The research was conducted on a post-coal mining land at PT. Arutmin Indonesia Asamasam Mine, Tanah Laut Regency, South Kalimantan, Indonesia (Figure 1), from October 2023 to September 2024. The research area was located at approximately -3.865000 latitude and 115.104324 longitude, with extensive flatland topographic characteristics. The site used to be a coal mining operation without a land rehabilitation history. This research included land preparation, soil ameliorants application (P1 to P6) in the research plot, sorghum planting, pest control, harvesting, and soil analysis. The soil properties are presented in Table 1.

A completely randomized design (CRD) was applied to analyze seven treatments (P0–P6) and four replicates, totaling 28 plots. Treatments were randomized across the experimental area; a serpentine layout was set to minimize directional gradients, but rows were not considered analytical blocks. Each plot comprised seven ridges with 33 planting holes per ridge (231 plants per plot). For data analysis, plot means (based on seven randomly selected plants—one per ridge) were used as the experimental units to avoid pseudo-replication.

Soil samples were collected from the reclamation land at post-mining sites in five representative locations to a depth of 20 cm (Widawati & Suliasih, 2019). The samples were analyzed for chemical properties, including pH, organic carbon, nitrogen, phosphorus, potassium, and cation exchange capacity (CEC).

Soil ameliorants used in this research included humic acid, dolomite (CaMg(CO₃)₂), and organic compost. The organic compost—made of 65% cattle manure and 35% chicken manure—was fermented for 3 weeks prior to application. The compost had a pH of 7.27, measured in a 1:5 ratio of compost to distilled water and suspended in a calibrated pH meter. The soil ameliorants were made into seven treatments and four replications, resulting in 28 soil plots (5 x 5 m). The treatments were control (P0) without ameliorants, P1 (28 l ha⁻¹ humic acid), P2 (5.8 t ha⁻¹ dolomite), and P3 (15 t ha⁻¹ organic compost). The combined treatments were P4 (28 L ha⁻¹ humic acid + 15 t ha⁻¹ organic compost), P5 (5.8 t ha⁻¹ dolomite + 15 t ha⁻¹ organic compost), and P6 (28 L ha⁻¹ humic acid + 5.8 t ha⁻¹ dolomite + 15 t ha⁻¹ organic compost). We excluded the combination of dolomite and humic acid treatment without compost to preserve the statistical power because the agronomic benefits of humic substances and liming are attenuated in low-SOC (soil organic carbon) matrices on carbon-poor post-mining soils with depauperate microbial activity. Therefore, compost was adopted as the baseline organic substrate to rebuild soil organic matter (SOM) and to support microbially mediated nutrient cycling (Heisey et al., 2022); (Miralles et al., 2021); (Miu et al., 2022)

The land was tilled using a hand tractor before staking and forming a ridge to incorporate ameliorants uniformly. Stakes were then installed to mark the borders of the 28 research plots (at 5 x 5 m, with a 2-m interval). Each plot was divided into seven ridges with a 75-cm spacing between ridges and 15-cm spacing between seeds within each ridge, resulting in 231 planting holes per plot. Ameliorants were applied only once, four weeks before planting, manually by spreading the material over the treatment plots. A base fertilizer (organic compost) was applied at 5 t ha⁻¹ two weeks before planting.

This study used S. bicolor cv. Bioguma-2 (Bioguma-2 sorghum) developed by the Agricultural Research and Development Agency (Balitbangtan) of the Ministry of Agriculture of the Republic of Indonesia. The sorghum seeds were planted in 231 holes dug into the soil. Prior to planting, the seeds were treated with the insecticide Confidor^® to deter ant infestations. Each hole was filled with 3 to 4 seeds at approximately a 5-cm depth and then covered with composted manure. Thinning was performed on days 5 and 14 after sowing (DAS), leaving two plants in each hole.

The first fertilization—with a combination of 300 kg ha^-1 urea, 100 kg ha^-1 SP36, and 60 kg ha^-1 KCl—was carried out at 14 DAS. Urea was applied in ratoon 2: 100 kg ha^-1 on 14 DAS and 200 kg ha^-1 at 30 DAS. The fertilizers SP36 and KCl were applied as a single dose on 14 DAS. Fertilization was conducted at the same growth stage and in the exact dosage for each planting cycle. Pest control was initiated once the sorghum plants emerged, with biweekly applications of Regent^® insecticide to control grasshoppers (Oxya serville) and brown planthoppers (Nilaparvata lugens), and Prevaton^® to combat armyworms (Spodoptera litura). The trial was conducted under rainfed conditions, without supplemental irrigation. Soil moisture was maintained by rainfall, typical of the site during the study period. Harvesting was performed when the sorghum reached the soft dough stage at 100 DAS; subsequent harvests (stages 2 and 3) were carried out 100 days after the previous harvest. The soft dough stage marks the period after the milk stage and before the stiff dough stage, characterized by fully developed grains that have started to harden but can still be compressed by hand.

The Bioguma-2 sorghum was harvested thrice—at the initial harvest, ratoon 1, and ratoon 2—100 days after sowing (DAS), corresponding to the soft dough stage of the sorghum. We observed the agronomic parameters (plant survival rate, plant height, stem diameter, leaf length and width, leaf number, and tiller count), the fresh biomass, dry weight of the sorghum, and Brix. The nutritional composition analyzed in this study includes dry matter content, ash content, crude protein, crude fat, and crude fiber. Soil conditions before and after the research were examined for the soil pH, content of carbon (C), nitrogen (N), phosphorus (P), potassium (K), and cation exchange capacity (CEC). The obtained data were subjected to analysis of variance (ANOVA), followed by Duncan’s multiple range test (DMRT) for significant differences between treatments. The analysis was performed using IBM SPSS Statistics software, version 27.0.

This study investigated the chemical characteristics of soil in experimental plots subjected to different treatments (P0–P6) and their influence on key soil fertility parameters—soil pH, organic carbon, nitrogen, phosphorus, potassium, and cation exchange capacity (CEC). Table 1 shows that the soil pH measured in distilled water (pH H₂O) varied significantly across treatments (p<0.001), ranging from 4.35 in P0 to 6.45 in P6. Similarly, soil pH measured in 1 N KCl showed significant variation (p<0.001) in an increasing trend, from 3.36 in P0 to 6.41 in P6. A steady increase across treatments was observed in organic carbon content, from 0.38% in P0 to 1.52% in P6 (p<0.001), and in total nitrogen (N-total), from 0.23% to 0.31%, with significant differences between treatments (p<0.001). Similarly, potential phosphorus (P₂O₅) content increased from 11.20 mg/100 g in P0 to 24.48 mg/100 g in P6, and potential potassium (K₂O) content rose from 19.38 mg/100 g to 50.50 mg/100 g (p<0.001 for both). Cation exchange capacity (CEC) also showed significant increases with treatment level (p<0.001), from 17.65 me/100 g in P0 to 33.64 me/100 g in P6.

The application of soil ameliorants significantly affected (p<0.01) the survival rate of Bioguma-2 sorghum grown on post-coal mining land (Figure 2). The highest survival rate was observed in treatment P6 (80.52%), followed by P5 (60.50%), P4 (56.82%), P3 (53.79%), P2 (45.24%), and P1 (44.48%). The lowest survival rate was recorded in the control group, P0 (21.43%). Statistical grouping based on superscripts (A–E) indicates significant differences between treatments at p<0.01 (see Figure 2).

The application of ameliorant treatments significantly affected the morphological performance of Bioguma-2 sorghum on post-coal mining land across the initial, ratoon 1, and ratoon 2 stages. We found that the plant height was consistently treatment-dependent (p<0.001). At the initial stage, P6 and P5 produced the tallest plants (215.60 and 213.10 cm), while the control (P0) resulted in the shortest (109.80 cm). Similarly, at both ratoon stages, P6 plants remained the highest and P0 plants were the lowest (112.50 cm vs. 40.60 cm). Stem diameter also differed significantly (p<0.001) at the initial stage, where P5, P6, and P4 had the thickest stems (2.23, 2.15, and 2.13 cm), while P0 had the thinnest (1.30 cm). These differences were consistent between ratoon 1 and 2.

Treatments significantly influenced leaf production at each stage. During the initial phase, P3 (11.75) had the most leaves, followed by P1 (8.50; p=0.002). In ratoon 1 and 2, P6 produced the most leaves (10.50 and 9.50, respectively), while P0 had the least (8.50 and 7.50; p<0.001). Leaf length also varied (p<0.001), with the longest leaves at the initial stage observed in P2 (77.00 cm), P3 (76.60 cm), and P4 (76.13 cm). P3 consistently maintained this superiority across all ratoons. A similar trend was identified in leaf width (p<0.001), in which the widest leaves were P4 (8.73 cm), P6 (8.68 cm), and P5 (8.54 cm) in the initial stage, and the narrowest was P0 (7.00 cm). In the ratoons, P6 consistently produced the widest leaves (8.15 cm and 8.00 cm).

We observed significant differences in tillering across treatments in ratoon 1 (p=0.015), where P6 produced the most tillers (2.50) and P0 the fewest (1.25). In ratoon 2, the variation was not statistically significant (p=0.188), although P6 still had the most tillers (2.00). Collectively, these results showed that the ameliorant treatments—particularly P6 and P5—produced sustained improvements in plant stature, leaf growth, and tillering, indicating robust morphological advantages for revegetation or bioenergy production on degraded mining soils.

Table 3 shows that across all harvest stages (ratoon 1, ratoon 2), ameliorant treatments strongly affected fresh and dry yields (all p<0.001). In the initial harvest, fresh yield ranged from 6.25 t ha⁻¹ (P0) to 40.84 t ha⁻¹ (P6) and 34.64 t ha⁻¹ (P5). Fresh yield in ratoon 1 varied from 0.56 t ha⁻¹ (P0) to 18.76 t ha⁻¹ (P6), and in ratoon 2 from 0.20 t ha⁻¹ (P0) to 10.25 t ha⁻¹ (P6). Dry yield followed the same ranking: initial at 1.96–13.26 t ha⁻¹ (P0–P6), ratoon 1 at 0.17–6.10 t ha⁻¹, and ratoon 2 at 0.06–3.23 t ha⁻¹, consistently identifying P6 (and generally P5) as the top-performing treatments.

Brix also improved with ameliorants (p<0.001). At the initial stage, it increased from 10.50% (P0) to 15.00% (P6), while ratoon 1 and 2 were 9.50%–14.50% and 8.50%–13.00%, respectively. P6 consistently showed the highest effect across treatments and stages. These results indicated that the combined ameliorants strategy markedly enhanced both quantity (fresh/dry yield) and quality (Brix) of Bioguma-2 sorghum on post-coal mining land across successive harvests.

The nutritional composition of Bioguma-2 sorghum varied across treatments (P0–P6) and harvest stages (initial, ratoon 1, and ratoon 2), as shown in Table 4. The dry matter (DM) content generally increased across treatments, with the highest values consistently found in P6 at all stages (32.47%, 32.49%, and 31.63%, respectively). The ash content exhibited significant variation among the treatments across all harvest stages (p<0.001). At the initial stage, P4 had the highest ash percentage at 14.67%, while P1 had the lowest at 12.42%. A similar pattern was found in the ratoon stages, where P0 and P1 had higher ash values compared to P3 and P4 in the second ratoon. Crude protein content significantly increased with the application of ameliorant across all stages (p<0.001). The highest crude protein was consistently recorded in P6 (13.47%, 14.04%, and 14.04%), while P0 had the lowest (11.64%, 12.00%, and 11.61%). Crude fat content was also significantly affected by treatments (p<0.001). During the initial stage, P3, P4, and P5 recorded the highest crude fat values, while P6 was the lowest. In the first ratoon, fat content peaked in P0 and P5, while the lowest was in P3 and P6. In ratoon 2, fat values remained consistent across treatments, ranging from 5.71% to 6.72%. Crude fiber content varied significantly across treatments and growth stages (p<0.001). Generally, the highest fiber values were recorded in treatments P0 and P3, while the lowest values were observed in treatment P6 during both the initial and first ratoon stages. In ratoon 2, P0 had the highest fiber content (36.76%), whereas P4 and P5 had the lowest.

Soil chemical quality improvements depend on the quantity of ameliorants applied to it and the functional complementarity of these substances. In acidic soils with low organic matter (SOM), a three-way combination of ameliorants offers synergistic benefits. First, dolomite neutralizes soil acidity and supplies Ca–Mg, thus raising pH and base saturation. Then, compost adds soil organic matter (SOM) that increases CEC, buffers pH, and delivers slow-release nutrients while supporting microbial activity. Lastly, humic acid complexes nutrients, enhances root physiological responses, and promotes aggregation, which increases nutrient availability and retention (Alsudays et al., 2024); (Rose et al., 2024); (Stewart-Wade, 2020). Compost efficacy is highly contingent upon the type of feedstock and maturity. The combination of well-matured plant manure with moderate carbon to nitrogen (C:N) typically yields the most consistent gains; therefore, quality testing prior to field use is recommended. For field conditions, base-dressing rates of ~10–15 t ha⁻¹ are generally effective on acidic, low-SOM soils. In addition, dolomite has reportedly improved soil conditions by supplying essential cations and elevating soil pH (Krismawati et al., 2022); (Wahyudi et al., 2019).

Consistent with this synergy, treatment P6 (humic acid + compost + dolomite) in our study produced the largest, statistically robust improvements in soil chemical properties (p<0.001), including pH (from 4.35 in P0 to 6.45), organic carbon (from 0.38% to 1.52%), total nitrogen (from 0.23% to 0.31%), available phosphorus and potassium, and CEC (from 17.65 to 33.64 me/100 g). Mechanistically, the liming effect of dolomite shifted pH into a range that reduces Al³⁺ toxicity and enhances phosphate availability; compost increased exchange sites and buffering through added soil organic matter (SOM); and humic substances improved nutrient complexation and root uptake—yielding greater nutrient availability than any single or two-way ameliorants.

lant survival is closely related to soil chemical quality. In this study, survival rate increases with the soil pH, indicating that ameliorant treatments have resulted in a more optimal pH. It is aligned with previous studies that the optimal range of soil pH allows more plants to survive (Crespo-Mendes et al., 2019) and that the survival rate of sorghum ranges from 60% to 80%, depending on the variety (Yartsev et al., 2024). In this study, the highest survival rate is 80.52%, observed in treatment P6, with the highest pH and nutrient content, whereas P0 (control) was only 21.43% (p<0.01). These results indicated a strong positive correlation between the use of ameliorant and plant viability.

Treatments incorporating different ameliorant materials showed increased survival rates. In this study, humic acid acted as a plant regulator and contributed to significant quantities of plant growth hormones. It was in line with previous studies that growth hormones can stimulate root and crown growth, thus maintaining plants in stressful conditions (Khan et al., 2023). In addition, organic compost can enhance stress resilience in plants by gradually providing nutrients (Ahmed et al., 2023) and promote robust plant growth and development by serving as a slow-release source of essential nutrients, including nitrogen, phosphorus, and potassium (Suvendran et al., 2025).

The improvement in soil quality has been reported to positively correlate with the morphological characteristics of the plants (Cuiyun et al., 2023); (Drăghici et al., 2024), including plant height (Maftuchah et al., 2021). In general, we observed that the combination of ameliorant materials (humic acid, organic compost, and dolomite) resulted in the best morphological characteristics of Bioguma-2 sorghum (see Table 2). First, plant height in P6 reached 215.60 cm at the initial stage, remained superior during ratoon stages, and was significantly higher than P0 (109.80 cm) (p<0.001). It has been reported that the determining factors for plant morphological characteristics include the availability of macronutrients such as nitrogen, phosphorus, and potassium. (Khalofah et al., 2022) reported that increasing nitrogen, phosphorus, and potassium levels significantly improved plant height, leaf length, and leaf width. The cation exchange capacity (CEC) enhances nutrient availability in the soil, reduces the competition effects between cations such as Ca, Mg, and K (Yang et al., 2024), and affects plant height. Secondly, we observed a statistically significant relationship between plant height and stem diameter, where taller plants in P5 and P6 also had thicker stems (2.23 cm and 2.15 cm, respectively). This finding confirms (Abdullah et al., 2024), who found a positive correlation between height and stem diameter.

The third morphological characteristic is the number of leaves. Calcium (Ca) and magnesium (Mg) in dolomite stimulate cell turgor and chlorophyll formation, which enhances the products of photosynthesis(Sambi et al., 2023). At the same time, dolomite supplies phosphorus nutrients that promote plant growth, which is evident in the increased number of leaves and taller plants. Composting, through the decomposition of organic materials, positively influences leaf parameters. These findings confirm a previous study that compost improves leaf characteristics (Kortei, 2016) and that organic fertilizers improve soil health by increasing soil organic matter (SOM), boosting nutrient uptake, enhancing water-holding capacity, and improving cation exchange capacity (CEC) (Liu et al., 2024). Therefore, enhancing soil health can naturally support better plant growth.

We found that water availability influenced the next morphological characteristic, the number of tillers in sorghum plants. A significant difference was observed in ratoon 1 (p=0.015), where P6 had 2.50 tillers while P0 only had 1.25 in P0, highlighting the role of improved soil structure and moisture retention. Despite all plants receiving the same irrigation, we discovered that different ameliorant treatments influenced soil conditions, resulting in varying water absorption capacities among the plants. It confirms (Dariah et al., 2021), who reported that soil ameliorant treatment positively affected water aggregate stability. Under water stress, ameliorants positively affect yields, suggesting improved water retention and nutrient availability (Ismail et al., 2025).

Healthy soils improve nutrient availability, water retention, and root development, all of which are essential for strong crop yields (Srivastava et al., 2024). In our study, yields declined across harvest stages in every treatment (see Table 3). Even in the top treatment (P6), the fresh yield decreased from 40.84 t ha⁻¹ (initial) to only 46% or 18.76 t ha⁻¹ in ratoon 1 and to 25% or 10.25 t ha⁻¹ in ratoon 2. A similar pattern was observed in dry matter yields, where they decreased from 13.26 t ha⁻¹ (initial stage) to 6.10 t ha⁻¹ (ratoon 1) to 3.23 t ha⁻¹ (ratoon 2), marking 46% and 24% of the initial stage in the respective ratoons. Brix values—an indicator of juice quality—were the highest in P6 across all stages (15.00%, 14.50%, and 13.00% for the initial stage, ratoon 1, and ratoon 2, respectively). It indicated a greater biomass and improved juice quality, relevant for both silage and bioethanol (Costa et al., 2021).

From a physiological standpoint, ratoon regrowth depends on non-structural carbohydrate (NSC) reserves stored in stubble and roots; repeated cutting and an aging root system reduce regrowth vigor. Biomass recovery of the rainfed, acidic, low-SOM post-mining land in this study was further limited by the nutrient drawdown—especially N and K—together with water stress and untilled rhizosphere (Wang et al., 2024); (Zhou et al., 2022). These constraints explain the consistent decline from the initial harvest to ratoon 1 and ratoon 2 across treatments. Conversely, (Leavitt et al., 2023) and (Qi et al., 2024) reported that the second cuts, which equaled or exceeded the first, usually occurred in well-managed stands with adequate N split/top-dressing and an appropriate cutting height that preserves basal buds, often under favorable moisture. Such conditions were nonexistent on our site, which explained the low ratoon yields. Consistent with these agronomic limitations, soil acidification has been shown to depress growth and yield in related ratooning systems (Pang et al., 2025). Here, poorer crop performance is frequently accompanied by modest declines in Brix, thus reinforcing Brix as a practical product-quality indicator (Costa et al., 2021).

To mitigate ratoon decline on acidic post-mining soils, future management should consider light post-harvest tillage to refresh the rhizosphere, supplemental organic fertilization to sustain nutrient supply, and optimized N management (rate and split/top-dressing). Where feasible, maintaining an appropriate cutting height (to protect basal buds) and improving soil moisture availability are also recommended (Wang et al., 2024); (Zhou et al., 2022).

The nutritional composition of Bioguma-2 sorghum was influenced by ameliorant treatments (P0–P6) across all harvest stages. The most consistent gain occurred in crude protein (CP), where P6 (humic acid + dolomite + organic compost) had the highest CP at each harvest (13.47–14.04% DM). This percentage is slightly above the figure reported for brown-midrib (BMR) forage sorghum, which averaged at 10.4%, 9.4%, 8.2%, and 8.1% DM at boot, flower, and milk and soft-dough stages, respectively (stage-specific means), and where the BMR trait primarily improves fiber digestibility rather than CP per se (Lyons et al., 2019); (McCary et al., 2020); (Pupo et al., 2022). In sorghum–sudangrass hybrids (SSG) in pasture settings, CP frequently remained less than 13% of DM across seasons and systems (Guretzky et al., 2021). In this study, CP in P6 exceeded 10% of DM, which was similar to the whole-plant sweet-sorghum silage/fresh material (Zhang et al., 2015) but markedly higher than the physiologically mature grain sorghum stover CP at 3.2–5.4% of DM (Tulu et al., 2025). It is evident that combined organic-inorganic ameliorants have raised CP concentration optimally, confirming previous findings that mixed ameliorants enhance N status and overall forage quality with possible fiber/lignin trade-offs affecting digestibility(Colombini et al., 2012).

Dry matter (DM) content also increased with ameliorant application, with P6 consistently having the highest values across stages, although not significantly different from other treatments (p>0.05). This increase may be attributed to improved nutrient availability and soil structure, which enhances biomass production and physiological maturity. These results are consistent with de (Silva et al., 2020), who found that modern sorghum hybrids respond positively to nitrogen fertilization with increased dry matter production and nutrient accumulation. This indicates that the water content of sorghum across treatments was relatively similar. In other words, the application of soil ameliorants enhanced total biomass production, thereby increasing the absolute dry matter yield, but did not alter the proportion of water retained in the plant tissues. Similar DM percentages across treatments suggest that the physiological water status of the plants remained stable despite differences in growth and biomass accumulation.

Ash content, reflecting total mineral accumulation, was significantly affected by treatment and harvest stages. Higher ash concentrations in P4 and P5 during the initial harvest and in P0 and P1 during the second ratoon suggested variations in nutrient uptake dynamics, likely influenced by organic matter interactions and nutrient release rates. These observations align with reports by (Koláčková et al., 2020) that sorghum thrives under variable fertility conditions and that nutrient uptake can be modulated by soil properties and ameliorant types.

Crude fat content showed inconsistent trends across treatments and stages. In the initial harvest, treatments P3–P5 exhibited higher fat content, whereas P6 had comparatively lower values. This suggests that fat synthesis may respond differently to ameliorant combinations, potentially linked to variations in metabolic allocation or plant stress response. By ratoon 2, differences in fat content diminished, indicating stabilization across treatments. Crude fiber (CF) content was the highest in P0 and P3 during the early stages but generally lower in the combined treatments of P4–P6, indicating improved forage quality and potential digestibility benefits. However, Sher et al. (Sher et al., 2022)insist that increased organic input can sometimes raise lignin levels, which may offset digestibility gains despite lower fiber concentrations.

In addition to nutrient composition, the broader adaptability of sorghum should be acknowledged. Sorghum is known for its resilience in suboptimal environments, including dry and nutrient-poor soils (Koláčková et al., 2020). The use of brown midrib (BMR) mutant lines, such as GH2.3, has shown the potential to improve forage digestibility (Wahyono et al., 2023).

These genetic improvements, combined with effective soil management strategies like P6 in this study, could further enhance forage value. Furthermore, while potassium is the most absorbed nutrient by sorghum, it may be unnecessary in soils with adequate K levels (Silva et al., 2020), suggesting the importance of site-specific fertilization strategies.