Explicating the fertilizer potential of anaerobic digestate on soil quality and growth performances of Solanum lycopersicum var. Kashi Aman

doi:10.21203/rs.3.rs-4809815/v1

Application of anaerobic digestates (ADg(s)) from organic wastes as bio-fertilizer in agricultural field is economically viable and environmentally sustainable alternative. The study aimed to utilize ADg(s) (25, 50, 75 and 100% w/w) from the organic proportion of flower-waste (FW), sewage-sludge (SS) and municipal solid wastes (OFMSW) as soil amendment to investigate soil nutrient status and growth performances of tomato (Solanum lycopersicum var. Kashi Aman). Organic carbon, nitrogen, phosphorous, exchangeable Na, K and Ca ions, and enzymatic activities were increased with increase in ADg(s) amendment in soil with relatively higher increase under OFMSW amendment. Metal contents in the soil amended with ADg(s) were in the order, Fe > Zn > Mn > Cu > Ni > Cr > Cd and their contents increased with increasing OFMSW, SS and FW. Plant biomass and fruit-yield were higher under all ADg(s) amendments compared to the control, with maximum yield under 100% SS. Contents of Fe, Zn, Mn, Cu, Cr and Pb in the entire plant were positively correlated with the yield under all ADg(s) amendments. Based on translocation and bioconcentration factors, tomato was found to be efficient in accumulation of metals except Cd. Content of Ni, Mn, Cu, Zn and Cd in the fruit were though below FAO/WHO limit, but Fe, Cr and Pb contents were above the limit. Hence, utilization of ADg(s) from OFMSW, SS and FW as fertilizer although improved the soil fertility and tomato yield, but due to high contents of Fe, Cr and Pb in the fruit, cultivation of tomato is not suggested.

Flower-waste

Heavy metals

Municipal solid wastes

Sewage-sludge

Solanum lycopersicum

Increase in global population, changing lifestyle, industrialization and urbanization have resulted in accelerated rate of waste generation. Waste generation and its management in developing nations are more challenging accredited to the availability of limited resources and inadequate planning (Udoh 2024). Globally, generation of municipal solid waste has reached to 2.3 billion tons in 2023 (UNEP 2024). India generates approximately 62 million tons (MT) of wastes each year, of which only 43 MT are gets collected, 12 MT are being treated before disposal, and rest are simply discarded in waste yards without proper pretreatment (TERI 2023). Improper waste disposal causes environmental pollution, causes food chain contamination and deteriorates public health which ultimately affects the quality of life (Srivastava et al. 2021; Gautam et al. 2016). Nevertheless, utilization of solid-waste as bio-fertilizer for agriculture purposes not only reduces the waste burden on land but also supports sustainable use of solid waste resources to improve soil quality and promotes economic production (Udoh 2024). Utilization of organic wastes through stabilized techniques such as vermicomposting, composting and anaerobic digestion benefits the environment in several ways viz. reduces the waste burden on landfill sites, greenhouse gas emission, consumption of chemical/inorganic fertilizers and cost of transportation (Panuccio et al. 2021).

Anaerobic digestion of organic wastes has turned to be economically viable, eco-friendly and sustainable option to manage solid wastes. Anaerobic digestates from domestic and agricultural wastes etc are exemplary that enhances the crop production and improves its quality when utilized as soil fertilizer (Vaish et al. 2022). Being rich in essential macro and micro nutrients, anaerobic digestates are known to enhance organic carbon content, NPK level and microbial activity in soil that support the yield as well as quality of Solanum melongena (Vaish et al. 2022) and Solanum lycopersicum (Panuccio et al. 2021). In India, vegetables’ production has reached a new height in recent years. Vegetables contributed a production of 212.91 tons per hectare during the year 2022-23 (Ministry of Agriculture & Farmers Welfare 2023). Solanum lycopersicum L. commonly called as tomato contributes second highest percentage (10.57%) amongst 80% of the total vegetable production in the country (Sarkar et al. 2023). After China, India ranks second in production of tomato (Dwary et al. 2023). An average production of tomato in India is 24.36 metric tons per hectare (Dwary et al. 2023).

Researches have shown that digestates’ residue from wastes also contain toxic metals, organic toxins and traces of antibiotics that may adversely affects environmental health and living beings (Wolak et al. 2023; Vaish et al. 2022; Manyi-Loh et al. 2018]. Therefore, it is essential to assess the characteristics and potential impact of digestates prior to their utilization in agricultural field. Inadequate studies have been conducted to explore the potential application of digestates generated from organic proportion of flower-waste, sewage-sludge and municipal solid wastes as soil fertilizer for tomato cultivation. Therefore, the current study has been conducted with the objectives to assess the biological and physico-chemical properties of anaerobic digestates (ADg(s)) from organic proportion of flower-wastes (FW), sewage-sludge (SS) and municipal solid wastes (OFMSW), to evaluate the growth performance and yield of S. lycopersicum var. Kashi Aman grown under different ADg(s)’ amendments, and to assess the impact of selected metals on growth as well as yield performances of tomato plant.

2.1 Experimental site

The experimental work was accomplished in the field condition at the IESD of BHU in Varanasi, India (geographical location illustrated in Vaish et al. (2022) between March and May 2019. Experimental duration was marked by following meteorological status- temperature range: 29.4°C to 34.7°C, relative-humidity: 59.9–67.5% and total rainfall: 43.32 mm. The soil at the experimental site showed the texture of sandy loam.

2.2 Experimental design and cultivation of the selected plant

A randomized block-design experiment was conducted using six different soil treatments (Table 1) of anaerobic digestates (ADg(s)) for each of the substrate i.e. OFMSW, SS and FW. Digestion of collected substrates was done in airtight glass bottles of 2L and evolved gases were collected through H₂O-displacement method. Thereafter, digested substrates were dried naturally and stored to 4°C for various analyses. The ADg(s) were produced in bulk as soil amendments for pot experiments. The ADg(s) were mixed uniformly with soil in definite ratios mentioned in Table 1. Physico-chemical properties of OFMSW, SS as well as FW are illustrated in Vaish et al. (2022). Agriculture soil without any amendments (C) and soil supplemented with standard dose of inorganic-fertilizers (IF) were used for comparative study against different soil treatments. Control and different soil combinations were filled in earthen-pots and placed at experimental site for a week to attain physico-chemical stabilization (Fig. 1).

Table 1

Details of different soil amendments (ADg) using IF, OFMSW, SS and FW
Treatments		Mixing ratios
Control (C)		Unamended agricultural soil
IF		Soil with recommended dose of inorganic fertilizer (urea, super-phosphate and potassium chloride (0.8 g N, 0.4 g P₂O₅ and 0.5 g K₂O)
T1		25% AD(g) + 75% soil
T2		50% AD(g) + 50% soil
T3		75% AD(g) + 25% soil
T4		100% AD(g)
Anaerobic digestate (ADg)	Treatments
OFMSW	C		IF	T1	T2	T3	T4
SS	C		IF	T1	T2	T3	T4
FW	C		IF	T1	T2	T3	T4
IF, Inorganic fertilizer; OFMSW, Organic Fraction of Municipal Solid Waste, SS, Sewage sludge,
FW, Flower-waste

Seeds of S. lycopersicum var. Kashi Aman were obtained from Indian Agricultural Research Institute, Varanasi. In each pot (diameter (30 cm) × depth (30 cm)), six seeds were sown and moisture contents of the soil was kept at 30 ± 0.63% before sowing. After 2 weeks of germination, three equidistantly spaced saplings were kept in each pot in an open field condition. Standard agricultural practices were followed to grow the plants during the study. Ploughing and thinning were done time to time, as per the requirements.

2.3 Sampling and analyses of soil

2.3.1 FTIR analysis of FW, SS and OFMSW

Fourier-transform infrared (FTIR) analysis was accomplished through Thermo-NICOLET iS5, USA using potassium bromide pellets. Spectral range used was 4000–400 cm^− 1 for identification of functional groups in anaerobic digestates of FW, SS and OFMSW.

2.3.2 Physico-chemical properties

Samples of soil, collected from control and different treatments (n = 3) before sowing and after plant harvest. The pH, electrical-conductivity (EC), total organic carbon (TOC), total nitrogen (TKN) and phosphorous (P) contents were measured following the methods illustrated in Vaish et al. (2022). Determination of exchangeable K⁺, Ca²⁺ and Na⁺ ions in soil were carried out through extraction in ammonium acetate using Hesse (1971) method followed by repeated leaching methodology. Contents of exchangeable cations were measured using flame photometer (Model 128, Systronics, India).

2.3.3 Biological properties

Fresh samples of soil from different treatments before sowing and after plant harvest (n = 3) were taken from the rhizospheric region from 10 cm depth and kept in sampling box having temperature below 4°C for analysis of enzymatic activities. The procedure for enzyme-assay was carried out under ≤ 4°C within the same day of soil sampling. The activities measured were dehydrogenase, urease, β-glucosidase, alkaline phosphatase and protease. The activities of dehydrogenase and urease were assessed following the methods of Tabatabai (1982) and Kandeler and Gerber (1988), respectively. Activities of β-glucosidase and alkaline phosphatase were assayed following Allison and Jastrow (2006) method. Soil protease activity was assessed through the Ladd and Butler (1972) method.

2.3.4 Metal analysis in soil

Oven-dried samples of soil were acid digested following Gaidajis (2003) method and contents of Ni, Fe, Pb, Cu, Mn, Zn, Cd and Cr were assessed through the Atomic Absorption Spectrophotometer (AAS) (AA-240 FS, Varian). Precision and accuracy of readings were assured following the method given in Gautam et al. (2018).

2.4 Plant sampling and analyses

2.4.1 Growth parameter, biomass and fruit yield

Random selection of the monoliths of the plant was done in triplicates from each experimental set-up at 45 and 80 DAS. Root and shoot lengths were measured using meter scale. Portable leaf-area meter (Systronics 211, India) was used to assess the area of the leaves plant^− 1. For plant biomass, monolith of the plant was splashed gently under running water to erode the soil constituents and dried at 80°C in an oven till we get a uniform weight. The plant was weighed separately in g plant^− 1 dry weight to obtained biomass. Post-harvesting (at 80 DAS), yield was determined as fresh weight of fruit (g) plant^− 1.

2.4.2 Metal contents in plant

The plant collected (n = 3) from each treatment was washed gently and thoroughly under running tap water, separated into fruit, leaves, stem and roots, and oven-dried until their constant weights were attained. The dried parts were grounded and sieved through 2 mm mesh size. For heavy metal analysis, 1 g of obtained sample was digested in 10 ml of di-acid (HNO₃: HClO₄, 9: 4) till a transparent color appeared (Gaidajis 2003). Post-filtration, the obtained solution was maintained to 25 mL using double distilled water. Concentrations of metals (Zn, Fe, Cu, Ni, Mn, Pb, Cr and Cd) were determined through AAS. Quality control of the sample analysis was assured following the method of Gautam et al. (2018).

2.5 Statistical analysis

The statistical analysis of obtained data-sets was accomplished by using SPSS-16 (Illinois, USA) software. The significant variation amongst different treatments for studied parameters was accomplished through Duncan’s-Multiple-Range test and one-way ANOVA. Principal component analysis (PCA) was performed to assess the relationship amongst growth parameters, yield and metals contents in the plant under different ADg(s) amendments in soil. Sigma Plot software (version 12) was utilized for graphical representations.

3.1 FTIR analysis of anaerobic digestate

Figure 2 presents the analysis of functional groups on the surface of OFMSW, SS and FW using FTIR spectra. Anaerobic digestates showed mid-IR spectral regions (400–4000 cm^− 1) with single bond region (2500–2500 cm^− 1), triple bond region (2000–2500 cm^− 1), double bond region (1500–2000 cm^− 1) and the fingerprint region (600–1500 cm^− 1) (Coates 2000). For OFMSW, the spectra were measured across wavenumbers ranging from 3603.13 to 462.92 cm^− 1 (Fig. 2A). In the FTIR spectra, a prominent and broad signal in the range of 3200–3600 cm^− 1 was observed for OFMSW, which corresponds to the stretching vibration of –OH groups in carboxylic, alcoholic and phenolic functional groups (Abdoli and Ghasemzadeh 2024). The peak at 3603.13 cm^− 1 showed hydrogen vibrations of the OH groups of alcohols and the peak at 3410.28 cm^− 1 was ascribed to NH stretch of aromatic primary amine (Coates 2000). The strong absorption between 2800 and 3000 cm^− 1 was attributed to C–H stretching vibration of the –CH₃ and –CH₂ functional groups, thus showing high degree of aliphaticity and aromaticity. The peak at 2344.50 cm^− 1 represents the presence of amino related component in OFMSW. The absorbance at 1882 cm^− 1 was the characteristic peak for C = O stretching for carbonyl compound (Nandiyanto et al. 2019). The peak at 1635 cm^− 1 was attributed to the presence of aromatic C = C bonds extending from the aromatic ring of lignin (Md Salim et al. 2021). The absorption at 1025 cm^− 1 was distinctive for the presence of CN stretch of primary amine, while at 772 cm^− 1 indicated the presence of aromatic C–H derived of phenyl compound (Md Salim et al. 2021). Similarly, the FTIR spectra of anaerobic digestates of SS and FW (Fig. 2B and C) showed peaks at 3603.13, 3410.28, 2947.60, 2344.50 (C = O stretching for carbonyl compound), 1635, 1387.19, 1025.10, 772.41, 711.32, 462.92 cm^− 1. Additionally, anaerobic digestate of SS (Fig. 2B) showed C-H stretch of methyl group at 2947.60 cm^− 1, C = O stretching for carbonyl compound at 1882 and 1387 cm^− 1 indicated the presence of trimethyl or tertiary butyl group, respevtively (Coates 2000). Furthermore, FTIR spectra of anaerobic digestate of FW showed nine peaks (Fig. 2C). Eights peaks were common to all the three digestates, hence showed similarities in the presence of functional groups in their structural pattern.

3.2 Soil properties and metal contents under different treatments

Before sowing, soil fertilized with IF showed significantly higher pH and EC values when compared to the control. Furthermore, decline in the pH value of soil treated with increasing ADg(s) concentrations was observed (Tables 2–4). On contrary, EC value increased with increasing ADg(s) concentrations in soil in comparison to the control. After plant harvest, pH as well as EC of treated soil showed similar trend as shown before seed sowing (Tables 2–4). Soil pH after harvest was decreased when compared to initial soil pH under different treatments with OFMSW; however no significant change in pH was observed in soil treated with SS and FW before seed sowing and after harvest. Post-harvest, EC of soil didn’t show much variation under different ADg(s) amendments when compared to its value before seed sowing. Amendment of ADg(s) to soil caused reduction in pH and significant rise in the value of conductivity (Tables 2A-C). This could be accredited to humic acid production through decomposition of organic matter resulting in decreased pH (Srivastava et al. 2018). Besides, presence of complex organic components such as lignin, lipids and steroids during anaerobic digestion are building blocks of humic acid (Lorenz et al. 2013; Tambone et al. 2009). Decreasing soil pH is also accomplished with the formation of amino-acid as well as decomposition of sugar molecules to acetic-acid via anaerobic digestion of organic substrate (Waqas et al. 2019). High humic acid level in soil is invariably responsible for enhancing the CEC and EC of soil amended with anaerobic digestates (Wu et al. 2017; Srivastava et al. 2015).

Table 2

Physico-chemical properties of the control, IF treated and OFMSW amended soil (Mean ± SE). Numbers with different letters in same row differ significantly at p < 0.05 as per the Duncan's test
Treatments	pH	EC (mS cm^− 1)	TOC (%)	TKN (%)	Avail. P (mg kg^− 1)	Ex. Na (mg kg^− 1)	Ex. K (mg kg^− 1)	Ex. Ca (mg kg^− 1)
Before sowing
C	7.31 ± 0.06^b	0.33 ± 0.006^f	4.21 ± 0.69^f	0.31 ± 0.007^bc	31.97 ± 2.11^d	182.1 ± 8.68^b	104.5 ± 1.65^f	98.00 ± 1.98^c
IF	7.64 ± 0.13^a	0.62 ± 0.04^d	13.84 ± 0.67^d	0.27 ± 0.08^c	94.32 ± 23.42^c	256.3 ± 22.49^b	179.8 ± 3.76^e	150.3 ± 16.36^a
T1	7.31 ± 0.09^b	0.46 ± 0.006^e	10.28 ± 0.72^e	0.38 ± 0.01^bc	115.9 ± 9.72^bc	288.5 ± 48.84^b	382.5 ± 2.51^d	121.8 ± 2.59^bc
T2	7.14 ± 0.09^bc	0.83 ± 0.02^c	17.61 ± 0.63^c	0.39 ± 0.01^b	135.0 ± 7.87^b	848.5 ± 256.9^a	567.8 ± 2.22^c	128.3 ± 2.16^ab
T3	7.12 ± 0.05^bc	1.19 ± 0.004^b	24.32 ± 1.13^b	0.42 ± 0.01^ab	147.0 ± 3.48^ab	1109.2 ± 151.1^a	1028.7 ± 8.80^b	142.3 ± 7.22^ab
T4	6.99 ± 0.07^c	1.65 ± 0.03^a	31.86 ± 1.48^a	0.52 ± 0.006^a	172.6 ± 1.38^a	1125.4 ± 155.5^a	1159.2 ± 5.76^a	146.3 ± 7.40^ab
After plant harvest
C	7.34 ± 0.10^a	0.36 ± 0.007^e	12.35 ± 1.85^d	0.27 ± 0.002^bc	52.75 ± 2.39^c	146.6 ± 43.41^b	145.97 ± 0.92^f	52.82 ± 1.67^f
IF	7.16 ± 0.02^ab	0.84 ± 0.03^c	19.44 ± 0.8⁰c	0.33 ± 0.06^abc	51.95 ± 4.22^c	301.7 ± 3.65^b	279.2 ± 7.08^e	97.09 ± 1.77^c
T1	7.07 ± 0.10^abc	0.48 ± 0.01^d	20.11 ± 0.51^bc	0.26 ± 0.008^c	64.74 ± 4.99^c	219.5 ± 35.97^b	321.67 ± 0.10^d	73.82 ± 0.64^e
T2	6.95 ± 0.06^bc	0.93 ± 0.03^c	23.95 ± 1.54^b	0.28 ± 0.020^bc	81.53 ± 2.76^b	417.4 ± 132.1^b	332.1 ± 4.60^c	86.52 ± 0.97^d
T3	6.89 ± 0.08^bc	1.51 ± 0.04^b	36.22 ± 1.07^a	0.36 ± 0.007^ab	97.52 ± 6.82^a	792.2 ± 163.5^a	668.6 ± 1.87^b	103.5 ± 1.79^b
T4	6.76 ± 0.13^c	1.89 ± 0.03^a	35.57 ± 1.86^a	0.41 ± 0.009^a	99.92 ± 6.24^a	848.0 ± 125.2^a	757.3 ± 2.07^a	127.0 ± 2.70^a
IF, Inorganic fertilizer; OFMSW, Anaerobic digestate of organic fraction of municipal solid waste; EC, electrical conductivity; TOC, total organic carbon; TKN, total Kjheldal nitrogen; P, phosphorous; Na, sodium; K, potassium; Ca, calcium, C, control; T1, 25% OFMSW amendment in soil; T2, 50% OFMSW amendment in soil; T3, 75% OFMSW amendment in soil; T4, 100% OFMSW amendment in soil

Table 3

Physico-chemical properties of the control, IF treated and SS amended soil (Mean ± SE). Numbers with different letters in same row differ significantly at p < 0.05 as per the Duncan's test
Treatments	pH	EC (mS cm^− 1)	TOC (%)	TKN (%)	Avail. P (mg kg^− 1)	Ex. Na (mg kg^− 1)	Ex. K (mg kg^− 1)	Ex. Ca (mg kg^− 1)
Before sowing
C	7.31 ± 0.06^b	0.33 ± 0.006^d	4.21 ± 0.69^e	0.31 ± 0.007^a	31.94 ± 2.11^c	182.1 ± 8.68^c	104.5 ± 1.65^f	098.09 ± 1.98^c
IF	7.64 ± 0.13^a	0.62 ± 0.04^c	13.84 ± 0.67^c	0.27 ± 0.08^a	94.32 ± 234.2^ab	256.3 ± 22.49^bc	179.8 ± 3.76^d	150.3 ± 16.36^a
T1	7.38 ± 0.08^ab	0.37 ± 0.01^d	7.92 ± 1.66^d	0.29 ± 0.06^a	55.15 ± 4.99^bc	225.9 ± 24.32^bc	121.2 ± 0.14^e	103.9 ± 3.99^bc
T2	6.98 ± 0.06^c	0.55 ± 0.007^c	20.90 ± 0.95^b	0.32 ± 0.05^a	74.34 ± 11.99^ab	378.2 ± 57.21^b	322.2 ± 2.94^c	125.4 ± 1.93^ab
T3	6.84 ± 0.07^c	1.00 ± 0.04^b	23.78 ± 1.52^b	0.37 ± 0.01^a	79.93 ± 8.90^ab	386.6 ± 48.98^b	392.1 ± 2.41^b	127.8 ± 11.02^ab
T4	6.84 ± 0.14^c	1.21 ± 0.007^a	31.45 ± 1.29^a	0.40 ± 0.06^a	99.12 ± 8.11^a	905.7 ± 110.3^a	906.9 ± 11.26^a	136.5 ± 2.73^a
After plant harvest
C	7.34 ± 0.10^ab	0.36 ± 0.007^e	12.35 ± 1.85^d	0.27 ± 0.002^a	52.75 ± 2.39^bc	146.6 ± 43.41^c	45.97 ± 0.92^d	52.82 ± 1.67^b
IF	7.16 ± 0.02^bc	0.84 ± 0.03^c	19.44 ± 0.80^c	0.33 ± 0.06^a	51.95 ± 4.22^bc	301.7 ± 3.65^b	279.2 ± 7.08^b	97.09 ± 1.77^a
T1	7.54 ± 0.14^a	0.37 ± 0.006^e	18.00 ± 2.55^c	0.24 ± 0.03^a	36.77 ± 4.45^c	149.6 ± 69.71^c	49.82 ± 0.16^d	55.24 ± 2.13^b
T2	6.99 ± 0.09^c	0.61 ± 0.01^d	25.87 ± 0.98^b	0.27 ± 0.02^a	67.14 ± 9.07^ab	334.5 ± 51.82^b	42.09 ± 2.36^c	67.01 ± 4.80^b
T3	6.95 ± 0.12^c	0.98 ± 0.01^b	24.76 ± 2.03^b	0.29 ± 0.07^a	72.74 ± 6.82^a	364.3 ± 42.21^b	293.5 ± 3.07^b	89.57 ± 4.07^a
T4	6.89 ± 0.05^c	1.23 ± 0.05^a	32.94 ± 1.43^a	0.31 ± 0.03^a	75.13 ± 6.96^a	722.0 ± 47.26^a	637.6 ± 18.65^a	95.74 ± 11.56^a
IF, Inorganic fertilizer; SS, Anaerobic digestate of sewage sludge; EC, electrical conductivity; TOC, total organic carbon; TKN, total Kjheldal nitrogen; P, phosphorus; Na, sodium; K, potassium; Ca, calcium, C, control; T1, 25% SS amendment in soil; T2, 50% SS amendment in soil; T3, 75% SS amendment in soil; T4, 100% SS amendment in soil

Table 4

Physico-chemical properties of the control, IF treated and FW amended soil (Mean ± SE). Numbers with different letters in same row differ significantly at p < 0.05 as per the Duncan's test
Treatments			EC (mS cm^− 1)		TOC (%)	TKN (%)	Avail. P (mg kg^− 1)		Ex. Na (mg kg^− 1)		Ex. K (mg kg^− 1)		Ex. Ca (mg kg^− 1)
Before sowing
C	7.31 ± 0.06^b	0.33 ± 0.06^d		4.21 ± 0.69^c		0.31 ± 0.07^a		31.97 ± 2.11^c		182.1 ± 8.68^c		104.5 ± 1.65^f		98.09 ± 1.98^c
IF	7.64 ± 0.13^a	0.62 ± 0.04^c		13.84 ± 0.67^bc		0.27 ± 0.08^a		94.32 ± 23.42^a		256.3 ± 22.49^c		179.8 ± 3.76^e		150.38 ± 16.36^a
T1	7.15 ± 0.09^b	0.63 ± 0.03^c		16.64 ± 2.01^ab		0.24 ± 0.04^a		53.55 ± 2.11^bc		335.0 ± 10.63^bc		1026.6 ± 9.91^d		119.5 ± 4.01^bc
T2	6.96 ± 0.09^b	1.26 ± 0.007^b		26.25 ± 0.44^a		0.27 ± 0.07^a		80.73 ± 8.11^ab		827.3 ± 251.8^ab		1121.1 ± 22.96^c		140.3 ± 5.94^ab
T3	6.98 ± 0.12^b	1.25 ± 0.003^b		28.55 ± 7.88^a		0.31 ± 0.02^a		81.53 ± 6.92^ab		987.9 ± 285.9^a		1414.4 ± 37.04^b		141.7 ± 3.30^ab
T4	6.60 ± 0.10^c	1.55 ± 0.004^a		29.06 ± 4.52^a		0.33 ± 0.05^a		107.1 ± 13.86^a		1212.5 ± 101.4^a		2163.5 ± 11.65^a		142.7 ± 9.39^ab
After plant harvest
C	7.34 ± 0.10^ab		0.36 ± 0.007^e		12.35 ± 1.85^d	0.27 ± 0.002^a	52.75 ± 2.39^bc		146.6 ± 43.41^c		45.97 ± 0.92^d		52.82 ± 1.67^b
IF	7.16 ± 0.02^bc		0.84 ± 0.03^c		19.44 ± 0.80^c	0.33 ± 0.06^a	51.95 ± 4.22^bc		301.7 ± 3.65^b		279.2 ± 7.08^b		97.09 ± 1.77^a
T1	7.54 ± 0.14^a		0.37 ± 0.006^e		18.00 ± 2.55^c	0.24 ± 0.03^a	36.77 ± 4.45^c		149.6 ± 69.71^c		49.82 ± 0.16^d		55.24 ± 2.13^b
T2	6.99 ± 0.09^c		0.61 ± 0.01^d		25.87 ± 0.98^b	0.27 ± 0.02^a	67.14 ± 9.07^ab		334.5 ± 51.82^b		42.09 ± 2.36^c		67.01 ± 4.80^b
T3	6.95 ± 0.12^c		0.98 ± 0.01^b		24.76 ± 2.03^b	0.29 ± 0.07^a	72.74 ± 6.82^a		364.3 ± 42.21^b		293.5 ± 3.07^b		89.57 ± 4.07^a
T4	6.89 ± 0.05^c		1.23 ± 0.05^a		32.94 ± 1.43^a	0.31 ± 0.03^a	75.13 ± 6.96^a		722.0 ± 47.26^a		637.6 ± 18.65^a		95.74 ± 11.56^a
IF, Inorganic fertilizer; FW, Anaerobic digestate of flower-waste; EC, electrical conductivity; TOC, total organic carbon; TKN, total Kjheldal nitrogen; P, phosphorous; Na, sodium; K, potassium; Ca, calcium, C, control; T1, 25% FW amendment in soil; T2, 50% FW amendment in soil; T3, 75% FW amendment in soil; T4, 100% FW amendment in soil

Total organic carbon, TKN and available P showed increasing trend with increasing amendments of OFMSW, SS and FW in soil (Tables 2–4). With OFMSW and FW amendments, TOC was slightly increased in soil after plant harvest when compared to soil before seed sowing. On contrary, TKN content in ADg(s) amended soil was decreased post-harvest compared to that before seed sowing. Sinatra et al. (2024), validate the result of increasing TOC and TKN in soil after long term application of solid anaerobic digestate in soil. Probably, post-digestate application improve the soil structure by enriching it with carbohydrates, lignin and protein like substances through the formation of cationic bridges, and decreasing the clay dispersibility (Voelkner et al. 2015). Increase in soil TOC could be ascribed to high organic matter contents in ADg(s) (Panuccio et al. 2021). High TKN content in the digestates is attributed to conversion of organic matter into CH_4, N and CO₂ concentrations (Tambone et al. 2009). Decomposition of organic form of nitrogen in digestate amended soil leads to production of ammonia resulting in its elevated level thereby supporting plants’ growth as well as development (Kang et al. 2021; Gutser et al. 2005). Furthermore, under appropriate environmental condition, produced ammonium ions are transformed into nitrates that augment plant-growth. Kataki et al. (2019) also showed that nitrogen supplements due to ADg amendments in soil improve soil-microbiological activity and crop-productivity. Zirkler et al. (2014), in their study revealed that phosphorus is reserved material of feedstock during anaerobic digestion. Organic N and P when transformed to their inorganic form during anaerobic digestion are relatively more available to plants for metabolic activity (Möller and Müller 2012).

Exchangeable cations viz. Na, K and Ca showed enhancement in their levels with increasing OFMSW, SS and FW percentages in the soil. However, their contents in different soil treatments were decreased after harvest as compared to before seed sowing (Tables 2–4). The result of the study is in concordance with Garcia-Sánchez et al. (2015), who showed enhancement in the levels of soil nutrients viz. inorganic N, P, K, Ca, and Mg after 30 days of application of anaerobic digestate. In addition, Panuccio et al. (2021) also showed increase in ionic contents of Na, Ca and K in both solid and liquid fraction of digestate-treated soils. High humic acid content is mainly accredited to enhanced cation-exchange-capacity in ADg enriched soil (Wu et al. 2017; Srivastava et al. 2015). Decrease in exchangeable cations after harvest indicated that fraction of Na, Ca and K have been absorbed by the plant due to decrease in soil pH resulting in their high bioavailability (Gatiboni et al. 2020).

Soil biological properties exhibit a pre-eminent role in assessing the soil health through nutrient status, microbial and enzymatic activities (Gautam et al. 2018). Activities of urease, dehydrogenease, β-glucosidase, alkaline phosphatase and protease were significantly higher under different soil treatments at initial stage compared to after plant harvest (Fig. 3). Their activities increased with increasing ADg(s) amendments with relatively higher increase found with OFMSW. Dehydrogenease activity in soil is the sensitive pollution indicator that participates in oxidation of organic-compounds by the process of dehydrogenation (Tabatabai 1994). Extracellular hydrolase enzymes viz. urease, β-glucosidase and alkaline phosphatase are related to the soil cycles of C, N and P, respectively. Protease enzymes hydrolyze protein components of organic compounds to simpler amino acids which is an important step in nitrogen cycle (Maddela et al. 2017). The increased soil enzymatic activities are mainly attributed to C, N, S and P mineralization due to high microbial activity and nutrient status (Jones et al. 2010). The finding is in consistent with Różyło and Bohacz (2020) found rise in the activities of urease, dehydrogenease, β-glucosidase, alkaline-phosphatase and protease in biogas-digestate amended soil.

Contents of Cu, Pb, Zn, Cd, Ni and Cr in soil under different treatments (Table 5) were within the intervention values causing risk to the environment (Cu, 96; Pb, 530; Zn, 350; Cd, 12 Ni, 100 and Cr, 220 mg kg^− 1) and the limits in soil required for plants (Cu, 70; Pb, 50; Zn, 50; Cd, 4; Ni, 30 and Cr, 1 mg kg^− 1) (Buchmann 2008). However, contents of Cr, Zn and Cu (in T3 treatment with SS) were above the limits in soil for plant. When compared to Indian standards (Pb, 250–500; Cu, 135–270; Ni, 75–150; Cd, 3–6; Cr, not available and Zn, 300–600 mg kg^− 1), all metals in different soil treatments complied with the permissible limit stated by Awashthi (Awashthi 2000). Noteworthy, no limits have been specified for Mn and Fe in soil. Essential micronutrients i.e. Ni, Cu and Zn play a significant role in minute quantity in plant metabolism (Jaishankar et al. 2014). Moreover, Cr, Pb and Cd do not have any biological role but may cause toxicological effects in plants when above their critical limits (Jaishankar et al. 2014).

Table 5

Total metal contents (mg kg^− 1) in soil amended with inorganic fertilizer (IF), organic fraction of municipal solid waste (OFMSW), sewage-sludge (SS), flower-wastes (FW). Value is mean ± SE. Numbers with different letters in same row differ significantly at p < 0.05 as per the Duncan's test
Metals	Anaerobic digestates	C	IF	T1	T2	T3	T4
Fe	OFMSW	379.03 ± 13.5^f	614.67 ± 2.65^d	499.65 ± 12.60^e	684.52 ± 16.54^c	964.00 ± 23.54^b	1011.27 ± 15.10^a
	SS	347.67 ± 6.54^f	386.00 ± 15.32^e	494.71 ± 17.30^d	650.99 ± 2.54^c	952.65 ± 65.32^b	966.51 ± 23.55^a
	FW	279.79 ± 6.54^e	326.00 ± 12.36^d	351.53 ± 14.36^c	458.97 ± 5.84^c	621.96 ± 18.32^b	941.44 ± 87.45^a
Ni	OFMSW	2.67 ± 0.56^d	4.67 ± 0.23^c	5.51 ± 0.25^b	5.49 ± 1.25^b	8.39 ± 0.56^b	11.57 ± 1.12^a
	SS	1.73 ± 0.54^f	6.16 ± 0.54^b	2.09 ± 0.20^e	3.06 ± 1.63^d	4.11 ± 0.32^c	8.02 ± 0.36^a
	FW	4.42 ± 0.23^e	5.83 ± 0.43^c	4.64 ± 0.36^e	5.13 ± 2.04^d	7.78 ± 0.57^b	9.26 ± 0.56^a
Cu	OFMSW	12.35 ± 1.1^f	16.92 ± 0.85^e	20.09 ± 0.06^d	35.86 ± 1.74^c	45.86 ± 1.20^b	48.42 ± 1.24^a
	SS	14.78 ± 0.85^e	8.13 ± 0.23^f	26.59 ± 0.58^d	48.75 ± 2.50^c	81.75 ± 8.02^b	83.36 ± 2.57^a
	FW	22.99 ± 0.25^e	21.34 ± 1.25^e	24.96 ± 1.24^d	44.74 ± 2.15^c	54.37 ± 3.64^b	57.89 ± 2.46^a
Zn	OFMSW	61.25 ± 2.31^f	168.00 ± 11.66^e	207.50 ± 11.64^d	245.83 ± 13.4^c	310.42 ± 2.45^b	331.25 ± 23.45^a
	SS	61.25 ± 2.64^f	101.33 ± 5.64^e	232.50 ± 11.36^d	254.17 ± 2.65^c	318.75 ± 2.05^b	339.58 ± 32.04^a
	FW	66.25 ± 1.34^f	151.33 ± 5.05^c	132.50 ± 6.32^e	145.83 ± 5.64^d	218.75 ± 1.36^b	272.92 ± 14.56^a
Mn	OFMSW	41.40 ± 1.51^e	74.80 ± 2.30^c	42.29 ± 1.25^e	55.33 ± 3.54^d	90.13 ± 7.89^b	100.43 ± 5.61^a
	SS	20.63 ± 0.35^f	68.13 ± 2.47^d	47.40 ± 2.36^e	77.33 ± 3.46^c	146.80 ± 5.64^b	213.77 ± 5.74^a
	FW	37.29 ± 1.65^e	61.47 ± 1.06^c	43.40 ± 4.02^d	65.33 ± 2.15^c	120.13 ± 4.78^b	207.10 ± 1.56^a
Pb	OFMSW	0.53 ± 0.04^e	2.63 ± 0.08^d	2.74 ± 1.65^d	3.47 ± 1.11^c	5.16 ± 0.58^b	5.82 ± 0.52^a
	SS	0.52 ± 0.01^f	2.30 ± 0.05^e	2.77 ± 0.87^d	2.96 ± 1.06^c	3.28 ± 0.76^b	3.91 ± 0.23^a
	FW	0.82 ± 0.02^f	1.14 ± 0.42^e	1.49 ± 0.06^d	1.58 ± 0.52^c	2.01 ± 0.11^b	2.25 ± 0.08^a
Cd	OFMSW	2.34 ± 0.06^f	7.08 ± 0.59^e	13.33 ± 1.02^d	18.26 ± 1.06^c	20.63 ± 1.56^b	25.97 ± 1.25^a
	SS	1.23 ± 0.01^f	10.87 ± 0.65^e	16.87 ± 1.21^d	20.83 ± 2.01^c	23.24 ± 0.87^b	29.02 ± 1.54^a
	FW	1.27 ± 0.06^d	13.08 ± 0.56^c	12.88 ± 0.98^c	17.61 ± 0.69^b	18.71 ± 0.94^b	24.17 ± 0.98^a
Cr	OFMSW	0.27 ± 0.01^f	0.32 ± 0.02^e	0.40 ± 0.31^d	0.52 ± 0.04^c	0.69 ± 0.02^b	0.78 ± 0.24^a
	SS	0.30 ± 0.02^e	0.32 ± 0.20^e	0.44 ± 0.24^d	0.55 ± 0.01^c	0.69 ± 0.04^b	0.79 ± 0.64^a
	FW	0.23 ± 0.01^e	0.34 ± 0.01^d	0.37 ± 0.22^d	0.44 ± 0.04^c	0.50 ± 0.02^b	0.76 ± 0.71^a
Fe, iron; Ni, nickel; Cu, copper; Zn, zinc; Mn, manganese; Pb, lead; Cd, cadmium; Cr, chromium; C, control; T1, 25% OFMSW amendment in soil; T2, 50% OFMSW amendment in soil; T3, 75% OFMSW amendment in soil; T4, 100% OFMSW amendment in soil

3.3 Plant parameters and metal contents

Plants’ growth under varying soil amendment has been illustrated in Fig. 4. Root length (RL) at 45 DAS showed significantly higher value under T2 treatment with OFMSW in comparison to the control and IF treatment (Fig. 5). With SS, maximum RL was found at T2 treatment, while no significant variation was observed amidst IF, T1 and T3 treatments. Furthermore, high RL without any significant variation was revealed under IF, T2 and T3 treatments compared to the control with FW amendment in soil. At 80 DAS, RL didn’t show any significant change amongst varying soil treatments amended with biodigestates viz. OFMSW, SS and FW. The shoot length (SL) at 45 DAS was high with no significant variation in IF, T1, T2, T3 and T4 treatments in soil amended with OFMSW and SS in comparison to the control, while maximum SL was reported at IF, T3 and T4 treatments with FW (Fig. 5). At 80 DAS, maximum SL was found at T2 followed by T4 and IF treatments with OFMSW. The SS treatment in soil did not cause much variation in SL amongst varying treatments. Furthermore, maximum SL was reported under T4 treatment in soil with FW, while no significant change was observed amongst IF, T2 and T3 treatments. Digestates are enriched with macro and micro nutrients, minerals as well as organic matter which play prominent role in improving soil fertility thereby promoting plant growth as well as development (Wang et al. 2023; Brtnicky et al. 2022). Cristina et al. (2020) also found a potentially positive impact on tomato grown under digestate amendment in soil.

Increase in leaf area by 42.90 and 42.00% under T3 treatment with OFMSW amendment compared to the control at both 45 and 80 DAS, respectively were observed. While, no significant change was found amongst other soil treatments (Fig. 5). The SS amendment in soil leads to increase in leaf area under T4 treatment at 45 and 80 DAS i.e. by 16.57 and 16.14%, respectively with respect to the control plant. Likewise, an increase in leaf area by 42.89 and 41.57% under T4 treatment with FW amendment in soil was observed at 45 and 80 DAS, respectively. Panuccio et al. (2021) also showed significant increase in leaf area under increasing percentage (10, 20 and 30%) of Fattoria sp. digestate in soil. Anaerobic digestates are rich in N, P, K and other micro nutrients that promote cell division and growth resulting in enhanced leaf number as well as area for photosynthesis, thus endorsing high organic content assimilation to facilitate plant growth (Vaish et al. 2022). Chew et al. (2019), presented that application of bio-fertilizers such as sewage-sludge and food waste compost increases N content in soil that strengthen the growth of both shoot as well as root systems.

The OFMSW amendment in soil caused insignificant change in root biomass (RB) at both the ages, while it was increased significantly by 30.86 followed by 30.15% compared to the control under T3 and T2 treatments, respectively with SS amendment in soil at 80 DAS (Fig. 5). Furthermore, maximum RB was found at T2 (53.8%) followed by T1 (48.6%) treatments under FW amendment in soil at 80 DAS. Stem biomass (SB) was significantly increased by 29.8% under T3 treatment with OFMSW at 45 DAS. While, no significant change was found amidst varying soil treatments with SS amendment (Fig. 5). The FW amendment in soil at 45 DAS showed maximum increase (29.8%) in SB against the control plant, whereas significant change was not found amongst different soil treatments at 80 DAS. Leaf biomass (LB) was maximum at T3 treatment with OFMSW and T4 treatment with both SS and FW amendments in soil at 45 DAS, while at 80 DAS, LB showed no significant variation amongst different soil treatments with three ADg(s) amendments (Fig. 5). Total plant biomass (TPB) was significantly higher under different soil treatments in comparison to the control. Maximum TPB was observed under T3 treatment (40.3%) with OFMSW, while no significant change was observed amongst other soil treatments at 45 DAS (Fig. 5). With SS and FW amendments, TPB was significantly increased by 47.3 and 64.1% under T4 and T2 treatments, respectively at 80 DAS. Vaish et al. (2022) showed significant increase in plant biomass under OFMSW, SS and FW amendments in soil accredited to increased nutrients contents to facilitate better growth of root and shoot system. The enhancements in growth and development of crops are well supported by bioactive components from digestate amendment in soil (Brtnicky et al. 2022).

Significantly higher yield of the fruit under different ADg(s) amendments in soil was observed in comparison to the control and IF treatment (Fig. 6). Maximum yield of the fruit was observed under T4 treatment with SS (173.47%), OFMSW (163.86%) and FW (96.43%) (Fig. 6). Similar result was found by Ferdous et al. (2018), who showed maximum yield of S. lycopersicum grown in soil amended with biogas slurry. Similar finding by Li et al. (2023) showed higher tomato yield cultivated in soil amended with biodigestate in comparison to that grown under chemical fertilizers’ application. Enrichment of digestate with K and N are reported to enhance tomato fruit yield and quality (Çolpan et al. 2013).

Metal (Fe, Cu, Ni, Mn, Zn, Cd, Pb and Cr) contents in root, stem, leaves (Fig. 7–8) and fruit (Fig. 9) under different ADg(s) amendment to the soil showed significantly higher values compared to the control and IF treatment. Content of Fe in different plant parts were above phytotoxic threshold level (10–20 ppm) for crop plants illustrated by Alloway and Ayres (1997). Moreover, Fe contents in roots, stem, leaves and fruits were above FAO/WHO (2001) safe limits (425.5 ppm) under T2, T3 as well as T4 treatments with OFMSW and SS amendments, and T3 and T4 treatments with FW amendment in soil. Contents of Ni and Cu in the plant parts were well within their phytotoxic threshold level (Ni, 10–100 and Cu, 20–100 ppm), while for Mn in plant, no phytotoxic threshold has been stated by Alloway and Ayres (1997). Furthermore, their contents (Ni, 67 ppm; Cu, 73.3 ppm and Mn, 500 ppm) in varying plant parts and the fruit complied with FAO/WHO (2001) safe limits. Contents of Cd, Zn and Pb in the plant were within phytotoxic threshold levels (Cd, 5–30; Zn, 100–400 and Pb, 30–300 ppm) for crop plants (Alloway and Ayres 1997). Content of Zn in root, stem and leaves was above FAO/WHO limit (99.4 ppm) (Alloway and Ayres 1997), whereas it’s content in the fruit was within the limit. Cd level in root, stem as well as leaves was above FAO/WHO (2001) safe limit (0.2 ppm) under T2, T3 and T4 treatments with SS amendment in soil. In addition, its content in fruit was within safe limit of FAO/WHO (2001) under all the soil treatments (Fig. 9). Content of Pb in root, stem, leaves and fruit was above FAO/WHO (2001) safe limit (0.3 ppm) under all treatments except control plant. Cr content in varying plant parts was within phytotoxic threshold range (5–30 ppm) defined by Alloway and Ayres (1997). On contrary, its content in root, stem, leaves and fruit was above FAO/WHO safe limit (2.3 ppm) (Alloway and Ayres 1997) under different soil treatments except in control plant.

3.4 Principal Component Analysis

The PCA was used to assess the relationship between total metal contents in the entire plant and selected plant parameters such as root length, shoot length, leaf area per plant, root biomass, shoot biomass, total plant biomass and fruit yield of tomato grown under three different amendments of anaerobic digestates in soil (Fig. 10A-C, Supplementary Tables S1, S2 and S3). With OFMSW amendment in soil, three principal components contributing 84.6% of total variance were extracted. PC1 with 63.26% of total variance (eigenvalue 9.49) showed strong positive loadings for Fe, Ni, Cr, Cu, Pb, Zn, Mn, leaf area, root biomass and yield. PC2 with 11.16% of total variance (eigenvalue 1.67) had positive loadings for root length, shoot length and total plant biomass, while PC3 (total variance 10.18%, eigenvalue 1.53) was loaded with shoot biomass only (Fig. 10A, Table S1). Amendment of SS in soil resulted in four principal components contributing 94.98% of total variance. PC1 (eigenvalue 8.85) with 59.01% of total variance had positive loadings for Cu, Fe, Mn, Cr, Pb, Zn, root biomass and yield. PC2 (16.02% of total variance, eigenvalue 2.40) was positively loaded with Mn, Pb, Ni, Zn, leaf area and yield, and negatively loaded with Cd. PC3 (eigenvalue 1.86) with 12.40% of total variance showed loadings for root biomass, root length, shoot length, total plant biomass and Cd (Fig. 10B, Table S2). PC4 (7.57% of total variance, eigenvalues 1.14) was only loaded with shoot biomass (Table S2). With FW amendment in soil, four principal components were extracted explaining 90.45% of total variance. PC1 (eigenvalue 7.91) with 52.72% of total variance showed high positive loadings for Ni, Fe, Mn, Zn, Cu, Pb, Cr, leaf area, shoot length and yield. PC2 (17.16% of total variance, eigenvalue 2.57) was loaded with Pb, Cr, total plant biomass, root biomass, and root length. PC3 with 13.08% of total variance (eigenvalue 1.96) was loaded with Cd, while PC4 (7.49% total variance, eigenvalue 1.12) showed loadings for shoot length and biomass only (Table S3). Contents of Zn, Mn, Cu and Ni in plants were within the phytotoxic thresholds (as stated previously), hence supported the plant growth and yield. Studies have shown that essential elements such as Fe, Zn, Mn, Cu and Ni play a significant role in plants’ metabolic, physiological and biochemical reactions and favor its growth and development (Rai et al. 2021). Grünzweig et al. (1998) also showed positive correlation between leaf area, shoot biomass and Cu content in L. esculentum grown in solarized soil at Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot, Israel. Increasing concentrations (0, 37, 55.6 and 74.1 t·ha^− 1) of water hyacinth compost in soil containing Cu, Ni, Zn and Pb increased plant height and yield of the growth of L. esculentum (Mashavira et al. 2015). Anaerobic digestate of SS contained relatively high content of Cd when compared to OFMSW and FW; hence its content was high under different soil amendments with SS and in the plant. However, being within phytotoxic threshold, it didn’t cause much negative impact on plant growth. High Mn content is primarily attributed to low Cd content in plant due to their antagonistic behavior (Gautam et al. 2017).

3.5 Translocation and bio-concentration factors

Translocation factor (TF) determines the metal movement from below to aboveground part of the plant, whereas bioconcentration factor (BCF) is an effective way to determine metals’ uptake and accumulation in plant biomass from soil (Deng et al. 2004). When BCF value is less than 1, it signifies plant’s inability towards metals’ uptake and accumulation from soil and such plants are metal excluder (Yanqun et al. 2005). On contrary, metal accumulator (BCF > 1) has an ability to uptake and accumulate metal efficiently in plant parts. Using BCF and TF values of metals, we can categorise plant as accumulator (BCF and TF values > 1), phytostabilizer (BCF > 1 and TF < 1) or excluder (BCF and TF < 1) (Gautam and Agrawal 2017). The TF values for Fe, Cu, Ni, Pb, Mn and Cr increased upto T3 treatment and for Zn and Cd upto T2 treatment followed by a decline under further OFMSW concentration in soil, and their values were > 1 (Table 6). The SS amendment in soil led to gradual increase in TF values for Fe, Cu, Ni, Mn, Zn, Cr and Pb under different soil treatment, while for Cd, it showed declining trend under increasing SS amendment (Table 6). The FW amendment in Fe (increase upto T3), Ni (decline upto T3), Cu and Zn, Pb (increase upto T3), Cr (decline), Mn, Cd (increase upto T2) and their values were > 1.

Table 6

Translocation (TF) and bioconcentration (BCF) factors for metals in tomato under control and different ADg(s) amendments in soil. Values are Mean ± SE. Different letters indicate significant differences at p < 0.05 according to Duncan's test
Metal	Parameters			OFMSW amendment in soil
		C	IF	T1	T2	T3	T4
Fe	BCF	3.30 ± 0.17^d	2.81 ± 0.28^d	3.38 ± 0.02^c	3.59 ± 0.25^b	3.83 ± 0.02^a	3.60 ± 0.08^b
	TF	2.71 ± 0.01^b	2.38 ± 0.01^e	2.53 ± 0.04^d	2.61 ± 0.03^c	2.87 ± 0.01^a	2.72 ± 0.01^b
Ni	BCF	1.48 ± 0.01^d	1.81 ± 0.10^bc	2.12 ± 0.21^ab	2.16 ± 0.12^a	2.17 ± 0.15^a	1.65 ± 0.11^cd
	TF	1.22 ± 0.10^d	1.20 ± 0.09^d	1.53 ± 0.12^c	1.61 ± 0.11^b	1.82 ± 0.08^a	1.17 ± 0.06^e
Cu	BCF	2.57 ± 0.05^c	1.78 ± .03^de	2.49 ± 0.14^cd	3.27 ± 0.30^b	3.46 ± 0.28^a	3.29 ± 0.09^b
	TF	1.81 ± 0.12^c	1.72 ± 0.10^cd	2.12 ± 0.08^b	2.55 ± 0.12^a	2.50 ± 0.09^a	2.56 ± 0.03^a
Zn	BCF	2.16 ± 0.20^e	2.58 ± 0.02^d	2.85 ± 0.14^c	3.17 ± 0.24^a	3.01 ± 0.17^b	2.79 ± 0.23^c
	TF	1.51 ± 0.06^e	2.15 ± 0.04^cd	2.08 ± 0.01^d	2.30 ± 0.03^b	2.38 ± 0.01^b	2.66 ± 0.17^a
Mn	BCF	3.39 ± 0.29^b	3.32 ± 0.37^b	2.19 ± 0.07^d	3.25 ± 0.20^c	3.63 ± 0.13^a	3.58 ± 0.06^a
	TF	2.53 ± 0.07^b	2.77 ± 0.07^a	2.28 ± 0.03^d	2.45 ± 0.02^c	2.75 ± 0.02^a	2.72 ± 0.02^a
Pb	BCF	2.13 ± 0.21^de	2.65 ± 0.23^c	2.69 ± 0.21^c	2.98 ± 0.05^b	3.31 ± 0.18^a	2.51 ± 0.24^cd
	TF	1.53 ± 0.08^d	1.99 ± 0.03^c	1.98 ± 0.05^c	2.15 ± 0.08^b	2.26 ± 0.04^a	2.06 ± 0.07^c
Cd	BCF	1.31 ± 0.05^a	0.92 ± 0.07^b	0.70 ± 0.01^c	0.29 ± 0.02^d	0.15 ± 0.01^e	0.20 ± 0.02^e
	TF	2.38 ± 0.15^b	1.27 ± 0.05^f	2.50 ± 0.09^a	2.26 ± 0.21^c	2.13 ± 0.17^d	1.40 ± 0.06^e
Cr	BCF	2.02 ± 0.02^c	2.06 ± 0.09^c	2.16 ± 0.03^b	2.15 ± 0.05^b	2.73 ± 0.19^a	2.78 ± 0.24^a
	TF	1.93 ± 0.16^a	1.23 ± 0.10^d	1.28 ± 0.03^d	1.76 ± 0.05^b	1.89 ± 0.03^a	1.35 ± 0.07^c
				SS amendment in soil
		C	IF	T1	T2	T3	T4
Fe	BCF	3.30 ± 0.22^d	2.96 ± 0.12^e	3.35 ± 0.27^d	3.76 ± 0.08^a	3.72 ± 0.09^b	3.49 ± 0.10^c
	TF	2.79 ± 0.02^a	2.33 ± 0.05^c	2.78 ± 0.03^a	2.80 ± 0.01^a	2.79 ± 0.01^a	2.70 ± 0.02^b
Ni	BCF	2.09 ± 0.18^c	1.72 ± 0.05^e	1.44 ± 0.10^f	1.98 ± 0.13^d	2.35 ± 0.20^b	2.40 ± 0.23^a
	TF	2.54 ± 0.09^a	1.27 ± 0.11^e	1.40 ± 0.08^d	1.56 ± 0.11^c	1.54 ± 0.11^c	1.70 ± 0.12^b
Cu	BCF	3.49 ± 0.31^a	1.37 ± 0.12^f	2.70 ± 0.17^d e	2.95 ± 0.24^d	3.03 ± 0.17^c	3.12 ± 0.22^b
	TF	2.25 ± 0.10^b	0.96 ± 0.12^d	1.96 ± 0.06^c	2.21 ± 0.03^b	2.46 ± 0.03^a	2.00 ± 0.06^c
Zn	BCF	3.57 ± 0.33^a	3.16 ± 0.25^b	2.21 ± 0.15^e	2.69 ± 0.25^d	2.82 ± 0.21^c	3.12 ± 0.17^b
	TF	2.81 ± 0.02^a	2.04 ± 0.16^d	1.88 ± 0.07^e	1.99 ± 0.08d^e	2.21 ± 0.21^c	2.41 ± 0.04^b
Mn	BCF	4.07 ± 0.03^a	1.90 ± 0.11^d	3.40 ± 0.04^b	3.44 ± 0.05^b	3.22 ± 0.02^bc	2.52 ± 0.09^c
	TF	2.63 ± 0.03^b	1.47 ± 0.01^d	2.79 ± 0.03^a	2.63 ± 0.02^b	2.15 ± 0.06^c	2.07 ± 0.07^cd
Pb	BCF	3.26 ± 0.19^b	2.68 ± 0.26^d	1.77 ± 0.03^e	3.08 ± 0.25^c	3.22 ± 0.25^b	3.63 ± 0.27^a
	TF	2.17 ± 0.09^c	1.63 ± 0.13^d	2.44 ± 0.01^a	2.30 ± 0.03^b	2.23 ± 0.06^b	1.56 ± 0.04^d
Cd	BCF	1.55 ± 0.08^d	1.78 ± 0.01^c	3.34 ± 0.08^a	2.09 ± 0.13^b	1.18 ± 0.02^e	0.85 ± 0.08^f
	TF	2.46 ± 0.04^c	2.67 ± 0.20^b	1.73 ± 0.07^e	2.37 ± 0.09^d	2.39 ± 0.04^d	3.82 ± 0.04^a
Cr	BCF	2.60 ± 0.03^d	2.30 ± 0.08^d	2.73 ± 0.04^d	3.88 ± 0.08^a	3.10 ± 0.02^c	3.28 ± 0.11^b
	TF	1.74 ± 0.14^d	1.76 ± 0.04^d	2.60 ± 0.05^c	2.64 ± 0.02^c	2.73 ± 0.08^bc	2.84 ± 0.04^a
				FW amendment in soil
		C	IF	T1	T2	T3	T4
Fe	BCF	2.69 ± 0.02^e	2.79 ± 0.20^d	3.05 ± 0.05^c	3.19 ± 0.12^b	3.65 ± 0.07^a	3.50 ± 0.06^a
	TF	2.26 ± 0.01^d	2.37 ± 0.05^c	2.29 ± 0.04^d	2.41 ± 0.01^c	2.78 ± 0.01^a	2.65 ± 0.03^b
Ni	BCF	1.45 ± 0.12^e	1.57 ± 0.11^d	1.93 ± 0.12^c	1.91 ± 0.18^c	2.09 ± 0.13^b	2.31 ± 0.10^a
	TF	0.87 ± 0.08^d	1.04 ± 0.04^c	1.53 ± 0.03^b	1.51 ± 0.13^b	1.52 ± 0.05^b	1.64 ± 0.11^a
Cu	BCF	1.75 ± 0.17^f	2.25 ± 0.21^e	2.91 ± 0.17^d	3.27 ± 0.09^c	3.45 ± 0.14^b	4.89 ± 0.10^a
	TF	1.60 ± 0.05^c	1.66 ± 0.08^c	2.41 ± 0.12^b	2.46 ± 0.06^b	2.48 ± 0.01^b	2.51 ± 0.04^a
Zn	BCF	1.94 ± 0.17^c	2.02 ± 0.02^c	2.98 ± 0.25^a	3.00 ± 0.03^a	2.90 ± 0.19^a	2.44 ± 0.21^b
	TF	1.38 ± 0.04^d	1.21 ± 0.10^e	2.34 ± 0.04^a	2.29 ± 0.02^a	2.21 ± 0.04^b	1.95 ± 0.06^c
Mn	BCF	2.37 ± 0.06^d	3.32 ± 0.23^b	1.02 ± 0.10^e	3.12 ± 0.05^c	3.42 ± 0.13^a	3.46 ± 0.17^a
	TF	2.51 ± 0.09^b	2.31 ± 0.07^d	2.39 ± 0.08^cd	2.43 ± 0.03^c	2.75 ± 0.01^a	2.78 ± 0.01^a
Pb	BCF	1.24 ± 0.19^e	1.93 ± 0.05^d	3.06 ± 0.19^a	2.64 ± 0.20^b	2.32 ± 0.15^c	2.29 ± 0.03^c
	TF	1.40 ± 0.10^d	1.15 ± 0.02^e	1.64 ± 0.06^b	1.71 ± 0.14^a	1.71 ± 0.12^a	1.50 ± 0.09^c
Cd	BCF	0.40 ± 0.04^b	0.53 ± 0.01^a	0.55 ± 0.02^a	0.22 ± 0.01^c	0.23 ± 0.01^c	0.17 ± 0.01^d
	TF	3.57 ± 0.12^a	1.98 ± 0.03^de	3.38 ± 0.12^b	2.17 ± 0.05^c	1.72 ± 0.02^e	1.60 ± 0.04^e
Cr	BCF	2.28 ± 0.08^e	3.06 ± 0.03^c	3.11 ± 0.02^b	3.68 ± 0.23^a	2.91 ± 0.17^d	2.78 ± 0.23^d
	TF	1.05 ± 0.03^e	2.44 ± 0.10^b	2.55 ± 0.07^a	2.33 ± 0.08^c	2.37 ± 0.05^c	2.21 ± 0.01^d
OFMSW, organic fraction of municipal solid waste; SS, sewage sludge; FW, flower-waste; Fe, iron; Ni, nickel; Cu, copper; Zn, zinc; Mn, manganese; Pb, lead; Cd, cadmium; Cr, chromium; C, control; T1, 25% OFMSW amendment in soil; T2, 50% OFMSW amendment in soil; T3, 75% OFMSW amendment in soil; T4, 100% OFMSW amendment in soil

BCF values for Fe, Ni, Mn, Cu, Pb and Cr increased with increase in OFMSW amendment in soil (upto T3 followed by a decline under T4 treatment), while BCF value for Zn increased upto T2 treatment (Table 6). On contrary, those for Cd decreased with increasing OFMSW amendment in soil upto T3 treatment followed by an increase under T4 treatment, and BCF values for studied metals were > 1. The SS amendment in soil leads to gradual rise in BCF values for Fe (upto T3 treatment), Ni, Cu, Pb and Cr (upto T2 treatment), while those for Zn, Mn and Cd decreased with increasing amendment in soil. Moreover, their values were above 1 for studied metals under all treatments. The FW amendment caused rise in BCF values for Fe, Ni Cu, Zn (increase upto T2 followed by a decline under T3) and Mn, while those for Pb, Cr and Cd decreased with increase in soil treatments. Notwithstanding, BCF values for studied metals were > 1 except for Cd (Table 6). Decrease in BCF for studied metals could be accredited to either less phyto-availability or translocation of selected metals from soil to aboveground plant parts (Gautam and Agrawal 2017). Birghila et al. (2023), showed BCF value for Cd less than 1 for Lycopersicon esculentum thus showing that the plant has the ability only to absorb but do not accumulate Cd in plant parts. In the present study, based on BCF values, tomato acted as a potential Cd excluder.

Anaerobic digestates (ADg(s)) from organic proportion of flower-waste, sewage-sludge and municipal solid wastes as bio-fertilizer led to significant improvement in soil organic matter and nutrient status of the soil. Increasing ADg(s) amendments increased the contents of Fe, Cu, Ni, Mn, Zn, Pb, Cr and Cd in soil. Moreover, contents of Cu, Zn, Pb, Cr, Ni and Cd in soil under different amendments were well within the NOAA intervention values causing risk to the environment. Plant biomass and fruit-yield were increased under different ADg(s) amendments with maximum yield reported at 100% SS amendment in soil compared to the control. The PCA analysis showed positive correlation between metals (Fe, Zn, Mn, Cr, Cu and Pb) and yield. Studied metals except Fe, Pb and Cr in tomato were within FAO/WHO safe limits for consumption. Hence, utilization of OFMSW, SS and FW though enhanced the soil properties and yield response of tomato, but due to high contents of metals in fruit, utilization of ADg(s) are not suggested for cultivation of tomato. However, detailed experimental study is recommended using lower doses of selected ADg(s) for tomato cultivation to minimize the risk of metal contamination in edible part of the plant.

CRediT authorship contribution statement

R.P.S.: Conceptualization, Review & editing, Supervision, Funding acquisition; M. G.: Visualization, Data curation and interpretation, Writing – review & editing, Funding acquisition; B.V.: Experimentation, Visualization, Investigation, Data curation; I. S.: Experimentation and Data curation and interpretation; V. S.: Reviewing and editing

Informed Consent Statement Not applicable

Data Availability Statement The data presented in this study will be shared on the request.

Acknowledgement

The authors are eternally thankful to the Dean & Head, DESD (Department of Environment and Sustainable Development) and Director, Institute of Environment and Sustainable Development, Banaras Hindu University, for providing needed facilities. Rajeev Pratap Singh is grateful to the authorities of Banaras Hindu University (BHU), Varanasi for providing required support. Dr. Meenu Gautam thankfully acknowledged the Raja Jwala Prasad Fellowship, Institute of Eminence, BHU for financial support.

Disclosure statement There is no potential conflict of interest amongst the author(s)

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Explicating the fertilizer potential of anaerobic digestate on soil quality and growth performances of Solanum lycopersicum var. Kashi Aman

Status:

Version 1

Abstract

Figures

1 Introduction

2 Materials and methodologies