Banana is a major fruit crop that serves as a food crop to meet the calorific needs of millions of people worldwide. It is commercially grown in more than 100 tropical and subtropical countries of the globe. India ranks first in global banana production. Naturally, banana crop is a heavy consumer of nutrients and requires large quantities for its growth, development and yield (Hazarika and Ansari 2010). Continuous use of chemical fertilizers poses environmental health hazards and negative effect on soil microbial population besides being quite expensive and making the high cost of production. Hence there is an urgent need to think of alternate sources of safe fertilizers which may enhance crop yields without having adverse effects on soil properties. Thus the use of biofertilizers seems to be array of hope in this direction. Biofertilizers have been considered as a cheap and eco-friendly way of improving soil fertility status. In addition to that, recent trends in farming with organic inputs have an inherent claim of improvement in quality and taste of the produce besides prevention of soil deterioration and a sustainable production in economically sound manner.

In India, banana cv Robusta (AAA) is one of the popular varieties grown extensively due to the premium price in the market. Application of fertilizers in sufficient quantities is crucial for a reasonable harvest and acceptable bunch quality. In such a situation the addition of biofertilizers along with inorganic fertilizers is known to enhance nutrient use efficiency and contributes to soil and plant health improvement. Sustainable production practice involves judicious application of chemical fertilizers with the combination of biofertilizers. Taking the above background into consideration, the study was conducted to assess the influence of combined application of inorganic fertilizers and biofertilizers on the yield and quality of banana cv Robusta (AAA).

The present investigations were carried out in the orchard of Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. Tissue-cultured banana plantlets were planted at a distance of 1.8 m x 1.8 m. The experiment was laid out in randomized block design (RBD) with seven treatments viz T₁: NPK 110:35:330 g/plant (100% RDF) + 25 g each of Azospirillum + phosphobacteria (PSB) + AMF (arbuscular mycorrhizae fungi), T₂: NPK 110:35:330 g/plant (100% RDF) + 50 g each of Azospirillum + PSB + AMF, T₃: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 25 g each of Azospirillum + PSB + AMF, T₄: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 50 g each of Azospirillum + PSB + AMF, T₅: NPK 55:17.5:165 g/ plant (50% RDF) + 25 g each of Azospirillum + PSB + AMF, T₆: NPK 55:17.5:165 g/plant (50% RDF) + 50 g each of Azospirillum + PSB + AMF and T₇: NPK 110:35:330 g/plant (100% RDF)- control, treatments replicated thrice.

The biofertilizers were applied at the time of planting. Chemical fertilizers such as nitrogen, phosphorus and potassium were applied as urea (46% N), single supper phosphate (16% P₂O₅) and muriate of potash (60% K₂O). Nitrogen and potassium were applied in three equal splits at 3^rd, 5^th and 7^th month after planting (MAP) and the required phosphorus was applied during 3^rd month after planting. At the time of harvest, the observations on yield and yield attributes such as bunch weight, number of fingers and hands, finger weight and yield per hectare were recorded. Observations on quality attributes were carried out on ripe fruits. Total soluble solids (TSS) were determined using hand refractometer (ERMA INC, Tokyo, Japan) and the results were expressed in percentage. Titrable acidity was estimated by adopting the procedure of Anon (1975) and expressed in terms of citric acid equivalent in percentage. Fruit sugar properties viz total, reducing and non-reducing sugars were estimated as per the method suggested by Somogyi (1952). The data obtained from the present investigations were subjected to statistical scrutiny.

Data given in Table 1 exhibit that fertilizing banana cv Robusta plants with different levels of N, P and K through chemical fertilizers in association with biofertilizers significantly enhanced yield, bunch weight, number of fingers, number of hands and finger weight rather than using N, P and K through chemical source as control. The treatment T₂ (100 % RDF + 50 g each of Azospirillum, PSB and AMF) performed superior to others by registering higher bunch weight of 26.10 kg/plant and yield of 31.58 tonnes/ha. The treatment T₁ was the next best, yielding 25.03 kg of bunch per plant. Higher bunch weight recorded in T₁, T₃ and T₄ were on par with the bunch weight recorded in the control. The treatments T₅ and T₆ recorded lower bunch weight than control or other treatments. Increased yield in T₂ might be due to the ability of biofertilisers to fix atmospheric nitrogen and solubilization cum mobilization of native soil nutrients like phosphorus, potassium, zinc, copper, iron and sulphur from the unavailable form to available form which were effective in association with inorganic nutrients. This might have enhanced the growth of yield attributing factors. Similar results were obtained in banana by Marwaha (1995), Das et al (2001) and Hussain et al (2017).

Even at 75 per cent RDF, bunch weight was maintained on par with control by applying biofertilizers. This implies that reduction in chemical fertilizers level by using biofertilizers is possible if current production level is to be maintained. Higher yield with full dose of recommended NPK levels and biofertilizers in T₁ and T₂ indicated better and higher utilization of inorganic fertilizers. Nalina (2002) has also recommended a higher dose of 50 per cent over the recommended practices (ie 150% RDF) implying additional requirement of nutrients for vigourously growing tissue-cultured banana cv Robusta.

Bunch weight is a primary function of number of fingers and finger weight (Ortiz 1997). Any factor that stimulates higher finger production and better finger development leads to better bunch weight. In banana, the floral differentiation requires minimum functional leaf area.

The floral transition coincides with intense mitotic activity in apical meristem of corm (Israeli and Blumenfield 1985). Higher photosynthetic assimilation favoured by improved nutrient status, better differentiation and efficient assimilate distribution to developing fingers could be attributed for higher bunch weight registered in the treatments receiving higher doses of biofertilizers and inorganic fertilizers.

Marginal improvement in bunch weight was also observed at higher biofertilizer dose of 50 g each compared to the lower doses (25 g each). When number of hands was considered, T₂ excelled other treatments by registering 10.63 hands per bunch. Number of hands was only 8.40 in T₅ and 8.61 in T₆. Number of fingers was also observed to be higher in T₂ and T₁ and lower in T₅ and T₆. Marginal but insignificant increase was noted in respect of both number of hands and fingers per bunch with the addition of 50 g each of biofertilizers. The presence of rhizobacteria and fungi might have enabled better nutrient mobilization compared to control that could have led to better in yield attributes of T₃ and T₄ over control. Biofertilizers are also known to synthesize gibberellin and cytokinin like substances (Janzen et al 1992, Zahir et al 2001, Dobbelaere et al 2003). When optimum resources were available, the accumulation of such growth promoting substances might have favoured better floral differentiation thus leading to higher number of hands and fingers per bunch in T₁ and T₂. In case of average finger weight, T₂, T₁, T₃ and T₇ revealed superior performance in that order. The treatments T₅ and T₆ recorded lower finger weight of 146.68 and 148.29 g respectively. Biofertilizers seemed to promote better finger development when plants were supplied with optimal nutrient concentrations as in case of T₁ and T₂. Similar results have also been reported Manamalar (1997), Pragatheswari (2002) and Singh and Singh (2004).

Except T₁, T₄ and T₅, other treatments registered higher non-reducing sugar that was on par with T₆ and T₃. Among the different treatments, reducing and total sugars were highest in T₂ (12.80 and 16.11% respectively). Except treatment T₅ (12.18 and 15.35% respectively), all other treatments were on par with treatment T₂. The quality attributes were similar to control in the treatments T₁, T₂, T₃ and T₄ for TSS and sugars. Marginal but significant reductions in these traits were noted in T₅. The results are contrary to increased quality of fruits due to biofertilizers application by Pragatheswari (2002). But in some of the earlier findings also, it was reported that quality improvement was not significant (Jeeva 1987, Manamalar 1997).

In conclusion, the study established the beneficial effect of chemical fertilizers and biofertilizers on the production of banana. Based on the performance, the treatment 100 per cent RDF with 50 g each of Azospirillum, phosphate solubilizing bacteria and AMF resulted in maximum yield with quality attributes.

T₁: NPK 110:35:330 g/plant (100% RDF) + 25 g each of Azospirillum + Phosphobacteria (PSB) + AMF (arbuscular mycorrhizae fungi), T₂: NPK 110:35:330 g/plant (100% RDF) + 50 g each of Azospirillum + PSB + AMF, T₃: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 25 g each of Azospirillum + PSB + AMF, T₄: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 50 g each of Azospirillum + PSB + AMF, T₅: NPK 55:17.5:165 g/plant (50% RDF) + 25 g each of Azospirillum + PSB + AMF, T₆: NPK 55:17.5:165 g/plant (50% RDF) + 50 g each of Azospirillum + PSB + AMF and T₇: NPK 110:35:330 g/plant (100% RDF)- control

T₁: NPK 110:35:330 g/plant (100% RDF) + 25 g each of Azospirillum + Phosphobacteria (PSB) + AMF (arbuscular mycorrhizae fungi), T₂: NPK 110:35:330 g/plant (100% RDF) + 50 g each of Azospirillum + PSB + AMF, T₃: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 25 g each of Azospirillum + PSB + AMF, T₄: NPK 82.5:26.25:247.5 g/plant (75% RDF) + 50 g each of Azospirillum + PSB + AMF, T₅: NPK 55:17.5:165 g/plant (50% RDF) + 25 g each of Azospirillum + PSB + AMF, T₆: NPK 55:17.5:165 g/plant (50% RDF) + 50 g each of Azospirillum + PSB + AMF and T₇: NPK 110:35:330 g/plant (100% RDF)- control

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