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Article

Anaerobic Soil Disinfestation as a Tool for Nematode and Weed Management in Organic Sweetpotato

by
Simardeep Singh
1,
Matthew Cutulle
1,
William Rutter
2,
Phillip A. Wadl
2,
Brian Ward
1 and
Churamani Khanal
3,*
1
Coastal Research and Education Center, Clemson University, 2865 Savannah Highway, Charleston, SC 29414, USA
2
United States Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414, USA
3
Plant and Environmental Sciences Department, Clemson University, Clemson, SC 29634, USA
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(3), 548; https://doi.org/10.3390/agronomy15030548
Submission received: 29 January 2025 / Revised: 19 February 2025 / Accepted: 21 February 2025 / Published: 24 February 2025
(This article belongs to the Special Issue Integrated Water, Nutrient, and Pesticide Management of Fruit Crop)
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Abstract

:
Anaerobic soil disinfestation (ASD) is a promising alternative to synthetic chemical-driven pest management methods facilitated by incorporating carbon sources into the soil, tarping the soil with plastic mulch, and irrigating to soil saturation. To evaluate the impact of ASD on southern root-knot nematode [Meloidogyne incognita (Kofoid & White), SRKN] and yellow nutsedge (Cyperus esculentus L.) management in organically grown sweetpotato, greenhouse studies were conducted. The treatments were structured as a factorial of two carbon amendments [chicken manure + molasses (CM + M), and no additional carbon (control)] by 20 sweetpotato genotypes with 4 replications using a randomized complete block design. The results suggest that the microcosms receiving the carbon amendment spent the most time under anaerobic conditions (<200 mvh). Planting of sweetpotato genotypes in CM + M-treated microcosms resulted in 60–90% and 56–92% suppression of soil population and egg reproduction of SRKN as compared to no additional carbon. The application of CM + M reduced overall weed cover by 79% relative to the control. Sweetpotatoes in CM + M-treated microcosms had significantly higher dry above-ground biomass (6.8 g) as compared to the control (3.6 g). The results of this study demonstrated that ASD has the potential to manage nematodes and weeds in organic sweetpotato production systems.

1. Introduction

Sweetpotato (Ipomoea batatas L.) is an edible storage root crop. It holds the fifth position for commodity sales in the US among vegetable crops [1]. It is also an excellent source of carbohydrates, fiber, vitamins, potassium, and other essential dietary nutrients [2,3]. The total area for organic sweetpotato in the US has almost doubled over the past decade, growing from 1707 hm2 in 2007 to 3340 hm2 in 2021 [4,5]. Despite the increase in organic sweetpotato area, managing plant-parasitic nematodes and weeds under organic conditions is challenging for growers. Among plant-parasitic nematodes and weeds, the southern root-knot nematode (Meloidogyne incognita, SRKN) (Kofoid & White) [6,7] and yellow nutsedge (Cyperus esculentus L.) are two of the most difficult to manage [8]. According to Nematode Guidelines for South Carolina, root-knot nematodes have damage and action thresholds of 10 and 50 nematodes 100 cm−3 of soil, respectively; these lower thresholds indicate its aggressiveness for sweetpotato [9]. The most common above-ground symptoms of root-knot nematode attack on sweetpotato are stunted growth, chlorosis, and wilting, whereas root galling, cracking, and distortion of storage roots are the primary below-ground symptoms [10,11]. In many cases, the above-ground symptoms of nematode damage are misinterpreted by growers as water or nutrient deficiencies [12].
Yellow nutsedge is one of the most troublesome weeds in sweetpotato production systems due to its ability to reproduce through seed and tubers [8,13]. This weed has sharp leaf tips that easily puncture plastic mulch, and its tubers degrade the storage root quality by partially growing in the roots [14,15]. Yellow nutsedge with densities at 5 to 90 shoots m−2 reduced the marketable yield of sweetpotato by 6 to 80%, respectively [16].
Managing these pests in organic sweetpotato production systems is challenging. Di Gioia et al. [17] reported an increase in nematode populations with increase in yellow nutsedge suggesting these weeds may serve as hosts for nematodes. Given the role of weeds as potential hosts for root-knot nematodes, exploring and developing environmentally sustainable alternatives for managing these pests in organic production systems is important.
Anaerobic soil disinfestation (ASD) has been recognized as a promising alternative to chemical soil fumigation for organic growers [18]. ASD has a broad-spectrum inhibitory effect on nematodes, diseases, and weeds [19]. This technique can be employed anywhere using locally available carbon amendments [20,21]. The process of ASD is facilitated by incorporating decomposable carbon amendments into the soil, followed by tarping the soil with impermeable plastic mulch to prevent any gaseous exchange and irrigating the soil to saturation [18,22,23]. The decomposition of carbon amendments during ASD results in a shift of soil microbial communities, formation of volatile compounds and organic acids, and changes in metal concentration, soil pH, and oxygen concentration. This all leads to a soil environment that is unfavorable for many weeds and soil-borne pathogens [21,23,24,25,26,27,28,29,30,31,32,33].
A handful of studies conducted in the past have reported ASD to be effective in suppressing nematodes and weeds in tomatoes (Solanum lycopersicum L.), strawberries (Fragaria ananassa Duch.) and leafy vegetables [34]. In our recent study, the utilization of ASD showed the potential to manage guava root-knot nematode (Meloidogyne enterolobii Yang & Eisenback) and weeds in sweetpotato [33]. SRKN is very common and damaging to sweetpotato, and ASD has potential to suppress this nematode. No studies have been conducted to evaluate the efficacy of ASD on SRKN management in organically grown sweetpotato. Therefore, the objectives of this study were to (i) evaluate the effectiveness of ASD on suppression of SRKN, yellow nutsedge, and carpetweed, and (ii) identify SRKN resistant sweetpotato germplasm with greater tolerance to ASD environment.

2. Materials and Methods

2.1. Establishment of Nematode Infested Soils

The pure cultures of the SRKN were obtained from the USDA, ARS, US Vegetable Laboratory (USVL) in Charleston, SC and were maintained on susceptible tomatoes (Solanum lycopersicum L., cv. Rutgers, Seedway, Hall, NY, USA) in a greenhouse of Clemson University in Clemson, SC. Surface horizon soil (0–15 cm) was collected from the Clemson University Simpson Farm, mixed with sand in equal parts v/v, and sieved using a 4 mm sieve. The chemical properties of soil employed in this study were recorded (Supplementary Table S1). The sieved soil was filled in 7.5 dm3 plastic buckets (microcosms) with 23 cm depth and 20 cm diameter (Lowes, Mooresville, NC, USA), which served as experimental units. To replicate naturally infested field conditions, individual three-week-old tomato seedlings were planted in each microcosm in the greenhouse and inoculated with 10,000 SRKN eggs. The inoculum was pipetted using a pipette into three depressions of 0.5 cm × 2.5 cm, which were positioned 2 cm apart from the tomato plant [35]. Tomato plants were inoculated in June and July 2023 for experiments 1 and 2, respectively. Inoculated tomato plants were grown for four weeks prior to initiation of the ASD treatment to ensure that nematodes complete at least one life cycle. The average daily day/night temperatures of 27/21 ± 1 °C, and 85% of relative humidity were maintained during both experiments using Argus® Controls system (Conviron, Langley, BC, Canada).

2.2. Preparation of Sweetpotato Slips

Twenty sweetpotato genotypes were obtained from the USVL (Table 1). These genotypes were selected based on growth habit from available genetic material for the South Carolina conditions. Each sweetpotato genotype was increased in the greenhouse using standard organic fertilization, watering, and insect pest management practices were conducted to increase the numbers of each sweetpotato genotype. Four-node stem cuttings (slips) were taken from each sweetpotato genotype and planted in microcosms in such a way that two nodes were below the soil surface for rooting and two nodes were above the soil surface for shooting [36].

2.3. ASD Initiation and Treatment Setup

Chicken manure (Pearl Valley Organix, Pearl City, IL, USA) and molasses (Unsulfured Blackstrap Molasses, North Georgia Still Co., Dahlonega, GA, USA) were selected as carbon sources for the ASD and were applied at the rate of 20,338 kg hm−2 and 3547 dm3 hm−2, respectively [30]. The nutrient composition of the carbon sources was recorded (Supplementary Table S2). The study was laid out in randomized complete block design with factorial of two carbon amendments [chicken manure + molasses (CM + M), and no additional carbon (control)] in main plots and twenty sweetpotato genotypes in sub plots (to be planted after ASD termination) with four replications. Ten tubers of yellow nutsedge and a hundred seeds of carpetweed (Mollugo verticillate L.) were mixed into the upper 15 cm of soil and the SRKN infected tomatoes were incorporated into the microcosms at time initiation of ASD. All microcosms were irrigated to saturation with tap water based on the air-filled porosity to initiate the ASD. All microcosms were covered with impermeable black polyethylene plastic mulch (Berry Global, IN, USA) to inhibit any gaseous exchange with the surrounding environment and were kept secured for three weeks with heavy-duty rubber bands (Global Industries, Buford, GA, USA) [20,30]. Oxidation–reduction potential sensors (S550C-ORP; Sensorex, Garden Grove, CA, USA) were positioned at a 15 cm depth in the middle of two microcosms (one sensor in each carbon amendment treatment) in each replication to monitor anaerobicity during ASD period. Hourly soil redox potential values were recorded with a data logger system (CR-1000X with AM 16/32 multiplexers; Campbell Scientific, Logan, UT, USA) and summed across the ASD period to determine the critical soil redox potential [CEh = 595 mV − 60 mV (soil, pH)]. Cumulative soil anaerobicity was calculated as summation of absolute value of the difference between calculated CEh and given redox potential over ASD period [20,37,38]. The ASD was initiated in July and August 2023 for experiment 1 and experiment 2, respectively. After three weeks of ASD treatment, plastic covers were removed from each microcosm to terminate the ASD.
Individual sweetpotato slips were planted in microcosms one-week post-termination of ASD. ‘Beauregard’ served as the control for sub plots, and planting ‘Beauregard’ under no additional carbon amendment treatment was termed double control. Plant vigor was recorded at 4, and 6 weeks after planting and at the time of the experiment termination (8 weeks). Plant vigor was visually assessed with a score of 0 to 10 (0 = the plant was completely dead, 10 = the plant is highly vigorous) in each replication [29]. Soil samples were collected from each microcosm, stored at 4 °C and SRKN extracted within 2 weeks using the centrifugal-flotation technique [39]. The extraction of nematode eggs from sweetpotato fibrous roots was conducted using the bleach method [40]. Nematode second-stage juveniles (J2) and eggs were enumerated at 40× magnification with a stereoscopic microscope (Martin Microscope Company, Easley, SC) within 72 h of extraction. Both above- and below-ground plant biomass samples were placed in individual brown paper bags and dried in an incubator (Model 1500E, VWR Scientific Products, Cornelius, OR, USA) for 14 days at 45 °C, and dry weights were recorded. The experiment was terminated two months post planting of sweetpotato slips. The entire experiment was repeated once under the greenhouse conditions. The average daily day/night temperatures of 29/24 ± 1 °C, 85% of relative humidity and 14 h of light were maintained during both experiments.

2.4. Data Collection

Data on cumulative anaerobicity, soil population of SRKN, weed cover (%), and individual weed counts of yellow nutsedge, and carpetweed were collected following termination of ASD. Nematodes were extracted from a 100 cm3 sub sample of soil collected from each microcosm using centrifugal-flotation method [39]. Weed cover (%) was recorded visually by comparing CM + M amended microcosms with control units in each replication on a scale of 0 to 100%, where 0% means no weed cover and 100% represents complete weed cover [41]. Data on soil population and eggs of SRKN were again recorded at the termination of experiment. Soil samples before and after ASD were taken and sent to the Agricultural Service Laboratory (Clemson University, Clemson, SC, USA) for soil nutrient analysis. Data on available soil phosphorus, potassium, nitrate nitrogen and organic carbon were recorded (Supplementary Figures S1–S4). The available soil phosphorus and potassium were extracted using Mehlich 1 procedure [42,43]. Nitrate nitrogen and organic carbon were extracted using cadmium reduction and Walkley–Black procedure, respectively [44].

2.5. Data Analysis

Data were analyzed in JMP PRO 17.2 (SAS Institute, Cary, NC, USA) using mixed model methodology. In all cases, residual analysis was conducted to evaluate the normality of data using Anderson-Darling and Shapiro–Wilk tests. The carbon amendments, sweetpotato genotype, and their interactions were considered fixed effects, while replication and experiments were considered random effects. Data were pooled whenever no significant experiment by treatment interactions were observed (p < 0.05); otherwise, they were presented separately. Data on cumulative anaerobicity, weed cover (%), weed counts (yellow nutsedge and carpetweed), soil populations of SRKN at termination of ASD and the experiment thereafter, nematode eggs g−1 dry root, and sweetpotato dry above- and below-ground biomasses were pooled due to absence of any significant experiment by treatment interactions. Data on plant vigor at 4 and 6 weeks after planting and at the termination of the experiment are presented separately due to significant experiment-by-treatment interactions. Soil populations of SRKN at termination of the experiment, nematode eggs g−1 dry root system, and sweetpotato below-ground biomass data were normalized using square root, rank, and Yeo-Johnson transformations, respectively, and the results were used only for statistical interpretations. Treatment means prior to transformation are presented in figures and tables. Fisher’s LSD test (p ≤ 0.05) was used to compare the treatment means.

3. Results

3.1. Impacts of ASD on Anaerobicity, Nematodes and Weeds After Termination of ASD

The carbon amendments significantly influenced the cumulative anaerobicity, weed count and soil population of nematode. Significantly higher values of cumulative anaerobicity (198,497 mV h) were recorded with the application of CM + M as a carbon amendment for ASD compared to the control, the increment being 71% (p = 0.0007, Figure 1). Soil populations of nematode (p < 0.0001, Figure 2), weed cover (%) (p < 0.0001, Figure 3) and individual shoot count of yellow nutsedge (p < 0.0001, Figure 4) and carpetweed (p < 0.0001, Figure 4) were significantly lower in microcosms containing CM + M in comparison to the control. The application of CM + M suppressed the soil population of nematode, weed cover (%), shoot counts of yellow nutsedge, and carpetweed by 59%, 79%, 75%, and 63% over control treatments, respectively.

3.2. Impacts of ASD on Nematodes, Sweetpotato Biomass and Plant Vigor

3.2.1. Nematode Reproduction

Carbon amendment (p < 0.0001), sweetpotato genotype (p < 0.0001), and their interaction (p < 0.0001) had a significant effect on SRKN reproduction (soil population of nematodes and egg production) as presented in Figure 5 and Figure 6, respectively. The use of CM + M as carbon amendment for ASD significantly lowered the soil population of nematodes over no carbon amendment treatment in 15 of the sweetpotato genotypes. However, no statistically significant difference was observed between CM + M and no additional carbon amendment treatment for five genotypes (USDA-04-136, USDA-19-096, USDA-20-053, ‘Jewel’, and ‘Regal’). Overall, the commercial susceptible control ‘Beauregard’ supported the highest soil population of nematodes. The use of CM + M lowered the soil population of nematodes in 10 screened genotypes below action threshold level (50 J2 100 cm−3), indicating efficacy of CM + M as a carbon amendment for ASD. Planting of sweetpotatoes in CM + M treated microcosms resulted in 60–90% suppression of SRKN soil population as compared to the double control.
The interactive effect of carbon amendment and sweetpotato genotype on egg reproduction followed the same trend to soil population of nematodes (Figure 6). In general, significantly lower number of eggs g−1 of dry root were supported by the planting of sweetpotato genotypes with the CM + M treated microcosms relative to the planting of sweetpotato genotypes with no additional carbon treatment, except for genotypes USDA-05-097, and USDA-18-020, whereas only numerically lower number of eggs g−1 of dry root were observed with the CM + M compared to the control treatment. Genotypes USDA-09-130, and USDA-04-284 with CM + M supported the least number of eggs g−1 of dry root (1928 and 1940, respectively), whereas significantly higher egg production was observed with genotypes ‘Porto Rico’, and ‘Orleans’ (31,204 and 25,820 eggs g−1 of dry root) under no additional carbon treatment. All of twenty genotypes with CM + M exhibited the significantly lower number of eggs g−1 of dry root relative to the double control (‘Beauregard’ with no additional carbon source) and resulted in 56–92% suppression of egg production. Overall, these results indicated that ASD treatment prior to sweetpotato planting has great potential to suppress nematode reproduction.

3.2.2. Sweetpotato Dry Above-Ground Biomass

The carbon amendment (p < 0.0001), sweetpotato genotype (p < 0.0001), and their interactions (p = 0.05) significantly influenced the sweetpotato dry above-ground biomass (Table 2 and Figure 7). Significantly higher values of sweetpotato dry above-ground biomass (6.8 g plant−1) were observed with CM + M treated microcosms relative to the control treatments (3.6 g plant−1), the increment being 47%.
The dry above-ground biomass of sweetpotato varied significantly among the genotypes as presented in Table 2. The dry above-ground biomass ranged from 2.2 to 8.5 g, with ‘Hayman White’, least and USDA-11-022 the greatest above-ground biomass, respectively. The genotypes having above-ground biomass statistically similar to ‘Beauregard’ were USDA-04-284, ‘Regal’, ‘Jewel’, ‘Monaco’, ‘Porto Rico’, ‘Murasaki’, USDA-17-037, USDA-04-671, USDA-19-096, and ‘Orleans’. All other remaining sweetpotato genotypes had significantly higher above-ground biomass relative to ‘Beauregard’.
The interaction between carbon amendments and sweetpotato genotypes was also significant for sweetpotato above-ground biomass as presented in Figure 7. Higher above-ground biomass was observed for genotype USDA-11-022, and ‘Ruddy’ (11.3 and 11.0 g plant−1, respectively) under CM + M treatment, whereas lower above-ground biomass was observed for genotype ‘Orleans’ with no additional carbon amendment treatment (2.0 g plant−1). In general, planting of all the sweetpotato genotypes in CM + M-treated microcosms resulted in greater above-ground biomass relative to the double control (‘Beauregard’ with no additional carbon), increment being 37–81%. The five genotypes (USDA-11-022, ‘Ruddy’, USDA-05-097, USDA-20-053, and USDA-09-130), showed greater compatibility to ASD and SRKN tolerance. These genotypes had higher dry above-ground biomass and supported soil population of nematodes below the threshold.

3.2.3. Sweetpotato Dry Below-Ground Biomass

Carbon amendment (p < 0.0002) and sweetpotato genotype (p < 0.0001) significantly influenced sweetpotato dry below-ground biomass (Table 2). However, their interactions failed to significantly influence (p = 0.3304) the dry below-ground biomass (Table 2). The application of CM + M as a carbon amendment for ASD resulted in significantly higher below-ground biomass (0.48 g plant−1) compared to no additional carbon amendment (0.36 g plant−1), the increment being 25%.
The dry below-ground biomasses of sweetpotatoes were more or less proportionate to their dry above-ground biomasses. The dry below-ground biomasses ranged from 0.26 to 0.62 g, with ‘Hayman White’ and USDA-18-020 having the least and the greatest below-ground biomass, respectively. Eight genotypes (USDA-17-037, ‘Regal’, ‘Monaco’, ‘Orleans’, ‘Porto Rico’, USDA-09-130, USDA-04-791, and USDA-04-284) had dry below-ground biomass statistically similar to the control genotype ‘Beauregard’ with a range of 0.30 to 0.40 g. All other genotypes had significantly higher dry below-ground biomass relative to the genotype ‘Beauregard’.

3.2.4. Plant Vigor

In both experiments, carbon amendments (p < 0.0001) and sweetpotato genotypes (p < 0.0001) significantly influenced the sweetpotato plant vigor at all time points. Significantly greater plant vigor was observed with CM + M treatments compared to control in both experiments at all time points as presented in Table 3. The plant vigor ratings indicated that the plants in CM + M treated microcosms were more vigorous than those in the no additional carbon treatments. Genotypes USDA-09-130, ‘Ruddy’, USDA-11-022, USDA-05-097, USDA-20-053, and USDA-04-791 under CM + M treatment consistently resulted in more vigorous plants relative to the other genotypes.

4. Discussion

The management of nematodes and weeds, including SRKN, yellow nutsedge, and carpetweed, in organic plasticulture sweetpotato production systems is challenging for the farmers due to a lack of effective pesticides. Organic sweetpotato production systems are dominated by small growers, and high-cost technologies such as steam sterilization are inaccessible to these growers. The present study evaluated the effectiveness of ASD in managing SRKN and yellow nutsedge and screened the compatibility of 20 sweetpotato genotypes for ASD with resistance to SRKN. The results of this study provide evidence that ASD has the potential to manage these pests. The successful adoption of this sustainable pest management technique would help farmers alleviate the problems of SRKN and weeds in organic sweetpotato production systems.
The development of anaerobic conditions is considered a strong indicator of soil-born pest suppression [45]. In the current study, cumulative anaerobicity was 71% higher in CM + M treatments as compared to the control (Figure 1). These cumulative anaerobicity values for our ASD treatments are similar to previously published results [18,20,21,29,30,33,46,47]. The application of organic amendments (CM + M) serves as the food source for microorganisms. The increased microbial respiration in response to organic amendments leads to depletion of oxygen and subsequent solely anaerobic decomposition [19,48,49,50]. Anaerobic gases (carbon dioxide, methane, nitrous oxide and ammonia), organic acids (acetic and butyric acids), microbial volatile compounds, and enzymes are also released during the anaerobic decomposition [27,48,49,50]. Further, the production of these gases and organic compounds, combined with changes in soil microbial communities and high temperatures, ultimately increases anaerobic conditions [46,51,52,53].
Anaerobic soil disinfestation has been successfully evaluated as a proven strategy for managing soil-borne phytopathogens on various crops utilizing a wide range of carbon amendments in greenhouse and field conditions [54]. SRKN is one of the most crop-limiting sweetpotato pathogen in the Southeastern US [55]. In the current study, the use of CM + M as a carbon amendment suppressed up to 67% of SRKN reproduction, indicating ASD is effective in managing SRKN. Furthermore, the use of CM + M as carbon amendment for ASD suppressed the soil population of nematodes in 10 sweetpotato genotypes below threshold level (Figure 5). Our results are in alignment with the findings of Butler et al. [46], who reported a decrease in root-knot nematode populations in plots amended with composted poultry manure and molasses. In another ASD study, composted poultry manure and molasses effectively controlled plant-parasitic nematode populations [45]. Similarly, lower disease severity of nematodes after ASD was reported by Katase et al. [56], Oka [57], Momma et al. [23], Shennan et al. [58], Testen and Miller [59], and Hu et al. [60].
In current study, the accumulation of gases and organic compounds in the headspace of CM + M treated microcosms were noticeable (Supplementary Figure S5). The production of various toxic anaerobic compounds during ASD could be responsible for the decline of the nematode reproduction. However, the exact mechanism of suppression of SRKN reproduction is largely unknown. It is hypothesized that the number of sulphate-reducing bacteria could increase with the use of molasses [61], which results in increased nematicidal hydrogen sulfide levels [62,63]. Oka [57] described various possible mechanisms that occur during the decomposition of the organic amendment, including the generation of various organic nematicidal compounds such as fatty acids and ammonia, antagonistic microorganisms, and various changes in soil properties that result in the suppression of nematodes. Katase et al. [56] also reported lower nematode populations after ASD due to the production of various microbial volatile fatty acids. Further, the decomposition of organic amendments during ASD produces high concentrations of ammonia, which is reported to be toxic to nematodes [24,64,65].
Weed management is consistently ranked among the top priorities of the US sweetpotato industry [66]. Yellow nutsedge is the most problematic weed throughout the US in organic sweetpotato fields [13,67] due to its specialized morphological features (strong midrib and sharp leaf tip) that allow it to puncture plastic mulch, reducing the longevity and durability of plastic mulch in addition to competing with the crop for resources [68,69]. Plastic mulch integrity loss due to punctures allows other grass and broadleaf weed species to emerge on raised beds, causing further crop yield reduction due to increased crop weed competition [70]. Despite significant efforts, sweetpotato weed management programs lag behind those of other specialty crops and row crops. More efficient and economically sound techniques are much needed to manage yellow nutsedge and other weed species in organic sweetpotato production systems. In this microcosm study, the use of CM + M significantly reduced the weed cover (%) and individual shoot counts of both yellow nutsedge, and carpetweed by 79%, 75%, and 63% relative to no additional carbon amendment treatment, respectively (Figure 3 and Figure 4). Our observations corroborate the meta-analysis conducted by Shrestha et al. [19], where they reported ASD strongly suppressed yellow nutsedge. The meta-analysis of 88 published studies showed that ASD with different carbon amendments suppressed weeds, ranging from 32% to 88%. In another study, yellow nutsedge tuber viability was reduced by 98% after ASD [8]. Similarly, Singh et al. [21,29,30], Khadka et al. [31], Liu et al. [32] and Singh et al. [33] observed significantly lower weed cover (%) and individual weed shoot counts of yellow nutsedge and grass weeds with ASD using different carbon sources. The combination of changes in soil microbial communities, high temperature, and increased anaerobic conditions during the ASD process are likely contributed to lower weed cover (%) and shoot count suppression of yellow nutsedge and carpetweed. Several researchers reported that the increased temperature and accumulation of various anaerobic compounds during ASD are the possible mechanism for weed seed and pathogen inactivation [54,55,71]. Further, Gao et al. [72] reported that poorly oxidized compounds (ethylene and methane gases, hydrogen sulfide, alcohol, and organic acids) are produced during the anaerobic decomposition of the carbon sources, which are inhibitory towards weed seeds.
Besides improving SRKN disease and weed suppression, ASD also improved sweetpotato biomass and plant vigor in the current study (Table 2 and Table 3). The use of CM + M resulted in more vigorous sweetpotato plants at all time points compared to the control in experiment 2. Similarly, significantly higher dry above- and below-ground biomasses (47 and 25%, respectively) were observed with CM + M treatments relative to the control. Furthermore, planting of the individual sweetpotato genotype in CM + M-treated microcosms resulted in higher dry above-ground biomasses compared to the control (Figure 7). Overall, sweetpotato genotypes planted in CM + M treatment recorded 37–81% increase in dry above-ground biomass relative to double control. These results are in alignment with the results of Ozores-Hampton et al. [73] and Butler et al. [18] who observed that the use of composted poultry manure and molasses as a carbon source for ASD improved tomato vigor and yield, which might be attributed to improved plant nutrition and water holding capacity. Furthermore, Singh et al. [29,30] reported higher plant vigor and biomass after ASD with various carbon sources. In another study use of wheat middlings and dried distilled grains as carbon source for ASD increased the strawberry yield relative to unamended control [74]. An increase in the root weight of cucumbers (Cucumis sativus L.) was also observed by Huang et al. [71] after ASD treatments. The decomposition of CM + M during the ASD process provides additional plant nutrition, which might be the possible reason for improved plant vigor and sweetpotato biomass. Significantly higher phosphorus and potassium values were recorded after ASD (Supplementary Figures S1 and S2) in the current study. Di Gioia et al. [17] also observed increased phosphorus and potassium in both soil and plants after ASD treatments. Furthermore, the decomposition of organic amendments during ASD improved the soil microbial profile, and these microbes positively correlate with soil nutrient mobilization and plant growth [59]. Huang et al. [71] concluded that the use of ASD shifts soil microbial communities to disease-suppressive from disease-conducive, which is beneficial for plant growth and development.

5. Conclusions

In conclusion, the results of the current study demonstrated the efficacy of ASD for managing SRKN and yellow nutsedge in organically grown sweetpotato. ASD could be a sustainable, viable SRKN and weed management alternative for organic growers who have limited options available worldwide. Overall, the sweetpotato genotypes USDA-11-022, Ruddy, USDA-05-097, USDA-20-053, and USDA-09-130, showed greater compatibility with ASD regarding SRKN suppression. Further research is needed to evaluate the performance of these sweetpotato genotypes in managing nematode disease severity and weeds under field conditions by using various locally available carbon sources.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy15030548/s1, Table S1: Chemical properties of the soil used for ASD initiation. Table S2: Nutrient content of the chicken manure and molasses employed in this study. Figure S1: Phosphorus content of soil as effected by different carbon amendment treatments expressed as mg kg−1. Figure S2: Potassium content of soil as effected by different carbon amendment treatments expressed as mg kg−1. Figure S3: Nitrate nitrogen content of soil as effected by different carbon amendment treatments expressed as mg kg−1. Figure S4: Organic carbon content of soil as effected by different carbon amendment treatments expressed as mg kg−1. Figure S5: Accumulation of various anaerobic gases and compounds during ASD process in the headspace of the chicken manure + molasses treated microcosms.

Author Contributions

Conceptualization, M.C. and C.K.; methodology, M.C., C.K. and S.S.; software, S.S.; formal analysis, S.S.; writing—original draft preparation, S. Singh; writing—review and editing, C.K., M.C., S.S., W.R., P.A.W. and B.W.; visualization, S.S.; supervision, CK. and M.C.; project administration, C.K. and M.C.; funding acquisition, M.C. and C.K. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the USDA NIFA Organic Transitions Program Proposal No. 2022-04689.

Data Availability Statement

Data will be made available upon reasonable request.

Acknowledgments

The authors are thankful for the technical support provided by William Bridges, members of the Vegetable Weed Lab, Nematology Lab, Manwinder Singh Brar, Davinder Singh, and Chahat Garg.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Figure 1. Average cumulative anaerobicity over a 3-week anaerobic soil disinfestation period as influenced by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
Figure 1. Average cumulative anaerobicity over a 3-week anaerobic soil disinfestation period as influenced by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
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Figure 2. Reproduction of Meloidogyne incognita as affected by different carbon amendment treatments during 3-week anaerobic soil disinfestation period at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). J2 refers to the second stage juveniles of M. incognita.
Figure 2. Reproduction of Meloidogyne incognita as affected by different carbon amendment treatments during 3-week anaerobic soil disinfestation period at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). J2 refers to the second stage juveniles of M. incognita.
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Figure 3. Weed cover (%) as affected by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
Figure 3. Weed cover (%) as affected by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
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Figure 4. Individual shoot count of yellow nutsedge (Cyperus esculentus L.) and carpetweed (Mullogo verticillata L.) as affected by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
Figure 4. Individual shoot count of yellow nutsedge (Cyperus esculentus L.) and carpetweed (Mullogo verticillata L.) as affected by different carbon amendment treatments at ASD termination. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
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Figure 5. Number of juveniles (J2) of Meloidogyne incognita on twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the number of J2 100 cm−3 of soil at experiment termination. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). J2 refers to the second stage juveniles of M. incognita.
Figure 5. Number of juveniles (J2) of Meloidogyne incognita on twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the number of J2 100 cm−3 of soil at experiment termination. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). J2 refers to the second stage juveniles of M. incognita.
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Figure 6. Number of eggs of Meloidogyne incognita on twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the number of eggs g−1 of dry root at experiment termination. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
Figure 6. Number of eggs of Meloidogyne incognita on twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the number of eggs g−1 of dry root at experiment termination. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
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Figure 7. Dry above-ground biomass of twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the g plant−1. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
Figure 7. Dry above-ground biomass of twenty sweetpotato genotypes as affected by different carbon amendment treatments and expressed as the g plant−1. Data were combined over two experiments and are means of eight replications. Data are expressed as mean ± standard error of mean; means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05).
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Table 1. List of sweetpotato genotypes employed in the current study.
Table 1. List of sweetpotato genotypes employed in the current study.
Sweetpotato GenotypeGrowth HabitSubjective Periderm
(Skin) Color		Subjective Stele (Flesh) ColorDry Weight (%)
USDA-04-136ViningRedOrange18.75
USDA-04-284ViningRedCream33.60
USDA-04-671ViningRedOrange24.90
USDA-05-097ViningPurple/redOrange20.30
USDA-09-130ViningBrownOrange23.23
USDA-11-022ViningPurple/redWhite25.60
USDA-17-037ErectPurple/redWhite24.60
USDA-18-020ErectRedOrange17.00
USDA-19-096ErectCopperOrange17.40
USDA-20-053ViningPurple/redOrange24.80
‘Beauregard’ ZViningRoseOrange19.85
‘Hayman White’ViningBrown/tanWhite/cream37.80
‘Jewel’ViningCopperOrange22.93
‘Monaco’Semi-erectRedOrange21.08
‘Murasaki-29’ViningPurpleWhite33.30
‘Orleans’ViningLight roseOrange22.51
‘Porto Rico’Semi-erectBrown/tanOrange31.60
‘Regal’ViningRedOrange25.01
‘Ruddy’ViningRedOrange19.60
Z Beauregard is a commercial cultivar and served as a susceptible control for Southern root-knot nematode.
Table 2. Dry above- and below-ground biomass of sweetpotato as affected by the main effects of carbon amendment treatments and sweetpotato genotypes in the greenhouse conditions y.
Table 2. Dry above- and below-ground biomass of sweetpotato as affected by the main effects of carbon amendment treatments and sweetpotato genotypes in the greenhouse conditions y.
Factor TreatmentsAbove Ground Biomass (g Plant−1)Below Ground Biomass (g Plant−1)
Carbon amendment (C)CM + M6.8 a0.48 a
Control3.6 b0.36 b
Genotype (G)USDA-04-1365.8 b–e0.44 a–g
USDA-04-2845.1 d–f0.43 b–h
USDA-04-6713.8 f–i0.51 a–e
USDA-05-0976.5 b–d0.38 d–i
USDA-09-1307.4 ab0.53 a–d
USDA-11-0226.6 b–d0.36 d–i
USDA-17-0378.5 a0.61 a–c
USDA-18-0203.8 f–i0.30 hi
USDA-19-0965.7 c–e0.62 a
USDA-20-0532.9 g–i0.42 c–h
USDA-04-1367.2 a–c0.46 a–f
‘Beauregard’ z3.7 f–i0.33 d–i
‘Hayman White’2.2 i0.26 i
‘Jewel’5.0 d–f0.40 d–i
‘Monaco’4.9 d–f0.32 f–i
‘Murasaki-29’4.2 e–h0.43 b–h
‘Orleans’2.7 hi0.32 f–i
‘Porto Rico’4.6 e–g0.36 d–i
‘Regal’5.1 d–f0.32 e–i
‘Ruddy’8.4 a0.61 ab
p-valueC<0.0001<0.0002
G<0.0001<0.0001
C × G0.050.3304
y Greenhouse experiments were terminated after eight weeks of planting of sweetpotato slips. Data of both greenhouse experiments were combined due to absence of experiment by treatment interactions and are means of eight replications. Within columns, means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). z Beauregard is a commercial cultivar and served as a susceptible control for the Southern root-knot nematode.
Table 3. Sweetpotato plant vigor of twenty sweetpotato genotypes as affected by different carbon amendment treatments at 4, 6, and 8 weeks after planting (WAP) of sweetpotato slips in the greenhouse conditions y.
Table 3. Sweetpotato plant vigor of twenty sweetpotato genotypes as affected by different carbon amendment treatments at 4, 6, and 8 weeks after planting (WAP) of sweetpotato slips in the greenhouse conditions y.
Treatment Plant Vigor
4 WAP6 WAP8 WAP
Exp. 1Exp. 2Exp. 1Exp. 2Exp. 1Exp. 2
Genotype (G)Carbon Amendment (C)
USDA-04-136CM + M8.0 a7.8 a–g7.6 a7.6 a–e7.9 a7.8 a–e
control6.4 a6.8 b–i6.8 a6.6 b–g6.8 a7 b–h
USDA-04-284CM + M7.8 a4 l7.9 a3.6 j8.1 a4 jk
control7.3 a5.8 g–l7.3 a6.8 b–g7.0 a 6.5 c–h
USDA-04-671CM + M8.1 a6.5 c–i8.0 a6.6 b–g8.1 a6.5 c–h
control6.8 a5.8 g–l6.9 a6 e–l7.0 a6.1 d–j
USDA-04-791CM + M7.5 a8.2 a–e7.6 a8.2 a–d7.8 a8.5 a–c
control7.1 a7.8 a–g7.4 a7.1 a–f7.1 a7.5 a–f
USDA-05-097CM + M8.8 a8.5 a–c8.8 a7.8 a–e9.0 a8.5 a–c
control7.6 a6.5 c–i7.4 a6.4 d–g7.1 a6.5 c–h
USDA-09-130CM + M9.0 a8.4 a–d8.8 a8.4 a–c8.6 a9.2 a
control6.9 a7 a–i6.8 a7.1 a–f7.0 a7.2 a–g
USDA-11-022CM + M9.1 a8.7 ab8.9 a8.5 ab9.0 a8.8 ab
control6.8 a7.4 a–i7.1 a7.1 a–f6.9 a7.2 a–g
USDA-17-037CM + M6.6 a4.4 kl6.6 a4.4 h–j6.9 a4.2 i–k
control5.3 a6.8 b–i6.1 a7 a–f5.9 a7 b–h
USDA-18-020CM + M8.8 a7.1 a–i8.6 a6.6 b–g9.0 a6.8 b–h
control8.3 a6.8 b–i8.0 a6.9 a–f8.3 a6.8 b–h
USDA-19-096CM + M8.3 a6.5 c–i8.4 a6.1 e–h8.4 a6.25 d–i
control6.6 a6.2 e–k6.8 a6.1 e–h6.8 a6 e–j
USDA-20-053CM + M8.8 a8.5 a–c8.9 a7.9 a–e8.6 a8.2 a–d
control7.6 a8.1 a–f7.5 a8.2 a–d7.6 a8.2 a–d
‘Beauregard’ ZCM + M8.0 a8.5 a–c7.6 a7.9 a–e8.3 a8 a–e
control 7.6 a6.5 c–i7.9 a6.1 e–h7.6 a6 e–j
‘Hayman’s White’CM + M7.0 a4.5 j–l7.0 a4.1 ij7.3 a4.2 i–k
control6.6 a6.1 f–k6.9 a6.5 c–g6.9 a6 e–j
‘Jewel’CM + M8.4 a7.4 a–i8.0 a6.9 a–f8.3 a7.5 a–f
control8.3 a6.9 a–i8.3 a6.9 a–f8.1 a6.8 b–h
‘Monaco’CM + M7.3 a7.7 a–h7.5 a7.6 a–e7.9 a7.5 a–f
control7.3 a4 l7.5 a4.1 ij7.3 a3.8 k
‘Murasaki-29’CM + M7.0 a 6.9 a–i7.3 a6.1 e–h7.4 a6.5 c–h
control5.0 a5.6 h–l5.8 a5.4 f–j5.8 a5.5 f–k
‘Orleans’CM + M7.4 a7.2 a–i7.8 a6.9 a–f7.6 a6.2 d–i
control7.3 a5.5 i–l7.1 a5.6 f–l6.9 a5.2 g–k
‘Porto Rico’CM + M8.6 a6.4 d–k8.5 a6.4 d–g8.5 a6.5 c–h
control7.8 a5.4 i–l7.5 a4.9 g–j7.5 a5 h–k
‘Regal’CM + M6.5 a8.2 a–e6.9 a8.1 a–d7.0 a8.5 a–c
control6.3 a6.8 b–i6.6 a6.6 b–g6.5 a7 b–h
‘Ruddy’CM + M9.0 a8.9 a9.5 a8.8 a9.3 a8.8 ab
control7.5 a7 a–i7.6 a6.4 d–g7.4 a7 b–h
p-valueC<0.0001 0.0014 <0.0001 0.0199 <0.0001 0.0045
G<0.0001 <.0001 <0.0001 <0.0001 <0.0001 <0.0001
C × G0.120.0394 0.060.0005 0.480.0092
y Greenhouse experiments were terminated after eight weeks of planting of sweetpotato slips. Sweetpotato plant vigor data at 4, 6, and 8 WAP of sweetpotato slips was presented separately for both experiments due to existence of significant experiment by treatment interaction. Within columns, means followed by different letters are significantly different according to Fisher’s LSD test (p ≤ 0.05). Plant vigor was visually accessed with a score of 1–10 (where 1 is the least vigorous plant and 10 is the most vigorous plant). Z Beauregard is a commercial cultivar and served as a susceptible control for the Southern root-knot nematode.
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Singh, S.; Cutulle, M.; Rutter, W.; Wadl, P.A.; Ward, B.; Khanal, C. Anaerobic Soil Disinfestation as a Tool for Nematode and Weed Management in Organic Sweetpotato. Agronomy 2025, 15, 548. https://doi.org/10.3390/agronomy15030548

AMA Style

Singh S, Cutulle M, Rutter W, Wadl PA, Ward B, Khanal C. Anaerobic Soil Disinfestation as a Tool for Nematode and Weed Management in Organic Sweetpotato. Agronomy. 2025; 15(3):548. https://doi.org/10.3390/agronomy15030548

Chicago/Turabian Style

Singh, Simardeep, Matthew Cutulle, William Rutter, Phillip A. Wadl, Brian Ward, and Churamani Khanal. 2025. "Anaerobic Soil Disinfestation as a Tool for Nematode and Weed Management in Organic Sweetpotato" Agronomy 15, no. 3: 548. https://doi.org/10.3390/agronomy15030548

APA Style

Singh, S., Cutulle, M., Rutter, W., Wadl, P. A., Ward, B., & Khanal, C. (2025). Anaerobic Soil Disinfestation as a Tool for Nematode and Weed Management in Organic Sweetpotato. Agronomy, 15(3), 548. https://doi.org/10.3390/agronomy15030548

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