Enhancing Agricultural Productivity through Nanotechnology

Enhancing Agricultural Productivity through Nanotechnology

Published: 2022.10.18
Accepted: 2022.08.22
121
Agricultural Systems Institute, College of Agriculture and Food Science, University of the Philippines Los Baños College, Laguna Philippines
Institute of Crop Science, College of Agriculture and Food Science, University of the Philippines Los Baños College, Laguna Philippines
Agricultural Systems Institute, College of Agriculture and Food Science, University of the Philippines Los Baños College, Laguna Philippines

ABSTRACT

Nanotechnology has been explored for its potential in enhancing agricultural productivity and ensuring environmental sustainability. Nanofertilizers containing the macronutrients N, P and K were formulated, characterized and their production and application on selected agricultural crops were optimized. Crop yields increased and the rates of application were reduced. In annual crops such as rice, corn and cabbage, the rate of application of the nanofertilizers can be reduced to 50% of the recommended rate of conventional fertilizers. For plantation crops like sugarcane, nanofertilizers increased cane tonnage by 46% and sugar yield by 40%. It also reduced the rate of application by 45%. For cacao, the rate of application of nanofertilizers can be reduced to 50% while supporting a 106% increase in cacao pod yield. Nanofertilizers increased the number of hands per bunch and reduced rejects in Cavendish banana, thereby increasing the marketable yield by 24%. With increased yield and reduced rates of application, the net income of the farmers also increased. The improvement in yield at lower rates of application indicate that the slower release of nutrients improved nutrient uptake, increased nutrient use efficiency and reduced nutrient loss. The synthesized Zinc oxide nanoparticles (ZnO NPs) applied as foliar fertilizers also improved the yield of tomato and reduced the severity of black leaf mold and blossom-end rot. The formulated nanoplant hormones have been shown to increase the survival rate of Robusta coffee and Cavendish banana. The effect of these nanoformulations on soil microbial community and diversity were also assessed.

KEYWORDS: nanofertilizers, ZnO nanoparticles, nano-plant hormones

INTRODUCTION

The world’s population is expected to grow to 9.6 billion by 2050 (UN 2013) and the biggest challenge is to increase agricultural productivity to feed the rapidly growing population. With limited arable land and scarce water resources, the use of fertilizers is among the key factors driving the increased global agricultural production.  However, in times of increasing economic constraints and pressure to maintain integrity of the environment, there is a need to use fertilizers efficiently. Nanotechnology has emerged as an innovative strategy in addressing the environmental effects of conventional fertilizers. Nanofertilizers have the potential not just to mitigate nutrient loss from fertilizers, particularly Nitrogen and Phosphorus, but also to reduce their application rates (Dimpka and Bindraban, 2018). 

The development of nanofertilizers often requires a nutrient carrier and recent studies use different carriers for a specified purpose. Zeolite has been prominently used as the nutrient carrier of most nanofertilizer formulations (Liu and Lal, 2014; Manikandan and Subramanian, 2016). Aside from having high cation exchange capacity due to its high surface area to volume ratio, the pores in the structure of zeolite perfectly fit the nutrient compounds which allows slow-release mechanism of the nanofertilizer upon hydration, to as much as 1% mineralization for two weeks (Lateef et al., 2016, Sangeetha and Baskar, 2016; Latifah et al., 2017; Manjunatha et al., 2016).This addresses problems such as leaching, volatilization, and surface migration, resulting in an improved nutrition and higher yields. In turn, nutrient losses to the environment are prevented thereby reducing N2O emissions and pollution of surface and ground waters (Shaviv 2000; Chalk et al., 2015)

Metal-based nanoparticles like ZnO have also gained considerable importance due to their unique properties compared to their bulk counterparts. Their potential to increase grain yield and enhance Zn uptake have been demonstrated on wheat (Dimpka et al., 2020) and on rice (Zhang et al. 2021).

Recognizing the need to increase and sustain agricultural productivity and to contribute in achieving Sustainable Development Goal 2 (no hunger), research efforts focused on the applications of nanotechnology in the development of nanofertilizers (FertiGroe® N, P and K nanofertilizers, ZnO NP) and nano-plant hormones (HormoGroe®). This paper presents the development, production and evaluation of these nanoformulations in enhancing agricultural productivity and ensuring environmental sustainability.

N, P and K NANOFERTILIZERS

N, P and K nanofertilizers were formulated at the University of the Philippines Los Baños (UPLB) through funding from the Department of Science and Technology-Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (DOST- PCAARRD). The initial phase of the project focused on laboratory scale production and preliminary efficacy trials on corn and sugarcane. Recognizing the potential of these nanofertilizers to improve nutrient uptake, reduce rate of fertilizer application and increase yield, a research program was again supported by DOST-PCAARRD to optimize the production and use of FertiGroe® N, P and K nanofertilizers on selected agricultural crops which included rice, corn, vegetables, sugarcane, coffee, cacao and banana (saba and cavendish).

Optimization of the production process

The overall schematic diagram for the optimization of the production of N, P, and K nanofertilizers is shown in Figure 1. The procedure was divided into two parts: (1) laboratory scale optimization and (2) pilot scale optimization. The results of the laboratory experiments were used as benchmarks to optimize the pilot scale production of the nanofertilizer formulations.  Scale up production of the nanofertilizers was carried out following the process outlined in Figure 2. Parametric and optimization studies to maximize N, P and K contents in the formulated nanofertilizer were conducted.

Characterization of the N, P and K nanofertilizers

The physical characteristics of the nanofertilizers such as surface morphology and particle size distribution were also determined. The surface micrographs of the fertilizers obtained using a Thermoscientific’s Prisma E SEM with EDAX’s EDS are shown in Figures 3-5 and the elemental analysis of the nanofertilizers expressed in terms of elemental weight percentages are presented in Tables 1-3.

The average particle sizes obtained using DLS were a little higher than those obtained using SEM (Table 4). This can be attributed to the aggregation of particles in the solvent (i.e., water). Nonetheless, nanoparticles were confirmed after obtaining measurements using SEM.

The FertiGroe® nanofertilizers were initially in powder form and to ensure the quality of the fertilizers, a series of nutrient content analysis were conducted, the range of which is presented in Table 5. The stability of the nanofertilizers was also evaluated by checking the monthly nutrient content of    the formulations.

To improve the application of the dry powder form of the nanofertilizers in the field and to prevent drift losses and possible inhalation of the particles, granulation of the fertilizers was done. The nutrient content of the granular form is still within the range of the powder form indicating that granulation (binder introduction) had minimal effect.

The final packaging of granular FertiGroe® is a properly labeled sack with a plastic lining inside to prevent leakage (from the inside) and contamination (from the outside). This packaging also prevents any losses in nutrient content (quality) due to changing weather and environmental conditions. The trademark of FertiGroe® has been registered at the Intellectual Property Office of the Philippines and patents for the nanofertilizers have been filed.

Nanofertilizer testing and field studies

The optimized nanofertilizer formulations were evaluated using several test crops (rice, corn, vegetables, sugarcane, coffee, cacao, and banana). Optimization and field validation trials were conducted to develop application protocols (rate and timing of application) for each of the selected crops. In annual crops such as rice, corn and vegetables (potato), the rate of FertiGroe® N, P and K nanofertilizers can be reduced to 50% of the recommended rate of conventional fertilizers (Tables 6-8). With increased yield and lower rates, the net income of the farmers also increased by 40% in rice, 20% in corn and 46% in potato.

In plantation crops, like sugarcane, FertiGroe® nanofertilizers increased cane tonnage by 46% and sugar yield by 40% (Table 9). It also reduced the rate of application by 45% of the recommended rate while improving the stalk length, stalk weight and stalk diameter of the millable cane yields. With FertiGroe® nanofertilizers, the amount of fertilizers to be applied can also be reduced to 50% of the recommended rate in cacao, while supporting a 106% increase in cacao pod yield (Table 10). With the considerable reduction in fertilizer inputs, a positive net profit of about PhP20,000 (US$360) after a year of application was realized in cacao. In banana, FertiGroe® nanofertilizers increased the number of hands per bunch and reduced rejects in cavendish, thereby increasing the marketable yield in cavendish by 24% and resulting in a net income of PhP 48,310.33 (US$868) per cycle in one hectare (Table 11).

NANO ZnO FOLIAR FERTILIZER

Nano particles of ZnO were synthesized through an alkaline precipitation technique that is ideal for large-scale and cost-effective production (Ybañez et al., 2020) Characterization using Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDS) revealed the presence of rod-shaped ZnO crystals with nanoscale dimensions, low degree of aggregation and high chemical purity (59.96% Zn via EDS) (Figure 6). Mineralogical analysis by X-ray Fluorescence (XRF) showed that the nano particles of ZnO were free from impurities (90.39% ZnO) while FTIR analysis confirmed the presence of Zn and O bonds. The characterization tests confirmed that nano ZnO can be successfully synthesized from ZnCl2 and thus can be a viable source of Zinc foliar fertilizer.

The application of the synthesized nano ZnO as foliar spray on tomato significantly increased marketable yield (11.74 t ha-1) compared to the commonly used Zn sources such as  bulk ZnO (6.56 t ha-1) and ZnSO4 (6.22 t ha-1), and with the untreated plants (4.99 t ha-1). It was also observed to reduce the severity of black leaf mold and blossom-end rot. Application of Zn NPs also resulted in improved postharvest quality (higher total soluble solids (TSS), total acidity (TA), vitamin C and firmness) of tomato.

NANO PLANT HORMONE

The formulation of controlled-release plant growth regulators (auxins, cytokinins and gibberellins) derived from naturally occurring plant growth-promoting bacteria (Fernando et al., 2017) was funded by the Department of Science and Technology - Philippine Council for Industry, Energy, and Emerging Technology Research and Development (DOST-PCIEERD). These naturally occurring plant growth regulators (HormoGroe®) have been shown to increase the survival rate of Robusta coffee and Cavendish banana (Fernando et al., 2022). Unlike other plant hormones and root promoter products, HormoGroe®) is encapsulated in nano-sized granules for controlled release and to prevent degradation in the soil.

TOXICOLOGY ASSESSMENT OF THE NANOFORMULATIONS

 

Despite the increasing benefits of the developments in nanotechnology, growing concerns on its sustainability and safety emerged. The effect of the different nanoformulations on soil chemical properties and microbial community and diversity were then assessed to determine any adverse effects of the material on the environment. In the evaluation of the nano-ecotoxicity of the tested products, microbes play an important role in determining the quality, health, and sustainability of the environment (Gupta et al., 2016). The close association of the soil microbial ecology to the environment, as a whole, could be used as a predictive unit for the impact assessment of the tested nano-formulated materials in the environment.

The application of FertiGroe® nanomaterials showed significant positive relationship with the bacterial cultures of Chloroflexia, Gemmatimonadetes, Nitrospira, Acidimicrobiia, and Actinobacteria, while Sordariomycetes, Agaricomycetes, Dothideomycetes, Eurotiomycetes, and Mortierellomycetes for fungi. The correlation of the observed microbial growths was attributed to the shifts in the chemical properties of the soil, particularly with soil pH, available P, and total N stimulated by the addition of the nanofertilizer (Pide et al., 2022; Sun et al., 2016; Xia et al., 2020). Despite the slight decrease in some of the pH sensitive microbial cultures, no adverse effects on the microbial ecology were noted in response to the applied FertiGroe® nanofertilizers. In a related study, the nano plant hormone (HormoGroe® )  did not have any adverse effect on the culturable bacterial population, soil dehydrogenase and urease activity. The degree of HormoGroe® influence on the microbial community was relative to the soil type and not to the applied nano-plant hormone treatments (Basay et al., 2021).

In the case of the ZnO NPs, Guerrero et al. (2020) found that material composition and not the nano-sized modification was the main inhibitory factor affecting the growth of the cultured R. solani, S. rolfsii, and F. oxysporum fungal pathogen species. Similar findings were reported by Rubina et al. (2017) and Jamdagni et al. (2018), where the tested nanoparticles of CuO and ZnO showed antagonistic effect against the tested fungal cultures of R. solani, S. rolfsii, and F. oxysporum despite having a size range of 2-3 nm for CuO and 12-32 nm for ZnO.

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