Ruchi Rajpoot, Shivank Prajapati, Pragya Chaturvedi, Anusuiya Panda, Sudipto Dhara
Rani Lakshmi Bai Central Agricultural University -Jhansi, Uttar Pradesh, 284003


Abstract
With the population of the world expected to cross 11.2 billion by the twenty-first century, food demand is set to increase more than 50%. Food must be produced in increased quantities for food needs. Yet fertilizers being more than half of the total crop production, are the major factors affecting production in agriculture. Conventional fertilizers do increase the harvesting of crops but cause serious damage to the environment. They contribute to climate change and illegal mining of minerals. Due to inefficient fertilizer use by farmers, expectedly fertilizer application remains high.One potential strategy to improve efficiency is to replace conventional fertilizers with nano fertilizers. Nano fertilizers provide smart nutrient delivery to the plant compared to conventional fertilizers and provide demonstrated efficiencies in crop productivity and environmental sustainability. Due to application methods and particle characteristics, plants can take up nutrients from nano fertilizers from the root or leaf system. Nano fertilizers can improve plants to withstand biotic and abiotic stressors. This reduces the impact on the environment and the cost of production. Many benefits of the NFs open avenues for mitigating climate change and for sustainable agriculture. Contrary to optimal benefits, the NFs at supra-optimal levels harmed soil health, crop growth, and environmental outcomes. NFs should be considered cautiously, as the consensual release of them into the environment and food chain may pose risks to human health.

1. Introduction
With the global population projected to rise from approximately 8 billion in 2022 to 9.7 billion by 2050, global food demand is expected to increase by over 50%, with animal-based food demand rising nearly 70%. Meeting this demand will largely depend on increasing productivity on existing agricultural land, as expanding cultivated areas faces major infrastructural, environmental, and political constraints.

Fertilizers have played a critical role in yield improvement, contributing at least 50% of crop yield increases during the 20th century. In temperate regions, 40–60% of yield gains are attributed to fertilizer use. However, nutrient use efficiency (NUE) of conventional fertilizers remains low—30–50% for nitrogen, 15–20% for phosphorus, 70–80% for potassium, and only 1–2% for micronutrients.

Although fertilizers are essential for food security, their inefficient use leads to nutrient losses through leaching, volatilization, and runoff, causing eutrophication, soil degradation, and greenhouse gas emissions. Therefore, optimizing fertilizer management practices, adopting precision agriculture, and developing advanced fertilizers are necessary to enhance NUE. NUE, defined as the ratio of crop yield output to nutrient input, serves as a key indicator for evaluating fertilizer performance and achieving sustainable agricultural intensification.

There are many ways to improve NUE
Taking up the 4R principles - right source of nutrient, right rate, right time and right place - help to ensure proper use of nutrient resources and maximize productivity. In this article we will discuss the right source of nutrient. Multiple plans have been carried out on ways to degrade fertilizers by methods such as fertigation, precision fertilizing, limit applications and by using nanofertilizers instead of fertilizers.

Nanotechnology offers significant assistance in the agricultural production of crops to meet the Earth's population increasingly challenging food demands along with the integrity of our environment, sustainability, and economic security. The prefix "nano" is derived from the Greek word which means "dwarf." Nano refers to the nanoscale size of a particle typically less than 100 nm in at least one dimension. Nanoparticles are an important class of materials since they possess unique properties that differentiate them from their bulk material counterparts because of their large surface area, crystallinity, and changes in the reactivity and interactions with the environment. These properties, relative to most other substances, have made modern nanoparticles capable of more direct and efficient interactions with plant roots and soil microorganisms allowing for better uptake of nutrients and eventual metabolism of plants .

2. Type of Nano-fertilizers
Nanofertilizers (NFs) are nanoscale materials that enhance crop productivity by improving nutrient uptake. Developed using nanotechnology, NFs show strong agricultural potential; however, their definition and classification remain unclear. They are often described both as a subset of nanotechnology and as fertilizers, leading to ambiguity in evaluating their value and applications.

NFs can be classified based on raw materials (carbon-based, polymeric, or metallic), nutrients carried, mode of action, and consistency. Their effectiveness depends on proper understanding and application methods, including foliar, soil, and water-based delivery.

2.1 Action based

2.1.1 Controlled‑release Nanofertilizers
Controlled-release nanofertilizers encapsulate nutrients in carrier materials consisting of polymers, lipids, or inorganic elements at the nanoscale. Controlled-release fertilizer is a type of slow-release fertilizer, which is defined as fertilizer that has a physical barrier. These fertilizers use nanoparticles to control nutrient release, which maximizes nutrition uptake and minimizes environmental impacts. They are designed to release nutrients over a prolonged period and exploit some form of diffusion, degradation or ion exchange .

2.1.2 Slow‑release nanofertilizers
Unlike water-soluble fertilizers, which have well-defined rates of nutrient release, slow-release nanofertilizers release nutrients slowly . The parameters that dictate the timing, rate and duration of nutrient release are not very rigidly controlled, as they are dependent on microbial mechanisms at work which, in turn, depend on soil moisture and temperature patterns. In some instances, slow-release fertilizers may release nutrients quickly at periods of high moisture and high temperature coinciding.

2.1.3 Nano fertilizers as a plant growth stimulation
Some nanofertilizers, including carbon nanotubes (CNTs) can stimulate plant growth through its interactions with plant root systems and under certain conditions, increase hormone production. CNTs can absorb and release nutrients, improve soil structure, hold moisture in the soil, and stimulate plant growth. In contrast to the negative consequences of the large-dose fertilizer assays, low carbon nanotube concentrations may stimulate germination, root growth, and water transport without phytotoxicity.

2.1.4 Water and nutrient control
Nanofertilizers contain NPs that have the ability to control the rate that fertilizers are released into the soil, allowing farmers to apply less fertilizer and still achieve the same crop production levels. There are several approaches to designing nanofertilizers that can control the nutrient release and reduce water loss. One approach uses a porous matrix to encapsulate the nanofertilizer which will slowly release the nutrients over time .

2.2 Nutrient Based

2.2.1. Inorganic Nanofertilizers
Consequently, inorganic nanofertilizers include metals, metalloids and non-metals, and can utilize nanometric scales to apply N, P, and K nutrients to crops. Inorganic nanofertilizers can be of exceptional value because they can be created by changing the proportions of what the plants need, thus allowing for targeted applications to increase yield.

2.2.2. Organic Nanofertilizers
Organic nanofertilizers consist of NPs sourced from organic materials that are meant to provide nutrients to the soil in a slow-release manner. They are environmentally friendly, derived from natural sources, and can potentially retain soil moisture and provide more pH alterations so that essential nutrients can be absorbed by the plants more effectively .

2.2.3. Hybrid Nanofertilizers
Hybrid nanofertilizers are a combination of conventional and nano-sized fertilizers that provide a slow and sustained release of nutrients while improving the availability of those nutrients. Conventional fertilizers addressed issues like addressing nutrient losses and capturing higher rates of fertilizers, however, the overall efficiency of these fertilizers can be improved through nanofertilizers with higher nutrient availability which reduces their environmental impact .

2.2.4. Nutrient-Loaded Nanofertilizers
Consistency-based nanofertilizers are nanocarrier-based and coating with technology which demonstrates promise in sustainable agriculture as it adds values in more nutrient utilization by plants, reduced nutrient loss, and lowered environmental impacts .

2.3 Consistency based

2.3.1. Surface-Coated Nanofertilizers
Surface-coated nanofertilizers are made by coating fertilizer particles with nanomaterials like gold, silver, carbon, and titanium dioxide. The coating helps fertilizer particles stick to surfaces of plant tissue and provide penetration into plant cells, which improves the absorption rate of the fertilizer, resulting in more effective fertilizer use and overall plant growth.

2.3.2. Synthetic Polymer-Coated
These types of nanofertilizers are shielded with a thin layer of synthetic polymer. The layer affords nanofertilizers advantages, such as ballooning environmental degradation and contributing to safer handling.

2.3.3. Biological Product-Coated
Nanofertilizers coated with biological products are used in organic farming and contribute to soil fertility, increasing water retention, and stimulating beneficial microbial activity. Nanofertilizers coated with plant growth regulators benefit plants by providing accessed nutrients while regulating the plant's growth and development.

2.3.4. Nanocarrier-Based Nanofertilizers
Nanocarrier-based nanofertilizers can transport and deliver nutrients to both soil and plants. Nanofertilizers can increase nutrient availability, decrease nutrient losses, and promote plant growth.

3. Ways of Nano-fertilizers use
Nanofertilizers can be used in many ways to appropriately deliver nutrients to plants. The proper method of nanofertilizer application is essential to managing nutrients in agriculture. Below are a few common methods of using nanofertilizers:

3.1 Foliar spray
Foliar application of nanofertilizers is the application of nanoparticles on leaf surfaces containing nutrients to be absorbed through the stomata or cuticle. Compared to conventional soil-applied fertilizers, there's a faster plant absorption time, is more cost-effective, and won't impact the soil.

3.2 Soil application
Nanofertilizers can be applied to soil as fertilizers through traditional methods including broadcasting and side-dressing and fertigation. Soil application of nanofertilizers presents multiple benefits including enhanced nutrient utilization and plant development but it encounters different constraints.

3.3 Seed treatment
Nano priming as a pre-sowing seed treatment using nanoparticles that alters seed physiology to promote faster germination and growth and yield through the regulation of metabolic and signaling cascade events.

4. Synthesis of Nanoparticles
The manufacturing of nanoparticles occurs by means of both top-down and bottom-up strategies. The top-down approach uses physical methods, and the bottom-up approach uses chemical processes.

1. Top-down approach
The process of breaking bulk materials into smaller nanostructures or particles represents the core of the top-down approach. The method continues the same procedures which create particles that measure in microns. Produces uniform nanoparticles with well-defined sizes and shapes but requires more energy input and this method is expensive due to costly equipment.

2. Bottom-up approach
The bottom-up method for creating nanoparticles requires building materials step by step starting from atoms and molecules through chemical reactions. Molecules in solution serve as the starting point for this process which continues through multiple stages of molecule joining until nanoparticles form. The chemical process enables exact control of particle dimensions together with composition characteristics. This method requires less energy input and its cheaper method.

5. Challenges in the commercialization of NFs
1. Higher costs
2. Lack of standardization
3. Negligible public perception Knowledge gaps in NF development
4. Safety concerns

6. Conclusions and future prospects
Chemical fertilizers function as a double-edged sword since they boost food production yet they lead to environmental damage and climate change. The creation of NFs creates an exceptional chance to enhance food production while reducing environmental damage. Through controlled delivery of essential nutrients NFs supply plants with needed elements according to their requirements and promote environmental sustainability. The application of NFs represents a sustainable replacement for chemical fertilizers however their repeated and excessive usage requires proper dosing and quality control and appropriate application methods to avoid potential harm to the food chain. The commercial spread of NFs needs objective evaluation of their environmental interactions and human health effects before widespread adoption.
  • The subsequent research should investigate nanomaterial toxicity to demonstrate how agricultural food industry applications of these materials avoid detrimental impacts on environmental resources and ecosystems.
  • Research on nanofertilizers primarily remains confined to laboratory settings while their formulation requires standardized approaches that address various pedoclimatic conditions.
  • Leguminous crops receive minimal research attention for nanofertilizers treatment compared to nonleguminous crops which represents a gap in current agricultural research regarding nanofertilizer applications.
  • This technique may include an integrative approach which includes combination of nanodevices so as to synchronize the uptake of nutrients by crops with their release from nanofertilizers.