Turning Waste into Fertilizer: Aloe vera Leaf Shavings Improve Plant Growth and Support Soil Fertility in Organic Systems

Abstract

The Aloe vera industry discards large amounts of outer leaf tissue (“shavings”), creating an opportunity to repurpose this byproduct as a sustainable fertilizer. This study evaluated whether aloe shavings can serve as a plant-based alternative to compost in organic Aloe vera production. A field trial in the Lower Rio Grande Valley of Texas tested three treatments: aloe shavings (applied to supply 39 kg N ha⁻¹), organic compost (39 kg N ha⁻¹), and a non-fertilized control. Laboratory incubations further assessed nitrogen mineralization and microbial respiration. Aloe shavings significantly enhanced vegetative growth: leaf number increased from 5.7 to 12.3 leaves per plant (+115% over the season), and leaf length rose from 20 to 32 cm, with the greatest gains in September and March (p < 0.05). At harvest, plants receiving aloe shavings produced 456 g total leaf weight and 151 g gel weight per plant, compared to 375 g and 108 g in the control. Incubations showed initial nitrogen immobilization (negative mineralization) but subsequent slow release, while microbial respiration was higher in compost (2.3 mg CO₂-C kg⁻¹ day⁻¹) than aloe shavings (1.4 mg CO₂-C kg⁻¹ day⁻¹). These results highlight aloe shavings as a low-cost, slow-release organic amendment that reduces waste, supports circular economy practices, and enhances Aloe vera growth without mineral nitrogen addition.

1. Introduction

Global Aloe vera production is estimated to be between 300,000 and 500,000 tons annually, with average yields ranging from 2 to 5 tons per hectare, which are strongly influenced by climatic conditions and agricultural practices [1,2]. The global Aloe vera market was valued at USD 890 million in 2024, with projections to grow to USD 1.53 billion by 2033 [1]. This strong market growth is directly related to its bioactive compounds, but also to the species’ adaptive characteristics, which allow it to thrive in different regions and climatic conditions [1].

In the United States, approximately 2000 acres of Aloe vera are cultivated, with the majority of production concentrated in the Lower Rio Grande Valley (LRGV) of Texas, near the U.S.–Mexico border [3]. This region offers optimal conditions for Aloe vera growth, and the crop plays an important role in the local agricultural economy. Consumer demand for organic Aloe vera products continues to rise, making organic production a necessity for growers.

Several studies have shown that organic fertilization of Aloe vera can enhance growth, yield, and nutritional quality. The authors of [4] reported that the application of organic compost, alone or combined with humus, significantly increased leaf length and width, dry matter, and N and S contents, with responses varying by site. Similarly, [5] observed yield improvements under arid conditions with organic fertilizer, with or without foliar application of Aloe vera extract. Complementing these findings, [6] demonstrated that the combined application of vermicompost and nitrogen maximized growth and sucker production.

Organic fertilizers applied during the growing season should contain nutrients readily available to plants. A commonly used option is animal waste slurry, valued for its high nutrient content; however, its use poses significant risks of microbial contamination [7,8], prompting organic producers to seek safer alternatives.

In this context, the Aloe vera industry, which currently focuses on extracting the inner gel of the leaves and discards the outer leaf tissue (“shavings”), could benefit from repurposing these byproducts as a nutrient source. Such residues have the potential to gradually release nutrients, improve soil properties, and reduce sanitary risks, while also lowering external input costs and enhancing the sustainability of Aloe vera production systems. Through a field trial, we investigated whether nitrogen (N) contributions from aloe shavings can support plant growth and soil health similarly to conventional organic compost. Given the importance of N for leaf production in Aloe vera, the study specifically assessed the timing and extent of nitrogen mineralization from shavings, as well as their impact on key indicators of soil quality. By evaluating nutrient dynamics and crop performance, this work aimed to determine whether post-processing Aloe vera residues can serve as a viable, plant-based fertilization strategy in organic systems.

2. Materials and Methods

2.1. Field Trial

2.1.1. Site Description

This study was conducted in San Benito, Texas, on the growing fields of Aloe Laboratories, Inc. Aloe Labs cultivates on USDA Organic Certified cropland. The study plot was located on 26°05′16.6′′ N 97°41′51.8′′ W. According to the USDA-NRCS’s Web Soil Survey, the singular soil map unit name in the study plot is a “LAA- Laredo silty clay loam 0 to 1 percent slopes, rarely flooded” [9]. However, a soil texture analysis yielded a percent composition of 12:37:51 (sand: silt: clay) via the hydrometer method. A baseline bulk density of 0.81 g cm⁻³ and a pH of 8.09 were also determined for the soil via a centralized location on the study plot.

The entire operation is flood irrigated from valves located at the corners of each field via laid out “poly-pipe”. Irrigation is supplied from 1 to 4 times per year, depending on the local water supply. In addition, according to Web Soil Survey, the field is characterized as a Loamy Bottomland ecological site, within a subtropical/subhumid climate averaging about 600 mm of precipitation a year.

Aloe vera plants were arranged in single rows with a uniform spacing of 0.45 m between plants and between rows. Field irrigation was applied twice during the experimental period, in October 2021 and February 2022. Weed management in the plots was performed manually and mechanically, using a tractor-pulled shredder operated by the Aloe Labs farm manager, as needed.

2.1.2. Experimental Design

The experimental treatments consisted of two organic fertilization methods (Aloe shavings and organic compost) and a non-fertilized control, distributed across 12 plots (6.10 m × 11.89 m each). A 3.05 m buffer zone was maintained between plots to minimize cross-contamination among treatments. The study followed a randomized complete block design (RCBD) with four replications. Each block contained one replicate of each of the three treatments (control, Aloe shavings, compost), arranged randomly within the block. Blocks were oriented along the field to account for potential variability in soil and irrigation distribution, thereby reducing environmental bias.

2.1.3. Fertilization Treatments

The treatments included a non-fertilized control (C), Aloe shavings (A.S.) obtained from post-production Aloe leaves, and an organic compost (O.C.) derived from Black Kow^® Cow Manure (0.5:0.5:0.5 N:P:K). The organic compost application rate was determined based on Aloe Labs’ historical fertilization practice of 39 kg N ha⁻¹, 25 kg P ha⁻¹, and 34 kg K ha⁻¹. Because it was not possible to match nitrogen, phosphorus, and potassium simultaneously, nitrogen was used as the reference nutrient, and Black Kow was applied at 0.785 kg m⁻². The Aloe shaving application rate was estimated from the average crude protein concentration in the rind (1.01% N) [10], resulting in 0.389 kg m⁻². No amendments were added to the control treatment. All fertilization materials were incorporated to a 15 cm depth and left to stabilize for 2 weeks prior to planting.

2.1.4. Aloe Shavings Source and Preparation

Mature outer Aloe vera leaves are typically harvested by hand and transported within a few hours to processing facilities to prevent gel oxidation and degradation. At the facility, leaves are washed to remove soil and debris before undergoing filleting, a process in which the green outer rind and the aloin-containing latex layer are separated from the inner gel. The gel is then crushed or ground into a pulp for commercial use, while the rind and latex residues constitute the byproduct commonly referred to as “shavings.” For this study, Aloe shavings were obtained from a local processor (Aloe Laboratories, Inc., Harlingen, TX, USA), ground and homogenized, weighted, and then applied by hand to the designated plots at the calculated application rate. The Aloe shavings were applied directly into furrows and incorporated to a depth of 15 cm with soil.

2.1.5. Soil Sampling

Over the duration of the study, soil was sampled from each plot at a depth of 15 cm using a standard soil sampling probe. Collection began with baseline samples on 30 March 2021, prior to the amendment and transplanting of Aloe vera, for the purpose of obtaining reference physical and chemical soil characteristics relating to soil health for each plot. On 11 June 2021, and monthly from thereafter until May 2022, samples were collected to periodically analyze the effects of the fertilization treatments on the soil. Samples were collected for each plot by taking one sub-sample from the middle of each row and combining them to create one composite sample for each plot. No sampling was conducted in December 2021 due to restricted access to the farm facilities during the holiday closure period.

2.1.6. Monthly Soil Analyses

Gravimetric soil moisture content was determined using the oven-drying method, in which soil samples were collected and dried at 60 °C for 48 h. Moisture percentage was calculated based on the difference between field moist and oven-dried weights.

Soil from each plot was analyzed for pH using a 1:1 soil-to-deionized water ratio (5 mL water to 5 g soil). The suspensions were agitated on an orbital shaker for 1 h and centrifuged for 5 min to separate the liquid phase, allowing for accurate measurements with a Vernier^® electrode pH probe (Beaverton, OR, USA).

Soil nitrate (NO₃⁻) and ammonium (NH₄⁺) were extracted by adding 50 mL of potassium chloride (KCl) solution to a 50 mL Falcon tube containing 10 g of soil from the corresponding subplot sample. Tubes were moderately agitated on an orbital shaker for 1 h and subsequently filtered through Whatman No. 42 filter paper to obtain a clear KCl extract.

NO₃⁻ quantification was performed by colorimetric spectrophotometry based on the modified Griess reaction, following the method described by [11].

[NO₃⁻-N] = (A540 − A_blank)/slope

(1)

where A₅₄₀ is the absorbance of the sample, A_blank is the absorbance of the reagent and KCl (extractant solution), and slope is the slope of the standard curve (absorbance per ppm of nitrate). The method detection limit (MDL) was estimated to be approximately 0.1 ppm N.

NH₄⁺ concentration was determined by colorimetric spectrophotometry based on the salicylate–hypochlorite reaction, following the method described by [12] Kempers & Zweers (1986). NH4+ concentration in the soil (NH₄⁺-N) was expressed in mg kg⁻¹, calculated based on the absorbance measured at 650 nm and the standard calibration curve. The concentration was calculated using the following equation:

NH₄⁺–N (mg kg⁻¹) = (C × V_extract)/M_soil

(2)

where

C = NH₄⁺ concentration obtained from the standard curve (mg L⁻¹ or mg NH₄⁺-N L⁻¹)

V_extract = total volume of the extract (L)

M_soil = mass of dry soil used in the extraction (kg)

Total inorganic N was calculated by summing the NO₃⁻ and NH₄⁺ concentrations, expressed as µg N per g of soil, for each plot and sampling month.

2.1.7. Monthly Plant Monitoring

Measurements of plant performance traits were conducted monthly. In each plot, five Aloe vera plants were randomly selected (one per row within the plot) for evaluation. The length of the tallest leaf was measured in centimeters, from the point of attachment at the posterior plant base to the leaf apex. The central width of the same leaf was measured at the midpoint along the total leaf length. The total number of leaves per plant was also counted, including dead or senescent leaves.

In May 2022, after 12 months of cultivation, these five plants were harvested from each plot. For each plant, total fresh weight (g), total leaf weight (g), and extracted gel weight (g) were recorded using a precision digital balance (minimum resolution of 0.1 g). Gel extraction was performed in the laboratory by filleting the leaves with a stainless steel knife and carefully removing the internal gel with a plastic spatula. The extracted gel was placed in plastic containers. Aloin, a compound considered toxic and typically removed from commercial Aloe products, was drained as thoroughly as possible from the leaves prior to placing the gel in the containers. The gel content was individually weighed using an analytical balance, and results were expressed in grams per plant.

2.2. Laboratory Incubations

2.2.1. Sample Collection and Preparation

Unfertilized soil samples were collected from the experimental site and transported to the laboratory, and they were sieved through an 8 mm mesh to remove coarse particles. The amendment rates for the incubation experiment were scaled to reflect the relative application rates used in the field, ensuring comparable nutrient inputs across treatments. Soil moisture was adjusted by adding 500 mL of deionized water per bucket, ensuring homogeneous water distribution. These mixtures were used for microbial respiration and nitrogen mineralization analyses under a completely randomized design.

2.2.2. Quantification of Nitrogen Mineralization

A total of 18 sealed Ziplock^® bags were prepared, with six replicates per treatment, each containing 100 g of soil. Over 14 consecutive days, 10 g soil samples were collected daily from each bag. The samples were extracted with 50 mL of 2 M KCl solution and agitated at medium speed for 1 h. The extracts were filtered through Whatman No. 42 filter paper and stored in labeled polyethylene Falcon tubes, then frozen to preserve stability prior to analysis. NH₄⁺ concentrations were determined following the method described in Section 2.1.5.

2.2.3. Microbial Respiration

Microbial activity was also estimated by measuring soil respiration, expressed as the production of carbon dioxide (CO₂) from the samples. Glass jars (473 mL) were hermetically sealed and filled with 20 g of soil mixture corresponding to each treatment. Each soil sample received 5 mL of distilled water and was immediately sealed. Five replicates were prepared per treatment, along with four additional jars containing only air (blank controls).

Gas samples (3 mL) were collected daily from each jar using graduated glass syringes and transferred to 12 mL evacuated exetainers (Labco^® Limited, Lampeter, UK) pre-filled with 12 mL of nitrogen gas (N₂) to maintain the overpressure of the exetainers. After 11 consecutive days of sampling, CO₂ concentrations were determined using thermal conductivity (TCD) gas chromatography (Agilent^® 8860 GC System gas chromatograph, Santa Clara, CA, USA), equipped with a Carboxen 1006 PLOT capillary column. The column, injector, and detector temperatures were set at 180 °C, 90 °C, and 230 °C, respectively. Results were expressed as mg CO₂-C kg⁻¹ soil day⁻¹.

2.3. Statistical Analysis

Plant and soil-related parameters were analyzed using linear models, as the data did not meet the assumptions required for ANOVA. To stabilize variance and improve normality, a Box–Cox transformation was first applied to each variable. The optimal transformation parameter (lambda) was estimated using an intercept-only linear model and applied to all values. Linear models were then fitted separately for each sampling month with fertilizer treatment as a fixed effect. Pairwise comparisons between fertilizer treatments were conducted using Tukey’s adjustment for multiple comparisons via the emmeans package version 1.11.2-8.

Nine correlation matrices were generated for the monthly data to analyze relationships among agronomic and soil health variables. For the harvest data, four correlation matrices were constructed to assess associations among yield-related parameters of Aloe vera. Additionally, principal component analysis (PCA) was applied to both monthly and harvest datasets to visualize variable groupings and evaluate the proportion of explained versus unexplained variability, potentially linked to external factors such as climatic conditions.

Cumulative ammonium mineralization and microbial respiration rates were analyzed by one-way ANOVA, followed by Tukey’s test for pairwise comparisons among treatments. All statistical analyses were conducted using R software (version 4.3.1) within the RStudio environment (version 2023.6.1.524).

3. Results and Discussion

3.1. Monthly Plant Monitoring

Figure 1A illustrates the monthly average number of Aloe leaves per treatment throughout the study. The number of leaves increased from approximately 5.7 leaves in June 2021 to 12.3 leaves in May 2022. Significant differences among treatments were observed in September, where the aloe shavings treatment outperformed the organic compost treatment. Over the remaining months, no statistical differences were detected.

A similar trend was observed for the length of the tallest Aloe leaf (Figure 1B), which increased from around 20 cm in June 2021 to 32 cm in May 2022. Significant differences were also detected in September 2021 and March 2022, with the aloe shavings treatment showing the highest means. No significant differences were found in the other months.

Figure 1C shows the monthly average width of the tallest Aloe leaf. Width remained within 3.3–4.0 cm during most of the production cycle; however, significant differences were observed in August 2021 and October 2021. In the other months, no significant differences were found. These results suggest that nutrient release through the decomposition of aloe residues contributed positively to vegetative development, consistent with Aloe’s long growth cycle and low nutrient requirements [13].

Table 1. Cumulative Aloe Harvest Data Under Organic Fertilization: Leaf Number, Total Weight, and Gel Yield per plant.

Fertilizer	Leaf Weight	Leaf Gel Weight	Extracted Leaf Weight
	Grams Per Plant	Grams Per Plant	Grams Per Plant
Control	374.9 ± 45.1	107.8 ± 39.6	261.9 ± 41.4
Aloe Shavings	455.5 ± 75.7	150.8 ± 63.4	362.8 ± 81.9
Organic Compost	452.6 ± 235.2	141.8 ± 82.5	358.8 ± 168.3

Within columns, mean (±standard deviation) values followed by the same letter were not significantly different by the minimum significant difference (MSD) of Tukey’s test at p = 0.05.

presents the cumulative Aloe harvest data for the parameters leaf gel weight, total leaf weight, and extracted leaf weight. Although our experimental results did not show statistically significant differences among treatments in terms of cumulative leaf weight, gel weight, or extracted leaf weight (p = 0.05) [14], demonstrated that the combination of 75% poultry manure and 25% inorganic fertilizer significantly increased fresh leaf and gel weight in Aloe vera, with up to 153% yield improvement compared to the control. The study also found that fresh gel weight was positively correlated with plant height, number of leaves, leaf area, and fresh leaf weight, correlations that were also significant in the present study.

Monthly measurements of nitrate, ammonium, and pH revealed no significant differences among fertilizer treatments; therefore, these data are not presented. Given this lack of treatment effect, a correlation analysis was subsequently conducted to explore potential relationships between soil attributes and plant growth variables. This approach aimed to identify underlying associations that could help explain variations in Aloe vera performance, independent of treatment effects.

Figure 2 presents a correlation matrix showing the relationships between soil health indicators (inorganic nitrogen, pH, and soil moisture; x-axis) and Aloe growth parameters (y-axis). Five correlations were highly significant (p < 0.001): pH and inorganic nitrogen were both positively correlated with the average number and width of leaves, while soil moisture showed a significant negative correlation with average leaf length. In contrast, three comparisons were not statistically significant: soil moisture (%) vs. average number of leaves, pH vs. average leaf length (cm), and soil moisture (%) vs. inorganic nitrogen (µg N g soil⁻¹).

A significant positive correlation was observed between average leaf length and inorganic nitrogen concentration in the soil, indicating that an increase in inorganic N availability favors leaf elongation in Aloe vera. This highlights the central role of N in photosynthesis and vegetative tissue development [15], with consistent positive associations across all measured growth parameters. Likewise, soil pH was positively correlated with leaf number, aligning with Aloe vera’s known preference for slightly alkaline soils [16,17].

Neutral pH soils are more suitable for the cultivation of Aloe vera, as observed by [18], since they may promote superior leaf production. In this pH range, nutrients such as calcium (Ca), magnesium (Mg), and molybdenum (Mo), essential for plant growth, become more available [19]. In addition, nitrogen in the form of nitrate, which is preferentially absorbed at higher pH, becomes more available, supporting protein synthesis and vegetative tissue development [20].

Figure 3 presents a cross-comparison matrix of each Aloe harvest parameter evaluated at harvest. Each parameter was correlated with the others to assess statistical significance. Two comparisons showed highly significant correlations (p < 0.001): total leaf weight (g) vs. total leaf gel weight (g), and total leaf weight (g) vs. total extracted leaf weight (g). One comparison was not statistically significant (–): total number of leaves vs. total leaf gel weight (g). One comparison showed statistical significance (p = 0.05): total number of leaves vs. total extracted leaf weight (g). Total leaf number exhibited a weak positive correlation with extracted leaf weight, suggesting that leaf production alone does not necessarily result in greater useful biomass yield. On the other hand, a strong positive correlation was observed between total leaf weight and both total leaf gel weight and total extracted leaf weight, indicating that the accumulation of leaf biomass is directly associated with gel productivity, which is the main product of interest in Aloe vera cultivation. These results suggest that leaf size and thickness, rather than merely the number of leaves, are key factors determining final yield.

The PCA biplot based on the monthly Aloe growth parameters and soil health indicators is presented in Figure 4A. The results indicate that 48.6% of the variability in the dataset was explained, while only 15.7% was attributed to unknown and/or untested factors.

Soil moisture, leaf length, and nitrate content were inversely positioned on the biplot, indicating that these variables are positively associated. This suggests that as soil moisture increases, both leaf length and soil nitrate levels also increase. In contrast, other variables, such as soil pH, leaf number, leaf width, ammonium, and inorganic nitrogen, were grouped together, indicating that changes in one of these factors tend to be accompanied by changes in the others.

It is important to highlight that parameters such as inorganic nitrogen, soil moisture, and pH are widely recognized as key indicators of soil health, as they directly influence nutrient availability, biological activity, and plant growth [21,22]. Inorganic nitrogen, in the forms of NO₃⁻ and NH₄⁺, represents the plant-available forms of nitrogen in the soil and serves as a proxy for short-term soil fertility status. While they do not directly measure the soil’s capacity to mineralize organic matter, their concentrations can reflect recent mineralization events or nitrogen inputs. Recent studies emphasize the importance of nitrogen indicators in monitoring soil health and guiding sustainable fertility management [23,24].

Soil moisture is critical for microbial activity, seed germination, and nutrient uptake by plant roots. It also reflects the soil’s physical structure and organic matter content [25] Soil pH regulates the solubility of macro- and micronutrients and influences the composition of the soil microbiome, being considered one of the most sensitive parameters to chemical imbalances [26]. Therefore, the observed correlations between these soil attributes and the morphophysiological traits of the plants reinforce their role as functional indicators of soil quality in sustainable production systems.

Figure 4B presents the PCA biplot summarizing the Aloe harvest data collected at the end of the study. The first principal component (Dim1) explained 84.5% of the total dataset variability, while the second component (Dim2) explained an additional 12.8%, indicating that together, these two components captured the majority of the observed variability. The biplot reveals a strong association among total leaf weight, extracted leaf weight, and total leaf gel weight, as evidenced by the similar direction and close proximity of their vectors. This suggests that these three variables are positively correlated and contribute similarly to the variability in the dataset. In contrast, the vector for the total number of leaves points in a different direction, indicating a weak correlation with the other variables and suggesting that leaf number is largely independent of leaf weight and gel content in this dataset.

The harvest data reinforce the trend that more vigorous plants (with greater leaf number and leaf weight) exhibited higher gel and total extractable weight, a parameter of particular relevance to the Aloe vera processing industry. The correlation between the total number of leaves and gel weight was not statistically significant (p = 0.05), but showed a positive trend, indicating potential increases with larger sample sizes or longer experimental duration.

3.2. Laboratory Incubations

Figure 5 illustrates the effects of different soil amendments (control, aloe shavings, and compost) on (A) mineralization rates and (B) soil respiration rates. In Figure 5A, compost-treated soil exhibited a significantly higher NH₄⁺ mineralization rate (p = 0.05) compared to the other treatments, indicating greater nitrogen release from organic matter decomposition. In contrast, the aloe shavings treatment showed negative mineralization values, suggesting net nitrogen immobilization. This pattern likely results from microbial assimilation of available nitrogen during the initial decomposition of Aloe vera residues, which are rich in carbon and stimulate bacterial growth, temporarily sequestering nitrogen from the soil solution.

In Figure 5B, soil respiration rates, an indicator of microbial activity, were also significantly higher in the compost treatment (p = 0.05), with no significant differences between the control and aloe shavings treatments. Although aloe shavings did not increase microbial respiration compared to the control, the observed nitrogen immobilization suggests active microbial colonization and ongoing decomposition processes.

These results indicate that, although aloe shavings may initially reduce nitrogen availability due to microbial immobilization, they may serve as a slow-release nitrogen source, offering potential benefits for long-term soil fertility management. This gradual mineralization pattern may better align with the long-term nutrient demands of Aloe vera, providing a more efficient nitrogen supply and reducing the risk of nitrogen losses through leaching, as evidenced by the increased number of leaves and greater leaf length observed in the field trial. Therefore, while compost provided a nutrient pulse associated with higher microbial respiration, Aloe shavings functioned more as a slow-release amendment. This distinction is particularly relevant for Aloe vera cultivation, where nutrient requirements are modest and spread across a long growth cycle. Under such conditions, the gradual nutrient release from shavings may be more beneficial than the rapid mineralization observed in compost.

From a biogeochemical perspective, the decomposition of aloe biomass occurs relatively slowly, likely due to its complex structural composition, rich in mucilages, fibers, and bioactive compounds such as polysaccharides and phenolics [10,27]. During this process, soil microorganisms utilize the organic compounds as energy sources, slowly converting them into mineral forms of nitrogen, phosphorus, and other essential nutrients [28]. The slow and continuous release of nutrients, especially ammonium, prevents sharp concentration peaks in the soil, promoting a more stable supply that better matches the nutrient uptake rate of Aloe vera. This represents an efficient strategy under conditions of low irrigation frequency [29,30].

Furthermore, the nitrogen mineralization dynamics, particularly the initial immobilization promoted by aloe residues, suggest that these residues act as a slow-release nutrient source [30,31]. This behavior may be particularly beneficial in agricultural systems with infrequent irrigation, such as those in the Lower Rio Grande Valley. Under these conditions, gradual nutrient release tends to be better synchronized with plant needs, reducing leaching losses and improving nitrogen use efficiency [29].

Soil respiration data revealed increased microbial activity in the organic compost treatments compared to the control and aloe shavings (Figure 5B). This observation is consistent with findings by [31], who demonstrated that compost and biochar amendments stimulated microbial respiration under sweet potato cultivation in a subtropical semiarid region. Respiration observed in the aloe shavings treatment indicates microbial activation and progressive decomposition of the fresh plant. This decomposition is associated with partial nitrogen mineralization, resulting in moderate NH₄⁺ release, which was lower than in the compost treatment but sufficient to sustain crop growth. This pattern is consistent with the literature, which links moderate mineralization rates to residues with intermediate C/N ratios [32].

The use of these residues, in addition to promoting improved agronomic performance, reduces the need for external inputs and minimizes environmental impact. This approach aligns with regenerative and low-cost practices, especially relevant for smallholder farmers. The fact that Aloe shavings do not require prior composting increases their practical applicability by reducing preparation time and costs [33]. Because Aloe shavings are typically discarded by the industry, their direct use as a soil amendment avoids waste and provides growers with a low-cost alternative to conventional inputs. The slow-release property is beneficial for Aloe vera cultivation, as it avoids excessive nutrient peaks in the soil, promoting a steady supply of essential elements, especially ammonium (NH₄⁺), which is critical for vegetative development.

The literature indicates that plant residues incorporated into the soil can improve its buffering capacity by increasing soil organic matter and stimulating beneficial microbial groups such as Actinobacteria and Proteobacteria, contributing to pathogen suppression and microbial community stability. Root exudates play a key role in modulating the soil microbiota, acting as signaling molecules and carbon sources that attract beneficial rhizobacteria [34]. This mechanism may be particularly relevant in Aloe vera cultivation, as this species has shallow roots adapted to poor soils, which may favor symbiotic interactions with plant growth-promoting microorganisms. Although this study did not assess the microbial composition of the soil, the observed increase in respiratory activity and strong vegetative performance suggest indirect positive effects on the soil biota, which deserve investigation in future studies.

4. Conclusions

This study demonstrated that Aloe vera leaf shavings, a commonly discarded byproduct of the aloe processing industry, have potential as a practical and effective alternative to conventional organic fertilizers. Field results showed that aloe shavings significantly improved vegetative growth, with plants increasing from 5.7 to 12.3 leaves per plant (+115%) and leaf length from 20 to 32 cm over the season. At harvest, aloe shavings produced 456 g total leaf weight and 151 g gel weight per plant compared to 375 g and 108 g in the control, although these gains did not translate into statistically significant differences in gel yield. Soil analyses revealed that aloe shavings initially led to nitrogen immobilization, consistent with microbial assimilation during decomposition, but subsequent mineralization released approximately 39 kg N ha⁻¹ as a slow but effective nutrient source. Correlation analyses confirmed that soil pH (8.1) and inorganic nitrogen were positively associated with key vegetative traits (r = 0.62–0.71, p < 0.001). Unlike compost, aloe shavings did not significantly increase microbial respiration (1.4 vs. 2.3 mg CO₂-C kg⁻¹ day⁻¹). From a practical perspective, aloe shavings offer a low-cost, plant-based fertilization strategy that repurposes production waste. Their direct application, without the need for composting, also enhances the feasibility for farmers. Further studies are warranted to assess cumulative effects over multiple growing seasons, particularly under water-limited conditions common to semi-arid regions like South Texas. Overall, aloe shavings represent a promising resource for organic nutrient management in sustainable Aloe vera production systems.