Nano-fertilization to Enhance Nutrient Use Efficiency and Productivity of Crop Plants

Abstract

Nutrients present in the soil are taken up by plants for their successful growth and survival. Loss of essential elements from soil, mainly by leaching, volatilization, erosion, and uptake by plants, reduces soil fertility and necessitates application of multiple-element fertilizer to make up this loss. Nutrient use efficiency of plants lies around 30–35%, 18–20%, and 35–40% for N, P, and K, respectively, with the conventional fertilizers. The use of biofertilizers in combination or in place of chemical fertilizers could not make much difference. Currently, nano-fertilizers (NFs) seem to hold promise to improve the nutrient use efficiency and hence the crop yield. They ensure a better delivery of elements such as P and Zn, which are otherwise poorly bioavailable. They also reduce the loss of runaway nutrients such as nitrate. Nano-fertilizers are produced mainly through encapsulation or coating of nutrients with nanoemulsions and nanoparticles (NPs), respectively. The NFs thus serve as nanocarriers of nutrients, which may be categorized as nanoclays, hydroxyapatite NPs, polymeric NPs, carbon-based nanomaterials (NMs), mesoporous silica, and miscellaneous materials. Interestingly, nanomaterials, including aptamer derivatives, carbon nanotubes, quantum dots, etc., are also used in agriculture sector as nanosensors (or nano-biosensors) to indicate the presence of microbes, contaminants, pollutants, toxins, pH level, nutrient level, and moisture content. In general, all NFs provide a slow, steady, and time-dependent release of essential nutrients to ensure their delivery to the plant in a balanced and need-based form. NFs can improve the nutrient use efficiency about threefolds and improve the crop productivity by promoting seed germination, seedling growth, nitrogen metabolism, photosynthetic activity, protein synthesis, antioxidant defense, etc. Some limitations and adverse effects of NFs have also been reported. However, these can be overcome by proper standardization of NF dose and selection of befitting NM for the test crop. Efficacy of the NF depends on its capacity of ionization and successful delivery of nutrients to the sink, which are modulated by the chemical composition of NMs, their concentration and aggregation state, metabolic potential of plant species, and the local environmental conditions. It is important to investigate whether NFs are fully transformed into ionic forms in the plant and later incorporated into proteins and different metabolites, or some of their parts remain intact and reach the consumers through food chain.