nano silica has great potential in controlling the detrimental effects of biotic and abiotic stresses.Nano-silica is a new opportunity for research in agronomy which

Table 1 .
). Application of nanosilica on several plants