Agronomic Biofortification of Zinc and Iron on Yield Potential and Zinc Fortification in Chickpea (Cicer arietinum L.) Varieties under Arid Western Plains Zone of Rajasthan

Chickpea (Cicer arietinum L.) is an important crop for vegetarian people as primary source of protein, it is third most important pulse crop grown in the world after dry beans and peas (Kaur et al., 2020). India ranks first in area and production of chickpea followed by Australia, Pakistan and Turkey. As per 4th advance estimates, it accounts an acreage of 10.17 million hectares contributing 11.35 million tonnes of production with an average productivity of 1116 kg ha^-1 during 2019-20 in India (DES, 2020). Zinc is one of the 8th essential trace elements require for growth and reproduction of plants. Zinc enriched finger proteins are required in signal transduction, regulation and transcription of deoxyribonucleic acid (DNA)/ribonucleic acid (RNA) or other proteins in the plant. Its deficiency causes poor synthesis of phytohormones viz. auxins, gibberellins and cytokinins resulted in lesser growth and development of crop (Hassan et al., 2020). Zinc involved in the root nodulation of plant and enables to the pulse crops to fix inert nitrogen in the root nodule. It is also participating in the signal transduction during stress condition in the plant system.
               
Similarly, zinc deficiency in the soil is more commonly found in cereal based cropping system of the world that affects succeeding pulse crops (Shukla and Mishra, 2020). Though, iron (Fe) also plays an important role in chlorophyll synthesis and act as structural component of hemes, hematin and leghaemoglobin involved in the nitrogen fixation in pulses catalyzed by an enzyme called ‘nitrogenase’. Moreover, iron is the most essential micronutrient for plant growth especially for chickpea grown on saline and alkaline soils (Larson et al., 2018). Although, ubiquitous presence of iron in earth’s crust, but low solubility make it lesser availability and finally poor uptake by crops. Similarly, saline and alkaline soils are also deficient in iron, which results in the chlorosis of leaves that reduces photosynthetic potential of chickpea and fails to complete its pod or grain formation ultimately pods may remain empty (Vadlamudi et al., 2020; Shukla and Mishra, 2018).

An experiment was carried out at Instructional Farm, College of Agriculture, Jodhpur (Rajasthan) during rabi season of 2019-20. This is situated at a distance of about 10 km from Jodhpur railway station. Geographically, it is located between 26°15'N to 26°45'North latitude and 73°00'E to latitude 73° 29'East longitude at an altitude of 231 meter above mean sea level. The experiment was comprised with two varieties namely GNG-1581 and RSG-974 and seven fortification treatments included various doses and modes of application of zinc (Zn) and iron (Fe) viz. control (F₀), ZnSO₄ @ 25 kg ha^-1 (SA) (F₁), FeSO₄ @ 25 kg ha^-1 (SA) (F₂), ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) (F₃), ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) (F₄), FeSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) (F₅) and FeSO₄ @ 25 kg ha^-1  (SA) + 0.5% FeSO₄ (FA) (F₆) in total fourteen treatment combinations were designed in factorial randomized block design (FRBD) with three replication that makes forty two plots in total. The soil of experimental plot was  sandy-loam in texture, slightly alkaline in soil reaction (pH 8.2), non-saline in conductivity (EC 0.12 d/Sm), low in organic carbon (0.14%) and available nitrogen (176 kg ha^-1), whereas medium in phosphorus (22.0 kg ha^-1) and high in available potassium (329 kg ha^-1). Similarly, the micronutrient analysis of the soil, inferred that the experimental soil was low in available Zn (0.48 mg kg^-1) and available Fe (3.21 mg kg^-1). The recommended dose of fertilizer (20 N and 40 kg P₂O₅ ha^-1) was given in chickpea at the time of sowing. However, zinc sulphate heptahydrate (Zn 21%) and ferrous sulphate (Fe 19.5%) were used as source of zinc and iron and applied as per the treatments as agronomic fortification. All cultural operations were followed as per recommendation package of chickpea. However, zinc and iron were analyzed by wet digestion in di-acid mixture (HNO₃ + HClO₄ in the ratio of 3:1) in the plant samples (seed and stover) by following all standard protocols given by Isaac and Kerber (1971) using Atomic Absorption Spectrophotometer at the most sensitive wavelength for zinc (213.7 nm) and iron (248.3 nm).

Effect of varieties on yield attributes and yield
 
The effect of varieties on yield attributes and yield are presented and summarized in Table 1. Perusal of data showed that significantly higher number of pods plant^-1 (41.55) and 100-grain weight (14.45 g) were produced under the RSG-974 as compared to GNG-1581 (38.43 pods plant^-1 and 100-grain weight 13.52 g). However, the number of seeds pod^-1 (1.99) recorded significantly higher under GNG-1581 as compared to RSG-974 (1.83 seeds pod^-1). It was found that variety GNG-1581 recorded significantly higher seed yield (1539 kg ha^-1), stover yield (2863 kg ha^-1) and biomass yield (4402 kg ha^-1) as compared to RSG-974, which recorded seed yield of 1326 kg ha^-1, stover yield of 2466 kg ha^-1 and biomass yield of 3792 kg ha^-1. Harvest index of chickpea did not affect by any of the chickpea varieties. However, maximum harvest index (34.96%) was recordedunder the chickpea variety GNG-1581 as compared to RSG-974 (34.95%). Increased in yield attributes of chickpea might be due to formation of more growth attributes which is the individual potential of variety that synthesizes more reproductive parts, which likely to enhances production of yield characters of chickpea ultimately yielded more. The results are also in conformity with the finding of Parmar and Poonia (2020) and Nandan et al., (2018).
 

 
Effect of varieties on zinc content and uptake
 
It was found that significantly higher zinc content in seed (30.78 mg kg^-1) and stover (22.68 mg kg^-1) as well as their uptake by seed (48.84 g ha^-1) and stover (656.13 g ha^-1) along with total uptake (704.97 g ha^-1) were recorded under variety GNG-1581 as compared to RSG-974 (Table 2).  The differences in zinc content and their uptake in seed and stover might have been caused due to varietal differences and genetic makeup of individual variety. Similar trends were also observed by Nandan et al., (2018) and Prasad and Shivay (2018).


 
Effect of agronomic biofortification of zinc and iron on yield attributes and yield
 
Yield attributing characters are outcomes of interaction between crop and applied treatments which synthesize more yield forming attributes. It was found that application of ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) and ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) significantly recorded higher number of pods plant^-1 (45.16 and 44.90), seeds pod^-1 (2.18 and 2.17) and 100-seed weight (15.98 and 15.12 g), which produced significantly higher seed yield (1827 and 1635 kg ha^-1) and stover yield (3049 and 2886 kg ha^-1) and biomass yield (4876 and 4521 kg ha^-1), respectively and showed their significant superiority over rest of the treatments, except stover yield where both of the treatments were statistically at par with each others (Table 1). These theories also supported by Parmar and Poonia (2020) and Shivay et al., (2014). Improvements in yield attributes of chickpea varieties might be due to the facts that combined application of Zn and Fe increased availability of major and minor nutrients to plant, which might have enhanced early root growth and cell multiplication leading to more absorption of other nutrients from deeper layers of soil ultimately resulting in increased supply of the major nutrients. This might results more formation of yield attributes as supplies of micronutrients (Zn and Fe) encourage differentiation of cell at reproductive stage. However, harvest index did not influence by any of the biofortification treatments, but maximum harvest index (37.47%) was obtained under the treatment applied with ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) followed by ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA), which recorded harvest index of 36.16 per cent.
 
Effect of agronomic biofortification of zinc and iron on zinc content and uptake
 
Among  treatments, application of  ZnSO4 @ 25 kg ha^-1 (SA) + 0.5% ZnSO4 (FA) and ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO4 (FA) significantly recorded higher zinc contents in seed (37.46 and 36.19 mg kg^-1) and stover (22.95 and 22.31 mg kg^-1), while owing to higher yield obtained by the application of ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) and ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) that significantly improved zinc uptake by seed (66.29 and 60.98 g ha^-1) and stover (685.64 and 667.03 g ha^-1) of chickpea as well as their total uptake (751.93 and 728.01 g ha^-1), respectively, however, both the treatments were at par with each others with respect to zinc contents and uptakes (Table 2). Zinc treated as hyper-accumulators in seed and this might be possible due to Zn transporters, vascular sequestration and detoxification mechanisms that maintained Zn-homeostasis results in higher accumulation of zinc in plant body (Nandan et al., 2018 and Shivay et al., 2014) and also regulates respiration, photosynthesis, nitrogen fixation, reduction of nitrates and sulphates might be have positive response to enhance its contents and uptake in crop (Pal et al., 2019 and Nandan et al., 2018).
 
Interaction effects of varieties and agronomic biofortification of zinc and iron (C × F)
 
Among treatment combinations, RSG-974 under the treatment application of ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) recorded significantly higher 100-seed weight (16.60 g), while GNG-1581 gave significantly higher seed yield (1939 kg ha^-1) as compared to rest of treatments (Table 3), but it was at par with ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) and FeSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA). This might be due to higher photosynthesis rate that improved the process of formation of growth and yield attributing characters in the variety GNG-1581 resulted in higher seed yield. Treatment combination of RSG-974 under application of ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) significantly recorded higher zinc contents (39.35 mg kg^-1) in seed, while higher concentration of zinc was recorded in stover (25.59 mg kg^-1) of GNG-1581 (Table 4). Furthermore, the results revealed that chickpea variety GNG-1581 under application of ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% FeSO₄ (FA) significantly recorded higher zinc uptakes by seed (75.10 g kg^-1) and stover (808.65 g ha^-1) along with total uptake (883.75 g ha^-1) as compared to variety RSG-974 under similar combination (Table 5). The results are also in conformity of the findings of Nandan et  al., (2018), Pal (2018) and Kayan et al., (2015). This was might be due to positive correlation of iron and zinc that stimulates various enzymes to form signal transduction through transcription factor for acquisition of more zinc and iron from roots to shoot (Pal, 2018 and Pingoliya et al., 2015).






 

Based on experimental results, it may concluded that growing of chickpea variety GNG-1581 under ZnSO₄ @ 25 kg ha^-1 (SA) + 0.5% ZnSO₄ (FA) showed better agronomic biofortification treatment which interactively and significantly produced higher yield attributes and seed yield (1,539 kg ha^-1) and also, enriched the seed with higher concentration of zinc as compared to variety RSG-974.

All authors declared that there is no conflict of interest.