Nano-Restoration for Sustaining Soil Fertility: A Pictorial and Diagrammatic Review Article

Abstract

Soil is a real treasure that humans cannot live without. Therefore, it is very important to sustain and conserve soils to guarantee food, fiber, fuel, and other human necessities. Healthy or high-quality soils that include adequate fertility, diverse ecosystems, and good physical properties are important to allow soil to produce healthy food in support of human health. When a soil suffers from degradation, the soil's productivity decreases. Soil restoration refers to the reversal of degradational processes. This study is a pictorial review on the nano-restoration of soil to return its fertility. Restoring soil fertility for zero hunger and restoration of degraded soils are also discussed. Sustainable production of nanoparticles using plants and microbes is part of the process of soil nano-restoration. The nexus of nanoparticle-plant-microbe (NPM) is a crucial issue for soil fertility. This nexus itself has several internal interactions or relationships, which control the bioavailability of nutrients, agrochemicals, or pollutants for cultivated plants. The NPM nexus is also controlled by many factors that are related to soil fertility and its restoration. This is the first photographic review on nano-restoration to return and sustain soil fertility. However, several additional open questions need to be answered and will be discussed in this work.

Keywords: degraded soil; polluted soil; salt-affected soil; soil conservation; soil degradation; soil–plant nexus; waterlogged soil.

Figure 1

Sustainable Development Goals and their relationships with soil management (Sources: Lal et al. [32]).

Figure 2

Soil restoration for sustainable agriculture including the forms, the approaches, and strategies (Sources: [31,38,39]). Abbreviations: Plant growth promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF).

Figure 3

Different applying approaches for soil fertility. Sources: [38,39].

Figure 4

Cultivation of sandy soils is a great challenge facing the arid and semi-arid regions because of low fertility and low ability to hold water. These photos represent cultivation of sandy soil with different horticultural crops in Egypt, including citrus, grapes (higher photo left from saline sandy and right), mango (middle photos, which represent saline sandy soils), and banana (lower photo left). Photos by El-Ramady.

Figure 5

Definition of salt-affected soil, sources of salts, different impacts of soil salinity on cultivated plants, mechanism of salinity tolerance, and different management approaches (Sources: [52,53,54,55]).

Figure 6

Some common features of saline-alkaline soils at the experimental farm of Kafrelsheikh Uni. (Egypt), which represent in sabkha on the soil surface and growing the purslane plants (the first higher 2 photos beside the middle photo left), the accumulation of salts during rice growing in saline soil in the middle photo right, and the lower photos (left) general view to saline soil during cultivating lettuce under drip irrigation and deep cracks due to heavy clay content (the lower right photo). Photos by El-Ramady.

Figure 7

Production of horticultural crops under arid climatic zones and salinity stress in salt-affected soils at the experimental farm of Kafrelsheikh University (Egypt). Many crops physiological and nutritional problems (mainly nutrient imbalances, dehydration, disease pressure due to decreased resistance) can be seen on the cultivated crops from top to bottom; lettuce, sugar-apple tree (top photos), persimmon (the middle photos), and citrus (lower photos). Photos by El-Ramady.

Figure 8

Salt-affected soils have general characteristics, including the accumulation of salts on the surface of the soil, missing plants due to high soil salinity in the field or under greenhouse conditions, high water table content due to poor drainage, especially in traditional greenhouses, and high temperature, which increases evaporation from the soil surface and thus accumulation of salts on the soil surface. Photos by El-Ramady.

Figure 9

Saline–sodic soils in Kafrelsheikh, Egypt, could be managed using the application of gypsum (seen as the white spots on the soils in the photos). Cleaning the agricultural canals and/or drains is common at the experimental farm of Kafrelsheikh University to avoid harmful impact of Na in such soils, which is necessary to provide good drainage and reduce anthropogenically-induced salinization of the soils. Photos by El-Ramady.

Figure 10

Cultivation of paddy rice is very important in managing salt-affected soils in the Kafr El-Sheikh region (Egypt), which depends on the flooding irrigation to overcome soil salinity in this area. Photos by El-Ramady.

Figure 11

The relationship between nanotechnology and sustainable agriculture including different applications, methods of nano-production, and their benefits and challenges in agricultural application (Sources: [106,107,108,109,110]).

Figure 12

The common methods used in nanoparticle synthesis and their classification into physical, chemical, and biological methods (Sources: [62,95,112]).

Figure 13

A simplified general overview of the interactions among soil microbes, cultivated plants, soil water (soil solution), and different kinds of nanoparticles (natural and atherogenic) in an agroecosystem. All these components interact together in soil, with many positive and negative impacts on soil fertility. Sources: [118,119,120].

Figure 14

The soil solution is the medium where several interactions among soil microbes, plants, pollutants, agrochemicals, and nanoparticles occur in agroecosystems. These interactions can happen in the soil, with many positive and negative impacts on soil health and fertility. Sources: [118,122,123,124].

Figure 15

The possible interactions that can happen in the soil–water–plant–microbe system. Sources: [39,46,119]). Abbreviation: Volatile organic compounds (VOCs).

Figure 16

The fate and behavior of nanoparticles (NPs) released into the atmosphere–soil–plant–groundwater system (adapted from [128]).

Figure 17

The main fate and interactions of nanoparticles in soil including various components of the soil system (Sources: [118,120]).

Figure 18

The interactions between soil microbes, plants, and nanoparticles involve pathways in the soil like forming biofilms on plant roots, adsorption, and bio-degradation in plants, but many mechanisms are still unknown and need more investigation. Sources: [118,122,123,124].

Figure 19

Different soil rhizospheric interactions between plant roots, agrochemicals (mainly mineral fertilizers and pesticides), organic/inorganic pollutants, soil micro-organisms (bacteria, fungi, actinomycetes, viruses), nanoparticles (NPs)/and or nanomaterials (NMs), and their interactions in the soil solution. Relationships between plants, microbes, and nano-materials during restoration of contaminated soil are still open questions that need more investigation. Sources: [118,122,123,124].

Figure 20

The suggested mechanisms of applied nanomaterials that may improve plant salinity tolerance depending on the kind of nanomaterials, the applied concentration, and plant species (Sources: [100,146,147,148]). Abbreviations: Reactive oxygen species (ROS), Abscisic acid (ABA), brassinosteroids (BR), gibberellin (GA), and salicylic acid (SA).