Full Text: 1 Introduction Modern agriculture is explained by high crop productivities that depend on systematic chemical inputs and improved machine technology. Increasing food production poses a challenge due to population growth and the upcoming demand for food. To meet the demand of the burgeoning global population, agricultural production should be doubled from the present levels by 2050 (Tahat et al., 2020). World’s population is growing day by day, thus the area under cultivation is limited to meet the food demand whereas the constraints of crop production in agricultural land are land degradation, water resource scarcity, which increases the climate variability. To meet the future demand of the world’s population natural resource base should be adequate to produce more food from less land in a sustainable way (Page et al., 2020). Thus, conservation agriculture (CA) is the multidimensional and holistic approach that can be considered for achieving this total system intensification. Conservation agriculture is gaining tremendous growing interest and support from the scientific community around the world, especially for its potential to conserve or improve soil quality and environmental sustainability. Assessment and monitoring of the soil quality, identification of physical, chemical, and biological properties of soil can serve as soil health indicators which became a major issue for land managers and food producers throughout the world (Laishram et al., 2012). CA has been reported to improve crop input-output relationship, conserving natural resources through lowering soil erosion, arresting water losses through reducing soil evaporation, sequestering atmospheric carbon in the soil, and reducing energy needs of the agricultural sector (Jat et al., 2005; Yadav et al., 2016a). For sustainable agricultural productivity and a stable environment, it is necessary to build up the soil carbon contents by increasing carbon inputs or decreasing the decomposition of organic matter in the soil. While, soil carbon can also be improved by adapting the conservation agriculture practices like no-tillage, intensifying crop rotation, and by optimizing the agronomic practices like fertilizer, pesticides, and irrigation, etc. Therefore, conservation agriculture could also play a major role in reducing C emission from the agricultural sector (Adeel et al., 2018). Soil organic matter which is one of the major components of CA particularly occurs at the soil surface and is associated with improvements of structural, fertility, and biological aspects of soil relative to conventional agricultural systems (Page et al., 2020). Conservation agriculture is rapidly gaining acceptance as a good farming practice to improve soil health. Conservation agriculture involves the minimum disturbance of the soil by tillage operation and increases organic matter by cover crop and crop rotation to benefit both the farmer and the environment. In conservation tillage, tillage is reduced (no-tillage) and crop residues are retained on the soil surface. It preserves the C in soil and plays a crucial role in increasing soil productivity as well as the reduction of greenhouses gases. In conservation agriculture, application of fertilizer like in conventional agriculture is amended with organic manure such as composts, crop residues and thus, they add more C in soil system as compared to the fertilizers as well as maintain soil health (Adeel et al., 2018) 2 Needs of Conservation Agriculture Conservation Agriculture is a response to sustainable land management, environmental protection, and climate change adaptation and mitigation. According to FAO Terra STAT globally around 6140 M ha areas of agricultural land, pasture, forest, and woodland had been degraded since the mid-twentieth century (FAO, 2017). Unchecked soil erosion, intensive cultivation, deforestation, industrialization is identified as key reasons responsible for massive land degradation (Kumari et al., 2019). Among them, intensive cultivation is one of the severe forces that reported to cause extended land degradation through the wind (semi-arid tropics areas) and water erosion (humid and sub-humid areas) and is also a major force that known to give birth to CA practices (IPCC, 2019). Under natural conditions annual mean soil formation rate is about 300 to 1400 kg ha^-1 while the annual mean soil loss through erosion is about 300 to 4000 kg ha^-1 which sometimes under extreme climatic conditions can reach as high as 10000 kg ha^-1 (Bai et al., 2008; Verheijen et al., 2009). Under the current scenario, to achieve the goal of agricultural sustainability and intensification, there is an urgent need to resolve the above-discussed issues associated with intensive crop production. For this purpose, CA practices like non-inversion tillage, no-tillage, implementation of crop rotations, cover cropping have been extensively evaluated, demonstrated, and found a potential alternative to conservation tillage and shows great prospective to mitigate these emerging challenges. The fundamental principles of CA include: minimum mechanical soil disturbance or reduced soil tillage, permanent soil cover by crop residues or crop growth, and crop diversification or rotation by including legume crops (Farooq & Siddique, 2015) (Figure 1) CA is grounded on the principles of soil rejuvenation, envisioned maximizing the use efficiency of agricultural inputs e.g. seed, nutrient, water, energy, and labor leading to higher profits to the grower (Yadav et al., 2017). The goals of CA are to optimizing crop productivity and farm income through maximum use of available resources and their effective recycling in the agroecosystem while arresting the adverse impacts on the environment (Jat et al., 2012). It has been widely tested and demonstrated that long term application of CA resulted in better water quality, provided excellent soil erosion control, and lowered the greenhouse gas emissions associated with agriculture production (Adeel et al., 2018). 3 Status of conservation agriculture in World and India CA production systems are universally applicable to all agricultural land with locally adapted practices. The global extent of CA cropland in 2008/09 and 2013/14 was covered about 106 M ha and 157 M ha which is 7.5% and 11% of global cropland respectively, representing a difference of some 51 M ha (some 47%) over the 5 years whereas in 2015/16, it was about 180 M ha which is 12.5% of global cropland, representing a difference of some 74 M ha (69%) over the 7 years since 2008/09 (Kassam et al., 2018). From the above records, it was observed that CA practices are experiencing increased interest in most countries all over the world. There are currently over 10 Mha of arable cropland under the CA system in Asia, corresponding to about 6.5% of the worldwide CA area mainly located in China (65.4% of the total Asian CA area) followed by Kazakhstan (19%) and India (around 15%)(FAO, 2017). The extent of adoption of conservation agriculture worldwide is given in table 1. The concept of conservation agriculture is relatively new in Asia. In the last 11 years, the CA system has expanded at an average rate of more than 6 Mha per year showing the increased interest of farmers in this technology, mainly in North and South America, and in Australia, and New Zealand, and more recently in Asia where large increases in the adoption of CA are expected. In Asia, a large share of the conservation agriculture is confined in India, and that is in the Indo Gangetic plain (Bhan & Behera, 2014) In India, efforts to adopt and promote conservation agriculture technologies have been underway for nearly a decade but it is only in the last 8 – 10 years that the technologies are finding rapid acceptance by farmers. Efforts to develop and spread conservation agriculture have been made through the combined efforts of several State Agricultural Universities, ICAR institutes, and the Rice-Wheat Consortium for the Indo-Gangetic Plains. The spread of technologies is taking place in India in the irrigated regions in the Indo-Gangetic plains where rice-wheat cropping systems dominate (Bhan & Behera, 2014). The focus of developing and promoting conservation technologies has been on zero-till seed-cum fertilizer drill for the sowing of wheat in the rice-wheat system. Other interventions include raised-bed planting systems, laser equipment aided land leveling, residue management practices, alternatives to the rice-wheat system, etc. It has been reported that the area planted with wheat adopting the zero-till drill has been increasing rapidly and presently 25% – 30% of wheat is zero-tilled in rice-wheat growing areas of the Indo-Gangetic plains of India. Besides, raised-bed planting and laser land leveling are also being increasingly adopted by the farmers of the north-western region (Kassam et al., 2018). 4 Fundamental principles of Conservation Agriculture Conservation Agriculture is a resource-saving agricultural production system that aims to manage agro-ecosystems for improved and sustained productivity, increased profits, and food security. Three major principles of CA are continuous minimum mechanical soil disturbance with direct seeding i.e. No-till, permanent soil organic cover with crop residues or cover crops, diversification of crop species through varied crop rotations including legumes or pulses. 4.1 Minimum Mechanical Soil Disturbance or No-Tillage (NT) No-tillage (NT) or reduced tillage is a very important agronomic practice which follows the criteria of minimum soil disturbance, without loosening the soil, which maintains various physical properties of soil such as soil structure, aggregation, aggregate stability, and porosity. It eases the permeability of water and good aeration (exchange of gases) to the roots (Bhan & Behera, 2014). It also provides a niche to diverse soil microbial populations. Thus, CA includes the use of minimum or no-tillage along with crop residue retention to address soil physical degradation problems by reducing subsurface compaction (Sayre & Hobbs 2004). Residue retention also increases soil carbon content in the soil (Das et al., 2014). Minimum soil disturbance regulates optimum respiration in the rooting-zone, moderate organic matter oxidation, porosity for water movement, retention, and release and limits the re-establishment of weeds and their germination (Kassam et al., 2015). 4.2 Soil Cover with Organic Materials Maintenance of soil cover permanently or semi-permanently with crop residue is essential to provide enough moisture during adverse conditions. Soil cover with crop residue protects the soil from erosion and runoff as well as provides congenial micro-climatic conditions for micro- and macro-organisms in the soil. Overall, it improves soil aggregation, soil biological activity, soil biodiversity, and carbon sequestration (Ghosh et al., 2010). Crop residues on the soil surface protect the soil and reduce its erosion and runoff (Thomas et al., 2007). The surface cover also favors enhanced levels of biological activity by providing food to soil microbes, especially in tropical and subtropical areas. Retaining crop residue and eliminating tillage improves infiltration and soil moisture content. Soil cover should ideally be above 100% which is measured immediately after planting operation whereas the ground cover of less than 30% is not considered as a conservation agriculture practice (Kassam et al., 2015). 4.3 Crop Rotation with Pulses or Legumes Crop rotation improves soil health by reducing the allelopathic effect of crops and increases crop productivity and soil fertility (Shah & Wu, 2019). Growing of the same crop in the same area for many years harms soil health, and soil quality starts diminishing. Balanced crop rotation or addition of legume or pulse crops into the rotation reduces the dominant pest and disease problems, the allelopathic effect of various crops which is harmful to beneficial crops by increasing the diversity and abundance of beneficial soil microorganism. A minimum of three different crops needs to be included in the rotation. Crop rotation will help to eliminate problems associated with yield reduction and infestations within the field as well as necessary to offer a diverse nutrient supply to the soil microorganisms. It can also help to maintain soil infrastructure by an extensive buildup of rooting zones which will allow for better water infiltration. 5 Conventional vs conservation agriculture Conventional farming refers to mono-cropping, various tillage operations i.e. moldboard or animal-drawn plow or harrowing, drilling, cultivator, etc, and residue removal, which often results in having adverse effects on soil functions. CA practice comprises of no-tillage combined with residue retention and crop rotation (Hobbs et al., 2007; Knowler& Bradshaw, 2007; Hobbs et al., 2008) as an alternative to optimizing the provision of soil functions. Conventional farming exposes the soil to air and sunlight which causes oxidation of organic matter and leads to the low carbon content in the soil which affects soil structure (Busari et al., 2015). The oxidation of organic matter releases CO₂ into the environment causing global warming or climate change (Grace et al.,2003). The conservation agriculture system involves specific agronomic field operations such as minimum soil disturbance or use of zero tillage, soil cover with green manure or crop residue (mulching), and crop rotation provides good soil structure, porosity, more accumulation of the organic matter in soil which provides better soil aggregation, water-holding capacity, soil moisture for the long term, nutrient recycling, and transformation. Meanwhile, the conservation tillage improves soil fertility, water, and crop productivity; the no-tillage gives better soil protection than conventional tillage. This happens as the conventional tillage system leaves 1–5% of the soil surface covered with crop residues (Hussain et al. 1998). 6 Effect of conservation agriculture on soil properties 6.1 Effect on soil physical properties 6.1.1 Soil Aggregation, Aggregate Stability and Structure Soil aggregate stability refers to the resistibility of the soil to change under natural or anthropogenic activities. There is a medium to high aggregate correlation between aggregate stability in water, aggregate size, and total organic carbon content (Liu et al., 2019). CA practices leave most of the crop residues on the soil surface, allowing improvement in soil aggregation and aggregate stability. It also protects surface aggregates against the effects of raindrops or splash erosion. CA which is dominated by minimal or no-tillage and crop residue retention is helpful for soil aggregation and the aggregate stability (Li et al.,2011). CA requires adequate soil cover to perform certain critical functions including improvement in infiltration, plant-available water, and aggregate stability (Palm et al., 2014). It also enhances the proportion of micropores in the soil, increases water-holding capacity, and reduces evaporation from the soil surface (Kassam et al., 2009; Palm et al., 2014). 6.1.2 Soil Moisture The CA helps in the conservation of soil moisture by encompassing soil cover with crop residues and mulches approach. Due to the crop residues being left over in the field, there is increased infiltration and water-holding capacity. Mulches also protect the soil surface from extreme variation in temperatures and greatly reduce surface evaporation, particularly in tropical and subtropical climates (Kodzwa et al., 2020). From the various studies, it has been found that conservation agriculture saves 20–30% of irrigation water because of lower evapotranspiration losses from the surface as it is covered with residues (Jat et al., 2012) and as the soil moisture is conserved, more water is available to the standing crop (Verhulst et al., 2010). 6.1.3 Soil temperature Soil temperature is an important transient physical property of soil that affects crop growth and development and governs the physical, chemical, and biological processes of soil (Buchan, 2000). It also influences the interspheric processes of gas exchange between the atmosphere and soil. Soil temperatures in surface layers may be significantly lowered during day time in summer in zero tillage (ZT) soils with residue retention compared to Conventional tillage (Johnson & Hoyt, 1999; Oliveira et al., 2001; Liebig et al., 2004; Malecka et al., 2012). Many researchers reported that crop residue and other surface mulches modify soil temperature (He et al., 2010) by changing different soil thermal properties i.e. volumetric heat capacity, thermal conductivity and thermal diffusivity. 6.1.4 Water Infiltration and Hydraulic Conductivity Hydraulic behavior of the soil was found to be significantly and positively correlated with the total soil macro-pores and tillage practices that alter the macro-pores of soil by affecting the setting and consolidation of soil particles over time (Rasse et al., 2000). Hydraulic conductivity was higher in zero tillage compared to conservation tillage due to the larger macropore conductivity as a result of the increased number of bio pores (McGarry et al., 2000; Eynardet al., 2004). CA enhances the rate of infiltration because of minimum disturbance of soil which results in better soil pores structure or porosity and enhances hydraulic conductivity (Mrabet, 2007). Mulch cover crops provide benefits for improved water infiltration and reduced soil surface evaporation especially under dry or moisture limited conditions. The faster infiltration rate was observed under the zero tillage system than in the conservation tillage system (Liebig et al., 2004; Bhushan et al., 2007). In CA practices under no-tillage systems, the infiltration rate due to rainfall is improved which increases the amount of available soil water in heavy textured soils (Mrabet, 2007). However, a few researchers, showed that infiltration and hydraulic conductivity was lower under no-tillage than conventional tillage (Castellini et al., 2019). In brief, CA improves hydraulic conductivity and infiltration and reduces evaporation rate, runoff, and soil erosion by crop residue. Azooz & Arshad (1996) reported that both saturated and unsaturated hydraulic conductivities were higher under zero tillage conditions than under conservation tillage on two Luvisols (silty loam and sandy loam soils). The significant increment in hydraulic conductivity over zero tilled plots may be due to the arrangement of soil pores and more macropores continuity (Bhattacharya et al., 2006). 6.1.5 Bulk density The beneficial effect of CA in terms of lower bulk density is more subjected to the topsoil (0-15 cm) (Thomas et al., 2007; D‘Haene et al., 2008,). Continuous adoption of the traditional method of farming leads to the formation of plough pan underneath the furrow slice, attributed to higher BD in this horizon as compared to CA. Through the adoption of CA practices, there is a reduction in the intensity of tillage operations that results in a progressive reduction in soil compaction over time. The decrease in soil BD under CA could be due to higher SOC, better aggregation, increased root growth, and biomass (Salem et al., 2015). Further, legume inclusion in crop rotations resulted in significantly lower soil BD compared to monocultures. The similar findings of lower BD due to pulses inclusion were also reported by Verhulst et al. (2010) and Thierfelder et al. (2014). Residue retention has a significant impact on soil BD in the upper soil surface (0-10 cm) while the difference at deeper soil depth (10-20 cm) cm were not found significant (Blanco-Canqui & Lal, 2008). Bulk density was more in no-tillage as the soil remains intact due to no disturbance. The increase of soil porosity in no-tillage might be due to the addition of organic matter through crop residues or cover crops and zero or minimum disturbance of soil (Alam et al., 2014). The impact of tillage and residue retention on soil bulk density (BD) is mainly confined to the surface soil layer. 6.2 Soil chemical properties 6.2.1 Soil Organic Matter Soil organic matter (SOM) plays a pivotal role in maintaining soil fertility, productivity, and sustainability and is a key indicator of soil quality (Chivenge et al., 2007). It also provides essential nutrients for crops and maintains soil aggregation and stability. The CA practices usually increase the SOM content and nutrient availability by utilizing the previous crop residues or growing green manure or cover crops (GMCs) and keeping these residues as surface mulch rather than burning. Usually, SOC changes proportionally to the number of crop residues returned to the soil and agronomic management practices that influence yield (Campbell et al., 2001). Returning more crop residues promotes an increase in SOC concentration of the soil (Wilhelm & Wortmann, 2004). Research has shown that during the first 4 years of tillage, a 10% loss of initial soil organic matter content was determined with plough tillage. Increased levels of tillage depleted SOM between 16% and 77% and increased tillage periods resulted in a reduction of total soil carbon. The emission of CO₂ from soil by the crop is reduced when conventional tillage is converted to conservation tillage due to negligible soil disturbance in CA. Long-term field experiments on CA showed that organic carbon was enhanced when crop residues were retained on the soil surface. The contents of OC in the soil can also be increased by CA by retaining crop residues which contain carbon and nutrients at the soil surface layer (Moreno et al., 2006). No-tillage improves soil quality, OC, aggregation, conservation of soil, evaporation of water, and soil structure. There was an increase in SOM of ~14% with no-tillage and 3.3% with conventional tillage over 11 years (Mrabet et al., 2001). Crop rotation with legume component and zero tillage tends to build up of SOC in the soil. 6.2.2 Soil Nitrogen Conservation tillage practice, crop residue management and crop rotation can strongly influence the nutrient dynamics of any soil through their effect on distribution, mineralization, transformation and recycling of soil nutrients (Galantini et al., 2000; Verhulst et al., 2010). As soil organic carbon increases under CA practices, this can have a significant effect on plant nutrient availability due to a greater amount of residue addition and input of nutrient containing organic material to the soil. Thus, the nature of crop residues and their management has a profound influence on the nutrient-supplying power of soils as well as lead to greater plant nutrient availability (Pheap et al., 2019). In the case of N, for example, while total stores of N may be higher under CA, the amount of plant-available N can decrease, particularly soon after CA is implemented and applications of N fertilizer may be required to maintain yield (Sithole & Magwaza, 2019). This is because of lower the rate of N mineralization and higher the rates of N immobilization in the soil as a higher amount of crop residues are added under CA (Page et al., 2020). 6.2.3 Soil phosphorus According to Mrabet et al. (2001), negligible loss in phosphorus and potassium was occurred under no-tillage due to less soil disturbance and application of crop residues on the soil surface. Thus, the concentration of nutrients like phosphorus and potassium was higher near the soil surface than tilled soil because P stratification in the soil is seen under different tillage systems where zero tillage system is associated with a higher concentration of P due to preferential movement of P in the soil (Dorneles et al., 2015). Moreover, incorporation of crop residues and fertilizer P with minimum P losses due to water erosion under CA leads to higher P concentration in the surface soil. Piegholdt et al. (2013) reported a 15% higher total P content in the topsoil (0-5 cm) of zero tillage plots as compared to conservation tillage due to larger P addition from residue decomposition being retained on the soil surface. The higher values of available P under CA practices are largely due to reduced mixing of the fertilizer P with the soil, leading to lower P-fixation(Dorneles et al., 2015). Other advantages of no-tillage and reduced tillage over conservation tillage, in terms of P availability, are related to the reduction of soil erosion, the accumulation of labile forms of P derived from the presence of organic residues in the soil and to the effect of OM negative charges maintaining freely available phosphate. Therefore, a combination of conservation tillage and P fertilization helps to improve soil P availability in soil because phosphorus accumulation is favored by minimal soil disturbance and this condition diminishes the contact surface between adsorption sites and phosphate ions (Shi et al., 2013). 6.2.4 Soil potassium According to Govaerts et al. (2007), permanent bed planting along with residue retention had 1.65- and 1.43-times higher concentrations of K in the 0-5 cm and 5-20 cm respectively, than CT. Du Preez et al. (2001) observed increased levels of K in zero tillage compared to conservation tillage, but this effect declined with depth. No effect of crop rotation on K concentrations was observed by Roldan et al. (2007). However, Yadav et al. (2016) reported that after seven years of CA the highest amount of N, P, and K (219.8, 24.9, and 203.1 kg ha^-1) in 0-15 cm soil surface was recorded under PB planting while the minimum amount of available N, P and K were observed under conservation tillage. The recycling of the higher amount of crop residue from previous higher biomass yield in PB treatments leads to the addition of more nutrients compared to conservation tillage. While in the case of conservation tillage the stover/ straw being incorporated into deep soil layer leads to rapid decomposition and might also lead to leaching of mineralized nutrients in much deeper soil layers which in turn reduces the available nutrients in conservation tillage. Moreover, the chelating of these nutrients with organic matter in non-disturbed soil lead to the improvement of soil nutrient status in different soil depths (Borie et al., 2006; Singh et al., 2014) and thus causes enhancement of soil NPK status. The similar findings of enhancement in available nutrients due to CA practices in soil were also reported by Borie et al. (2006) and Wang et al. (2014) for N; Malhi et al. (2011) for P and Du Preez et al. 2001 and Govaerts et al. (2007) for potassium. 6.2.5 Exchangeable Ca, Mg and micro-nutrients in the soil Rahman et al. (2008) reported that exchangeable Ca, Mg, and K were significantly higher in the surface soil under no-tillage compared to the plowed soil. Soil nutrient supplies and cycling are enhanced by the biochemical decomposition of organic crop residues at the soil surface that are also important as nutrient material for the soil microbes. Micronutrient (Zn, Fe, Cu, and Mn) tends to be present in higher levels under zero tillage with residue retentions compared to conservation tillage, especially near the soil surface (Franzluebbers & Hons, 1996). In contrast, Govaerts et al. (2007) reported that tillage practice had no significant effect on the concentration of extractable Fe, Mn, and Cu, but that the concentration of extractable Zn was significantly higher in the 0-5 cm layer of PB planting compared to conservation tillage with full residue retention. Similar results were reported by Du Preez et al. (2001) and Franzluebbers & Hons (1996). 6.3 Soil biological properties Under CA practices no-tillage coupled with residue retention which is the major cause of accumulation of the higher amount of soil organic carbon compared to conventional agriculture. Soil organic carbon present in CA systems serves as a good source of energy for soil microbes and positively affects the growth of microbes and hence influences their distribution (Page et al., 2020). Due to the exponential increase in the global population, the demands for food are increasing substantially, the major challenge being the ability to enhance food production with the use of soil management practices that can maintain or improve soil biodiversity. Intensive cultivation of the soil for a longer period leads to reduced microbial biodiversity compared to uncultivated soils and/or less disturbed soil. CA practices’ including the basic principles are widely tested and have the potential to reach the goal of safe productivity conserving or sustaining soil biodiversity (Holland, 2004). Alteration in tillage, crop residue, and crop rotation practices induce major shifts in the number and composition of soil fauna and flora, including both pests and beneficial organisms (Anderson, 2003). Microbial diversity is generally negatively correlated with the intensity of tillage (Kladivko, 2001; Jinbo et al., 2007). The impact of soil tillage over microbial parameters of soil is mostly determined through climate, location, and below as well as above environmental conditions. 6.3.1 Soil microbial biomass carbon Continuous use of CA-based management practices leads to a reduction in soil disturbance which can stimulate soil microbial biomass and improve its metabolic rate, resulting in better soil quality, which in turn, can increase crop productivity (Hungria et al., 2009). Dong et al. (2009) also reported that the mean annual MBC was highest in the ZT with residue, while lowest in CT without residue. Similarly, Silva et al. (2010) consistently found higher values of MBC and microbial biomass nitrogen up to more than 100 % under NT in comparison to CT. The rate of organic C input from crop biomass is generally considered the dominant factor controlling the amount of soil microbial biomass (SMB) in soil. The SMB reflects the soil’s ability to store and cycle nutrients (C, N, P, and S) and organic matter, and has a high turnover rate relative to the total soil organic matter (Dick,1992; Carter et al.,1999). Spedding et al. (2004) found that residue management had more influence than tillage system on microbial characteristics, and higher MBC and N levels were found in plots with residue retention than with residue removal, although the differences were significant only in the 0-10 cm layer. NT system increased total carbon by 45%, microbial biomass by 83%, and MBC: total carbon ratio by 23% at 0-5 cm depth over conservation tillage after 21 years. Mineralization rate of carbon and nitrogen increased by 74% with no-tillage compared to conservation tillage systems in surface soil (Zhang et al., 2018). 6.3.2 Soil enzymatic activities CA based tillage increases the enzymatic activities in the soil profile due to the vertical distribution of organic residues and microbial activity and this positively alters soil enzymes which play a significant role in the catalyzation of reactions obligatory for organic matter decomposition and nutrient cycling as well as involved in energy transfer, improvement of environmental quality and crop productivity (Dick, 1992). Roldan et al. (2007) reported higher dehydrogenase and phosphatase in the 0-5 cm soil layer with zero tillage than conservation tillage. Likewise, Singh et al. (2009) reported that the dehydrogenase enzyme activity of soil under the permanent bed planting method registered significantly higher (62%) than conservation tillage. Hota et al. (2014) noticed that the incorporation of organic residues along with zero tillage showed greater acid phosphatase activities than the con without residue. 7 Important Barriers to the Adoption of Conservation Agriculture The CA is a great challenge between the scientific community and the farmers to change the mindset and explore the opportunities that offer for natural resource management. The CA is considered a way to sustainable agriculture. A shift from the conventional method of farming that degrades soil quality to resource conservation practice i.e. CA is the need of the hour. The following are the constraints which restrict wide-scale adoption of CA: • Lack of appropriate machinery especially for small and medium farmers Initially, high investment is required for the purchase of specialized sowing and/or planting implements and requirement of technical knowledge for better management of these practices which is a short-term drawback associated with CA (Page et al., 2020). Although significant efforts have been made in developing and promoting machinery for seeding wheat in no-tillage systems, successful adoption will require rapid effort in developing, standardizing, and promoting quality implements aimed over a range of crops and cropping sequences (Bhan & Behera, 2014). • Competition for Crop residues: Especially under Indian conditions, farmers face scarcity of fodder due to less biomass production of different crops so there is competition for crop residues between CA practices and animal feeding which becomes a major problem for the adoption of CA (Bhan& Behera 2014). • Burning of crop residues: For the timely sowing of the next crop, farmers prefer to sow the crop in time by burning the residue which is becoming a common feature present in the rice-wheat system in North India. This creates environmental problems like pollution and health hazards for the region. Burning of crop residues leads to the release of greenhouse gases namely carbon dioxide, methane, and nitrous oxide, causing global warming and loss of plant nutrients like N, P, K, and S.  Heat generated from the burning of crop residues elevates soil temperature causing the death of active beneficial microbial population (Thakur et al., 2019). • Knowledge gap about the potential of CA: The whole range of practices being included in CA i.e. planting, harvesting, water and nutrient management, diseases and pest control, etc., need to be properly explained, evolved, evaluated, and matched in the context of new systems to agriculture leaders, extension agents, and farmers (Bhan & Behera 2014). • Skilled and scientific manpower:  Managing CA systems, need for enhanced capacity of researchers to face problems from a systems perspective and to be able to work in close relationship with farmers and other stakeholders. Strengthened knowledge and information sharing mechanisms are urgently needed (Page et al., 2020) 8 Future prospects of conservation agriculture The system of CA can have clear advantages over conventional agricultural systems of management i.e. helps in improving soil health, saving inputs, reducing the cost of production, increasing farm income, efficient use of natural resources as well as increase yields and also most importantly alleviating global warming by sequestering carbon into the soil  (Adeel et al., 2018). The advantages of CA practices are easy to adopt in individual regions and environments but there is a need of taking some initiatives for arranging some demonstration and awareness programs for skill development of farmers. Thus, a global movement is needed to promote conservation agriculture for the betterment of the future of agriculture. Some of the major constraints of CA practices are improper removal of weeds, pests, and diseases due to no-tillage, stratification of immobile nutrients at the upper surface of the soil profile, decreased availability of nitrogen due to leaching losses, improper plant establishment, and development surface crust and compaction (Dang et al., 2015). As SOC is the key component of CA, it can also be a difficult task to maintain crop residue and cover crops on the soil surface and build-up of SOCto improve soil fertility, prevent erosion and suppress weeds (Andersson & D’Souza, 2014). Thus, locally adapted species for crop rotations/cover crops and seeding equipment should be developed to solve the problems of plant establishment and weed, pest and disease pressures in no-tillage practices (Verhulst et al., 2010; Thierfelder et al., 2018). A combination of CA practices and adequate application of fertilizers is one of the better options to deal with problems of nutrient availability and also helps to produce more plant biomass to increase residue cover and improve soil fertility (Verhulst et al., 2010). Incorporation of cover crops and legumes in crop rotation under CA practices can keep the soil cover during the periods when the main crop is not growing and help in extra addition of organic matter to soil (Tittonell et al., 2012; Veloso et al., 2018; Williams et al., 2018). Surface maintained crop residues act as mulch and therefore reduce soil water losses through evaporation and maintain a moderate soil temperature regime (Gupta & Jat, 2010). However, at the same time crop residues offer an easily decomposable source of organic matter and could harbor undesirable pest populations or alter the system ecology in some other way (Bhan & Behera, 2014). No-tillage systems will influence the depth of penetration and distribution of the root system which, in turn, will influence water and nutrient uptake and mineral cycling (Dang et al., 2018). Nowadays due to the growing population, we are facing revolutionary challenges to food security. Thus, food production should increase by 70% to feed 9 billion people by 2050 without damaging natural resources. To meet the global challenges of food production and conserving the environment, conservation agriculture has been identified as one of the technological options to improve food and nutritional security as well as alleviates poverty. As the agricultural practices under CA are the future of sustainable agriculture, its benefits can be achieved over all types of agro-ecosystems. The focus of CA in the future is to address the technology needs for Sustainable Intensification. Therefore, CA has increasingly been endorsed as Climate Smart Agriculture, contributing to both climate change adaptation, and mitigation as well as conserving natural resources. Conclusion Conservation agriculture offers a new paradigm for agricultural research and development different from the conventional one, which mainly aimed at achieving specific food grains production targets as well as offers an opportunity for arresting and reversing the downward spiral of resource degradation, decreasing cultivation costs and making agriculture more resource – use-efficient, competitive and sustainable. CA systems are well-designed and adapted to local conditions, they can improve the SOC content of many soils and lead to significant improvements in soil physical, chemical, and biological properties to sustain soil health to minimize weather variability on soil and reducing the negative impacts on productivity. Overall, CA as an approach where new crops and management practices evolve in future conservation management schemes for sustainable production and offer many benefits to producers, the economy, consumers and the environment. With CA, production becomes a matter of output rather than inputs. So, CA is not only climate-smart but smart in many other ways. Over the long term, continuous use of CA will lead to the improvement of soil structure that will contribute to resilient soil systems that can withstand climate variability. To satisfy the challenges in agriculture, a mission mode program is needed for promoting conservation agriculture to increase and sustain agricultural production and raise the income of farmers in developing countries. In India, the concept of conservation agriculture may be integrated with various government programs by sensitizing policy advisors, professionals and financial institutions. Conservation agriculture gives promising results in the fight against the environment as well as agricultural problems in numerous ways including reducing anthropogenic carbon emissions by minimizing the use of agricultural machinery, reducing the greenhouse gas emission, improving soil organic carbon at root zone level above the threshold level, sustainable and increase in agricultural productivity, improve the use efficiency of agricultural inputs and buffer against soil and plant disease, reducing the risk of accelerating non-point source soil pollution and erosion, increasing nutrient and water holding capacity and restoring soil quality and its ecosystem functions.CA based crop production system is one of the pathways for improving productivity as well as food security while sustaining and preserving the natural resources in a variety of agro-ecological regions. CA may be recommended to farmers both in small and medium scale for ensuring food security and enhancing soil quality/health. Conflict of Interest Authors would hereby like to declare that there are no conflicts of interest that could arise.