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INTRODUCTION

Sustainable increase in productivity is the key objective of commercial fruit cultivation to meet the per-head demand of fruits for human nutrition. High density planting (HDP), mediated by canopy management, was found to be very useful for increasing the productivity of fruit crops. However, the commonly used canopy management tools for perennial fruit trees (training, pruning and dwarfing rootstocks) were not feasible for canopy management and HDP of herbaceous perennial plants such as banana (Debnath et al., 2015). Productivity in bananas is governed by the ‘source’ and ‘sink’ components of the plant system and its usefulness necessitates distinguishing between physiological and agronomic approaches (Turner, 1998). HDP in banana was found to have direct effect on growth and yield parameters, viz., pseudostem height, girth, leaf number, leaf area index, absorption of solar light, bunch weight and productivity (Nalina et al., 2000; Thippesha et al., 2005; Debnath et al., 2017). This, therefore, indicated the need forregion-specific fine-tuning of agronomic practices including spacing, plant density, nutrition and so on, for successful HDP in banana. For HDP of cv. Martaman (AAB) in the Gangetic alluvium region of West Bengal, the identified optimum leaf area index (LAI) was 5.50, corresponding to a plant population of 5000/ha, accommodating 3 plants/pit at 2m × 3m spacing (Debnath et al., 2015). These technological inputs on HDP in banana through research works are essentially needed for intervention and betterment of the much-skewed distribution of banana productivity across the different states in India. The average national productivity of banana in India is 34.86 t/ha, of which only five states recorded a productivity of more than 45 t/ha - Madhya Pradesh (69.52 t/ha), Gujarat (65.62 t/ha), Andhra Pradesh (56.24 t/ha), Maharashtra (52.04 t/ha) and Uttar Pradesh (45.72 t/ ha). In fact, banana is grown in rest of the states with much lower productivity (3.40 to 44.94 t/ha) (Anon, 2018). With this back ground, an experiment was conducted to study the HDPand nutrient requirement of banana across the different states in the country for increasing productivity and profitability of the farmers.

MATERIALS AND METHODS

The Indian Council of Agricultural Research (ICAR), through its All India Coordinated Research Project (AICRP) on Fruits, conducted an experiment between 2009 to 2015 to study the HDP and nutrient requirement of banana at six research centres across the country, including Bhubaneswar (Orissa), Gandevi (Gujarat), Jalgaon (Maharashtra), Jorhat (Assam), Kannara (Kerala) and Mohanpur (West Bengal) to ensure higher productivity of banana and profit for farmers (Table1). The experiment was laid out in Randomized Block Design (RBD), replicated four t imes with 15 plants per replication and 13 treatment combinations, including four plantingdensities (S 1 P 2 , S 1 P 3 , S 2 P 2 and S 2 P 3 , where S1=2mx3m, S2 =1.8m x3.6m, P2=2 suckers/hill, P3=3 suckers/hill), three nutrition levels (F1, F2 and F3=100%, 75% and 50% of RDF) and with one

region-specific conventional planting density and nutrition (100%RDF) practice as control. For a particular region/ state, existing package of practices (POP) was fixed and followed both for conventional density and treatment densities. Compared the impact of density and nutrition level (variable factor) only, while the POP (including irrigation method and amount) was a constant for the same region/state. Details were given above on the variable factors only, viz., plant population (S1P2, S1P3, S2P2& S2P3) and nutrition levels (F1, F2 & F3). Uniform, healthy sword suckers were disinfected and planted in 1m3 pits as per spacing treatments. Region-specific recommended varieties and POP (nutrition, irrigation, protection, and so on) were followed for the respective research centres (Table 2). Initial soil nutrient status was estimated from the soil samples randomly collected

from experimental field during final land preparation (Table 3). Observations on growth characters (viz., pseudostem height (m), girth (cm), leaf number, leaf area index, days taken for shooting) and leaf nitrogen, phosphorus and potassium content (N, P & K in %) were recorded at shooting or flowering stage of the plant. The crop duration (days), finger number per bunch, finger weight (g), bunch weight (kg), yield (t/ha), TSS (0B), acidity (%), shelf-life (days) of fruits, yield increase over control (%), B: C ratio and soil nutrient status (available N, P2O5and K2O in kg/ ha) were recorded after harvest. Quality of fruit was analyzed as per A.O.A.C. (1984) methods. The available nitrogen was determined by using the alkaline potassium permanganate method (Subbiah and Asija, 1956). The available soil phosphorus was estimated by Olson method (Jackson, 1967). Available soil potassium was determined by using Flame photometric method, whereas Walkley and Black’s rapid t itration method was used to determine the organic carbon content of the soil (Jackson, 1967). The micro-kjeldahl method as described by Black (1965) was used to estimate the leaf N content. The Leaf P content was estimated by using the Vanado-molybdate yellow colour method and the leaf K content was determined by using Flame photometry (Chapman and Pratt, 1961). The amount of nutrients applied per hectare was estimated on the basis of plant population per hectare under HDP and conventional systems and the recommended fertilizer dose (RDF) at the respective centres, considering that per ton FYM contributed 0.5 kg N, 0.2kg P2O5 and 0.5 kg K2O. The amount of nutrients removed through fruit harvest from HDP (those that produced higher yield and highest B:C ratio) and conventional systems was calculated based on fruit yield and nutrient removal (6.7 kg N, 1.7 kg P2O5and 6.7 kg K2O) 2011). Pooled data for three crop cycles’ was analyzed for statistical inference by following the statistical method for RBD, as described by Gomez and Gomez (1983).

RESULTS AND DISCUSSION

The Major objective of this study was to investigate productivity increase, if any, due to variations in per unit plant population and nutrition level. Yield increase for each region/state was estimated separately, in respect of its variety and POP only, by comparing the yield under HDP & conventional density of that particular variety. It was reflected from the observations that HDP could increase productivity in different region/state with the same variety & POP of respective region, only including intervention of HDP system.

It was observed that the plant growth characters showed significant variations (C.D. at 5%) due to density of planting and a level of nutrition at all centres (Tables 4, 5 and 6). Maximum height of the pseudostem was recorded with a planting density of 5000/ha with 100% RDF (S1P3F1) at all centres per ton banana produce (Ganeshamurthy et al.,

except at Gandevi, whereas maximum girth of pseudostem was recorded with conventional planting density and nutrition at all centres. Leaf number per plant at the shooting stage was recorded to be maximum in conventional planting at all centres except Jorhat, however, the leaf area index was recorded to be maximum in highest density of planting with 100% RDF (S1P2F1) at the Bhubaneswar, Kannara and Mohanpur centres. It was seen that more time (days) was required from planting to harvesting under the higher density of planting (5000 plant/ha), when compared to a lower plant population of 3086, 3333 and 4630 /ha. Such variations in plant growth characters viz., increase in pseudostem height, leaf area index, durations for shooting and harvesting, but reduction in pseudostem girth and leaf number per plant at shooting, as a result of high-density planting in banana were also established by the findings of Rodriguez et al. (2007), Thippesha et al. (2007), Pujari et al. (2011) and Debnath et al. (2015).

Fruit yield and quality parameters were found to vary significantly due to different densities of planting and nutrition levels, across the centres (Tables 7,8 and 9).

Finger number per bunch was recorded as being higher under lower density of planting, including control, at all centres except Jalgaon. Similarly, the weight of an individual bunch was also higher under lower density of planting. But the total fruit yield per unit area, that is, the productivity of banana showed steady increase due to increase in the density of planting. Maximum content of total soluble solids and shelf life of fruit were recorded under conventional plant density and nutrition at the Bhubaneswar, Jorhat and Mohanpur centres, whereas non-significant effect was recorded on the total soluble solids content of the fruit at Gandevi and Kannara centres. A plant population of 5000/ha with 100% RDF resulted in maximum fruit acidity at all centres. These results corroborated with the findings of Nalina et al. (2000), Thippesha et al. (2007), Pujari et al. (2011) and Debnath et al. (2015).

The per cent increase in productivity over control due to different planting densities and nutrition levels varied from 8.3 to 50.6 at Bhubaneswar, 8.8 to 21.9 at Gandevi, 2.4 to 7.4 at Jorhat, 4.5 to 43.5 at Kannara and 5.7 to 79.0 at Mohanpur centre (Table 10). Maximum productivity and B: C ratio

were estimated due to highest planting density of 5000 plants/ha at all centres, except Jalgaon. It varied from 28.9% to 50.6% at Bhubaneswar, 15.2% to 21.9% at Gandevi, 4.0% to 7.4% at Jorhat, 33.5% to 43.5% at Kannara and 46.5% to 79.0% at Mohanpur, over the conventional system (control). However, the estimated B: C ratios varied with the levels of nutrition (50%, 75% and 100% of RDF) within the same planting density of 5000/ ha. For Kannara centre, maximum B: C ratio was 2.65 with 5000 plant/ha and 100% RDF, whereas, for Mohanpur and Bhubaneswar centres, it was 2.65 and 2.67, respectively with 5000 plants/ha and 75% RDF. In case of Jorhat and Gandevi centres, the B:C ratio was 4.94 and 5.40, respectively with 5000 plants/ha and 50% RDF. Hence, there were savings in fertilizer input by 25% at the Mohanpur and Bhubaneswar centres and by 50% at the Jorhat and Gandevi centres. It was noted that although the bunch weight of an individual plant under high density planting decreased, the total number of plants and bunches per unit area was much higher and hence the productivity much higher (Debnath et al., 2015). Increase in the photosynthetic canopy surface and light interception under high density planting are reported to be the major contributing factors for higher productivity in banana (Thippesha et al., 2007, Debnath et al., 2015).

Significant variations were recorded in the soil nitrogen, phosphorus and potassium content (kg/ha) after harvesting of banana and in the leaf N, P and K content at the shooting stage of the fruit at all centres (Tables 11, 12, 13 and 14). As compared with soil nutrient status after harvest inthe conventional system (control), no significant depletion was observed due to the combination of high density planting and nutrition treatment (that resulted in higher yield and maximum B:C ratio) in the available soil nitrogen content (except at the Gandevi, Jalgaon and Jorhat centres), the available soil phosphorus content (except at the Gandevi and Jalgaon centres) and the available soil potassium content (except at the Jalgaon and Jorhat centres). At the Bhubaneswar centre, maximum leaf N and P content was recorded in control, whereas it was lowest in the 5000 plants/ha with 50% RDF treatment. But leaf K content was recorded as being maximum under the 3086 plants/ha with 100% RDF treatment and lowest in the 4630 plants/ha with 50% RDF treatment. However, leaf N, P and

K content showed no specific trend at the Jorhat and Kannara centres. At the Mohanpur centre, minimum leaf N, P and K content was recorded under the highest planting density (5000 plants/ha) with the lowest nutrition level (50% RDF). The nutrients applied to and nutrients removed through fruit harvest from HDP (producing higher yield and highest B:C ratio) and conventional systems were calculated and are presented in Table 15. Under the HDP system, the region-specific, per-plant RDF was increased in proportion to the increase in plant population per unit area, therefore, any remarkable

depletion in soil and plant nutrient status may not have shown at many centres. It was observed by Debnath et al. (6) that the root zone of plants under the high density planting system had more density of effective feeder roots compared to the root zone of plants under the conventional (low density) planting system and it indicated better uptake of applied manures and fertilizers. In present study, the site-specific application of nutrients (RDF) to the high-density feeder root zones of banana plants under HDP might have caused better utilization of applied nutrients, resulting in 25%-50% savings of RDF.

CONCLUSION

The results of this experiment showed that high density planting (HDP:5000plants/ha) of banana, accommodating three suckers per hill at 2m x3m spacing,increased productivity over the conventional planting system at the Bhubaneswar, Gandevi, Jorhat, Kannara and Mohanpur centres. Under the HDP system, the nutrient requirement was 100% RDF at the Kannara centre, 75% RDF at the Bhubaneswar and Mohanpur centres and 50% RDF at the Gandevi and Jorhat centres. This indicated a savings in cost of fertilizer input by 25% at the Bhubaneswar and Mohanpur centres and by 50% at the Gandevi and Jorhat centres. It was therefore, recommended that HDP (5000 plants/ha) in banana be adopted, accommodating three suckers per hill at 2m x3m (6.6 ft x 3.8 ft) spacing with 50% RDF in the agro-climatic region of Gandevi and Jorhat, with 75% RDF in the agro-climatic region of Bhubaneswar and Mohanpur and with 100% RDF in the agro-climatic region of Kannara for higher productivity and return on investment to farmers.

Acknowledgments

This work was carried out with the financial support of the Indian Council of Agricultural Research (ICAR) and the collaborative organizations (SAUs/ICAR Institutes) under ICAR-All India Coordinated Research Project (AICRP) on Fruits. The authors wish to acknowledge the ICAR and the collaborative organizations for providing the required research facilities and support.

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