Influence of Various Methods of Zinc Fertilization on Growth and Yield of Finger Millet (Eleusine coracana) Varieties

Finger millet commonly known as ragi and grown in both kharif and rabi seasons. It is short duration (<120 days) day-neutral crop and thus can be grown more than once a year in certain regions. Finger millet grains have long storability even under normal conditions and have made them “famine reserves”. This aspect is at most important as Indian agriculture suffers from vagaries of monsoon (Michaelraj and Shanmugam, 2013). These features have made finger millet an important cereal in low rainfall areas, affordable for the poor.
       
Finger millet is known for several health benefits and some of the health benefits are attributed to its polyphenol and dietary fiber contents. Finger millet contains about 5-8% protein, 1-2% ether extractives, 65-75% carbohydrates, 15-20% dietary fiber and 2.5-3.5% minerals and it has 30 times more calcium content than rice (344 mg/100 g). They are also recognized for their health beneficial effects, such as anti-diabetic, anti-tumerogenic, atherosclerogenic effects, antioxidant and antimicrobial properties (Chethan and Malleshi, 2007a). Apart from calcium content, grains are also rich in iron, phosphorus and vitamin content. The iodine content is said to be highest among all the food grains (Sandhya Rani, 2017). However, zinc content of finger millet grain is low (2.3 mg/100 g).
       
Zinc (Zn) is considered as one of the essential micronutrient which limit the crop production. Almost 40 per cent of cultivated soils in India facing the problem of zinc deficiency and it strongly correlates to zinc deficiency in humans hence, zinc recognized as one of the most widespread mineral deficiencies in global human nutrition. Zinc deficiency is 5^th leading cause of death and disease in the developing world and 8,00,000 people die annually due to zinc deficiency (WHO), of which 4,50,000 are children under the age of five years old. As most of the soils of Andhra Pradesh (AP) are also deficient in Zn and there is a dietary need to increase grain Zn content of finger millet.

Description of experimental site
 
The experiment was carried out during kharif, 2019 and 2020 at College Farm, S.V. Agricultural College, Tirupati, ANGRAU. The experimental site is geographically located at 13.5°N latitude and 79.5°E longitude with an altitude of 182.9 m from mean sea level. The soil of the experimental site was sandy clay loam in texture which is medium in organic carbon (0.5-0.75%) and available nitrogen (<280 kg ha^-1), high in available phosphorus (>56 kg ha^-1) and potassium (>300 kg ha^-1) and sufficient in available zinc (>0.6 ppm).
 
Treatments and experimental design
 
The experiment was laid out in split plot design with two finger millet varieties as main treatments viz., Vakula and Tirumala varieties released from Agricultural Research Station, Perumallapalli and zinc fertilization at different methods of application at various crop stages as sub treatments viz., T₁: Control (No fertilizers and manures), T₂:  30-30-20 kg N-P-K + FYM @ 10 t ha^-1, T₃: T₂ + Soil application of ZnSO₄ @ 25 kg ha^-1 as basal, T₄: T₂ + Soil application of chelated zinc sulphate @ 5 kg ha^-1, T₅: T₂ + Foliar application of 0.2% ZnSO4 at ear head emergence stage, T₆: T₂ + Foliar application of 0.2% ZnSO4 at grain filling stage and T₇: T₂ + Foliar application of 0.2% ZnSO₄ at ear head emergence and grain filling stages. The treatments were randomized in split plot design with three replications. The recommended dose of 30 kg N, 30 kg P₂O₅ and 20 kg K₂O ha^-1 applied through urea, SSP and MOP, respectively. Nitrogen fertilizer was applied in two equal splits as first half dose at the time of transplanting and second half at 30 DAT and the full dose of FYM @ 10 t ha^-1, phosphorus and potassium applied at the time of transplanting.
 
Estimation of growth parameters
 
The growth parameters like plant height, number of tillers per plant, leaf area and total dry matter were recorded at 20, 40 and 60 days after transplanting (DAT) and at harvest. The crop was harvested with the help of a sickle. The yield attributes [number of productive tillers per plant, number of fingers per plant and test weight (g)] and yield [grain yield (kg ha^-1), straw yield (kg ha^-1)] were recorded at harvest. From each plot, five plants were randomly selected for observations and value of each parameters was averaged to get mean value.
 
Statistical analysis
 
The experimental data were analyzed statistically by following standard procedure outlined by (Panse and Sukhatme,1985). Significant difference was tested by comparing ‘F’ value at 5 per cent level of probability. Treatmental differences that were non-significant were denoted as NS and the data analysed by OPSTAT.

Experiment was conducted two years (2019 and 2020). The response was almost similar among main, sub plots and interactions in two years of research and hence only pooled date was presented.
 
Growth parameters
 
There was no significant variation between the two varieties with respect to the growth parameters. The effect of zinc on growth parameters at 20 days interval of crop was found significant between the zinc application treatments and non-significant between the varieties. Significantly higher plant height and more number of tillers per plant (25.47 and 57.98 cm) and (1.57 and 1.97) respectively at 20 and 40 DAT was recorded with T₃ i.e., T₂ + Soil application of ZnSO₄ @ 25 kg ha^-1 as basal, (102.92 and 106.43 cm) however, at 60 DAT and at harvest it was recorded in T₇ i.e., T₂ + Foliar application of 0.2% ZnSO₄ at ear head emergence and grain filling stages (2.32 and 2.40, respectively) compared to control (T₁). Higher plant height may be due to better availability of nutrients resulting in improved crop establishment with better development. With the change in levels and methods of application of Zn from soil application to foliar application, the plant height gradually increased, which might be attributable to greater photosynthetic activity and chlorophyll synthesis due to Zn fertilization resulted into better vegetative growth. Jakhar et al., (2006) also observed higher plant height with the application of zinc. The pooled data was given in the Table 1.
 

       
The influence of zinc application on leaf area at 20 days interval in finger millet was found to be significant. Among the treatments, at 20 and 40 DAT, T₃ i.e., T₂ + Soil application of ZnSO₄ @ 25 kg ha^-1 as basal registered significantly higher leaf area (626.36 and 739.67 cm² plant^-1 respectively) and at 60 DAT and at harvest, T₇ i.e., T₂ + Foliar application of 0.2% ZnSO₄ at ear head emergence and grain filling stages (1220 and 1120 cm² plant^-1 respectively) was depicted maximum leaf area compared to other treatments. The increase in the leaf area might be due to foliar application at two critical stages of finger millet which helps to quick absorption of zinc through leaf and this helps in increase in cell division and elongation and photosynthesis. Foliar application of zinc might increase the translocation of photosynthesis from source to sink. Similar findings were observed by Chand, (2017).
 
Dry matter accumulation
 
Total dry matter per plant was recorded at 20 days interval. The pooled data was given in the Table 2 and Fig 1. Significantly higher total dry matter per plant was recorded at 20 and 40 DAT by T₃ i.e., T₂ + Soil application of ZnSO₄ @ 25 kg ha^-1 as basal (6.18 and 10.76 g plant^-1) respectively and at 60 and at harvest by T₇ i.e., T₂ + Foliar application of 0.2% ZnSO₄ at ear head emergence and grain filling stages (34.45 and 39.45 g plant^-1) respectively compared to other treatments. The increase in dry matter accumulation may be due to increased leaf area and biomass. Application of Zn was found to have significantly positive influence on growth of finger millet compared to control (Shankar et al., 2015).
 

 

 
Yield and yield attributes
 
The pooled data was given in the Table 3. The significant difference was observed in grain yield among the two varieties i.e., tirumala yielded better compared to vakula variety with the application of zinc. The influence of zinc on yield and yield attributes was found to be significant. Among the treatments, T₇ i.e., T₂ + Foliar application of 0.2% ZnSO₄ at ear head emergence and grain filling stages registered higher grain (3150 kg ha^-1) as shown in Fig 2, straw (7364 kg ha^-1) yield, 1000 seed weight (3.05 g), number of productive tillers per plant (1.88) and number of finger per plant (21.58) compared to control. Whereas, higher grain yield was recorded in soil application rather than foliar application in rice (Venkatesh et al., 2018) and maize (Ariraman et al., 2020). The favorable influence of applied zinc on yield may be due to its catalytic or stimulatory effect on most of the physiological and metabolic process of plants (Mandal et al., 2009) participation of Zn in biosynthesis of indole acetic acid (IAA) and its role in initiation of primordial reproductive parts and partitioning of photosynthates towards them are responsible for increased yield.
 

The result of the above study indicates that application of zinc along with FYM and RDF increased dry matter accumulation and grain yield as compared to control. The favorable influence of applied zinc on yield may be due to its catalytic or stimulatory effect on most of the physiological and metabolic process of plants. Among the zinc application treatments, during early stages i.e., up to ear head emergence stage, the T₃ (T₂ + soil application of ZnSO₄ @ 25 kg ha^-1 was applied as basal) increased the growth parameters compared to other treatments. After ear head emergence stage, the T₇ (T₂ + foliar spray of 0.2% ZnSO₄ at ear head emergence and grain filling stages) treatment proved to be the best.