Effects of Long-Term (7 Years) Adoption of Conservation Agriculture and Nutrient Management Practices on the Soil Properties, System Crop and Water Productivity and Farm Economics of a Maize–Chickpea Rotation

Conservation agriculture (CA)-based practices have been promoted and recouped, as they hold the potential to enhance farm pro�ts besides a consistent improvement in soil properties. The CA-based crop establishment practices (CEP) along with adequate fertilizer inputs in the diversi�ed maize-chickpea rotation (MCR) could be a pro�table choice to sustain the crop production of Indo-Gangetic plains in the posterity. Therefore, a seven years' �eld experiment consisting of three CEP viz., zero till �atbed (ZTFB), permanent beds (PNB), conventional system (CT) along with the three nutrient management practices; nutrient expert assisted: site-specic nutrient management (NE®), recommended fertilization (RDF), and farmers’ fertilizer practice (FFP), was carried out from 2013–2020 in a sandy loam soil of the north-western Indo-Gangetic plains. Seven years’ mean maize grain yield under the ZTFB (4.34 Mg ha -1 ) and PNB (4.37 Mg ha -1 ) was signi�cantly (p<0.05) higher than the CT (3.79 Mg ha -1 ). The NE® and RDF had 25.7% and 22.3% greater maize grain yield than the FFP, respectively. Similarly, ZTFB and PNB had 12.2% and 21.5% greater chickpea seed yield, respectively over the CT. The NE® and RDF gave 12.1% and 8.4% higher chickpea seed yield over the FFP, respectively. The CA-based CEP (ZTFB / PNB) produced 13.9–17.6% (seven years’ mean) higher maize grain equivalent yield (MGEY) compared to the CT, while NE® and RDF had 10.7–20% higher MGEY than the FFP. Furthermore, the PNB and ZTFB gave 28.8% and 24% additional net returns than the CT, while NE® and RDF had 22.8% and 17.4% greater returns, respectively over the FFP. The mean data showed that PNB had 7.5% and 30.8% greater system water productivity (SWP) than the ZTFB and CT, the NE® and RDF had 20% and 14% greater SWP than the FFP, respectively. After harvest of the 7 th year maize, the PNB and ZTFB had 2.3–4.1% (0.0-0.20 m soil layers) lower bulk density (ρb) than the CT, however NE® and RDF had 1–1.9% lower ρb compared to the FFP. The CEP had a signi�cant (p<0.05) impact on the soil organic carbon (OC) in 0.0-0.20 m soil layers but it remained unaffected due to the nutrient management beyond 0.10 m soil depth. Microbial biomass carbon (MBC) increased by 8–19% (0.0-0.50 m soil layers) in the ZTFB / PNB over the CT, and by 7.6–11.0% in the NE® / RDF over FFP. The sustainability yield index (SYI) was also greater under the CA-based CEP and with the NE® or RDF compared to the CT practices. Hence, the present study suggests that the CA-based CEP coupled with the NE® or RDF could enhance the yields, farm pro�ts, soil properties of the maize-chickpea rotation, thereby, could sustain the production in long-run.


Introduction
The importance of conventional rice-wheat system (RWS) in the Indo-Gangatic Plains (IGPs) in securing the food and nutrition has been negated due to the greater water requirement and exacerbating soil fertility status 1 coupled with the higher production costs and ine cient inputs usages 2,3 .The ever-changing climate and exaggerating soil degradation poses a constant threat to the sustainability of the conventional farming practices.To redress these effects, conservation agriculture (CA)-based practices have been propounded to restore the degrading soil fertility, enhance the resource use e ciency (RUE) and improve the crops yield 4 .
Maize (Zea mays L), an emerging versatile crop with wider adaptability and photo-insensitivity under different ecological scenario, may replace the rice crop in the wet season.It has potential to address issues such as food and nutritional security 5 , water scarcity and climate change 4 .Also, there is an increasing demand of maize in the industrial sector with the increased population pressure 6 .Similarly, chickpea (Cicer arietenium) is a protein rich (17-22% of total dry seed mass, and best among all legume proteins) legume, grown on an area of ~14.5 m ha with an annual production of ~11.5 m t globally, with the most production centered in India 7 .Maize-based rotations with improved soil and crop management practices have proved a better alternative over the intensive conventional RWS through realization of better system yields, enhanced soil properties, better utilization and savings of irrigations along with the reduced labor costs 8 .The development of single cross high yielding maize hybrids coupled with the energy e cient chickpea genotypes have given an ample scope for diversifying the existing cereal-cereal rotations.In India, maize-chickpea rotation (MCR), is important and next to the maize-wheat, maize-mustard only.The inclusion of chickpea in a cereal based rotation helps in sustaining the soil health and system yields further.It may also help in saving the water over the RWS.
Conventional mode of crop production has been deemed un-sustainable, as it is less energy e cient, consumes more water with lesser productivity, employs improper usage of inputs and obsolete crop establishment methods 9,10 .Consequently, poor residue management under conventional tillage (CT) practices compelled the farmers either to burn them in-situ or feed to the cattle 11,12 .Moreover, intensive tillage not only degrades the soil organic matter (SOM) due to the enhanced oxidation but also disrupts the organic carbon (SOC), hence impairs the soil properties 13 .The mismanagement and exacerbating environment through CT practices could be reoriented by adhering to the CA-based practices i.e., no-or minimum tillage, residue retention and diversifying the crops, thereby, enhancing the soil health and yields 14,15 .Also, adoption of the CA-based crop establishment practices (CEP) (ZTFB / PNB) in different rotations signi cantly improves the water use e ciency 16 , system yields 12 and net returns 13,17,10 .Besides, it improved the soil physical properties 18,19 , built-up the SOC 20,21 , and enhanced the soil MBC 22 .
Nutrient management in MCR under the CA-based systems needs to be enumerated considering the contribution through the residue retention, atmospheric Nxation and the residual soil fertility rather than the usual blanket recommendation.To mitigate and cope up the exacerbating issues, nutrients need to be applied as per the crop demands and its potential yielding ability.Hence, the NE® based site-speci c nutrient management principles focusing on the balanced and crop-need based nutrition 23,24,25 would help in increasing the nutrient use e ciency and provide more pro ts.This is fundamentally based on the internal nutrient e ciency (INE), and is predicted considering the QUEFTS (quantitative evaluation of the fertility of tropical soils) model.The International Plant Nutrition Institute (IPNI) and International Maize and Wheat Improvement Center (CIMMYT) have developed the user-friendly NE® that could enhance and sustain the productivity apace with the improved soil health 26,27,28 .Initially, it was hypothesized that using the NE® would enhance the yields and reduce the fertilizer use.Further, this hypothesis was validated at multi-locations (n=104) eld trials conducted in the southern Indian states by the All India Coordinated Research Project (AICRP) and IPNI on maize following NE® principles.The positive results of these validation trials showed that the eld-speci c fertilizer recommendations based on NE® not only increased the crops yields, but also optimized the fertilizer application rates 29,30,31 .
However, the impacts of CA-based CET (ZTFB / PNB) coupled with the precise nutrient management using NE® in MCR are yet to be evaluated thoroughly.Therefore, this study was undertaken for seven years' (2013-2020) to assess the impacts of the conservation agriculture and nutrient management practices on the system yields, farm economics and soil properties in the MCR of north-western India.

Results
Weather parameters during the study period During the cropping seasons (July-April), the highest rainfall of 1368 mm was received in 2013-14, followed by 1230.2 mm in 2016-17, while only 600-900 mm was received in 2014 -15, 2015-16, 2017-18, 2018-19 and 2019-20.Most of the rainfall was received during the three months (July-September), accounting for nearly 80% of the total rainfall.During winters, the common occurrence of the western disturbances in the north-western India resulted in a very less rainfall.The amount of rainfall received during the October-April was least in 2015-16 (22 mm) and 2017-18 (39.4), while 100-350 mm was received in rest of the years (Supplementary Table 1).
Seven years' trends and pooled grain and stover yields of maize Crop establishment practices (CEP) had a signi cant (p<0.05)effect on the grain and stover yields of maize over the study years.In this study, initial years showed a reduction in the grain yield, but from third year onward, the yield increased signi cantly in the CA plots over the CT.Grain yield under the ZTFB and PNB signi cantly outperformed the CT across the years, except during 2014 and 2015, whereas, the CT had similar yield to the ZTFB in 2013.(Fig. 2a).Across the years, nutrient expert (NE®) and the recommended fertilization (RDF) resulted in similar yield, but being signi cantly superior to the FFP.However, the NE® had signi cantly higher yield over the RDF during 2019 (Fig. 2b).On the basis of the pooled data, the PNB and ZTFB had similar grain yield, which was 13.3% and 12.7% higher over the CT, respectively.Similarly, the NE® and RDF recorded signi cantly higher pooled grain yield, which was 25.7% and 22.3% higher than the FFP, respectively (Table 2).
In all the years, the ZTFB and the PNB had similar stover yields, but being signi cantly higher than the CT (Fig. 2c), and had 12.4% and 12.2% higher pooled yield over the CT, respectively.Furthermore, the stover yield under the NE® and RDF signi cantly outdo the FFP across the years, whereas the NE® had signi cantly greater stover yield than the RDF, except during 2017 and 2018 (Fig. 2d).The seven years' average showed that the NE® and RDF produced 25.8% and 17.6% greater stover yields than the FFP, respectively (Table 2).
The PNB and ZTFB had similar chickpea stover yield, being signi cantly (p<0.05)greater than the CT, but in 2014-15, 2015-16 and 2019-20, the ZTFB was at par to the CT (Fig. 3c).In contrast, the NE® recorded signi cantly greater stover yield than the RDF and FFP, but was at par with the RDF in 2019-20 (Fig 3d).
The PNB had registered maximum stover yield, which was signi cantly higher over the ZTFB and CT.However, the NE® plots had signi cantly 11.9% and 19.3% greater stover yield over the RDF and FFP, respectively (Table 2).
Interaction effect (CEP × nutrient) on the MGEY CEP and nutrient management had a signi cant (p<0.05)interaction effect on the MGEY across the years.In 2013-14, the PNB-NE® had maximum MGEY, and at par to the PNB-RDF and CT-RDF.Similarly, in 2014-15, the PNB-NE® produced the highest MGEY, but did not differ to the PNB-RDF, ZTFB-NE®, ZT-RDF and CT-NE®.In 2015-16, the PNB-NE® had similar yield to all the treatment combinations, except CEP practices with FFP.In contrast, the ZTFB-NE® had the greatest MGEY during 2016-17, 2017-18 and 2019-20.However, it was at par to the RDF and NE®, irrespective of the CEP practices during 2016-17, 2017-18 and 2019-20.Whereas in 2018-19, the PNB-NE® exhibited the highest MGEY, and signi cantly greater than the ZTFB-FFP and CT (Table 3).The results of the current study also suggested that the NE® and RDF either with the PNB or ZTFB tended to have relatively more MGEY than the other conventional based CEP practices.

Farm economics
The seven years' mean data indicated that the CT (US$ 639.9 ha -1 ) was the most expensive CEP, which was 15.3% and 16.9% costlier than the PNB (US$ 541.7 ha -1 ) and ZTFB (US$ 531.6 ha -1 ), respectively.Likewise, the RDF (US$ 582.7 ha -1 ) accounted for the highest cultivation cost, closely followed by the NE® (US$ 576.7 ha -1 ), being 5% and 4.1% higher over the FFP (US$ 553.3 ha -1 ), respectively.In all the years, the PNB had highest net returns, whereas, in 2016-17, the ZTFB accounted for the greater returns.However, the ZTFB and PNB did not differ for the system net returns, except during 2013-14, 2016-17 and 2018-19.
Sustainable yield index (SYI) Among the CEP in maize, the PNB had the greater SYI, but being at par to the ZTFB, which was 15% and 13.2% greater than the CT.Further, SYI was the highest under the NE®, similar to RDF, being 29.1% and 25.6% greater than the FFP.In case of chickpea, the SYI was highest under the PNB, which was 12.4% and 23.6% higher than the ZTFB and CT, respectively.The SYI in the NE® and RDF were at par, being 8.9-12.8%greater than the FFP (Table 2).
Soil properties -bulk density (ρb), organic carbon (OC) and microbial biomass carbon (MBC) After harvest of the seventh season maize, soil samples were collected from the 0.0-0.50m soil depth (Fig. 6a).Among the CEP, the PNB and ZTFB had signi cantly lower ρb than the CT up to the 0.20 m soil depth.The decrement was to the tune of 2.3-4.1% over the CT, though there was no difference in the ZTFB and PNB.In contrast, beyond the 0.20 m soil depth, ρb did not differ signi cantly among the CEP practices (Fig. 6a).Across the soil sections, nutrient management practices were at par for ρb (Fig. 6b).The CEP had a signi cant (p<0.05)impact on the soil OC up to the 0.20 m soil depth, the ZTFB and PNB were at par, but greater than the CT in the 0.0-0.20 m depth.However, there was no difference in the 0.20-0.50m soil section (Fig. 6c).The NE® and RDF had the similar values for the OC, but signi cantly greater than the FFP in the 0.0-0.10m depth, however, the SOC did not differ among the nutrient management beyond the 0.10 m soil depth (Fig. 6d).
At the silking stage of the seventh season maize, the ZTFB and PNB had similar values for the MBC, but signi cantly greater by 8.3-20.3%than the CT in the 0.0-0.30m soil depth (Fig. 6e).Likewise, the NE® and RDF had similar MBC, but signi cantly greater than the FFP in the 0.0-0.10m depth.However, beyond the 0.10 m soil depth, these practices did not show a signi cant in uence on the MBC (Fig. 6f).
For the OC stock (Mg ha -1 ), the ZTFB and PNB had 15.5-16% higher OC stock in the upper 0.10 m soil layer, but in the 0.10-0.50m soil depth, CEP practices did not have a signi cant impact on the OC stock, though relatively greater values across the depths were recorded in the ZTFB / PNB than the CT plots.
Nevertheless, the total OC stock up to the 0.50 m soil depth was 9.5-12.3%greater under the CA-based CEP than the CT (Fig. 7a).The NE® had the highest OC stock across the soil layers (0.0-0.50 m), which was similar to the RDF, but 6.2% greater than the FFP (Fig. 7b).Also, the MGEY had strong relationship with the OC stock under the CA-based CEP (r 2 = 0.87; p < 0.05) and the nutrient management (r 2 = 0.94; p < 0.05).

Discussion
Diversifying the existing dominant rice-wheat system (RWS) towards maize-based, particularly maize followed by legumes under the CA-based CEP (ZTFB / PNB) along with the balanced nutrition, could enhance and stabilize yields and the farm pro ts 32,12 , besides the improved soil properties in long-run 33 .RWS in the IGPs of South Asia is facing challenges of exaggerating decline in the ground water table and the input use e ciencies 34 .Henceforth, maize-chickpea rotation (MCR) has potential to combat the twin challenges of the declining ground water by 30-40 cm year -135 , and the import of pulses.In this study, the CAbased CEP had greater maize (12-13%) and chickpea (12-21%) yields across the years over the CT.It could be associated with the commendatory soil temperature / moisture conditions 36 , improved soil properties 13,37 , better water and nutrient uses 18 besides, amalgamating the effects of the residue retention 38 .Further, these practices also help in the better retention and in ltration of the water and favour better growing conditions that may have resulted in the greater crops yields.
Despite the wide variability in the precipitation (excess / de cit ranis) during the study, the PNB / ZTFB with residues recorded 16.5-17.6%greater MGEY than the CT, it is of course, due to the improved levels of SOM / SOC stocks and other soil properties, reinforcing previous nding in the cereal-based rotations 19,9,10 .
In this study, a relatively higher mean yields were exhibited in the NE®, however being comparable to the RDF.The yield differences in the NE® and RDF plots could be due to the variation in the fertilizer rates, besides the NE® entailed applications of the balanced and location-speci c, which is fundamentally based on the nutrient carrying capacity, thereby it may have enhanced the internal nutrient e ciency 19,39,12 .Possibly, optimal nutrition would have led to the better partitioning of the photosynthates, thereby, more vigorous plant growth with the stiffer rooting and greater resistance against the abiotic stresses 40 .Residual fertility in the NE® and RDF was outlined with the higher chickpea yield than the FFP.Results of multi-location trials in the South Asia had shown that the NE® gave greater yields under the CA than the CT system 30,24,41 .
Feasibility of any technology / management practice could be assessed ultimately through the farm economics.In this study, the CT incurred US$ 84-123 ha - 1 greater cultivation cost compared to the ZTFB / PNB.This higher cost in CT was mainly attributed to the additional tillage 10 , apart from higher labour cost needed for extra intercultural operations.On the contrary, increment in the returns under the ZTFB / PNB was to the tune of US$ 380-481 ha -1 over the CT.
Indeed, the CT plots had the higher farm cultivation cost with the lower MGEY, which in turn re ected in the lower net returns 10,42,43 .Greater net returns under the NE® could be due to a balanced and crop need based fertilizer application 24,25 resulting in more yields, and the returns.The comparative eld studies (n=82) of the NE® with the state recommendation and FFP in the Southern India, reasoned out that, farmers risk could well be reduced, when the NE® was adopted, as it directs and provides proper and the balanced rate of fertilizers 30 .Hence, optimized nutrient use apace with the higher yields and pro tability under the maize and maize-based rotations.
With respect to SWP, the ZTFB and PNB had 25.6% and 30.9% greater values than the CT, which could be ascribed to the better soil moisture regimes due to the surface residue retention coupled with a higher yield gains 37,44 .Furthermore, higher OC stock in the CA-based CET enhanced the moisture retention and opportune time for the water movement in soil 45,46 , hence it facilitates a greater water and nutrient acquisition and ultimately SWP.
The major impacts of the CA-based CEP is conspicuous through higher SOM, especially in the top soil layers apace with the better soil structural stability and biological diversity in contrast to the CT systems 47 .After seven years', the ZTFB and PNB with residues improved the OC content by 18-20% and total OC stock by 15-16% (0.0-0.10 m depth) than the CT.This would be associated with a better physical protection of particulate organic matter, greater amount of C-residues remain on the soil surface coupled with lesser turnover of macro-aggregates as well as minimal contact between residue and soil 48 .Perhaps, extensive tillage reduces OC, as it breaks open the previously protected SOM leading to the increased microbial decay 49,50 , as observed under the CT system.The implications of the higher OC under the NE® and RDF could well be attributed to the proper growth and development of the crop, hence greater above / below-ground biomass production, and eventually the increases in SOM over the FFP.
The effect of the CA-based CEP on the bulk density (ρb) had shown contradictory results, with some studies reported higher ρb 51,52 , on the contrary, some had reported lower ρb 53 or no changes 54,55 relative to the CT system.Nevertheless, in our study the ZTFB / PNB with residues brought down soil ρb by 2.3-4.1% in the top 0.0-0.20 m soil layer, while the nutrient management did not differ for soil ρb.The lower ρb associated with the residues retention leads to a greater soil faunal activities 53,51 , thereby, resulting in better soil aggregation and porosity.In contrast, the increased ρb under the CT, is due to the compaction particularly in the plough soil layer 13,19 .The MBC depicts nutrient cycling ability of a soil under different management practices 56,57 in concurs with the SOM content.The CA-practices coupled with the NE® / RDF favours build-up of the SOC through, rhizo-deposition of root stubbles 58,39 , that certainly increased the MBC 59 and crop yields 60,61 .Besides, the greater SOM would expedite the soil MBC and other biological activities 62 .This seven years' study clearly indicates a synergy between the CA-based CEP and NE® or RDF through improvements in yields, MGEY, farm returns and SWP apart from the soil properties.Also, this is well synthesised by a greater SYI, hence could be propounded for its adoption at present and in the posterity.

Conclusions
The CA-based CEP (ZTFB / PNB) apace with the enhanced resource use-e ciency should be a norm, not the exception, as clearly outlined in our seven years' experiment, wherein, the ZTFB / PNB with the NE® or RDF exceled for the system yields, net returns, SWP, ρb, OC and SYI.The seven years' mean showed that the MGEY under the ZTFB and PNB increased by 13.9-17.6%,respectively compared to the CT, however, the NE® and RDF registered 10.7-20% greater MGEY than the FFP.Furthermore, the CA-based CEP along with the NE® or RDF gave an additional net return of US$ 376-481 ha -1 yr -1 and US$ 265-373 ha -1 yr -1 (seven years' av.) than the CT-FFP, respectively.Also, these practices signi cantly improved the OC stock (15-16%) and MBC (8-19%) with lower ρb (2.3-4.1%) in the top soil layers.The improved soil properties coupled with the greater yields, was well substantiated with the simultaneous improvement in SWP under the ZTFB (7.5%) and PNB (30.8%).The greater SYI also signi ed the superiority and sustainability of the rotation in the long-run.Thus, the ZTFB / PNB with the NE® or RDF in the maize-chickpea rotation can be well adopted in the semi-arid Indian ecologies to realize its several bene ts under the changing climate.

Materials And Methods
Experimental site A eld experiment on the maize-chickpea rotation (MCR) was established during the rainy season of 2013 at the research eld of the ICAR-Indian Agricultural Research Institute (28 º 38′ N; 77 º 09′ E; 228.6 m MSL), New Delhi, India.Prior to the establishment of this study, a uniformity eld trial on wheat was conducted during the winters of 2012-2013 (November-April).The climate of the region is semi-arid and experiences the dry-hot summers and cold winters.During the growing season of maize (July-October) and chickpea (October-April), the maximum rainfall of 1368 mm was received in 2013-14, while the lowest of only 604.6 mm in 2017-18.On an average, ~80% of the total rainfall was received from the south-west monsoon (July-September), and the average relative humidity across the years ranged between 69-87%.The minimum and maximum temperatures during the cropping period ranged from 5-28ºC and 18-38ºC, respectively (Supplementary Table 1).The Typic Haplustept sandy loam soil of the experimental site had 7.31 pH, 0.40% Walkley-Black carbon 63 , 159.9 kg ha -1 alkaline KMnO 4 oxidizable-N 64 , 15.6 kg ha -1 NaHCO 3 extractable-P 6 , and 161.3 kg ha -1 NH 4 OAc extractable-K 66 .

Experimental treatment details
This eld experiment consisted of the combinations of three CEP; zero till atbed (ZTFB), permanent beds (PNB) and conventional tillage (CT) in main-plots, and three nutrient management practices; farmers' fertilizer practices (FFP), recommended fertilization (RDF), and nutrient expert assisted-site speci c nutrient management (NE®) in sub-plots .Split-plot design was employed for the xed plot experiment with three replicates during the entire study period (Table 1).
Prior to the start of the experiment, the eld was deep ploughed using chisel plough (0.30-0.45 m) and laser levelled.The CT plots involved one ploughing (0.25-0.30m), followed by harrowing / rotavator (0.15-0.20 m) and then levelling, while for the ZTFB, no ploughing was accomplished.Initially, the PNB were prepared using the ridge maker (0.67 m), and subsequently the disc coulter once in a year before the maize sowing for the reshaping of the beds in during the each following crop seasons.The gross plot size under each CEP practices was 20 m × 8.5 m.Maize at maturity was harvested from 0.40 m height and standing residues retained in the eld under the ZTFB / PNB plots.Similarly, the chickpea residues ~2.5 Mg ha −1 (root stubbles along with the above ground stover) on dry weight basis were retained in the plots (Fig. 1).

Crop management practices
A quality protein maize hybrid 'HQPM1' was used for the experiment, which was later replaced by the hybrid 'PMH1' in 2017.In each cropping season, the maize seeds were dibbled manually in the rows at a spacing of 0.67 × 0.20 m during the rst week of July.Similarly, sowing of the chickpea genotype 'Pusa 372' was done at the end of October in each year i.e., after the maize harvest.Under the RDF practice, full dose of phosphorous (P) by di-ammonium phosphate (DAP) and potassium (K) using muriate of potash along with the nitrogen (N) were applied as basal to both the maize and chickpea crops, after that two equal N splits to maize were applied at the knee-high and owering stages.The fertilizer doses for FFP were based on the Participatory Rural Appraisal (PRA) i.e., how most of the farmers' in the region follow fertilization to the crops.While, for NE® treatment, fertilizer rates / splits were followed as per the NE® software, available at the http://www.ipni.net.Fertilizers were placed basally in the top soil layer, while the required N was top dressed in bands near to the rows (side dressing).Since there is no NE® for chickpea, hence, fertilizers were applied as per the RDF in the NE® sub-plots.The non-selective herbicide glyphosate at 1 kg ha -1 was sprayed about a week before the sowing of the crops both in the ZTFB / PNB plots.A pre-emergence (2 days after sowing, DAS) spray of atrazine at 0.75 kg ha -1 to maize and pendimethalin at 0.75 kg ha -1 to chickpea was applied, manual weedings were done in the CT.
Crop protection practices such as pest and disease management were followed as per the requirement of both the crops.Irrigation water was applied considering the rainfall pattern coupled with critical crop stages, in which maize crop received three to six irrigations, while for chickpea it was one to two per crop season.

Soil sampling and processing
Five soil samples were collected from the 0.0-0.30m depth (June 2013) for initial analysis, and in 2019 (after harvest of 7 th season maize) from different soil sections i.e., 0.0-0.10,0.10-0.20,0.20-0.30,0.30-0.40 and 0.40-0.50m up to 0.50 m depth using the core.The samples were shade dried and ground gently using the wooden pestle and mortar, sieved in a 2 mm sieve and stored in the air tight polythenes for further analysis of soil properties.For soil MBC analysis, the moist soil samples were collected using the tube auger from 0.0-0.50m depth at 0.10 m intervals at the silking stage of maize.Finely sieved soil samples were stored at 5 0 C (18-24 h) for MBC analysis.

Soil organic carbon
The soil organic carbon (SOC) was determined by the chromic acid wet oxidation method 63 .The nely ground and sieved soil from the different depths (0.0-0.10, 0.10-0.20,0.20-0.30,0.30-0.40 and 0.40-0.50m) was used for its determination.The SOC in 0.10 m intervals up to 0.50 m soil depth was computed by using Eq. ( 1) 67 .

Soil bulk density
Soil bulk density (ρb) was measured from the different soil sections to a pro le depth of 0.50 m, and ve samples were collected randomly from the each plot using the core sampler i.e., 0.05 m d, 0.05 m h.The collected samples were then dried at 105 ºC for 48-72 h until a constant weight reached, and then the soil ρb (Mg m -3 ) was computed using Eq. ( 2) 4 .
Where, Ms indicates dry weight of the sample (Mg), and Vc is the volume of the core (m 3 )

Soil microbial biomass carbon (MBC)
The fumigation extraction 68 method was employed to analyse the MBC in soil samples.The pre-weighed soil samples were taken in a closed capped amber colour bottle and fumigated with the ethanol free chloroform.The un-fumigated samples were also taken in a transparent capped bottle and maintained.Both the fumigated and non-fumigated samples were incubated in the dark for 24 h, after which fumigated samples were evaporated by opening the cap and exposing it to the sun for ~20-25 min.and later in a hot air oven at 50 0 C for ~20 min.The processed samples were added 0.5 M K 2 SO 4 (soil: extractant 1:4) and kept on a mechanical shaker for 30 min.and soil suspension was ltered using the Whatman No.42 lter paper.The carbon content was determined through dichromate digestion superseded by back titration with 0.05 N ferrous ammonium sulphate, then the MBC content was computed using the Eq (3).
Where, EC = (C in fumigated soil -C in un-fumigated soil)

Yield measurements
During the seven years of the experimentation, the crop yields were estimated from the net plot area (9 m × 8 m), leaving the border rows in both the crops.The border plot area was harvested rst, and then the net plot area for recording the grain / seed yields.The harvested maize cobs were sundried for 45-50 d and the stover for about a month in the open eld conditions, and then threshed by a mechanical thresher.The chickpea was harvested manually, and the harvested produce was sundried, then threshed using a tractor drawn pull man thresher.For grain yield, the moisture content was adjusted to 12% in both the crops.The stover / stalk yields were obtained by subtracting the grain / seed yields from their respective total biomass yield.To estimate the system productivity of MCR, chickpea seed yield was converted into the maize grain equivalent yield (MGEY) as given in the Eq (4) 10,61 .
Tables Table 1 Description of the crop establishment practices (CEP) and nutrient management adopted in the maize-chickpea rotation during the seven years' of experimentation.

S.
No.

Treatment Treatment notations
Residue/nutrient management

Figures Figure 1
Figures

Figure 2 Seven
Figure 2 Seven years' grain (a, b) and stover (c, d) yields trend of the maize under the CA-based CEP and nutrient management in the maize-chickpea rotation.The vertical bars indicate the LSD at p=0.05.

Figure 3 Seven
Figure 3 Seven years' seed (a, b) and stover (c, d) yields trend of the chickpea under the CA-based CEP and nutrient management in the maize-chickpea rotation.The vertical bars indicate the LSD at p=0.05.

Figure 4 Seven
Figure 4 Seven years' trend in the MGEY (a, b) under the CA-based CET and nutrient management in the maize-chickpea rotation.The vertical bars indicate the LSD at p=0.05.

Figure 5 Seven
Figure 5 Seven years' trends of SWP (a, b) in the CA-based CEP and nutrient management under the maize-chickpea rotation.The vertical bars indicate the LSD at p=0.05.

Figure 6
Figure 6 Soil pb (a, b), OC (c, d) and MBC (e, f) under the CA-based CEP and nutrient management after 7th season maize in the maize-chickpea rotation.The horizontal bars indicate the LSD at p=0.05.

Figure 7
Figure 7 Seven years' trends of OC stock (a, b) under the CA-based CEP and nutrient management in the maize-chickpea rotation.The vertical bars indicate the LSD at p=0.05.

Table 2
Seven years' mean grain / seed and stover yields (Mg ha −1 ) (±S.D.) and sustainable yield index (SYI) under the CA-based CEP and nutrient management in the maize-chickpea rotation.
#Means followed by a similar uppercase letters within a column are not signi cantly different (p<0.05) according to Tukey's HSD test.

Table 3
Interaction effect of the CA-based CEP and nutrient management on the system productivity (±S.D.) in terms of MGEY during the seven years' of the study in the maize-chickpea rotation.548 b Means followed by a similar uppercase letters within a column are not signi cantly different (p<0.05) according to Tukey's HSD test.Price of one US $ = 62.9