Among the micronutrients required by banana, iron, zinc and boron are found to be major yield limiting factors in India. Nearly, 5.9, 4.7 and 1.27 kg of Fe, Zn and B, respectively are absorbed per hectare for optimum production of banana based on the total uptake of these micronutrients (Lahav, 5). Generally, the micronutrients are given to banana through either soil or foliar application. In soil, where pH is greater than 8.5, the availability of micronutrients to banana crop is not at sufficient level, even though the soil is rich or applied with sufficient quantities of micronutrients. Turner et al. (10) found that zinc deficiency was more common in high pH soils or on excessively limed soils because Zn ions in the chelated complex can be replaced by calcium ions. They also found that banana yield declined from more than 60 t/ha at soil pH 4.5 to about 30 t/ha at pH 8.7. This was thought to be associated with changing supply of Zn to the plants and leaf analysis data supported this interpretation. Under such conditions, micronutrients can be given to banana through foliar sprays. In contrast, Hernandez and Lugo Lopez (3) found that foliar spray of trace elements gave a markedly lower response than soil applied mixtures. Absence of Fe and Zn depressed performance to the level of NPK only. Das and Mohan (2) proved that application of 6g B, 9g Zn, 6g Cu and 6g Mn per plant significantly increased bunch length, number of hands and fingers in banana cultivars, Jahaji (AAA), Brajahaji (AAA) and Chenichampa (AAB). Studies on soil and foliar applications of micronutrients in banana, and its evaluation and comparison in high pH soil are meagre. Hence, an attempt was made in the present study to compare the soil and foliar applications of micronutrients in banana in high pH soil.

A field experiment was conducted during 2003–05 with Karpuravalli (ABB) banana (plant crop and ratoon crop) in 3³ factorial randomized block design with three levels namely, 0, 1 and 2. The level 0 indicates control (no micronutrient application). The level 1 indicates soil application of 5 g of FeSO₄ or ZnSO₄ or borax per plant at 3 months after planting (MAP). The level 2 indicates foliar application of 0.5% FeSO₄ or 0.5% ZnSO₄ or 10 ppm boric acid of each of three factors (micronutrients), Fe, Zn and B at 3 MAP, 5 MAP and 7 MAP. Using above three factors (micronutrients - Fe, Zn and B) of three levels each (control, soil application and foliar application), twenty-seven treatment combinations (3³) were made. They were (0,0,0), (0,0,1), (0,0,2), (0,0,0), (0,1,1), (0,1,2), (0,2,0), (0,2,1), (0,2,2), (0,0,0), (0,0,1), (0,0,2), (1,0,0), (1,1,1), (1,1,2), (1,2,0), (1,2,1), (1,2,2,), (2,0,0), (2,0,1), (2,0,2), (2,0,0), (2,1,1), (2,1,2), (2,2,0), (2,2,1) and (2,2,2). In each treatment combination, the levels of micronutrients were given in the order of Fe, Zn and B respectively. Common N, P₂O₅ and K₂O doses of 200, 50 and 400 g plant⁻¹, respectively were given to all the plants. The soil of experimental field was of pH-8.7, EC-0.2 dS m⁻¹, OC-0.23%, CaCO₃-5.2%, CEC-11.5 cmol (P⁺) kg⁻¹, N-230 kg ha⁻¹, P₂O₅-8.5 kg ha⁻¹, K₂O-150 kg ha⁻¹, Fe-2 ppm, Zn-1.8 ppm, B-0.4 ppm, Cu-0.3 ppm and Mn-1.5 ppm, silty clay loam texture, Typic Ustropept, mixed, hyperthermic. The treatment combinations were replicated thrice. Eight banana plants per treatment were maintained in every replication. The soil applications of above micronutrients were given at 3 months after planting. The foliar applications of above micronutrients were given at 3, 5 and 7 MAP. The leaf samples were collected (Martin-Prevel, 6) at flowering stage from all the treatment combinations for nutrient analysis. The oven dried leaf samples were finely ground and analysed for nitrogen by Kjeldahl method (Piper, 7). Finely ground, oven dried leaf samples were digested in tri-acid mixture and, phosphorus was estimated by vanadomolybdo-phosphoric yellow colour colorimetric method, potassium by flame photometric method (Chapman and Pratt, 1) and micronutrients by atomic absorption spectrometer (Varian Spectr AA-200). Data on bunch weight (kg) were recorded at the time of harvest. The correlation coefficients of the growth and yield parameters, and leaf nutrient concentrations with the bunch weight were worked out. The correlation coefficients of leaf micronutrient concentrations under different mode of applications with bunch weight were worked out to study the effects of different modes of application of micronutrients on the bunch weights. The fruit quality parameters like total soluble solids (TSS in°Brix) and acidity (%) were estimated and TSS/acid ratios were also worked out.

Micronutrients like Fe, Zn and B, both as soil and foliage application, influenced the plant growth and yield parameters significantly (Table 1). The treatment, (1,2,2) recorded the highest pseudostem height, girth, total leaf area and bunch weight. Total number of leaves was the highest in the treatment (0,2,2) and was 80 percent more than that of the control. The highest number of fingers per bunch was recorded in the treatment (0,2,0). Application of Fe alone in soil increased the bunch weight slightly by 11.5 percent over control, while foliar spray of Fe alone increased the bunch weight significantly by 30.8 percent over control. Thus, foliar application of Fe alone was found to be better than soil application in high pH soil. Soil application of Zn alone had not increased the bunch weight but foliar spray of Zn alone increased the bunch weight significantly by 23.1 percent over control. Since Zn is fixed under alkaline conditions, it is easy to correct its deficiency with a foliar spray of 0.5 percent ZnSO₄ (Jordine, 4) rather than soil application. Thus, foliar spraying of Zn alone was found to be better than the soil application in high pH soil. Neither soil application nor foliar application of B alone influenced the bunch weight significantly. However, either mode of B application along with foliar spray of Zn influenced the bunch weight significantly and similar trend was also observed with foliar spray of Fe on bunch weight. These observations indicated the synergistic effects of foliar applied Fe and Zn on the uptake of B applied in either mode and are in agreement with Srivastava (8).

No significant effects of these soil or leaf applied micronutrients on leaf concentrations of N and Ca were observed. Though soil or foliar application of Fe alone had not influenced the leaf K concentration significantly, Fe along with Zn and B increased the leaf K concentration significantly. The treatment combination (1,2,2) recorded the highest leaf K concentration. Soil application of Zn reduced the P concentrations in the leaf significantly by 21 to 42 percent as compared to control, while foliar application of Zn recorded leaf P on par with that of control (Fig. 1). This indicated the antagonistic effect of soil applied Zn on P uptake by banana. This may be due to the formation of less soluble zinc phosphate in the soil (Tisdale et al., 9) leading to reduction in phosphorus uptake in banana. Thus, these observations suggested that foliar application was better than soil application of Zn. The leaf micronutrient concentrations were significantly influenced by soil and leaf applications of micronutrients under high pH soil condition (Table 1). Soil application of Fe increased leaf Fe concentration by 37.3 percent and foliar application of Fe increased leaf Fe concentration by 45.1 percent, when compared to control. Soil application of Zn increased the leaf Zn concentration by 30 percent and foliar application of Zn increased the leaf Zn concentration by 50 percent when compared to control. The treatment of 1, 2, 2 recorded the highest leaf Zn concentration. Soil applied B increased the leaf B concentration by 25 percent and the foliar applied B increased leaf B concentration by 75 percent, when compared to control. The highest leaf B concentration was recorded in treatment 2, 1, 2. Higher leaf Cu and Mn concentrations were observed with foliar application of micronutrients as compared to soil applications. The correlation coefficients of the growth and yield parameters with the bunch weight were highly significant at 1% probability. The correlation coefficients of leaf nutrient concentrations, except of boron and copper, with the bunch weight were highly significant at 1% probability (Table 1). The correlation coefficients between the leaf nutrient concentrations under different modes of application of micronutrients and corresponding bunch weights are given in the Table 2. The leaf Fe concentrations due to soil applied Fe influenced the bunch weight more than those due to foliar sprayed Fe. But, in cases of Zn and B, the trend was reverse. The foliar sprayed Zn or B was more effective in increasing bunch weights than soil applied Zn or B.

The fruit quality parameters like total soluble solids, acidity and TSS/acid ratio were significantly influenced by the soil or foliar application of micronutrients. The highest TSS, lowest acid and the highest TSS/acidity ratio were recorded in the treatment 1, 2, 2. Thus, keeping over all performance and correlations coefficients, the treatment 1, 2, 2 was found to be superior to other treatment combinations, based on its influence on plant growth, yield, and nutritional status in the leaf tissues and fruit quality. In conclusion, soil application of Fe (5 g FeSO₄ per plant at 3 MAP), foliar applications of Zn (0.5 percent ZnSO₄ each at 3, 5 and 7 MAP) and B (10 ppm boric acid each at 3, 5 and 7 MAP) with recommended dose of NPK (N: P₂O₅: K₂O-200: 50: 400 g plant⁻¹), produced the highest bunch weight and best quality fruits.

References