Perspective Chapter: Conservation and Enhancement of Soil Health for Sustainable Agriculture

Abstract

Despite increasing crop yields, the indiscriminate use of chemical fertilizers in conventional agriculture damages soil health, reduces crop productivity, and negatively impacts agricultural sustainability. Therefore, restoring soil health and the environment is imperative. Higher crop productivity can be achieved with natural fertilizers such as biofertilizers, vermicompost, green manures, farmyard manures, and crop residues, which are a sustainable approach to nourishing the soil and the environment. This chapter addresses the importance of healthy soils, how they can be influenced by agricultural inputs and practices, and strategies for enhancing soil health.

1. Introduction

Ensuring sustainability in agriculture and meeting the increasing demand for food depend on maintaining water and soil quality, soil organic matter (SOM), recycling and storing nutrients, efficient use of natural resources, and controlling soil degradation [1]. In addition to air and water, the soil is also critical to life on Earth [2]. As a materially and morphologically diverse ecosystem, the soil is critical for its ecosystem services, including nutrient supply, long-term soil and crop productivity maintenance, and preservation of environmental quality, requiring appropriate characterization of its physical, chemical, and biological properties. Soil health plays a pivotal role in the sustainability of agriculture. Soil health is defined as ‘The continuing potential of a given type of soil to function as a vital living system within managed or natural ecosystem limits, to sustain animal and plant productivity, to maintain or improve the quality of the air and water, and to support human health and habitation’ [3]. The term soil health is not limited to increasing crop productivity. It also includes other functions, such as maintaining an appropriate balance between different soil functions, plant and animal health, and environmental interaction and regulation [4].

World literature shows that the productivity of soils per hectare is very low and constantly decreasing due to faulty agricultural practices. Current agricultural practices rely heavily on inorganic fertilizers and pesticides; over the years, they have impaired biological activities in the soil and processes such as nutrient transformation, thus affecting nutrient availability in the soil [5, 6]. The introduction of improved crop varieties with high yield potential, chemical fertilizers, pesticides, weedicides, and farm equipment such as tractors, drills, harvesters etc. increased crop productivity. However, their long-term effects on soil health are a serious concern. Recent research reports indicate that the overuse of fertilizers and pesticides has seriously affected soil health in many parts of the world, leading to a decline in crop productivity [7]. This decline in crop productivity has been attributed to imbalanced nutrient ratios, micronutrient deficiencies, reduced microbial activity, and disturbed soil physical structure due to the heavy use of agricultural equipment [8].

2. Impact of current agricultural practices on soil health

A wide range of inefficient or faulty agricultural practices can be classified into physical, chemical, and biological categories (Figure 1) that affect the productive capacity of the soil, as briefly illustrated below.

Figure 1.

Flowchart depicting the types, causes, and impacts of soil degrading processes on soil functioning.

2.1 Physical soil degradation

Physical soil degradation occurs when agricultural practices degrade the physical properties of the soil to such an extent that its critical functions are impaired. For example, intensive tillage often results in soil compaction and hardening at the plowing depth when heavy farm machinery is used repeatedly during tillage. Burning crop residues, repetitive tillage, little or no recycling of agricultural wastes, and other agricultural practices that reduce SOM content make soils more susceptible to physical degradation.

2.2 Chemical soil degradation

It refers to the adverse change in the chemical environment of soils and affects their yield potential. Of the common agricultural practices, inappropriate chemical fertilizers and pesticides contribute significantly. Evidence shows that heavy fertilizer use over long periods can lead to increased soil acidification, which negatively impacts soil productivity [9, 10]. The chemicals used in controlling pests (weeds, insects, etc.) also harm soil organisms, which are crucial to soil health and productivity.

2.3 Biological soil degradation

A significant part of our biodiversity is found in the soil. Soil organic matter is the basis of life, and living organisms are critical to maintaining soil productivity. The range and diversity of microorganisms in soil have decreased due to the decline in organic matter recycling. Agricultural practices that do not emphasize integrated nutrient management (INM), involving the best use of crop residues in agriculture, burning crop residues (CR), etc., deplete SOM, which in turn leads to a loss of soil biology and thus contributes to soil degradation. Monocropping, i.e., continuous cultivation of the same crop without crop rotation, also reduces soil biodiversity.

Therefore, researchers worldwide have implemented several research options that could improve soil health in one or more ways. The proven agricultural practices to improve soil health are described in the following sections.

3. Strategies to enhance soil health and sustain agricultural food production

3.1 Increase inputs of organic matter

Soil organic matter has several useful functions: It improves soil structure, is a nutrient storehouse, increases the water holding capacity (WHC) and cation exchange capacity (CEC) of the soil, chelates micronutrients and dissolves phosphates, etc. Therefore, its availability in the soil is paramount in improving soil health and crop productivity. However, soils in tropical and subtropical climates are naturally deficient in organic carbon; therefore, management practices to increase soil organic carbon (SOC) are strongly emphasized. These practices include the addition of CR, reduced tillage, compost and vermicompost (VC), biochar, and green manures (GM). Apart from increasing SOM, these practices add significant amounts of plant-available nutrients and reduce nutrient requirements from fertilizers [11].

3.2 Tillage practices

A brief comparison of conservation (CA) and conventional tillage and their effects on soil is shown in Table 1. The summary of studies showing the effects of CA or tillage with or without CR is given in Tables 2 and 3. Baker et al. [27] defined CA as an umbrella term that generally refers to minimum tillage (MT), direct drilling, no-tillage (NT), and/or ridge-tillage aimed at conserving some resources.

Parameter	Conventional tillage	Conservation tillage
Soil physical health	Very poor	Comparatively good
Soil biological health	Lowest due to frequent disturbance	More diverse and healthy
Soil fertility	Low, heavily rely on inorganic fertilizers	Medium, organics supplement mineral fertilizers
Soil disturbance	Very high	Minimal
Soil erosion	Maximum	Comparatively reduced
Soil Aggregates	Breakdown	Protection and enhancement
Soil surface	Bare	Well protected with crop residues
Soil organic matter	losses	Build-up
Water infiltration	Lowest after clogging of soil pores	Best
Overall soil health	Poor	Good

Table 1.

A comparison of the impact of conventional vs. conservation tillage practices on soil.

Reference	Location	Soil type	Treatments studied	Results reported
[12]	Delhi, India	Sandy loam	Zero tillage (ZT), Permanent beds (PB), Conventional tillage (CT)	Adoption of PB/ZT resulted in ∼22.5% higher SQI than CT. ZT had 22, 18, 25, 28, 29, and 15% higher water-stable aggregates (WSA), hydraulic conductivity (HC), dehydrogenase enzyme (DHA), B-glucosidase activity, available phosphorus (Av. P), and potassium (Av. K), respectively, over CT.
[13]	Pakistan	Sandy clay loam	Minimum tillage (MT), CT, Deep tillage (DT)	With MT, nitrate is less likely to leach into the soil, and bulk density (BD) was about 10% lower than with DT.
[14]	Germany	Silt loam	CT and Reduced tillage (RT)	RT had greater air capacity, HC, macro porosity, and pore connectivity but lower BD.
[15]	China	Clay loam	CT, and NT	Microbial biomass was 21% higher after NT treatment than after CT treatment. Additionally, a higher fungus to bacterial ratio was seen after NT treatment compared to CT treatment.
[16]	Ohio, USA	Loam	CT and NT	The NT practice had 68, 18, 60, and 53% higher mineralizable carbon, basal soil respiration, total carbon (TC), and total nitrogen (TN) than the CT practices.
[17]	Romania	Clay loam	NT, chisel tillage, and CT	NT systems were found to have higher TC, non-labile fraction, very labile fraction than CT treatments.
[18]	Denmark	Sandy loam	Residue retention + tillage (NT and plowing)	In plowed land, the residue retention had a significant effect soil C while there was no discernible effect in NT soils.
[19]	South Africa	Alluvial origin, (Haplic Cambisol)	CT, NT with crop rotation and residue removal, retention, and biochar.	NT treatment had 23% higher SOC, over CT. NT increased PR, MWD and BD of soil compared to CT.
[20]	Northern Ethiopia	Vertisol	Permanent bed (PB), conventional tillage (TRAD), and terwah (a traditional water conservation technique (TERW))	SOM and aggregate stability followed order: PB > TERW>TRAD, while reverse was true for runoff and soil loss amounts.
[21]	USA	Silt loam	NT, disk (DP), chisel (CP), moldboard plow (MP), and NT with winter wheat cover crop (NTW)	At 0–15 cm depth, MP exhibited comparable BD to NT, NTW, and CP; however, the geometric mean diameter (GMD) of aggregates was much greater under NT and NTW.

Table 2.

Summary of studies revealing the effect of tillage practices on soil health.

Reference	Location	Soil type	Treatments studied	Results reported
[22]	Punjab India	Sandy clay loam	Rice straw incorporation at varying doses @ 0, 5, 7.5, and 10 t ha^−1	Incorporating rice straw (7.5 and 10 t ha^−1) increased soil properties such as aggregation, porosity, water retention, and nutrient availability.
[23]	USA	Silt loam	NT and chisel tillage practices with no, partial, and complete residue removal	When all crop residue was left in the field, the SOC stock under chisel tillage was 13% lower than in NT plots.; In comparison to tilled plots, NT plots showed 5% and 39% greater BD and PR, respectively, while residue removal considerably enhanced PR under NT.
[24]	Punjab India	Sandy loam	CT, NT with and without residue (R), and Deep tillage (DT)	NTR and DT had approximately 30 and 37% lower HC, respectively, and 7 and 22% lower PR than CT.
[25]	China	Silty clay	CT with crop residues incorporation (CRI), rotary tillage with (RT + CRI), NT with CR retention; rotary tillage with CR removed (RTO)	NT treatment had higher SOC while humic compounds were higher under RT and CT treatments.
[26]	Central Mexico	Sandy loam	CT, NT with 0, 33, 66, 100% residue cover and planting of vetch (Vicia sp.) and ayocote bean (Phaseolus vulgaris L.) in different combinations	Over CT, NT with crop residue increased aggregate stability by around 22%, TOC by 48%, Av. P by 80%, and Av. K by 11%.

Table 3.

Summary of studies revealing the effect of tillage practices with crop residue (incorporation, retention, removal) on soil health.

The core idea of classifying agricultural practice for CA is that at least 30% CR should be left on the soil surface, with subsequent conservation of time, power, fuel, soil, and soil properties. Thus leaving CR on the soil alone does not adequately describe all CA practices. The overall goals of CA include improving and sustaining agricultural production and conserving the environment, soil, and human health. FAO states that CA practices should be resource efficient and include three essential ideas: Crop rotation, minimal soil disturbance, and maintaining soil cover through residues. Controlled traffic was recently added to this list by FAO.

Agricultural practices and modern tillage cause SOM to decrease over time due to increased oxidation, leading to soil degradation, loss of biological fertility, and long-term soil resilience [28]. Mineralization of SOM can improve yields in the short term by releasing nitrogen (N), but there is always some leaching of nutrients into the subsoil. This is particularly important in soils under tropical climates, where SOM is rapidly degraded so that SOC levels are low after only one or two decades of intense soil tillage.

In contrast, cropping under zero-tillage (ZT) has resulted in a build-up of SOC in the surface layers [29] since permanent soil cover is maintained with crop residue. By using NT, it is possible to minimize SOM losses and build soil C and N stocks [30]. Though tillage is sometimes effective in reducing compaction, it is also one of the significant causes of compaction, especially tillage breaks the soil aggregates, disturbs the surface soil, and accentuates soil runoff and erosion. Repeated passes with a tractor are used for seedbed preparation or to maintain a fallow pasture. Tillage exposes the soil to the air, increasing evaporative loss of soil moisture and thus affecting soil biotic activity, which is essential for healthy soil. The biological properties of the soil are altered by this form of disturbance, which has numerous negative implications on soil productivity. For instance, some microorganisms can be severely damaged, negatively impacting soil biodiversity. Repeated plowing can disrupt the extraradical hyphal network of fungi, resulting in poor nutrient supply to plants. To address the problems described above, farmers in agricultural systems that rely on tillage for good crop yields need to increase organic matter input through compost, VC, or GM.

3.3 Organic source of nutrients

The mechanism of how long-term organic management improves soil health and agricultural production is illustrated in Figure 2. The studies that demonstrate the effect of organics (cover crops, crop rotations, manures, green manures, and vermicompost) on soil health are listed in Table 4. Cover crops (CC) (legumes or non-legumes) are used in cropping systems as a nutrient management tool [43] that protects the soil from raindrops and soil erosion and alters the temperature regime, thus improving soils [44]. The type of CC to be included in the cropping system is goal-oriented. For example, the legume CC is a source of nutrients, especially N, for the following crop [45], while grasses are mainly used to reduce soil erosion and NO3-N leaching [46]. Initially, CC has a protective effect on the soil, and later, when they decompose, they add significant amounts of SOM, which improves soil aggregate stability and microbial activity. Incorporating legumes CC has several advantages, namely the supply of essential nutrients when they decompose, biological N fixation, reducing the need for N fertilizer [47], and the extensive root system of legumes, which explores nutrients in the subsoil [48]. However, soil nutrient enrichment with legumes varies depending on the type of CC, the amount of dry matter produced, the ability to assimilate nutrients, and the root system. Therefore, including CC between the rows of the main crops can lead to improved soil health [49].

Figure 2.

Flowchart depicting the impact of long-term agricultural use of organics on soil health and crop production.

Reference	Location	Soil type	Treatments studied	Results reported
[31]	Indo-Gangetic plains (India)	Typic Ustocrept	Farmyard manure (FYM), RDF and their combination (IPNS), Inclusion of forage cowpea or forage berseem	Continuous rice-wheat cultivation with RDF raised soil BD, while incorporating fodder berseem or cowpea every third year helped reduce it.
[32]	Meghalaya (India)		Control, RDN through FYM, RDN through poultry manure (PM), RDN through vermicompost (VC) as well as their varying doses	In comparison to control, organics (FYM, PM, vermicompost) enhanced TOC and microbial biomass carbon by 57 and 62%, respectively. There was an increase in available N, P, and K inorganic treatments over control.
[33]	Central Chile	Coarse-textured soil	cover crops + and N fertilization	The addition of L. multiflorum improved soil organic pools and microbial activity.
[34]	Italy	loam soil	Two species of legume cover crop and non-legume cover crop	Cover cropping with legumes increased the SOC content of soil.
[35]	western Illinois	Silty clay loam	Continuous corn (CCC), corn-soybean (CS) rotation for 2 years, corn–soybean–wheat rotation for 3 years, and continuous soybean (SSS).	The 3-year CSW rotation and CCC had higher total N and WSA than the CS or SSS rotations.; In comparison to SSS, Av. K levels were higher in CCC and CSW.; In terms of storing nitrogen and preserving soil aggregates, the two crop rotations, CCC and CS, were comparable.
[36]	New York	Silt loam soil	Crop rotation with Soybean, corn, wheat, and clover.	Soybean-wheat/clover-corn rotation showed the increased infiltration rates and highest earthworm populations.
[37]	Akola (India)	Vertisol	RDF, FYM, Wheat Straw, Gliricidia green leaf manuring and their combinations.	Adopting minimum tillage with 50% N through gliricidia GLM and compensation of RDF through chemical fertilizers helps improve soil quality with higher yield and maximum net returns.
[38]	North China plain	Silty loam	control, fertilizers, and FYM	Continuous FYM application for 15 years significantly increased soil N and organic matter contents, and enzyme activities.
[39]	Brazil	Fluvisol	Effect of four legume species Cajanus, Crotalaria, Canavalia, and Mucuna used as green manure	Crotalaria plots had the highest soil P and K concentrations, while Mucuna plots had the highest soil Ca content. When compared to other green manure species, the plot containing Mucuna had a higher level of soil microbial biomass. Mucuna was more effective in enhancing the biological properties of the soil, but Crotalaria appeared to be more effective at enhancing the chemical characteristics.
[40]	Himalayan region of Kashmir, Pakistan	Loam	Repeated application of wheat straw residue and poultry manure alone or in combination with urea	Organic amendments, either alone or in combination with UN, significantly enhanced soil physical properties by lowering BD and PR, while increased aggregate stability and HC.
[41]	Turkey	sandy loam, loam and clay	Vermicompost application	Vermicomposting considerably enhanced organic matter content and wet aggregate stability in all three textural soils.
[42]	Bangladesh	Silt clay loam	Control, cowdung, green manure, compost, and rice straw and three levels of N.	Different organic materials that are applied over a long period of time enhance soil SOC, total N, P, and S, and lowered pH. Increased in SOC maximum under green manure.

Table 4.

Summary of studies revealing the effect of organics on soil health.

An adequate and balanced supply of plant nutrients is essential for improving soil health. Improving the availability of less available nutrients in the soil is becoming increasingly important. In this regard, crop rotation involving the cultivation of different crops with different rooting habits, nutrient requirements, and leaf litter deposition can be efficient, which helps to regulate soil nutrient supply [50]. For example, the water requirements of rice and sugarcane are very high, which lowers the water table. If a crop with lower water demand (millet) is grown instead, this could help conserve water and nutrients in the soil. A meta-analysis conducted by Venter et al. [51] found that crop rotation increased the diversity and richness of microbial communities. Similarly, microbial diversity due to crop rotation resulted in beneficial changes in soil physicochemical properties [52], improved water use efficiency, and controlled temperature fluctuations [53]. Thus, crop rotation can manage soil and soil fertility, improve soil workability, increase nutrient and water availability, reduce soil losses due to erosion and crusting, and recycle nutrients in the soil, ultimately improving soil health [54]. However, increasing crop diversity in crop rotation is an effective strategy for long-term resilience [55].

SOC can be maintained or restored by the application of organic manure. In addition, manure increases total N content, which is essential for plant growth. Manure provides better soil structure by increasing SOC and keeping soil pH in an optimum range for crop growth [56]. Organic manure differs significantly in its influence on soil properties. The nature and composition of manure primarily affect its residence time in the soil and thus influence soil properties. Therefore, it is always advantageous to use a variety of organic sources. For example, well-decomposed compost may not improve soil aggregation but can rapidly increase the soil’s biological activity and nutrient content, persisting for a short period, while dairy cow manure may stimulate soil aggregation [57].

Vermicompost (VC) is a nutrient-rich organic amendment produced by earthworms [58]. A VC consists of earthworm casts, humic substances, seeds or cocoons, and partially decomposed bedding materials. VC is usually added to soil as a source of essential plant nutrients and to reduce fertilizer dose, but simultaneously, it improves soil microbial composition, diversity, and thus nutrient transformation, structural stability [59], and soil health. Adding VC to soil alone or with chemical fertilizers can improve soil structural stability and WHC [60]. In VC-rich soils, earthworm populations proliferate, resulting in porous soil with good aeration, water absorption, and drainage. The application of VC enhances soil microbial diversity. Numerous N-fixing bacteria have been reported to reside in earthworm burrows [61].

Green manuring is the addition of undecomposed green plants to improve soil nutrient content and supply to subsequent crops. It can also be considered a system for incorporating green plants into the soil at a green stage before flowering in the same or another field. GM technology improves nutrient supply and soil fertility, structure, and WHC, curbs soil erosion, and increases soil microbial populations. This practice is environmentally friendly and poses no threat to soil, water, and air [62]. Like chemical fertilizers, they do not negatively affect soil properties and food production. GM plants with high nutrient concentrations and low C/N ratio are more valuable as organic fertilizers in crop production [63]. Using GM crops in conjunction with proper residue management and crop rotation can help maintain soil health, promote soil fertility, support nutrient cycling in deeper soil profiles [64], limit weed growth, and eliminate the need for external fertilizers [65, 66]. GM Plants are often referred to as soil-building plants because they are grown primarily for the benefit of the soil. In addition to improving the soil’s physical, chemical, and biological properties, GM plants enrich the soil with organic matter and nutrients [67, 68, 69, 70]. They also facilitate soil and nutrient conservation, promote biological activity, reduce soil compaction, increase soil porosity and water permeability, and ultimately improve soil health [71, 72, 73] and crop productivity [74, 75]. GM Intercropping plants pull nutrients and prevent leaching from the soil. Nutrients contained in GM plants become plant-available upon decomposition and can feed the following crop. This cycle of nutrient recycling contributes to a healthier soil environment. GM Plants also increase phosphorus utilization by crops [76, 77], reducing nitrate leaching and the need for nitrogen fertilizer for subsequent crops [78]. By growing GM crops between main crops, soils are protected from erosion, degraded soils become productive again, and chemical fertilizers can be replaced to some extent [79, 80].

3.4 Biochar

The studies showing the effect of biochar on soil health are listed in Table 5. Biochar is the carbon-rich byproduct of biomass pyrolysis formulated under oxygen-limited conditions, intentionally applied to soils, and optimized for agronomic and environmental benefits [89]. Biochar has many of the same characteristics as charcoal, such as the presence of stable recalcitrant organic carbon [90], but differs from similar materials in its intended use as a soil amendment [91] and as a long-term carbon storage material [92]. It is possible to produce biochar from various materials, including agricultural crop residues, municipal waste, forestry waste, and animal manure [93]. There are several fundamental properties of biochar, including pH, specific surface area, CEC, and porosity, which are affected by the feedstock and the production process [94]. These properties affect how biochar interacts with soil constituents, especially physically, chemically, and biologically, and its fate within an ecosystem [95]. As a soil amendment, biochar can maintain crop productivity by improving the soil’s physical environment, nutrient availability [96], and nutrient supply to plants, reducing leaching losses and the need for fertilizer [97, 98].

Reference	Location	Soil type	Char type	Results reported
[81]	China	Clay loam	Maize straw	Increase in SOC by 28%, TN, Available P, and K
[82]	Korea	clay	Rice hull-derived biochar	Increase in WSA; Reduced ESP
[83]	Pakistan	Aridisol	Corn cob	Increased C seq; Enhanced microbial C
[84]	USA	Entisol	Switchgrass	Increased soil moisture by 38%; Reduced BD by 15%
[85]	Punjab India	Sandy loam	Rice straw-derived biochar	Higher SOC, available P, and K; Increased Nutrient use efficiency
[86]	Australia	Sandy loam	Acacia green waste	About 23% increment in SOC was observed for biochar.
[87]	A meta-analysis Kenya			In general, adding biochar to soils alone or in combination with fertilizer increases the soil’s availability of P.
[88]	Kenya	Variables texture sites		Biochar addition slightly increased pH, Av. porosity, and N mineralization from native SOM

Table 5.

Summary of studies revealing the effect of biochar type on soil health.

Biochar also stimulates microbial activity, diversity, and nutrient transformation [99]. Biochar can improve soil WHC and reduce greenhouse gas emissions [100]. In addition, biochar can control the contaminants in soil: toxicity, mobility, and bioavailability [101]. It is well known that biochar has tremendous potential to mitigate global climate change by sequestering carbon in the soil. For example, biochar application has increased SOC by 4.9–6.3 g kg⁻¹ [102], 4.3 kg⁻¹ [103], and 0.52% [104]. However, after pyrolysis of organic plant material, the long-term potential of biochar to sequester C depends on the composition of stable and resistant forms of organic C.

3.5 Inorganic fertilizers

Although inorganic or chemical fertilizers can improve crop growth and yield relatively quickly, chemical fertilizers are associated with certain disadvantages. Studies on long-term fertilization show that much of the increase in crop production yields in recent decades can be attributed to mineral fertilizers [105]. Higher productivity also results in more plant residues returning to the soil after harvest, which boosts SOM in the long run. According to Körschens et al. [106], NPK fertilization increased SOC by 10% compared to the control. One notable exception is when the pH of a crop is subsided by ammonium or urea fertilizer applications. In such cases, yield is significantly reduced and may fall below that of an unfertilized crop [107]. The acidic condition of the soil may decrease the soil aggregates, making the soil susceptible to erosion.

It has been found that soil biotic activity is significantly affected by soil pH [107]. Since chemical fertilizers are highly soluble, their continued use leads to groundwater contamination. These chemicals subsequently combine with clay to form hard pans in the soil that impede the growth of plant roots in the soil [108]. Chemical fertilizers also destroy soil structure, leaving highly compacted soils with a restricted pore network and air circulation [99]. The life of beneficial soil microorganisms, such as bacteria that fix N, is threatened by the repeated use of inorganic fertilizers [109, 110]. Mineral fertilizers differ in their ability to alter specific microbial communities over time. In general, fungi have demonstrated the benefits of mineral fertilization even when soil pH had little effect on their growth [23, 111, 112, 113].

Nevertheless, Kirchmann et al. [109] found lower fungal biomass in fertilized soils in two long-term field studies in Sweden. They attributed this to N-rich residues with a reduced C/N ratio, which may have favored bacterial activity over that of fungi. According to Melkamu and Alemayehu [10], applying N or sulfate fertilizers led to a decrease in microbial C, accompanied by a decrease in soil pH.

3.6 Need-based input application

To prevent the inefficient use of external inputs, the golden rule is to use them as needed and control their waste, such as tillage, water, fertilizers, etc. Fertilizers are crucial in crop production, as nutrients determine more than 50% efficiency. Nitrogenous fertilizers need special treatment. In addition, research on the site-specific application of N and P, the timing of the application, and placement is essential for determining the exact amount of nutrients and calibrating the amount of fertilizer needed to increase the efficiency of their use. For example, in soils with a high P-fixing capacity, application of P near the root zone is generally recommended, especially for water-soluble P fertilizers (SSP), while citric acid-soluble P fertilizers (dicalcium phosphate) can be applied as such. Split application is recommended in the case of N and K since a significant amount of these nutrients is lost through leaching. Depending on soil conditions, rainfall intensity and duration, and crop requirements, two to three splits are recommended for most crops. This synchronizes nutrient supply with crop needs at critical growth stages.

In addition, using coated technologies such as sulfur-coated urea, neem-coated urea, urea granules, nitrification inhibitors, and urease inhibitors is also very promising to reduce N losses from the agroecosystem. The coated materials provide a controlled release of N in the soil, increasing its availability and accessibility to plant roots. Nitrification inhibitors can reduce nitrate leaching and denitrification, especially in flooded soils.

3.7 Role of Nano fertilizers

The waste of nutrients in conventional fertilizers is alarming, leading to calls for environmentally friendly fertilizers with high use efficiency. In this context, nanotechnology has emerged as a potential substitute for conventional fertilizers. As nano-fertilizers, they contribute to nutritional management by improving nutrient use efficiency. In response to various environmental factors, such as heat, moisture, and other unfavorable circumstances, the nano-fertilizer distributes nutrients in a controlled manner. Using nanoscale fertilizers, it may be possible to control the release of nutrients and properly deliver the right amount of nutrients to plants.

3.8 Precision farming and agricultural sustainability

Precision farming, also known as site-specific agriculture, aims to identify how external and controllable factors such as fertilizer, seeding rate, herbicide, pesticide use, and available water affect crop response to personalize soil and crop management practices to the unique circumstances of each field. The basic idea is to provide nutrients precisely for a particular site. Because there is high soil variability, the concept of precision agriculture measures these variations in soil properties to make the proper adjustments in fertilizer inputs, rates, application method and timing, seed rates, and pesticide doses in near “real-time.”

4. Conclusions

Since the advent of agriculture, people have used various chemicals to enrich the soil to increase crop yields. This overuse of chemicals damages the environment and the health of the soil. Although fertilizers and pesticides are used to meet the world’s food needs, they are now a cause for concern; as a result, we have lost a large area of fertile land worldwide. In this context, maintaining soil fertility and restoring the health of stressed or degraded soils are paramount. The use of cost-effective natural practices such as FYM, vermicompost, green manures, biofertilizers, and integrated nutrient management, as well as conservation farming practices such as reduced tillage and no-till, have proven to be the best methods to improve and sustain agricultural production, soil health, and the environment. Recent advances in the use of nutrients, i.e. nano fertilizers, need-based nutrient management, and the concept of precision agriculture, can also be explored to improve soil health and agricultural sustainability.

Acknowledgments

No financial support is received in connection with publishing this document. I thank Mr. Kartik Madankar for his assistance throughout all aspects of our study.

Conflict of interest

The authors declare no conflict of interest.