Nitrogen Gradient Optimization with Kharif Legumes on Agronomic Parameters in Zero-till Rabi Maize

With the advancement in developing countries, use of cereal-cereal system had reached the threshold levels of production further leading to deteriorating the soil fertility. With the population growth in an exponential way adopting the age-old practises leading to downfall of the production potential (Ammaji et al., 2022). So, in context to maize cropping system demands substantial nitrogen fertilizer inputs, posing challenges for resource-constrained farmers due to high costs and limited accessibility (Sravanthi et al., 2016). The energy-intensive production of nitrogen fertilizers further raises concerns about the sustainability of such farming practices (Yadav et al., 2017).
 
Maize possesses broad adaptability and thrives across varied soil and climatic conditions, making it a prime choice for cultivation alongside different crops within various agricultural settings (Bharathi et al., 2015). Its C4 nature, coupled with rising demand in livestock and processing industries, further solidifies its status as a viable substitute.

Maize [Zea mays (L.) Merrill] stands as a versatile crop, holding the third position in terms of importance in India, following rice and wheat. Its cultivation spans over 14.34 lakh hectares, yielding a production of 224.82 lakh tonnes with an average productivity of 2965 kg ha^-1. This contributes significantly, constituting 8% of the national food basket (Directorate of Economics and Statistics, Government of India, 2023). In the Telangana State alone, during the 2023-2024 period, maize cultivation covered an area of 4.10 lakh hectares, resulting in a production of 9.95 lakh tonnes, with an impressive productivity rate of 5730 kg ha^-1.
 
Crop rotations, a key aspect of diversified sustainable agriculture, often incorporate legumes for their nitrogen-fixing capacity (Meena et al., 2011). These rotations i.e. Legume-based cropping systems (LCS) are considered instrumental to sustainable intensification in small-holder systems with multiple ecological, social and economic benefits (Monika et al., 2022). Legume crops can fulfil 80%-90% of their N requirements during one crop season from this biological nitrogen fixation and transfer 0%-70% of this biologically fixed N to the succeeding crops (Sikka et al., 2022 and Parihar et al., 2016).
 
Leftover legume residues in cereal systems provided added benefits to nutrient status and improved plant and soil architecture. The combination of added residues and zero-tillage balanced input credit loads with output productivities, fostering soil microbial fauna (Shukla et al., 2021 and Hailemarian et al., 2021). So, with this knowledge of thought and added source of information we further highlighted our research line with the suitable legume- maize cropping system with added nitrogen gradient levels and residual retention in irrigated conditions.

The present experiment was carried out at Maize Research Centre, Agricultural Research Institute, P.J.T.S.A.U, Rajendranagar, Hyderabad during kharif and rabi seasons of two years i.e. 2021-22 and 2022-23. The farm is geographically situated at an altitude of 542.3 m above mean sea level at 17°19' N latitude and 78°23' E longitude in the Southern Telangana Agro-Climatic Zone of Telangana State and it falls under Semi-Arid Tropics (SAT) according to Troll’s classification. Ideal weather conditions prevailed during the crop season for the legume-maize sequence, with temperatures at a normal range (12.60 to 33.20°C), consistent rainfall of 878.54 mm and sufficient sunshine (0.9 to 10 hours day^-1) in both years. The experiment was planned in a split-plot design with 6 main-plots and 3 sub-plots which consisted of C₁N₁: _{groundnut100% RDN}- maize, C₁N₂: _{groundnut75% RDN-} maize, C₂N₁: _{soybean100% RDN}- maize, C₂N₂: _{soybean75% RDN}- maize, C₃N₁: _{greengram100% RDN}- maize, C₃N₂: _{greengram75% RDN}- maize cropping systems and sub-plots: F₁: 100% RDN, F₂:125% RDN, F₃:150% RDN in rabi respectively during two years.
 
Kharif legumes viz. (groundnut, soybean and greengram) were sown on June 25^th with spacing 30 cm x 10 cm and subsequently rabi maize was sown on 25^th September after harvest of greengram and 23^th October in case of soybean and groundnut as sequence crop under zero-tillage conditions with mechanical planter in both the years of 2021-22 and 2022-23. However, the spacing followed for rabi maize was 60 cm x 20 cm with recommended doses of 80 P₂0₅ and 80 K₂0 kg ha^-1 respectively were applied at basal, along with varied levels of nitrogen as per the treatments in both years. Need based management practices were adopted for both legumes and maize during the crop growth period. The recommended dose of nitrogen applied for groundnut, soybean and greengram during kharif are 20, 60, 20 and 240 kg ha^-1 for rabi maize respectively.
 
Plant height was recorded from 5 randomly selected plants at harvest by measuring from the base of the stem (ground level) to the top most node in Maize. Leaf area from five destructively sampled plants was measured at regular intervals using the LI-COR Model LI-3100 leaf area meter with transparent conveyor belt having electronic digital display and expressed in cm². SPAD reading was measured from five tagged plants of the net plot with the instrument CCM-200 plus chlorophyll content meter regular intervals by putting the leaf between the sensors of the instrument. Five plants were selected randomly from second row leaving the border rows were destructively sampled at respective intervals for all the crops for the estimation of drymatter production. The sun dried five cobs were weighed before shelling from each plot and after shelling grain weight was recorded separately. The ratio of grain to total weight of cob was expressed in percentage.   
 

 

 
From the net plot, cobs were picked, sun dried, threshed and cleaned separately for each treatment. Finally, the yield obtained from net plot was expressed on hectare basis as kg ha^-1. Grain yield of five tagged plants assigned for post-harvest observations were also added to the net plot yield. The statistical analysis of the data was performed in Split Plot Design and the representation of growth parameters were done by heat maps using r software. 

Plant height (cm)
 
In both years, zero-tillage maize following kharif greengram displayed notably taller plants, with heights ranging from 37.33 to 221.82 cm surpassing soybean and groundnut. Notably, when rabi maize applied with 150% RDN showed superiority followed by 125% RDN and 100% RDN. Further, the interaction effect at 60 DAS only was found significant (Table 1a and 1b).






 
At 60 DAS, significantly higher plant height was noticed in maize grown after greengram with 100% RDN in kharif and 150% RDN in rabi (129.95 and 131.35 cm) which is on par with 125% RDN in rabi (126.74 and 129.42 cm) followed by soybean. The improved plant height was ascribed due to retention of large quantity of greengram residues which favoured for the improved moisture and nutrient mobility status and enhanced decomposition and availability and thus, facilitated overall crop growth. Similar findings were reported by Kumar et al., (2015) and Baryal et al., (2019).
 
Leaf area (cm²)
 
Leaf area of succeeding zero-till maize was significantly higher when preceded by greengram with 100% RDN, compared to soybean and groundnut. Application of 150% RDN significantly increased leaf area in rabi maize across various growth stages compared to 125% and 100% RDN levels in both years.
 
The interaction was found significantly at 60 DAS, higher leaf area was noticed in maize grown after greengram with 100% RDN in kharif and 150% RDN in rabi (239.62 and 227.14 cm²) which was on par with 125% RDN in rabi (228.35 and 223.50 cm²) followed by soybean (Table 2a and 2b). This could be attributed due to higher cell division and elongation until vegetative phase, further decline in flowering. Further better synergistic effect of residual decomposition and nitrogen feasibility that supplemented the growth and development of the leaf. The finding was in tune of Singh et al., (2015) and Rao et al., (2014).

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Leaf chlorophyll content
 
Higher leaf chlorophyll content was observed in maize when grown after greengram with 100% RDN during 2021-22 and in 2022-23 respectively followed by soybean. In sequential rabi maize, the F₃ treatment (150% RDN) exhibited significantly higher leaf chlorophyll content compared to F₂ (125% RDN) in both years.
 
In 2021-22 and 2022-23 at 60 DAS, the interaction effect was found significant when prior greengram residues with 100% RDN in kharif and 150% RDN in rabi (48.45 and 47.70) which was onpar with 125% RDN (46.32 and 45.76). Lowest was noticed in groundnut with 75% RDN in kharif and 100% RDN in rabi (Table 3a and 3b). This might be due to the residual influence in collaboration of the nitrogen levels have positively correlated for the effective greenness of the leaves due to the higher photosynthates accumulation that further decreased due to lower doses of nitrogen. Familiar findings by Monika et al., (2022).

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Dry matter production (kg ha^-1)
 
kharif greengram residues showed significantly higher dry matter in 2021-22 (7788 to 21275 kg ha^-1) and 2022-23 (7542 to 20443 kg ha^-1) over soybean and groundnut. With varied nitrogen levels, significantly higher dry matter production when 150% RDN was applied over other treatments (Table 4). The interaction effect was found to be significantly at 60 DAS only. Thus, the effect of greengram residues @ 100% RDN in kharif and 150% RDN on rabi maize had significant higher dry matter production (16473 and 16299 kg ha^-1) but was onpar with greengram residues @100% RDN in kharif and 125% RDN on rabi maize (15754 and 15287 kg ha^-1) (Table 4a). Enhanced dry matter production in growth stages due to nutrient availability in key developmental phases and lower C:N ratio hasten the decomposition helped for effective accumulation of root-shoot biomass. Similar finding were reported by Mercy et al., 2012 and Onwonga et al., (2017).

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Shelling percentage (%)
 
Greengram with 100% RDN had significantly higher shelling percentage in rabi maize, followed by soybean and groundnut. Further 150% RDN in rabi maize was significantly higher, while 100% RDN showed lowest in two years. Apart, interaction was non-significant. Varied nitrogen fertility, combined with residue retention, reduced nutrient losses, enhancing cob weight and development for improved shelling percentage. Finding were inline with Laxmi et al., (2022) (Table 5).

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Grain yield (kg ha^-1)
 
During 2021-22 and 2022-23, residues of kharif greengram with 100% RDN recorded significantly higher grain yield with a tune of 8-9 % than greengram with 75% RDN, 11-14% with 100% and 17-20% with 75% RDN of soybean. Significantly lowest grain yield was recorded with groundnut at 75% RDN with tune of 32-34%. Addition of 150% RDN to rabi maize registered significantly higher grain yields followed by 125% RDN with a tune of 6-9% and lowest with 100% RDN with a tune of 18% was represented in Fig 1.


 
The interaction revealed that, maize grown after kharif greengram with 100% RDN followed by 150% RDN in rabi maize recorded significantly higher grain yields (9799 and 9704 kg ha ha^-1) but was onpar with 125% RDN in rabi maize (9386 and 9276 kg ha^-1) and significantly lowest kernel yields registered with groundnut at 75% RDN and 100% RDN in maize (6148 and 6001 kg ha^-1) respectively in two years.
 
Enhanced grain yields attributed to increased biomass and quicker decomposition of greengram residues, providing ample nutrients for rabi maize. Under zero-till conditions, minimal soil disturbance and nitrogen immobilization likely contributed to maize’s heightened response to higher nitrogen levels, with 250% and 225% levels showcasing superior performance in yield. Similar findings quoted by Ndiso et al., (2018) and Monika et al., (2022) (Table 5a and 5b).

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Stover yield (kg ha^-1)
 
During 2021-22 and 2022-23, the greengram residues with 100% RDN in kharif recorded significantly higher stover yields than 75% RDN followed by soybean and groundnut in zero-till rabi maize sequence. With application of 150% RDN in zero-till maize registered significantly higher stover yields than 125% RDN and 100% RDN in two years of study. However, the interaction effect was found significant. Further stating that maize when grown after kharif greengram with 100% RDN followed by 150% RDN in rabi maize recorded higher stover yields but was onpar with 125% RDN.
 
The preceding greengram residue with 100% RDN contributed to higher dry matter accumulation and exhibited a positive N x K synergetic effect, enhancing stover biomass during both vegetative and reproductive stages. (Table 5c and 5d). Findling inline with (Shafi et al., 2007 and Hailemariam et al., 2021). 

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The study revealed that the cropping sequence of greengram as preceding legume in kharif followed by zero-till maize in rabi showed significant results in terms of growth parameters and yield. Specifically, nitrogen levels at a recommended dose of 100% in kharif and 150% in rabi exhibited the superior performance, followed closely by 100%-125% RDN and 75% -150% RDN. This suggests that a balanced approach, with reduced nitrogen in the preceding season but higher doses with legume residue retention, significantly enhances crop growth phenology as well as productivity during the both years.

I greatly acknowledge the Professor Jayashankar Telangana State Agricultural University for fulfilling my Doctoral research.
 

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this manuscript.