The performance, yield and quality of statice flowers is however often affected by the abiotic and biotic environments such as soil fertility and insect pests among other major factors (Kumar and Chaudhary, 2018). Production of good yields and high quality statice flowers requires good soil fertility management practices. Adequate nitrogen (N) supply is critical for cut flower production and deficiency will result in poor plant growth and fewer low-quality flowers, while too much may result in too much vegetative growth, weak stems and delayed flowering. Phosphorus and potassium deficiencies on the other hand may result in smaller plants with shorter flowering stems and reduced overall yield.

The Kenya’s flower industry which is among the largest in world (Leipold and Morgante, 2013) is often faced with volatile costs of chemical fertilizers and pesticides among other inputs. Expensive chemical fertilizers may therefore not be an appropriate solution to correct nutrient deficiencies and poor soil properties in low resource poor smallholder production systems. There is essential to evaluate affordable and locally available organic nutrient options that can enhance statice production in Kenya. There is an urgent need for innovations and adoption of good agricultural practices to support profitability and environmental sustainability as well as bring more small-scale farmers into growing of summer flowers so as to realize growth in floriculture sub-sector.

Technologies such as composting, vermicomposting and bioslurry from biogas digesters provide plant nutrient sources alternative to chemical fertilizers with the additional benefit of organic waste management (Munnoli et al., 2010; YSDPL, 2006). Vermicomposts increase bioavailability of phosphorus in the soil, while enhancing soil nitrogen mineralization (Ansari, 2008). Bioslurry from biogas digesters on the other hand has an average plant nutrient content of about 0.75% nitrogen, 0.65% phosphorus and 1.05% potassium (Demont et al., 1991). These two organic fertilizers can therefore have a great potential to reduce fertilizer budgets among small-holder floriculture, while contributing to organic waste management and environmental sustainability. The main objective of this study was to establish the applicability, efficacy  and  benefits   of  different   vermicomposts  and bioslurry combinations in the production of statice.

Experimental site

The study was carried out at Horticulture Research and Teaching Field, Egerton University-Njoro campus in Kenya. The site lies at a latitude of 0° 23′ South and longitude of 35° 35′ East in the Lower Highland III Agroecological Zone with an altitude of approximately 2,238 m above mean sea level. The temperature range of the area is 14.9-21.9°C with mean annual rainfall range of 850 to 1100 mm (Jaetzold and Schmidt, 1983). The soils are predominantly vitric mollic andosols (Kinyanjui, 1979).

Soil media preparation

The garden soil used in potting media for this experiment was obtained from Egerton University’s Horticulture Teaching and Research Farm, Field Three.

Vermicompost preparation

The different vermicomposting substrates were collected within the campus. Food waste was collected from the various on campus kitchens at Egerton University including the student messes and the Agriculture Resource Centre Hotel. Bones and egg shells were removed. Mowed lawn grasses were gathered from the various on-campus lawns where machine mowing had taken place. The garden weed biomass was gathered from Egerton University’s Horticulture Teaching and Research Farm in Njoro, Kenya. The various materials were put into their respective vermicomposting bins already stocked with the red wriggler earthworms (Eisenia fetida). Watering was done at three-day intervals to keep the substrate moderately moist and avoiding waterlogging. The worms fed on the substrates and their excrement known as worm casts was eventually harvested as vermicompost. Each of the different vermicompost was harvested from the respective bins after 30 days when all the substrate compost had been converted to worm casts.

Bioslurry preparation

The bioslurry used in the experiment was obtained from the biogas digester at Egerton University’s Tatton Agricultural Park in Njoro, Kenya.

Plant materials

Seedlings of white statice were obtained from Limuru Farm late in the evening to minimize withering. The nursery bed was thoroughly wetted and uniform size plants were lifted and placed in polythene bags containing moist soil. The seedlings were established by transplanting singly into uniform plastic potting bags measuring 30 cm diameter and 40 cm depth, filled to three quarters of depth, with appropriate potting media as per the randomly assigned treatments. The seedlings were transplanted at sufficient depth to cover all roots. All the experimental units received uniform cultural practices as described by HCDA and MOA (2003). The different vermicomposts were applied to assigned plots at a rate of 40% by volume (being a reduction of 100% under which Ali et al. (2007) reported poor performance in lettuce). Bioslurry (B₁) was applied to the  assigned  plots  as  a  drench at a rate of 7.8 t/ha (Jeptoo et al., 2012) in 4 equal splits and at 15 days’ interval from 35 DAT. The root media was kept moist by watering according to need during plant growth. Pest and disease scouting were done to inform decisions on control.

Soil, vermicomposts and bioslurry analyses

Samples of the garden soil, the different vermicomposts and bioslurry used in growing media in the present study were analyzed at Kenya Agriculture and Livestock Research Organization’s soil chemistry laboratories at Njoro, in Kenya, to establish their characteristics.

Determination of pH

The pH was measured using pH-meter (digital ion analyzer). Air dried samples weighing 50 g for each of the different growing medium components were taken into separate 100-ml glass beakers. Into each beaker, 50 ml distilled water was added using a graduated cylinder and mixed thoroughly before being allowed to stand for 30 min. The resulting suspensions were stirred after every 10 min. The pH of the different suspensions was determined according to the procedure described by Okalebo et al. (2002).

Determination of water holding capacity

The water holding capacity of the garden soil and the different vermicomposts was determined according to the procedure described by Okalebo et al. (2002).

Determination of total organic carbon

For each of the growing medium components, one gram of air-dried growing medium was placed into separate 500-ml beakers. Ten milliliters of 1 N potassium dichromate solution and 20 ml concentrated sulphuric acid was added in each beaker and swirled to mix the suspension. 20 ml of distilled water was added along with 10 ml concentrated orthophosphoric acid into each beaker after 30 min and the mixtures were then allowed to cool. Ten drops of diphenylamine indicator were added. Each of the solutions was then titrated with 0.50 M ferrous ammonium sulphate solution and the reading was recorded upon colour change from violet blue to green. Organic carbon was determined by method of Walkley and Black (1934).

Determination of nitrogen content (Kjeldahl method)

Nitrogen content was determined using Kjeldahl method (1883) as follows. A sample weighing 0.3 g was digested in a digestion tube using a digestion mixture comprising of HCl, HNO₃, Se and CuSO₄. The heating block temperature was maintained at 360°C for 2 h after which the sample were allowed to cool before transfer into a 50 ml volumetric flask and the volume made to the mark. It was then allowed to settle and 5 ml of the aliquot was put into the distillation bottle where 10ml of 40% NaOH was added. It was then steam distilled into 5ml 1% Boric acid containing 4 drops of mixed indicator for 2 min, from the time the indicator turned green. The distillate was titrated using HCl with the end point being reached when the indicator turned green through grey to definite pink. A blank experiment was prepared using the same procedure described by Kirk (1950).

Determination of nitrate -N by calorimetric method

The nitrate content was determined by calorimetric method as described in Okalebo et al. (2020). A set of six clean well labeled 100 ml volumetric flasks was set up into which 0, 2.0, 4.0, 6.0, 8.0 and 10.0 ml of the standard solution (50 μg ml^-1) were separately transferred. These were the working standards and contained 0, 2, 4, 6, 8, and 10 μg NO₃-N ml^-1. Each volumetric flask was filled to the 100 ml mark with 0.5 M potassium sulphate. 0.5 ml of the sample extract, blanks and the standard series K₂SO₄ soil were transferred each into suitably marked test tube. 1.0 ml of salicylic acid was added to each test tube and mixed well and left to stand for 30 min. 10 ml 4M sodium hydroxide was added to each test tube, mixed well and left for 1 hour to allow development of full yellow colour. The colour was stable for the day. The absorbency was measured at wavelength 419 nm. A calibration curve was plotted and the absorbency calculated for each particular standard in the series, read off the value of the samples and the blanks. The concentration of nitrate N was calculated using the following formula.

where a = concentration of NO₃⁺-N in the solution, b = concentration of NO₃⁺-N the blank, v = volume of the extract; w = weight of the fresh soil; MCF = moisture correction factor.

The aliquot taken for both the standards and the unknown are the same therefore no multiplication factor is required within the calculations.

Determination of total phosphorous

Total phosphorus in the substrate samples was determined by the method described by Juma et al. (2018). A sample of 0.3g for each of the growing medium components was separately digested in digestion tubes using a digestion mixture comprising of HCl, HNO₃, Se and CuSO₄. Temperatures in the heating block were kept at 360°C for 2 h and then left to cool before transfer into separate 50-ml volumetric flasks and volume made to the mark. Five ml of each of the aliquots was transferred into the sample bottles with 1 ml of developing colour solution (ammonium vanadate and ammonium molybdate in the ratio of 1:1). The samples were stood for 30 min after and then transferred to cuvettes. Readings of atomic absorbance were taken using a spectrophotometer at λmax= 430 nm. Calibration curve was done using laboratory certified standards containing 0, 0.2, 0.4, 0.6, 0.8 1.0 and 1.2 ppm P respectively

Determination of potassium content

A sample weighing 0.3 g for each of the growing medium components was separately digested in digestion tubes using a mixture comprising HCl, HNO₃, HF and H₃BO₃. The temperatures in the block was maintained at 360°C for 2 h, thereafter samples were cooled, transferred to 50-ml volumetric flasks and volume made to the mark. Calibration was done for potassium using certified standards. Samples were analyzed by atomic absorption spectrophotometer (AAS), Varian spectra AA10 AAS machine. The characteristics of the various growing medium components used in the present study are as presented below.

Soil characteristics

The   characteristics  of   the   soil  sample  taken  from  the  site  for analysis were established as given in Table 1.

Characteristics of the different vermicomposts

The characteristics of the different vermicomposts after analysis of respective samples were established as given in Table 2.

Bioslurry characteristics

The characteristics of the bioslurry established after analysis of sample were as given in Table 3.

Experimental design and treatment application

Two different trials were conducted to determine the effects of treatment with different vermicomposts and bioslurry on growth and yield of statice. The first trial was established in February 2013 and harvested in June 2013 and the second was planted  in  June  2013 and harvested in November 2013. The experiment was a 2 × 4 factorial in a randomized complete block design (RCBD) with four replications. The treatments applied included 100% garden soil (V₀) as the control, o 60% garden soil with 40% kitchen waste vermicompost (V₁), 60% garden soil with 40% mowed lawn grass vermicompost and 60% garden soil with 40% garden weed biomass vermicompost (V₃) with. The different vermicomposts were applied at 40% of the rate used by Ali et al. (2007) who reported poor growth performance in lettuce under 100% vermicompost.  Bioslurry (B₁) was applied at 7.8 t/ha (Jeptoo et al., 2012) as a drench in 4 equal splits untreated control (B₀). The eight treatments applied in the experiment were V₁, V₂, V₃, B₁, (V₁× B₁), (V₂×B₁) and (V₃×B₁) with the control plot being the untreated (B₀ or V₀ or B₀×V₀).

Data collection

The seedling takeoff was observed by a stand count at 14 DAT and at 21 DAT and expressed as a percentage for each treatment. Gapping was done to replace any seedlings that did not survive initial    transplanting.  The   number   of   days   from   the   date   of transplanting to the 50% flower opening of the earliest flower stem for each treatment was recorded and used to calculate the average duration to flowering. The number of suckers produced by each plant was counted and the average for each treatment was calculated and recorded as a measure of growth and yield potential. The number of harvested flower stems of at least 30 cm length, from apex to point of cut, per plant by the end of data collection (10 weeks after first flowering) was recorded for each growing bag and used to calculate average yield for each treatment. The stem lengths of all the flower stems harvested from each growing bag, measured from the apex to the point of cut was recorded and used to calculate the mean response to the different treatment applications. The data obtained was subjected to analysis of variance (ANOVA) and significant means were separated by Tukey’s test at 5% level of significance. Data analysis was done using JMP (ver. 10) by SAS Institute.

Effect of vermicompost and bioslurry on seedling take off, number of stems, days to flowering, and stem length

The results obtained show that the different vermicomposts had a significant effect on the number of stems, days to flowering, and stem length except seedling takeoff at p≤0.05 (Table 4). Plots treated with 40% kitchen waste vermicompost (V₁) resulted in a significantly higher number of flower stems (22.9 and 26.0) compared with the control (V₀) which recorded 11.3 and 13.3 in season one and two respectively. This was followed by the plots treated with 40% garden weed biomass vermicompost (V₃)  with  17.0  in  season  1  and 18.5 in season 2 and 40% mowed lawn grass vermicompost (V₂) with 16.5 and 18.0 stems but was not significantly different from the control in (15.2) in season one. Similarly, bioslurry treatment had significant effect on the number of stems produced per plant (Table 5). Application of bioslurry at 7.8 t/ha (B₁) resulted in significantly higher number of stems (18.7 and 19.8) in seasons one and two respectively when compared with the control treatment (.15.2 and 18.1).

Combined effect of vermicompost and bioslurry on number of stems, days to first flowering and flower stem length at 60 DAT

The applications of the different vermicompost types at a rate of 40% by volume in combination with bioslurry at a rate of 7.8 ton/ha on statice significantly affected the number of stems produced per plant, the days to flowering and stem length at 60 DAT when compared to the untreated plots (Table 6). Respectively in season one and two, application of treatments combining any of the different vermicomposts with bioslurry (V₁ × B₁, V₂ × B₁ and V₃ × B₁) on statice resulted in significant increase on the number of stems produced per plant (18.8 to 26.3 stems, and 19.0 to 27.5 stems) when compare with the control (15.2 and 18.1 stems). These responses were also significantly greater than the main effects of the different vermicomposts (16.5 to 22.9 stems in season one and 18.0 to 26.0 stems in season two) as well as from bioslurry 18.7 and 19.8 stems respectively in season one and two). The combination of kitchen waste vermicompost and bioslurry (V₁ × B₁) produced significantly the greatest response (26.3 and 27.5 stems respectively in season one and two) compared to V₂ × B₁ and V₃ × B₁ (18.8 and 19.0 stems respectively in season one and two) and the untreated plots (15.2 and 18.1 stems respectively in season one and two).

Vermicomposts   and   bioslurry  applications  significantly affected the parameters of growth, yield, and postharvest quality in statice when observed at P≤0.05 except seedling take off. While, bioslurry could not affect seedling take off as its application commenced after seedling establishment, higher seedling takeoff tended to associate with the application of vermicompost. The higher seedling takeoff, though insignificant, was possibly due to suppression of soil plant pathogens while promoting growth of seedlings (Jack, 2011; Pathma and Sakthivel, 2012), improved soil health (Majumder et al., 2014) or due to improved soil physical, chemical and biological fertility including better soil porosity, structure, texture, bulk density, water tension capacity, and biological activities (Asciutto et al., 2006) which probably enhanced seedling take off over the control. According to Ahmad et al. (2013), humic acid present in the bio fertilizers promoted uniform sprouting, more foliage growth per plant, and greater leaf area as well as total leaf chlorophyll contents, and earlier spike emergence in gladiolus.

Effect on growth and yield

Application of vermicomposts and bioslurry on statice had significant main and combined effects on the number of stems produced per plant, flower stem length attained at 60 days after transplanting, the number of days to flowering and the fresh weight of flower stems at harvest when compared with the control at P≤0.05. There was a significant increase in number of stems produced, days to first  flowering, and  flower stem length. The application of kitchen waste vermicompost resulted in the highest number of flower stems per plant that were also significantly longer in both season one and two. Results obtained with vermicomposts from mowed lawn grass and garden weed biomass though significantly higher in these parameters than the control, they had no significant difference between them in both seasons. The combined effect of kitchen waste vermicompost and bioslurry significantly exceeded the main effects observed under the different vermicompost and bioslurry applications.

The observations of the present study suggesting promotive effect of vermicomposts on vegetative growth are consistent with the findings of Mahmud et al. (2020) who reported insignificant difference in plant height and foliage parameters between pineapple plants treated with vermicompost and chemical fertilizer. While working with strawberry cv. “Winter dawn”, Sahana et al. (2020) reported the best response in vegetative growth, yield and yield attributes from treatment combination that included vermicompost. Similarly, Pansuriya et al. (2018) reported significantly enhanced growth and yield parameters in gladiolus from treatment combinations containing bio fertilizers. Sharma et al. (2017) also reported increased plant height, number of branches, plant spread, flowering duration and flower yield in African marigold under vermicompost treatments. Abubaker et al. (2015) attributed superior plant performance under application of bioslurry to the inhibition of ammonia oxidation and denitrification which potentially benefits crop growth due to reduced losses of soil nitrogen. Srivastava et al. (2014) reported enhanced vegetative growth and yield with use of vermicompost in tuberose var. Shringar. Geeta and Prabhat (2009) reported in gladiolus significant effect on both fresh and dry weight of spike, days taken to spike emergence, maximum diameter of first floret and number of florets opened from pre-harvest bio fertilizer treatments. Srivastava and Govil (2007) also reported improvement in the various characters of gladiolus resulting from the activity of rhizospheric bacteria attributable to bio fertilizer inoculation. Nikbakht et al. (2008) reported up to 52% increase in the number of harvested flowers per plant in Gerbera from humic acid treatments. Atiyeh et al. (2000) observed faster growth on tomatoes when vermicompost was applied compared to the control probably due to supply of phosphorus and calcium, important nutrients for cell growth and development. While working with basil (Ocimum basilicum L.) and tomato (Solanum lycopersicum L. ‘Roma’), Huang et al. (2020) reported superior growth indexes from substrates mixes combining vermicompost and commercial peat-based substrate which they attributed to favourable substrate amendment including higher pH and better porosity. Furthermore, the reviews by Bhat et al. (2018) and Joshi et al. (2015) on effects of vermicomposts on growth, yield and quality of crops, assert that the enhanced observations on the studied parameters are due to positive effects of higher amounts  of  humic  substances  in  the  bio  fertilizers  on growth of plants.

The meta-analysis by Blouin et al. (2019) also asserts that the presence of bio fertilizers promotes the increase in plant growth and yield due to effects of humic acids and growth promoting bacteria. Similarly, Kumar et al. (2018) in their review of the potential benefits of vermicomposts in crop production and soil fertility concluded that the bio fertilizer improves soil physical, chemical and biological properties sustainably supporting crop production.

Effect on postharvest quality

Application of the different vermicomposts and bioslurry significantly enhanced postharvest quality of statice when compared with the control at P≤0.05. Combined treatment applications of the different vermicomposts with bioslurry also had significant interaction effect on postharvest quality parameters in statice when compared with the control at P≤0.05 although they were not significantly different from the main effects of the vermicomposts and bioslurry. The different vermicomposts and bioslurry significantly enhanced water uptake during vase life in statice and also resulted in a gradual decline in water uptake throughout the observation period. They also significantly extended vase life when compared to the plain garden soil. While no specific literature on statice came up, findings similar to the present study have been reported from various studies involving treatments with organic manures on other crops. These findings are supported by Sharma et al. (2017) who when working with marigold (var. Pusa Narangi) reported maximum shelf life and flower vase life from treatments that included application of farm yard manure as organic manure alongside bio fertilizers and NPK in integrated plant nutrient management. Palagani and Alka (2017) observed significantly improved water uptake from treatments with bio-fertilizers inoculation alongside spermine foliar sprays. They also reported significantly improved flower quality parameters in Gerbera including improved postharvest physiology of flowers and higher retained flower fresh weight. Bohra and Kumar (2014) reported extended vase life in Chrysanthemum cv. Little Darling resulting from treatment that applied vermicompost at a rate of 300g/m². Longchar and Keditsu (2013) reported significantly improved floral characteristics and flower vase life in Gerbera from treatments that included application of vermicompost as an organic nutrient source. Srivastava et al. (2007) reported maximum water uptake in tuberose under treatments incorporating vermicomposts. They also reported significantly longer vase life from treatments that had vermicompost while Ikram et al. (2012) reported enhanced shelf life and vase life from application of farm yard manure obtained from leaf compost. Geeta and Prabhat (2009) reported significantly extended vase life in gladiolus   under    treatments    that   combined  vascular arbuscular mycorrhiza with vermicompost and vermiwash suggesting a positive contributive effect of vermicompost. Tejada et al. (2008) reported improved vase life in Gerbera from treatments that incorporated phosphorous solubilizing bacteria found among the diverse nutrient solubilizing microbes (Ayyadurai et al., 2007) present in vermicomposts and other organic manures (Sinha et al., 2010).

From the results of the present study, soil amendment with 7.8 t/ha bioslurry significantly enhances stem elongation and ultimate flower stem length, increases number of stems produced per plant and the duration to flowering, while also increasing the fresh weight of flower stems in potted statice when compared to plain soil. However, these effects were significantly lower than those produced by the different vermicompost used in the present study. On the other hand, when compared to plain garden soil and application of 7.8 t/ha of bioslurry, all the three vermicomposts used in the present study, regardless of type, significantly enhance stem elongation, flower stem length, number of stems produced per plant in potted statice. They also increase the duration to flowering, while also increasing the fresh weight of flower stems. Kitchen waste vermicompost consistently gives the highest significant responses for all the statice growth and yield parameters studied. Vermicomposts prepared from kitchen waste and mowed lawn grass had similar effect on statice stem length, with both producing the longest flower stems. Therefore, potting mixtures containing 40% vermicompost by volume for any of the types, and drenching with bioslurry at a rate t of 7.8 t/ha significantly promote growth and yield responses in statice.

Findings of the present research study recommend the use of 40% vermicompost obtained from the readily available kitchen waste, mowed lawn grass and garden weed biomass as well as the use of 7.8 t/ha of bioslurry improved growth and yield in statice. However, there is need for further work to test the use of vermicomposts at varied rates in order to establish the optimal rate of application in statice.

The authors have not declared any conflict of interests.