In modern agriculture, fertilizers are the most significant prerequisite to ensure sustainable crop production, and the intervention of chemical fertilizers has markedly increased crop production and quality. Unfortunately, plants cannot uptake a significant amount of nutrients (>50%) from the applied fertilizers, resulting in low fertilizer use efficiency. The nutrient losses due to leaching, volatilization, denitrification, fixation, erosion, and runoff could result in low fertilizer use efficiency and create environmental pollution as well as a rise in the cost of fertilizer application. To minimize such losses, researchers have suggested various strategies, one of which is the synthesis and application of slow-release fertilizers to extend the bioavailability of nutrients by the sustained release throughout the crop growth period. However, the high cost of current slow-release fertilizers is a major challenge for their widespread use. Carbon-based materials, especially biochar and lignite, have been shown to be effective as soil amendment in recent times. Additionally, these materials have an excellent ability to adsorb nutrients due to their high porosity, surface area, and abundance of functional groups. The cost-effective and abundant supply of these materials across the world can serve as an excellent nutrient-carrier in order to formulate climate-smart and cost-effective slow-release fertilizers. In this review paper, the potential of these materials as nutrient carriers, nutrient adsorption and desorption mechanisms, synthesis methods, nutrient release behavior, and agronomic and environmental implications are discussed in detail for future research priorities as the literature in this direction is very limited and scattered.

Carbon-Based Slow-Release Fertilizers for Efficient Nutrient Management: Synthesis, Applications, and Future Research Needs

Nanotechnology has opened up a number of scopes for novel applications in the field of agricultural industries, because of several unique physicochemical properties of nanoparticles (NPs), i.e., high surface area, high reactivity, tunable pore size, and particle morphology. Nanoparticles may be treated as “magic bullets,” containing nanopesticides, nanofertilizers, etc., which will trigger specific cellular organelles in the plant to release their contents. So far, little information is available on the behavior of nanofertilzers in soil system, as well as utilization of nanoparticles for smart delivery of fertilizers. Still NPs have already shown promise for their potential utility in crop production in the form of nanofertilizers, nanopesticide, nanoherbicides around the world. The present chapter highlights the key role of nanoparticles in soil systems, their characterization, behavior, mobility, and effective means for the smart delivery of fertilizers that has a strong bearing on the growth and yield of plants. Nano-based slow-release or controlled-release (CR) fertilizers have the potential to increase the efficiency of nutrient uptake. In this chapter, utilization of nanoparticles for delivery of fertilizers in an agricultural production system for the sustainable environment has been described.

Agri-nanotechniques for Plant Availability of Nutrients

Agrochemical represented mainly by fertilizers and pesticides are vital inputs for agricultural production. However, their conventional application in field is poorly effective, with significant losses due mainly to volatilization and/or lixiviation of soluble agrochemicals. In some cases, the application exceeds two times the optimal quantity, meaning that other undesired consequences take part, such as environmental contamination or production of greenhouse gases. A considerable scientific effort has been made to develop viable systems for the controlled or slow delivery of agrochemicals, in order to adjust the nutrient availability in soil to minimal doses required for pest control or to levels needed by plants. Besides other technologies, the association of soluble materials containing fractions of minerals with very high surface area has shown to be an effective way for the optimization of agrochemical application, where the cation-exchange capacity (CEC) of minerals plays an important role. Then, the association of mineral structures (high CEC clays and layered double hydroxides, etc.) opens a new research field in the tailoring of nanocomposites, where the properties of minerals, polymers, and additives that are associated with agrochemicals (considered as the active moiety of the nanocomposites) can produce novel properties to the release control. Therefore, this chapter reviews the underlying principles in controlled or slow release of agrochemicals, the fundamentals of key technologies, and the current perspectives in the production of new materials, comparing their potential with conventional materials regularly produced.

Perspectives in Nanocomposites for the Slow and Controlled Release of Agrochemicals: Fertilizers and Pesticides

The effect of bentonite and sand, as natural capping agents, on the fluxes of nutrients and trace metals across the sediment-water interface was studied through sediment incubation, and the ecotoxicological impact was assessed by using Daphnia magna. Bentonite and sand were layered on the sediment at 15, 75, and 225 mg cm−2, and the concentration of cations, nutrients, and trace metals was measured. Sediment incubation showed that bentonite reduced the N flux but increased the P flux as a result of dissolution of non-crystalline P from bentonite, while sand slightly decreased the N fluxes but not the P flux. The concentration of Na increased in the overlying water with increasing application rates of bentonite, while that of Ca decreased. However, regardless of the rate of sand application, concentrations of all cation species remained unchanged. The concentration of As and Cr increased with bentonite application rate but decreased with sand. Both capping materials suppressed fluxes of Cd, Cu, Ni, and Zn compared to control, and the extent of suppression was different depending on the trace metal species and capping agents used. During sediment incubation, the survival rate of D. magna significantly decreased in bentonite suspension but began to decrease at the end in sand suspension. Sediment capping of mildly polluted sediments by using bentonite and sand lowered the level of nutrients and trace metals. However, unexpected or undesirable side effects, such as influxes of P and As from bentonite to the overlying water and a possibility of toxic impacts to aquatic ecosystems, were observed, suggesting that capping agents with an adequate assessment of their side effects and toxicity should be predetermined for site-specific sediment management strategies.

Fluxes of nutrients and trace metals across the sediment-water interface controlled by sediment-capping agents: bentonite and sand.

Massive Intercalation of Urea in Montmorillonite

Purpose
A large amount of nitrogen (N) fertilizers has been broadcasted over soil surface for reliable crop production. Unfortunately, the broadcasted N vulnerable to volatilization and leaching can lead to serious environmental problems. As a new approach to mitigate N loss of broadcasted fertilizers, massive intercalation of urea into montmorillonite (MMT) was recently proposed to innovatively enhance the urea use efficiency. This study focuses on demonstrating the behaviors of the urea intercalated into MMT in soils.

Seok In Yun

Papers

Suppression of NH3 and N2O emissions by massive urea intercalation in montmorillonite