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Soil acts as a major sink and source of atmospheric CO₂ and has a huge role to play in carbon capture and storage activity. Judicious use of combinations of organic and inorganic resources is a feasible approach to overcome soil fertility constraints [1]. Combined organic and inorganic fertilization could enhance carbon storage in soils and reduce emission from N fertilizer use, while contributing to high productivity in agriculture [2]. Sustaining soil health through inclusion of manure in the fertilization schedule is important since it can improve the organic carbon status and available N, P, K and S in soil [3]. To improve soil physical properties, addition of various organic materials could be undertaken and combined use of NPK and FYM increases soil organic matter compared to application of NPK through inorganic fertilizers [4].

Mitigation of CO₂ emission from agriculture can be achieved by increasing carbon sequestration in soil which implies storage of carbon as soil organic matter. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kg/ha for Wheat, 10 to 20 kg /ha for Maize and 0.5 to 1 kg/ha for Cowpea. The potential of soil carbon sequestration in India was estimated at 7 to 10 Tg C/yr for restoration of degraded soils and ecosystems, 5 to 7 Tg C/ yr for erosion control, 6 to 10 Tg C/yr for adoption of recommended practices on agricultural soils and 22 to 26 Tg C/yr for secondary carbonates [5]. Adequate supply of nutrients can enhance biomass production and soil organic carbon content. Application of organic manure in combination with chemical fertilizer for crop is more useful to obtain high yields. It has been stated that the atmosphere is annually absorbing 3.4 gigatons of carbon more than it’s releasing. Judicious nutrient management is crucial to soil organic carbon (SOC) sequestration in tropical soils [6]. It has been estimated that global potential scale of carbon sequestration in soils used for agricultural purposes is around 0.3 t C ha^-1 Y^-1 on arable lands and around 0.5 – 0.7 t C ha^-1 Y^-1 on grasslands [7]. Promoting soil carbon sequestration is an effective strategy for reducing atmospheric CO₂ and improving soil quality. Moreover, quantification of soil organic carbon in relation to various crop management practices is of importance in identifying sustainable systems for carbon sequestration in soils and subtropical environments.

Carbon sequestration (CS) is the process of removal of carbon dioxide (CO₂) from atmosphere in to green plants where it can be stored indefinitely. The rate of carbon sequestration depends on the net balance between carbon inputs and carbon losses per unit time. Climate change, together with other megatrends population growth, rapid urbanization, food insecurity and water scarcity increases competition for resources and heightens tensions and instability. Global climate change has already manifested itself through increase in global temperature by 0.6 to 0.8°C during the 20th century and increase in frequency of extreme events like very high intensity precipitation, frequent drought, heat waves etc. carbon in the form of methane (CH4) and CO₂ is the major player in contributing to this global climatic shift. Global warming potential, methane (25), nitrous oxide (298) and Chlorofluorocarbons (10,900) are equivalent to units of CO₂ (ISA, 2017). Mitigation of CO₂ emission from agriculture can be achieved by increasing carbon sequestration in soil which implies storage of carbon as soil organic matter as minimum soil disturbance (i.e. tillage), increasing the mass and quality of plant and animal inputs to soils, improving soil microbial diversity and abundance and maintaining continuous living plant cover on soils year-round.

By means of various practices and technologies, sequestration needs to be enhanced and in turn the storage ability of all potential sinks and expand the number and type of sinks in which carbon storage is possible. The research is conducted to find the carbon uptake by fodder crops to finally analyse the total carbon sequestration in alluvial soils.

The experiment was conducted in field of Department of Environmental Sciences, Centre for College of Agriculture (RVSKVV), Gwalior (M.P.). The topography of the field was uniform with proper drainage with sandy clay loam & pre-sowing irrigation was given. Oat seed was sown @ 100 kg /ha and maize seed was sown @ 50 kg/ha by funnel attached with desi plough, keeping row to row distance of 22.5 cm. The sowing was done on 18th November, 2017. Among the growth parameters, only plant-height and tiller counts were recorded at each cutting (3 cuts) of fodder crops. Total four irrigations (7.00 cm each) were given to the crop as scheduled. Ten plants were tagged randomly for taking observations at equal intervals from all the 36 plots. The crop spacing was 20 × 20 cm. The experiment was conducted in randomized block design with three replications and 12 treatments. Two fodder crops: Oat & maize and 6 fertilizer levels: 20 kg vermi compost (VC), 32.55 gm urea +37.5 gm ssp, 25 gm urea + 28.125 gm ssp +7.5 kg VC, 20 kg FYM, 25 gm urea + 37.5 gm SSP + 7.5 kg FYM, & 25 gm urea + 38.125 gm ssp +7.5 kg VC were taken along with plots having Oat as control & Oat + maize as control.

Plant-height (cm) was measured on the main culm from the ground level to the base of well emerged last leaf with the help of meter scale at each cutting.

The total number of tillers (m^-2) were counted and further it was converted to number of tillers m^-2 basis by multiplying tiller population per tussock with mean number of observed tussock per meter square.

Green forage yield was recorded from crops when cut from about 5 cm above the ground level and a border of 50 cm from all sides of a plot was first cut and removed immediately. Thereafter, the crops growing within the net plot area was cut and forage yield was recorded with the help of spring balance. In all 3 cuttings were taken from all plots at 60, 100 and 140 DAS in oat including intercrop.

In Oat the biomass production was measured manually by harvesting the aboveground biomass by cutting at the ground level and belowground biomass (Root) by excavation method. Dry biomass is determined by drying the freshly harvested crops in hot air oven at 700 C for 24 hours.

On the basis of plant dry biomass conversion into carbon, is natural reservoir of carbon that accumulates and stores some carboncontaining chemical compound for an identifiable period and the process by which carbon stock removes carbon dioxide from the atmosphere was determined as formula used by Rajput [8].

Carbon stock was determined by using dry biomass converted into carbon by Ash method. Dry biomass was multiplied by carbon content to give carbon stock as per the formulae used by Rajput [8].

Carbon stock = Dry biomass × Carbon content

Carbon dioxide sequestration potential (t ha^-1) by forage crops was determined by multiplying biomass carbon stock with a factor of 3.67 for all species a formulae used by Rajput [8].

C sequestered = Carbon stock × 3.67

The atomic weight of Carbon & Oxygen is 12 & 15.9 respectively.

The weight of CO₂ is C + 2 O (O+O) = 43.9

The ratio of CO₂ to C is 43.9/12=3.67

Organic carbon (%) was determined by Walkey and Black method [9]. It is expressed in percentage. Composite soil samples were collected from different soil depths (0-15 cm) with the help of soil augur.

Soil organic carbon stocks (t ha^-1) was calculated by multiplying the organic carbon with weight of the soil (bulk density and depth) for a particular depth and expressed as tonne per ha^-1 (t ha^-1) as the equation given by Pearson et al. [10].

C (t ha^-1) = [(soil bulk density, (g/cc^-1) × soil depth (cm) × % C)]×100

Growth Parameters

Data pertaining to plant population m^-2 was recorded at 20 DAS and final cutting (Table 1) and found that plant population was non-significant at both the stages under all the treatments. The plant height of oat at each cutting was significantly influenced by the maize intercrop and nutrient level on height on fodder Oat (Table 2) During vegetative stage, maximum average plant height observed under Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) 119.7, 90.2, 78.0 and 96.0 cm at first, second, third and mean of cutting respectively with at par Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂). Number of tillers (Table 3) of fodder oat as influenced by different maize intercrop and nutrient level. Maximum tillers were observed under Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) 293.3, 289.4 and 72.3 at first, second and third cutting respectively which was at par with Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂).

Table 1: Effect of maize intercrop and nutrient levels on green fodder by Oat and soil and total at different cutting interval.

Table 2: Effect of maize intercrop and nutrient levels on height on fodder Oat at different cutting interval.

Table 3: Effect of maize intercrop and nutrient levels on tillers of fodder Oat at different cutting interval.

Green fodder yield

Maize intercrop and fertilizer level on fodder Oat significantly affected the green fodder yield (Table 4). Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) exhibited significantly higher green fodder yield (44.2, 47.8, 60.2 and 152.2 t ha^-1) at first, second and third cutting respectively & at par with Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂).

Table 4: Effect of maize intercrop and nutrient levels on green fodder yield t/ha   on Oat at different cutting interval.

Dry fodder yield

Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) exhibited significantly higher dry fodder yield (9635.6, 10320.0 and 14000.3 kg ha^-1) at first, second & third cutting respectively which was at par with Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂) (Table 5).

Table 5: Effect of maize intercrop and nutrient levels on dry fodder yield kg/ha on Oat at different cutting interval.

Carbon accumulation (Stock)

There was a significant variation (Table 6) under different maize intercrop and nutrient level on fodder Oat for aboveground carbon accumulation (stock). Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) exhibited significantly higher carbon (34.0, 1012.5 and 1046.5 t ha^-1) plant, soil and total which was at par with Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂).

Table 6: Effect of maize intercrop and nutrient levels on c accumulation by fodder Oat and soil and total at different cutting interval.

CO₂ sequestration potential

The carbon stock of crops were converted into carbon dioxide sequestration potential (CSP) under different treatments maize intercrop and nutrient level on fodder Oat, which were presented in (Table 7). Significant variation was observed under different treatments, maize intercrop and nutrient levels on fodder Oat for carbon dioxide sequestration potential.

Table 7: Effect of maize intercrop and nutrient level on CO₂ sequestration potential by fodder Oat and soil and total at different cutting interval.

During the experimentation, the fodder oat CSP was found significantly maximum under Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) exhibited significantly carbon dioxide sequestration (124.6, 3715.9 and 840.5 t ha^-1) plant, soil and total which was at par with Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀) over the treatment Oat + maize control (T₁₂).

The growth parameters of fodder oat under different maize intercrop and fertilizer level vary considerably, which is primarily controlled by factors such as growth habit, climatic and edaphic attributes, age, genetic makeup, management practices viz., fertilizer, irrigation and cultural practices applied to the fodder oat. Present study also showed a wide variation in height under different land use systems. Significantly highest height was found under Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) 119.7, 90.2, 78.0 and 96.0 cm at first, second, third and mean of cutting respectively due to due to positive interaction between for sharing the resources like light, nutrient, water as well as the cultural practices applied to it. Similar results revealed by Kumar [11], Bhattacharya et al. [4], Kaur et al. (2008), Thornton and Herrero [12], Yadava et al. [13], Ghannoum et al. [14], Panchal [15], Rajkumar et al. [16], Thennarasu et al. [17] and Gupta et al. (2017).

Biomass production under different land use systems depends on number of factors viz., choice of crops, growth habit, site quality, soil type, age of crop, management practice applied, frequent intercultural operations, moisture conservation and their interaction with belowground crops have also contributed towards the increasing aboveground biomass production. In the present study, the highest aboveground biomass production may be due to growth habit of fodder oat. Results supported by Kaisi and Grote [19], Ahadiyat and Ranamukhaarachchi [20], Chimento et al. [21], Javanmard et al. [22], Anita et al. [23], Sharma [24], Chaplot [25], Ram , Sathiya and Babu, Meena et al. [26] and Jha and Tiwari [27].

The variation in total biomass production may be due to crop compatibility, genetic makeup of crop, management practice applied, frequent intercultural operations, presence of hard pan in subsoil layers and the above and belowground interaction of crop for sharing of nutrient, water, light and space as also reported by In the present experiment, the maximum total biomass was observed by Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) system may be due to genetic makeup of fodder oat and also may due to positive interaction between them for sharing the resources viz., nutrient, water, light and space. Similar results found by Mohammed and Bekele [28], Meena et al. [26] and Jha and Tiwari [27].

The variation in total carbon stock under different fodder oat depends primarily upon the ash content and the ash content depends upon the amount of structural components of respective crops. Variability may also depend on nature of components, crop density, growth habit, genetic makeup, age, structure, functional components and their number, soil type and intensity of management. Similar results revealed by Kumar [11], and Nishanth et al. [17].

Significantly highest total CO₂ sequestration potential was observed under Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆). Total CO₂ sequestration potential by plant is directly related to biomass production of the different plant components. Highest CO₂ sequestration potential in Oat + maize + 25 gm urea + 38.125 g ssp +7.5 kg VC (T₆) may due to more biomass and more carbon stock was observed. Higher carbon sequestration in intercropping system compared to sole cropping system. Similar results found by Mohammed and Bekele [28-31], and Nishanth et al. [17].

Based on the foregoing discussion, the study comes to the conclusions that Oat + maize + 25 gm urea + 38.125 gm ssp +7.5 kg VC (T₆) found significantly superior for the morphological growth parameters viz., plant height, tillers, green fodder yield, dry fodder yield, carbon accumulation and carbon dioxide sequestration. The next best crop and nutrient level was under the treatment combination Oat + maize + 25 gm urea + 37.5 gm SSP +7.5 kg FYM (T₁₀). So for better carbon stock and in turn higher carbon sequestration in long duration time can be achieved by the oat fodder crop along with these two nutrient levels in alluvial soils of Gwalior region of Madhya Pradesh.