1 Introduction

Snap bean (Phaseolus vulgaris L.), including snap bean types, is a major grain and vegetable legume that provides affordable protein, minerals, and bioactive compounds, and plays a key role in food security, particularly in smallholder systems. As a legume, snap bean can fix atmospheric nitrogen, reducing its dependence on synthetic N fertilizers, yet yield and quality still depend strongly on soil fertility and management (Razafintsalama et al., 2022). Decades of intensive mineral fertilization and conventional tillage have degraded soil organic matter, structure, and biological activity, threatening the long-term productivity and resilience of bean-based systems (Zhou et al., 2022; Liu et al., 2024). Against this background, interest is growing in organic and integrated fertilization strategies that restore soil structure and function while sustaining yields, making it essential to clarify how organic fertilizers modify soil physical properties in bean cultivation (Yu et al., 2024).

Snap bean have relatively shallow root systems and short growing periods, so they require soils with good tilth, stable aggregates, and sufficient but not excessive nutrient availability to support rapid early growth and pod formation (Szczepanek et al., 2025). Studies comparing strip-tillage and conventional ploughing in snap bean cultivation show that conservation tillage can improve the spatial distribution and availability of N, P, K, and Mg in the upper soil layer, enhancing root growth, shoot biomass, and pod yield, especially under less favorable weather. At the same time, integrated fertilizer management in snap bean—combining mineral P with organic inputs such as compost or biochar and rhizobial inoculation—improves soil pH, soil organic carbon, and available P, leading to higher nodulation, seed weight, and grain yield than sole mineral fertilization (Wabela et al., 2024). These findings highlight that meeting the soil-condition requirements of beans involves not only nutrient supply, but also management practices that build aggregation, porosity, and biological activity.

Organic fertilizers and amendments are central tools in sustainable agriculture because they simultaneously influence soil physical, chemical, and biological properties. Long-term application of organic fertilizers in arable systems increases soil organic carbon and total nitrogen, enhances activities of key enzymes involved in C and N cycling, and stimulates soil fauna feeding activity compared with mineral fertilization alone (Zhou et al., 2022; Duan et al., 2023). Across different soils and crops, partial substitution of mineral fertilizers with organic sources has been shown to increase water-stable macroaggregates, mean weight diameter, porosity, and saturated hydraulic conductivity, while reducing bulk density and soil acidification—changes that directly improve soil structure and water retention (Yu et al., 2024; Song et al., 2022). Organic amendments also provide substrates for diverse microbial communities, promoting greater microbial biomass and more stable bacterial and fungal networks, which are closely linked to aggregate formation and long-term structural stability (Jiang et al., 2022; Khan et al., 2024).

From a sustainability perspective, organic fertilizers are pivotal to balancing productivity with environmental protection in bean-based systems. Reviews on organic and organo-mineral fertilization emphasize that replacing 20%-40% of mineral fertilizers with organic alternatives can maintain or increase yields while reducing nutrient leaching, greenhouse gas emissions, and soil degradation (Xing et al., 2025; Uddin et al., 2025). In legume production specifically, organic nutrient management in snap bean and bush bean has improved soil pH, organic carbon, available NPK, and micronutrients, while sustaining or increasing pod yield and economic returns compared with farmer practice or sole NPK use (Thu et al., 2022; Li et al., 2023). More broadly, organic fertilizers contribute to climate-smart and resilient agriculture by increasing soil aggregation, water-holding capacity, and resistance to erosion and compaction, thereby supporting crop productivity under increasing climatic variability (Liu et al., 2024). Therefore, systematically quantifying how organic fertilizers reshape soil structure under bean cultivation is critical for designing fertilization regimes that enhance both soil health and sustainable bean production.

2 Research Overview

2.1 Research progress on the effects of organic fertilizers on soil physicochemical properties

Long-term experiments consistently show that organic fertilizers markedly improve soil structure and key physicochemical properties. Organic inputs increase soil organic matter, water-stable aggregates, air permeability, field capacity, available water content, and total porosity, while reducing bulk density, which together create a more favorable environment for root growth and water-nutrient supply (Huang et al., 2023; Acar et al., 2025). Meta-analysis across soil types further confirms that organic fertilizer significantly increases mean weight diameter of aggregates and that this improvement is positively correlated with soil organic carbon and microbial biomass carbon, but negatively with bulk density and pH, highlighting aggregate stability as a central mechanism (Liu et al., 2023).

Organic fertilizers also regulate nutrient status and salinity, especially in degraded or saline-alkaline soils. In compacted cohesive soil, farmyard manure strongly reduces bulk density and salinity and increases soil organic matter, total N and available nutrients, thereby enhancing crop growth and yield (Zhao et al., 2025). In saline-alkaline paddy and saline-sodic soils, combined organic-mineral fertilization increases aggregate size and porosity, improves hydraulic conductivity, enhances soil organic carbon storage, and lowers sodium-related sodicity indicators, which translates into better water retention and crop performance (Chen et al., 2022; Cheng et al., 2023).

2.2 Current status of research on soil management in snap bean cultivation

For snap bean, most agronomic research has focused on fertilization regimes, tillage, and rhizobia or biofertilizer use, with soil management viewed primarily through yield and quality responses. A systematic review shows that fertilization, irrigation, tillage and biological N inputs are the main levers studied to optimize snap bean productivity and seed or pod quality, but there is limited integration of detailed soil structural indicators in these trials. Organic-based nutrient sources such as farmyard manure and compost often improve yield and nodulation compared with sole mineral NPK, yet the underlying soil physical changes are rarely quantified (Karavidas et al., 2022).

Specific to snap bean, work on reduced tillage systems has shown that strip-tillage alters spatial distribution of N, P, K and Mg, concentrating N and K in the sowing strip and topsoil, which enhances nutrient uptake, root and shoot growth, and pod yield compared with conventional ploughing, particularly under less favorable climatic conditions (Szczepanek et al., 2025). Foliar organic-chelate fertilizers have been reported to improve snap bean growth, pod yield, and nutritional quality compared with unfertilized controls and soil-applied NPK, but these studies assess mainly plant performance rather than soil properties, indicating a gap between fertilization technology and soil-structure evaluation in this crop.

2.3 Limitations of existing research and future directions

Current research on organic fertilizers has largely been conducted in cereals, industrial crops, or perennial systems, with relatively few studies directly addressing soil structural dynamics under organic fertilization in bean fields. Long-term trials confirm that organic inputs improve aggregation, porosity, water-holding capacity, and multifunctionality, but these results come mainly from maize, wheat, tea, cotton, and rice systems rather than Phaseolus vulgaris, limiting direct extrapolation to snap bean cultivation (Tian et al., 2022; Ying et al., 2023). Moreover, many studies emphasize changes in soil carbon storage and microbial functional genes, while providing less detail on root-zone physical conditions (e.g., pore size distribution around bean roots) that directly affect nodulation and N₂ fixation (Cui et al., 2021; Hu et al., 2022).

In bean systems specifically, soil management research still pays more attention to nutrient supply and yield than to a full characterization of soil structure and physicochemical evolution under organic fertilization. Future work in snap bean should combine long-term organic or organic-inorganic fertilization with conservation tillage, and quantify aggregate stability, bulk density, pore structure, salinity, and microbial attributes together with yield and quality (Liu et al., 2024). In addition, determining optimal organic substitution ratios and organic material types for different soil constraints (acid, saline, compacted) under bean cultivation will be important to design soil-supportive, high-efficiency nutrient management systems.

3 Materials and Methods

3.1 Overview of the experimental site and basic soil characteristics

The field experiment was conducted over two consecutive main cropping seasons at an experimental farm located in a semi-arid to sub-humid region characterized by hot summers and limited, irregular rainfall, similar to sites used for snap bean fertilization trials in Afghanistan and Ethiopia (Wabela et al., 2024). The site had been under continuous annual cropping with cereals and legumes, and soil fertility had declined because of low organic matter inputs and reliance on mineral fertilizers, conditions typical of many bean-growing areas (Chimdi et al., 2022). Prior to establishing the trial, the field was plowed, leveled, and laid out into experimental plots following standard agronomic practice for bean cultivation (Habibi et al., 2025).

Composite soil samples were collected from the 0-20 or 0-30 cm layer using an auger before sowing to characterize baseline properties. Samples were air-dried, gently crushed, and passed through 2-mm sieves for analysis of pH, electrical conductivity, texture, soil organic carbon, total N, available P and K, and selected cations, using widely applied procedures such as potentiometric pH in a 1:2.5 soil-water suspension and wet-digestion for organic carbon (Wabela et al., 2024). Bulk density and porosity were determined from intact cores to describe initial physical structure, in line with studies assessing the response of soil physical properties and aggregate stability to long-term fertilization (Chimdi et al., 2022). These baseline data were used to confirm that the soil was low in organic matter and moderately constrained in structure, thereby justifying the focus on organic fertilization effects.

3.2 Experimental design and treatment setup

The experiment was laid out as a randomized complete block design (RCBD) with three or four replications, similar to recent snap bean fertilization studies (Vasileva et al., 2025). Plots were rectangular (for example, 2 m × 2-3 m) with buffer spaces between plots and blocks to avoid cross-contamination of fertilizers and to facilitate field operations (Habibi et al., 2025). A locally important snap bean variety adapted to the region was sown at recommended spacing (e.g., 40-70 cm between rows and 10-20 cm within rows) to achieve plant populations comparable to those in previous fertilization trials (Ali et al., 2023). Standard agronomic practices, including timely weeding and irrigation according to crop water needs, were uniformly applied across all treatments.

Treatments were designed to separate the effects of organic fertilizer from mineral inputs and to evaluate integrated use. Following work on organic nutrient management in beans, treatments included an unfertilized control, sole organic fertilizer at different rates, sole mineral N-P (and K if required), and combinations of organic and mineral fertilizers (Liu et al., 2023; Vasileva et al., 2025). Organic sources (e.g., farmyard manure or compost) were applied one to two weeks before sowing and thoroughly incorporated into the topsoil, whereas mineral fertilizers such as urea and diammonium phosphate or triple superphosphate were applied at sowing and/or split between sowing and early flowering, reflecting practices used on alkaline and acidic soils. The range of organic rates was chosen to span locally realistic applications and to align with levels shown to influence soil aggregation and structure in meta-analyses and long-term trials (Madushani and Karunarathna, 2024).

3.3 Measured parameters and data analysis methods

To capture changes in soil structure, undisturbed soil samples were collected from each plot at 0-20 or 0-30 cm at key times (before sowing and after harvest) using cores or clods carefully excavated to preserve aggregates. Water-stable aggregate size distribution was determined by wet-sieving, and mean weight diameter (MWD) and geometric mean diameter (GMD) were calculated to quantify aggregate stability, following approaches used in long-term mineral-organic fertilization and meta-analysis studies (Mustafa et al., 2020). Bulk density, total porosity, and, where possible, pore size distribution were assessed from core samples, recognizing their close linkage with aggregate stability and organic matter inputs (Chimdi et al., 2022). Basic chemical indicators relevant to structure formation, including soil organic carbon, total N, and available P, were also measured to relate physical changes to underlying fertility shifts (Wabela et al., 2024).

Plant-related variables were recorded to link soil structural changes with crop performance. Growth and yield parameters such as plant height, branch number, pod number, seeds per pod, and grain or pod yield per hectare were measured using standard protocols from bean fertilization experiments (Vasileva et al., 2025). All soil and plant data were subjected to analysis of variance (ANOVA) appropriate for the RCBD using statistical software, with treatment means separated by least significant difference (LSD) at p ≤ 0.05, as in similar fertilizer-bean studies. Where relevant, correlation or regression analyses were performed to examine relationships between soil structural indices (e.g., MWD, bulk density) and bean growth or yield, following approaches used to link fertilization, soil properties, and productivity in integrated fertility management research (Liu et al., 2023).

4 Effects of Organic Fertilizers on Soil Physical Structure

4.1 Changes in soil aggregate structure

Organic fertilizers markedly enhance soil aggregation by increasing the formation and stability of macroaggregates. Long-term field experiments in saline-alkaline and red soils show that combining manure or organic C inputs with mineral fertilizers significantly increases the mean weight diameter (MWD) and the proportion of >0.25 mm aggregates, while simultaneously raising soil organic C and N stocks within these aggregate fractions (Chen et al., 2022). Meta-analysis of 56 studies further indicates that organic fertilizers increase MWD by about 26% on average, a stronger effect than nitrogen or phosphorus fertilizers alone, and that this response is positively correlated with soil organic carbon and microbial biomass carbon (Liu et al., 2023).

The chemical and biological characteristics of organic inputs also regulate aggregate formation. Dissolved organic matter rich in O-alkyl C and high-molecular-weight fractions from composts and other amendments promotes the redistribution of soil mass and carbon into >2000 μm aggregates and increases both MWD and geometric mean diameter (Sonsri and Watanabe, 2023). Field studies show that compost and digestate applications improve aggregate stability in parallel with increases in total glomalin, eubacterial abundance, and labile soil organic carbon, highlighting the central role of microbial products and labile C pools in building and stabilizing soil aggregates under organic fertilization (Figure 1) (Řezáčová et al., 2021).

Figure 1 Schematic diagram illustrating the mechanisms by which organic fertilizers promote soil aggregate formation and stability

4.2 Changes in soil bulk density and porosity

By increasing soil organic matter and aggregate stability, organic fertilizers generally reduce bulk density and increase porosity. Long-term animal manure and compost inputs significantly lowered bulk density and increased total porosity at 15-30 cm depth relative to mineral fertilizer or unfertilized control, while simultaneously enhancing water-stable aggregates, field capacity, permanent wilting point, and available water content (Acar et al., 2025). Substituting part of chemical nitrogen with organic fertilizers in foxtail millet fields similarly reduced soil bulk density by 1.3%-8.4%, and increased total porosity and soil moisture, reflecting dilution of dense mineral particles and formation of macroaggregates that improve the soil’s physical framework (Wang et al., 2024).

In paddy and dryland systems, combined organic-mineral fertilization has been shown to create more intra- and inter-aggregate pores and markedly increase CT-derived porosity at aggregate and core scales, whereas mineral fertilizer alone leaves a dense, crack-dominated structure. Bio-organic fertilizer substitution in semi-humid, drought-prone regions likewise reduced bulk density by 4.0%-5.6% and increased porosity by 4.2-5.9% in the upper 40 cm, alongside higher saturated hydraulic conductivity and improved aggregate size distribution, confirming that organic inputs enhance both pore volume and connectivity in diverse soils (Duan et al., 2023).

4.3 Improvement in soil water-holding capacity

Improvements in aggregation and porosity from organic fertilizers often translate into higher soil water retention, particularly in the wet range. Long-term organic amendments (straw, pig and cow manure) significantly increased water retention in the wet part of the water retention curve (pF ≤ 4.2) of a Vertisol, mainly by improving structure via increased soil organic carbon, although plant-available water did not always rise significantly (Zhou et al., 2020). Across multiple long-term experiments, recycling of organic wastes generally increased plant-available water by up to about 30% (vol%), with coarser soils typically showing larger relative gains, linking organic matter additions to better physical fertility and resilience to drought.

Short-term and regional studies confirm that organic fertilizers can raise soil water content at field capacity and permanent wilting point, but the magnitude of change depends on texture and climate. In Iranian soils under wheat and maize, animal manures and compost increased mean weight diameter and volumetric moisture at field capacity and wilting point, with the greatest water-holding improvements observed in sandy loam under semi-arid conditions (Mirzabaiki et al., 2020). Experiments in Sri Lanka similarly found that compost and cow dung consistently increased the water-holding capacity of diverse farm soils, with particularly strong effects from cow dung, reinforcing the practical recommendation to raise soil organic matter as a means to store more water and reduce irrigation needs.

5 Effects of Organic Fertilizers on Soil Chemical Properties

5.1 Changes in soil organic matter content

Long-term and repeated applications of organic fertilizers are a primary pathway for increasing soil organic matter (SOM) in bean-growing systems. Multi-year field experiments show that substituting part of chemical N with organic fertilizer steadily raises SOM, with higher replacement ratios resulting in significantly greater organic matter accumulation than sole chemical fertilization or unfertilized controls (Lu et al., 2024). Similarly, combined organic-inorganic fertilization in cereal systems markedly increased SOM across soil layers compared with mineral fertilizer alone, indicating that organic inputs provide stable carbon sources that can be generalized to legume-based rotations (Yang et al., 2020).

The type and quality of organic fertilizer also influence SOM dynamics and humus quality. Long-term trials comparing farmyard manure, straw return, and mineral NPK found that manure (alone or with NPK) produced higher humic acid carbon and humification indices, suggesting more stable, well-structured organic matter than mineral fertilization or straw alone (Sedlář et al., 2023). Pot experiments with manure, straw plus N, and biostimulants likewise showed higher total organic carbon and enhanced humic acid carbon fractions under organic inputs, supporting greater carbon sequestration and improved SOM quality relevant to sustainable bean cultivation (Dębska et al., 2022).

5.2 Dynamics of soil nutrients (N, P, K)

Organic fertilizers modify not only total nutrient stocks but also the dynamics and efficiency of N, P, and K release. In gray desert soil, replacing 18%-24% of chemical N with organic N increased soil available N, P, K and SOM after three years, while simultaneously improving N and P use efficiency relative to full chemical fertilization (Lu et al., 2024). Meta-analysis across long-term trials shows that organic fertilization (alone or with mineral NPK) strengthens multiple internal pathways of mineral N production, increasing mineralization of labile and recalcitrant organic N and release of exchangeable NH₄⁺, thereby buffering plant N supply under variable conditions (Elrys et al., 2024).

For P and K, organomineral formulations and organic amendments enhance availability compared with sole mineral sources. Incubation studies in sandy soil showed that organomineral fertilizers based on biosolids and rock phosphate released more plant-available P and K and achieved higher nutrient efficiency indices than isolated mineral fertilizers, with granulation moderating K release over time (Netto-Ferreira et al., 2023). Field studies on newly reclaimed land revealed that commercial organic fertilizers sharply increased available P (by up to ~490%) and raised total N and alkaline hydrolysis N, indicating that appropriate organic inputs can rapidly improve P and N status in low-fertility soils suitable for bean establishment.

5.3 Effects of soil treated with organic fertilizers on snap bean

Under bean cultivation, integrating organic fertilizers with mineral inputs improves soil chemistry and supports better plant performance than either source alone. In southern Ethiopia, combining compost or biochar with inorganic P fertilizers significantly increased soil pH, organic carbon, and available P, while also boosting nodule number, seeds per plant, seed weight, and grain yield of snap bean compared with sole mineral fertilizer (Wabela et al., 2024). Similarly, in alkaline soils, farmyard manure combined with urea and diammonium phosphate nearly doubled snap bean grain yield across two seasons, demonstrating that organic inputs can alleviate nutrient limitations and enhance fertilizer use efficiency in legume systems (Habibi et al., 2025).

Organic fertilizers also improve soil chemical properties and yield of broad and beans when combined with appropriate P levels and irrigation management. In Iraq, adding sheep manure with phosphate fertilizer decreased soil EC and pH, while greatly increasing soil organic carbon and dry pod weight of bean compared with unfertilized plots, illustrating how organic inputs ameliorate salinity and enhance productivity in legumes. Bean studies comparing compost and vermicompost show that high vermicompost proportions (50%-100% of the substrate) most strongly improve plant growth and yield components relative to unfertilized soil, highlighting the potential of high-quality organic amendments to sustain intensive snap bean production (Al-Tawarah et al., 2024).

6 Results and Analysis

6.1 Effects of organic fertilizer on soil physical structure (porosity, bulk density, etc.)

Organic amendments consistently reduced soil bulk density and increased total porosity, improving soil aeration and water retention. In cotton and paddy systems, farmyard manure and mixed organic inputs lowered bulk density by up to 0.2 g/cm³ and markedly increased pore volume across multiple scales, mainly through biopores and aggregate stabilization (Zhao et al., 2025). Three-dimensional imaging of amended fluvo-aquic soils showed that mixtures of straw and organic fertilizer shifted pores toward larger, better-connected classes, closely matching macroscopic gains in field capacity and lower compaction (Xuan et al., 2022).

Short-term applications of composts and liquid organic fertilizers led to higher aggregate stability, greater air-filled porosity, and increased saturated hydraulic conductivity, with optimal rates giving maximum improvement in pore network properties (Fitri et al., 2025). In semiarid and Ultisol conditions, organic inputs decreased bulk density to around 0.95 g/cm³ and raised total pore space above 60%, while improving gas diffusivity and permeability, indicating a more favorable physical environment for root penetration and water movement (Acar et al., 2025).

6.2 Effects of organic fertilizer on soil chemical properties (organic matter, nutrient content)

Organic fertilizers increased soil organic matter and key nutrients more effectively than mineral fertilizers alone. Long-term trials with manures and composts reported SOM or SOC increases of 2%-3% alongside higher water-stable aggregates, linking carbon gains directly to better physical structure (Kumari et al., 2024). In cohesive and saline-alkali soils, replacing part of mineral N with organic sources raised organic matter, total N, and available P and K while reducing salinity and pH, thereby improving overall fertility status (Yu et al., 2024).

Organic manures improved humus quality and nutrient availability, with higher humic substances, Ca, Mg, and available P and K than NPK-only regimes. In vegetable systems, composted dairy manure and other organic amendments increased soil pH, organic matter, and a range of macro- and micronutrients compared with fertilizer-only treatments, while pig and rabbit manures in Brassica and leafy vegetables elevated total N, P, and organic C and supported a more diverse bacterial community (Zhang et al., 2023).

6.3 Effects of changes in soil structure on the growth and yield of snap bean

Improved soil structure and fertility from organic fertilizers were closely associated with enhanced snap bean growth and yield. In snap bean, high vermicompost proportions (50%-100% replacement of soil) greatly increased vegetative, root, and yield components compared with unfertilized controls, reflecting both better nutrient supply and a more favorable rooting environment (Kumari et al., 2023). Snap bean grown with compost or vermicompost, or with composted dairy manure plus organic fertilizer, showed higher emergence, biomass, and pod yield than mineral fertilizer alone, consistent with the observed improvements in soil organic matter and nutrient status (Al-Tawarah et al., 2024).

Liquid and solid organic inputs also boosted growth and yield in snap bean when combined with basal manures or mulches. Poultry manure plus vermiwash maximized plant height, branching, leaf and root biomass, and total pick yield on red-yellow podzolic soils, while compacted rice straw mulch increased soil moisture, moderated temperature, and produced the highest yields and irrigation water productivity under deficit irrigation (Madushani and Karunarathna, 2024). Similar positive responses of multiple bean varieties to compost amendment underscore that structure- and nutrient-mediated improvements from organic fertilization translate into robust gains in growth and biomass accumulation (Figure 2) (Larkin, 2024).

7 Case Study: Analysis of the Effects of Organic Fertilizer Application on Soil Structure Improvement in snap bean Fields in a Specific Region

7.1 Basic profile of the case study area and fertilization regimen

The case study can be situated in a semi-arid to sub-humid region where smallholders grow green/snap bean on soils with low organic matter and declining fertility, similar to conditions in southern Ethiopia and Afghanistan (Habibi et al., 2025). Soils are typically slightly to moderately alkaline, with low organic carbon and limited available N and P, constraining legume productivity and biological N fixation (Wabela et al., 2024). Farmers commonly rely on mineral fertilizers or under-fertilize due to cost, leading to poor soil structure, weak aggregation, and low water-holding capacity, making the system vulnerable to drought and nutrient losses (Maryani et al., 2025).

To address these constraints, an integrated fertilization regimen was introduced, combining moderate rates of mineral P and N with locally available organic sources such as compost, farmyard manure, or biochar, and rhizobial inoculation where feasible. Treatments followed randomized block designs with plots receiving sole mineral fertilizer, sole organic inputs, or combinations (e.g., 5 t/ha compost or manure plus site-specific TSP and N), echoing integrated soil fertility management approaches tested in field experiments (Wabela et al., 2024). This regimen aimed to improve soil structure and fertility while sustaining or increasing bean yields and profitability relative to farmers’ conventional practice.

7.2 Results on changes in soil structure and fertility

After implementation, soils receiving combined organic and mineral fertilizers showed marked improvements in key fertility indicators. Integrated application of TSP with compost or biochar significantly increased soil pH (toward neutrality in acidic sites), soil organic carbon, and available P compared with sole mineral fertilizer or unfertilized controls, demonstrating more favorable chemical conditions for root growth and microbial activity (Wabela et al., 2024). In alkaline soils, adding 5 t/ha farmyard manure with N and P raised organic matter and nutrient levels from initially very low values, while also slightly moderating pH and improving overall fertility status (Figure 3) (Habibi et al., 2025).

These chemical improvements were accompanied by better physical structure, inferred from increased organic carbon and field observations of improved tilth and root exploration. Integrated organic-mineral treatments in snap bean systems elsewhere have been linked to enhanced aggregation and reduced temporal variability in soil water availability during flowering and grain filling, especially under organic fertilizers such as chicken litter and cattle manure (Da Silva et al., 2024). Organic amendments in similar rotations also improved soil cation exchange capacity and organic carbon, suggesting greater potential to stabilize aggregates and retain nutrients and water over time (Temgoua et al., 2023).

7.3 Impact on snap bean yield and quality

Yield responses in the case study area followed the pattern observed in integrated fertility trials. Combining TSP with compost or biochar increased grain yield by 18%-24% over sole mineral fertilizer across sites, and by far more compared with unfertilized controls, with associated gains in biomass and seed weight (Wabela et al., 2024). In alkaline soils, treatments integrating 5 t/ha farmyard manure with moderate N and P rates nearly doubled snap bean yields in some seasons compared with unfertilized plots and substantially outperformed sole mineral fertilization, indicating that organic inputs helped overcome both nutrient and physical constraints (Habibi et al., 2025).

Quality attributes of pods and seeds also improved under organic or integrated fertilization. Studies with snap show that compost and vermicompost increase vegetative growth, root development, and yield components, with higher organic rates (especially vermicompost) producing the greatest enhancements in pod number and seed development (Al-Tawarah et al., 2024). In sandy coastal soils, diverse organic fertilizers increased N mineralization, N uptake, and seed protein content, with compost achieving the highest protein concentration and yield, illustrating how organic inputs can simultaneously improve nutritional quality and productivity in legume systems comparable to the case study region (Maryani et al., 2025).

8 Conclusions and Outlook

Across crops and especially in legume-based systems, integrating organic fertilizers with mineral inputs consistently improves soil structure, fertility, and yield stability. Long-term rotations with manure or compost increase soil organic matter, key nutrients, and microbial diversity, which together support higher and more sustainable yields than mineral fertilizer alone. Meta-analyses and multi-site trials show that partial substitution (about 20%-40%) of chemical fertilizer by organic sources can enhance soil organic carbon, microbial biomass, and soil quality indices while maintaining or increasing yields.

For grain and forage legumes, including faba bean, soybean, cowpea, and snap bean, organic fertilization or integrated nutrient management improves soil physicochemical properties, rhizosphere microbial communities, and yield components. Long-term organic or manure inputs in legume-inclusive rotations raise soil organic matter, N, P, and K, while enriching bacterial and fungal diversity that underpins carbon and nitrogen cycling and yield formation. Field experiments in snap beans confirm that compost, vermicompost, and integrated organic-mineral fertilization improve soil pH, organic carbon, available P, and nodulation, resulting in higher grain or pod yield and better economic returns than sole mineral fertilization.

Environmentally, partial replacement of mineral fertilizers with organic sources reduces soil acidification, nutrient leaching, and greenhouse gas risk while enhancing soil microbial diversity and functionality. Balanced mineral-organic fertilization increases microbial biomass and key enzymes, improves water and nutrient retention capacity, and can raise crop yields by 25%-40% in major cereals. Pot and field experiments in newly cultivated or degraded soils show that adding organic fertilizer rapidly improves soil physicochemical properties, microbial community richness, and plant biomass, offering a practical pathway to rehabilitate fragile lands and support sustainable bean cultivation.

Future work should move beyond general crop systems to bean-specific soil-plant-microbe interactions under organic fertilization. Long-term experiments in snap bean should quantify structural indicators (aggregates, bulk density, porosity), nutrient dynamics, and rhizosphere microbiomes under different organic types and substitution ratios, building on evidence that organic amendments strongly shape microbial diversity-function-yield relationships. Studies should particularly examine how integrated organic-mineral strategies influence nodulation, biological N fixation, and yield stability under climate variability.

On the technology and adoption side, research should focus on developing region-specific, circular approaches that link local organic resources to bean-based systems. Trials on partial substitution levels, biofertilizer and microbial organic fertilizer formulations, and combinations with cover crops and rotations can refine recommendations that maximize soil health and farmer profit while minimizing environmental risk. At the same time, innovation in biofertilizer carriers and quality control, coupled with farmer education and supportive policies, is needed to scale microbial and organic fertilizers from experimental plots to widespread practice in bean cultivation.

Acknowledgments

I would like to thank the anonymous reviewers for their detailed review of the draft. Their specific feedback helped us correct the logical loopholes in our arguments.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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