Influence of Nitrogen-Potassium Fertilizers on the Growth and the Productivity Parameters of Plantain Banana PITA 3, FHIA 21 and CORNE 1

This study was undertaken to measure the impact of fertilizers (nitrogen-po-tassium) on the growth and the development of plantain banana. Different doses of fertilizers (T2, T3, T4, T5 and T6) were applied to two hybrid varieties (PITA 3 and FHIA 21) and a traditional variety (CORNE 1) on an experimental split plot plan with a planting density of 2500 plants per hectare. Results showed that fertilizers improve parameters of plantain than control (T1). T6 with high potassium content (240 kg·ha −1 N and 987 kg·ha −1 K) improved the growth (35.72 ± 0.95 cm·month −1 ) and the widening (9.56 ± 0.17 cm·month −1 ) of PITA 3, and performed FHIA 21 agronomic parameters by reducing the length of the production cycle and increased the length of fruits. T2 treatment improved FHIA 21 agronomic and yield parameters. Also, the weight of CORNE 1 regimens (9.00 ± 0.67 kg) and fruits (296.59 ± 4.50 g), the length (33.37 ± 0.31 cm) and the circumference (14.73


Introduction
Among cultivated banana, plantain constitutes a homogeneous group with cultivars whose genome is triploid and bispecific (ABB). Plantain fruits are staple food and important cash crop for many developing countries. It is important for food security [1]. In contrast to dessert bananas, plantain fruits must be cooked before eating and are energy food able to provide body 120 kcal or 497 kJ per 100 g.
With a production of 1.6 million tons, the plantain crop ranks third in annual food production after yam and cassava in Côte d'Ivoire [2]. It is a means of diversifying and increasing income, due to the external markets that are developing [1]. Unfortunately, the low crop density (1667 plants·ha −1 to 2500 plants·ha −1 ) has long led to low yields [3]. A decade ago, [4] showed that increasing planting density in pure culture improves yields. Thus, since 2016, the crop density has increased to 2500 plants·ha −1 for traditional varieties CORNE 1 and Orishele and hybrids PITA 3 and FHIA 21 [5].
Moreover, population growth is leading to an ever-increasing demand, which far exceeds supply [6]. As a result, the strong pressure on agricultural land reduces its availability and causes a significant drop in soil fertility and crop yields [7] [8]. To compensate for this state of affairs, chemical fertilizers are used to correct the soil's deficiency in mineral elements and improve crop productivity [9]. To this end, [10] showed that plants need essentially and significant quantities of nitrogen (N), phosphorus (P) and potassium (K) to complete their growth cycle.
Among minerals, nitrogen and potassium are especially recommended for plantain cultivation [11] as opposed to phosphorus requirements [12]. [5] showed in a recent study that for an intensive crop (2500 plants·ha −1 ) of plantain (COR-NE 1, FHIA 21 and PITA 3), the doses of 240 kg·ha −1 (N) and 658 kg·ha −1 (K) are recommended which were opposed to those previously proposed by [3] with 100 kg·ha −1 (N) and 240 kg·ha −1 (K). According to [13], beyond the quantities of minerals, it is indispensable to consider nitrogen-potassium interaction for better appreciation of plants response. Indeed, nitrogen contributes to the vegetative development of all aerial parts of the plant [14] while potassium has a great influence on fruit quality attributes and plant yield [15]. However, the physiological functions of nitrogen and potassium in plant production are closely related [16]. Thus, potassium intake may increase the efficiency of nitrogen use or exert a limiting effect. Similarly, higher potassium uptake results in a parallel increase in nitrogen uptake [13] [16]. This indicates that the nitro- gen-potassium interaction is the most important interaction with potassium [13]. The objective of this contribution to the improvement of plantain productivity in Côte d'Ivoire is to determine the impact of different doses of nitrogen and potassium on the development and the yield parameters of plantain PITA 3, FHIA 21 and CORNE 1 produced in Côte d'Ivoire.

Vegetal Material
The plant material is made up of vivo plants of 3 varieties of plantain including 2 tetraploid hybrids, PITA 3 (AAAB) and FHIA 21 (AAAB), high yield and tolerant to Black Berry Disease (BBD) and a local variety CORNE 1 (AAB). These vivoplants were produced at the research station of the National Centre for Agronomic Research (CNRA) in Bimbresso.

Study Area
Experimental field was conducted in Bimbresso research station (Anguédédou) at 25 km west of Abidjan with the following geographical coordinates: 5˚25' North latitude, 4˚08' West longitude and 25 m altitude ( Figure 1). The soils in this area, clayey-sandy by nature are ferrallitic. Before mineral input, total nitrogen content was 0.11 g·kg −1 . The cationic exchange capacity and potassium content were respectively 5.34 méq/100g and 0.35 méq/100g. The acid soils (pH

Setting Up of the Experimental Field
Experimental device was in split plot plan with plantain varieties as the main factor and doses of fertilizers as secondary factor. Planting density was 2500 plants per hectare with plants equidistant of 2 m. Each experimental unit or elementary plot of 60 m 2 had 15 useful plants. Plantain variety was composed of three modalities: PITA 3, FHIA 21 and CORNE 1. Fertilization was defined by the doses of nitrogen and potassium to be applied to the plants as a treatment (T). According to [5], for a density of 2500 plants·ha −1 , 240 kg·ha −1 of nitrogen and 658 kg·ha −1 of potassium (T2) are recommended. Based on this recommendation, 5 doses (T2-T6) were considered and compared to control without fertilizer (T1): -T1. Without fertilizer (Control), -T2. 240 kg·ha −1 N and 658 kg·ha −1 K (Conventional or recommended dose), -T3. 120 kg·ha −1 N and 658 kg·ha −1 K, -T4. 360 kg·ha −1 N and 658 kg·ha −1 K, -T5. 240 kg·ha −1 N and 329 kg·ha −1 K, -T6. 240 kg·ha −1 N and 987 kg·ha −1 K.
The number of treatments was defined according to factorial plan which was plantain variety (3) × fertilizer doses (6), i.e. 18 treatments. The 18 experimental plots were repeated on 3 blocks on an area of 5184 m 2 .

Fertilizer Application during Cultivation
Fertilizers were brought to plants in form of urea containing 46% nitrogen and potassium chloride containing 60% potassium. The quantity of urea applied per plant was calculated by mathematic formula: For treatments, amounts of urea and potassium chloride were shared into 8 periods where doses 1 to 3 were applied on separate occasions with 3 weeks inter-vals and doses 4 to 8 were applied on separate occasions with 4 weeks intervals (Table 1).

Plant Maintenance and Stabilization Treatment
Others plant growth essential minerals were brought to plantain plants in single dose. A week after planting, plants received 100 g of dolomite CaMg(CO 3 ) 2 containing calcium and magnesium and 80 g of tricalcium phosphate (Ca 3 (PO 4 ) 2 ) to provide plants needs in phosphorus. "Nematicide" treatment was carried out at the flowering of the plantain plants, with a dose of 30 g per plant to destroy all dangerous parasitic worms. Insecticide treatment was carried out quarterly. Weeding was manual and monthly up to 6 months after planting and then bi-monthly up to 12 months after planting.

Evaluation of Growth and Development Parameters of Plantain Trees
Growth parameters (height and circumference of pseudo trunk) and development parameters (number of leaves released, Plantation-Flowering Interval (PFI) and Plantation-Harvest Interval (PHI)) were measured per month from 3rd to 10th months after planting, and then at flowering and harvesting. The measurements concerned all the useful plants of the plot ([17] [18]). Height was carried out from the collar to V formed by the last two emitted leaves and circumference PFI was the average of the duration in days between planting and flowering of 50% of the plants when PHI was the average of the duration in days between planting and optimal maturity of fruits.

Evaluation of Yield Parameters of Plantain Trees
Bunches of 3 plantain trees per treatment were randomly selected at optimal maturity. The weight (kg) was determined using a hand scale. The number of hands and fingers was counted directly on the bunch. Fruits characteristics were determined using the three median fruits of the second hand of each bunch. Fruit weight was taken on an electronic scale and the length and circumference were measured with a tape measure from pedicel to apex.

Statistical Analysis of the Results
Triplicated data were presented as mean ± standard deviation. Statistical analysis was performed using SPSS version 16.0 software where data were subjected to analysis of variance and then compared with Newmann-Keuls test at the 5% threshold. PCA was used to discriminate treatments according to growth, development and yield characteristics of plantain.

Height of Pseudo Trunk
The effect of fertilization on the height and the circumference of plantain trees is presented in

Characteristics of Fruits Plantain 1) Fruits weight
2) Fruits length Reductions in fruits length with T2-T6 treatments compared to T1 control were noted (Table 5) The greatest increase of fruits length was observed in CORNE 1 and PITA 3 compared to T1 and T2.respectively. CORNE 1 fruits length was significantly (p ≤ 0.05) greater than those of PITA 3 and FHIA 21. The highest CORNE 1 fruit length obtained with T6 treatment was 8.8 cm and 11.64 cm higher compared to those of FHIA 21 and PITA 3 respectively.

Classification of Treatments According Plantain Agronomic Parameters
PCA allowed the characterization of treatments on the basis of plantain agronomic parameters (Figures 2-4). For PITA 3 (Figure 2), F1 and F2 axes contributed to 92.45% of total variation observed. Height and circumference of pseudotrunk, number of sheets, regimen weight, hands number, fingers number, and fruits weight, length and circumference were negatively correlated to F1 axis with T3, T4 and T6 treatments. PFI and PHI were associated to T1. T3, T4 and T6 fertilizers performed agronomic parameters of PITA 3 plantain. F1 and F2 axes contributed to 85.67% of total variation observed in FHIA 21. Height and pseudo-trunk circumference, number of sheets, PFI, PHI, regimen weight, fruit weight and circumference were negatively correlated to F1 axis with the T2 and T6 treatments. Regimen hands number, fingers number and fruit length were negatively correlated to F2 axis with T4 and T5. Treatment T1 showed preponderance for PFI and PHI variables. T2 and T6 treatments resulted in a better The contribution of F1 and F2 axes was 73.83% of variations observed with CORNE 1 (Figure 4). Four groups of variables were observed: pseudotrunk height and circumference, regimen weight, hands number, fruits length and circumference were negatively correlated to F1 axis with T2 and T6 (group 1); sheets and fingers number were positively correlated to F2 axis with T5 (group 2), PFI and PHI were positively correlated to F1 axis with T1 treatment (group 3) and T3 and T4 treatments showed a preponderance for fruit weight (group 4). T2, Agricultural Sciences

Discussion
Growth is a biological phenomenon of increasing size over time, involving the appearance of new tissues [19] [20]. In general, T1 treatment without fertilizer induced significantly (p ≤ 0.05) lower values of growth, development and yield parameters compared to treatments with fertilizer (T2-T6). This lack of improvement in performance indicates the positive effect of fertilizer on plantain growth as highlighted by [21]. When banana was subjected to fertilizers, data showed that PITA 3 performed in growth by an increase of height and circumference with T6 treatment, unlike T5 treatment. T5 and T6 differ by their potassium inputs. So, the growth of PITA 3 would be strongly influenced by the amount of potassium. Potassium has a positive effect on the growth of plantain as mentioned by [22]. However, an amount of nitrogen higher than 120 kg·ha −1 would be necessary because with T3 treatment (low dose of nitrogen), plantain reduced its enlargement. Nitrogen is involved in the main processes of plant development [14]. It contributes to the vegetative development of all aerial parts of the plant.
For FHIA 21, a strong increase of height, circumference and leaf production was observed with recommended T2 treatment. This impact on those parameters could be due to a positive correlation between growth, enlargement and leaf emission of FHIA 21 banana trees as reported by [23]. Data showed that growth drops when nitrogen input is higher than 240 kg/ha (T4). This could be explained by acidification of the root environment in the presence of high doses of nitrogen [24]. It leads to a reduction in the growth of plants sensitive to acid pH [25]. The FHIA 21 variety is adapted to low amounts of nitrogen and the T2 treatment with the doses of 240 kg/ha N and 658 kg/ha K is optimal for the cultivation of FHIA 21. Increased potassium inputs did not significantly improve plant growth. However, FHIA 21 tolerated the high potassium levels better than the high nitrogen levels. CORNE 1 had high growth for all treatments (T2, T5 and T6) providing 240 kg·ha −1 .
Leaf release was uniform regardless of the rates applied to PITA 3 and FHIA 21. PFI was shorter with T4 (PITA 3), T2 and T6 (FHIA 21) and T2 and T5 (COR-NE 1) treatments. Plantain trees are herbaceous plants. The pseudo-trunk is formed by the winding of sheaths into each other. It is at the top of each sheath that the petiole develops, which extends into the central vein supporting the leaf blade to give a leaf. The appearance of the leaves would be a logical continuation in the growth of the tree. Whatever the size of the sheaths, it would be able to produce leaves [26].
Flowering was accelerated by treatments with a nitrogen dose greater than or equal to the recommended nitrogen dose [5]. It would be the consequence of the effect of nitrogen on plant growth. Indeed, the inflorescence is formed at the level of the underground stem and travels throughout the false trunk before appearing in the center of the leaf cluster [27] [28] [29]. That hypothesis was confirmed by the half dose of nitrogen (T3) resulted in a longer PFI duration in CORNE 1.
PITA 3 had a maximum growth in height and circumference with T6 treatment. FHIA 21 reached its maximum with T2 treatment. CORNE 1 grew faster with T4 and T6 treatments. These data corroborated that varieties differ in their ability to use potassium and the effect of nitrogen and potassium is a function of the plant material grown [13]. PITA 3 subjected to T3, T4 and T6 treatments resulted in larger bunches with higher numbers of hands and fingers. Also, T3 and T4 treatments produced heaviest fruits and shortest crop cycle. The T3 and T4 treatments were 120 kg·ha −1 (N) and 360 kg·ha −1 (N) respectively associated to 658 kg·ha −1 (K). The same effect of these two treatments (nitrogen dose was three times in T4) could be due to nitrogen absorption as a function of the amount of potassium as related by [16]. Thus, the quantity of potassium may increase the efficiency of nitrogen use or have a limiting effect. Higher potassium absorption results in a parallel increase in nitrogen absorption [13] [16]. However, the production cycle (PHI) was 25 days longer with the T3 treatment than those of T4 treatment. That demonstrated easily that nitrogen is involved in the main plant development processes for yield determination as mentioned in literature [14] [30].
Regimens had equivalent weight regardless of treatments applied to FHIA 21. However, the largest fruits were only obtained with T2 treatment followed by those of T3. In this study, T2 and T3 were treatments with a reduced dose of nitrogen. Regimen include the stem, fruit and spine [31] and the ability to induce these different parts depends on treatments [32]. The T2 treatment is the reference treatment and the T3 treatment is the reduced nitrogen dose treatment. These treatments with the T6 have resulted in a shorter production cycle. That shows that FHIA 21 variety grow in the presence of potassium compared to nitrogen, and the dose of 120 kg·ha −1 of nitrogen seems to be an important amount to stimulate the growth and development of this plant.
In CORNE 1, the heaviest bunches were obtained with T2 and T6 treatments. Only T2 gave heaviest fruits with a shorter production cycle. T6 (high dose of potassium) induced a longer production cycle of 137 days compared to T2. For potassium, by its quantity can have a limiting effect on the plant's use of nitrogen [16]. Especially since the T5 treatment offering half a dose of potassium resulted in a production cycle close to T2 and PHI was 31 days longer than those of T2 treatment. On the other hand, T3 resulted in minimum values for regimen weight, hands and fingers number, and fruit length. Nevertheless fruits under T3 treatment were of high weight. Nitrogen is involved in plant growth and potassium fertilization ensures fruit development in weight and size. Indeed, there is a positive correlation between potassium and fruit weight [15] [33].
The PITA 3 variety had the fastest growth with the shortest production time. In fact, it is a short-cycle hybrid variety [34]. The hybrid varieties PITA 3 and FHIA 21 have given the largest regimes and therefore a better yield. There are high-yielding varieties [35] [36]. The CORNE 1 variety was noted for the quality of its large fruits. It is indeed a product that is highly appreciated for the marketable quality of its fruit. This has led to its high demand by the population on the national, sub-regional and international markets [37] [38].

Conclusion
PITA 3 had an improved growth by the treatment with high dose of potassium (987 kg·ha −1 ) with 240 kg·ha −1 . FHIA 21 had optimal growth with the reference treatment T2 with 240 kg·ha −1 (N) and 658 kg·ha −1 (K). Increasing the nitrogen dose resulted in a drop in growth. For CORNE 1, growth was maximal in the presence of high doses of nitrogen and potassium. However, the repetition of these tests over 2 or 3 crop cycles in various areas would allow to better appreciate the relevance of this study findings.