Abstract The potential of cow bone biochar combined with calcium fertilizers to enhance tomato shelf life remains insufficiently explored. This study evaluated the effects of biochar and calcium sources on soil chemical properties, growth, yield, quality, and shelf life of tomato in a screen house experiment. Treatments consisted of five biochar rates (0, 10, 20, 30, and 40 t ha⁻¹) and four calcium sources (control, calcium sulphate, calcium nitrate, and poultry manure) arranged in a 5 × 4 factorial using a Completely Randomized Design with three replications. Poultry manure produced the highest fruit yield, increasing production by 22% over mineral calcium sources and 382.5% over the control. Increasing biochar rates improved nutrient availability, with 40 t ha⁻¹ enhancing yield by 294% compared with the control, likely due to improved soil fertility, nutrient retention, and higher cation exchange capacity. Calcium sulphate was most effective in reducing fruit weight loss and extending shelf life, increasing storage duration by up to 69% relative to the control. This improvement is attributed to enhanced calcium uptake, which strengthens cell walls and reduces membrane degradation during storage. Significant interaction effects were observed: 30 t ha⁻¹ biochar combined with calcium sulphate extended shelf life by 123% compared with the control. This synergy suggests that biochar enhances calcium retention and availability, thereby improving fruit structural stability. The combined application of 30 t ha⁻¹ biochar and calcium sulphate is recommended to improve tomato yield and postharvest quality, although field validation is necessary for large-scale adoption.

Keywords: Calcium nitrate, Calcium sulphate, Cow bone biochar, Poultry manure, Shelf life, Tomato

Funding: Research supported by Bowen University for data collection.

Citation:  Adekiya, A.O., Ogunbode, T.O., Esan, V.I., Adedokun, O., Olatubi, I.V., and Ayegboyin, M.H. 2026. Soil and postharvest responses of tomato to biochar and calcium amendments. Natural and Life Sciences Communications. 25(3): e2026062.

Graphical Abstract:

INTRODUCTION

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops globally, valued for its nutritional, economic, and industrial significance. It ranks second only to potato in global vegetable production. Global tomato production exceeded 186.821 million metric tonnes in 2020 (FAOSTAT, 2022), and more recent statistics indicate continued increases in production due to rising global demand. Tomatoes are consumed fresh and processed into soups, juices, ketchup, pastes, and purees. Nutritionally, tomatoes are rich in vitamins A and C, essential minerals, sugars, amino acids, iron, fiber, and phosphorus (Collins et al., 2022). They are also a major source of lycopene, a carotenoid with strong antioxidant properties associated with reduced risks of cancer and cardiovascular diseases (Shafe et al., 2024).

Despite high production levels, tomato cultivation faces significant postharvest losses worldwide. Globally, substantial portions of harvested tomatoes are lost due to their climacteric nature and rapid ripening. In Africa, weak transportation systems, inadequate storage facilities, and limited processing infrastructure exacerbate these losses. In Nigeria, tomato production is estimated at approximately 3.6 million tonnes cultivated on about 0.8 million hectares, with an average yield of roughly 4.2 t ha⁻¹ (FAO, 2022). Although the country ranks among Africa’s leading tomato producers, recent reports indicate that post harvest losses driven by poor handling, inadequate storage, and supply chain inefficiencies  reduce as much as 40–45 % of total production each year (Salasi et al., 2025). State-level reports further illustrate the severity of the problem. As a major tomato producing region in Nigeria, Kano State experiences substantial losses along the tomato value chain, with recent research documenting significant physical and economic waste due to inadequate handling, storage, and transportation practices (Suleiman et al., 2024). In Benue State, farmers also face considerable postharvest losses, as traditional handling and limited storage infrastructure contribute to large quantities of tomatoes being discarded before reaching markets (Akor and Akor, 2025). These losses significantly undermine farmer income and national food security.

Various preservation strategies have been explored to extend tomato shelf life. Chemical treatments, including hydrogen sulphide (Yao et al., 2020), abscisic acid (Tao et al., 2020), calcium chloride (El-Mogy et al., 2020; Shehata et al., 2021), hydrogen peroxide, and ozonated water (Shehata et al., 2021), have shown effectiveness in delaying ripening and reducing decay. Biological and natural treatments, such as chitosan coatings (Zhu et al., 2019; Shehata et al., 2021) and essential oils (Tzortzaki et al., 2019), have also demonstrated potential in preserving tomato quality. However, despite their effectiveness, these postharvest interventions often present limitations including food safety concerns, potential environmental and health risks, sensory alterations, economic inefficiency, and limited accessibility for smallholder farmers. Consequently, attention has shifted toward preharvest strategies that improve fruit quality and storage potential through soil nutrient management.

Calcium is widely recognized as a critical nutrient in maintaining fruit firmness and structural stability. It strengthens cell walls through calcium-pectate formation and stabilizes membrane integrity, thereby reducing physiological disorders such as blossom-end rot and delaying senescence (Hernández-Muñoz et al., 2006; Guo et al., 2020). Calcium deficiencies in soil or plant tissues can significantly reduce fruit quality and shelf life. Therefore, improving soil calcium availability offers a promising strategy for enhancing tomato postharvest performance.

Biochar has emerged as a sustainable soil amendment capable of improving soil chemical properties, enhancing nutrient retention, increasing water holding capacity, and stimulating microbial activity (Agbede and Oyewumi, 2023; Janyasupab et al., 2023). In addition to its agronomic benefits, biochar contributes to long-term carbon sequestration and climate change mitigation (Lehmann et al., 2009). Several studies have demonstrated the positive effects of biochar on tomato production. For example, biochar application significantly improved soil pH, bulk density, soil organic matter, and yield components in tomato grown on acid soils (Adekiya et al., 2025). Similarly, Lei et al. (2024) reported that biochar increased tomato yield by 29.55%, total soluble solids by 4.28%, and vitamin C content by 6.77% compared with control treatments. Adekiya et al. (2020) also reported improvements in soil fertility and crop performance following organic amendments.

Among various biochar sources, cow bone biochar is particularly distinctive due to its exceptionally high calcium and phosphorus content, primarily in the form of calcium phosphate compounds. Unlike plant-derived biochars that are mainly carbon-rich, cow bone biochar provides substantial mineral calcium alongside stable organic carbon. Almaroai and Eissa (2020) reported that cow bone biochar applied at 5 and 10 t ha⁻¹ increased tomato fruit yield by 20% and 30%, respectively, relative to no biochar application. Similarly, Farouk and AL-Huqail (2022) demonstrated its effectiveness in enhancing quinoa growth and seed quality. The utilization of cow bone biochar also promotes waste valorization by converting abattoir waste into valuable soil amendments, thereby supporting circular agriculture.

Calcium fertilizers such as calcium nitrate, calcium sulphate, calcium silicate, poultry manure, and pressmud have been used to improve tomato growth, quality, and shelf life (Santhosh et al., 2021). Calcium nitrate provides readily available calcium and nitrogen (Barker, 2019), while poultry manure supplies calcium and other nutrients more gradually and improves soil fertility (Adekiya et al., 2020). However, while both biochar and calcium fertilizers individually enhance soil properties and crop performance, their combined influence on tomato mineral composition and shelf life has received limited attention.

To our knowledge, no previous studies have investigated the combined effects of cow bone biochar and different calcium fertilizer sources on tomato shelf life, mineral composition, and weight loss. Most existing research has focused primarily on soil improvement (Lehmann et al., 2009), crop growth and yield enhancement (Adekiya et al., 2020), or postharvest chemical treatments. The potential synergistic interaction between calcium-rich cow bone biochar and supplemental calcium fertilizers in improving both soil fertility and fruit structural stability remains largely unexplored. It was hypothesized that: (i) cow bone biochar and calcium fertilizers applied separately would improve soil chemical properties, tomato growth, yield, mineral composition, and shelf life. (ii) their combined application would produce synergistic effects, resulting in greater improvements than single applications. Therefore, the objectives of this study were to:

1.    Evaluate the effects of cow bone biochar and different calcium fertilizer sources on soil chemical properties;

2.    Determine their influence on tomato growth and yield;

3.    Assess their impact on fruit mineral composition; and

4.    Examine their effects on tomato shelf life and weight loss.

MATERIALS AND METHODS

In 2024, two concurrent studies were carried out at locations A and B within the same screen house from February to May at Bowen University's Teaching and Research Farm in Iwo, Osun State, Nigeria. The experiment at site B was designed to validate the results obtained from site A. Bowen University is located at coordinates 7.6236°N, 4.1890°E and has an elevation of 312 meters above sea level. The screen house was constructed with a galvanized iron framework, features UV-protective covering, insect-resistant netting on the sides, and a granite floor. Temperature and humidity levels inside the screen house were monitored using a thermograph and barograph, recording averages of 31°C and 75%, respectively. The soil in the Iwo area is classified as Oxic Haplustalf according to the USDA's Alfisol order (Soil Survey Staff, 2014) or as Luvisol (IUSS Working Group WRB, 2015).

 Sample preparation and experimental design

Soil samples were collected randomly from around the Research Farm using a soil auger. The samples were then combined and passed through a 2 mm mesh to eliminate stones and debris. Subsequently, 15 kg of the processed soil was placed into perforated grow bags to ensure adequate air and water circulation. Each treatment consisted of four grow bags, which were placed randomly within the screen house to ensure an unbiased distribution of amendments, representing site A. An identical set of grow bags was placed adjacent to these within the same screen house, representing site B.

The experiment comprised of five levels of cow bone biochar (0, 10, 20, 30 and 40 t ha^-1) and 4 four calcium fertilizer types (0 (no fertilizer), calcium sulphate, calcium nitrate and poultry manure) applied at 160 kg Ca ha^-1(Adekiya et al., 2025) in a 5 × 4 factorial experiment. The 20 treatments combinations were arranged in a Completely Randomised Design (CRD) replicated three times.

Preparation of soil amendments

The biochar utilized in this research was derived from cow bones sourced from an abattoir in Iwo town. After being dried, the bones underwent pyrolysis in a sealed metal drum equipped with vents for gas escape, achieving temperatures of approximately 500 °C. Once the pyrolysis process was complete, the biochar was cooled, ground, and sieved through a 2 mm mesh to ensure consistency. Calcium sulphate and calcium nitrate were acquired from suppliers, while poultry manure was sourced from the poultry unit at Bowen University's Teaching and Research Farm.

Application of soil amendments

Cow bone biochar was applied at the rates of 0, 10, 20, 30 and 40 t ha^-1. The application per 15 kg soil in the grow bag was based on the fact that 1 ha of land is equivalent to 2,000,000 kg (Agbede, 2009). It means 10 t (10,000 kg) was applied to 1 ha = 2,000,000 kg

Therefore, application to 15 kg of soil in the grow bag      = 0.075 kg =75 g/15 kg soil.

Following the above, 20, 30 and 40 t ha^-1 cow bone biochar was applied at 150 g, 225 g and 300 g, respectively. The fertizers were applied based on 160 kg Ca ha^-1 (Adekiya et al., 2025). The ca in poultry manure, calcium sulphate and calcium nitrate were 6.08, 29.4 and 24.3 respectively (Table 3).

Therefore, poultry manure  = 2,631 kg ha^-1

But 1 ha = 2,000,000 of soil, it means then that 1 ha = 2,000,000 of soil = 2,631 kg poultry manure.

Therefore, 15 kg soil  = 0.0197 kg = 19.7 g poultry manure/ 15 kg soil

In the same process, calcium sulphate was applied at 4.08 g / 15 kg soil and calcium nitrate was also applied at 4.9 g/ 15 kg. The cow bone biochar was added into the soil using a hand trowel and allowed to settle for four weeks prior to transplanting the tomatoes into the grow bags (Adekiya et al., 2025). The poultry manure was added into the soil one week before transplanting. Watering commenced immediately and continued every other day until transplanting day. Calcium sulfate and calcium nitrate treatments were applied five days after the tomatoes were transplanted.

Nursery and transplanting of tomato

In this experiment, a local variety of tomato (Iwo local) was utilized. Iwo local variety is an indeterminate variety with fruits that are round to irregular in shape, often medium to fairly large in size. The fruits are soft-skinned and more prone to cracking and mechanical damage compared with improved varieties, but the variety is well adapted to the humid rainforest and coastal conditions of South-West Nigeria. The tomato seed was purchased from the market and sown in a seed tray filled with good loamy soil in the screen house. Watering was done daily in the evening. Transplanting took place after three weeks in the nursery. The seedlings were carefully transferred in the evening, ensuring that a ball of soil was retained around the roots to minimize damage. Each grow bag was planted with one tomato seedling, maintaining a single healthy plant per bag. The experiment was replicated three times. Four grow bags constituted one treatment, resulting in 80 (grow bags) plants per block replicated three time to give a total of 240 (grow bags) plants at site A and another 240 at site B. Immediately after transplanting, watering was performed, followed by morning watering sessions to keep the soil moisture close to field capacity throughout the experiment. Weeding was conducted by hand, removing any weeds that emerged in each grow bag. The entire experiment for both crops lasted 150 days after transplanting days.

Chemical analyses of soil, biochar and poultry manure

The physico-chemical properties of the soil were determined before application of treatments. The hydrometer method was used to determine the particle size distribution of the soil (sand, silt, and clay). This method relies on the principle of sedimentation, where soil particles settle in a suspension at different rates depending on their size, as described by Stokes' law.  The Walkley and Black method was used to determine the soil organic carbon (SOC) content. It is based on the oxidation of organic matter by potassium dichromate in the presence of sulphuric acid. The micro-Kjeldahl digestion method was employed to determine total nitrogen (N) in the soil. This method involves the conversion of organic and inorganic nitrogen compounds into ammonium through digestion, followed by quantification. The Bray-1 method was used to determine the available phosphorus (P) in the soil. This method involves extracting phosphorus using an acid-fluoride solution, followed by quantification using the molybdenum blue colorimetric method. The determination of exchangeable cations (K, Ca, Mg and Na) in the soil was carried out using 1M ammonium acetate extraction. This process involves extracting these cations from the soil exchange complex, followed by quantification using atomic absorption spectrometry (AAS) (Hendershot et al., 2007).

Furthermore, the nutrient composition of the biochar and poultry manure utilized in the experiment was assessed in accordance with AOAC (2012) standards.

The bulk density of the biochar was determined by filling a container with a known weight and volume with the biochar, ensuring it was not compacted. After weighing the container filled with biochar, the bulk density (bd) was calculated using the formula outlined by Unal et al. (2008).

The solid density of the biochar was determined using the liquid displacement method. Following this measurement, the porosity of the biochar was calculated using the formula.

bd = bulk density of biochar and sd = solid density of biochar

Moreover, the nutrient content of the biochar and poultry manure utilized in the experiment was assessed. Both materials were air-dried, passed through a 2 mm mesh, and analyzed for its nutrient contents following AOAC (2012) standards.

Assessment of growth and yield parameters in tomato plants

To evaluate the growth and yield parameters of tomatoes, three plants were randomly selected from each treatment group. Growth measurements, including plant height, stem diameter, and the number of leaves per plant, were taken at the mid-flowering stage which was approximately 28 days after transplanting. Plant height was measured from the base of the plant to the shoot tip using a meter rule, while the stem diameter was determined with a vernier caliper. The number of leaves per plant was manually counted. Ripe and mature fruits were harvested, counted, and weighed to determine the tomato yield. Yield measurements continued up to 150 days after transplanting.

Determination of tomato fruits' shelf-life

The first set of harvested tomato fruits (about 80 days after transplanting) were cleaned with a dry, clean cloth and sorted into different treatment groups, with each group consisting of five (5) fruits and three replicates. The fruits were then properly arranged on a clean table in the laboratory for shelf-life determination. They were stored under ambient laboratory conditions, with temperatures ranging from 27–32 °C, relative humidity of 65–80%, and natural daylight (approximately a 12-hour photoperiod) entering the laboratory without direct sunlight exposure.

Parameters accessed include:

1. Weight loss: The weight of each tomato fruit was recorded immediately after harvesting and on each experimental day using a weighing scale. Total weight loss was determined by calculating the difference between the initial weight and the final weight measured at five-day intervals until complete deterioration that is when the fruits have undergone irreversible physical, physiological, and microbial degradation such that it becomes unmarketable and unfit for human consumption. This was expressed as a percentage using the formula provided below.

    

2.      WL = Weight loss

3.  Shelf life

This was carried out by calculating the days elapsed from the starting date of harvesting the tomato, to the day it was considered bad and below marketable condition.

Determination of mineral and proximate components of tomato fruits

At harvest, mature tomato fruits of uniform size (about 5.0 – 6.5 cm) were selected from each treatment for chemical analysis to assess their mineral content, following AOAC (2012) guidelines. For this purpose, one gram of each fruit dried sample was digested using a blend of HNO₃, H₂SO₄, and HClO₄ in a 7:2:1 volume ratio. The mineral contents, specifically Cu, Fe, Mg, K, Ca, and Na, were then measured using atomic absorption spectrophotometry.

Statistical analysis

Soil chemical properties, tomato performance, quality, and shelf life data were evaluated using analysis of variance (ANOVA). Treatment means were compared using Duncan’s Multiple Range Test (DMRT) at a 0.05 significance level.

RESULTS

Soil properties before experimentation and analysis of amendments used

Tables 1 and 2 present the results of the soil properties in grow bags before experimentation and the chemical composition of the soil amendments used, respectively. Particle size analysis revealed that the soil had a sandy loam texture, characterized by high sand content and low levels of both silt and clay. The soil was deficient in organic matter (2.04%) (Akinride and Obigbesan, 2000), total nitrogen (0.10%) (Akinride and Obigbesan, 2000), available phosphorus (4.99 mg kg⁻¹) (Akinride and Obigbesan, 2000), calcium (1.70 cmol kg⁻¹) (Akinride and Obigbesan, 2000), and magnesium (0.30 cmol kg⁻¹) (Akinride and Obigbesan, 2000), but contained adequate exchangeable potassium (0.19 cmol kg⁻¹) (Akinride and Obigbesan, 2000) (Table 1). Biochar exhibited higher levels of organic carbon, phosphorus, and magnesium compared to poultry manure (PM), while PM contained greater amounts of nitrogen, potassium, and sodium than biochar (Table 2). Among the soil amendments, calcium levels increased in the order: biochar < PM < calcium nitrate < calcium sulphate.

Table 1. Physical and chemical properties of the soil prior to planting.

Note: Mean ± standard deviation of soil physical and chemical properties (0–15 cm depth) of the soil used prior to experimentation in; Low: nutrient content value below the critical level recommended for crop production (Akinrinde and Obigbesan, 2000); Adequate: nutrient content value above the critical level recommended for crop production. Three replicates were used for the analysis in the table.

Table 2. Physical and chemical properties of the amendment used.

Note: NA = not applicable

Impact of biochar and various sources of calcium fertilizers on soil chemical characteristics

The effects of biochar and various calcium fertilizer sources on soil chemical characteristics are summarized in Table 3. As an individual factor, all Ca sources of soil amendment (PM, calcium sulphate and calcium nitrate) improved soil chemical characteristics compared with the control. PM increased soil organic matter (SOM), phosphorous potassium and magnesium contents of the soil relative to calcium nitrate and calcium sulphate. Calcium sulphate treatment increased Ca levels of the soil relative to PM, calcium nitrate, biochar and no application of treatment (control). There were no significant differences between calcium sulphate and calcium nitrate treatments for P and Mg.  As an individual factor, biochar alone also increased soil chemical properties compared with no application of treatment. The values of OM and N did not differ statistically among the biochar levels of 10 t ha⁻¹, 20 t ha⁻¹, and 30 t ha⁻¹. The results for P, K, Ca, and Mg indicated a trend where 40 t ha⁻¹ > 30 t ha⁻¹ > 20 t ha⁻¹ > 10 t ha⁻¹. The 40 t ha^-1 biochar + PM has the highest values of SOM (3.14% at site A and 3.15% at site B), P (25.5 mg kg^-1 at site A and 25.0 mg kg^-1 at site B), K (3.15 cmol kg^-1 at site A and 3.16 cmol kg^-1 at site B), and Mg (17.22 cmol kg^-1 and 17.21 cmol kg^-1 at site A and B respectively). The 40 t ha^-1 biochar + calcium sulphate has the best values of N (0.21 % at site A and 0.23% at site B) and Ca (20.29 cmol kg^-1 at site A and 20.31 cmol kg^-1 at site B).

The interaction between biochar (B) and calcium fertilizer (Ca) (B × Ca) was significant for all soil chemical properties except nitrogen (N).

Table 3. Effect of biochar and different Ca fertilizer sources on soil chemical properties.

Note: Values followed by similar letters under the same column are not significantly different at P = 0.05 according to Duncan’s multiple range test.

Effect of biochar and different Ca fertilizer sources on tomato growth and yield parameters

The results demonstrate that the application of biochar and different calcium fertilizer sources significantly influenced tomato growth and yield parameters (Figures 1-5). When applied individually, the calcium fertilizer sources used as soil amendments enhanced vegetative growth, including plant height, stem diameter, and number of leaves, compared with the control treatment. Similarly, yield components, particularly number of fruits and fruit weight, were improved relative to the control. The treatment with poultry manure (PM) resulted in greater growth and yield parameters for tomatoes compared to the other sources of calcium fertilizers. Additionally, no statistical differences were found in plant height, stem diameter, leaf and fruit numbers between the calcium sulfate and calcium nitrate treatments. The decreasing order of growth and yield was: PM > calcium sulphate = calcium nitrate > control. Average from the two sites and across all biochar levels, PM increase fruit yield of tomato by 22.5 %, 20.16%, and 382.5% relative to calcium nitrate, calcium sulphate and control treatment respectively. As an individual factor, biochar enhanced plant height, stem diameter, number of leaves, number of fruits, and fruit weight of tomatoes compared to the control. These parameters showed improvement as the biochar application rate increased from 0 to 40 tons per hectare. However, there were no significant differences in stem diameter and leaf count between the biochar levels of 10 and 20 tons per hectare. On average across the two sites, the application of 40 tons per hectare of biochar improved tomato yield by 21.96%, 97.19%, 161.73%, and 294.39% compared to the levels of 30 tons per hectare, 20 tons per hectare, 10 tons per hectare, and the control, respectively. The interaction effects between biochar and calcium (B × Ca) were significant for all growth and yield parameters except for plant height. The highest tomato yield was achieved with the combination of biochar at 40 tons per hectare and poultry manure.

Figure 1. Effect of biochar and different Ca fertilizer sources on tomato plant height; Vertical bars show standard error of paired comparisons; B = biochar.

Figure 2. Effect of biochar and different Ca fertilizer sources on stem diameter; Vertical bars show standard error of paired comparisons; B = biochar.

Figure 3. Effect of biochar and different Ca fertilizer sources on number of leaves; Vertical bars show standard error of paired comparisons; B = biochar.

Figure 4. Effect of biochar and different Ca fertilizer sources on the number of fruits; Vertical bars show standard error of paired comparisons; B = biochar.

Figure 5. Effect of biochar and different Ca fertilizer sources on fruit weight; Vertical bars show standard error of paired comparisons; B = biochar.

Effects of biochar and different Ca fertilizer sources on mineral contents of tomato fruit

The effects of biochar and various calcium fertilizer sources on the mineral content of tomato fruits are shown in Table 4. As single factors, the addition of amendments increased the concentration of minerals (Ca, Mg, Fe, Zn, Cu and Na) in tomato fruits compared to the control. Except for Ca, PM significantly increased the mineral contents of tomato relative to calcium sulphate and calcium nitrate and the control. Calcium sulphate significantly increased Ca concentration relative to others. There were no significant differences between calcium sulphate and calcium nitrate for Cu and Fe. Also, as an individual factor, application of biochar increased Ca, Mg, Fe, Zn, Cu and Na contents of tomato relative to the control. The mineral content of tomato increased with biochar application, ranging from 0 to 40 t ha⁻¹. The interaction between biochar (B) and calcium fertilizer (Ca) (B × Ca) was significant for Ca, Mg, Fe, Zn, Cu and Na, but not for Cu.

Table 4. Effect of biochar and different Ca fertilizer sources on mineral contents of tomato fruit.

Note: Values followed by similar letters under the same column are not significantly different at P = 0.05 according to Duncan’s multiple range test.

Effect of biochar and different Ca fertilizer sources on shelf life of tomato fruits

The impact of biochar and various calcium fertilizer sources on the weight loss and shelf life of tomato fruits is illustrated in Figures 6 and 7, respectively. As a single factor, different sources of Ca reduced tomato fruit weight loss relative to no application (control) (Figure 6). At both sites, among different Ca sources, calcium sulphate fertilizer treatment reduced weight loss less and PM reduced most. Using the average from the two sites and relative to calcium nitrate, PM and control, calcium sulphate treatment reduced weigh loss by 24.81%, 55.59%, and 104.99%, respectively. Application of amendment increased the shelf life of tomato relative to the control (Figure 7). The order of increasing shelf life using the various treatments was: control < PM < calcium nitrate < calcium sulphate.  Using the average from the two sites and relative to calcium nitrate, PM, biochar and control, calcium sulphate fertilizer increased the shelf life of tomato by 14.78%, 29.79%, and 69.44%, respectively. Also, as a single factor, biochar application reduces weight loss of tomato relative to no application. Although 40 t ha^-1 biochar level has the most reduced weight loss, there were no significant differences between 10 and 20 t ha^-1 in term of weight loss. Biochar improved the shelf life of tomato relative to the control. The biochar application rate of 40 t ha^-1 yields the longest shelf life for tomatoes. Across the two sites, the application of 40 t ha^-1 of biochar resulted in a 41.70% reduction in weight loss and a 65.10% increase in the shelf life of tomatoes compared to the control. Additionally, the interaction between biochar and calcium (B × Ca) had a significant effect on both weight loss and shelf life. The combination of 40 t ha⁻¹ biochar and calcium sulphate resulted in the lowest weight loss (27.69% for Site A and 27.86% for Site B) and the longest shelf life (21.8 days for Site A and 21.7 days for Site B). However, these values were not significantly different from those obtained with 30 t ha⁻¹ biochar combined with calcium sulphate, which recorded 28.90% and 28.14% weight loss for Sites A and B, respectively, and shelf lives of 21.4 and 21.5 days for Sites A and B, respectively. Based on the average from two sites, the combination of biochar at 30 t ha^-1 with calcium sulphate enhanced the shelf life of tomatoes by 123.43% compared to the control, and by 23.27%, 37.5%, and 48.44% when compared to calcium sulphate alone, calcium nitrate alone, and poultry manure (PM) alone, respectively.

Figure 6. Effect of biochar and different Ca fertilizer sources on weight loss; Vertical bars show standard error of paired comparisons; B = biochar.

Figure 7. Effect of biochar and different Ca fertilizer sources on shelf life; Vertical bars show standard error of paired comparisons; B = biochar.

DISCUSSION

Effect of biochar and different Ca fertilizer sources on soil chemical properties

The increase in soil nutrient levels following amendment application may be attributed to the inherent nutrient composition of the applied materials (Table 2). Poultry manure (PM), which is rich in organic matter and essential nutrients, gradually releases nutrients into the soil during decomposition. This process enhances soil fertility by increasing the availability of nitrogen, phosphorus, potassium, and magnesium. In addition, the organic matter from PM improves soil structure, increases water retention, and stimulates microbial activity, thereby enhancing nutrient mineralization and nutrient cycling (Brady and Weil, 2017). Similar improvements in soil chemical properties following organic manure application have been reported by Adekiya et al. (2019).

Calcium sulphate and calcium nitrate contributed directly to soil calcium enrichment. Calcium plays a crucial role in improving soil structure by promoting flocculation and aggregation of soil particles, particularly in soils susceptible to dispersion. Improved aggregation reduces soil compaction, enhances aeration, and creates favorable conditions for microbial activity (Brady and Weil, 2017). Enhanced microbial activity facilitates organic matter decomposition and nutrient mineralization, thereby increasing nutrient availability. Calcium nitrate, in addition to supplying Ca²⁺, contributes readily available nitrate-nitrogen, which enhances soil nitrogen status and supports plant uptake efficiency.

Biochar application significantly enhanced soil chemical properties due to its unique physicochemical characteristics. First, biochar contains a high proportion of stable organic carbon (approximately 59% in the present study), contributing to increased soil organic carbon content and long-term carbon stabilization (Lehmann and Joseph, 2015). Second, biochar possesses high surface area and considerable porosity, enabling it to adsorb and retain essential nutrients, thereby reducing nutrient losses through leaching (Glaser et al., 2002; Lehmann et al., 2011). Third, biochar increases soil cation exchange capacity (CEC) through the presence of surface functional groups and oxidation processes that generate negative charges (Liang et al., 2006). This enhances the soil’s ability to retain exchangeable cations such as Ca²⁺, Mg²⁺, and K⁺ (Karimi et al., 2020), improving nutrient availability and establishing a nutrient reservoir within the soil. Furthermore, cow bone biochar contains appreciable quantities of Ca²⁺, Mg²⁺, and K⁺ (Table 2), which directly contribute to increased soil nutrient levels. These findings are consistent with Adekiya et al. (2020), who reported that increasing biochar application rates enhanced soil chemical properties.

The progressive improvement in soil chemical properties as biochar rates increased from 0 to 40 t ha⁻¹ reflects the cumulative effects of its high porosity, large surface area, elevated CEC, liming potential, and gradual nutrient release. Similar dose-dependent improvements have been reported in tropical soils amended with biochar (Jeffery et al., 2011; Lehmann et al., 2011).

However, while higher biochar rates improved soil chemical properties in this study, excessive application may pose potential risks. High biochar rates can significantly increase soil pH due to the presence of ash fractions and basic cations, particularly in already neutral or slightly alkaline soils (Yuan and Xu, 2011). Excessive pH elevation may reduce the availability of micronutrients such as Fe, Zn, and Mn, potentially inducing deficiencies. Moreover, very high application rates may cause nutrient imbalance due to disproportionate accumulation of certain base cations, thereby affecting nutrient uptake interactions (Lehmann and Joseph, 2015). In some cases, excessive biochar can also immobilize nitrogen temporarily depending on its C:N ratio and production conditions (Clough and Condron, 2010). Therefore, although increasing biochar rates enhanced soil fertility under the present conditions, optimal application rates should be determined based on initial soil characteristics to avoid unintended adverse effects and ensure balanced nutrient management.

Effect of biochar and different Ca fertilizer sources on tomato growth and yield parameters

General effects of soil amendments

All soil amendments significantly improved tomato growth and yield compared with the control, indicating that nutrient limitation was a major constraint in the experimental soil. The overall yield trend was: Poultry manure > Calcium sulphate ≈ Calcium nitrate > Biochar > Control.

The improvement in tomato performance following amendment application can be attributed to enhanced soil fertility and improved soil physical conditions. Organic and inorganic amendments supplied essential nutrients and created a more favorable root environment, thereby enhancing vegetative growth, flowering, fruit set, and ultimately yield.

Comparison between calcium sources

Both calcium sulphate and calcium nitrate improved tomato growth relative to the control due to their contribution of Ca²⁺, which enhances soil aggregation and reduces compaction (Ackerman, 2013). Improved soil structure promotes better root proliferation, water uptake, and nutrient acquisition. Calcium nitrate additionally supplies nitrate-nitrogen, a readily available form of nitrogen that promotes rapid vegetative growth and photosynthetic activity, thereby supporting fruit development. However, its nutrient supply is relatively specific compared with organic amendments, which may explain why its performance did not exceed that of poultry manure.

Poultry manure produced the highest tomato yield, likely due to three primary mechanisms. First, it provides a more balanced nutrient composition, including N, P, K, Ca, Mg, and micronutrients (Table 2), supporting both vegetative and reproductive stages. Second, its organic matter improves soil structure, water retention, and microbial activity, thereby enhancing nutrient mineralization and root health (Adeyemo et al., 2019; Adekiya et al., 2020). Third, nutrients in poultry manure are released gradually during decomposition, ensuring sustained nutrient availability throughout the growing season and reducing leaching losses. Although poultry manure contained higher potassium levels than the inorganic calcium sources (Table 2), potassium likely acted synergistically with other nutrients rather than as a sole determining factor in yield improvement.

Effects of biochar on tomato growth and yield

Biochar application improved tomato growth and yield compared with the control, though its effect was less pronounced than poultry manure and calcium fertilizers when applied alone. In the present study, biochar application increased fruit yield by approximately 294% relative to the control, depending on application rate and site. This magnitude of increase is substantially higher than the 29.55% yield improvement reported by Lei et al. (2024) under greenhouse conditions. The greater response observed in our study may be attributed to differences in soil type, initial soil fertility status, biochar feedstock (cow bone biochar), and application rate (up to 40 t ha⁻¹), as well as field versus controlled-environment conditions.

The positive response may be attributed to biochar’s ability to enhance nutrient retention, improve soil water-holding capacity, and increase cation exchange capacity (Lehmann and Joseph, 2015; Lei et al., 2024). The porous structure of biochar enhances soil aeration and root penetration while improving moisture availability—an important factor for tomato, particularly during flowering and fruiting stages. In addition, cow bone biochar contributes certain base cations and phosphorus, which may support plant nutrition.

However, unlike poultry manure, biochar functions more as a soil conditioner and nutrient retention agent rather than a complete nutrient source, which may explain its comparatively moderate yield response when applied alone. While Lei et al. (2024) reported modest yield gains primarily linked to improved soil physicochemical properties, the markedly higher yield response in the present study suggests that biochar’s effectiveness may be amplified under low-fertility tropical Alfisols where baseline nutrient limitations are more severe. Similar improvements in tomato growth and yield following biochar application have been reported in other tropical field studies, although the magnitude of response varies widely depending on soil condition, biochar characteristics, and management practices.

Interactive effects of biochar and calcium fertilizers (B × Ca)

The significant interaction between biochar and calcium fertilizers suggests a synergistic relationship. Calcium fertilizers supplied essential nutrients required for plant growth, while biochar enhanced the soil’s capacity to retain these nutrients and reduce leaching losses.

Biochar’s high surface area and CEC improve the retention of Ca²⁺, NO₃⁻, and other nutrients, thereby increasing nutrient use efficiency (Lehmann and Joseph, 2015). Additionally, improved soil structure and moisture retention created a more favorable root environment for nutrient uptake. The combined application therefore optimized nutrient availability, uptake efficiency, and root development, resulting in superior tomato growth and yield compared with individual applications. This synergistic interaction indicates that integrating nutrient sources with soil-conditioning amendments may be more effective than applying either alone, particularly in nutrient-depleted tropical soils.

Effects of biochar and different Ca fertilizer sources on mineral contents of tomato fruit

The increase in tomato mineral content observed with Ca fertilizers, relative to no applications, was ascribed to enhanced presence of nutrient in the soil due to mineralization, which facilitated greater absorption by tomato plants. Poultry manure resulted in the highest concentrations of Ca, Mg, Fe, Zn Cu and Na in the tomato fruits.

This could be attributed to the distinct chemical composition of poultry manure (PM) compared to calcium sulphate and calcium nitrate, as well as its beneficial impact on soil environment and plant absorption (Hassan et al., 2012). Calcium sulphate contains Ca and S only and calcium nitrate contains Ca and N only, whereas poultry manure has low C: N ratio (4.24) and contains a wide range of essential nutrients, including macronutrients like nitrogen (N), phosphorus (P), and potassium (K), as well as micronutrients such as magnesium, sulfur, copper, zinc, and manganese. This balanced nutrient composition supports not only tomato growth but also the development of nutrient-rich tomato fruits.

 Calcium sulphate increased the Ca contents of tomato fruits relatives to calcium nitrate and PM because Calcium sulphate contains a relatively high concentration of calcium (about 29.4% Ca) relative to calcium nitrate (24.39% Ca) and PM (6.08% Ca). When applied to the soil, it directly increases the soil's calcium content, providing a readily available source for tomato plants.

The mineral concentrations in tomato plants responded to biochar application in a manner consistent with the observed improvements in soil chemical properties under these treatments. The application of biochar increased nutrient availability in the soil, which in turn enhanced nutrient uptake by the tomato plants. This observation is supported by previous studies showing that organic amendments like biochar can elevate nutrient levels in plant tissues (Olowoake et al., 2021).

Effect of biochar and different Ca fertilizer sources on shelf life of tomato fruits

Poultry manure, calcium sulphate, and calcium nitrate reduced weight loss and extended shelf life relative to the control by improving nutrient uptake and fruit structural integrity. Calcium strengthens cell walls by forming calcium pectate in the middle lamella (Melelli et al., 2020; Obomighie et al., 2025), stabilizes membranes, reduces transpiration (Khanal et al., 2022), delays ethylene production (Iqbal et al., 2017), and inhibits cell wall-degrading enzymes (Langer et al., 2019). These mechanisms maintain firmness and reduce spoilage (Gao et al., 2019).

Calcium sulphate produced the longest shelf life and lowest weight loss, consistent with its higher Ca content. Significant correlations were observed between amendment Ca content and weight loss (R = -0.979) and shelf life (R = 0.953) at P < 0.05.

Biochar also reduced weight loss and extended shelf life by supplying Ca and P and improving water retention. Its porous structure supports steady fruit development and reduces cracking and dehydration (Gidado et al., 2024). Calcium in biochar reduces ethylene sensitivity (Jaime-Guerrero et al., 2024), while biochar lowers oxidative stress (Hasnain et al., 2023). Biochar has also been associated with higher total soluble solids and vitamin C (Lei, 2024), contributing to improved fruit quality.

The significant B × Ca interaction on shelf life likely resulted from enhanced calcium uptake under combined application. Biochar’s nutrient retention capacity improves calcium availability, strengthening fruit tissues, reducing water loss, and extending shelf life compared to sole applications (Dodgson et al., 2023).

Although the screenhouse experiment allowed for strict control of environmental variables and minimized confounding factors, several limitations must be acknowledged when extrapolating the results to field conditions. The use of 15 kg soil in perforated grow bags restricted root exploration compared with open-field systems, potentially influencing nutrient uptake dynamics and water relations. In addition, the screenhouse environment reduced exposure to natural rainfall variability, wind effects, fluctuating temperature regimes, and pest and disease pressures that typically affect tomato performance under field conditions. Soil heterogeneity, microbial diversity, and long-term biochar–soil interactions may also differ substantially in open-field systems. These factors could alter nutrient mineralization rates, calcium mobility, and the persistence of biochar effects. Therefore, while the results provide strong evidence of the agronomic potential of biochar and calcium sulphate under controlled conditions, field-based trials across different agroecological zones are necessary to validate the consistency, scalability, and economic feasibility of these treatments under practical farming conditions.

Advantages, limitations, and cost-effectiveness of using biochar and calcium fertilizers compared to conventional methods

The integration of cow bone biochar with calcium fertilizers offers several agronomic and postharvest advantages compared with conventional crop management practices. The present study demonstrated that biochar application improved soil chemical properties, enhanced nutrient retention, and significantly extended tomato shelf life. Notably, tomato shelf life increased by approximately 123.43% relative to the control treatment, suggesting that biochar–calcium integration may serve as a viable alternative to refrigeration or chemical preservation methods, particularly for smallholder farmers with limited access to cold storage infrastructure.

From an economic perspective, biochar-based soil amendment systems may provide long-term cost advantages despite relatively high initial production and application costs. Biochar production cost varies depending on feedstock type, pyrolysis technology, and labour input. Reported estimates indicate that biochar production can range from approximately USD 50–200 per tonne under smallholder and semi-mechanized production systems (Shackley et al., 2012; Crombie et al., 2013). At application rates of 30–40 t ha⁻¹, the upfront investment may therefore be substantial for resource-constrained farmers. However, long-term benefits include improved soil fertility, reduced dependence on synthetic fertilizers, enhanced yield stability, and extended postharvest storage life.

In contrast, refrigeration-based storage systems require continuous energy supply, maintenance costs, and infrastructure investment, which may be difficult for smallholder farming systems in developing countries. Although cold storage can effectively slow fruit deterioration, its adoption is limited in many rural agricultural settings due to electricity costs and facility availability (Kitinoja et al., 2011). Therefore, biochar and calcium sulphate application represents a more sustainable and environmentally friendly alternative for long-term crop quality preservation.

Importantly, no negative effects on soil chemical properties or crop performance were observed within the biochar application range of 0–40 t ha⁻¹ in this study. The discussion of potential risks associated with excessive biochar application, such as soil pH alteration, heavy metal accumulation, or nutrient imbalance, reflects theoretical considerations supported by previous literature rather than experimental observations in the current work (Chen et al., 2018).

Biochar application also contributes to climate change mitigation through carbon stabilization in soil systems. By converting agricultural residues into stable carbon forms, biochar enhances soil organic carbon storage and supports sustainable land management (Lehmann and Joseph, 2015). However, adoption by smallholder farmers may be constrained by production costs, labour requirements, and delayed economic returns. Policy interventions such as agricultural subsidies, carbon credit incentives, and commercialization support for biochar production could facilitate wider adoption and improve sustainability outcomes.

CONCLUSION

This study confirmed the hypothesis that the combined application of biochar and calcium sources would improve soil properties, tomato growth, yield, fruit mineral composition, and postharvest performance compared with the untreated control. While poultry manure enhanced vegetative growth, yield, and mineral content most effectively, calcium sulphate was superior in extending shelf life and reducing weight loss. Biochar application progressively improved agronomic and postharvest parameters, with 30–40 t ha⁻¹ producing the greatest benefits. Importantly, 30 t ha⁻¹ biochar combined with calcium sulphate extended shelf life to approximately 21–22 days while maintaining high yield, statistically comparable to 40 t ha⁻¹. This rate therefore represents an efficient and practical recommendation, avoiding unnecessary biochar application.

Although biochar + poultry manure may be preferred where yield maximization is the sole objective, 30 t ha⁻¹ biochar + calcium sulphate provides a balanced strategy for farmers seeking both strong productivity and improved postharvest shelf life. Because the experiment was conducted under screenhouse conditions, field validation across diverse agroecological zones is required to confirm scalability under open-field production systems.

ACKNOWLEDGEMENT

The authors want to appreciate the Management of Bowen University for Financing this research with grant number BURG/2024/02.

AUTHOR CONTRIBUTIONS

Aruna Olasekan Adekiya: Conceptualization (Lead), Methodology (Lead), Formal Analysis (Lead), Validation (Lead), Resource (Lead), Writing – Original Draft (Lead), Writing – Review & Editing (Lead), Investigation (Lead), Supervision (Lead), Project Administration (Equal); Timothy Oyebamiji Ogunbode: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Equal); Vincent Ishola Esan: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Olajire Adedokun: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Iyabo Victoria Olatubi: Methodology (Supporting), Formal Analysis (Supporting), Validation (Equal), Resource (Lead), Data Curation (Lead), Writing – Review & Editing (Equal), Investigation (Supportive), Supervision (Equal), Project Administration (Supportive); Modupeola Hellen Ayegboyin: Conceptualization (Lead), Methodology (Lead), Formal Analysis (Equal), Validation (Lead), Resource (Equal), Writing – Original Draft (Lead), Writing – Review & Editing (Lead), Investigation (Equal), Supervision (Lead), Project Administration (Lead).

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

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