The soil management practices which involve(s) tillage, and diversified cropping system in conservation agriculture (CA) may alter the bulk density (BD) and soil organic carbon (SOC). The decrease in the intensity of tillage and continuous maintenance of crop remains under CA are essential tactics for the preservation of soil resources and sustenance of agro-ecosystems with limited mechanical practices and judicious use of chemical inputs [41]. Soil play a key role as a source or sink for carbon, depending on advanced agricultural management techniques, and also contributes significantly in carbon cycling [42]. These interface implementations can modify nutrient pathways and availability to the crop, slow-down rates of evaporation, and decomposition of SOM and, consequently improve carbon repository capacity [43]. In this present investigation, lower BD values were observed in the top soil layer under conventionally tilled (CT) plots probably due to intensive tillage operations. In contrast to that, the BD exhibited an increasing trend in the upper soil layer for zero tilled plots which might be the result of low soil disturbance. Similar findings were reported by Abaganduru et al. [44] who have observed that the BD in the top soil, from 0 − 20 cm was higher for Zero tillage (ZT), accompanied by minimum tillage (MT), which demonstrated that lowering of tillage intensity slow-down soil disturbance, thus, leading to a rise in BD in the top soil. The increase in the depth of the soil profile demonstrated an increase in BD particularly under CT practices and could be attributed to heavy farm machinery load and continuous removal of crop residues having a negative impact on soil compaction. These results are supported by Hobbs and Gupta [45]. Similarly, Alabi et al. [46] have reported that sub-surface soils encounter low soil disturbance relative to surface soils, which result in an increased BD.
Less BD exhibited by conservation tillage i.e., ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS in the 15–30 cm could be associated with continuous retention of cotton and Sesbania crop residues on fixed plots, and enhanced SOC content. The impact of weed control strategies on BD and SOC remain unknown and this is consistent with the findings of Anshuman et al. [47] who observed non-significant influence on BD and SOC by four hand-weeding and integrated weed control.
In the present investigation, soil organic carbon (SOC), stocks and nutrient availability such as soil available nitrogen (N) and phosphorus (P) are favored by reduced tillage with cumulative retention of the crop residues in CA practices, proven by the results of the present experiment. These findings are in congruence with the discovery of Sapre et al. [48] in which the increments on soil N and P availability where Sesbania rostrate and maize residues were retained in rice, rice residues in wheat and wheat residues in maize in a four-years CA experiment, and SOC stocks [49] in the eastern Himalaya zone with the adoption conservation tillage. This could be due to regular build-up of crop residues, which augmented the soil system with N and P from decomposed SOM. Significantly higher N availability was also announced by Alam et al. [50] in the upper soil surface under ZT in wheat-mungbean cropping sequence. Cotton and maize crops are predominant and exhaustive in nature [2] and absorb vast amounts of available soil nutrients particularly in CT systems which removes the crop leftovers subsequent to harvest. This could be the result for soil nutrient availability to fall below the initial values. These results concur with that of Sapre et al. [48] who observed a non-remarkable variation of N, P, K under CT managed system relative to the initial soil nutrient availability status. The SOC stocks, pools and total organic carbon (TOC) were significantly reduced when soil sampling depth increased ascribed to soil surface residue accrual and less concentration of the roots in the soil sub-surface. These research findings concur with that of Yadav et al. [51], Choudhary et al. [52] and Kumar et al. [53]. However, non-labile (NLL) pool of SOC was observed to be significantly higher under CT(C)-CT(M)-Fallow(NSr) in the 15–30 cm in comparison with 0 − 15 cm soil depth probably due to its recalcitrant.
The gains for sequestering SOC as to sustain the soil resources and crop production through adoption of a suitable tillage practice are well-established and documented [54–55]. In the current study, the greatest cumulative SOC sequestration rate, carbon retention efficiency (CRE), TOC observed under ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS could be attributed to no-disruption of the soil aggregates and high SOM content brought about by added crop residues and permanent soil cover under diverse cropping system, indicating more rapid turn-over for active C (CACT) pool and tillage as a determinant factor over CRE and SOC sequestration rate. Yadav et al. [51] also reported the beneficial effects of no-till with the addition of crop residues and adequate C-inputs on enhancing C-reserves and transposing the process of soil degradation over conventional tilled systems. The distribution of SOC pools were lower under conventional tillage plots probably due to intensive ploughing and removal of the plant residues after crop harvest. Similar results were discovered by Khambalkar et al. [56], and Chivane and Battacharyya [57] in which the distribution of SOC pools were very less in the CT tillage systems in the absence of crop residues probably due to less biomass production. In contrast to that, several studies have reported a reduction in the tillage intensity along-with the addition of crop residues to have resulted in the build-up of very labile and labile carbon under CA scenarios [58–59] and modification of SOC lability and its indices viz., lability index (LI), carbon pool index (CPI) and carbon management index (CMI), consequently influencing the soil quality [60], which agrees with the results of the present investigation. Lability index (LI) was significantly higher in the 0–15 cm under ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS ascribed to a greater amount of CL pool in such treatment. LI has been elucidated by Hazra et al. [61] as the sum of of the corresponding weightage of CL pool, thus a greater LI signifies productive soil with the highest CACT. The CPI was used to show the accrual of carbon (C) with respect to the reference C (C was drawn from virgin soils in the trees adjacent to the study area). Parihar et al. [62] had indicated that the greater CPI signifies the accrual of SOC in the soil relative to the lower CPI. It is well-known that SOC under the trees particularly from virgin soils is more than that of the cultivable lands. It is also well-established and documented that agricultural management practices such as CA, can bolster the CPI under diversified cropping systems. Conservation tillage i.e., ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS adopted in the current experiment had recorded a higher CPI particularly in the 15–30 cm possibly due to inclusion of Sesbania rostrata well-known to have a rapid decomposition rate due to less lignin content and low C:N ratio leading to more C input, which revealed more accrual of SOC for the entire soil profile (0–30 cm). Similar research findings were reported by Yadav et al. [51].
No-till and or reduced tillage (RT) under intensive cropping systems is broadly deemed as a viable alternative for enhancing CMI under various agro-ecological systems [36]. The CMI is acquired from TOC pool, and is essential for assessing the magnitude of agricultural systems adopted for promoting soil quality and enhancing SOC sequestration [36; 60; 63]. The higher CMI value (s) signifies the best agricultural management practices significant to elevate SOC and bolster the soil quality [64]. In the present study, the adoption of tillage practices and weed management options in the 0–15 and 15–30 cm soil depths have positively influenced CMI. The higher CMI values were observed in the15-30 cm than 0–15 cm soil depth with significantly higher values observed under by ZT(C) + SrR- ZT(M) + CR-ZT(Sr) + MS which could be interlinked with appropriate adoption of tillage and weed management combinations, C inputs and less soil disruption.
The ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS when combined with single hand-weeded control resulted in significantly higher CACT: CPSV in the 15–30 cm soil layer, and was the dominant contributor of CACT pool to TOC for the entire soil sampling profile depth (0–30 cm) which could probably be due to less soil disturbance, crop residue addition in conjuction with cultural weed control, well-known to harbor a vast diverse group of microbes for decomposition of the crop residues. The CACT: CPSV was more than 1 in the ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS in combination with all weed management practices in the 15–30 cm soil layer, signifying more easily labile or oxidizable fractions than recalcitrant form of carbon. In contrast, Kumar et al. [65] reported CACT: CPSV ratio of less than 1 under CT and weed management combinations, indicating more of recalcitrant carbon than easily oxidizable pools.
The stratification ratio (SR) is a great measure of soil quality, and values of SR are normally higher at deeper soil profile. The SR becomes significant where a huge variation between the soil surface and sub-surface exist. In the present study, the SRs were found to be equal to or greater than 1 in the overall treatments. However, the significantly higher SRs were notable under the ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS which could be due to less soil disturbance and high SOM content resultant to addition of continuous crop residues. These results concur with Franzlueebbuers [18] who had reported the variation for SR of SOC as 1.1–1.9 in the 0–15: 12.5–20 cm soil sampling depth under CT and 2.1–3.4 under ZT induced by continuous build-up of soil surface C input, although the sampling depth was different from the present investigation. Similarly, Sapre et al. [48] announced the overall significant rise on SR for SOC and total nitrogen (TN) in the deeper soil depths under all the tillage treatments with greatest (2.24) being observed under ZT followed by reduced tillage (RT) with 1.62 and CT with 1.42. However, there is no consistent figure for SR which has been reported to signify a high soil quality [66]. Among all soil attributes studied, SOC and available soil N were found to have higher SRs indicating that the soil quality can be assessed better through SRs of SOC and soil N availability.
Better growth/development of crops and increased yield rely to a large extent on tillage practices, as these play a crucial role in determining the development of the crop's rooting system, the soil volume explored by the roots for moisture and nutrients, the availability of air, and the regulation of soil temperature, among other factors. The importance of crop-weed interaction in determining the competition faced by the crop plants for the light, moisture and space is well-established. Confined root growth lead to decreased nutrient uptake and poor crop growth [77]. The meta-data analysis of ZT with residue retention indicated that the effect on crop yields in comparison with CT, is inconsistent and impacted substantially by cropping systems followed by aridity index, crop residue maintenance, ZT duration, and weed management strategies [25]. In this present investigation, maize grain, and harvest index demonstrated higher values when subjected to the ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS treatment in comparison to other tillage methods. This superior performance can be interconnected to the development of robust, deep-rooted systems in the crops facilitated by the practice of zero tillage.
The implementation of ZT is thought to augment the nutrient absorption capacity of the crops, thereby fostering their physiological growth and overall development. Furthermore, the preservation of crop residues on the soil surface under the ZT(C) + SrR-ZT(M) + CR-ZT(Sr) + MS treatment likely contributed to the enhanced retention and availability of soil moisture. This aspect proves especially crucial during the post-tasseling stage of the maize crop, which coincided with a hot period from mid-March to May. Given the limited moisture conditions during this period, supplemental irrigation was applied to ensure optimal soil moisture levels throughout the crop development. The research outcomes by You et al. [67] also indicated that short-term reduced tillage (rotary-till and no-till) and residue incorporation enhanced soil properties and spring maize grain yield, growth and attributes and increased root biomass and shoot ratio. Furthermore, the interaction of tillage and residue treatments can increase crop biomass and yield [68–69]. Several previous studies conducted on short-term conservation tillage have not paid full attention as to how yield can be improved.
No-till enhances root biomass, shoot biomass, regulate shoot to root ratio, and increase yield in comparison with plow-till and rotary-till [70–71]. Residue incorporation can also enhance crop biomass and yield due to enhanced soil buffer capacity [72–73]. The post-emergence tank-mix combination of atrazine and tembotrione herbicide was applied at recommended rates in both W1 and W2 which resulted in effective weed control and no phyto-toxicity. The absence of phytotoxic effects suggests the efficacy and safety of the tembotrione and atrazine combination in weed management, contributing to better crop performance. Poor crop performance was also observed under unweeded control which ultimately reflected in yield. This could be due to high weed density at critical crop growth stage which out competed with the crop for available moisture, nutrient, light and rooting space. Ganapathi et al. [74] also recorded higher kernel, harvest index, and least weed dry weight with IWM compared to the use of only advocated herbicides and non-weeded treatments due to less weed infestation. Similar results were obtained by Kumar et al. [53] who observed that when pre-emergence herbicide was applied followed by one rotary hoeing at 35 DAS led to increased grain and stover yield. The results of Ahmad et al. [75] concur with the findings of this present investigation, who noticed that Nicosulfuron application and one-hand weeding with a hoe at 15 DAS led to greater kernel yield, whereas the least kernel yield was obtained from unweeded control. In the current study, there was an increase in corn yield and HI when employing a zero tillage with crop residue retention (ZT + R) and chemical weed control and IWM. This improvement could be attributed to the synergistic effects of efficient weed management achieved through the use of both chemical and cultural mechanical control tactics, along with the moisture and nutrient preservation facilitated by no-till practices that retained crop residues. These results are supported by Ahmad et al. [75] who deduced that maize can flourish when cultivated in zero tillage either with application of atrazine, glyphosate or with hand weeding (HW) at 40 DAS alternative to manual weeding in spring seasons to attain higher grain yield.