Agronomic Biofortification through Integrated Nutrient Management on Maize (Zea mays L.) Hybrids

Maize (Zea mays L.) is very popular due to its diverse functionality as a food source for humans and animals. In recent years, intensive cropping, imbalanced fertilization, changes in soil and climatic conditions have exacerbated deficiencies of micronutrients, especially Zn and Fe, in the soil-plant systems in many countries, thereby threatening human nutrition.
        
Recently escalated calls emerged towards micronutrient deficiency that greatly disturbs plant yield, quality and the health of domestic animals and humans. Iron (Fe) and zinc (Zn) are two heavy metal micronutrients playing vital roles in plants. Although present in soil, their availability to plant roots is limited because of complicated soil processes and conditions. By supplying plants with micronutrients, foliar spray improved yield, quality and macronutrient efficiency by 50%, besides higher absorption rate and cure deficiency symptoms. This can also be an effective method in biofortification in food crops. Micronutrient deficiencies are particularly prevalent in the rural population, where they mainly rely on a cereal-based diet as a staple food. The challenge, therefore, is to deliver nutritious, safe and affordable food to reduce the impact of nutritional insecurity. It is therefore of great interest to improve Fe and Zn nutrition in maize grains through soil-crop system management to improve food security and provide human health benefits.
        
As an alternative, agronomic biofortification, which consists of increasing the accumulation of target nutrients in edible plant tissues through fertilization, has been increasingly proposed in recent years as a simpler, short term approach to develop functional staple crops and address micronutrient deficiency.
        
The objective of this research was to evaluate the influence of agronomic biofortification through integrated nutrient management on maize hybrids under cauvery delta condition. The results from these experiments will be useful for providing guidance on agronomic practices aimed at improving the Fe and Zn nutritional qualities in maize grains in the field, thereby providing health benefits to humans.

A field experiment was conducted on sandy clayey loam soil during rabi season 2020-2021 at ICAR-KVK Farm, Hans Roever campus, Perambalur, Tamil Nadu, India (11.3°N, 78.9°E at an altitude of 124 meters above mean sea level). During the crop growing period, maximum and minimum temperatures were 33.4°C and 16.4°C. The total rainfall received during the crop growing period was 683.3 mm. 
        
The soil of the experimental field was alkaline pH (8.3), medium electrical conductivity (0.37 dSm^-1), low available N (235.2 kg ha^-1), medium available P (12.7 kg ha^-1) and medium available K (148.2 kg ha^-1). Maize QPM hybrid obtained from CIMMYT, Hyderabad and non-QPM (NK6668) was sown directly at a spacing of 60 cm × 20 cm under split-plot design (SPD) with 2 hybrids comprising of M1: Non-QPM, M2: QPM, as main plot and 6 nutrient level treatments (three replications each) comprising of S₁: 100% RDF through NPK, S₂: 100% RDF through FYM, S₃: 50% RDF through NPK + 50% RDF through FYM, S₄: S₁ + Iron and Zinc as foliar application @0.5% conc, S₅: S₂ + Iron and Zinc as foliar application @0.5% conc, S₆: S₃ + Iron and Zinc as foliar application @0.5% conc., as sub-plots.
        
The recommended dose of nutrients for maize hybrids (both QPM and non-QPM) was 150 kg nitrogen, 75 kg phosphorus and 75 kg potassium per hectare. The full amount of P₂O₅ and K₂O were applied as basal dose along with 50 per cent N and the remaining 50 per cent was top-dressed after 25 and 45 days after sowing (DAS). The N, P and K concentrations in organic manure used were 0.60, 0.20 and 0.50% in farmyard manure (FYM) and the required quantity as per the treatments was applied in the field before the last tillage operation on a dry weight basis. The net plot size was 5 m × 4 m. Ridges and furrows were formed at 60 cm intervals with bullock-drawn ridge former and rectification were done manually. Foliar application of 0.5 per cent FeSo₄ and ZnSo₄ as per treatments was done twice at active vegetative (45 days) and reproductive stage or grain filling stage (90 days), respectively with the help of a knapsack sprayer. All other standard agronomic practices were followed as per the schedule. 
        
The growth and yield attribute parameters were collected at harvest from randomly selected 10 plants. Grain and stover yield were recorded in kg ha^-1. The crude protein (%), starch (mg g^-1), Fe and Zn content in maize grain were recorded in mg kg^-1.
        
The data were subjected to analysis of variance technique as per the statistical procedure and the treatment means were compared at 5% level of significance.

Growth attributes
 
The data on growth attributes are presented in Table 1. It showed that the maximum plant height at harvest was observed with the nutrient level treatment S₆ in which 50 percent RDF through NPK + 50 percent RDF through FYM with Fe and Zn foliar application @0.5% Conc., helps to increase by 3.67% and 8.94% of plant height from S₁ and S₂ but statistically it was unaffected with all nutrient levels.
 

 
Among all treatments, maximum LAI was observed with S₆ was significantly higher than all other nutrient levels as 7.47% from S₁, 63.35% from S₂, 3.60% from S₃, 11.65% from S₄ and 18.55% from S₅.
        
The data revealed that among all nutrient levels higher DMP was observed under S₆ was significantly higher from all nutrient levels as 2.30% from S₁, 7.92% from S₂, 1.53% from S₃, 3.55% from S₄ and 4.50% from S₅. Better utilization of N with Fe and Zn spraying enabled the leaf area duration to extend and provided an opportunity for the plants to increase the photosynthetic rate leading to the higher accumulation of dry matter. Results were agreed with the study of Prasad and Naik (2013). 
        
The data revealed that among all nutrient levels early days were evident under S₆ with lower days taken to tasselling from all other nutrient levels as 1.85% from S₁, 6.25% from S₂, 2.50% from S₃, 0.85% from S₄ and 4.39% from S₅. The data showed that earlier days of silking were observed under S₆ with lower days taken to silking from all other nutrient levels as 1.90% from S1, 6.71% from S₂, 2.83% from S₃, 0.99% from S₄ and 5.06% from S₅.
 
Yield attributes
 
The data on yield attributes was presented in Table 1. It showed that among all the nutrient level treatments, the maximum cob length was recorded with S6 which was statistically higher than all other nutrient level treatments as 5.54% from S₁, 16.95% from S₂, 8.99% from S₃, 2.30% from S₄ and 11.42% from S₅.
        
The maximum cob girth was recorded from S₆ which was significantly higher among all nutrient level treatments as 7.51% from S₁, 24.60% from S₂, 11.52% from S₃, 4.77% from S₄ and 13.05% from S₅.
        
The data showed that among all nutrient level treatment, maximum grains row^-1 was observed with S₆ which was significantly higher than all other nutrient level treatments as 4.82% from S₁, 18.80% from S₂, 6.79% from S₃, 3.21% from S₄ and 9.48% from S₅. An increase in the number of grains row^-1 is attributed to the genetic potential of hybrids takes most advantage to withstand higher densities, availability of nitrogen and other nutrients from organic source with the presence of micronutrient fertilizers required for plant development up to cob formation. This corroborated the findings of Ahmad et al., (2017).  
        
The data presented revealed that among all nutrient level treatments the maximum number of rows cob^-1 was observed under S₆ which was significantly higher than all other treatments as 10.10% from S₁, 27.23% from S₂, 14.33% from S₃, 5.82% from S₄ and 19.78% from S₅.
        
The maximum cob weight was found from S₆ which was significantly higher among all nutrient level treatments as 2.81% from S₁, 7.24% from S₂, 4.24% from S₃, 1.76% from S₄ and 5.50% from S₅. It is prevalent, that cob may store the highest amount of food from green parts of plants which causes the increased weight of cob. The results were also in agreement with the findings of Maidul Hasan et al., (2018).  
        
The interactions of non-QPM hybrid with S6 nutrient level had a significant (P= 0.05) effect on plant height, leaf area index, dry matter production, days taken to 50% tasselling and days to 50% silking, cob length, cob girth, no. of grains row^-1, no. of rows cob^-1 and cob weight.
 
Yield
 
The data on yield components are given in Table 2. The highest shelling % were recorded under S₆ was significantly higher than all nutrient level treatments as 4.88% from S₁, 8.86% from S₂, 7.21% from S₃, 2.89% from S₄ and 8.11% from S₅.
 

        
The data proved that the maximum test weight was observed with the nutrient level treatment S₆ in which 50 percent RDF through NPK + 50 per cent RDF through FYM with Fe and Zn foliar application @ 0.5% Conc., contributes to an increase by 7.86% from S₁, 16.68% from S₂, 11.72% from S₃, 4.69% from S₄ and 14.06% from S₅. An increase in seed weight might also be due to the synergistic effects of combined fertilizers for better growth and grain filling of maize. This was in agreement with the finding of Admas et al., (2015).
        
The data represented that among all the treatments, the maximum grain yield was recorded with S₆ which was statistically higher than all other nutrient level treatments as 2.89% from S₁, 7.30% from S₂, 2.28% from S₃, 4.28% from S₄ and 5.57% from S₅. The mineral (Fe and Zn) foliar nutrition enhanced plant growth, total dry matter production and chlorophyll content as a result of better uptake of Zn and Fe and their translocation to reproductive parts. Such favorable crop growth enhanced the yield attributes and increased the yield ultimately (Kumar and Salakinkop, 2018).
        
The maximum stover yield was recorded from S₆ which was statistically higher among all other nutrient level treatments as 0.87% from S₁, 5.07% from S₂, 0.68% from S₃, 1.27% from S₄ and 2.67% from S₅. The increase in stover yield is due to adequate biomass production and better nutrient uptake. These results corroborated with the findings of Naveed et al., (2018).
 
Grain quality
 
The data on quality components are given in Table 2. It showed that among all nutrient level treatments, maximum crude protein content was obtained from S6. Results showed that S₆ was statistically higher at 33.30% from S1, 40.18% from S₂, 28.15% from S₃, 5.14% from S₄ and 7.79% from S₅. The maximum crude protein percent was significant with combined treatments is due to the congenial and favorable environment with the extended benefit of biochemical relations (i.e., respiration, photosynthesis and chlorophyll content) in the plants.
        
The analysis of data revealed that among all nutrient level treatments, maximum starch content in maize grain was obtained from S₆. Results noted that S₆ was statistically higher as 8.58% from S₁, 10.32% from S₂, 6.89% from S₃, 2.70% from S₄ and 4.08% from S₅. The production factors which improved the grain yield also improved the starch content of the grain.
        
The data revealed that among all the nutrient level treatments, maximum iron content was obtained from S6. Results showed that S₆ was statistically higher as 53.92% from S₁, 71.80% from S₂, 46.46% from S₃, 2.98% from S₄ and 5.93% from S₅. Foliar Zn spraying facilitated the transport of endogenous Fe, simultaneously improved the concentrations and bioavailability of Zn and Fe in maize grains. Lower kernel Fe and Zn concentration in non-biofortified hybrids was reported as compared to biofortified hybrids. Similar findings were reported by Chakraborti et al., (2009).
        
The data regarding zinc content in (mg kg^-1) maize grain showed that the maximum zinc content was obtained from S₆. Results showed that S₆ was statistically higher as 52.46% from S₁, 70.14% from S₂, 47.11% from S₃, 4.26% from S₄ and 7.50% from S₅. An increase in Zn concentration in maize grain is positively correlated with grain yield, test weight, cob diameter and cob length. These results corroborated with the findings of Sadiq Naveed et al., (2018). 
        
The interactions of QPM hybrid with S₆ nutrient level had a significant (P= 0.05) effect on shelling %, test weight, grain yield, stover yield, crude protein, starch, Fe and Zn content in maize grain.  

The findings of the present investigation revealed that among different nutrient level treatments, 50% RDF through NPK + 50% RDF through FYM with Fe and Zn foliar application @0.5% Conc., (S₆) registered the maximum highest growth attributes and yield components with non-QPM hybrid and highest in grain quality parameters with QPM hybrid. It can be recommended to farmers that agronomic biofortification with INM, achieves more benefit from maize hybrids during rabi season under cauvery delta condition.

The authors gratefully acknowledge the advice and guidance provided by Dean (Agriculture) and Research Advisory Council members, Faculty of Agriculture, Annamalai University, Chidambaram, Tamil Nadu, India.