Potentials of plantain peel and Tithonia diversifolia leaves as soil amendments in enhancing performance and nutritional contents of tomato (Solanumlycopersicum)

Abstract

Screen house experiment was conducted in 2020 at the Landmark University Teaching and Research Farm Omu-aran, Kwara State. The experiment was carried out to evaluate the potential of dried unripe plantain peel and Tithonia diversifolia as soil amendments and its effect on growth, yield and fruit quality of tomato. Four rates each of dried plantain peel (0, 5, 10 and 15 t/ha) and Tithonia diversifolia (0, 10, 20 and 30 t/ha) were applied sole and combined. The experimental layout was a completely randomized design (CRD) with three replicates. Parameters were collected on the plant height, number of leaves, number of branches, stem girth, yield and fruit quality. Data collected were subjected to Analysis of variance (ANOVA) using the GENSTAT Discovery Software, Edition 4. Comparison of the treatment means were carried out using Duncan Multiple range test (DMRT) at 0.05 level of probability. Results showed that dried plantain peel and Tithonia diversifolia improved, number and weight of fruits as well as the fruit quality of tomato and were comparable to the application of NPK fertilizer. Treatment P₅T₃₀ (T₈) increased number of leaves and number of branches while P₁₅T₂₀ (T₁₅) and P₁₀T₃₀ (T₁₂) increased plant height and stem girth respectively. Treatment P₅T₃₀ (T₈) and P₁₀T₂₀ (T₁₁) also significantly improved the fruit quality (minerals, lycopene and Vit. A) of tomato fruits. It can therefore be concluded that application of dried plantain peel and Tithonia diversifolia at P₅T₃₀ (T₈) and P₁₀T₂₀ (T₁₁) increased the vegetative, yield and quality parameters of tomato in the screen house of the study area.

1. Introduction

Tomato is a common vegetable that is widely grown in the world, it is an important horticultural crop which has promising areas for expansion and development in many developing countries like Nigeria (Hartmann, 2003). It is known to be cultivated throughout the Americas (North, Central and South) tropical Africa and Southern Italy [1]. In Africa, Nigeria is ranked as the second largest producer of tomatoes where about 2.3 million metric tonnes of fresh tomato are produced per year (FAOSTAT 2021). Cultivation of tomatoes can be done on different kinds of soils, both on a small scale for family use and on a large scale for commercialization. However, for optimum productivity to be achieved in tomato production, adequate fertility must be ensured during the growth and developmental phase (Pandey et al., 2015). Fertilizer application is a common and important soil management practice as it improves the fertility of the soil and increases agricultural productivity [2]. Inorganic fertilizers are known to be high in nutrient and are readily available in forms that can be rapidly utilized by plants. The need to meet the ever-increasing demands from intensive agriculture all over the world has necessitated the increase in the quantity of inorganic fertilizers applied to soils. However, increase in the use of chemical fertilization continuously poses a threat to preservation of biodiversity, maintenance of soil fertility and conservation of resources at an alarming rate [3]. Organic fertilizers such as animal droppings and dungs or plant/vegetable residues provide benefits like balanced nutrient supply and sustainable fertility of soils unlike the use of chemical inorganic fertilizers [4]. Organic fertilizers from plant and animal sources have the ability to improve the physical conditions of the soil via soil aggregation improvement, reduction of soil hydraulic conductivity and mechanical resistance as well as bulk density [5,6]. The use of organic resources for the supply of nutrients to plants are often proposed as alternatives means to the use of chemical mineral fertilizers (Palm et al., 1996).

There are many agricultural wastes that are available and within the reach of small holder farmers. Some of them are relatively high in their nutrient concentration however there is little information about their potential to supply nutrient and improve the fertility of the soil thereby increasing yield. According to Ref. [7]T. diversifolia used as green manure reduced soil bulk density and increased porosity, soil organic matter, nutrient content, growth, yield and mineral contents of tomato crop. Also, studies carried out in the highlands of western Kenya identified that green biomass of T. diversifolia was effective for the supply of nutrients for maize [8,9]. T. diversifolia application at 20 tons ha⁻¹ in maize increased number of leaves, plant height and stem girth than other treatments applied [10].

In Nigeria and many parts of Africa, plantain (Musa paradisiaca) fills in as a significant staple food. The major wastes of plantain and banana handling and processing in Nigeria are their peels (created because of mechanical or manual expulsion of the external covers of plantain and banana pulps during processing). The peels represent 40% of the overall weight of fresh bananas or plantains and these peels are at present either utilized as compost or disposed of in numerous nations [11]. Plantain is rich in phyto-nutrients and consequently has dietary benefit [12]. The peels contain bioactive compounds however they are disposed of and not utilized effectively. Many studies have been carried out to determine the nutrient composition of plantain peel (Mohapatra et al., 2010) [13,14,15] and it has been discovered to contain varying nutrient composition that when incorporated into the soil could aid the growth, development and even improve the quality of agricultural produce.

Despite the fact that plantain peel to contain varying and important nutrients which when applied to the soil could positively affect the growth, yield and even the nutritional content of agricultural crops planted, very little or no information is available on its effect on different crops especially on its effect on the nutritional content of agricultural vegetable fruit plants like tomato.

This study evaluate the use of cheaper and economical plant based sources (dried plantain peel and T. diversifolia) of plant nutrients in comparison with NPK fertilizer on the growth, yield, and nutritional contents of tomato.

2. Material and methods

2.1. Growth conditions and plant materials

Screen house experiment was conducted at the Teaching and Research Farm of Landmark University, Omu-Aran, Kwara State Lat 8° 9′N and Long 5° 61′E with an altitude of 495 m elevation above the sea level in the derived savannah zone of Nigeria. Top soil still with moisture was collected from 0 to 15 cm depth around the screen house where no agricultural activities has been carried out for five years, the soil was thoroughly mixed, and 18 kg was put in polythene bags of size 30 cm × 17 cm which was perforated to allow for aeration and water drainage. Pre-cropping soil samples for the experiment were randomly taken from some polythene bags and bulked to obtain composite samples for laboratory analysis. Analysis was done for soil physical (particle size) and chemical (organic carbon, N, P, K, Ca, Mg, Zn) properties. The hydrometer method was used for the determination of particle size [16]. Soil organic carbon (OC) was determined by the procedure of Walkley and Black using the dichromate wet oxidation method [17]. Total N was determined by the micro-Kjeldahl digestion method [18]. Available P was determined by Bray-1 extraction followed by molybdenum blue colorimetry [19]. Exchangeable K, Ca, and Mg was extracted using 1 M ammonium acetate (Hendershot et al., 2007). Thereafter, the concentration of K was determined on a flame photometer, while Ca and Mg were read on an Atomic Absorption Spectrophotometer.

Unripe plantain peels was obtained from plantain vendors, dried in an open space under the sun for 5 days and grounded using a mechanical grinding machine. Fresh T. diversifolia leaves, a common and abundant weed during the rainy season was obtained from around the research farm of Landmark University, Omu-Aran. Samples of both the grounded plantain peels and fresh T. diversifolia leaves were taken to the laboratory to determine their nutrient composition.

The experiment was laid out in Completely Randomized Design (CRD) and each treatment was replicated three times. Four levels of plantain peel at 0 t/ha, 5 t/ha, 10 t/ha, 15 t/ha which is equivalent to (0 g, 90.0 g, 135.0 g, 180 g) per 18 kg of soil and T. diversifolia at 0 t/ha, 10 t/ha, 20 t/ha, 30 t/ha which is equivalent to (0 g, 90 g, 180 g and 270 g) per 18 kg of soil. NPK 15: 15: 15 fertilizer was applied at 150 kg/ha [20]. The treatment combinations includes:

Treatment 1 = P₀T₀; Treatment 2 = P₀T₁₀; Treatment 3 = P₀T₂₀; Treatment 4 = P₀T₃₀;

Treatment 5 = P₅T₀; Treatment 6 = P₅T₁₀; Treatment 7 = P₅T₂₀; Treatment 8 = P₅T₃₀;

Treatment 9 = P₁₀T₀; Treatment 10 = P₁₀T₁₀; Treatment 11 = P₁₀T₂₀; Treatment 12 = P₁₀T₃₀;

Treatment 13 = P₁₅T₀; Treatment 14 = P₁₅T₁₀; Treatment 15 = P₁₅T₂₀; Treatment 16 = P₁₅T₃₀;

Treatment 17 = NPK.

Copra F1 tomato variety which was gotten from Technisem, a seed distribution company in Nigeria was used for the experiment. It has a semi-indeterminate growth habit, it is resistant to fusarium wilt disease, and it is known for its extended shelf life, very good vigour and fruit firmness as well as high productivity. It is also very popular for processing into cans and tomato paste.

2.2. Agronomic practices

In a covered and protected nursery, the seeds were pre-germinated using a germinating tray and sterilized soil as the germinating medium. Watering was carried out daily. Twenty-one days after sowing, two healthy seedlings were transplanted in each pot and watered regularly until they stabilized, after which thinning was carried out to one seedling per pot. The two amendments i.e. dried, grounded plantain peel and fresh T. diversifolia leaves were applied two weeks before transplanting for mineralization to take place while NPK fertilizer was applied one week after transplanting. Weed control was carried out manually by hand picking of weeds that emerge from each pot.

Staking was carried out by using ropes in the screen house. Drip irrigation method was adopted throughout the period of the experiment, irrigation was carried out for 30 min, once every day. The drip irrigation dispenses 0.5 L per 30 min. Mature and ripped fruits of tomato were harvested at three to five days’ interval for 3 weeks from 56 days after transplanting, weighed and values recorded after which some of the harvested fruits were taken to the laboratory for quality assessment.

2.3. Data collection

Vegetative parameters (plant height, number of leaves, number of branches and stem girth) at 2, 4, and 6 weeks after transplanting (WAT), yield (number and weight of fruits) and quality parameters were collected during the study.

2.4. Laboratory analysis

Samples of grounded dried plantain peel and fresh T. diversifolia leaves were collected and analysed for N, P, K, Ca and Mg as described by Ref. [21]. At harvest, tomato fruits of uniform sizes were randomly collected from each pot and analysed for their minerals, lycopene, vitamin A and heavy metal contents. Mineral elements of tomato fruits were determined according to methods recommended by the Association of Official Analytical Chemists [22]. One gram of each dry sample was digested using 12 cm³ of the mix of HNO3, H₂SO₄ and HClO4 (7:2:1 v/v/v). Contents of Cu, Fe, Zn, Al, Mn, K and Ca were determined by atomic absorption spectrophotometry [6]. Fresh tomato fruits were cut up and mixed. The samples were homogenised and stored under oxygen-free conditions. Lycopene from tomato juice was extracted with n-hexane–methanol–acetone (2:1:1, v/v) containing 0.5gL−1 butylated hydroxytoluene (BHT). The optical density of the hexane extract was measured at 502 nm with a Lambda 3B UV/VIS spectrophotometer (PerkinElmer Instruments, Shelton, CT, USA).17. The lycopene level was calculated by applying the molecular extinction coefficient of 158 500.

2.5. Statistical analysis

Data collected from the experiment was subjected to analysis of variance using the GenStat statistical package (GENSTAT Discovery Software, Edition 4) and treatment means were compared using Duncan's multiple range test at p < 0.05 probability level.

3. Results

3.1. Initial soil properties

The laboratory analysis of the soil prior to transplanting is as shown in Table 1. The soil pH was slightly acidic, with a textural class of sandy loam, the soil's nitrogen content was very low, organic matter content was low, the available phosphorus was adequate, and the exchangeable K was moderate, while the exchangeable Ca was low though Na and Mg are all suitable.

Table 1.

Soil physical and chemical properties prior planting (0–15 cm).

Parameter	Values	Parameters	Values	Parameters	Values
Sand (%)	76.22	K (cmol/kg)	0.23	ECEC (cmol/kg)	5.73
Silt (%)	12.96	Na (cmol/kg)	0.67	Available Phosphorous (mg kg-1)	15.20
Clay (%)	11.94	Mg (cmol/kg)	1.28	Zn (mg kg-1)	0.45
Textural Class	Sandy Loam	Ca (cmol/kg)	1.28

4. Chemical composition of T. diversifolia leaves and dried plantain peel

Table 2 shows that T. diversifolia leaves had varying quantities of nutrients, it had higher values for N and Mg compared to plantain peel. However, dried plantain peel had higher values for P, K, Ca, Na, Fe and Zn.

Table 2.

Chemical composition of T. diversifolia leaves and dried plantain peel.

Nutrient (mg kg−1)	N	P	K	Ca	Mg	Mn	Na	Fe	Zn	Cu	Cr	C:N
Tithonia diversifolia leaves	1.80	0.65	0.05	0.14	0.004	0.002	0.11	0.22	0.038	ND	ND	7.76
Dried plantain peel	0.37	57.10	1.84	1.62	0.0012	ND	1.28	0.81	0.11	0.60	0.48	14.45

ND - Not Detected

4.1. Vegetative parameters

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on plant height and Stem girth of tomato.

Table 3 shows that at 2 WAT, application of dried plantain peel and T. diversifolia leaves at P₁₅T₁₀ (T₁₄) had the highest value for plant height compared to other treatment and was statistically similar to NPK (T₁₇) except P₀T₃₀ (T₄) and control (T₁) which had the least value. At 4 WAT and 6 WAT, P₁₅T₂₀ (T₁₅) had higher value for plant height which was statistically similar to NPK (T₁₇) and other treatments except control (T₁).

Table 3.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on plant height and stem girth of tomato.

	Plant height (cm)			Stem girth(cm)
Treatment	2 WAT	4 WAT	6 WAT	2 WAT	4 WAT	6 WAT
P0T0 (T1)	11.25c	20.15b	32.90b	0.90a	1.70b	2.05bc
P0T10 (T2)	28.25abc	36.80ab	42.95ab	1.50a	3.05ab	3.63ab
P0T20 (T3)	30.80abc	37.50ab	42.90ab	1.35a	2.70ab	3.75a
P0T30 (T4)	24.40bc	39.50ab	46.85ab	2.10a	3.50a	4.70a
P5T0 (T5)	23.25abc	35.00ab	39.20ab	1.75a	2.65a	3.00ab
P5T10 (T6)	23.50abc	37.00ab	41.50ab	1.35a	2.70ab	3.35ab
P5T20 (T7)	35.25abc	42.50ab	48.20a	2.40a	3.65a	4.90a
P5T30 (T8)	34.85abc	44.75a	51.55a	1.90a	3.30a	4.65a
P10T0 (T9)	26.00abc	35.80ab	41.25ab	1.35a	2.65a	3.55ab
P10T10(T10)	33.50a	44.25a	50.05a	2.10a	3.05a	3.45ab
P10T20 (T11)	35.25abc	42.00ab	49.10ab	1.60a	2.75ab	3.48ab
P10T30(T12)	40.25ab	47.00ab	50.00a	1.20a	2.55ab	5.50a
P15T0(T13)	31.50ab	41.50ab	52.25ab	1.25a	2.20ab	3.35ab
P15T10(T14)	47.75a	55.50a	62.00a	2.45a	3.50a	4.65a
P15T20(T15)	44.50a	56.00a	63.35a	1.90a	3.10a	4.10ab
P15T30(T16)	35.50ab	45.00a	53.10a	1.80a	2.90ab	4.15a
NPK (T17)	28.05abc	41.75ab	45.95ab	0.85a	2.09ab	2.90b
SED ±	11.25c	20.15b	32.90b	0.693	0.718	4.714

Means follwed by the same letter(s) are not significantly different from each other at 5% level of probability.

Treatment P₁₅T₁₀ (T₆) had higher value for stem girth, it was statistically similar to NPK (T₁₇) and other treatment. However, the value obtained for NPK (T₁₇) at 2 WAT performed least. At 4 WAT, P₅T₂₀ (T₇) had higher value for stem girth and was statistically similar to other treatment except for control (T₁) while at 6 WAT, NPK (T₁₇) and control (T₁) had the least values for stem girth.

5. Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on number of leaves and number of branches of tomato

The result of application of dried plantain peel, T. diversifolia leaves and NPK on number of leaves of tomato is as shown in Table 4, At 2, 4, 6 WAT application of P₅T₃₀ (T₈) produced more number of leaves, P₀T₁₀ (T₂), P₀T₀ (T₁), and NPK (T₁₇) had the least number of leaves.

Table 4.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on number of branches and leaves of tomato.

	Number of branches			Number of leaves
Treatment	2 WAT	4 WAT	6 WAT	2 WAT	4 WAT	6 WAT
P0T0(T1)	1.00a	1.00c	2.00c	4.00b	8.50 ab	11.50c
P0T10(T2)	1.00a	5.00a	8.50bc	4.00b	12.00 ab	17.00bc
P0T20(T3)	1.00a	4.00a	7.00bc	10.50 ab	12.50 ab	17.00bc
P0T30(T4)	1.00a	4.00a	7.00bc	6.00 ab	9.50 ab	14.00bc
P5T0(T5)	1.00a	1.50bc	9.50bc	4.50 ab	11.00 ab	15.50bc
P5T10(T6)	1.00a	1.50bc	11.00bc	4.50 ab	12.00 ab	16.50bc
P5T20(T7)	2.00a	8.00b	18.00 ab	6.50 ab	17.50 ab	22.00abc
P5T30(T8)	1.00a	14.00a	27.00a	12.00a	25.50a	36.00a
P10T0(T9)	1.00a	3.00bc	13.00b	4.50 ab	13.00 ab	16.50bc
P10T10(T10)	1.00a	5.00bc	14.50a	6.50 ab	12.50 ab	15.50bc
P10T20(T11)	1.00a	7.0bc	11.00bc	5.50 ab	15.00 ab	20.50abc
P10T30(T12)	1.00a	2.50bc	5.50bc	6.00 ab	12.00 ab	19.50abc
P15T0(T13)	1.00a	4.00bc	13.00bc	6.50 ab	11.50 ab	15.50bc
P15T10(T14)	1.00a	4.00bc	13.00b	6.50 ab	13.50 ab	19.50abc
P15T20(T15)	3.50a	12.00a	23.00 ab	7.50a	24.00a	30.00 ab
P15T30(T16)	1.00a	5.50bc	15.50 ab	8.00a	14.50a	20.50abc
NPK(T17)	1.00a	1.00c	3.00c	4.00b	11.00a	13.50bc
SED ±	3.073	7.650	7.180	1.697	4.733	11.445

Means follwed by the same letter(s) are not significantly different from each other at 5% level of probability.

The effects of dried plantain peel, T. diversifolia leaves and NPK on number of branches of tomato is as shown in Table 4. At 2 WAT, P₁₅T₂₀ (T₁₅) had more number of branches but was statistically similar to NPK (T₁₇) other treatments except treatments P₀T₀ (T₁) and P₀T₁₀ (T₂). At 4 WAT, P₅T₃₀ (T₈) had higher number of branches but was statistically similar to P₁₅T₂₀ (T₁₅). Control (T₁) and NPK (T₁₇) had the least number of branches. At 6 WAT, application of Tithonia diversifolia leaves and dried plantain peel at P₅T₃₀ (T₈) significantly increased the number of branches as it had higher value for number of branches. NPK (T₁₇) while control (T₁) had the least number of branches and were both statistically similar.

6. Yield parameters

6.1. Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on yield of tomato

Fig. 1, Fig. 2 shows the effects of the application of dried plantain peel, T. diversifolia leaves, and NPK on yield of tomato. Result showed that relative to the control (T₁) and application of P₀T₁₀ (T₂) which gave the least value for all the yield parameters, combined application of dried plantain peel and T. diversifolia leaves significantly increased values for number of fruits/plot and fruit yield. Higher value was observed for the number and weight of fruits at application of P₁₀T₂₀ (T₁₁) though the value was statistically similar with the values obtained at the application of NPK (T₁₇) for number of fruits alone. Treatments P₁₀T₂₀ (T₁₁), P₁₅T₁₀ (T₁₄), P₅T₂₀ (T₇), P₅T₃₀ (T₈), P₁₀T₃₀ (T₁₂), P₁₅T₁₀ (T₁₄), P₁₅T₂₀ (T₁₅) and P₁₅T₃₀ (T₁₆) was statistically similar to treatment P₁₀T₂₀ (T₁₁) for both number of fruits and weight of fruits in the screen house.

Fig. 1.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on number of fruits of tomato.

Fig. 2.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on weight of fruits of tomato.

6.2. Anti-oxidant composition

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on lycopene and Vit-A composition of tomato.

Data presented on Fig. 3, Fig. 4 showed that application of dried plantain peel, T. diversifolia leaves and NPK resulted in varying quantity of lycopene and Vit A in tomato fruits in the screen house. Lycopene content increased with the application of P₁₀T₂₀ (T₁₁) as it had the highest value for lycopene content followed by P₁₅T₂₀ (T₁₅), P₅T₁₀ (T₆), P₀T₂₀ (T₃), P₀T₁₀ (T₂), P₁₀T₃₀ (T₁₂) and NPK (T₁₇). Lower values were observed with the application of P₅T₀ (T₅) and P₁₀T₁₀ (T₁₀). P₀T₂₀ (T₃) gave the highest content value for Vit-A followed by, P₁₀T₂₀ (T₁₁), P₁₀T₁₀ (T₁₀), and NPK (T₁₇). P₅T₁₀ (T₆), P₀T₃₀ (T₄) and control (T₁) increased lycopene content of tomato.

Fig. 3.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on lycopene content of tomato.

Fig. 4.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on Vitamin A content of tomato.

6.2.1. Mineral composition

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on mineral composition of tomato.

Data presented on Fig. 5 showed that application of dried plantain peel, T. diversifolia leaves and NPK resulted in varying quantity of Ca, Mg, K and Na in tomato fruits. Significantly, higher value for Ca (Fig. 5c) was observed when P₀T₃₀ (T₄), P₀T₂₀ (T₃) and P₅T₃₀ (T₈) were applied. Significantly, lower value for fruit Ca was observed on the application of NPK (T₁₇), P₀T₁₀ (T₂) and control (T₁).

Fig. 5.

Effects of application of dried plantain peel, T. diversifolia leaves and NPK fertilizer on mineral composition of tomato.

Treatment P₅T₃₀ (T₈) significantly produced higher value for Mg (Fig. 5d). This value was followed by the application of P₅T₂₀ (T₇) while P₅T₀ (T₅) and P₅T₁₀ (T₆) gave similar values for fruit Mg. Least value for fruit Mg was observed at the application of control and P₁₅T₀ (T₁₃). P₅T₃₀ (T₈) gave higher value for K (Fig. 5b), control (T₁) gave the least value for K.

Na (Fig. 5a) content in the fruit also increased with the application of P₁₀T₂₀ (T₁₁), NPK (T₁₇) and P₁₀T₁₀ (T₁₀) except P₅T₀ (T₅), P₅T₁₀ (T₆) and control (T₁) that resulted in a significantly lower value for Na in the fruit.

6.3. Heavy metal composition

Effects of application of dried Plantain peel, T. diversifolia leaves and NPK fertilizer on heavy metal composition of tomato.

Data presented on Fig. 6, shows the effects of application of dried Plantain peel, T. diversifolia leaves and NPK on heavy metal composition of tomato in the Screen house. Higher values for Fe (Fig. 5a) was obtained for treatments NPK (T₁₇), P₁₀T₂₀ (T₁₁), P₁₀T₁₀ (T₁₀), P₁₀T₀ (T₉) and lower values was obtained for treatments P₁₅T₁₀ (T₁₄) and P₀T₁₀ (T₂). Treatments P₁₅T₁₀ (T₁₄) had the highest value for Al (Fig. 5b) while P₅T₂₀ (T₇) had the lowest value. For Mn (Fig. 5c), treatment P₁₀T₀ (T₉) had higher value while treatments P₁₅T₃₀ (T₁₆), P₁₅T₂₀ (T₁₅), P₁₀T₃₀ (T₁₂) and P₅T₃₀ (T₈) had zero content of Mn. Treatment P₁₅T₁₀ (T₁₄) had the highest value for both Cu (Fig. 5d) and Zn (Fig. 5e). P₁₅T₀ (T₁₃) had the lowest value for Cu while P₅T₃₀ (T₈) had the lowest value for Zn.

Fig. 6.

Effects of application of dried Plantain peel, T. diversifolia leaves and NPK fertilizer on heavy metal composition of tomato.

7. Discussion

Laboratory determination of the nutrient elements contained in T. diversifolia leaves and dried unripe plantain peel revealed that they both contained mineral elements in varying proportions appropriate for tomato cultivation. Results obtained from the laboratory analysis of the physical and chemical properties of the soil prior to planting suggested that the soil used for the experiment was relatively low in nutrients and that the rapid response of the tomato to the treatments used could be attributed to the fertility status of the soil prior to planting.

The low nutrient content of the soil used for these study is a general characteristic of most Nigerian soils which indicated that the soil could not be cropped profitably without fertilizer application for optimal productivity (Ojuola 2015).

There was a significant vegetative and yield response of tomato to the application of dried plantain peel and T. diversifolia. The application of T. diversifolia, dried plantain peel, and NPK significantly affected vegetative parameters (plant height, number of branches, number of leaves and stem girth) positively. Increase in plant height may have been the result of integrated application of T. diversifolia leaves and dried plantain peel which thereafter increased soil availability of nutrients. Aboyeji et al. [20] found that incorporating green manures increased soil availability of OM, N, P, K and Mg which invariably had a positive effect on radish vegetative parameters. Laboratory study of dried plantain peel showed that it is relatively high in P compared to other nutrients, P assists in various plant functions such as photosynthesis, nutrient movement inside the plant, energy transfer and sugar transformation [23].

Application of P₅T₃₀ (T₈) also resulted in wider stem girth. This result could be attributed to the findings by Ref. [20] that application of Parkia biglobosa and T. diversifolia increased both the vegetative and yield parameters of radish. Increased values for vegetative parameters with the application of T. diversifolia and dried plantain peel at P₅T₃₀ (T₈) for most of the parameters could be as a result of the quick availability of minerals essential for the growth and development of tomato because T. diversifolia leaves decompose faster compared to the dried plantain peels. Results of this study showed that application of T. diversifolia and dried plantain peel at P₁₅T₂₀ (T₁₅), P₅T₂₀ (T₇), P₅T₃₀ (T₈) and P₁₀T₁₀ (T₁₀) increased the different vegetative parameters compared to NPK (T₁₇).

Wider stem girth at the application of P₅T₃₀ (T₈) could also result in longer and bigger roots thereby increasing the surface area which promotes the availability and assimilation of other nutrients, hence increased vegetative parameters which could also culminate into increased yield. These results are in support of the findings of [10]; who reported that application of T. diversifolia significantly increased the number of Celosia argentea leaves, plant height, stem girth and yield. Ademiluyi et al. [24] also recorded higher growth of vegetative and reproductive in soils applied tithonia than soils applied NPK fertilizer.

Increased number of leaves as a result of application of P₅T₃₀ (T₈) could be attributed to high moisture content and low C: N ratio of T. diversifolia leading to early mineralization and fast release of nutrients. This report is in line with the findings by Aboyeji et al.s [25] that T. diversifolia leaves have low C: N ratio leading to their faster mineralization thereby allowing for increased vegetative and yield performance of cocoyam. Lower performance of NPK (T₁₇) for number of leaves and number of branches compared to other treatments in most cases could be as a result of leaching and or volatilization. Ojeniyi et al. [26] reported that spent grain and cocoa husk have increased tomato growth and yield significantly compared to NPK fertilizer.

Results on yield parameters showed that application of T. diversifolia and dried plantain peel at P₁₀T₂₀ (T₁₁) gave increased values for number and weight of fruits. Increased yield at the application of P₁₀T₂₀ (T₁₁) could be because of the increased availability of Ca, Mg and K contained in the dried plantain peel as well as increased N availability from T. diversifolia. Application of NPK (T₁₇) increased yield parameters however, it was statistically similar to the application P₁₀T₂₀ (T₁₁), P₁₅T₁₀ (T₁₄), P₅T₂₀ (T₇), P₅T₃₀ (T₈), P₁₀T₃₀ (T₁₂), P₁₅T₁₀ (T₁₄), P₁₅T₂₀ (T₁₅) and P₁₅T₃₀ (T₁₆). This result is in line with [8] who reported that green manure from T. diversifolia was able to provide P and N in quantities and rates sufficient for increased yield of maize. Adekiya et al. [24] also reported that green manures increased growth and yield of Okra compared to NPK. These result also agrees with the findings of [27]; that there was increased maize and grain yield with T. diversifolia biomass than NPK.

Application of plantain peel and T. diversifolia increased the mineral composition of tomato fruits. Increased values for Ca, Mg and K was at the application of P₅T₃₀ (T₈), while values for Na increased with the application of P₁₀T₂₀ (T₁₁). Increased mineral composition of tomato fruits could be as a result of the increased availability of the minerals in the soil as a result of mineralization of the amendments used during the study, thereby allowing for easier uptake by the roots and deposit in the fruits. NPK (T₁₇) was relatively low in mineral content compared to most of the other treatments except control. Adekiya et al. [24] reported that green manures had increased amount of mineral in Okra. Shokalu et al. [10] also reported that N, P, K and Ca were significantly increased in Celosia argentea with the application of T. diversifolia.

Lycopene content increased at the application of plantain peel and T. diversifolia at P₁₀T₂₀ (T₁₁) compared to NPK (T₁₇). Vitamin A content significantly increased with the application of P₀T₂₀ (T₃) and P₁₀T₂₀ (T₁₁). According to Ref. [20]; green manures increased the vitamin C content of radish. Increased lycopene and Vit A at P₁₀T₂₀ (T₁₁) could be because of the increased anti-oxidant content contained in the plantain peel. Uzama et al., (2015) reported that unripe plantain peel contains increased anti-oxidant content.

Values obtained for heavy metal composition on the application of plantain peel, T. diversifolia and NPK showed that they were all below the permissible level as stipulated by the [28]. Higher Fe content was noted at the application of NPK (T₁₇) while treatment P₁₅T₁₀ (T₁₄) contained higher contents for Cu, Al, Zn and Mn. Increased heavy metal composition at the application of P₁₅T₁₀ (T₁₄) could be because of the increased amount of plantain peel. According to Ref. [15]; unripe plantain peel contains good amounts of Pb, Fe, Zn, and some other heavy metals. This could have helped to increase its Al, Zn, Mn, Cu and Fe composition in the tomato fruits.

8. Conclusion

Results of this study showed that integrated application of Plantain peel and T. diversifolia significantly increased tomato production, yield and fruit quality (Lycopene, Vit-c, Minerals and heavy metal content). This study therefore demonstrates that application of T. diversifolia and dried plantain peel favourably competes with NPK fertilizer. Application of plantain peel at P₅T₃₀ (T₈) increased the vegetative and yield parameters of tomato. Application of P₁₀T₂₀ (T₁₁) increased the yield of tomato. Increased mineral composition was also noted for application of plantain peel and T. diversifolia at P₅T₃₀ (T₈) while application of plantain peel at P₁₀T₂₀ (T₁₁) increased anti-oxidant content of tomato. Therefore, for increased yield and quality application of dried plantain peel and T. diversifolia at P₅T₃₀ (T₈) and P₁₀T₂₀ (T₁₁) is recommended for the cultivation of tomato in the study area.

Author contribution statement

Faith Oluwatobi Okunlola, Aruna Olasekan Adekiya and Christopher Muyiwa Aboyeji: Conceived, designed the experiments and Wrote the paper. Charity Aremu and Wutem Sunny Ejue: Analysed and interpreted the data. Adebukola Elizabeth Adewumi, Omotayo Mary Owoojuona and Avwerosuo Erere: Contributed reagents, materials, analysis tools or data. Olasunkanmi Peter Olajide: Performed the experiments.

Funding statement

This researchwas funded by Landmark University Centre for Research and Innovations Development.

Data availability statement

Data included in article/supp. material/referenced in article.

Declaration of interest's statement

The authors declare no comflicting interets.