Abstract Reducing mineral fertilizer use while maintaining crop productivity is crucial for sustainable agriculture. Field studies in 2022 and 2023 examined the effects of biodigestate application (0, 2,500, and 5,000 L ha⁻¹) alone and in combination with N, P, and K fertilizers on soil properties and maize performance. The experiments followed a factorial design with two years, three biodigestate rates, and nine NPK combinations (N1P1K1, N1P1K2, N1P2K1, N1P2K2, N2P1K1, N2P1K2, N2P2K1, N2P2K2, and a control N0P0K0). The nutrient rates were as follows: N1 = 60 kg N ha⁻¹, N2 = 120 kg N ha⁻¹, P1 = 30 kg P₂O₅ ha⁻¹, P2 = 60 kg P₂O₅ ha⁻¹, K1 = 30 kg K ha⁻¹, and K2 = 60 kg K ha⁻¹, arranged in a randomized complete block design with three replications. Results showed that biodigestate application improved soil fertility and maize growth compared to the control. The year 2022 had better soil chemical properties and higher yields than 2023. In 2023, applying 2,500 and 5,000 L ha⁻¹ of biodigestate increased grain yield by 13.43% and 20.92%, respectively, relative to the control, highlighting its residual effect. Integrating biodigestate with NPK fertilizers enhanced yields more than their individual applications, ensuring a balanced nutrient supply. The highest yield was achieved with 5,000 L ha⁻¹ biodigestate combined with N1P1K1. Biodigestate is an effective soil amendment that can improve maize productivity in poor soils while reducing dependency on mineral fertilizers. Its integration with NPK fertilizers offers a viable strategy for sustainable maize production.

Keywords: Biodigestate, Residual effect, Soil chemical properties, Maize, Mineral fertilizer

Citation:  Adekiya, A.O., Ande, O.T., Dahunsi, S.O., Adedokun, O.D., and Micah, M.M. 2026. Optimizing mineral fertilizer use in maize cultivation: A Study on biodigestate and N, P and K fertilizers integration. Natural and Life Sciences Communications. 25(4): e2026077.

Graphical Abstract:

INTRODUCTION

The issue of food security remains a major challenge for millions of people worldwide, particularly in developing nations (FAO, 2018). To meet the demands of an estimated 401 million individuals in Nigeria by 2050 (FAO, 2018), there is an urgent need for a significant increase in food production in tropical regions. However, soil-related challenges pose a substantial barrier to achieving food security in these areas.

The predominant soil order in Nigeria, Alfisols, exhibits various unfavorable characteristics, including low fertility, soil acidity, weak structure, and high susceptibility to crusting, compaction, and accelerated erosion (Lal, 1997). Additionally, the expansion of agriculture into less fertile regions, deforestation, shortened fallow periods, poor farming practices, and limited resource use have significant ecological and economic impacts on tropical soils, which have a low capacity for natural recovery Awoonor et al. (2025). Consequently, many small farms in Africa face declining soil fertility, a problem exacerbated by continuous cultivation without adequate efforts to replenish soil nutrients (Nandwa, 2001; Agbede and Oyewumi, 2023).

Although inorganic fertilizers can enhance agricultural productivity, their use is constrained by factors such as high costs, seasonal shortages, soil acidification, and nutrient imbalances (Agbede et al., 2019). Therefore, recycling all available nutrient sources is essential to supplement mineral fertilizers and ensure the long-term sustainability of agricultural systems (Rosemarin et al., 2020).

Biodigestate, a by-product of biogas production from organic agricultural residues, can be used as a fertilizer (Bach et al., 2021). This relatively novel waste product is rich in organic matter and essential nutrients, promoting plant growth and benefiting soil microorganisms (Głowacka et al., 2020). Biodigestate contains high levels of organic carbon and total nitrogen, which contribute to improved soil fertility (Różyło et al., 2015; Stefaniuk et al., 2015; Pivato et al., 2016). Research has shown that applying biodigestate significantly increases soil pH and enhances organic carbon, total nitrogen, and the availability of phosphorus, potassium, and magnesium (Galvez et al., 2012; Stefaniuk et al., 2015). According to Smith et al. (2014), biodigestate has considerable potential to enhance soil carbon sequestration due to the stabilization of organic matter during anaerobic digestion, which degrades the most labile fractions (Marcato et al., 2009). Additionally, biodigestate improves soil structure and nutrient availability while enhancing the population of beneficial microorganisms, particularly in marginal or nutrient-depleted soils (Cajamarca et al., 1995; Saveyn and Eder, 2014). By increasing organic matter, enhancing soil structure, replenishing nutrients, and supporting microbial life, biodigestate could play a vital role in reversing soil degradation especially in tropical region where soil degradation is a common phenomenon. Its use as a soil amendment helps restore fertility, reduce erosion, and improve long-term agricultural sustainability.

Numerous studies have shown that digestates provide comparable or superior crop performance compared to undigested animal manures and slurries (Bachmann et al., 2011; Alburquerque et al., 2012; Lee et al., 2020). Furthermore, research indicates that biodigestate can be as effective as mineral fertilizers, as demonstrated by studies conducted by Cristina et al. (2020), Haraldsen et al. (2011), and Tiwari et al. (2000). Recent investigations have also examined the impact of digestate application on soil nutrient levels and the potential for nutrient loss through leaching (Spagnolo et al., 2019). The nitrogen in digestate is primarily in the form of ammonium, making it susceptible to leaching and volatilization when converted into nitrate or ammonia (Möller and Stinner, 2009). This can lead to environmental issues, such as algal blooms in surface water (eutrophication), and reduce fertilizer efficiency due to nitrogen loss through ammonia emissions (Yaseen et al., 2021). Consequently, the effectiveness of biodigestate may be limited to the year of application, and its long-term residual effects remain poorly understood, necessitating further research. Similar to organic manures, biodigestate may have residual benefits for crops and soil, but evidence in this area is limited (Azangue et al., 2019).

The large quantity of biodigestate required for effective use can be a limiting factor (Adekiya et al., 2024). To address this challenge, integrating biodigestate with inorganic fertilizers may be a viable strategy. This approach could reduce dependence on chemical fertilizers and potentially lower costs for farmers. Increasing the use of nitrogen, phosphorus, and potassium fertilizers is essential to meeting food demand, especially in developing countries like Nigeria, where crop yields are constrained by low fertilizer application rates and the high cost and scarcity of fertilizers during planting seasons (Dawson and Hilton, 2011). Thus, reducing mineral N, P, and K fertilizer applications while preventing nutrient deficiencies remains a key challenge for sustainable agricultural production and global food security (Moe et al., 2017; Recena et al., 2022).

Several studies have examined the combined effects of organic and inorganic fertilizers on maize performance (Faisal et al., 2015; Abd El-Gawad et al., 2017; Adekiya et al., 2020). However, limited research has explored the use of biodigestate in this context. Given the importance of maize cultivation, further research is needed to determine optimal levels of N, P, and K fertilizers in combination with biodigestate to enhance soil chemical properties and maize yield. Over application of any fertilizer can be economically unfeasible due to associated costs. This paper presents a
two-year study investigating the effects of biodigestate application at different rates, both alone and in combination with varying levels of N, P, and K fertilizers, on soil chemical properties and maize performance.

MATERIALS AND METHODS

Site description and treatments

Field experiments were carried out in 2022 and 2023 cropping seasons at Bowen University in Iwo, Osun State, Nigeria. The University is located at coordinates 7.6236°N, 4.1890°E, with an altitude of 312 meters above sea level. This area exhibits a bimodal precipitation pattern. The total annual precipitation, mean relative humidity and average air temperature of the area in 2022 and 2023 is presented in Table 1. The soil in this region is composed of sandy loam, which originates from fine-grained granite gneiss and schist. It is classified as the Egbeda series (plinthic), as documented by Smyth and Montgomery (1962) in their research on soils in Southwestern Nigeria.

The experimental design was a randomized complete block of 27 treatments and three replicates. The field study included three biodigestate treatments (0 L ha^-1, 2,500 L ha^-1 and 5,000 L ha^-1) in factorial combination with and without nine NPK fertilizer applications. The study was designed to evaluate both the direct effects (2022) and residual effects (2023) of biodigestate application under varying NPK fertilizer regimes. To enable assessment of residual effects, biodigestate was not reapplied in 2023. The study was replicated across 2 years using the same treatment design and treatment plot locations. Factorial combination of (2×3×9) results in 54 treatments. The nine N, P and K fertilizer combination rates were: (1). N applied at 60 kg ha^-1, P applied at 30 kg ha^-1 and K applied at 30 kg ha^-1 (N1P1K1), (2). N applied at 60 kg ha^-1, P applied at 30 kg ha^-1 and K applied at 60 kg ha^-1 (N1P1K2), (3). N applied at 60 kg ha^-1, P applied at 60 kg ha^-1 and K applied at 30 kg ha^-1 (N1P2K1), (4). N applied at 60 kg ha^-1, P applied at 60 kg ha^-1 and K applied at 60 kg ha^-1 (N1P2K2), (5). N applied at 120 kg ha^-1, P applied at 30 kg ha^-1 and K applied at 30 kg ha^-1 (N2P1K1), (6). N applied at 120 kg ha^-1, P applied at 30 kg ha^-1 and K applied at 60 kg ha^-1 (N2P1K2), (7). N applied at 120 kg ha^-1, P applied at 60 kg ha^-1 and K applied at 30 kg ha^-1) (N2P2K1), (8). N applied at 120 kg ha^-1, P applied at 60 kg ha^-1 and K applied at 60 kg ha^-1 (N2P2K2), (9). Control - No di-gestate and no NPK fertilizer (N0P0K0). The source of N was Urea fertilizer, P was single superphosphate while K was muriate of potash. The application rates of biodigestate and N, P and K fertilizer were selected based on ranges commonly reported in previous studies evaluating biodigestate effects on soil fertility and crop productivity in southwest Nigeria (Adekiya et al., 2024).

Table 1. Metrological data of the study area in 2022 and 2023.

Land preparation, field layout, and sowing of maize seeds

Prior to field layout utilizing ropes, pegs, and tape, the experimental field was initially ploughed and harrowed. Each plot had dimensions of 12 × 3 meters and was subjected to distinct treatments, with three replicates for each treatment. The plots were arranged at intervals of 0.5 meters, with a gap of 1 meter between each block. The biodigestate utilized in this experiment was acquired via the spontaneous anaerobic decomposition of cow dung in a biodigester, resulting in the production of biogas. The slurry obtained was added to the soil at rates of 0, 2,500, and 5,000 L ha^-1 (equal to 0, 9, and 18 L plot^-1) just after the field was prepared and just before planting. The biodigestate was incorporated into the soil using a handheld hoe, reaching a depth of around 20 cm. In 2023, there was no application of biodigestate. Instead, the area was cleaned of weeds by spraying Roundup (Glyphosate) one week prior to planting, in the same plots as in 2022. Seedco's high-yielding hybrid maize seeds were planted on August 8, 2022, and June 9, 2023, at a depth of 2-3 cm. Two seeds were planted in each hole, with a spacing of 75 cm × 25 cm. After a period of two weeks, the seedlings were reduced to one plant per stand, leading to a total of 192 plants each plot, which is roughly equivalent to 53,333 plants per hectare. Phosphorus (P) fertilizer was administered in the form of single superphosphate at two different rates: 30 kg ha^-1 (P1) and 60 kg ha^-1 (P2), which is equivalent to 0.22 kg and 0.43 kg per plot, respectively, at the time of planting. Three weeks following sowing, potassium fertilizer in the form of Muriate of Potash was applied at a rate of 30 kg ha^-1 (K1) and 60 kg ha^-1 (K2), which corresponds to 0.18 kg and 0.36 kg per plot, respectively. The urea fertilizer was treated in two separate doses: the first dose of 30 kg ha^-1 (N1) and 60 kg ha^-1 (N2) was supplied 3 weeks after sowing (WAS), and the remaining dose was applied 6 weeks after sowing. The urea fertilizer quantities applied were 0.48 kg per plot for N1 treatments and 0.96 kilogram per plot for N2 treatments. The fertilizer was applied at a distance of 8-10 cm from the seeds during planting and at the base of the plants after germination. Weed management was achieved with Paraforce (paraquat dichloride) and atrazine (Atrazine 80% WP). To combat autumn armyworm, Caterpillar Force (Emamectin Benzoate 5% WDG) was administered two weeks after planting and then repeated at 4-week and 6-week intervals. Each plot was marked with tags to facilitate data gathering on the plants.

Soil and biodigestate analyses

Before starting the experiment in 2022, surface soil samples were randomly collected from the experimental field at a depth of 0-15 cm for physical and chemical analyses. These samples were air-dried, sieved through a 2-mm sieve, and stored for further analysis. The sand, silt, and clay contents were determined using the hydrometer method as described by Gee and Or (2002). Soil pH was measured with a pH meter using a 1:2.5 soil-to-water ratio. Total nitrogen content was determined using the micro-Kjeldahl method (Bremner, 1996). Available phosphorus was evaluated using the Bray 1 method (Frank et al., 1998). Calcium and magnesium were analyzed using Atomic Absorption Spectrophotometry (AAS). Potassium and sodium levels were measured using flame emission photometry, following the Association of Official Analytical Chemists (AOAC, 2005) procedures. Organic carbon content was determined using the dichromate wet oxidation method (Nelson and Sommers, 1996).

At the end of each growing season in 2022 and 2023, soil samples were again randomly collected from five locations within each plot. These samples were combined to create composite samples for each plot and subjected to the same chemical analyses as initially conducted.

A sample of the biodigestate was also collected for analysis of total nitrogen, available phosphorus, and exchangeable potassium, calcium, and magnesium, as described by Tel and Hagarty (1984).

Determination of growth and yield parameters of maize

For data collection in each experimental plot, ten maize plants were chosen, with a specific focus on growth-related information during the tasseling stage. The measured metrics encompassed plant height, number of leaves, stem girth, and leaf length. Plant height was assessed by measuring the distance from the base to the tassel using a measuring tape, while the number of leaves was estimated through direct counting. The stem girth was assessed using a vernier caliper, while the leaf length was measured from the sheath to the tip using a measuring tape.

Prior to harvest, the maize plants were left to undergo natural drying. Throughout the harvest, various yield-related characteristics were documented, including biomass weight, cob weight, and shelled grain weight. The biomass weight was determined by harvesting and weighing the complete maize plant, encompassing the stalks, leaves, ears, and cobs. The cob weight was calculated by measuring the weight of the cobs, whereas the shelled grain weight was determined by removing the kernels from the cobs and weighing them.

Data analysis

The data obtained on growth and yield parameters was subjected to statistical analysis using Analysis of Variance (ANOVA) with the Statistical Analysis System (SAS). The mean results were subsequently compared and differentiated using Tukey pairwise comparisons with a significance level of P < 0.05.

RESULTS

Experimental soil prior to sowing of maize and the chemical analysis of biodigestate used

The experimental soil's results before to seeding maize in 2022 and the chemical analysis of the biodigestate utilized are shown in Tables 2 and 3, respectively. The soil had a little acidic pH and has a sandy loam texture. The soil exhibited low levels of organic matter (OM), nitrogen (N), and phosphorus (P). Nevertheless, the levels of exchangeable bases potassium (K), calcium (Ca), and magnesium (Mg) were discovered to satisfy the suggested key levels for achieving optimal crop production in the particular agroecological zone of Nigeria (Akinrinde and Obigbesan, 2000). The recommended amounts are as follows: 3.0% for organic matter, 0.20% for nitrogen, 10.0 mg/kg for phosphorus, 0.16–0.20 cmol/kg for potassium, 2.0 cmol/kg for calcium, and 0.40 cmol/kg for magnesium. The biodigestate was subjected to chemical analysis (Table 3) which determined its composition to be as follows: 20.1% OC, 1.5% nitrogen, 1.1% phosphorus, 1.00% potassium, 0.46% calcium, 1.01% magnesium, 0.36% copper, 0.15% iron, 0.14% manganese, and 4.20% zinc. The pH level measured 7.8. The substance had an alkaline pH and consisted of vital nutrient elements including nitrogen, phosphorus, potassium, calcium, and magnesium, as well as minor nutrients. These nutrients are crucial for the growth of cereal crops such as maize.

Table 2. Initial soil characteristics of the experimental site before maize sowing.

Note: Adekiya et al. (2024)

Table 3. Nutrient values of the biodigestate used.

Effects of years, biodigestate and N, P and K fertilizers on soil chemical properties

Table 4 presents the findings about the impact of years, biodigestate, and N, P, and K fertilizers on soil chemical characteristics. When examined independently, the factors of year (Y), biodigestate (B), and N, P, and K fertilizers (NPK) had a substantial impact on soil chemical characteristics. In 2022, the soil chemical characteristics (pH, OC, N, P, K, Ca, Mg, and Na) were higher compared to 2023. The average values of soil pH, organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) in the year 2022 were 6.57, 1.83%, 0.173%, 15.77 mg kg^-1, 0.19 cmol kg^-1, 3.61 cmol kg^-1, 2.35 cmol kg^-1, and 0.374 cmol kg^-1, respectively. In the year 2023, the corresponding values for soil pH, OC, N, P, K, Ca, Mg, and Na were 5.91, 1.76%, 0.157%, 13.64 mg kg^-1, 0.16 cmol kg^-1, 3.21 cmol kg^-1, 2.06 cmol kg^-1, and 0.333 cmol kg^-1, respectively. The 2022 to 2023 increases for soil pH, OC, N, P, K, Ca, Mg, and Na were 11.2, 3.98, 10.2, 15.61, 18.75, 12.46, 14.08, and 12.32, respectively. The application of biodigestate resulted in an increase in soil chemical characteristics compared to the control group. A volume of 5,000 L ha^-1 of biodigestate resulted in greater improvement in soil chemical characteristics compared to a volume of 2,500 L ha^-1. There were no significant differences in the pH values between 5,000 L ha^-1, 2,500 L ha^-1 and the control (without the use of biodigestate). In addition, the application of combinations of N, P, and K fertilizers resulted in an increase in soil pH, (OC), N, P, K, Ca, Mg, and Na levels compared to the absence of any fertilizer application (N0P0K0). Treatment N2P2K2 exhibits optimal values for pH, OC, N, P, K, Ca, Mg, and Na. The Y × B interaction produced significant results for N, P, K, Ca, Mg, and Na, but pH and OC did not show significant results. Furthermore, the Y × NPK interaction had a significant impact on all soil chemical characteristics, with the exception of OC. The interaction between B and NPK had a substantial effect on all soil chemical characteristics, with the exception of pH. Similarly, the interaction between Y × B × NPK did not have a significant effect on pH, OC, and Na, but it did have a significant effect on N, P, Ca, and Mg. The treatment of 5,000 L ha^-1 + N2P2K2 produced the most favorable soil chemical parameters, with the exception of soil pH and calcium levels.

Table 4. Effect of years, biodigestate and N, P and K combinations on soil chemical properties.

Effects of years, biodigestate and N, P and K fertilizers on growth and yield of maize

Tables 5 and 6 display the outcomes of the impacts of year, biodigestate, and N, P, and K fertilizers on the growth and yield characteristics of maize. The individual factors Y, B, and NPK have a major impact on the growth and production of maize. The growth metrics (plant height, leaf length, and stem girth) and yield characteristics (biomass weight, cob weight, and grain yield) of maize were higher in the year 2022 compared to 2023. The variable Y did not have a significant impact on the number of leaves of maize cultivated in 2022 and 2023, as seen in Table 5. The treatment of biodigestate at rates of 2,500 and 5,000 L ha^-1 also resulted in higher growth and yield parameters of maize compared to no application. The rate of biodigestate did not have a significant impact on the number of maize leaves. The maize yield order, ranked from highest to lowest, was as follows: 5,000 L ha^-1 > 2,500 L ha^-1 > control. By calculating the average of both years, it was shown that the application of 5,000 L ha^-1 of biodigestate resulted in a 25.3% increase in maize grain production compared to the control group. The application of 2,500 liters of biodigestate resulted in an 18.9% increase in maize grain yield compared to the control group. The growth and maize yield parameters, with the exception of the number of leaves, are influenced by the single factor NPK. The application of N, P, and K fertilizers resulted in enhanced growth and yield parameters compared to the absence of fertilizer application (N0P0K0). The application of Treatment N2P2K2 resulted in the greatest improvement in plant height, leaf length, stem girth, number of leaves, and biomass weight. On the other hand, treatments N1P2K2 and N1P1K1 showed the most significant improvement in maize grain yield. The maize plant height showed a declining trend across several combinations of biodigestate rates and years (2022 and 2023). The order of reduction, from highest to lowest, was as follows: N2P2K2 > N2P2K1 > N1P2K2 > N1P1K1 > N1P2K1 > N2P1K2 > N1P1K2 > N2P1K1 > N0P0K0. The order of decreasing maize grain yield (in t/ha) is as follows: N1P2K2 (6.42) = N1P1K1 (6.40) > N2P2K2 (6.18) = N1P1K2 (6.12) = N2P2K1 (6.06) > N2P1K2 (5.40) = N2P1K1 (5.25) = N1P2K1 (5.10) > N0P0K0 (2.53). The interaction between Y and B was statistically significant for all growth and yield metrics, with the exception of the number of leaves. In 2022, the application of 2,500 L ha^-1 and 5,000 L ha^-1 of biodigestate resulted in an increase of 8.75% and 20.32% in maize grain yield, respectively, compared to the control. In the year 2023, the application of 2,500 L ha^-1 and 5,000 L ha^-1 of biodigestate resulted in a 13.43% and 20.92% increase in maize grain yield, respectively, compared to the control group. Furthermore, the interactions between Y and B were shown to be significant for all growth and yield factors, with the exception of the number of leaves. The interaction between B and NPK was statistically significant for all growth and yield parameters, with the exception of the number of leaves. By calculating the average of the two years, it was determined that applying 5,000 L of biodigestate with N1P1K1 fertilizers resulted in the highest maize yield of 7.02 t ha^-1. Furthermore, the interactions between Y × NPK and Y × B × NPK were shown to be statistically significant for all growth and yield metrics, with the exception of the number of leaves.

Table 5. Effect of years, biodigestate and N, P and K combinations on growth parameters of maize.

Table 6. Effect of years, biodigestate and N, P and K combinations on yield parameters of maize.

DISCUSSION

The low levels of organic carbon, total nitrogen, available phosphorus, and low pH observed prior to the 2022 experiment (Table 2) indicate significant soil fertility challenges likely due to soil degradation from continuous cropping practices. The alkaline nature of biodigestate, as confirmed by previous studies (Głowacka et al., 2020; García-López et al., 2023), can influence soil pH, thereby affecting nutrient availability and microbial activity (Stefaniuk et al., 2015; Galvez et al., 2012). The high levels of nitrogen, phosphorus, and potassium in biodigestate is consistent with the nutrient-rich nature of animal-derived organic materials, suggest its potential effectiveness as a fertilizer for promoting plant growth (Adeyemo et al., 2019).

The enhanced soil chemical properties (pH, organic carbon, nitrogen, phosphorus, potassium, calcium, magnesium, and sodium) observed in 2022 compared to 2023 can be attributed to the higher nutrient reserve in the first year, which depleted over time. Consequently, the second year started with a lower baseline of available nutrients, resulting in lower observed values. The application of biodigestate increased soil chemical properties relative to the control due to its rich content of essential nutrients (Table 3), which are crucial for plant growth and soil fertility. Biodigestate releases these nutrients into the soil, making them available for plant uptake and enhancing soil fertility compared to the control. The increase in soil pH observed with biodigestate application may be associated with enhanced base cation content and organic matter, both of which contribute to soil buffering capacity. However, long-term monitoring is required to fully understand the stability of these changes.

Additionally, biodigestate introduces beneficial microorganisms to the soil (Odlare et al., 2008). These microorganisms play a critical role in nutrient cycling, organic matter decomposition, and overall soil health, leading to better nutrient availability and improved soil chemical properties. The alkaline pH of biodigestate (7.8) also helps neutralize acidic soils, promoting the availability of essential nutrients like calcium and magnesium. This effect was similarly reported by Ragályi et al. (2025) with bio-slurry application. Studies have shown that biogas digestate application significantly raises soil pH and increases organic carbon, total nitrogen, and available forms of phosphorus, potassium, and magnesium (Galvez et al., 2012; Stefaniuk et al., 2015). Several studies have demonstrated the effects of repeated biodigestate applications across multiple growing seasons. In a long term field experiment established in 2011, digestate applications over several years significantly improved soil physical properties such as aggregate stability and porosity compared to mineral fertiliser and control plots, indicating structural benefits from sustained use of digestate in crop rotations (Mayerová et al., 2023). Similarly, a three year application of biogas digestate on acidic, nutrient poor soils enhanced soil fertility and increased switchgrass biomass yield, suggesting cumulative soil improvements with repeated annual digestate use (Glowacka et al., 2020). Multi year digestate application has also been shown to influence soil carbon balance and nutrient dynamics, with repeated use enhancing water infiltration and bioavailable phosphorus over four years (Mayerová et al., 2023). Additionally, some field studies report that continued digestate application led to sustained increases in crop grain yields in the third year of treatment compared to unfertilised controls (Doyeni et al., 2021).

In multi year field experiments, digestate and compost both improved soil physical properties relative to unfertilised controls, although compost showed stronger effects on organic carbon and nitrogen accumulation than digestate over time (Mayerová et al., 2023). Comparative trials involving digestate, chicken manure, and cow dung demonstrated that poultry manure tended to increase soil phosphorus and organic matter more than fresh digestate, although digestate still supplied significant nutrient inputs for plant growth (Afriyie et al., 2013). Other research evaluating poultry manure based amendments indicated that both compost and digestate increased crop biomass relative to unfertilised soils, with differences in stability and nutrient release patterns depending on amendment type (Rizzo et al., 2022).

 Applying 5,000 ha^-1 of biodigestate provides a greater quantity of nutrients and organic matter than 2,500 ha^-1, enhancing soil chemical properties more significantly by increasing nutrient content, improving soil structure, boosting microbial activity, stabilizing soil pH, and enhancing nutrient retention and availability.

The N2P2K2 treatment showed the best values of pH, organic carbon, nitrogen, phosphorus, potassium, calcium, magnesium, and sodium compared to other N, P, and K combinations due to the higher nutrient concentrations in N2P2K2. The interaction of biodigestate with NPK fertilizers (B × NPK) was significant for organic carbon, nitrogen, phosphorus, potassium, calcium, magnesium, and sodium compared to biodigestate alone. This enhancement is due to the higher quantity of nutrients in urea, single superphosphate, and muriate of potash fertilizers compared to biodigestate alone. Biodigestate provides a diverse range of nutrients due to its organic origin, including nitrogen, phosphorus, potassium, and various micronutrients. Combining biodigestate with concentrated sources of N, K, and P offers a more comprehensive and balanced nutrient supply, enriching soil chemical properties more effectively than either biodigestate or NPK fertilizers alone.

Year 2022 increased the growth (plant height, leaf length and stem girth) and yield (biomass weight, cob weight and grain yield) parameters of maize relative to 2023. Maize is a heavy feeder (Adekiya et al., 2020), meaning it requires significant amounts of nutrients, especially nitrogen, phosphorus, and potassium. After the first planting in 2022, the soil may have become depleted of these essential nutrients, leading to poorer growth and yield in 2023. The residual nutrients might not have been sufficient for optimal growth in 2023.

Another reason why there was a low yield of maize in 2023 relative to 2022 was that of the erratic rainfall during its growth especially during tasseling and silking. Although 2023 recorded higher total rainfall relative to 2022 (Table 1), there was mostly no rains when it was mostly needed (during tasseling). Maize planted in 2022 tasseled late September with abundant of rains relative to 2023 that tasseled in late July with few rains that badly affected maize silking. The total annual rainfall was 1,284 mm in 2022 and 1,443.9 mm in 2023, with distinct differences in monthly distribution. In 2022, July received the highest rainfall (417.8 mm), which coincided with key vegetative and reproductive stages, promoting higher plant height, leaf length, and stem girth (Table 5). In contrast, 2023 exhibited more evenly distributed rainfall with lower peaks in July (200 mm), potentially reducing water availability during critical growth periods despite a higher total annual rainfall. Reduced water uptake during silking can lead to significantly reduced grain yield, primarily due to silk desiccation and ineffective pollination (Li et al., 2023). Research has shown that water deficit, as indicated by studies (Bolaños and Edmeades, 1996; McLaughlin and Boyer, 2004), contributes to decreased kernel numbers by prolonging the anthesis-silking intervals and inducing kernel abortion. Li et al. (2023) further demonstrated that under water deficit conditions, 58% of kernels were lost, with 68% attributed to arrested silks within husks due to lower water potentials, and 32% to ovaries where silks emerged possibly due to impaired carbohydrate metabolism. Studies have examined the effects of biodigestate application to maize over multiple growing seasons. A three year field experiment conducted in Serbia (2016–2018) demonstrated that annual digestate applications (50 t ha⁻¹) before sowing significantly increased maize plant height, biomass yield, and biogas and methane outputs in each year of the trial, with the highest values recorded in the third year, suggesting cumulative benefits from repeated digestate use (Popović et al., 2024).

Biodigestate increased the growth and yield of maize in this study compared with the control. The reason for these being: 1. Biodigestate is rich in essential nutrients such as nitrogen (N), phosphorus (P), potassium (K), and a range of micronutrients. These nutrients are vital for plant growth and development and are often more readily available in biodigestate than in untreated soil. 2. Biodigestate adds organic matter to the soil, which helps improve nutrient availability and retention. The organic matter acts as a slow-release fertilizer, providing a continuous supply of nutrients throughout the growing season. 3. The organic matter in biodigestate improves soil structure by enhancing soil aeration and water-holding capacity. Better aeration promotes root growth and function, while improved water retention ensures that plants have access to water for longer periods, especially in drought conditions. 4. Like organic manure, biodigestate may introduces beneficial microorganisms and also stimulates their growth. Microbes play an essential role in decomposing organic matter, mineralizing nutrients, and enhancing soil fertility.

Similarly, Adekiya et al. (2024) and Makádi et al. (2012) demonstrated that the application of digestate, rich in nutrients, significantly increased aboveground biomass yields in maize and winter and spring wheat, respectively. Šimon et al. (2015) also observed enhanced wheat (Triticum aestivum) grain yield with biodigestate application (9.88 t ha^-1) compared to non-fertilized controls (5.68 t ha^-1). In another study, Dahunsi et al. (2021) utilized biodigestate from Carica papaya (pawpaw) fruit peels and maize, finding superior performance in various parameters such as leaf number, leaf area, plant height, stem girth, total shoot and root biomass, and root length compared to untreated controls.

The 5,000 L ha^-1 biodigestate increased yield of maize relative to 2,500 L ha^-1, this means that doubling the amount of biodigestate provides more essential nutrients like nitrogen, phosphorus, and potassium. These nutrients are crucial for various stages of plant growth, including root development, leaf formation, and grain filling.

The finding that in 2023, 2,500 L ha^-1 and 5,000 L ha^-1 biodigestate increased maize grain yield by 13.43% and 20.92 %, respectively relative to the control showed that biodigestate has residual effect. Despite the fact that there was no application of biodigestate in 2023 there was still significant increase in the yield of maize. The residual effect of biodigestate was due to its organic carbon content and the gradual mineralization of its nutrients. This sustained effect supports long-term soil fertility and reduces the need for frequent fertilizer applications. Unlike synthetic fertilizers, the nutrients in biodigestate are released slowly over time, providing a prolonged supply of nutrients to plants. This slow-release effect reduces the risk of nutrient leaching and improves nutrient use efficiency by keeping the unused nutrient for the coming season.

The combinations of N, P and K fertilizers increased the growth and yield parameters relative to no application (N0P0K0). This can be attributed to the deficiency of these major elements in the study site that are important for the growth and yield of maize. Onasanya et al. (2009) reported an increase in maize yield due to nitrogen and phosphorus fertilizers. Adediran and Banjoko (1995) also reported increase in yield of maize due to N, P and K fertilizers. This can be due to the fact that Nitrogen is a vital component of amino acids, the building blocks of proteins, and is essential for the synthesis of chlorophyll, nucleic acids (DNA and RNA), and ATP (adenosine triphosphate), phosphorus is a key component of nucleic acids, ATP, and phospholipids, playing a crucial role in energy transfer, photosynthesis, and nutrient transport. Potassium supports stem development, cell division, and the formation and movement of carbohydrates from source to sink (Adekiya et al., 2024).

Treatment N2P2K2 most improved plant height, leaf length, stem girth, number of leaves and biomass weight. This is consistent with the soil chemical properties of this treatment. Nutrients are present in the soil and are absorbed by plant for its growth and development. Treatments N1P2K2 and N1P1K1 although not endowered with the best soil chemical properties has the most improved grain yield of maize. Imbalance in nutrient ratios (in case of N2P2K2) can cause deficiencies or toxicities. For example, excessive nutrients can lead to lush foliage but poor fruit or grain production. Treatments N1P2K2 and N1P1K1 with lower growth might have allocated more resources towards reproductive structures, resulting in a higher yield despite limited vegetative growth.

The integration of biodigestate with NPK (B × NPK) produced better yield due to several synergistic effects: 1. Biodigestate typically contains a wide range of nutrients, including micronutrients and organic matter, that are not present in synthetic N, P and K fertilizers. Combining biodigestate with N, P and K fertilizers ensures a more comprehensive nutrient supply, addressing both macro and micronutrient needs of the plants. 2. Organic matter from biodigestate can help in the slow release of nutrients, ensuring that they are available to plants over a longer period. This can complement the quick-release nature of synthetic N, P and K fertilizers, leading to sustained nutrient availability. 3. The organic matter in biodigestate can help bind nutrients in the soil from N, P and K fertilizers, reducing the risk of leaching and ensuring that more nutrients remain available to plants rather than being washed away. 4. The combination of biodigestate and NPK fertilizer can create a synergistic effect where the benefits of each component are enhanced. For example, the organic matter in biodigestate can improve the efficiency of N, P and K fertilizers, leading to better overall plant growth and yield.

Interacting 5,000 L ha^-1 of biodigestate with N1P1K1 fertilizers give the best value of maize yield which could be a result of optimum nutrient supply from N, P, and K fertilizers and better physical soil environment created by the biodigestate.

It was worth noting that the absence of adverse crop responses which includes stunted growth, leaf chlorosis, reduced biomass, or diminished grain yield across all biodigestate treatments suggests that the biodigestate applied was agronomically safe under the conditions of this study. This observation indicates that nutrient concentrations were within levels suitable for maize growth and that no detectable phytotoxic effects or short-term soil contamination occurred. While this does not replace formal analyses for heavy metals or pathogens, the healthy growth and productivity of maize provide practical evidence that the biodigestate did not exert negative effects on crop performance during the experimental period.

Feasibility considerations for farmers in Nigeria

While the results of this study demonstrate the potential of biodigestate as an effective fertilizer for improving soil fertility and maize yields, several important feasibility considerations must be addressed before its widespread adoption by farmers in Nigeria. These considerations include the cost of production, availability, and the challenges related to scaling up its application across diverse farming communities.

Cost analysis: The economic viability of biodigestate use in Nigeria depends on factors such as the cost of producing or sourcing biodigestate, the rates at which it is applied, and the potential savings from reduced dependence on synthetic fertilizers. While biodigestate is often considered a more sustainable alternative to conventional chemical fertilizers, initial investments in biogas production infrastructure or sourcing biodigestate from local biogas plants can be costly. However, the long-term benefits, such as reduced fertilizer costs and increased crop yields, may offset the initial expenses. A study by Adekiya et al. (2024) suggested that using organic fertilizers like biodigestate could help Nigerian farmers reduce their reliance on expensive synthetic fertilizers, contributing to improved profitability over time.

Availability and access: In Nigeria, the availability of biodigestate is closely linked to the presence of biogas production systems, which are concentrated in specific regions and may not be widely available in rural areas where many smallholder farmers are located. For biodigestate to be widely accessible, there is a need for improved local biogas infrastructure or for farmers to access biodigestate from large-scale biogas plants. A study by Audu et al. (2020) highlighted the potential for decentralized biogas production in rural Nigeria, suggesting that small-scale biogas systems could increase access to organic fertilizers, providing a sustainable source of biodigestate for farmers in underserved areas.

Scale-up challenges: Scaling up the application of biodigestate to meet the demands of larger farming operations or multiple regions presents several logistical challenges in Nigeria. These include the transportation, storage, and distribution of biodigestate in a way that meets the application rates required by farmers. In addition, ensuring consistent quality and preventing contamination are essential factors that need to be managed at a larger scale. The study by Dahunsi et al. (2019) emphasized that efficient logistics and quality control mechanisms would be critical for successful large-scale adoption, as farmers must be assured of the reliability and safety of the product.

Potential drawbacks of biodigestate application

While biodigestate offers numerous benefits for improving soil fertility, its application also comes with potential drawbacks that need to be carefully considered.

Decomposition rates and nutrient release

The rate at which biodigestate decomposes and releases nutrients into the soil can vary significantly depending on factors such as temperature, moisture, and the nature of the feedstock used. In general, the decomposition process is governed by environmental conditions, including temperature and soil moisture, with decomposition rates tending to be lower under very dry or very wet soil conditions and higher under moderate, moist conditions because of microbial activity dynamics in the soil environment (Liang et al., 2003).

While biodigestate generally provides a slow-release source of nutrients, this decomposition and mineralization of organic N and other nutrient fractions may happen more slowly than expected under certain conditions, especially in soils with limited microbial activity or unfavorable physical conditions. Under cooler temperatures or drier soils, microbial decomposition slows, reducing the immediate availability of nutrients for plant uptake (van Midden et al., 2023).

Furthermore, although digestate contains a significant proportion of mineral forms of nutrients (which are more readily available), the supply of readily available nitrogen from digestate can be limited, as much of its nitrogen is initially in organic form and must first undergo mineralization (García-López et al., 2023). This can delay nutrient availability relative to plant demand, particularly during peak growth stages. The slow release of nutrients can lead to temporal nutrient imbalances if plants are unable to access nutrients at the optimal times for growth. This temporal mismatch can be more pronounced when biodigestate decomposition is slower due to soil or climatic constraints, which may necessitate supplemental fertilization or adjusted timing of application to better match crop nutrient demand.

Nutrient leaching

One of the significant concerns with biodigestate application is the potential for nutrient leaching, particularly nitrogen (N) and phosphorus (P). The alkaline nature of biodigestate can increase soil pH, which may enhance the solubility of nutrients such as nitrogen and phosphorus, making them more susceptible to leaching, especially in sandy soils or areas with high rainfall (Głowacka et al., 2020; García-López et al., 2023). Excessive nutrient availability due to high levels of biodigestate application can lead to nutrient runoff and contamination of nearby water bodies, resulting in eutrophication and poor water quality (Mgxaji et al., 2025). This leaching is particularly problematic in agricultural systems that rely heavily on nutrient management to prevent environmental degradation. Long-term monitoring and careful management of biodigestate application rates are essential to prevent such environmental risks.

Modifications to soil microbial communities

Biodigestate has the potential to alter the composition and activity of soil microbial communities. The introduction of new microbial populations from biodigestate can affect the natural balance of soil microbes, potentially leading to unintended consequences. In some cases, biodigestate can introduce beneficial microorganisms that improve nutrient cycling and organic matter decomposition (Odlare et al., 2008). However, the impact of these microbial changes is not fully understood, and in some instances, the introduction of foreign microorganisms can disrupt the natural microbial equilibrium of the soil. This disruption may result in negative effects on soil health, such as reduced microbial diversity, increased susceptibility to pathogens, or altered nutrient cycling processes (Galvez et al., 2012; Stefaniuk et al., 2015). Long-term monitoring is essential to assess whether these changes positively or negatively affect soil health and plant productivity.

Impact on soil pH and fertility over time

While biodigestate improves soil pH and enhances nutrient content in the short term, its long-term effects on soil pH may be a concern. The alkaline nature of biodigestate can significantly raise soil pH, which, while beneficial for some crops, may be detrimental to others, particularly those requiring acidic soils for optimal growth (Odlare et al., 2008). Over time, repeated applications of biodigestate can lead to sustained increases in soil pH, potentially disrupting the availability of micronutrients that are essential for plant growth, such as iron, manganese, and zinc. The gradual depletion of nutrients in the soil following repeated applications, combined with soil pH changes, may necessitate the use of complementary soil amendments to restore the nutrient balance and maintain soil fertility in the long term.

CONCLUSION

This study highlights the significant benefits of biodigestate fertilizer on soil chemical properties, maize growth, and yield under specific conditions. The application of biodigestate at 2,500 L ha^-1 and 5,000 L ha^-1, both alone and in combination with N, P, and K fertilizers, resulted in enhanced soil fertility and maize performance over two growing seasons (2022 and 2023). The year-to-year improvements in soil chemical properties, along with maize growth parameters such as plant height, leaf length, and stem girth, were evident, alongside significant yield increases in biomass weight, cob weight, and grain yield.

Remarkably, even in the absence of biodigestate application in 2023, residual positive effects on soil and plant growth were observed, underscoring the potential long-term benefits of biodigestate use. Specifically, maize grain yields increased by 13.43% and 20.92% for the 2,500 L and 5,000 L ha^-1 biodigestate treatments, respectively, compared to the control.

The synergistic effect of combining biodigestate with NPK fertilizers (B × NPK) led to higher yields than the use of either fertilizer type alone, suggesting that biodigestate provides a complementary source of macro- and micronutrients. The highest maize yields were observed with the combination of 5,000 L ha^-1 biodigestate and N1P1K1 fertilizers, which highlights biodigestate's potential as an effective supplement to mineral fertilizers.

Although the study focused on soil chemical fertility, it is important to note that this research was conducted on Alfisols, a specific type of Nigerian soil. The generalizability of these findings to other soil types remains uncertain, and further research is needed to assess whether similar outcomes can be achieved in different soil environments. Future investigations should also consider additional soil health indicators, such as microbial biomass, enzyme activity, and water retention, to deepen our understanding of the mechanisms by which biodigestate improves soil health and supports sustainable agricultural practices.

AUTHOR CONTRIBUTIONS

Aruna Olasekan Adekiya: Conceptualization (Equal), Methodology (Equal), Formal Analysis (Lead), Validation (Lead), Resource (Lead), Writing – Original Draft (Lead), Writing – Review & Editing (Lead), Investigation (Lead), Supervision (Equal), Project Administration (Equal); Olufunmilayo Titilayo Ande: Conceptualization (Lead), Methodology (Lead), Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Equal); Samuel Olatunde Dahunsi: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Olajire Damilola Adedokun: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Malia Michael Micah: Methodology (Supporting), Formal Analysis (Supporting), Validation (Equal), Resource (Lead), Data Curation (Lead), Writing – Review & Editing (Equal), Investigation (Supportive), Supervision (Equal), Project Administration (Supportive).

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

REFERENCES

Abd El-Gawad, A.M. and Morsy, A.S.M. 2017. Integrated impact of organic and inorganic fertilizers on growth, yield of maize (Zea mays L.) and soil properties under upper Egypt conditions. Journal of Plant Production Sciences. 8(11): 1103-1112. https://doi.org/10.21608/jpp.2017.41121

Adediran, J.A. and Banjoko, V.A. 1995. Response of maize to nitrogen, phosphorus, and potassium fertilizers in the Savanna zones of Nigeria. Communications in Soil Science and Plant Analysis. 26(3-4): 593-606. https://doi.org/10.1080/00103629509369320

Adekiya, A.O., Ogunboye, O.I., Ewulo, B.S., and Olayanju, A. 2020. Effects of different rates of poultry manure and split applications of urea fertilizer on soil chemical properties, growth, and yield of maize. The Scientific World Journal. 2020: 4610515. https://doi.org/10.1155/2020/4610515

Adekiya, A.O., Ande, O.T., Dahunsi, S.O., and Ogunwole, J. 2024. Sole and combined application of biodigestate, N, P, and K fertilizers: Impacts on soil chemical properties and maize performance. The Scientific World Journal. 2024: 6685906. https://doi.org/10.1155/2024/6685906

Adeyemo, A.J., Akingbola, O.O., and Ojeniy, S.O. 2019. Effects of poultry manure on soil infiltration, organic matter contents and maize performance on two contrasting degraded alfisols in southwestern Nigeria. International Journal of Recycling of Organic Waste in Agriculture. 8(6): 73-80. https://doi.org/10.1007/s40093-019-0273-7

Afriyie, E., Mensah, E., and Lohri, C.R. 2013. Comparative study of composted and uncomposted digestates, chicken manure and cow dung as fertilizers and their effects on soil properties. Global Journal of Engineering, Science and Technology. 2(4): 12-22

Agbede, T.M., Adekiya, A.O., Ale, M.O., Eifediyi, E.K., and Olatunji, C.A. 2019. Effects of green manures and NPK fertilizer on soil properties, tomato yield and quality in the forest-savanna ecology of Nigeria. Experimental Agriculture. 55(5): 793–806. https://doi.org/10.1017/S0014479718000376

Agbede, T.M. and Oyewumi, A. 2023. Effects of biochar and poultry manure amendments on soil physical and chemical properties, growth and sweet potato yield in degraded Alfisols of humid tropics. Natural and Life Sciences Communications. 22(2): e2023023. https://doi.org/10.12982/NLSC.2023.023

Akinrinde, E.A. and Obigbesan, G.O. 2000. Evaluation of the fertility status of selected soils for crop production in five ecological zones of Nigeria. Proceedings of the 26^th Annual Conference of Soil Science Society of Nigeria. (Ed. O. Babalola), 30 October-3 November, Ibadan, Nigeria.

Alburquerque, J.A., de la Fuente, C., Campoy, M., Carrasco, L., Nájera, I., Baixauli, C., Caravaca, F., Roldán, A., Cegarra, J., and Bernal, M.P. 2012. Agricultural use of digestate for horticultural crop production and improvement of soil properties. European Journal of Agronomy. 43: 119–128. https://doi.org/10.1016/j.eja.2012.06.001

AOAC. 2006. Official methods of analysis of the association of official analytical chemists. AOAC International, 18^th Edn. AOAC International. Gaithersburg, MD., USA.

Audu, I.G., Barde, A., Yila, O.M., Onwualu, P.A., and Lawal, B.M. 2020. Exploring biogas and biofertilizer production from abattoir wastes in Nigeria using a multi-criteria assessment approach. Recycling. 5(3): 18. https://doi.org/10.3390/recycling5030018

Awoonor, J.K., Amoakwah, E., Buri, M.M., Dogbey, B.F., and Gyamfi, J.K 2025. Impact of land use on soil quality: Insights from the forest-savannah transition zone of Ghana. Heliyon. 11(1): e41183.  https://doi.org/10.1016/j.heliyon.2024.e41183

Bach, I.M., Essich, L., and Müller, T.  2021. Efficiency of recycled biogas digestates as phosphorus fertilizers for maize. Agriculture. 11(6): 553. https://doi.org/10.3390/agriculture11060553

Bachmann, S., Wentzel, S., and Eichler-Löbermann, B. 2011. Co-digested dairy slurry as a phosphorus and nitrogen source for Zea mays L. and Amaranthus cruentus L. Journal of Plant Nutrition and Soil Science. 174: 908-915. https://doi.org/10.1002/jpln.201000383

Bolaños, J. and Edmeades, G.O. 1996. The importance of the anthesissilking interval in breeding for drought tolerance in tropical maize. Field Crops Research. 48(1): 65–80. https://doi.org/10.1016/0378-4290(96)00036-6

Bremner, J.M. 1996. Nitrogen-total. In: Methods of soil analysis, part 3. chemical methods, 2^nd Edn., SSSA Book Series No. 5. pp. 85-121. ASA and SSSA, Madison, WI, USA. https://doi.org/10.2136/ sssabookser5.3.c37.

Cajamarca, S.M.N., Martins, D., da Silva, J., Fontenelle, M.R., Guedes, Í.M.R., de Figueiredo, C.C., and Pacheco Lima, C.E. 2019. Heterogeneity in the chemical composition of biofertilizers, potential agronomic use, and heavy metal contents of different agro-industrial wastes. Sustainability. 11: 1995. https://doi.org/10.3390/su11071995

Cristina, G., Camelin, E., Tommasi, T, Fino, D., and Pugliese, M. 2020. Anaerobic digestates from sewage sludge used as fertilizer on a poor alkaline sandy soil and on a peat substrate: Effects on tomato plants growth and on soil properties. Journal of Environmental Management. 269: 110767. https://doi.org/10.1016/j.jenvman.2020.110767

Dahunsi, S.O., Oranusi, S., Efeovbokhan, V.E., AdesuluDahunsi, A.T., and Ogunwole, J.O.  2021. Crop performance and soil fertility improvement using organic fertilizer produced from valorization of Carica papaya fruit peel. Scientific Reports. 11(1): 4696. https://doi.org/10.1038/s41598-021-84206-9

Dahunsi, S.O., Adesulu-Dahunsi, A.T., Osueke, C.O., Lawal, A.I., Olayanju, T.M.A., Ojediran, J.O., and Izebere, J.O. 2019. Biogas generation from Sorghum bicolor stalk: Effect of pretreatment methods and economic feasibility. Energy Reports. 5:  584-593. https://doi.org/10.1016/j.egyr.2019.04.002

Dawson, C.J. and Hilton, J. 2011. Fertiliser availability in a resource-limited world: Production and recycling of nitrogen and phosphorus. Food Policy. 36: 14–22. https://doi.org/10.1016/j.foodpol.2010.11.012

Doyeni, M.O., Stulpinaite, U., Baksinskaite, A., Suproniene, S., and Tilvikiene, V. 2021. The effectiveness of digestate use for fertilization in an agricultural cropping system. Plants. 10(8): 1734. https://doi.org/10.3390/plants10081734

FAO, 2018. The future of food and agriculture – Alternative pathways to 2050. Rome: p. 224

Faisal, S., Ahmad Inamullah, B., Akhtar, K., Ali, S., and Ullah, I. 2015. Effect of organic and inorganic fertilizers on penology of maize varieties. Pure and Applied Biology. 4(3): 434-440. https://doi.org/10.19045/bspab.2015.43020

Frank, K., Beegle, D., and Denning, J. 1998. Phosphorus. In: Recommended chemical soil test procedures for the north central region, north central regional research, Revised, Missouri Agric. Exp. Station. Publication No. 221. pp. 21- 26, Columbia.

Galvez, A., Sinicco, T., Cayuela, M.L., Mingorance, M.D., Fornasier, F., and Mondini, C. 2012. Short term effects of bioenergy by-products on soil C and N dynamics, nutrient availability and biochemical properties. Agriculture, Ecosystems & Environment. 160: 3-14. https://doi.org/10.1016/j.agee.2011.015

García-López, A.M., Delgado, A., Anjos, O., and Horta, C. 2023. Digestate not only affects nutrient availability but also soil quality indicators. Agronomy. 13: 1308. https://doi.org/10.3390/agronomy13051308

Gee, G.W. and Or, D. 2002. Particle-size analysis. In: Methods of soil analysis, part 4, J.H. Dane and G.C. Topp (eds.). Physical methods. Soil Science Society of America Book Series No. 5: 25593. Madison, WI, USA. https://doi.org/10.2136/sssabookser5.4.c12

Glowacka, A., Szostak, B., and Klebaniuk, R. 2020. Effect of biogas digestate and mineral fertilisation on the soil properties and yield and nutritional value of switchgrass forage. Agronomy. 10(4): 490. https://doi.org/10.3390/agronomy 0040490

Haraldsen, T.K., Andersen, U., Krogstad, T., and Sørheim, R.  2011. Liquid digestate from anaerobic treatment of source-separated household waste as fertilizer to barley. Waste Management Research. 29: 1271–1276. https://doi.org/10.1177/0734242X11411975

Lal, R. 1997. Long-term tillage and maize monoculture effects on a tropical alfisol in western Nigeria. I. crop yield and soil physical properties, Soil and Tillage Research. 42(3): 145–160. https://doi.org/10.1016/S0167-1987(97)00006-8

Lee, M.E., Steiman, M.W., and St. Angelo, S.K.  2020. Biogas digestate as a renewable fertilizer: Effects of digestate application on crop growth and nutrient composition. Renewable Agriculture and Food Systems. 36(2): 173–181. https://doi.org/10.1017/ S17421705200001

Li, Y., Huang, S., Meng, Q., Li, Z., Fritschi, F.B., and Wang, P. 2024. Pre-silking water deficit in maize induced kernel loss through impaired silk growth and ovary carbohydrate dynamics. Plant-Environment Interactions. 5: e10141. https://doi.org/10.1002/pei3.10141

Liang, C., Das, K.C., and McClendon, R.W. 2003. The influence of temperature and moisture contents regimes on the aerobic microbial activity of a biosolids composting blend. Bioresource Technology. 86(2): 131-137. https://doi.org/10.1016/S0960-8524(02)00153-0

Makádi, M., Tomócsik, A., and Orosz, V. 2012. Digestate: A new nutrient source – Review. In: S. Kumar (ed.): Biogas. Croatia, InTech Europe. 295–310. https://doi.org/10.5772/31355

Marcato, C.E., Mohtar, R., Revel, J.C., Pouech, P., Hafidi, M., and Guiresse, M. 2009. Impact of anaerobic digestion on organic matter quality in pig slurry. International Biodeterioration & Biodegradation. 63(3): 260–266. https://doi.org/10.1016/j.ibiod.2008.10.001

Mayerová, M., Šimon, T., Stehlík, M., Madaras, M., Koubová, M., and Smatanová, M. 2023. Long-term application of biogas digestate improves soil physical properties. Soil and Tillage Research. 231: 105715. https://doi.org/10.1016/j.still.2023.105715

McLaughlin, J.E. and Boyer, J.S. 2004. Sugar-responsive gene expression, invertase activity, and senescence in aborting maize ovaries at low water potentials. Annals of Botany. 94(5): 675–689. https://doi.org/10.1093/aob/mch193

Mgxaji, Y., Mutengwa, C.S., Mukumba, P., and Dzvene, A.R. 2025. Biogas slurry as a sustainable organic fertilizer for sorghum production in sandy soils: A review of feedstock sources, application methods, and agronomic impacts. Agronomy. 15(7): 1683. https://doi.org/10.3390/agronomy15071683

Moe, K., Mg, K.W., Win, K.K., and Yamakawa, T. 2017. Combined effect of organic manures and inorganic fertilizers on the growth and yield of hybrid rice (palethwe-1). American Journal of Plant Sciences. 8: 1022–1042.

Möller, K. and Stinner, W. 2009. Effects of different manuring systems with and without biogas digestion on soil mineral nitrogen content and on gaseous nitrogen losses (ammonia, nitrous oxides). European Journal of Agronomy. 30(1): 1–16. https://doi.org/10.1016/j.eja.2008.06.003

Nandwa, S.M. 2001. Soil organic carbon (SOC) management for sustainable productivity of cropping and agroforestry systems in Eastern and Southern Africa. Nutrient Cycling in Agroecosystems. 61(1–2): 143–158. https://doi.org/10.1023/A:1013386710419

Nelson, D.W. and Sommers, L.E. 1996. Total carbon, organic carbon and organic matter. In: Methods of soil analysis, part 3, Chemical methods, Sparks, D.L., Page, A.L., Helmke, P.A., and Loeppert, R.H. (Eds.). Soil Science Society of America, American Society of Agronomy. Madison, WI, USA. https://doi.org/10.2136/sssabookser5.3.c34

Odlare, M., Pell, M., and Svensson, K. 2008. Changes in soil chemical and microbiological properties during 4 years of application of various organic residues. Waste Management. 28: 1246-1253. https://doi.org/10.1016/j.wasman.2007.06.005

Onasanya, R.O., Aiyelari, O.P., Onasanya, A., Oikeh, S., Nwilene, F.E., and Oyelakin, O.O. 2009. Growth and yield response of maize (Zea mays L.) to different rates of nitrogen and phosphorus fertilizers in Southern Nigeria. World Journal of Agricultural Sciences. 5(4): 400-407.

Pivato, A., Vanin, S., Raga, R., Lavagnolo, M.C., Barausse, A., Rieple, A., Laurent, A., and Cossu, R. 2016. Use of digestate from a decentralized on-farm biogas plant as fertiliser in soils: An ecotoxicological study for future indicators in risk and life cycle assessment. Waste Management. 49: 378–389. https://doi.org/10.1016/j.wasman.2015.12.009

Popović, V., Vasileva, V., Ljubičić, N., Rakašćan, N., and Ikanović, J. 2024. Environment, soil, and digestate interaction of maize silage and biogas production. Agronomy. 14(11): 2612. https://doi.org/10.3390/agronomy14112612

Ragályi, P., Szécsy, O., Uzinger, N., Magyar, M., Szabó, A., and Rékási, M. 2025. Factors influencing the impact of anaerobic digestates on soil properties. Soil Systems. 9(3): 78. https://doi.org/10.3390/soilsystems9030078

Recena, R., García-López, A.M., Quintero, J.M., Skyttä, A., Ylivainio, K., Santner, J., and Delgado, A. 2022. Assessing the phosphorus demand in European agricultural soils based on the Olsen method. Journal of Cleaner Production. 379: 134749. https://doi.org/10.1016/j.jclepro.2022.134749

Rizzo, P.F., Young, B.J., Viso, N.P., Carbajal, J., Martínez, L.E., Riera, N.I., Bres, P., Beily, M.E., Barbaro, L., Farber, M., et al. 2022. Integral approach for the evaluation of poultry manure, compost, and digestate: Amendment characterization, mineralization, and effects on soil and intensive crops. Waste Management. 139: 124-135. https://doi.org/10.1016/j.wasman.2021.12.017

Rosemarin, A., Macura, B., Carolus, J., Barquet, K., Ek, F., Järnberg, L., Lorick, D. Johannesdottir, S., Pedersen, S.M., Koskiaho, J., et al. 2020. Circular nutrient solutions for agriculture and wastewater—A review of technologies and practices. Current Opinion in Environmental Sustainability. 45: 78–91. https://doi.org/10.1016/j.cosust.2020.09.007

Saveyn, H. and Eder, P. 2014. End-of-waste criteria for biodegradable waste subjected to biological treatment (compost and digestate): Technical proposals. EUR 26425. Luxembourg (Luxembourg): Publications Office of the European Union. 2013: JRC87124.

Šimon, T., Kunzová, E., and Friedlová, M.  2015. The effect of digestate, cattle slurry and mineral fertilization on the winter wheat yield and soil quality parameters. Plant, Soil and Environment. 61(11): 522–527. https://doi.org/10.17221/530/2015-PSE

Smith, J., Abegaz, A., Matthews, R.B., Subedi, M., Orskov, E.R., Tumwesige, V., and Smith, P. 2014. What is the potential for biogas digesters to improve soil carbon sequestration in Sub-Saharan Africa? Comparison with other uses of organic residues. Biomass and Bioenergy. 70: 73–86. https://doi.org/10.1016/j.biombioe.2014.01.056

Smyth, A.J. and Montgomery, R.F. 1962. Soils and land use in central western Nigeria. Ibadan, Nigeria: Government Printer. pp. 265.

Spagnolo, S., Tinello, A., Cavinato, C., Zabeo, A., and Semenzin, E. 2019. Sustainability assessment of two digestate treatments: A comparative life cycle assessment. Environmental Engineering and Management Journal. 18: 2193–2202.

Stefaniuk, M., Bartminski, P., Rózylo, K., Debicki, R., and Oleszczuk, P. 2015. Ecotoxicological assessment of residues from different biogas production plants used as fertilizer for soil. Journal of Hazardous Materials. 298: 195-202. https://doi.org/10.1016/j.jhazmat.2015.05.026.

Tel, D.A. and Hargerty, M. 1984 Soil and plant analyses: Study guide for agricultural laboratory directors and technologists working in tropical regions, International Institute of Tropical Agriculture, Ibadan, Nigeria.

Tiwari, T.N., Tiwari, K.N., and Upadhyay, R.M. 2000. Effect of crop residues and biogas slurry incorporation in wheat on yield and soil fertility. Journal of the Indian Society of Soil Science. 48: 515–520.

van Midden, C., Harris, J., Shaw, L., Sizmur, T., and Pawlett, M. 2023. The impact of anaerobic digestate on soil life: A review. Applied Soil Ecology. 191: 105066. https://doi.org/10.1016/j.apsoil.2023.105066

Yaseen, M., Ahmad, A., Naveed, M., Ali, M.A., Shah, S.S.H., Hasnain, M., Ali, H.M., Siddiqui, M.H., Salem, M.Z.M., and Mustafa, A. 2021. Subsurface-applied coated nitrogen fertilizer enhanced wheat production by improving nutrient-use efficiency with less ammonia volatilization. Agronomy. 11(12): 2396. https://doi.org/10.3390/agronomy11122396

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