The study orchard’s soil was loam in texture, andlow in organic matter with pH 8.42. Nutritionally, the soil was deficient inavailable P and Zn and adequate in K and B concentrations (Table 1). Noindications of salinity were found. 1.
1. Yield and quality parametersNo significant between-years changesin fruit yield and quality parameters were found; therefore, only 3-yr meansare provided in Table 2. Application of foliar and soil B and Zn resulted inoverall significant increases in fruit quality (pulp recovery, TSS, Acidity)and yield (weight, volume) parameters as compared to control (Table 2).
The significantincreases in fruit weight (320 g), volume (308 cm3), pulp recoverypercentage (62%) and total soluble solids (17.8), and a significant decrease intitratable acidity (0.32%) was recorded in response to T5.Similarly, T7 resulted in significant increases in fruit weight (274g), volume (279 cm3), pulp recovery percentage (59%) and titratableacidity (0.35).
The T4 (foliar application; ZnSO4 0.5%)resulted in the second highest TSS contents as compared to T5 andother treatments. Bahadur, Malhi, and Singh (1998)reported the similar findings of enhanced yield and better fruit quality (TSS,acidity, aroma, flesh color and taste) inresponse to the soil application of Zn as compared to control. Conversely, Masroor et al. (2016)reported the similar responses from two foliar applications of Zn in Novemberand March in contrast to our single foliar application at flowering. Supportiveresponses of yield and quality parameters of Strawberry and pomegranate fruitswere reported by Abdollahi, Eshghi, and Tafazoli (2010)and by Khorsandi, Yazdi, and Vazifehshenas (2009),respectively.
Both investigations found that the soil application had overallbetter results than those in response to foliar application of micronutrients.The positive responses of mango fruit quality and yield to the combinedapplication of Zn and B may be due to improvements in concentrations of sugars,vitamins and some physiological parameters (Hegde and Venkatesh 2007).1.2.
Leaf mineral contentsWe noticed significant increases in leaf B and Zn contents in the 3rdyear of study in response to the year-over-year applications of soil B and Zn(T5). Across all years,the soil application of micronutrients resultedin significantly higher concentrations in leaves, as compared to control (Table3) as reported by Khan et al. (2012)for their research on sweet orange leaf concentrations of micronutrients. The T5and T7 showed the highest concentration of Zn in all years ascompared to the other treatments. Similarly, T5 and T6were the highest in increasing the leaf concentration of B as compared to othertreatments in all years (Table 3). Based on overall leaf mineral B and Zncontents, our research supports thefindings of Zia et al.
(2006)who suggested that the soil applications are better than the foliarapplications of these nutrients in enhancing leaf mineral micronutrients. No significant between-years changesin leaf mineral N, P and K were found; therefore, only 3-yr means are providedin Table 4. Overall significant increases in leaf N, P and K contents wereobserved in response to the Zn and B applications as compared to control.
The T5resulted in the highest concentration of NPK (1.06%, 0.19%, 0.57%)respectively, compared to all other soil or foliar applications ofmicronutrients; however, all micronutrient applications improved the mineralcontents in mango leaves in general.
We also found that the optimumconcentrations of leaf mineral contents improved fruit quality and mango cropyield (Table 3, 4; Figure 1, 3). The balanced application of fertilizers withZn and B ensures optimum nutrient concentrations in leaves which may lead tobetter quality and sustainable increase in mango production. South-Asian soils,typically under orchards, are Zn and B deficient (e.
g., Zia et al. 2006)and may lead to reduced uptake of N and K by plants. No antagonistic impacts ofsoil Zn and P are reported upon each other’s uptake (when applied at differenttimes); however, Razzaq et al. (2013)found that the P depressed the uptake of Zn when the two nutrients were appliedin combination to the soil.1.
3. Fruit retention percentageWe present responses of fruitretention and yield to foliar and soil B and Zn applications separately for allyears as well as for 3-yr means (Figure 1).Since no significant between-years differences for treatments were found;therefore, significance letters are associated with3-yr means only. A significantly higher fruit shedding percentage andsignificantly lower fruit yield were noticed in control as compared to those atall treated plots. Significant and the highest fruit retention percentage(0.
88%) and fruit yield (112 kg plant-1) were found in response to T5.The second highest yield (106 kg plant-1) was observed in T6;it indicates that the foliar application of Zn and B also resulted in yieldincrease but lesser than that in response to the soil application. The plant Znconcentration is found to be directly related tofruit drop as it is involved in the synthesis of tryptophan; therefore, greaterthe concentration of Zn in shoot and twigs, more will be the synthesizedtryptophan or auxin (Indole Acetic Acid), potentially leading to a reduction infruit drop (Singh, Malik, and Davenport 2010, Ahmed et al. 2012).Likewise, B application increases fruitsetting and yield due to physiological changes or improvement in reproductivedevelopment (Chaplin, Stebbins, and Westwood 1977).
Conversely, B deficiency causes rupture of internal and external tissues whichmay result in fruit drop (Westwood and Stevens 1979).Application of B and Zn may improve the biochemistry of fruit, and lead toenhanced number of fruit set per panicle and fruit retention percentage,resulting in sustainable mango yield (Alloway 2009);however, more research work is suggested to formulate the best managementconditions and practices for sustainable increases in fruit quality and yieldto be able to increase exports and contribute to meet potentially growing foodsecurity challenges.1.
4. Relationships – fruit yield and qualityparametersThe fruit yield had significant andpositive correlations with number of fruit set per panicle (R2 =0.61; p = 0.039; Figure 2A) and fruit retention percentage (R2 =0.
91; p < 0.001; Figure 2B); the fruit retention was in turn related withthe number of fruit set per panicle (R2 = 0.64; p = 0.031; Figure2A). The highest leaf mineral B, Zn, N, P and K concentrations (Table 3 andTable 4), and the highest number of fruit-set per panicle, fruit retentionpercentage and fruit yield (Figure 1) were recorded in response to the combinedsoil application of B and Zn in T5.
More and thorough investigationsincluding all possible combinations of foliar and soil applications need to beconducted to formulate best management practices for enhanced yields of betteror export quality.We also present the correlationbetween individual and clustered ranks assigned by 10 different testers basedon sensory evaluation technique and Hedonic scale ranking (1-8) of variousorganoleptic parameters: taste, flavor,texture, aroma, and acceptability (Figure3). Overall, significant Spearman rankcorrelation (R2 = 0.68; p < 0.05 in all cases) was found betweenthe rankings of the mango fruit parameters.
Significant differences were alsofound between individual parameter ranks among all treatments, with the highestranks in response to T6 and the lowest overall ranks to T4.In contrast to our findings, Masroor et al. (2016) reported the highestacceptability and fruit quality in response to soil Zn application.Conclusions1. Soil application of B and Zncombination significantly increased the leaf mineral B and Zn contents, numberof fruit set per panicle, fruit retention percentage, and fruit yield (volume,weight), pulp recovery and TSS at harvest or after ripening, whereas it reducedthe titratable acidity and early fruit shedding.
2. The combined applicationsignificantly improved the fruit quality parameters of taste, flavor, texture,aroma, and the overall acceptability. Therefore, the combined soil applicationof B and Zn mitigates B and Zn deficiency and improves fruit yield and qualityof mango cv. Chaunsa (white) more efficiently than the other individual orcombined foliar or soil treatments used in this study under the specificexperimental conditions.