Dry Matter Accumulation and Physiological Growth Parameters of Maize as Influenced by Different Nutrient Management Practices

Maize plays an important role in food security in the world (Maitra et al., 2019). In India, maize is cultivated in wide range of agroclimatic conditions (Panda et al., 2021). Maize produces a large volume of biomass including economic yield within a short period of time. Proper vegetative growth of the crop and conversion of dry matter into seed yield is important physiological phenomenon to obtain a good productivity.
       
The above ground DMA is directly related to the quantity of grain yield production (Sairam et al., 2021). To contribution of dry matter to grain yield was up to 70%, indicating the vital role of DMA in grain filling and higher productivity (Rivera-Amado et al., 2019; Liu et al., 2021).  The DMA is mainly dependent on the potential of the genotype and agronomic practices. The leaf area index (LAI) is a genotypic character which can affect the DMA (Rivera-Amado et al., 2019). Among the agronomic management practices, the nutrient management can affect the DMA in a large extent (Sairam et al., 2020). Nutrient management in cereals can be well optimized by observing the crop demand and supply during critical stages of the crop based on site-specific management. Balanced nutrient application can increase the DMA and source to sink ratio; hence, enhances the overall leaf area and photosynthetic rate (Sagar et al., 2021).
       
The maize hybrids, presently cultivated in India, are nutrient responsive and nutrient uptake which ultimately enhances the biomass production (Szulc et al., 2021). Maize hybrids can produce huge leaf area and canopy, thereby, allocating the photo assimilates to different parts of the plants including grain at different growth stages (Midya et al., 2021). In this context, application of optimum nutrients with more specific application of nitrogen through real time crop requirement can enhance the growth and productivity of the crop. Application of nutrients by site specific approach can be managed through sensors like chlorophyll content meter and decision support systems like nutrient expert (Singh et al., 2021).
       
Considering the above, there is a need to assess the DMA of maize at different growth stages and the response of the crop towards different nutrient management practices with a special emphasis to nitrogen application (Zewide et al., 2023). In maize hybrids, nutrient management has a significant impact on both growth and yield of the crop (Midya et al., 2021). The quantification of the growth can be calculated by using different physiological growth indices such as leaf area index (LAI), crop growth rate (CGR), relative growth rate (RAR) and net assimilation ration (NAR) (Azeem et al., 2015). These physiological indices can clearly show the photosynthates produced per unit area in a time interval and thereby, calculate the actual amount of stored dry matter in the plant parts (Azeem et al., 2015). By analyzing the physiological growth indices, the DMA can be assessed in a better way for quantifying the production of biomass and yield. Based on the above, the present study has been planned to assess the influence of nutrient management on growth parameters, relationship between DMA of maize and LAI and the role of physiological growth indices in quantifying the growth rate of maize.

The study was conducted during rabi season for two consecutive years (2021-2022 and 2022-2023) at the P. G. Research Farm of Centurion University of Technology and Management, Odisha, India (18^o48'18"N and 84^o10'45"E). The cropping period was 20^th November to 20^th March in 2021-22 and 15^th November to 17^th March in 2022-23. The agrometeorological data was collected from the Meteorological Observatory, Centurion University of Technology and Management. The mean maximum temperature varied from 27^oC-37^oC and 28^oC-36^oC during both the years, respectively. The mean minimum temperature for two years ranged from 12^oC-23^oC and 14^oC-21^oC respectively. The mean maximum and minimum relative humidity ranged from 88%-96% and 39%-80% for 2021-22 and 79%-91% and 37%-68% during 2022-23, respectively. The crop received 145.9 mm and 71.8 mm rainfall during both the years, respectively. The mean bright sun shine hours recorded/day was between 7-9 hrs/day. The soil was sandy loam and the chemical properties of the initial soil are mentioned in Table 1.
 

       
The experiment was laid out in randomized block design. The treatments were, T₁: well fertilized N, T₂: recommended dose of fertilizer (RDF), T₃:125% RDF, T₄:75% RDF, T₅: 150% RDF, T₆: RDF + nano urea, T₇: 75% RDF + nano urea, T₈: leaf colour chart (LCC) 4-based nitrogen management, T₉: LCC 5-based nitrogen management, T₁₀: sufficiency index(SI)-based nitrogen management at SI 85-90%, T₁₁: SI-based N management at SI 90-95% T₁₂: nutrient expert (NE) based nutrient recommendation for targeted yield of 7t/ha, T₁₃: nutrient expert based nutrient recommendation for targeted yield of 9t/ha and T₁₄: control. The details of the treatments are mentioned in Table 2. The dent corn hybrid Pioneer P3396 was considered for the experiment during both the years. The net plot size for each treatment was 6.2 m × 4.8 m which was replicated thrice.


       
The DMA and leaf area were collected at 20 days interval during both the years and the physiological growth indices, namely, LAI, CGR, NAR and RGR were calculated by the equations provided by Williams (1946) and Watson (1947). The data was statistically analysed by using analysis of variance (ANOVA), standard error of means (S.Em. ±) and critical difference (C.D.) at 5% probability level of significance (Gomez and Gomez, 1984). Further, the Excel software (Microsoft Office Home and Student version 2021-en-us, Microsoft Inc was used for statistical analysis.

Dry matter accumulation
 
The highest DMA was noted at harvesting and there was a gradual increase in DMA from 20 days after sowing (DAS) to harvest as noted during both the years (Table 3). The highest DMA during all the growth stages of maize was observed in ample dose of nitrogen application (T₁). At 20 DAS, the treatment T₅ (150%RDF) recorded significantly at par DMA with ample dose of nitrogen application (T₁); however, at 100 DAS and harvest the treatment T₅ and T₁₁ (SI-based N management at SI 90-95%) remained on par with T₁ during both the years. Some other precision nutrient management practices such as LCC and NE were also performed marginally well when compared with 100 % RDF and other treatments. The results showed the significant role of nitrogen in attaining maximum DMA of maize. Application of ample N might increase the nutrient availability and uptake and maintained better canopy. Further, split applications of N through SI-based nutrient management practice resulted in a promising effect on DMA. The results are similar with the findings of Zhang et al., (2023), Liu et al., (2023) and Mohapatro et al., (2021).
 

 
Leaf area index
 
The LAI of maize was increased from germination to 60DAS and later gradual decrease was observed due to senescence of older leaves towards maturity (Table 4). The highest leaf area in all the growth stages was recorded in ample dose of nitrogen application (T₁); whereas, the lowest leaf area index was observed in control (T₁₄). At 20 DAS, the treatments T₅ and T₁₁ performed well and remained statistically at par with T₁; whereas, the remaining treatments did not perform well during initial stages of growth. During the peak growth stage at 60DAS, the maximum LAI was observed with the treatment T₁ and some other treatments such as T₅ (150%RDF), T₁₁ (SI-based N management at SI 90-95%), T₂ (125%RDF) and T₉ (LCC 5) remained on par with T₁. During the harvest, the LAI was decreased to a higher extent and the maximum LAI was observed in T₁. Moreover, the treatment T₁ remained on par with T₅ and T₁₁. The application of sufficient nitrogen and optimum phosphorous and potassium resulted in obtaining higher leaf area. Also, the timely application nitrogen by using precision tools enhanced the leaf area compared to 200% nitrogen application. The results are confirmatory with the findings of Cao et al., (2021) and Swamy et al., (2022).
 

 
Crop growth rate
 
During both the years, at the initial growth stage of 20-40 DAS and 40-80 DAS, the maximum CGR was observed in T₅ (150% RDF) and during 60-80 DAS and 80-100 DAS, the treatment T₁ (ample dose of nitrogen) resulted in the maximum CGR (Table 5). At harvesting stage, the treatment T₁₁ (SI-based N management at SI 90-95%) recorded the maximum CGR. At the initial growth stage of maize, due do ample dose application of nitrogen and phosphorous and potassium together resulted in obtaining better CGR. However, during tasseling and silking stage, ample dose of nitrogen might result in better leaf area as well as a greater photosynthate assimilation. Increasing the nitrogen splits also improved the CGR of maize at later stage when nitrogen was applied through SI-based management, the CGR was improved than other treatments (Hu et al., 2023; Cao et al., 2021).
 
 

 
Net assimilation rate
 
The NAR revealed that there was a constant accumulation of dry matter from initial stage to grain filling (Table 6). However, a little increase in the NAR was recorded during 40-80DAS in all the treatments. During both years, at initial stages (20-40 DAS and 40-60 DAS), the treatment T₅ performed to show the NAR. Similarly, during 60-80DAS and 80-100DAS, the treatment T₁ produced the maximum NAR. At harvest, the treatment T₁₁ (SI-based N management at SI 90-95%) obtained the highest NAR during both the years. However, during all the growth stages for both the years, the lowest NAR was observed in T₁₄ (control) and T₄ (75%RDF) probably because of insufficient application of nutrients. The NAR followed a similar trend as it was noticed in the CGR and such results were obtained due to variation of growth and assimilates production as influenced by different treatments. The results corroborate with the findings of Azeem et al., (2015) and Cai et al., (2023).
 

 
Relative growth rate
 
The experimental data for both the years proved that the RGR of maize showed the highest values during 20-60DAS and there was a sharp decline in the RGR as the crop progressed towards maturity (Table 7). During the initial growth stage of 20-40DAS, the treatment T₁₃ recorded the maximum RGR and the minimum was noted with the treatment T₁ (ample dose of nitrogen). During 40-60 DAS and 60-80DAS, the treatments T₉ and T₃ obtained the maximum RGR for two consecutive years and the treatment T₁₄ as well as T₄ recorded the least RGR. However, during 80-100DAS and 100DAS to harvest, the treatment T₄ recorded the maximum RGR of maize. As the RGR a significant physiological index for determination of growth, the results clearly mentioned that the nutrient management practices had a significant impact on RGR of maize (Koca and Erekul, 2016).
 

 
Regression analysis of dry matter accumulation with leaf area index
 
The regression analysis of two-year mean data of DMA with mean data of LAI are plotted and presented in Fig 1. The LAI of maize had a direct proportion to total dry matter accumulation. The more the leaf area of maize, the higher the photosynthates assimilation resulting in higher dry matter production. The analysis showed that there was a moderate to strong correlation between the DMA and the LAI. The relation of the LAI and DMA was found to be strongly correlated during 20 DAS, 80 DAS, 100 DAS and harvest with a mean R2 value ranged from 0.75 to 0.86. However, during 40 and 60 DAS, the correlation was found to be moderate with a R² value of 0.69 and 0.71, respectively.
 

The present study revealed that various nutrient management practices played a significant role in growth as well as physiological indices of maize throughout the growing season. This experiment concludes that ample dose of nitrogen (200%N) along with optimum amount of phosphorous and potassium can be recommended for obtaining better growth and physiological indices in maize. Further, the split application of optimized nitrogen application through sufficiency index-based nitrogen management can also be considered to enhance crop growth rate and better leaf area index at later stage of maize, which may result in optimum grain filling and improved dry matter accumulation for enhancing productivity.