Analysing Root Architecture and Nutrients Uptake in Zero-till Rabi Maize with Kharif  Legumes and Nitrogen Gradient Levels

In contemporary agriculture, the primary objective is to enhance food production sustainably, while minimizing environmental impact. The global practice of intensive mono-cropping, particularly in cereals, has indeed increased staple crop production but has also disrupted ecological balance, leading to issues like pollution and resource overexploitation (Srivastav et al., 2021; Shah et al., 2003).
       
Maize, the “Queen of Cereals”, plays an important role in the worldwide agricultural economy, ranking third among cereals behind rice and wheat. Its agility, heavy feeder, cost-effectiveness and nutritional importance for both humans and animals make it a key crop (Tiwari et al., 2022). Legumes in cropping systems appear to be a promising answer from both an environmental and economic standpoint. This integration not only improves soil nitrogen levels but also decreases reliance on inorganic fertilizers (Rahman et al., 2014). Growers may make a major contribution to indigenous nitrogen generation by growing legumes, which are natural nitrogen factories in the field. Furthermore, root architecture is very important to above-ground development and yield production, specifically nutrient absorption and use efficiency and tolerance to adversity (Postma et al., 2014). While the root system and canopy compete for energy and nutrient resources (York et al., 2013), they also maintain the dynamic balance and development of plant growth (York et al., 2015 and Chimungu et al., 2014). Thus, it is essential to study root morphological characteristics and mechanisms of how N application rates regulate the root morphology in maize. Root characteristics are essential to root growth and their distribution significantly influences the uptake of nutrients and soil moisture (Liu et al., 2019), which directly affects crop growth and development (Li et al., 2019).
       
Root morphological characteristics are closely related to root absorption, assimilation and transport to above-ground plant parts. The root system includes root length, lateral root branching, root occurrence, three-dimensional distribution in space, root growth angle, root growth and available soil water (Wang et al., 2020; Mu et al., 2015). Nitrogen (N), aside from roots, is the most crucial nutrient for crop growth and increasing grain output and over use of artificial fertilizers has contributed significantly to agricultural yield increases (Lynch et al., 2013; Zhao et al., 2018). N-efficient maize varieties have much more underground nodes, longer length and developed cortical ventilation tissue, which are beneficial to absorb more nitrogen from the soil. (Peng et al., 2010; Kishore et al., 2025; Sinha et al., 2018; Makwana et al., 2016).
       
Therefore, understanding the relationship between root architecture and above-ground growth, productivity and N absorption may improve N use efficiency that might increase grain yield (Jia et al., 2018; Lodha et al., 2021). The purpose of the study is to determine how kharif legumes affect the morphology of the roots and the uptake of nutrients by the plants in rabi maize.

In the years 2021-2022 and 2022-2023, the experimental research location is situated at MRC-ARI, Rajendrangar, Hyderabad. The trail farm is located at 542.3 meters above sea level, with latitude 17^o19^oN and longitude 78^o23^oE. It lies in the Southern Telangana Agro-Climatic Zone and is categorized by Troll as Semi-Arid Tropics.
       
Climate conditions were suitable for crop growth throughout the course of the two years, with mean minimum temperatures ranging from 12.6^oC to 21.2^oC and mean maximum temperatures ranging from 26.3^o to 33.2^oC. During the crop-growing season in both years, the optimal rainfall (878.54 mm) and sunlight hours (0.9 to 10 hours day^-1) were noted.
       
The research was organized in a split-plot design with 6 main-plots which includes C₁N₁: groundnut_100% RDN-maize, C₁N₂: groundnut_{75% RDN}-maize, C₂N₁: soybean_100% RDN-maize, C₂N₂: soybean_75% RDN-maize, C₃N₁: greengram_100% RDN-maize, C₃N₂: greengram_75% RDN-maize cropping systems and 3 sub-plots: F₁: 100% RDN, F₂:125% RDN, F₃:150% RDN in rabi respectively during two years. Legume crops (groundnut, soybean and greengram) were planted on June 25th of the kharif season with a 30 cm x 10 cm spacing in both years.
       
In 2021-2022 and 2022-2023 respectively, zero-till conditions were used to plant rabi maize on September 25^th and soybean and groundnut on October 23^rd, after the greengram harvest. The maize crop was planted with a 60 cm x 20 cm spacing and fertilized with 80 kg ha^-1 of phosphate and potash as a base dose.
       
The prescribed nitrogen was applied in various levels based on the treatments. For groundnut, soybean and greengram, the required nitrogen dosages during kharif are 20, 60, 20 and 240 kg ha^-1 for rabi maize, respectively.
       
Weedicides and pesticides were used based on necessity, assessing crop damage and field circumstances. A statistical study of the legume-maize system data with nitrogen levels in split-plot design was carried out using SPSS software to compare the data and examine it for treatment interactions.
 
Root length and root volume
 
Root length and root volume of respective crops viz., greengram, soybean, groundnut during kharif and maize during rabi were recorded at 30, 60, 90 DAS from the five plants pulled out of the gross plot with residual soil moisture. Root volume was assessed using water displacement method and results were expressed in cm3. Root length was measured using meter scale and expressed in cm.
 
Root dry weight
 
Root dry weights were determined at 30, 60 and 90 DAS, when the representative plant samples are harvested at the soil surface level with a core sampler of 7.0 cm in diameter by 80 cm deep which was designed for two-person operation. The roots were separated from the soil and washed. The roots were dried at 75^oC to obtain constant weight and weighed in grams.
 
Plant samples
 
The crop samples collected at different intervals were sundried for 2 days and then dried in hot air oven at 60^oC to a constant weight were used for analysis after grinding by using the Willey mill and this powder was used for estimation of N, P and K content.
 
Nitrogen uptake (kg ha^-1)
 
Firstly, the nitrogen content (%) in the plant was estimated by micro Kjeldhal method using Kelplus N analyser after digesting the samples with H₂SO₄ and H₂O₂ (Piper,1966). The uptake was calculated by the formula:

   

 
Phosphorus uptake (kg ha^-1)
 
The tri-acid (HNO₃, HClO₄ and H₂SO₄) in the ratio of (9:3:1) respectively digested plant were analyzed for phosphorus content by Vanado-molybdo phosphoric acid. The intensity of yellow colour developed was measured by using spectrophotometer at 420 nm (Piper, 1966). Finally, the uptake was calculated by the formula:
                

  

 
Potassium uptake (kg ha^-1)
 
Potassium content in the tri-acid was determined with flame photometer (Piper, 1966). The uptake was calculated by formula:
 

Root parameters
 
The root metrics (root length, root dry weight and root volume) during crop phenophases of the zero-till rabi maize sequence were influenced by nitrogen doses and prior legume residues in both years of study (Table 1, 2, 3 and Fig 1).



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According to data obtained from 30, 60 and 90 DAS and at harvest, greengram 100% RDN as kharif, followed by rabi maize, demonstrated significantly longer root length, dry weight and volume than greengram 75% RDN, soybean and groundnut (75 and 100% RDN). In terms of nitrogen levels, 150% RDN also showed noticeably higher root length, dry weight and volume than 125% and 100% RDN.

Furthermore, the interaction between legume residues (kharif) and nitrogen gradient levels (rabi) was found non-significant.
       
Additionally, the covering of legume wastes on the ensuing maize fields improved the availability of soil moisture and even decreased the volatility of phosphate and nitrogen, which allowed the root to develop morphologically till harvest (anchorage, elongation and breadth dimensions). Similar results from Choudhary and Behera (2014); Kumar et al., (2015); Singh et al., (2022) and Karunakaran et al., (2014).
 
Nutrient studies
 
The nitrogen gradient levels at 30, 60, 90 DAS and at harvest on zero-till rabi maize during the two years of the study, as well as the preceding kharif legume, affected the nutrient studies, specifically the N, P and K uptake (Table 4,5 and 6).






       
The results suggested that, among the different kharif legume crops, rabi maize absorbed more nitrogen, phosphorus and potassium from greengram residues at 100% RDN than from greengram residues at 75% RDN, soybean and groundnut. Furthermore, compared to lesser dosages (125 and 100% RDN), the application of 150% RDN in no-till rabi maize resulted in increased plant uptakes (N, P and K), whereas the association between the nitrogen gradient levels and kharif legumes was not significant in 2021-22 or 2022-23 at any of the crop stages.
       
The synergistic effect of green gram residues combined with nitrogen application enhanced nutrient assimilation, mobilization and translocation from source to sink, promoting efficient biomass accumulation and dry matter production in rabi maize. These results agreed with those of Wortmann et al., (2011); Gantayat et al., (2021); Roshan et al., (2013); Mauriya et al., (2024); Meena et al., (2011) and Usman et al., (2013).
 
Yields study
 
Studies on nitrogen, phosphorus and potassium uptake in zero-till rabi maize show that root morphology synergistically enhances crop growth during the critical tasseling and silking stages. This enhancement led to yields beyond the potential and resulted in higher residual biomass, as observed with kharif greengram. These were in-line with Sairam et al., 2024 (Table 7, Fig 2, 3, 4 and 5).





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The research trial demonstrated that applying 100% RDN to greengram followed by 150% RDN to maize in the rabi season significantly enhanced residue decomposition and stimulated robust root proliferation. This nutrient management approach improved nutrient mobility and accumulation in above ground plant tissues across key phenological stages (30 DAS to harvest) over two consecutive years, highlighting its potential to optimize crop nutrient dynamics and productivity.

The authors duly acknowledge the partial support received by Professor Jayashankar Telangana State Agricultural College, Rajendranagar, Hyderabad. Our sincere thanks are due to Head and Principal Scientist, ARI, Maize Research Centre, Rajendranagar, Hyderabad for their advice and support.

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.