Nutritional qualities of Kapok ( Ceiba pentandra L. Gaertn.) in response to fertilizer management

Ceiba pentandra (L.) Gaertn, is a leafy vegetable that is under-utilized due to lack of information about the nutritional potential and agronomic practices. Minerals, vitamins, and protein content of succulent leaves of C. pentandra plants grown under different fertilizer rates (Control (No fertilizer), 5 t ha -1 of poultry manure (PM) + 200 kg ha -1 of NPK, 10 t ha -1 of PM, 20 t ha -1 of PM, 450 kg ha -1 of NPK, and 20 t ha -1 of PM + 100 kg ha -1 of NPK) in the Department of Crop Science Garden, University of Nigeria, Nsukka were evaluated using standard analytical procedures in a replicated trial. Analysis of variance indicated a non-significant effect of fertilizer rates on vitamin contents assessed. Protein and the minerals evaluated showed non-significant response to fertilizer except zinc and calcium. Highest concentration of zinc (0.46 mg/100g) was attributed to 20 t ha -1 of PM which was statistically similar to 0.43 and 0.42 mg/100g obtained from leaves of plants grown without fertilizer and 5 t ha -1 of PM + 200 kg ha -1 of NPK, respectively. Soil amendment at 5 t ha -1 of PM + 200 kg ha -1 of NPK resulted in high accumulation of calcium (145.00 mg/100g). Conclusively, application of 20 t ha -1 of PM or 5 t ha -1 of PM + 200 kg ha -1 of NPK may be appropriate for growing C. pentandra . The study established that C. pentandra can be brought under regular cultivation culture without compromising the nutritional quality.


INTRODUCTION
Ceiba pentandra (L.) Gaertn. is an under-utilized indigenous plant species usually f ound in the wild, it belongs to Malvaceae f amily. The matured tree can reach 56 m in height with a girth of 10 m or more, it has a long cylindrical and huge buttresses of 8 m height and wide spreading (Friday et al., 2020). The trunk and larger branches are of ten crowded and armed with conical spines. It has palmate leaves of about 5 to 9 leaf lets, each up to 20 cm long (Osuntokun et al., 2017). It is known as Araba in Yoruba, Akpu-Ogwu in Igbo, Rimi in Hausa and Bamtami in Fulani.
In Nigeria, C. pentandra is under-utilized, the leaf y vegetable is known in local communities especially in Kogi State. The rural people cherish the leaf which is harvested, processed into powder and used to make delicious soup known as ' Kuka'. Friday et al. (2020) reported that dried leaf made into powder is used in preparing soup during the dry season. The succulent leaves can be boiled and made into soup comparable to Okra which is served with starchy balls made f rom cassava, yam and millet. Ethnobotanical evidences established that mashed leaves of the plant can be applied on tumors as dressing (Burkill and Dalziel, 1997;Kuruvilla and Anilkumar, 2018). The plant extract is also employed in treating eye and skin inf ections, dysentery, diabetes, arthritis, insect bite, diarrhea, bronchitis and chronic f ever (Elumalai et al., 2012). According to Alagawadi and Shah (2011), pharmacological studies attest to the antiinf lammatory properties of the plant parts. In addition, it possesses hepatoprotective (Bairwa et al., 2010) and antiulcerogenic compounds (Anosike et al., 2014).
The oil extracted f rom the seed has some potential as a bio f uel and it can also be used in paint preparation. The plant is a good source of f ibre and timber (Osuntokun et al., 2017). The f loss f rom the f ruit can be used f or making mattresses, pillows, absorbent materials and tinder (Adeniji et al., 2019). Several studies have shown that C. pentandra leaves contained minerals and vitamins. Shahin et al. (2016) reported 153.66 mg/100g of potassium, 177.0 mg/100g of calcium, 48.15 mg/100g of magnesium, 1.54 mg/100g of iron and 27.09 mg/100g of zinc. According to Adepoju and Ugochukwu (2019), C. pentandra leaves contain vitamin B2 (0.19 mg/100g) and B12 (0.24 mg/100g). Friday et al. (2020) reported that C. pentandra possessed vitamin C (4.91 mg/100g).
Increase in dietary diseases and malnutrition ravaging most developing countries like Nigeria has been linked to nutritional def iciencies such as minerals and vitamins (Stevens et al., 2021). Balanced and healthy diet can be ensured by consuming leaf y vegetables as sources of minerals and vitamins accompanied with staple f ood. Vegetables have the potential to improve the diet of the people and reduce the risk of developing cancer, cardiovascular and other chronic diseases (Umakanta et al., 2020). Despite the enormous benef its of Ceiba pentandra, it is under-utilized and the crop has not been brought under regular cultivation culture like the other indigenous plant species in Nigeria as a result of inadequate knowledge of its nutritional value, soil and f ertilizer requirements, germination, agronomic practices and pests. The quality of f arm produce is a f unction of the growing environment in which soil f ertility management is a major determinant. Soil f ertility could be enhanced using organic or inorganic f ertilizers and could be integrated (Aba et al., 2020).
Theref ore, investigating into this indigenous crop can provide evidence-based inf ormation that can encourage the domestication of this plant to remedy f ood security challenge, improve peoples' diet and prevent the crop f rom going into extinction. There is, theref ore, the need to examine response of C. pentandra to dif f erent f ertilizers especially with respect to the nutritional contents of the leaves. The aim of this study was to determine the leaf nutritional qualities of C. pentandra in response to dif f erent f ertilizer management.

Location of the Experiment
The f ield experiment was carried out at the Department of Crop Science teaching and research f arm of University of Nigeria, Nsukka (07 ° 29' N, 06 ° 51' E and 400 m above sea level), Enugu State, Nigeria. Succulent leaves harvested at ten months af ter transplanting were analyzed f or minerals, vitamins and protein content at Simuch Scientif ic Analytical Laboratory, Nsukka.

Collection of C. pentandra germplasm and treatment application
Dried pods of Kapok were sourced f rom Unosi town in Ajaokuta Local Government Area of Kogi State in June, 2020. The pods were opened and the seeds extracted. The seeds were planted in nursery bags f illed with cured sawdust. One month af ter seedling emergence, seventy-two unif ormly sized seedlings were selected and transplanted to the f ield (see Fig. 2). The treatments were six rates of f ertilizer application (Control (No f ertilizer), 5 t ha -1 of poultry manure + 200 kg ha -1 of NPK, 10 t ha -1 of poultry manure, 20 t ha -1 of poultry manure, 450 kg ha -1 of NPK, and 20 t ha -1 of poultry manure + 100 kg ha -1 of NPK). The f ield experiment was a randomized complete block design (RCBD) and replicated f our times. The seedlings were transplanted at inter-row distance of 3 m and intra-row distance of 2 m on a single row plot of 3 plants. Planting holes (35 cm x 35 cm x 35 cm dimension) were dug in accordance to the plant spacing. An alleyway (3.0 m) separated two blocks. Fertilizers were applied to the seedlings at f our weeks af ter transplanting. The f ertilizer application was done in split doses, 40% and 60% of the required quantity was applied in September, 2020 and November, 2020, respectively. The plants were watered heavily af ter the second application in order to allow plant roots to absorb the nutrients. Weeding was carriedout at 4 weeks interval with the use of glyphosate.

Collection of plant material
Succulent leaves ( Fig.1) f rom the above experiment were collected and analyzed for minerals, vitamins and protein content. In this study, f irst to f ourth leaf f rom the tip of the shoot were harvested and used f or laboratory analyses. The experiment was arranged in a completely randomized design (CRD) with three replicates. The f ield experiment was set up having f our replications while the laboratory experiment was replicated three times. Leaf samples were collected f rom replicate three and f our, bulked together and used as replicate three f or the nutritional qualities. The plant sample was authenticated by Mr Chijioke John Onyeukwu, Department of Plant Science and Biotechnology, Faculty of Biological Sciences, University of Nigeria, Nsukka.

Analysis of minerals
The of f icial method of AOAC (2007) was adopted f or the mineral analysis of the samples. Two gram of each ground sample was weighed into a silica dish, then placed in a muf f le f urnace and heated at 600 0 C f or three hours, allowed to cool in a desiccator and weighed. The samples were dissolved with HCl and prepared f or reading using atomic absorption spectrometry (AAS).
Atomic absorption spectrometer (AA-7000) was used to determine calcium, magnesium, zinc and iron and absorbance read at wavelength of 422.7 kk-nm, 285.2 kk-nm, 213.9 kk-nm and 248.3 kknm, respectively.

Vitamins determination
Vitamins were determined f ollowing the analytical procedure of AOAC (2007). In determining vitamin A, 2.0 g of sample was weighed into a set of conical f lasks. The sample was saponif ied, extracted with 10 ml of xylene-kerosene mixture, shaken f or 30 minutes and centrif uged f or 25 minutes. The supernatant was run on the spectrometer at 328 nm and 460 nm respectively. Concentration of vitamin B12 was determined using Spectrophotometer (Labomedspectronic 21D) and the absorbance of samples was read at a wavelength of 510 nm. At a wavelength of 460 nm, absorbance, the standards and samples were read using f luorescent spectrometer to determine vitamin B2. Spectrophotometer (Spectronic 21D) at a wavelength of 15 seconds and 30 seconds was employed to determine vitamin C. At wavelength of 540 nm, vitamin B6 was determined using Spectrophotometer (752P).

Protein determination
Content of crude protein in the samples was determined by the routine micro Kjeldahl procedure/technique.

Statistical analysis
Following the procedure f or CRD, analysis of variance (ANOVA) was perf ormed on triplicates data collected using GENSTAT (2013) statistical sof tware. Comparison of treatment means was conducted using least signif icant dif ference (LSD) at 5% probability level.

RESULTS
Soil properties of the experimental site prior to transplanting and the sample of poultry manure utilized in the experiment.
Properties of the soil f rom the study site prior to transplanting and the analysis of poultry manure used is shown in Table 1. The nitrogen content (0.098%) was very low and the available phosphorus (12.59 ppm) was also considered to be low. The potassium content, cation exchange capacity and base saturation were 0.10 mg/100g, 10.80% and 51.48%, respectively. The organic carbon (1.857%) and organic matter (3.201% ) contents indicated that the soil was not f ertile. The soil was characterized as sandy loam.
The poultry manure used had high organic matter, nitrogen, potassium and sodium contents with respective values of 85.12%, 1.315%, 0.18% and 0.0155%. The poultry manure also had high pH (8.5) in water which was strongly alkaline. Table 2 presents the ef f ect of fertilizer application rates on vitamin contents of C. pentandra. Fertilizer application rates had no signif icant (p > 0.05) ef f ect on vitamin contents of C. pentandra. However, application of poultry manure (PM) at 20 t ha -1 which was supplemented with 100 kg ha -1 NPK has the tendency to yield more vitamin A (0.110 mg/100g), B12 (0.473 mg/100g) and B2 (5.080 mg/100g) than others. Vitamin B6 (6.030 mg/100g) was highly concentrated in leaves of C. pentandra grown with no f ertilizer application, this will reduce cost of production. Application of 10 t ha -1 of PM exhibited superiority in producing more vitamin C (4.790 mg/100g) than other treatment combinations. Ef f ect of f ertilizer rates on mineral constituents (mg/100g) and protein content (%) of C. pentandra is shown in Table 3. Except f or zinc and calcium contents, the rest of the mineral constituents and protein content were not signif icantly (p > 0.05) inf luenced by f ertilizer treatment. Sole application of 20 t ha -1 of PM had the highest content of zinc (0.457mg/100g) which was not statistically dif ferent f rom the values (0.433 and 0.417 mg/100g) obtained in leaves of plants grown in plots without any soil amendment and 5 t ha -1 of PM + 200 kg ha -1 of NPK, respectively. The least value f or zinc (0.370 mg/100g) was obtained when PM was applied at 10 t ha -1 . Combined application of 5 t ha -1 PM + 200 kg ha -1 NPK had more concentration of iron (0.090mg/100g) than other treatments. Application of 5 t ha -1 of PM combined with 200 kg ha -1 NPK and 20 t ha -1 PM + 100 kg ha -1 NPK had the tendency to yield more magnesium (0.642 mg/100g) than others. More concentration of calcium (145.000 mg/100g) was recorded in the leaves of plants treated with PM at 5 t ha -1 and supplemented with NPK at 200 kg ha -1 while the least (119.200 mg/100g) was obtained in the control plot. Plants in the control plot had the highest protein content (19.860%) than other treatments, this imply that the production cost will drastically reduce.

DISCUSSION
The result of this present work revealed that C. pentandra leaf contained vitamins. Fertilizer application rates did not have signif icant ef f ect on vitamin contents of C. pentandra. The nonsignif icant f ertilizer dif f erence obtained in vitamin contents indicated that vitamin constituents in the leaves were similar across the f ertilizer treatments. The result is in agreement with the studies of Ndubuaku et al. (2015) who f ound nonsignif icant ef f ect of PM on vitamin contents of Moringa oleifera leaves in Nsukka. However, they reported lower values (0.58, 0.66 and 1.07 ppm) f or vitamin A, B2 and B6, respectively in leaves of poultry manure treated Moringa oleifera plants f rom Nsukka. The vitamin B12 and B2 f ound in the leaves of C. pentandra in this present study were higher compared to those obtained by Adepoju and Ugochukwu (2019) who reported vitamin B12 and B2 to be 0.24 and 0.19 mg/100g, respectively. Vitamin B2 value recorded in this work was higher than (0.8 mg/100g) obtained by El Sohaimy et al. (2015) in Moringa oleifera leaves. The vitamin C value recorded in this present study is comparable with 4.91 mg/100g reported by Friday et al. (2020) in Kapok leaves f rom Kogi State, Nigeria.
Vitamins are considered necessary f or cellular metabolism. Vitamin C protects against inf ection, hastens woundhealing, boosts the immune system and its antioxidant properties may lower the risk of developing cancer (Tsado, 2015). The variation in the contents of the nutrients reported by the various researchers could be linked to the dif f erences in the environmental conditions (Ndubuaku et al., 2015).
Fertilizer application rates positively inf luenced some of the mineral contents assessed. The quality of any f arm produce is a f unction of the growing environment in which soil f ertility management is a major determinant (Aba et al., 2020). Higher accumulation of zinc in leaves harvested f rom plants grown with 20 t ha -1 of PM might have resulted f rom availability of nutrients and general nutrition of C. pentandra plants by this rate. Aba et al. (2020) noted that organic f oods generally possess a higher content of mineral than those derived f rom conventional production system. Calcium content obtained in this study was more in leaves harvested f rom plants in plots that received PM at 5 t ha -1 and augmented with NPK at 200 kg ha -1 . This indicated that the complimentary use of PM and NPK f ertilizer provided balanced nutrition f or C. pentandra plants that resulted to higher concentration of calcium in the leaves. The values f or iron obtained in this work were comparable to 62.20 ppm reported by Ndubuaku et al. (2015) in Moringa oleifera leaves grown with poultry manure in Nsukka, but values f or zinc obtained in this study were higher than the 2.86 ppm f ound in their work. However, our value for magnesium was lower than the value (0.75%) they reported. Iron, zinc and calcium values recorded in this work were higher compared to 0.35, 0.04 and 7.66 mg/100 g reported by Friday et al. (2020) in f resh leave of C. pentandra f rom Kogi State. The values obtained f or calcium in this work was higher compared to the report of Adepoju and Ugochukwu (2019) who obtained 119.38 mg/100g of calcium in C. pentandra leaves f rom Imo State. These minerals are required f or normal f unctioning of the body. Calcium and phosphorus give bones their rigidity and are the major and essential component of bones and teeth in the human and animal body (Zhao et al., 2019). Zinc is important f or the maintenance of protein structure and nucleic acids (Soni et al., 2017). Magnesium has extensive cellular ef f ects as it supports normal f unctioning of ATP (adenosine triphosphate) and glucose metabolism (Enzonga et al., 2019). Iron is important due to its role in metabolic processes including respiration and DNA synthesis (Okunlola et al., 2019).
The protein content observed in this work (16.320 -19.860%) is higher in comparison with 12.40% f ound by Ndubuaku et al. (2015) in Moringa oleifera leaves treated with dif f erent poultry manure rates in Nsukka. It is also higher than that of C. pentandra leaves f rom Anyigba (12.97%) as obtained by Friday et al. (2020). In contrast the crude protein value of 28.47% reported by Obi-Abang et al. (2019) in C. pentandra leaves is higher than the values obtained in this work. Proteins are essential in body building, boosts the immune system and aids cell division as well as growth (Osuntokun et al, 2017). The variation observed in minerals and protein content may be due to genetic makeup and environmental dif f erences. Olajide et al. (2020) reported dif f erences in proximate composition of 10 accessions of Af rican walnut which suggested the probable roles of genetic diversity and variability in soils the accessions grew on.

CONCLUSION
The study indicated that f ertilizer treatment did not inf luence vitamin contents which imply that application of f ertilizers produced similar ef f ect on the vitamin contents irrespective of the rate. The study also established variation in some mineral contents of C. pentandra across the f ertilizer rates. Zinc was more concentrated in the leaves of C. pentandra harvested in plots treated with poultry manure at 20 t ha -1 . Generally, the iron values were f ound to be low in this study. Harvested leaves f rom plants in plots amended with poultry manure at 5 t ha -1 and augmented with inorganic f ertilizer at 200 kg ha -1 had greater accumulation of calcium. Application of poultry manure at 20 t ha -1 or poultry manure at 5 t ha -1 supplemented with 200 kg ha -1 NPK may be appropriate f or growing C. pentandra since zinc and calcium were more concentrated in the leaves of plants treated with these rates. This inf ormation could guide the utility and domestication of C. pentandra f or commercial cultivation. Sensitization campaign on the nutritional potential of this crop and f urther research on the ef f ect of f ertilizer application rates on nutritional qualities of C. pentandra is recommended.