Role of tillage and straw management on SOC sequestration: a sustainable approach of soil conservation

Soil organic carbon (SOC) sequestration can be achieved by changing the conventional practices to less intensive methods, i.e., no-tillage with straw management. The present review aimed to comprehend the existing knowledge on the impact of tillage and straw management practices on SOC sequestration. Along with the benefits/effects of no-tillage and straw management practices, the limitations and prospects in the context of SOC sequestration were also discussed. The present review provided the contemporary synthesis of existing information on the benefits of soil conservative practices over conventional tillage concerning physicochemical and biological properties. No-tillage with straw management have the potential effects for SOC on surface layers. However, additional studies are wanted to investigate the potential influences of tillage and straw management practices on the SOC distribution either in the surface layer or deeper layers. It has been widely reviewed from the complied litrature review that no-till soils have increased the SOC in surface layers but might not be accompanying with increased SOC throughout the soil profile. There is still knowledge gaps exist especially about SOC sequestration, which must be talked, i.e., sampling depth, and study places distribution, etc. Moreover, the mechanisms of SOC sequestration are still not fully understood. The valuation of soil quality is complex, and demands widespread and systematic research. The present review also summarized the suitable options to increase the SOC sequestration by tillage and straw management practices. Innovative approaches are needed for the application of straw management in combination with no- tillage, require further practical assessment under long-term field experiments. Available evidence still evokes that soil management practices in the agriculture have the potential in long-term studies to increase terrestrial SOC sequestration with potential benefits to environmental ecosystems.

management practices. Innovative approaches are needed for the application of straw management in combination with no-tillage, require further practical assessment under long-term field experiments. Available evidence still evokes that soil management practices in the agriculture have the potential in long-term studies to increase terrestrial SOC sequestration with potential benefits to environmental ecosystems. Keywords: No-tillage; Organic matter; Soil aggregates; Soil carbon sequestration; Straw management; Tillage Introduction Soil organic carbon (SOC) plays a vital role in crop productivity, soil health, soil fertility and associated environmental changes [1, 2, 3, 4, 5]. Different tillage methods (conventional tillage and notillage) are used for loosening the soils to cultivate the crops, preserve soil structure, conserve soil water, incorporate plant residues [6, 7] but long-term tillage practices are believed to be one of important factor that stimulates marked changes in SOC pools [8]. Intensive 17, 18, 19]. The straw management system is different in many countries and regions. In developed countries, straw mulch is usually retained in the field to increase soil fertility and productivity [20, 21]. Unfortunately, in many developing countries farmers like to remove the straw from fields for fuel or burning of crops straw residues [22, 23]. The straw burning in environment is undesirable and prohibited way and has a broad impact on global environmental change and ecosystem through the release of some greenhouse gases, is a significant threat to the stability of soil fertility and environment [24, 25]. In many countries, farmers follow conventional tillage (CT) practice, i.e., moldboard plowing, this kind of exhaustive cultivation has engaged to severe land degradation, decline soil quality and decline of SOC in agroecosystem [1,13]. While NT practice, which protects the soil and water with a minimum disturbance to the soil surface and cover the topsoil with at least 30% or more straw mulches or residues on the surface of soil [26, 27], has been recently promoted in developing countries. Various recent studies have advocated the NT, and straw management is effective management practices to manage the crop residues and has indicated the marked potential for enhancing the soil carbon storage in the cropland soil ecosystem [4, 28]. In the scenario of global climate change, it is imperative to enumerate the benefits observed under NT and straw management practices and to understand their effects on SOC dynamics and sequestration. The objectives of the present review were to comprehend the available knowledge on the impact of different tillage and straw management practices on SOC sequestration. Along with the benefits/effects of tillage and straw management practices, the limitations and prospects in the context of SOC sequestration were also discussed. Soil organic carbon and sequestration dynamics Soil organic matter management had a significant role in agriculture ecosystem by retaining and contributing the nutrients, enhancing the soil aggregation, reducing soil erosion, and improving the water holding capacity of soil [29, 30, 31]. The maintenance of SOC in farmland is necessary, not only for the higher production of crops but as well as to reduce SOC emissions [32]. However, due to the temporal and spatial variability, it is difficult to perceive the short-term and medium-term variations of SOC in agriculture ecosystem [33, 34]. Continuous turnover of the SOC in the soil, however, the SOC is not a consistent material, but a complex mixture of the organic compounds at different decomposition stages [35, 36]. It is a suitable way to discrete the total SOC into to numerous pools which be governed by on the ease of the decomposition, ordinarily named as slow, inert and labile pool [31, 37, 38]. However, the labile SOC pool rapidly undergo oxidation and play important role in the managing of the soil food web and the effects on nutrient driving for the conservation of quality and efficiency of the soil [39, 40, 41]. The generally labile pool comprises the fresh material of crop residues inputs in the soil along with micro-organism activities. Though slow pool includes the well decomposed soil organic matter (the hummus), the inert pool is the creation of the last stage of the decaying organic matter, denotes to the old, impervious to break down (e.g., Charcoal) (Table 1). Furthermore, the contemporary synthesis of existing data on SOC sequestration has been compiled in (Table 1). SOC sequestration is a conversion in total carbon storage, generally expressed a conversion in the total SOC stocks with time [3, 10, 53]. The residence period of the particles in nature is in link with the mark of physical protection (i.e. no-tillage and straw management practices). Different separation and extraction methods and multiple approaches based physico-chemical principles have been usually used to separate and quantify the C pools [23, 54]. Most significant basis of the soil breathing in the soils is in line for to the decomposition of organic matter in the soil from the crop residues [55, 56], the sequential variations of the SOC fractions is connected When soil breathing is measured after tillage practices [57, 58]. It is supposed to hypothesize that tillage has an impact on the effectiveness of relations between the availability of these labile fractions and respiration. This section highlights the importance of soil organic carbon sequestration dynamics in the agroecosystem. SOC has a significant role in supplying the plant nutrients, improving the soil aggregation, balance soil fertility and enhancing the water holding capacity of the agricultural land. The SOC sequestration dynamics can be divided into labile, slow and inert carbon pool, the changes in land use practices can bring changes in these C pools and SOC sequestration.

Impact of SOC in agriculture ecosystem and decomposition
Variations in the soil quality that is due to the result from erosion, salinization, and losses of the SOM and the nutrient, the soil compaction also cause decline of the soil quality and had the great concern in the agricultural ecosystem  (Table 2). Additionally, the up-todate synthesis of current data on the benefits/effects of NT over CT practices on SOC is collected in (Table 2). [77] Canada 30 Woolwich silt loam 0-20

Impact of straw management on soil organic carbon
Straw management is an essential way to increase the fertility of the soil and increase the SOC sequestration in soil, also protective and improving the soil quality in agriculture ecosystem.  soil [16, 82, 93]. In no-tillage system, organic activities associated with soil organic matter, modify or stratified in the soil layers agreeing to the burial compactness of straw residues and manures in the soil [21, 36, 67].
The amount and quality of straw management and animal manures added determines the total inputs of SOC which becomes accessible in the soil [112, 113, 64]. Therefore, though we can assume that the interactive influences of no-tillage and straw management could increase soil organic matter and subsequently increase the availability of a nutrient in the soil [53, 74]. No-tillage in the existence of straw inspires soil microbial activities to improve the soil aggregates and develop soil structure [114]. Awareness about the soil bulk density is necessary for the land use and management, and knowledge about the soil compaction is also essential for the development of modern farming practices. Bulk density values are also compulsory to compute the soil porosity which is by the amount of pore space in the soil [115]. Sonnleitner et al. [112] reported that straw management improved the aggregation stability of the soil and further physical properties in contrast to farmyard manure. [1, 9] also found that crops straw residues inputs in the agricultural soil had a significant influence on soil aggregation, water content, soil porosity and the bulk density of the soil. Furthermore, most of the tillage practices effect on the SOC and related properties appears to be the site-specific. For instance, Varvel and Wilhelm [116] described that that SOC values were greater in the NT as compared to PT in 0-75 and 15-30 cm in a silty clay loam textured soil after 24 years of the tillage management. Though, on a silt loam textured soil, in 23 years tillage management, NT treatment had 1.3-fold higher SOC content the 0-20 cm layer, but in 20-25 cm layer it had 2.0 fold lower SOC, nonetheless equivalent in the 0-45 cm depth when NT treatment was compared with the plow tillage (PT) (Dolan et al. 2006). Similarly, In a clay loam soil of Canada, NT treatment had greater SOC in the 0-5 cm, smaller at 20-30 cm, and equal in the 0-60 cm depth after 13 years long-term practices as compared with PT treatment [117]. Notillage and straw returning had a remarkable effect on soil physico-chemical properties, but it may differ liable on the particular system, quality and quantity of soil organic matter, topography, climate, soil type, tillage, fertilization and time of the crop rotation [51, 104]. Future of agriculture land will be in the way of minimum soil disturbance, less input and higher energy production systems [73]. .In this background, NT is an auspicious technology for refining the environment and the whole profit margin [1]. A corresponding effort is wanted to improve research, education and extension work about NT in the globe. Investigators must pay attention on knowledge-based agricultural production systems for NT. The agricultural crop production system needs to be high yielding, and costeffective but simple to use [8, 9]. Agriculturalists must permanently be ready to study innovations and be aware with modern developments. Policymakers must sustenance with researchers for learning the impacts of NT on a long-term basis and must also inspire farmers to adopt NT from side to side payments for ecosystem services [8, 9]. In the future, it is necessary to change the attitudes of farmers and researchers towards the sustainable management practices like NT management system [60, 117]. However Hobbs and [61] reported that the essential approach in the acceptance of no-tillage and straw management practices is about the mindset to other tillage practices. It is claimed in the research interests that to convince the farmers about the successful farming, it could be possible when reduced tillage or no-tillage is considered as significant tillage practice on a large scale. Although, it is a very challenging assignment to inspire the farmers about NT and straw management practices in the fields, about its potential to decrease the production costs. Recently, No-tillage and straw management practices are considered as a necessary route to the sustainability of the environment and agricultural ecosystem. There are some restrictions which may obstruct the adoption of NT and straw management practices, i.e., lack of appropriate seeders, mindset about the use of crop residues for livestock, fuel and burning [75, 114].

Limitations and restrictions
No-tillage with straw management practices is gaining much interest since decades. Still, knowledge gaps exist especially about SOC sequestration, which must be addressed, i.e., sample depth, and regional distribution, etc. [11]. Soil degradation processes (wind or water erosion) is affected by NT including straw management practices. Nevertheless, the mechanisms of SOC by decrease of erosion under NT are quiet not completely understood [45]. Global issue is to understand the destiny of SOC delighted by erosional processes (i.e., burial, emissions, deposition, and redistribution) [9]. However, valuation of soil quality is multifaceted and needs comprehensive and systematic research. The sequestration rate of SOC is greatly influenced by various factors, containing soil type, climate, cropping system, and farming operations [52, 75, 121]. A tillage system can modify the microbial environment, which affects soil biological processes and ultimately SOC sequestration. Soil erosion can increase the loss of SOC ultimately reduce the ability of the soil to sequester the atmospheric carbon [9]. This is due to an increase in the soil erosion which decreases the carbon storage in the soil [1, 9]. The soil organic matter increased or declined in the soil because of the better or less agricultural land use management Hence, the mechanisms leading by tillage effects on SOC sequestration have not been wellknown. The soil C cycle comprises complex processes, the duration of experiments is rather short (conducted for only about five years) [8]. Though, tillage practices influenced the variations in soil properties, particularly soil physical properties, happen over short-and long time periods. Therefore, the date from long-term experiments illustrates that conversion of CT practice to NT practices may play a significant role in SOC sequestration for long-term research [9, 52].

Conclusion
In croplands, SOC sequestration can be increased by modifying tillage practices and management of straw incorporation back to the soils. The less intensive practices such as no-tillage system in the presence of straw creates a suitable biological and ecological protective interface between the soil and atmosphere. Positive improvement in the SOC sequestration could be achieved with the improved tillage and straw management strategies. In contrast, conventional practices with or without straw crop residues result in low carbon sequestration. Therefore, the less intensice practices like NT in combination with management of crop straw are recommended for efficient usage of the soil nutrients and effective long-term sequestration of SOC. Longterm studies should be conducted to access the dynamics of SOC, as effects under short-term studies might be varied. Available evidence still evokes that soil management practices in the agriculture have the potential in long-term studies to increase terrestrial SOC sequestration, with potential benefits to environmental ecosystems.