Physiological Indices, Productivity and Profitability Assessment at Varying Nitrogen Levels of Wheat Under Conservation Agriculture

Conservation agriculture (CA) is a promising management practice adopted by spring wheat growers in the Indo-Gangetic plains (IGPs) of India, particularly in areas where residue burning is prominent. Effective nitrogen management is essential to achieve maximum profitable wheat yield under CA to promote agricultural sustainability. A field experiment conducted during the winter seasons of 2020–21 and 2021–22 comprising seven treatments with varying nitrogen doses from 0 to 250 kg/ha was used to find the best nitrogen management strategy. Instrument-based physiological indices, including the chlorophyll content index (CCI), normalized difference vegetation index (NDVI), Dualex meter-based values, and flavonoids, were used to investigate the relation between these indices and growth stages. Increasing nitrogen levels from 0 to 250 kg/ha resulted in increased growth and physiological indices. However, the increase beyond 150 with or without CA was non-significant in case of many indices. The enriched treatment (250 kg N/ha) recorded a lower grain yield (5123 kg/ha) compared to 100 kg N/ha treatments (5595 kg/ha). The thousand-grain weight was also found to be reduced by 21.2% in 250 kg N/ha compared to the 150 kg N/ha treatment. The application of 200 kg N/ha under CA produced a significant increase (9.6%) in grain yield (6673 kg/ha) as compared to the farmer’s practice of 150 kg N/ha. Applying 150 kg N/ha under CA increased grain yield by 231 kg/ha over the same N level without CA, although the difference was non-significant. The application of 200 kg N/ha under CA yielded the highest gross return (2271.8 $/ha), net return (1545.0 $/ha), and B:C (3.1) due to the reduced cost of cultivation in CA and maximum grain yield. Additionally, if this technology is adapted to 13.7 m ha rice–wheat area in South Asia then additional net return from 200 kg N/ha application under CA over farmers practice will be $3.32 billion annually, which is huge amount. Therefore, using 200 kg N/ha under CA can further increase grain yield, productivity, and profitability per unit area. However, for resource-limited growers in rice–wheat growing areas, 150 kg N/ha under CA can still be a viable and economically sound option.


Introduction
Wheat is the second most widely grown crop in India, after rice, and it is the most widely grown crop in the world.India accounts for approximately 13.9% (106.84 mt; 4th estimate by GoI, 2022) of the global wheat production, which is 770.3 mt (FAO, 2022).However, the wheat productivity in India is comparatively lower than the world average, and this is due to several factors such as improper management of monetary and non-monetary inputs, including sowing time, tillage practices, and nutrient management.
One major issue in the rice-wheat system in the Indo-Gangetic Plains (IGPs) of India is the burning of crop residue, particularly of rice, which leads to degradation of soil health and environmental pollution.To address these negative consequences, farmers in the IGPs are increasingly adopting Conservation Agriculture (CA).
Conservation agriculture (CA) practices involve keeping more than 30% of plant residues on the soil surface with minimal soil disturbance for seeding.CA is a potential agricultural strategy due to its capacity to store carbon, slow down global warming (Lal, 2015;Zhang et al., 2014), and promote timely crop sowing, cost reduction, improved soil aggregate stability, and long-term environmental protection (Coventry et al., 2011).Residue retention or incorporation into the soil is a crucial management strategy for crop leftovers (Jiang et al., 2001) and can impact crop production, soil fertility, and physico-chemical characteristics (Eagle et al., 2000;Khalid et al., 2014;Wang et al., 2001).CA can also mitigate terminal heat stress in wheat by conserving moisture and reducing the impact of increasing temperatures.
Among various monetary inputs, nutrient management plays a crucial role in achieving self-sufficiency in food grain production.Nitrogen (N) is the most limiting nutrient for wheat and directly impacts crop yield and quality.N is an essential component of proteins, nucleic acids, chlorophyll, and certain hormones (Ata- Ul-Karim et al., 2016).It is therefore crucial to accurately and quickly identify the wheat nitrogen status to enhance productivity and quality via agricultural management practices (Yang et al., 2019).Non-destructive and precise tools, such as chlorophyll meters (SPAD-502), normalized difference vegetation index (NDVI), and chlorophyll polyphenol meters, are increasingly used for monitoring and diagnosing nitrogen status in wheat.Green Seeker and chlorophyll meters are the most commonly used instruments for precision nitrogen management.The SPAD meter is a rapid and non-destructive tool that can determine leaf chlorophyll concentration, identify N condition, propose fertilizer N, and locate N distribution issues (Noulas et al., 2018).The Green Seeker uses red and near-infrared wavebands to calculate the normalized difference vegetation index (NDVI) and provides in-season N recommendations for winter wheat (Lukina et al., 2001;Raun et al. ,2002).The chlorophyll polyphenol meter, which estimates leaf phenolics content, is not widely used for precision nitrogen management.Dualexderived UV absorbance and leaf N concentration were found to be strongly inversely correlated by Barthod and Epron (2005).However, it has been used to evaluate N status and estimate phenolics content in both wheat and corn (Cerovic et al., 2005;Tremblay et al., 2007).According to Tremblay et al. (2007), the chlorophyll/phenolics ratio was the most robust and sensitive indicator of applied N dose for corn.The accuracy of these instruments can be tested in the field by correlating them with nitrogen application rates, making them useful for future nitrogen application.
In order to increase wheat output, the application of nitrogen fertilizer is regarded as a crucial tactic.Farmers in the Indo-Gangetic Plains (IGP) of India typically use more nitrogen fertilizer to improve wheat output (Sapkota et al., 2014).However, higher doses of nitrogen application (> 180 kg/ha) in spring wheat under conventional practices can enhance lodging and reduce grain yield (Tripathi et al., 2004(Tripathi et al., , 2005)).In contrast, conservation agriculture (CA) practices, where crop lodging is minimal (Mondal, 2020) due to less soil disturbance, offer a chance to further increase yield by enhancing nitrogen levels.Additionally, as both rice and wheat are exhausting crops (Mandal et al., 2004), there is constant nutrient mining from the soil, and the use of excessive nitrogenous fertilizers in conventional tillage practices not only reduces productivity and profitability, but also causes environmental risks (K.Kumar & Goh, 1999).Therefore, keeping all these factors in mind, the present investigation was carried out to find the best nitrogen management strategy in wheat under the rice-wheat system at varying nitrogen levels under conservation agriculture.

Study site, Treatments, Agronomic Practices and Experimental Design
A 2-year study was conducted during the winter seasons of 2020-21 and 2021-22 at the Research Farm of the Division of Resource Management, ICAR-IIWBR, in Karnal, Haryana, India (29°43′ N; 76°58′ E; altitude 245 m above mean sea level) as shown in Fig. 1.Before the experiment began, the field had been used for transplanted rice with traditional farmers' practices to ensure homogeneity of soil fertility.The initial physico-chemical properties of the soil were analyzed prior to the experiment.The soil was found to be sandy loam (62.4% sand, 27.5% silt, and 10.1% clay) with a pH1:2.5 of 7.6 and electrical conductivity1:2.5 of 0.25 dS/m.The soil had 0.42% organic carbon, 193 kg/ha of available nitrogen, 17.9 kg/ha of available phosphorus, and 241 kg/ha of available potassium.At the beginning of the experiment, soil samples were analyzed for organic carbon (Walkley & Black, 1934), available nitrogen using the Jackson method from 1958 (Jackson, 1958), available phosphorus using the Olsen method from 1954 (Olsen, 1954), available potassium using the Merwin and Peech method from 1951 (Merwin & Peech, 1951), as well as electrical conductivity and pH (using a 1:2.5 soil-to-water solution).
To assess the impact of different nitrogen management practices on wheat, with and without conservation agriculture, the experiment was set up in a randomized block design, comprising of seven treatments with three replications.The gross plot area was 8.0 × 2.2 m, and the net plot was 6.0 × 1.8 m.Before sowing, glyphosate herbicide was sprayed to remove weeds in plots where conservation agriculture was followed.We sowed the wheat variety "DBW-222" with 100 kg/ha seed rate with a row to row spacing of 20 cm using a zero till drill (Kamboj happy seeder).We retained the residue of the previous crop (rice at the rate of 6 t/ha) in plots that followed residue retention.We sowed wheat on November 1, 2020, and November 10, 2021, for the 2020-21 and 2021-22 trials, respectively.
The experimental plots received different doses of nitrogen using urea (46% N) according to the seven treatments: T1: Control (no nitrogen), T2: 50, T3: 100, T4: 150 (farmers' practice), T5: 150 under CA, T6: 200 under CA, and T7: 250 kg N/ha.All treatments received a full dose of phosphorus at 60 kg P 2 O 5 /ha using single superphosphate (16% P 2 O 5 ) and potassium at 40 kg K 2 O/ha using muriate of potash (60% K 2 O) at the time of sowing.One-third of the nitrogen was applied as a basal dose, with the remaining two-thirds applied in two equal splits at the first node stage (DC31, (Zadoks et al., 1974) and the flag leaf just visible (DC 37) based on the treatment.Narrow and broad-leaved weeds were controlled by applying sulfosulfuron at 25 g ha-1 and metsulfuron at 4 g ha-1 in 400 L of water at 30-35 days after sowing.Approximately 7-10 days after physiological maturity, a net plot of 10.8 m 2 was manually harvested with the help of sickles, excluding border rows and half a meter at both ends.All recommended packages of practices were adopted, and yield and yield attributing characters were obtained using methods described by (Bell & Fischer, 1994).

Weather Conditions
The experimental site is located in Haryana, India, and falls under a sub-tropical and semi-arid climate characterized by cold winters from November to January and mild temperatures during February and March.The mean weekly meteorological observations for the cropping seasons of November 2020 to April 2021 and November 2021 to April 2022 are presented in Figs. 2 and 3, respectively.
The weekly maximum and minimum temperatures ranged from 14.9 to 37.8 °C and from 3.5 to 17.1 °C in 2020-21, and from 12.6 to 40.6 °C and from 4.9 to 19.4 °C in 2021-22.During 2021-22, the rise in temperature during post-anthesis led to shrivelling of the grain, resulting in a decrease in 1000-grain weight and ultimately lowering the grain yield.The weekly average of morning and evening relative humidity varied between 50.4 and 100.0 and 20.7 to 92.4 per cent in 2020-21 and 49.3 to 100.0 and 13.1 to 91.9 per cent in 2021-22, respectively.
During the crop seasons of 2020-21 and 2021-22, the total rainfall received was 124.2 mm and 111.2 mm, respectively.The total evaporation from the Class A open pan evaporimeter during the crop growing period was 63.7 and 69.8 mm for 2020-21 and 2021-22, respectively.Wind velocity ranged from 0.6 to 3.6 km/hr in 2020-21 and 0.2 to 3.6 km/hr in 2021-22.With the exception of an increase in temperature during the grain development stage in 2021-22, all weather parameters were conducive to the growth and development of wheat. 1 3

Physiological Indices Measurement
Rapid and non-destructive plant probing instruments like chlorophyll meter (SPAD-502), Green Seeker (NDVI) and Chlorophyll polyphenol meter (Dualex® Scientific) were used for the quantification of chlorophyll.Out of these instruments, GreenSeeker and SPAD meter are the most widely used instruments for precision nitrogen management (Fig. 4).But, use of Dualex meter is not much explored for nitrogen management.The SPAD index was determined using the chlorophyll sensor SPAD-502® (Konica Minolta Inc., Japan), NDVI values were determined by using GreenSeeker hand held crop sensor (Trimble, Sunnyvale, CA, USA) and the indices Nitrogen Balance Index (NBI), Anthocyanin Index (ANTH) and Flavanoid Index (FLAV) were obtained using the Dualex® Scientific (Force-A, Orsay, France) on Zadoks scale at DC37 and DC65.Five randomly selected plants from each plot were used to record the SPAD index and the indices NBI, ANTH, and FLAV, and the resulting data were averaged as a single value for each plot.In contrast, NDVI values were obtained by moving the GreenSeeker over the crop canopy in the net plot area.

Observations Recorded
"Plant height (PH) and spike length (SL) of ten plants were taken from the net plot, and an average value was calculated thereafter.The number of tillers (TN) per meter row length was counted from two positions in each plot and then converted to tillers per square meter.Grain yield was calculated from the net plot area and converted into kg/ha.In the case of wheat, straw yield (SY) was calculated by subtracting the grain yield (GY) from the respective biomass yield (BY) in each plot.Harvest index (HI) was calculated by dividing the grain yield by biomass.The number of grains per earhead (GPEH) was calculated by counting the grains from ten selected spikes, and an average value was calculated.The 1000-grain weight (TGW) was calculated by taking random grain samples, counting them using the Contador electronic seed counter (Pfeuffer, Germany), and weighing them.All the other recommended packages of practices were adopted in wheat, and the yield and yieldattributing characters and grain number per m 2 (GPMS) were obtained using methods as described by (Bell & Fischer, 1994).

Economics
Wheat yield was multiplied by the minimum support price of US $246.8/tonset by the Ministry of Agriculture and Farmers Welfare, PIB, GoI.The straw yield was also multiplied by the market rate of $50/ton and added to calculate the gross return.In addition to these, the cost of cultivation included field preparation, seed, fertilizer, irrigation, transportation, herbicide application, harvesting and threshing, management fees, rental value of the land, interest on fixed capital, and depreciation cost of implements and farm buildings.The cost of cultivation was subtracted from the gross return to determine the net return.The benefit-cost ratio was calculated by dividing the gross return by the entire cost of cultivation.The gross return, cost of cultivation, and net return were converted to US dollars by dividing them by the prevailing exchange rate of $1 = Rs 80.

Growth Parameters
Application of 100 kg N/ha and above did not result in a significant increase in plant height, while applications below this level led to a significant decrease in plant height.Leaf area index (LAI) was highest at the tillering stage and was directly correlated with nitrogen levels (Fig. 5).The maximum LAI (6.55) was recorded with the application of 250 kg N/ha under CA, and this treatment also showed higher LAI values compared to the non-CA plots.

Yield and Yield Attributes
The maximum number of effective tillers per square meter (532.0) was recorded with the application of 200 kg N/ha under CA, which was not significantly different from the number of tillers recorded at 150 kg N/ha or higher (Fig. 5).There was no significant difference in the number of tillers per square meter between treatments with CA and those without CA at the same nitrogen level, but the count was higher in the treatments with CA.Spike length, which indicates the number of grains in a spike and is an important yield attributing characteristic, was recorded as highest at the application of 250 kg N/ha.
The application of 250 kg N/ha resulted in a significantly higher number of grains per earhead (37.4), which was comparable to all other treatments, and significantly more than the control (16.4).Meanwhile, the highest number of grains per m 2 was recorded with the application of 200 kg N/ha under CA.The application of 150 kg N/ha along with CA resulted in a non-significant difference in the number of grains/m 2 as compared to without CA.However, the former treatment resulted in a gain of 702 grains/m 2 compared to the latter.
The application of different doses of nitrogen, with or without CA, has a significant impact on grain yield (Fig. 5).Pooled grain yields ranging from 1674 to 6673 kg/ha were recorded at different nitrogen levels.The significantly highest grain yield (6673 kg/ha) was obtained with the application of 200 kg N/ha along with CA, as all the yield attributing characters were higher in this treatment.The application of 150 kg N/ha with CA showed a nonsignificant difference in grain yield compared to without CA, but an increment of 231 kg/ha of grain yield was recorded with CA.The decrement in yield with 250 kg N/ha was due to more than 50% lodging during the grain-filling period.Similar results for biological and straw yield were also observed.
The application of 100 kg N/ha and beyond resulted in a non-significant increase in harvest index (HI), while application below this level significantly decreased the HI.The highest 1000-grain weight was recorded in control plots, whereas the lowest weight was recorded with the application of 250 kg N/ha.This decrease in weight could be attributed to lodging, which caused improper grain development and shrinkage.

Physiological Parameters
Significant NDVI values were observed at the flag leaf (DC37) and anthesis (DC65) stages of wheat.The maximum NDVI value at DC37 (0.78) and DC65 (0.49) was recorded with the application of nitrogen at 250 kg/ha (Fig. 6).The decrease in NDVI values at DC65 was due to the decrease in greenness at anthesis.The application of 150 kg N/ha with or without CA recorded non-significant NDVI values at DC37, but at DC65, the NDVI value of 150 kg N/ha under CA (0.41) was higher compared to without CA at the same fertility level (0.39).The lowest NDVI values were recorded in the control plots at both stages.
According to Fig. 6, canopy temperature (CT) was highest when the canopy cover was minimum and vice versa.The highest CT was recorded in control plots at both stages, i.e., DC37 (21.1 °C) and DC65 (30.8 °C).At DC37, CT was statistically similar among all the treatments, while at DC65, the plot with 250 kg N/ha application had the lowest CT.CA plots also had a lower canopy temperature compared to non-CA plots at the DC65 stage.
The increase in nitrogen dose resulted in higher chlorophyll content index (CCI) or SPAD values (Fig. 6).The application of 250 kg N/ha (45.9) recorded the highest CCI at DC37, while the minimum was recorded in control plots (32.5).CA with 150 kg N/ha (42.5) recorded a statistically similar CCI compared to treatments without CA at the same nitrogen level (42.2).The control plots at DC37 recorded the least CCI among all treatments.At DC65, CA treatments recorded higher CCI than the plots without CA or with higher nitrogen rates.The application of 200 kg N/ha (37.6) recorded a significantly higher CCI and was at par with 150 kg N/ha with or without CA and 250 kg N/ha.The minimum CCI was recorded in the control treatments (23.5).
The Dualex readings like nitrogen balance index (NBI), flavonoids (FLAV) and anthocyanin (ANTH) were significant for different nitrogen doses at both the stages (Fig. 6).At DC37, maximum value of NBI was recorded with the application of 250 kg N/ha (80.9).Increase in dose of nitrogen has significantly increased the NBI values.Minimum value of NBI was recorded in control treatment (21.6).At DC65, almost similar trend of NBI was observed but lower values in a range of 15.0 to 33.2 were recorded.
Higher values of FLAV and ANTH were recorded in stressed plots, whereas fully fertilized plots recorded much lower values comparatively (Fig. 6).The fully fertilized plot (250 kg N/ha) recorded minimum FLAV values at both DC37 (0.45) and DC65 (0.58), whereas the no nitrogen plots recorded the maximum values at both stages (DC37: 0.90, DC65: 0.90).Increase in nitrogen dose has decreased the FLAV values.In the case of ANTH, the control treatment had more accumulation of anthocyanin in leaves (0.06), whereas fertilized plots had much lower ANTH values at DC37.At DC65, ANTH values increased due to the commencement of senescence.ANTH values ranging from 0.04 to 0.11 were recorded at DC65, depending on nitrogen doses.
Regarding the transformation energy potential of PS-II (Fv/o), the highest value was recorded at DC37 with the application of 250 kg N/ha, while plots without nitrogen recorded the minimum Fv/o value of 3.3 (Fig. 6).The Fv/o value increased with the dose of nitrogen but was not significantly different among N rates from 100 to 200 kg/ ha.At DC37, the application of 250 kg N/ha resulted in non-significant photochemical efficiency (Fv/m) with all nitrogen doses except 50 or 0 kg N/ha.The plots without nitrogen treatment recorded the minimum Fv/m value of 0.77 at DC37 (Fig. 6).

Economics
The maximum gross return ($2271.8/ha),net return ($1545.0/ha)and B:C ratio (3.1) were observed with the Fig. 6 Effect of nitrogen levels and management practices with or without CA on physiological parameters application of 200 kg N/ha with CA (Fig. 7).The use of CA with 150 kg N/ha was non-significant compared to the previous case, but still resulted in a significantly higher return than all other N levels.Additionally, the use of CA with 150 kg N/ha resulted in a 6.9% cost saving over conventional tillage at the same fertility level.The application of 250 kg N/ ha not only increased the cost of cultivation, but also yielded less net income due to a decrease in yield caused by lodging.The cultivation of high-yielding wheat varieties without nitrogen resulted in a B:C ratio of 0.8, causing a loss.If, this saving is extrapolated to 13.7 m ha of rice-wheat area in South Asia then it comes out to be $727.88 million annually.Additionally, if additional net return from 200 kg N/ha application under CA over farmers practice is extrapolated to same area then it comes out to $3.32 billion annually, which is huge amount.

Relationship Between Nitrogen Level and Physiological Parameters
Biomass yield increased more rapidly over grain yield with increasing fertilizer levels up to 200 kg N/ha application and there after decreased owing to lodging (Fig. 8).NDVI values in leaves were significantly affected by N fertilization at developmental and reproductive stages.NDVI generally increased with increasing N fertilization and found highly positively correlated with N fertilization.NDVI, CT, SPAD and NBI were having higher slope at vegetative stage (DC37) over to reproductive stage (DC65) indicating that these physiological indices depend on N content of the leaf.In contrast, the transformation energy potential of PS-II (Fv/o) showed positive trend with increasing levels of N whereas photochemical efficiency (Fv/m) was independent of N levels.FLAV displayed negative trend with increasing doses of N at both stages and more sharply at vegetative stage (DC37).

Correlation Between Grain Yield and Physiological Parameters
Grain yield recorded at varying nitrogen doses under conventional and conservation tillage have showed highly positive and significant correlation with NDVI (0.886), SPAD based CCI (0.813), NBI (0.725), Fv/m (0.713), Fv/o (0.754) and LAI values (0.768) at DC37 growth stage (Fig. 9).Whereas grain yield was negatively and significantly correlated with FLAV (− 0.810) and ANTH (− 0.705) values at DC37.These parameters are good indicator of nitrogen status in the plants either nitrogen stressed or adequate.The correlation of grain yield with these physiological parameters decreased at DC65.Canopy temperature also negatively correlated with the grain yield but have not showed the stronger relationship with the grain yield.These parameters can be best fitted in wheat for precise nitrogen management.

Discussion
Nitrogen is the most limiting plant nutrient that affects the growth and development of wheat (Wang et al., 2015).Under the rice-wheat cropping system, retention of previous crop leftovers can build better agro-ecosystems by retaining moisture, suppressing weeds, and providing nutrients through slow decomposition (Chaudhary et al., 2019;Kumar et al., 2023).CA in wheat crop has increased growth and yield (3.8% at 150 kg N/ha and 9.6% at 200 kg N/ha) compared to without CA (150 kg N/ha).This increase can be attributed to the slow provision of nutrients by rice leftovers to wheat and moisture retention in the rhizosphere during later stages of increased minimum temperature.These results are supported by (Ali et al., 2016;Korav et al., 2022;Mandal et al., 2004).An earlier study under the rice-wheat system showed that CA increased wheat grain yield by 5.4% compared to non-CA at 150 kg N/ha application (Tripathi et al., 2015).Due to the sandy loam texture and poor fertility condition of the soil, it responded well to increasing fertilizer N application.Wheat growth attributes and yield increased in N-fertilized plots compared to no-N plots (Sahoo et al., 2022).Crop yield increased with an increase in nitrogen dose up to a point, but after that point, the increase in yield is negligible.Application of either 200 or 150 kg N/ha in combination with CA can contribute effectively to improving wheat grain yield.Crop leftovers decay slowly over the growing season, releasing nutrients that improve plant growth and increase yield.Roozbeh and Rajaie (2021) and Ali et al. (2016) reported that the rate of applied nitrogen can be decreased under an effective residue management strategy, reducing the risk of N losses and improving wheat grain yield (Ali et al., 2003;Belete et al., 2018;Kubar et al., 2021).The increase in the nitrogen dose to 250 kg/ha resulted in lower grain yield, even though all growth, physiological indices, and yield attributing characteristics were higher.This was due to lodging of wheat caused by application of nitrogen beyond the optimum, which raised plant height and the weight of the upper section of the plant and thus caused yield loss (Liu et al., 2005;Wu et al., 2019;Zhang et al., 2014Zhang et al., , 2017)).Higher N application without CA practices also leads to lodging of the wheat, which ultimately reduced grain yield by 8.9% (Tripathi et al., 2004(Tripathi et al., , 2005)).
Three different optical instruments, namely Green-Seeker, SPAD meter, and Dualex meter, were used to diagnose wheat N status at varying N fertilization rates, with or without CA.NDVI values and CCI were positively correlated with nitrogen application rates in wheat.An increase in the application of nitrogen from zero to higher dosages eventually resulted in an increase in chlorophyll content and subsequently higher grain yield due to higher Fig. 9 Correlation between grain yield and physiological parameters uptake by roots.To achieve the ideal leaf N content and soil accessible N status for increasing grain production, improving SPAD values at critical stages (active tillering, earhead initiation, and flowering) may be helpful (Ecarnot et al., 2013;Ghosh et al., 2020).NDVI values were also positively correlated with nitrogen application.As the rate of nitrogen application increased from zero to the maximum, the NDVI values also increased due to the increase in greenness, leaf area index, and vigorous growth of wheat (Ali, 2020;Ali and Ibrahim, 2020;Kaur et al., 2018).According to Sulochna et al. (2019), GreenSeeker sensor-based N management increased fertilizer N use efficiency while producing wheat grain yield comparable to that seen with the recommended suggestion.Dualex-based Nitrogen Balance Index (NBI) also showed a similar trend of results, like CCI and NDVI values.NBI seems to be a good reflector of leaf N status in wheat at the early as well as later stages of growth.It is positively correlated with applied nitrogen doses due to enhanced nitrogen uptake by roots, which increases chlorophyll content and photosynthesis efficiency of plants.These results are in conformity with Song et al. (2022) and Cartelat et al. (2005).As the Dualex meter is seldom used, the values of flavonoids and anthocyanin showed a negative correlation with applied nitrogen doses in wheat.The values of flavonoids reflected greater in the initial growth stages, so they can be utilized for need and time-based nitrogen application in the future.The values of flavonoids were higher at low application rates of nitrogen, which might be due to phenylalanine development due to the restriction of protein synthesis under stress conditions, i.e., nitrogen deficiency in wheat (Awad & de Jager, 2002;Ibrahim et al., 2011).Anthocyanin values reflect the nitrogen status in complete arrival of stress conditions, so more accurate scientific evaluation of this parameter is needed.Sensor based physiological tools viz., NDVI, CCI and Dualex meter have showed strong and significant correlation with grain yield of wheat for different nitrogen status of plants.Studies by showed highly correlation of SPAD readings (Akhter et al., 2016;Islam et al., 2014), NDVI values (Sultana et al., 2014), Dualex based NBI, FLAV and ANTH values (Tremblay et al., 2010) with grain yield to assess the nitrogen status in plants.These have shown reliable indication of nitrogen stress and strong relationship to the relative yield (Kizilgeci et al., 2021;Tremblay et al., 2010).Higher net returns can be obtained by reducing excessive expenditure on cultivation practices, including tillage, residue management, and blind application of nitrogen.CA in wheat has shown cost advantages over conventional tillage by Sapkal et al. (2019) and Keil et al. (2020).Optimization of the nitrogen level for conventional as well as novel cultural practices is also necessary to fetch maximum monetary output.So, the application of 150 or 200 kg N/ha is economically sound under CA practice for high-yielding varieties.Nitrogen doses beyond 150 or 200 kg/ha were found to be uneconomical by Kumar and Singh (2018) and Sommer et al. (2014).

Conclusion
After 2 years of experimentation, it can be concluded that the application of 200 kg N/ha under CA in wheat is the most beneficial option for growers.As residue burning is a major concern in the Indo-Gangetic Plains of India, the use of 200 kg N/ha under CA not only yields the highest productivity but also helps to maintain agro-ecosystem sustainability.For high-nutrient-responding varieties such as DBW-222, farmers can opt for 200 kg N/ha along with CA to achieve maximum grain yield with reduced costs.The highest net returns and B:C ratio can be achieved by applying 200 kg N/ha with CA.The long-term effects of applying 200 kg N/ha under CA need to be evaluated from a sustainability perspective.For resource-limited farmers, applying 150 kg N/ha under CA is also a good option in terms of productivity and economics.While SPAD meterbased CCI and GreenSeeker-based NDVI are frequently used in wheat, the use of the Dualex meter (which measures NBI, FLAV, and ANTH values) has been explored to a lesser extent.Based on the results, further exploration of the Dualex meter for precision nitrogen management in wheat is recommended.

Fig. 1 Fig. 2 Fig. 3
Fig. 1 Location and layout of experimental trial at resource management farm of ICAR-IIWBR, Karnal

Fig. 4
Fig. 4 Instruments used for recording of physiological parameters

Fig. 5
Fig. 5 Effect of nitrogen levels and management practices with or without CA on growth, yield attributes and yield.RRR Rice residue retention

Fig. 7
Fig. 7 Effect of nitrogen levels and management practices with or without residue retention on economics