Impact of Organic Compost Prepared From Different Plant-Based Residues on Seed Germination and Early Seedling Growth Performance of Vigna Radiata (L.) Wilczek

doi:10.21203/rs.3.rs-2352649/v1

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Impact of Organic Compost Prepared From Different Plant-Based Residues on Seed Germination and Early Seedling Growth Performance of Vigna Radiata (L.) Wilczek

https://doi.org/10.21203/rs.3.rs-2352649/v1

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The investigation was aimed to study the physio-chemical characteristics and evaluation of the quality of three different organic composts (Plant compost, Coir pith compost and Vermi compost) made by local and standard preparations. All the organic composts were prepared from different feedstocks/raw materials. All the physiochemical parameters and mineral analysis of the compost samples were done using standard methodologies. An early seedling growth performance study was also carried out using Vigna radiata seeds in respective compost samples to find out the maturity and quality of the composts as a growth substrate and for wider application in agriculture. All the organic composts had variations in their physiochemical characters and growth performance of seedlings in the treatments. Except for standard plant compost, where no germination was seen, all the other composts exhibited germination. No higher levels of heavy metals were identified in any of the samples. The outputs of the present study could be due to elevated pH and electrical conductivity of the compost, and also maybe of the allelopathic potential of the compost since it is plant-based compost. Therefore, before advocating any organic compost into fields, physiochemical characteristics and quality of the composts should be ensured so that it won’t affect the soil quality undesirably and also the plant nutrition.

Organic compost

Seed germination

Vermicompost

Coir Pith compost

Plant compost

Primarily with population growth, the generated amounts of solid waste have exponentially increased almost all over the world. Further, the way of lifestyles, economic development along with rapid urbanization have greatly increased waste generation. It is estimated that about 2.24 billion tons of solid waste were generated in the world’s cities in 2020 (The world bank 2022). This increase in waste generation has put pressure on or even disturbed the various components of the environmental system. At this juncture, the implementation of an appropriate and environment-friendly management strategy for solid waste is recognized as an urgent need worldwide, whereas reuse and recycling of these wastes are categorised as the most preferable approaches in integrated solid waste management systems under the clean India program and smart city program in a framework of circular economy (Sayara et al. 2020). Since residential garbage makes up a significant amount of the accumulated waste, this biodegradable fraction might be recovered and utilised as a possible source of plant nutrients rather than being lost through improper disposal or treatment. It is important to point out that the direct application of fresh organic solid waste to land is not recommended. The immobilisation or imbalance of nutrient elements, phytotoxicity, the presence of heavy metals, pathogenic bacteria, and inorganic salts are just a few instances of how the addition of immature/non-stable organic solid waste to soil may influence the plant growth. Such factors eventually inhibit plant growth. Significantly, compost could replace the use of inorganic fertilisers, which are extensively used in farming practices. Inorganic fertilisers can have a detrimental effect on the soil characteristics and other environmental elements when used continuously and more intensively. In order to improve soil aggregation, restore soil organic carbon and nitrogen, and increase agricultural sustainability, compost application is being advocated as a substitute for synthetic fertilizers (Choudhary et al. 2018).

The disposal of biodegradable wastes such as pruned branches, leaves, cut grass, and weeds is a substantial ecological issue for the local public. The main method used for the removal of these biodegradable materials from urban green spaces is still dumping at landfills (Milinkovic et al. 2019). Even if these wastes are organic and do not pose much environmental risk, production of the same in large quantities poses major environmental (offensive odors, contamination of groundwater and soil) and disposal problems. Mainly in urban areas, the shortage of landfill space has been a limiting factor for the disposal of wastes (Fialho et al. 2010). Conversely, the biodegradable portion of municipal waste is a potential source of plant nutrients, and appropriate techniques of composting can convert it to compost with high nutrient content and low prevalence of pathogenic microorganisms.

For the organic portion of wastes, composting is one of the finest alternatives as it reduces the volume and weight of the wastes by almost 50% and results in a stable product that can be used in agricultural applications (Sanchez-Monedero et al. 2002). The main products of the composting process are CO₂, water, and stabilized organic matter consisting mainly of humic acids-like (HA-like) fractions (Lopez et al. 2002). This resulting compost is more nutrient-rich and more stable than the original feedstock material and can increase soil quality and productivity as well (Farrel and Jones 2009). Also, the cost of chemical fertilizers and their potential environmental risk renewed the interest in using soil organic matter amendments such as plant residues, manures, and compost. Also, these municipal and green waste composting and its application have confirmed to reduce some adverse effects that urbanization has upon soil properties and also improve environmental services like nutrient cycling, water holding capacity of soil, carbon storage, biocontrol of pathogenic microorganisms etc. (Milinkovic et al. 2019).

On the other hand, compost can also have adverse effects on soil and plant growth due to its different physical and chemical properties. Low-quality composts and immature composts will affect soil fertility and plant growth in an opposing way. In the case of plant-based composts, the allelopathic nature of the plants used as feedstock may have negative effects on the compost quality. The secondary metabolites often referred to as allelochemicals produced by the plants are supposed to be used by them to defend themselves from pathogens (Jiao et al. 2021). Allelochemicals are plant metabolites or their products that are released from plant residues through biocompost into the environment, which may affect plants at different stages of plant growth and development, flowering and fruiting, vegetation formation and succession, species regeneration (Turk and Tawaha 2003; Duk 2007; Kong et al. 2006). Nonetheless, allelochemicals affect the germination and growth of neighboring plants by disrupting various physiological processes including photosynthesis, respiration, water and hormonal balance (Braine et al. 2012). For instance, the raw and composted extracts of Ageratina adenophora have inhibited seedling germination and growth in rye grass (Wang et al. 2020; Jiao et al. 2021), maize (Ma et al. 2020), and Rice (Yang et al. 2011). These biochemicals are released from plants due to different processes such as leaching, volatilization, exudation and decomposition found in seed germination and seedling growth of surrounding plants (Das et al. 2018). So, during the composting process since the plants undergo complete decomposition, there are chances for the release of these allelochemicals. Hence, the physio-chemical and biological properties of the compost differ widely depending on feedstocks and composting procedure (Chatterjee et al. 2013). Therefore, the analysis of compost quality is very essential before using them in fields.

Almost all the previous literature provides information regarding the physical properties of the compost during the compost production stage or the composting stage. The physical properties of commercially available composts, ready for application or at the application stage are not much studied. Hence the present study has been carried out to evaluate the physio-chemical characteristics of three different composts at its application stage namely, Vermicompost, Plant compost and Coir-pith compost made of different feedstocks by local and standard procedures. Also, an early seedling growth assessment was undertaken in all the composts with seeds of Vigna radiata to evaluate the quality of these composts to check whether they possess any phytotoxicity and their suitability for field application.

Sample Collection

Three different composts of diverse feedstock compositions were selected for the study. In which, each compost was of the local, particularly plant residues from agrowastes, home gardens and plant residues generated from households (prepared at households itself without any controlled conditions for their own use) and standard organic composts (prepared under controlled conditions by adopting standard procedures). Thus, a total of six compost samples were used for the study. The samples were Local Plant Compost (LPC), Standard Plant Compost (SPC), Local Vermicompost (LVC), Standard Vermicompost (SVC), Local Coir pith Compost (LCPC) and Standard Coir pith Compost (SCPC). SVC and SCPC were procured from Tamil Nadu Agricultural University (TNAU Agritech portal), Coimbatore and Central Coir Research Institute (CCRI), Alappuzha, Kerala respectively. All other samples were collected from an Eco-shop of the Kudumbasree unit of Alappuzha Town, Kerala.

Different raw materials have been used for each of the composts. The extraction/preparation of coir from coconut husk produced a large number of dusty/fibrous materials (coir pith), which was the primary raw material of coir pith compost. Generally, all biodegradable wastes, both fresh and dry can be used in vermicompost. Here crop residues, weed biomass, vegetable wastes, food wastes, and leaf litter were used in both the abovesaid standard and local vermicompost. In plant compost, mainly fresh plant cutting and pruning wastes, crop and weed residues were added rather than food/vegetable wastes.

Since the local compost contained inerts, the samples were initially sieved through large, pored sieves. All the compost samples were spread over trays and air-dried for 24 hours and then stored in labeled containers for further analysis.

Physico-chemical Analysis

The pH and electrical conductivity (EC) of the compost samples were determined using their 1:10 (w/v) aqueous suspension using Digital pH, Conductivity and Temperature meter (LT-23, Labtronics Instruments). As soon as all the samples were carried to the lab, moisture content was analysed using Moisture Analyser MA35 (Sartorius AG, Germany). Moisture measurements using an infrared moisture balance are found to be more accurate and less time-consuming than gravimetric methods (Agnew and Leonard 2003). Ash content was determined using AOAC methods by placing 5g of each sample in a Muffle furnace (Kemi Lab Equipments) at 550°C for 2 hours. The bulk density of all the samples was analysed by following Ahn et al. 2008. Total Organic Carbon (Walkley and Black 1934) and Phosphorous content (Bray and Kurtz 1945) of the samples were analysed. Nitrogen percentages in the samples were quantified using Kjeldhal Nitrogen Analyser (Kelplus Classic-DX Vats (B), Pelican Equpiments). Flame photometric analysis (Labtronics, LT-671, India) were carried out for estimating the amount of sodium, potassium, calcium and lithium in the compost samples. One gram of each compost was used to prepare the samples. The prepared samples were then fed into a flame photometer (Labtronics, 671) which was calibrated with a standard solution of sodium, potassium calcium and lithium.

Extraction of Humic substances

Extraction of humic substances from the sample is done by a modified method by Ramdani et al. (2015). Humic and Fulvic acid was extracted by placing 10 g of compost added to 100 ml of 0.1 M NaOH in a 250 ml Erleneymer flask in a shaking water bath (Neolab Instruments) for 2 hours at 98–100°C. Then the solution was filtered using Whatman filter paper (125mm) and the filtrate was centrifuged at 2500 rpm for 25 min (Research Centrifuge, REMI; R-23). After overnight refrigeration of the centrifuged solution at 4°C, the solution was acidified with 6M HCl until the pH of the solution reaches 1. This soluble and insoluble fraction of Fulvic acid and Humic acid was separated by centrifugation at 10000 rpm for 10 min. The two fractions were transferred into Petri plates and dried in a hot air oven (Universal Digital (Memmert type) “MAC” MSW-211, India) at 105°C for 48 hours. The initial weight of Petri plates and the final weight after drying were noted and the difference gives the amount of fulvic and humic acid in which the insoluble fraction represents the humic content.

Mineral Analysis

Mineral analysis of triacid digested compost samples were analysed through ICP-MS (Agilent-7800, US) (Wilbur and Jones 2021).

Germination and Early Seedling Growth Performance

Experimental setup

Certified seeds of Vigna radiata were procured from the TNAU seed center are used for the experimental study. The study was conducted in the greenhouse at the Department of Environmental Sciences for 23 days. Approximately 180g of all compost samples were taken in seedling trays of approximately 200 g capacity. For each sample, triplicates were run with 24 seeds for each treatment. The average temperature and humidity during the study period were 28.9°C and 50.33% respectively and the crop intercepted nearly 6–8 hours of bright sunshine during the growth period. Before germination approximately 5–8 ml and after germination around 10–15 ml of water is sprinkled daily for each treatment. The plants were carefully uprooted after the study period and the above-ground and below-ground responses were recorded.

Agro botanical Characters

The following Agro botanical characters were evaluated

Germination index (GI)
The above and below-ground responses recorded were shoot length, root length, total plant length, number of leaves, and leaf length. And the fresh weight as well as dry weight of Total plant, Leaf, Root and stem were also noted.

Chlorophyll Content and Carotenoids

The Chlorophyll pigments were extracted with 60% acetone and the contents of chlorophyll a, chlorophyll b and total chlorophyll were estimated following the methods of Arnon (1949).

Statistical analysis

The data were subjected to a one-way analysis of variance (ANOVA), and the significance of difference between means was determined by Duncan’s multiple range test (P < 0.05) using SPSS (version 13.0, SPSS Inc., Waker drive Chicago, USA). Values expressed are means of triplicate determination ± standard deviation.

Physico-chemical and Mineral Analysis

All the composts analysed in this study differed in a range of properties (Table 1). The standard preparation of plant compost (SPC) and local plant compost (LPC) showed superior results in pH (8.80 and 8.25) and EC (0.87 and 0.306). Moisture percent by weight was higher in LCPC and least in SPC.

Table 1

Physiochemical parameters of compost samples
Parameters	LPC	SPC	LCPC	SCPC	LVC	SVC
pH	8.25 ^b ±0.035	8.80 ^a ±0.04	7.68 ^e ±0.03	7.79 ^d ±0.02	7.87 ^c ±0.02	7.83 ^cd ±0.04
Conductivity (mS)	0.306 ^b ±0.002	0.87 ^a ±0.0057	0.05 ^f ±0.0057	0.203 ^c ±0.003	0.195 ^d ±0.003	0.096 ^e ±0.0017
Moisture content (%)	59.84 ^c ±0.03	25.53 ^f ±0.49	89.2 ^a ±0.2	84.07 ^b ±0.1	55.03 ^d ±0.65	40.9 ^e ±0.24
Ash content (%)	45.36 ^c ±0.30	49.1 ^b ±0.2	6.56 ^e ±0.057	4.06 ^f ±0.20	40.05 ^d ±0.35	55.13 ^a ±0.37
Bulk density (kg/m³)	8.62×10^− 4	7.76×10^− 4	1.21×10^− 3	4.74×10^− 4	7.94×10^− 4	8.15×10 ^˗4
TOC (%)	54.6 ^d ±0.30	59.7 ^c ±0.47	50.9 ^e ±0.2	44.86 ^f ±0.37	93.4 ^b ±0.05	96 ^a ±0.20
Nitrogen (%)	0.55 ^d ±0.015	1.15 ^b ±0.015	0.16 ^e ±0.002	0.12^f ± 0.002	0.67 ^c ±0.015	1.27 ^a ±0.015
Phosphorous (g/kg)	0.33 ^d ±0.02	0.38 ^c ±0.035	0.07 ^e ±0.015	0.066 ^e ±0.011	1.53 ^b ±0.02	1.9 ^a ±0.02
Potassium (%)	0.19 ^c ±0.0015	1.3 ^a ±0.2	0.015 ^d ±0.0015	0.39 ^b ±0.001	0.20 ^c ±0.002	0.017 ^d ±0.002
Sodium (%)	0.211 ^b ±0.001	0.73 ^a ±0.001	0.07 ^d ±0.002	0.22 ^b ±0.02	0.16 ^c ±0.002	0.04 ^e ±0.001
Calcium (%)	0.06 ^f ±0.001	0.213 ^a ±0.002	0.07 ^e ±0.002	0.09 ^d ±0.002	0.17 ^b ±0.001	0.11 ^c ±0.001
Humic acid (g/kg)	0.225 ^b ±0.0012	0.39 ^a ±0.0006	0.055 ^e ±0.0006	0.057 ^e±0.0006	0.18 ^c ±0.0006	0.15 ^d ±0.005
Fulvic acid (g/kg)	0.5 ^b ±0.0005	0.589 ^a ±0.0005	0.277 ^f ±0.0005	0.315 ^e ±0.001	0.436 ^c ±0.0005	0.416 ^d ±0.006
Lithium (%)	0.003 ^b ±0.002	0.005 ^a ±0.001	BDL*	0.001 ^b±0.0005	0.002 ^b ±0.001	BDL*
Values of triplicate determinations (mean ± SD; n = 3) in same column with different letters are significantly different (P < 0.05); LPC-Local Plant Compost, LCPC- Local Coir pith Compost, SCPC- Standard Coir pith Compost, LVC-Local Vermicompost, SVC- Standard Vermicompost. *BDL-Below Detectable Level

The nutrient concentrations of compost will greatly differ based on its feedstock and the nutrient values will be dependent on the macronutrients such as N, P and K. The total N content of all the composts ranged from 0.12% (SCPC) to 1.27% (SVC). Compost with dried materials has shown lower nitrogen contents than fresh grass clippings and plant residues as feedstock. Phosphorous content also showed a similar pattern of concentration in the compost ie; higher in SVC (1.9 g/kg) and least in SCPC (0.06g/kg). The concentration of N in different compost based on their feedstock was Vermicompost > Plant compost > Coir pith compost. Phosphorous concentration also followed the same order of concentration. Whereas potassium concentration was higher in SPC (1.3%) and lowest in LCPC (0.015%) but higher in standard coir pith compost (SCPC) than both standard and local preparation of vermicompost. The total organic carbon was higher observed in vermicompost and lower values in coir pith composts. But the TOC in all the compost was far higher than the minimum required concentration as per the Fertilizer Order control, 1985.

The heavy metals present in the samples (Table 2) were compared with CPCB standards for municipal solid waste compost which were all under the permissible limits only. Concentration exceeding CPCB standards (2006) was not recommended to use for food crops. Nickel, Aluminium, and Iron were exceptionally higher than other heavy metals, but within the limits of CPCB and other previous literatures (Brinton 2000; Bazrafshan et al. 2016; Lodolini et al. 2016). Different mitigation measures may have reduced the heavy metal concentration of source materials/raw materials which eventually balance the amount of heavy metals in the final compost.

Table 2

Micro-macro nutrients and heavy metals content of compost samples in mg/100g.
Elements (mg/100g)	SPC	LPC	SCPC	LCPC	SVC	LVC	Concentration not to exceed in mg/kg (CPCB, 2006)
Be	0.0006	0.0006	0.0006	0.0006	0.0004	0.0005
Mg	0.922	1.0545	1.015	0.3205	0.5987	0.9062
Al	5.2375	5.3075	5.455	6.375	5.5475	5.515
Ti	0.6915	0.6807	0.6482	0.7887	0.755	0.7552
V	0.2082	0.1784	0.1826	0.2076	0.2090	0.2052
Cr	0.8537	0.8475	0.8387	0.8702	0.8607	0.8642	50.00
Mn	0.1380	0.2274	0.2389	0.271	0.2434	0.2527
Fe	8.765	8.9025	9.88	13.132	10.972	11.235
Co	0.0116	0.0119	0.0144	0.0170	0.0141	0.0147
Ni	11.895	11.537	10.135	5.1875	9.865	8.895	50.00
Cu	0.0649	0.1299	0.1786	0.2997	0.2364	0.2363	300.00
Zn	0.3615	0.0819	0.0024	0.3592	0.507	0.4347	1000.00
As	0.5947	0.6005	0.605	0.613	0.604	0.6045	10.00
Se	0.0750	0.0608	0.0467	0.0603	0.0689	0.0649
Sr	0.0346	0.0507	0.0354	0.0324	0.0037	0.0105
Mo	0.0163	0.0022	0.0080	0.0173	0.0179	0.0169
Ag	0.0033	0.0022	0.00007	0.0035	0.0038	0.0036
Cd	0.0048	0.0039	0.0040	0.0040	0.0055	0.0046	5.00
Sn	0.0149	0.0022	0.0014	0.0136	0.0135	0.0134
Sb	0.0226	0.0125	0.0123	0.0196	0.0209	0.0216
Ba	0.0149	0.0680	0.0811	0.0229	0.0071	0.0224
Tl	0.0003	0.0006	0.0016	0	0.00005	0.0003
Pb	0.0247	0.0247	0.0184	0.0313	0.0399	0.0256	100.00
SPC-Standard Plant Compost, LPC-Local Plant Compost, SCPC- Standard Coir pith Compost, LCPC- Local Coir pith Compost, SVC- Standard Vermicompost, LVC-Local Vermicompost.

Humic and Fulvic acid contents followed the same trend in all the composts. Both were at higher concentration in SPC (0.39 g/kg, 0.589 g/kg) and lower in LCPC (0.05 g/kg, 0.27 g/kg) respectively. During the composting process the humic content increases in the compost showing the humification of organic matter in the feedstock (Iqbal et al. 2012). The humic substances formed during the composting process promote the building of soil fertility, and there is an actual increase in organic matter content in the soil (Bertoncini et al. 2008).

Germination and Early Seedling Growth Performance

Agrobotanical characters

After 23 days of growth, the plants were harvested and different agrobotanical characteristics of the plants were observed. The plants at the stage of harvesting are shown in Fig. 1 and samples of plants from each compost are shown in Fig. 2.

Plant growth differed in all composts in terms of total length, root length, shoot length, number of leaves, and leaf length. All the plants showed growth except in the compost SPC. The average total length of the plant was observed higher in compost SVC (28.5 ± 1.7 cm) whereas the average root length was exceptionally higher in compost LCPC (30.5 ± 5.5 cm) compared to other 5 composts which are relatable to the lower bulk density of the same hence providing more space for root growth. Hence, coir pith is used as an eco-friendly and soilless substrate for plant growth in horticulture and other agricultural practices (Machado et al. 2021). While comparing all the above and below-ground responses recorded plants grown in SVC show an overall better growth and healthy plants whereas LVC and LCPC growth was less compared to plants grown in other composts which are precisely visible in Fig. 2. All the plant growth parameters observed are provided in Table 3.

Table 3

Effect of biocompost on plant growth parameters
Growth Parameters	LPC	SVC	LCPC	SCPC	LVC
Total length (cm)	22.4 ^ab ±6.47	27.06 ^a ±1.76	15.2 ^c ±2.30	20.23 ^bc ±1.35	16.46 ^bc ±2.69
Root length (cm)	9.9 ^b ±3.915	16.4 ^b ±12.057	30.5 ^a ±5.51	16.06 ^b ±5.60	9.46 ^b ±3.06
Leaf length (cm)	6.2 ^ab ±3.48	9.55 ^a ±1.68	3.13 ^b ±1.79	7.8 ^a ±0.519	6.4 ^ab ±1.47
Shoot length (cm)	16.2 ^a ±2.98	16.9 ^a ±2.61	12.1 ^b ±0.79	12.4 ^b ± 1.43	10.6 ^b ±1.70
No. of leaves	3.66 ^b ±1.52	4 ^a ±0	3 ^b ±0.577	4 ^a ±0	3 ^b ±0.577
Germination (%)	6.9	11.1	94.4	56.9	18
Total plant fresh weight (g)	1.1 ^ab ±0.54	1.1 ^ab ±0.38	0.41 ^c ±0.08	1.47 ^a ±0.15	0.8 ^bc ±0.18
Total plant dry weight (g)	0.2 ^ab ±0.08	0.22 ^a ±0.08	0.1 ^b ±0.01	0.23 ^a ±0.01	0.15 ^ab ±0.02
Leaf fresh weight (g)	0.79 ^c ±0.008	1.7 ^a ±0.006	0.2 ^d ±0.004	0.9 ^b ±0.002	0.23 ^d ±0.01
Leaf dry weight (g)	0.16 ^b ±0.03	0.25 ^a ±0.01	0.04 ^c ±0.009	0.05 ^c ±0.005	0.06 ^c ±0.007
Root fresh weight (g)	0.07 ^c ±0.0006	0.09 ^b ±0.0008	0.2 ^a ±0.0009	0.07 ^c ±0.001	0.02 ^d ±0.001
Root dry weight (g)	0.03 ^b ±0.003	0.05 ^a ±0.006	0.02 ^bc ±0.006	0.02 ^b ±0.005	0.01 ^c ±0.006
Stem fresh weight(g)	0.38 ^b ±0.015	0.6 ^a ± 0.006	0.12 ^d ±0.007	0.32 ^c ± 0.002	0.08 ^e ±0.0004
Stem dry weight (g)	0.05 ^c ±0.003	0.09 ^a ±0.004	0.01 ^d ±0.003	0.06 ^b ±0.002	0.01 ^d ±0.002
Values of triplicate determinations (mean ± SD; n = 3) in same column with different letters are significantly different (P < 0.05); LPC-Local Plant Compost, LCPC- Local Coir pith Compost, SCPC- Standard Coir pith Compost, LVC-Local Vermicompost, SVC- Standard Vermicompost.

Germination Percentage

All the germinated seeds showed growth till the day of harvest except 12 seedlings from compost LPC which died before harvest. The highest germination percentage was observed in LCPC (94.4%) followed by SCPC (56.9%) indicating its non-toxicity, whereas comparatively, all the other compost had low germination percentages such as LVC (18%), SVC (11.1%), LPC (6.9%) and SPC with no germination at all.

Leaf pigments: Chlorophyll and carotenoids

Chlorophyll a, b and total chlorophyll content is an indication of photosynthetic and metabolic activity which is used as an index of plant production capacity (Liu et al. 2019). The observed values of leaf pigments of the harvested plants are illustrated in Fig. 3. The least chlorophyll content was found in LCPC (8.11 ± 0.08) and the highest chlorophyll content was found in SVC (12.25 ± 0.07). The total plant length, number of leaves and total biomass were also found to be higher in SVC which corresponds to a significantly (P < 0.05) higher value of total chlorophyll also when compared to other organic compost treatments. The carotenoid content of the leaves was analyzed and the least carotenoid content was observed in SCPC (0.324 ± 0.003) and the highest was observed in LVC (0.676 ± 0.004).

Values of triplicate determinations (mean ± SD; n = 3) in same column with different letters are significantly different (P < 0.05); LPC-Local Plant Compost, LCPC- Local Coir pith Compost, SCPC- Standard Coir pith Compost, LVC-Local Vermicompost, SVC- Standard Vermicompost.

Physico-chemical and Mineral Analysis

The composts to be used in soil or field should satisfy several quality demands (Brinton 2000; CPCB 2006; FAI 2007), which should be confirmed before field applications. Increased pH indicates a higher concentration of ammonia in compost materials. Also, pH values lower than 6 or higher than 8 and EC > 1 can be a character of immature or unstable composts (Jagadabhi et al. 2019). In the case of urban soils, which have elevated pH ranges, adding composts with high pH may further increase the overall pH which inversely affects the nutrient availability to the plants (Milinković et al. 2019). Electrical conductivity also reflects the salinity content of the compost, and it also suggests the possibility of phytotoxic/Phyto inhibitory effects (Husaini et al. 2018). With an increase in moisture content, a decrease in bulk density was observed in all the samples. Since water is less dense than organic matter, a solid matrix containing more water will be obviously less dense (Ahn et al. 2008). While comparing the NPK contents with the Indian Fertilizer order control, 1985 (Singh and Nain 2014), the N and P concentrations seem to be slightly higher than the minimum concentration in vermicompost.

It is proven that heavy metals can cause noticeable delay in seed germination and affects the plant growth (Munzuroglu and Geckil 2002). Majority of the heavy metals tend to remain in the final product even after composting, which becomes a significant concern from both environmental and agricultural perspective (Ko et al. 2008; Bazrafshan et al. 2016). Hence it is essential to evaluate the heavy metal concentration of composts as well as their phytotoxic effects before field application.

Germination and Early Seedling growth performance

Germination Percentage

The less germination in LPC and zero germination in SPC may be due to elevated pH, conductivity, and nutritional values of the same when compared with the other compost. Immature composts may also show fewer germination percentages (Warman 1999; Jagadabhi et al. 2019). According to Rashad et al. (2010), a pH range of 7.96 to 8.4 is characterised as mature and well-structured compost. Here the zero germination in SPC (pH – 8.80) can be correlated to these results. Due to high conductivity, osmotic balance can be a limiting factor for germination. So, adjusting electrical conductivity by dilution may increase the chances of germination. Similar observations were stated in the study of Milinkovic et al. (2019) in which compost with higher conductivity showed less germination which was less pronounced when water dilution was applied. A compost-soil mix and thereby reducing the concentration of compost may give positive results for seed germination. However, such nutrient-enriched compost materials can appropriately be diluted with a mixture of other organic composts or soil and further application may provide adequate nutrient sources for crop productivity in the field conditions particularly, under climate change resilience. Compost based on vegetable wastes were identified as a potential bio-fertilizer for better yield and growth of paddy crops (Jelin et al. 2013). This may also reduce the biodegradable waste accumulation in urban and semi-urban vicinity. As said above, the electrical conductivity also reflects the phytotoxic/phyto inhibitory characteristics of the compost. While diluting the composts with normal soil, the phytochemicals present in the compost if any also can be diluted, thus reducing the negative impacts. These Phyto inhibitory characters can be from the plants/ weeds, which are used as the feedstock for the preparation of the particular compost. Among the six composts used in this study, LPC and SPC only showed less/and or no germination and variations in the physiochemical characteristics which are purely made from fresh plant residues. Therefore, there is a considerable scope that allelopathic crops may be included while preparing this compost, which could change its characteristics and have an adverse effect on plant growth. But we can’t firmly say that the less germination and no germination in LPC and SPC are due to the allelopathic effects only because we are not sure about the complete feedstock list of the respective composts. The soil amended compost of Ageratina adenophora an invasive weed and allelopathic species has reduced seed germination and seedling growth of Triticum aestivum and Brassica campestris. And the study says that it might be due to the allelochemicals released by Ageratina plant residues in the soil (Das et al. 2018).

In the case of coir pith compost, coconut husk fibers are the core ingredient and plants are not used. In vermicompost, several biodegradable materials are used including plants. But studies have shown that vermicomposting of certain allelopathic weeds has reduced or even completely removed the allelopathic/toxic character of the particular weed plant making it suitable to use in fields (Karthikeyan et al. 2014; Hussain et al. 2020). So, in the present study, there is a chance for the allelopathic interaction of the plants used in the SPC inhibited germination. The less germination/no germination of Vigna radiata cannot be generalised to all seeds/plants. Some other seeds, which have more resistance potential may germinate in the same compost. Because different plant species have different preferences and tolerance levels for biochemical characteristics. Chinese cabbage (Brassica rapa) and Dia sorghum (Sorghum bicolor) seeds were grown in Eupatorium (Eupatorium adenophorum Spreng.) and Lantana (Lantana camara L.) composts. In which, Chinese cabbage germinated in both the compost showing that composting has eliminated its allelopathic potential whereas the germination potential of Dia sorghum indicated that eupatorium compost still had the inhibitory potential (Rajbanshi and Inubushi 1998). So, the effects may vary for different seeds and different preparation methods.

Considering the fact that urban green waste could be contaminated with different inorganic and organic compounds (Nitsche et al. 2017), further studies related to that such as the concentration of micro-macro elements and heavy metals are important for compost quality estimation. Further research on microbial interactions, as well as plant-microbe interactions should lead to more explained mechanisms of determined effects.

Leaf pigments: Chlorophyll and carotenoids

One of a plant's most key parts is its leaf area, which aids in the supply of nitrogen for the production of green plant biomass and influences photosynthesis by converting solar radiation into chemical energy. The most important aspect for grain yield and biomass was leaf photosynthesis, as well as the interaction between crops' photosynthetic ability and biochemical photosynthetic elements like leaf chlorophyll or carotenoid concentration to create biomass or yield (Houborg et al. 2013). To produce nicotinamide adenine dinucleotide phosphate and chemical energy in the form of adenosine triphosphate, photosynthesis requires the utilisation of chlorophyll, which is a crucial component of the Calvin-Benson cycle. Chlorophyll is also essential for capturing light during photosynthesis (Croft et al. 2017). Furthermore, the leaf area index has been widely used in farming as a biophysical indicator for vegetation to predict crop yields and growth. Additionally, the capability to screen solar radiation, which promotes CO2 assimilation and the formation of dry matter, is regarded as a key indicator of seedling growth and potential grain output (Huang et al. 2015).

By proper utilisation and recycling of wastes in terms of organic composts, it is possible to conserve the national resources, reduce the cost of production in many cases, solve the problem of pollution as well as may generate some employment. And the usage of compost instead of chemical fertilisers can bring economic prosperity to farmers. A better understanding of the physical and biological properties of compost enables us to use the compost wisely in agricultural practices. Also, it helps to deal with the overnutrition or undernutrition of plants by using these composts. A perfect database on compost quality enables us to do this. In the case of compost with fewer nutrient concentrations, we should provide the plant with additional nutrient supplements and vice versa. Besides the bright side of compost on plant growth and soil fertility, immature or unstable compost may be harmful to plants, soil, and soil microorganisms too. Therefore, quality assessment of compost is essential before using it for any type of agricultural activities which will lead to environmentally safe and sustainable farming practices. The present investigation was a modest agronomic trial with limited laboratory facilities to add some knowledge on the effect of different sources of compost with different biodegradable feedstocks on green gram crop germination. In this study, the compost is used as a substrate for seed germination and not as a fertiliser. So, more investigations must be done in the future to interpret the growth of different crops, their yield and the role of these different composts in it. Using the composts by mixing with soil in different ratios may also give different results, as one of our treatments didn’t show any germination. However, such nutrient-enriched compost materials can appropriately be diluted with a mixture of other organic composts or soil and further application may provide adequate nutrient sources for crop productivity in the field conditions particularly, under climate change resilience. This may also reduce the biodegradable waste accumulation in urban and semi-urban vicinity.

Declaration of Competing Interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

This work was supported by the Department of Science and Technology (DST), New Delhi under INSPIRE Fellowship program (Grant No: IF180788).

Author’s Contribution

Haritha Thulaseedharan Nair made substantial contributions to the conception or design of the work, Investigation/analysis, interpretation of data and drafted the manuscript. Gokul R Nath made contributions in Investigation and interpretation of data. Siddhuraju Perumal made considerable contributions to the conception or design of the work, interpretation of data and critical revision of the manuscript. All authors read and approved the final manuscript

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No competing interests reported.

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Impact of Organic Compost Prepared From Different Plant-Based Residues on Seed Germination and Early Seedling Growth Performance of Vigna Radiata (L.) Wilczek

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Abstract

Figures

Introduction

Materials And Methods

Sample Collection

Physico-chemical Analysis

Extraction of Humic substances

Mineral Analysis

Germination and Early Seedling Growth Performance

Experimental setup

Agro botanical Characters

Chlorophyll Content and Carotenoids

Statistical analysis

Results

Physico-chemical and Mineral Analysis

Germination and Early Seedling Growth Performance

Agrobotanical characters

Germination Percentage

Discussion

Physico-chemical and Mineral Analysis

Germination and Early Seedling growth performance

Germination Percentage

Leaf pigments: Chlorophyll and carotenoids

Conclusion

Declarations

References

Additional Declarations

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