Impacts of Different Tillage and Straw Management Systems on Herbicide Degradation and Human Health Risks in Agricultural Soils

Abstract

Pesticide residues pose risks to the environment and human health. Little is known about how tillage and straw management affect herbicide behavior in soil. This study investigated the effects of different tillage practices under varying straw incorporation scenarios on the degradation of five commonly used herbicides in a long-term experimental field located in the maize belt of Siping, Jilin Province. Post-harvest soil samples were analyzed for residual herbicide concentrations and basic soil physicochemical properties. A human health risk assessment was conducted, and a controlled incubation experiment was carried out to evaluate herbicide degradation dynamics under three management systems: straw incorporation with traditional rotary tillage (ST), straw incorporation with strip tillage (SS), and no-till without straw (CK). Residual concentrations of atrazine ranged from not detected (ND) to 21.10 μg/kg (mean: 5.28 μg/kg), while acetochlor showed the highest variability (2.29–120.61 μg/kg, mean: 25.26 μg/kg). Alachlor levels were much lower (ND–5.71 μg/kg, mean: 0.34 μg/kg), and neither nicosulfuron nor mesotrione was detected. Soil organic matter (17.6–20.89 g/kg) positively correlated with available potassium and acetochlor residues. Health risk assessments indicated negligible non-cancer risks for both adults and children via ingestion, dermal contact, and inhalation. The results demonstrate that tillage methods significantly influence herbicide degradation kinetics, thereby affecting environmental persistence and ecological risks. Integrating straw with ST or SS enhanced the dissipation of atrazine and mesotrione, suggesting their potential as effective residue mitigation strategies. This study highlights the importance of tailoring tillage and straw management practices to pesticide type for optimizing herbicide fate and promoting sustainable agroecosystem management.

1. Introduction

Human activities introduce numerous hazardous substances into the environment, and pesticides are among the most widely used agrochemicals for maintaining high crop yields [1,2,3,4,5,6]. Their widespread application has resulted in extensive environmental contamination, which poses serious risks to both ecosystems and human health [2,7,8,9,10,11]. Globally, herbicide use now exceeds one million tons annually, raising concerns over their residual effects on soil ecosystems and public safety [12,13,14]. Although increasing research has focused on pesticide behavior in soils, especially their degradation pathways and environmental fate, the combined effects of tillage practices and straw incorporation on the persistence and degradation dynamics of multiple herbicides remain insufficiently understood [15].

Soil represents one of the most critical resources on Earth, serving as a primary reservoir for nutrients and playing a central role in global material storage and energy cycling [16,17]. However, compared to air and water pollution, soil contamination is more complex and difficult to assess due to the interactions between pollutants and soil components such as organic matter, pH, clay content, and microbial communities [18,19,20].

In recent years, sustainable agricultural practices such as straw return and conservation tillage have received increasing attention for their potential to enhance soil fertility and promote carbon sequestration [21,22]. Incorporating straw into the soil can improve nutrient content, stimulate microbial activity, and potentially influence the fate of pesticide residues [23,24,25,26,27]. Different tillage systems, including conventional tillage, no-tillage, and strip tillage, can alter soil structure, nutrient distribution, and microbial communities, thereby affecting herbicide behavior [28]. Conventional tillage involves significant physical disturbance of the topsoil, resulting in a more uniform layer with consistent physical and chemical properties. This practice may reduce soil organic matter, change microbial and arthropod community structures, lower overall soil biodiversity, and increase the abundance of aerobic microorganisms [29,30]. In contrast, no-tillage minimizes soil disturbance during planting. It promotes the accumulation of organic matter and nutrients, reduces erosion, improves water retention, and stabilizes soil moisture and temperature [31]. Strip tillage is a type of conservation tillage. It is characterized by limited soil disturbance within the planting zone, while the rest of the field remains undisturbed. Studies show that strip tillage can alleviate soil compaction, increase soil temperature, retain moisture, and create favorable seedbed conditions. These benefits can support germination, plant growth, and ultimately improve crop productivity and soil health. Compared to conventional tillage, no-tillage has been associated with higher levels of total nitrogen, enhanced nitrification potential, increased microbial biomass, greater substrate-induced respiration, elevated enzyme activities, and improved nitrogen mineralization. These improvements occur without compromising crop yields, although there may be a slight increase in weed and pathogen pressure [32]. Therefore, it is essential to investigate how strip tillage, conventional tillage, and no-tillage impact soil health. Such research can help identify optimized conservation tillage strategies to support food safety and sustainable agricultural development globally.

Despite growing research interest in this field, few studies have comprehensively examined how combined management strategies involving both tillage and straw return affect the environmental fate of multiple herbicides with different physicochemical properties. This knowledge gap limits our ability to develop effective approaches for reducing pesticide risks while supporting sustainable soil management.

To address this issue, the present study was designed with four specific objectives: (1) To quantify the impact of common local tillage and straw incorporation practices on residual levels of five widely used herbicides in agricultural soils, based on field surveys and soil residue analysis; (2) To evaluate how different tillage methods influence key soil properties that may affect herbicide behavior, through analysis of soil physicochemical parameters; (3) To assess potential environmental and human health risks associated with herbicide residues in soil, using hazard index (HI) calculations; (4) To investigate the degradation kinetics of selected herbicides under various tillage and straw management scenarios, through controlled soil incubation experiments conducted under simulated field conditions. By combining field surveys with controlled incubation experiments, this study aims to provide scientific insights that can support the optimization of sustainable agricultural practices. These practices are intended to reduce pesticide environmental impacts while maintaining soil health and crop productivity.

2. Materials and Methods

2.1. Materials and Reagents

The standards for alachlor, acetochlor, and atrazine were obtained from Beijing ManhageBio-Technology Co., Ltd., Beijing, China, with purities of 99.9%, 98.00%, and 99.5%, respectively. The standards for nicosulfuron and mesotrione were sourced from Sigma-Aldrich (Shanghai) Trading Co., Ltd. (Shanghai, China), with purities of 98.0% and 98.0%, respectively. High Performance Liquid Chromatography (HPLC)-grade acetone and petroleum ether were obtained from Sigma-Aldrich Trading Co., Ltd. (Shanghai, China). Sodium chloride (NaCl) was supplied by TITAN Technology Co., Ltd. (Shanghai, China). Ultra-pure water was used throughout all experimental procedures. All additional chemicals were of analytical purity and sourced from reputable commercial vendors.

2.2. Incubation of Soils

Based on a long-term field experiment involving corn straw incorporation, the experimental soil was collected from the top 20 cm of soil in Lishu County, Siping City, Jilin Province, China (Figure 1). Prior to the experiment, crop residues, roots, and gravel were removed from the soil. The soil samples were analyzed using gas chromatography–mass spectrometry (GC–MS, Clarus 680/600 T, PerkinElmer Inc., Waltham, MA, USA) to determine the concentrations of existing pesticide residues. To activate soil microorganisms, the soil was preincubated by adding an appropriate amount of water for seven days at 25 °C in the dark. The experiment adopted a pot culture method without crops, utilizing specialized pots measuring 25 × 45 cm and filling each with 8 kg of soil. Prior to the initiation of the experiment, five commonly used herbicides—alachlor, acetochlor, atrazine, nicosulfuron, and mesotrione—were applied to the soil at their maximum recommended field application rates to simulate realistic residual conditions in agricultural soils. The application rates were as follows: 400 mL/mu (1 mu = 666.7 m²) for formulations containing 8% alachlor, 9% acetochlor, and 25% atrazine and 200 mL/mu for formulations containing 2% nicosulfuron and 5% mesotrione.

Three tillage methods were selected based on their common use in the study area: straw incorporation with traditional rotary tillage (ST), straw incorporation with strip tillage (SS), and no-till without straw incorporation (CK). These practices represent typical agricultural management systems in the maize belt of Jilin Province. When combined with herbicide application, they allowed for the evaluation of pesticide degradation under realistic field conditions. The experimental design included a total of fifteen treatments, with three replicates for each treatment. The incubation experiment lasted for 70 days and was conducted in a climate chamber maintained at 25 °C and 50% relative humidity. Light exposure was prevented by continuous shading throughout the experiment. Soil moisture was kept at 60% of water-holding capacity for all samples during the entire incubation period.

Samples were collected at predetermined time intervals, specifically on days 0, 3, 7, 27, 40, 55, and 70. At each sampling time point, 100 g subsamples were taken from each container and analyzed in triplicate for the residues of five herbicides. All samples were immediately stored at –20 °C until further analysis.

2.3. Pretreatment Method

At predetermined time intervals, 2 g of soil was precisely weighed from the collected samples and placed into a 50 mL polyethylene centrifuge tube. Subsequently, 10 mL of a 1:1 mixture of acetone and petroleum ether, along with 2 g of sodium chloride, were added to the tube. The resulting mixture was vigorously shaken for 3 min, followed by ultrasonic extraction using an ultrasonic cleaner for 30 min (LC-10KB, Shandong Lianchao Inc., Shandong, China). The sample was then centrifuged at 4000 rpm for 5 min using a centrifuge (GT10-2, Guangdong Foheng Inc., Guangzhou, China). The supernatant was carefully collected and evaporated to dryness under a stream of nitrogen gas using a water-bath nitrogen blow-down instrument (ZGDCY-36S, Shanghai Zigui Inc., Shanghai, China). Finally, the residue was reconstituted in 1 mL of acetone and filtered through a 0.22 µm nylon syringe filter prior to gas chromatograph–mass spectrometer (GC–MS) analysis.

2.4. Analysis Method

A precise and reliable analytical method was developed for the simultaneous detection of five herbicides using an Agilent 7890A-7000C GC–MS (Agilent Technologies, Palo Alto, CA, USA) equipped with an HP-5MS quartz capillary column (30 m × 0.25 mm i.d., 0.25 µm film thickness). The analysis was performed in electron impact (EI) ionization mode. The interface and ion source temperatures were set to 280 °C and 250 °C, respectively. Helium was used as the carrier gas at a constant flow rate of 1 mL/min under non-split injection conditions. The injection volume was 5 µL, with the inlet temperature maintained at 280 °C. The oven temperature program was as follows: initial temperature of 60 °C held for 1 min, ramped to 170 °C at 40 °C/min (no hold), then increased to 260 °C at 10 °C/min and held for 3 min.

2.5. Human Health Risk Assessment Method

The potential non-carcinogenic health risks for both adults and children were assessed using the commonly accepted methodologies outlined by the U.S. Environmental Protection Agency (USEPA) [33]. The human health risk assessment considered the exposure pathway of pesticide ingestion through contaminated soil. The non-dietary chronic daily intake (${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e}}$) of pesticides (mg kg⁻¹ day⁻¹) resulting from incidental soil ingestion by adults and children was estimated using the following equations [34,35].

$${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e}}=({\mathrm{C}}_{\mathrm{s}}\times \mathrm{E}\mathrm{F}\times \mathrm{E}\mathrm{D}\times {\mathrm{I}\mathrm{R}}_{\mathrm{i}}/\mathrm{A}\mathrm{T}\times \mathrm{B}\mathrm{W})\times \mathrm{C}\mathrm{F}$$

(1)

where ${\mathrm{C}}_{\mathrm{s}}$ (mg/kg) is the concentration of pesticide residue in the soil, $\mathrm{E}\mathrm{F}$ is the exposure frequency (days/year), ED is the exposure duration (years), ${\mathrm{I}\mathrm{R}}_{\mathrm{i}}$ is the rate of contaminated soil ingestion (mg/day), $\mathrm{A}\mathrm{T}$ is the average lifetime (days), BW is the average body weight (kg), and CF is the conversion factor (kg mg⁻¹).

$${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{d}\mathrm{e}\mathrm{r}\mathrm{m}\mathrm{a}\mathrm{l}}=({\mathrm{C}}_{\mathrm{s}}\times \mathrm{D}\mathrm{A}\times \mathrm{D}\mathrm{A}\mathrm{F}\times \mathrm{A}\mathrm{F}\times \mathrm{E}\mathrm{F}\times \mathrm{E}\mathrm{D}/\mathrm{A}\mathrm{T}\times \mathrm{B}\mathrm{W})\times \mathrm{C}\mathrm{F}$$

(2)

where ${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{d}\mathrm{e}\mathrm{r}\mathrm{m}\mathrm{a}\mathrm{l}}$ is the estimated non-dietary $\mathrm{C}\mathrm{D}\mathrm{I}$ (mg/kg/day) of pesticide-contaminated soil particles via dermal contact, $\mathrm{D}\mathrm{A}$ is the exposed dermal area (cm² day⁻¹), $\mathrm{D}\mathrm{A}\mathrm{F}$ is the dermal adherence factor (mg cm⁻²) for soil, and $\mathrm{A}\mathrm{F}$ (dimensionless) is the dermal absorption factor.

$${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{i}\mathrm{n}\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}={\mathrm{C}}_{\mathrm{s}}\times \mathrm{E}\mathrm{F}\times \mathrm{E}\mathrm{D}\times {\mathrm{I}\mathrm{R}}_{\mathrm{i}\mathrm{h}}/\mathrm{P}\mathrm{E}\mathrm{F}\times \mathrm{A}\mathrm{T}\times \mathrm{B}\mathrm{W}$$

(3)

where ${\mathrm{C}\mathrm{D}\mathrm{I}}_{\mathrm{i}\mathrm{n}\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}$ is the estimated non-dietary $\mathrm{C}\mathrm{D}\mathrm{I}$ (mg/kg/day) of pesticide-contaminated soil particles via the inhalation pathway, ${\mathrm{I}\mathrm{R}}_{\mathrm{i}\mathrm{h}}$ is the rate of inhalation (m³/day), and $\mathrm{P}\mathrm{E}\mathrm{F}$ is the particle emission factor (m³/kg).

The non-cancer risk of pesticides is expressed as a hazard quotient (HQ), whereas the hazard index (HI) is the sum of $\mathrm{H}\mathrm{Q}$ of individual pesticides, which was calculated following the equation [36,37,38].

$$\mathrm{H}\mathrm{Q}=\mathrm{C}\mathrm{D}\mathrm{I}/\mathrm{R}\mathrm{f}\mathrm{D}$$

(4)

$$\mathrm{H}\mathrm{I}=\sum {\mathrm{H}\mathrm{Q}}_{\mathrm{P}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{d}\mathrm{e}}$$

(5)

where $\mathrm{R}\mathrm{f}\mathrm{D}$ is the reference dose (mg/kg/day) of a pesticide. The maximum acceptable reference doses ($\mathrm{R}\mathrm{f}\mathrm{D}\mathrm{s}$) in humans for atrazine, acetochlor, alachlor, nicosulfuron, and mesotrione considered are 0.10, 0.02, 0.002, 1.25, and 0.007 mg/kg/day [39,40,41,42,43].

In this study, the ingestion rate (IR_i) for both human adults and children was set at 100 mg/day, and the inhalation rate (IR_ih) for both groups was established at 17.50 m³/day. The body weight (BW) was determined to be 62 kg for adults and 12 kg for children. The averaging lifetime (AT) for both populations was considered to be 70 years (equivalent to 25,550 days). The exposure frequency (EF) for both human adults and children was standardized at 350 days/year. Regarding exposure duration (ED), it was set at 30 years for adults and 3 years for children. The exposed dermal area (DA) was estimated at 5700 cm²/day for adults and 1050 cm²/day for children. The dermal adherence factor (DAF) was assigned values of 0.07 mg/cm² for adults and 0.20 mg/cm² for children. Both groups shared a common dermal absorption factor (AF) of 0.13. Additionally, the particle emission factor (PEF) for both adults and children was fixed at 1.36 × 109 m³/kg, and the conversion factor (CF) was uniformly taken as 1 × 10⁻⁶ kg/mg across both populations. These parameters were selected to standardize the assessment of environmental exposure effects across different age groups in the population [44,45,46].

2.6. Degradation Kinetics

The degradation rate constants (k) of the five herbicides were determined using the first-order kinetic equation [47]:

$${\mathrm{C}}_{\mathrm{t}}={\mathrm{C}}_0{\mathrm{e}}^{-\mathrm{k}\mathrm{t}}$$

(6)

$${\mathrm{T}}_{1/2}=\mathrm{l}\mathrm{n}2/\mathrm{k}=0.693/\mathrm{k}$$

(7)

where ${\mathrm{C}}_{\mathrm{t}}$ and ${\mathrm{C}}_0$ are the amounts (mg kg⁻¹) of pesticide remaining in soil at a given time t and zero, respectively, and k is the degradation rate constant (day⁻¹). The five herbicides’s half-life (${\mathrm{T}}_{1/2}$) for dissipation was calculated using Formula (7), as follows.

2.7. Data Analysis

Soil pesticide residue concentration data were processed using Microsoft Excel to determine descriptive statistics such as means, ranges, and standard deviation. Principal Component Analysis (PCA) and Pearson’s correlation were used to explore possible relationships between pesticides and soil physical and chemical properties. The pesticide degradation data were recorded and analyzed using Microsoft Excel and subjected to ANOVA tests using SPSS version 26.0 software.

3. Results

3.1. Pesticide Residues in Soil Samples

To assess the effects of different tillage practices on pesticide residue levels in agricultural soils, soil samples were collected after the autumn harvest under three distinct treatments: CK, SS, and ST. The study focused on five commonly used herbicides: atrazine, acetochlor, alachlor, nicosulfuron, and mesotrione (

Table 1. Pesticide concentrations in selected soils.

Tillage Method	Pesticide (ug/kg)	Min	Max	Mean	SD	CV
CK	Atrazine	ND	11.62	5.06	5.70	1.13
	Acetochlor	19.35	30.62	23.78	4.47	0.19
	Alachlor	ND	ND	ND	ND	ND
	Nicosulfuron	ND	ND	ND	ND	ND
	Mesotrione	ND	ND	ND	ND	ND
SS	Atrazine	ND	12.31	3.94	5.12	1.30
	Acetochlor	2.29	48.79	23.66	18.34	0.78
	Alachlor	ND	5.71	1.02	2.30	2.25
	Nicosulfuron	ND	ND	ND	ND	ND
	Mesotrione	ND	ND	ND	ND	ND
ST	Atrazine	ND	21.10	6.83	8.25	1.21
	Acetochlor	4.38	120.61	28.34	45.46	1.60
	Alachlor	ND	ND	ND	ND	ND
	Nicosulfuron	ND	ND	ND	ND	ND
	Mesotrione	ND	ND	ND	ND	ND
Total	Atrazine	ND	21.10	5.28	6.23	1.18
	Acetochlor	2.29	120.61	25.26	26.79	1.06
	Alachlor	ND	5.71	0.34	1.34	3.95
	Nicosulfuron	ND	ND	ND	ND	ND
	Mesotrione	ND	ND	ND	ND	ND

ND: not detected; CV: coefficient of variance.

).

The residue levels of selected herbicides in agricultural soils are as follows: atrazine concentrations ranged from ND to 21.10 μg/kg, with a mean of 5.28 μg/kg and a standard deviation of 6.23 μg/kg. The CV was calculated as 1.18, indicating moderate variability in its distribution.

Acetochlor displayed a much broader concentration range, from 2.29 to 120.61 μg/kg, with an average of 25.26 μg/kg and a standard deviation of 26.79 μg/kg. The CV is 1.06.

Alachlor residues were generally low, ranging from ND to 5.71 μg/kg, with an average of 0.34 μg/kg. The CV is 3.95. Neither nicosulfuron nor mesotrione was detected in any of the soil samples analyzed.

Under CK conditions, Atrazine concentrations ranged from ND to 11.62 μg/kg, with a mean of 5.06 μg/kg and a coefficient of variation (CV) of 1.13. Acetochlor showed a narrow range of 19.35–30.62 μg/kg, with an average of 23.78 μg/kg and a CV of 0.19. Alachlor, nicosulfuron, and mesotrione were not detected.

In SS treatment, Atrazine residues ranged from ND to 12.31 μg/kg, with an average of 3.94 μg/kg and a coefficient of variation (CV) of 1.30. Acetochlor concentrations ranged from 2.29 to 48.79 μg/kg, averaging 23.66 μg/kg, with a CV of 0.78. Alachlor was detected in some samples, ranging from ND to 5.71 μg/kg, with an average of 1.02 μg/kg and a CV of 2.25. Nicosulfuron and mesotrione were not detected.

Under ST conditions, Atrazine residues ranged from ND to 21.10 μg/kg, with an average of 6.83 μg/kg and a CV of 1.21. Acetochlor showed the highest variability across all treatments, ranging from 4.38 to 120.61 μg/kg, with a mean of 28.34 μg/kg and a CV of 1.60. Alachlor, nicosulfuron, and mesotrione were not detected.

3.2. Soil Physicochemical Properties Under Different Tillage Practices

The soil physicochemical properties were significantly affected by the combined influence of straw incorporation and tillage practices under the three treatments. The results showed notable differences in organic matter content, nitrogen, phosphorus, potassium levels, and pH across the treatments. These variations may directly or indirectly influence herbicide degradation kinetics in the soil (

Table 2. Soil physical and chemical properties under different tillage methods.

Tillage Method	pH	SOM (g/kg)	Available Nitrogen (mg/kg)	Available Phosphorus (mg/kg)	Available Potassium (mg/kg)
CK	7.1	20.89	84.02	23.46	208
SS	6.59	18.9	64	26.27	203
ST	6.34	17.6	82.6	20.7	172

).

Soil physicochemical properties exhibited notable variations across the different tillage treatments, reflecting the influence of management practices on nutrient dynamics. The organic matter content ranged from 17.6 to 20.89 g/kg, available nitrogen from 64 to 84.02 mg/kg, available phosphorus from 20.7 to 26.27 mg/kg, and available potassium from 172 to 208 mg/kg. Soil pH values varied between 6.34 and 7.1. Soil property variations across treatments are presented below.

Among all treatments, the highest organic matter content was observed under conventional CK, reaching 20.89 g/kg. This value was followed by SS at 18.9 g/kg and ST at 17.6 g/kg. The organic matter content was lowest in the ST treatment, while the available nitrogen content was 82.6 mg/kg, slightly lower than that of CK (84.02 mg/kg).

The available phosphorus concentrations varied across treatments, with the highest value observed in SS at 26.27 mg/kg, followed by CK at 23.46 mg/kg and ST at 20.7 mg/kg. For available potassium, the highest value was observed in CK at 208 mg/kg, followed by SS at 203 mg/kg and ST at 172 mg/kg. The highest soil pH was recorded under CK at 7.1, while the lowest was found under ST at 6.34.

3.3. Correlation Analysis

A Pearson correlation analysis was conducted to examine the relationships between various soil properties and pesticide concentrations. The results are presented in Figure 2, which illustrates a comprehensive matrix of correlations among pH, SOM, available nitrogen, available phosphorus, available potassium, atrazine, acetochlor, and alachlor.

pH showed a strong positive correlation with SOM (0.9), indicating that as soil pH increases, so does the content of organic matter. pH also had a moderate positive correlation with available potassium (0.82).

SOM exhibited a very strong positive correlation with available potassium (0.81), suggesting that higher levels of organic matter may enhance potassium availability. SOM also had a strong positive correlation with acetochlor (0.92), implying that organic matter content could influence the concentration of this pesticide. A moderate positive correlation was observed between SOM and available phosphorus (0.38).

Available nitrogen showed a strong negative correlation with available phosphorus (−0.78), indicating an inverse relationship between these two nutrients. It had a moderate positive correlation with pH (0.25) and SOM (0.21). There was a weak positive correlation between available nitrogen and acetochlor (0.47).

Available phosphorus had a strong positive correlation with available potassium (0.78), suggesting that factors affecting phosphorus availability might similarly influence potassium. It showed a moderate positive correlation with pH (0.3) and SOM (0.38). There was a weak positive correlation between available phosphorus and atrazine (0.28).

Available potassium exhibited a strong positive correlation with pH (0.82) and SOM (0.81), indicating that both pH and organic matter content can significantly influence potassium availability. It had a moderate positive correlation with available phosphorus (0.78) and acetochlor (0.58).

Atrazine showed a strong positive correlation with alachlor (0.9), suggesting that these two pesticides may share similar environmental fate mechanisms. Acetochlor had a strong positive correlation with SOM (0.92) and alachlor (0.9), indicating that organic matter content and other pesticide concentrations could influence its presence. It showed a moderate positive correlation with available potassium (0.58) and pH (0.82). There was a weak positive correlation between acetochlor and available nitrogen (0.47). Alachlor exhibited a strong positive correlation with atrazine (0.9) and acetochlor (0.9), suggesting that these pesticides may be influenced by similar environmental factors.

3.4. Human Health Risk Assessment

The human health risk assessment data presented in

Table 3. Human health risk assessment of five pesticides in three tillage method soils.

Pesticide	Tillage Method	Adults				Children
		HQi	HQd	HQih	HI	HQi	HQd	HQih	HI
	CK	3.36 × 10−8	1.74 × 10−8	4.32 × 10−12	5.10 × 10−8	1.73 × 10−8	4.73 × 10−9	2.23 × 10−12	2.21 × 10−8
Atrazine	SS	2.61 × 10−8	1.35 × 10−8	3.36 × 10−12	3.97 × 10−8	1.35 × 10−8	3.68 × 10−9	1.74 × 10−12	1.72 × 10−8
	ST	4.52 × 10−8	2.35 × 10−8	5.82 × 10−12	6.87 × 10−8	2.34 × 10−8	6.38 × 10−9	3.01 × 10−12	2.98 × 10−8
	CK	7.89 × 10−7	4.09 × 10−7	1.01 × 10−10	1.20 × 10−6	4.07 × 10−7	1.11 × 10−7	5.24 × 10−11	5.18 × 10−7
Acetochlor	SS	7.84 × 10−7	4.07 × 10−7	1.01 × 10−10	1.19 × 10−6	4.05 × 10−7	1.11 × 10−7	5.21 × 10−11	5.16 × 10−7
	ST	9.39 × 10−7	4.87 × 10−7	1.21 × 10−10	1.43 × 10−6	4.85 × 10−7	1.33 × 10−7	6.25 × 10−11	6.18 × 10−7
	CK	ND	ND	ND	ND	ND	ND	ND	ND
Alachlor	SS	3.38 × 10−7	1.76 × 10−7	4.35 × 10−11	5.14 × 10−7	1.75 × 10−7	4.77 × 10−8	2.25 × 10−11	2.23 × 10−7
	ST	ND	ND	ND	ND	ND	ND	ND	ND
	CK	ND	ND	ND	ND	ND	ND	ND	ND
Nicosulfuron	SS	ND	ND	ND	ND	ND	ND	ND	ND
	ST	ND	ND	ND	ND	ND	ND	ND	ND
	CK	ND	ND	ND	ND	ND	ND	ND	ND
Mesotrione	SS	ND	ND	ND	ND	ND	ND	ND	ND
	ST	ND	ND	ND	ND	ND	ND	ND	ND

reveal significant insights into the exposure risks associated with five herbicides under different tillage methods. These calculations were informed by established models and exposure factors recommended by the USEPA, ensuring alignment with regulatory frameworks for environmental risk evaluation.

The HI values for atrazine vary across different tillage methods. In the CK method, the HI for adults is 5.10 × 10⁻⁸. For children, it is 2.21 × 10⁻⁸. The SS method shows an adult HI of 3.97 × 10⁻⁸ and a child HI of 1.72 × 10⁻⁸. In the ST method, the adult HI is 6.87 × 10⁻⁸, while the child HI is 2.98 × 10⁻⁸. These data indicate that adults face higher risks compared to children in all tillage methods.

Acetochlor presents distinct HI values. In the CK method, the HI for adults is 1.20 × 10⁻⁶. For children, it is 5.18 × 10⁻⁷. In the SS method, the adult HI is 1.19 × 10⁻⁶, and the child HI is 5.16 × 10⁻⁷. The ST method shows an adult HI of 1.43 × 10⁻⁶ and a child HI of 6.18 × 10⁻⁷. These findings highlight the influence of tillage practices on exposure risks for acetochlor.

Alachlor’s HI values also differ by tillage method. In the CK method, all HI values are ND. In the SS method, the adult HI is 5.14 × 10⁻⁷, and the child HI is 2.23 × 10⁻⁷. The ST method shows all HI values as ND. Nicosulfuron and mesotrione consistently show ND HI values across all tillage methods for both adults and children. This suggests minimal non-carcinogenic health risks from these herbicides.

3.5. Degradation of Soil Pesticides Under Different Tillage Methods

This study systematically evaluates how different tillage practices influence the environmental fate of five commonly used herbicides: atrazine, acetochlor, alachlor, nicosulfuron, and mesotrione. The assessment was based on the analysis of degradation kinetics, including ${\mathrm{T}}_{1/2}$ values and R², across three tillage regimes. All pairwise comparisons of degradation efficiency were conducted using Tukey’s Honestly Significant Difference test. Statistically significant differences were identified at p < 0.05.

Even under identical tillage treatments, significant variations were observed in the dissipation rates among the selected herbicides. Conversely, individual pesticides exhibited differing persistence levels when exposed to distinct soil management systems.

Supplementary Table S2, together with Figure 3 and Figure 4, provides a comprehensive summary of the degradation rate constants (k, day⁻¹) and corresponding ${\mathrm{T}}_{1/2}$ values for all tested compounds under the three tillage treatments. These data offer valuable insights into how soil disturbance influences the persistence and transformation of herbicides in agroecosystems.

3.5.1. The Degradation of Pesticides Under the Same Tillage Treatment

Under identical tillage regimes, substantial variations in the degradation rates (as reflected by ${\mathrm{T}}_{1/2}$ values) and transformation pathways among the five selected herbicides were observed.

Under the CK treatment, the order of degradation rates was nicosulfuron (${\mathrm{T}}_{1/2}$ = 11.55 d) > atrazine (14.14 d) > mesotrione (22.35 d) > acetochlor (31.50 d) > alachlor (40.76 d).

The incorporation of SS treatment markedly altered the degradation patterns of the tested herbicides. The most striking change was the significant reduction in the ${\mathrm{T}}_{1/2}$ value of mesotrione from 22.35 d under CK to 14.14 d under SS, making it the fastest-degrading pesticide in this treatment. On the other hand, the degradation of atrazine, acetochlor, alachlor, and nicosulfuron slowed down under SS compared to CK, with ${\mathrm{T}}_{1/2}$ values increasing to 19.80 d, 43.31 d, 49.50 d, and 19.25 d, respectively.

The impact of the ST treatment was more complex. The degradation rate of atrazine under ST (${\mathrm{T}}_{1/2}$ = 13.86 d) was slightly faster than under CK. Degradation dynamics indicated a significantly higher degradation rate by day 3 (30% vs. CK and SS), reaching a high degradation efficiency of 94% by day 55. In contrast, the degradation of alachlor was significantly inhibited under ST (${\mathrm{T}}_{1/2}$ = 53.31 d). Although its early-stage degradation rate (39% by day 7) was higher than under CK (15%) and SS (21%), the degradation rate plateaued in later stages, resulting in a lower final degradation efficiency (70 days) compared to the other pesticides.

3.5.2. Degradation Patterns of Individual Herbicides Under Different Tillage Treatment

The degradation kinetics of five herbicides—atraine, acetochlor, alachlor, nicosulfuron, and mesotrione—were evaluated under three tillage treatments (CK, SS, ST), based on ${\mathrm{T}}_{1/2}$ values and degradation profiles.

Atrazine showed significant variation in degradation across treatments. Under SS, its ${\mathrm{T}}_{1/2}$ increased from 14.14 d (CK) to 19.80 d, whereas under ST, it decreased to 13.86 d. Degradation kinetics further showed that under ST, atrazine degradation started rapidly, reaching 30% within the first three days. This rate was significantly higher than those observed under CK and SS. A marked acceleration was also observed during the mid-to-late incubation phase (40–55 days), ultimately resulting in the highest final degradation efficiency of 94%. Although degradation started more slowly under CK, nearly complete degradation (>95%) was achieved by day 55. This indicates the potential for strong atrazine biodegradation under conventional tillage practices.

Acetochlor and alachlor, both chloroacetamide herbicides, showed similar responses to the tillage treatments tested. Straw incorporation significantly extended their half-life values under both SS and ST treatments. For acetochlor, the ${\mathrm{T}}_{1/2}$ increased from 31.50 days under CK to 43.31 days under SS and 36.47 days under ST. The increase was even greater for alachlor: from 40.76 days under CK to 49.50 days under SS and 53.31 days under ST. Degradation kinetics revealed that acetochlor degraded relatively evenly over time. By day 55, degradation rates were only slightly higher under SS and ST (0.56% and 0.58%, respectively) compared to CK (0.45%). In contrast, alachlor showed notable differences in early-stage degradation. Under ST, 39% degradation was observed by day 7, followed by SS (21%) and CK (15%). However, degradation rates became more similar during later stages. As a result, final degradation efficiencies for both herbicides were relatively low (<60%), compared to other herbicides studied.

For nicosulfuron, the SS treatment significantly increased the ${\mathrm{T}}_{1/2}$ from 11.55 days under CK to 19.25 days. The ST treatment resulted in an intermediate value of 15.40 days. By day 70, degradation exceeded 95% in all treatments.

Mesotrione exhibited the most distinctive response to tillage practices among the five herbicides. Compared to CK (${\mathrm{T}}_{1/2}$ = 22.35 d), degradation was markedly accelerated under SS (${\mathrm{T}}_{1/2}$ = 14.14 d) and moderately so under ST (${\mathrm{T}}_{1/2}$ = 17.77 d). Degradation kinetics clearly demonstrated rapid breakdown under both CK and SS, with degradation rates reaching 65% and 57%, respectively, within the first 3 days, considerably higher than the 39% observed under ST.

The results indicate that different herbicides respond uniquely to tillage and straw incorporation practices. This highlights the importance of conducting pesticide-specific evaluations when assessing their environmental fate.

3.5.3. The Degradation of Pesticides at the Mid-Incubation Period

The mid-incubation phase, approximately 40 days post-application, serves as a critical time point for evaluating relative differences in degradation rates among various pesticides under uniform tillage conditions. This study reveals that mesotrione consistently exhibited the highest degradation efficiency across all tillage treatments at this stage.

Under CK conditions, mesotrione’s degradation efficiency was significantly greater than that of atrazine, acetochlor, and alachlor. Nicosulfuron showed comparable degradation to mesotrione at 40 days under CK.

Under SS conditions, mesotrione’s degradation efficiency surpassed that of all other herbicides, including nicosulfuron.

Under ST conditions, mesotrione showed significantly higher degradation efficiency compared to the strongly adsorbed and slowly degrading chloroacetamide herbicides acetochlor and alachlor. However, no statistically significant differences were found between mesotrione and either atrazine or nicosulfuron at day 40. Alachlor exhibited a relatively high degradation rate during the early stage under ST, with 39% degradation observed by day 7. Nicosulfuron showed a steady degradation pattern throughout the incubation period under the same treatment.

In summary, mesotrione consistently showed the highest degradation efficiency among the five tested herbicides across all tillage treatments at the mid-incubation stage (approximately 40 days after application). Under CK and SS conditions, mesotrione degraded more rapidly than acetochlor and alachlor. Its advantage was especially notable under SS, where it also outperformed nicosulfuron. Under ST, mesotrione remained more efficiently degraded than the chloroacetamide herbicides. However, no significant differences were found between mesotrione and either atrazine or nicosulfuron. These findings highlight mesotrione’s relatively rapid dissipation and its distinct response to tillage practices compared to other commonly used herbicides.

4. Discussion

4.1. Implications of Pesticide Residue Variability

For atrazine, compared to previous studies conducted in similar agroecosystems, the observed atrazine levels were significantly lower than those reported in agricultural soils from Liaoning Province (18.38 μg/kg), riverbank soils of the Songhua River Basin (11.28 μg/kg), and soils surrounding Xingkai Lake (26.09 μg/kg) [4,48]. These differences may be attributed to variations in application history, climatic conditions, or soil physicochemical properties that influence herbicide persistence.

For acetochlor, the corresponding CV of 1.06 suggests substantial spatial heterogeneity in its residual distribution. This level is notably higher than the previously reported acetochlor residues in agricultural soils from Huangdao (10.70 μg/kg) [49], which could reflect differences in pesticide usage patterns or environmental fate characteristics under varying management practices.

For alachlor, the high CV of 3.95 indicates highly uneven distribution, possibly due to localized application or differential degradation rates influenced by microsite-specific factors. Neither nicosulfuron nor mesotrione was detected in any of the soil samples analyzed, suggesting either limited use, rapid degradation, or low persistence under the prevailing environmental conditions.

Under CK conditions, the relatively high CV for atrazine under CK suggests significant spatial variability, which may be related to uneven application or limited mixing in no-till systems. Acetochlor showed low CV, indicating a more uniform distribution, possibly due to consistent application practices or stable environmental behavior under CK conditions. The absence of alachlor, nicosulfuron, and mesotrione under CK may reflect rapid degradation, low application rates, or both.

Under SS treatment, the moderate variability in acetochlor suggests uneven application or localized environmental effects. The detection of alachlor in some samples, along with its high CV, indicates inconsistent presence, possibly linked to differential degradation or application patterns.

Under ST conditions, higher atrazine residues may reflect increased soil retention or slower degradation under more intensive mixing. Acetochlor showed the greatest variability among all treatments, likely due to higher adsorption or microsite-specific degradation rates. The absence of alachlor, nicosulfuron, and mesotrione under ST suggests either rapid dissipation or limited use under this management system.

Collectively, these findings indicate that different tillage practices can exert distinct influences on the distribution and persistence of herbicide residues in agricultural soils. The observed variability across treatments highlights the complex interplay among soil physicochemical properties, microbial activity, and tillage-induced alterations in soil structure and moisture dynamics. A deeper understanding of these processes is essential not only for assessing the environmental fate of herbicides but also for evaluating their potential implications for human health and ecosystem safety. Given the detected presence of several herbicides at varying concentrations, it becomes increasingly important to conduct a comprehensive human health risk assessment to determine whether these residues pose unacceptable risks through direct exposure or food chain transfer. Furthermore, elucidating the underlying degradation mechanisms under different tillage regimes is crucial for predicting herbicide persistence and developing effective mitigation strategies. These investigations will provide a scientific basis for optimizing pesticide use and tillage practices, ultimately supporting the design of more sustainable and environmentally responsible agricultural systems.

4.2. Impact of Different Tillage Practices on Soil Physicochemical Properties

The highest organic matter content was observed under conventional CK, followed by SS, with the lowest levels under ST. This indicates that without straw incorporation and through the use of no-till practices, the soil may retain more organic matter due to less disturbance and slower decomposition rates compared to straw incorporation scenarios [50]. This may be due to reduced soil disturbance in no-till practices, which helps retain more organic material on the soil surface or in the shallow layer, thus enhancing the organic matter content [51,52].

Although the ST treatment showed the lowest organic matter content, it had relatively high available nitrogen, slightly lower than that under CK. This suggests that while straw incorporation may contribute to nutrient input, the tillage method plays a key role in determining nutrient availability. Ridge tillage may promote the transformation of nitrogen into forms that are not immediately accessible to plants [53,54].

Available phosphorus levels varied to some extent across treatments. The differences may reflect variations in phosphorus mobilization mechanisms influenced by tillage practices. Strip tillage may promote microbial activity, which in turn enhances the solubilization of available phosphorus [55,56].

Available potassium levels were higher under CK compared to the other treatments. This may be related to the reduced soil disturbance in no-till systems, which helps maintain soil structure and minimize nutrient loss through leaching [57,58,59].

Differences in soil pH across treatments also suggest that tillage practices influence soil chemical properties. These changes in acidity can affect nutrient availability and overall crop growth conditions [60,61,62].

Different tillage practices affect soil physical and chemical properties to varying degrees. Under CK, higher levels of organic matter are maintained, along with more stable nutrient conditions. These factors contribute to improved soil structure stability and the preservation of long-term fertility. In contrast, strip tillage and rotary tillage with straw incorporation may cause short-term fluctuations in certain nutrient contents. However, these practices enhance overall soil health by promoting microbial activity and nutrient cycling. Understanding how such soil properties interact with pesticide behavior—including adsorption, mobility, and degradation—is essential for assessing both environmental impacts and food safety.

4.3. Discussion on Correlation

The observed correlations suggest that soil physicochemical properties play a key role in determining the fate and persistence of pesticide residues. These findings are consistent with previous studies indicating that the environmental behavior of pesticides is strongly influenced by soil composition [63,64,65]. In addition to agricultural practices such as pesticide application rates and timing, soil properties such as organic matter content, pH, and nutrient status can influence pesticide adsorption, mobility, and degradation. These findings emphasize the need to consider both anthropogenic inputs and inherent soil characteristics when evaluating pesticide occurrence and predicting their environmental impacts.

Notably, a positive correlation was observed between soil pH and both available potassium and acetochlor concentrations. This relationship can be attributed to the influence of soil acidity on pesticide speciation and adsorption [66,67]. SOM exhibited a positive correlation with available potassium and acetochlor, which aligns with the well-documented role of SOM in enhancing pesticide adsorption [68,69]. Atrazine and alachlor also exhibited a significant positive correlation, suggesting potential similarities in their environmental behavior or co-application patterns [70]. In contrast, available nitrogen and available phosphorus displayed a negative correlation. This inverse relationship might be driven by competitive nutrient utilization dynamics within soil microbial communities, where preferential uptake of one nutrient over another disrupts stoichiometric balances. Furthermore, intensified anthropogenic activities—such as excessive nitrogen fertilizer application in agricultural systems and rapid urbanization—are likely contributing factors. These disturbances can lead to imbalances in the natural nitrogen and phosphorus cycles, altering biogeochemical processes and reducing soil nutrient efficiency [71,72]. Collectively, these findings underscore the complex interplay between pesticide contamination and soil properties, shaped by both intrinsic soil characteristics and extrinsic human pressures. The observed patterns suggest that agricultural intensification, characterized by repeated fertilizer use and pesticide overapplication, has significantly altered soil geochemistry and ecological functioning. Therefore, systematic monitoring and integrated management strategies are urgently required to mitigate soil degradation and protect soil environmental quality. Effective interventions not only contribute to maintaining and enhancing soil productivity but also support the long-term sustainability of agroecosystems, ultimately safeguarding the health of terrestrial ecosystems for future generations.

4.4. Discussion on Human Health Risk Assessment

To evaluate the potential human health risks associated with herbicide residues in local farmland soils, we conducted a comprehensive non-carcinogenic risk assessment based on the residual levels of five commonly used herbicides. The exposure assessment focused on adult and child populations, employing widely accepted methodologies and standardized parameters (Table 3) to estimate CDI via three primary exposure pathways: soil ingestion, dermal contact, and inhalation.

The HQ, defined as the ratio of estimated CDI to the RfD of each pesticide, was used to quantify the non-cancer health risk associated with each exposure route. As shown in Table S1, the calculated CDI values (mg kg⁻¹ day⁻¹) for adults across all exposure pathways were consistently higher than those for children. Similarly, HQ values for adult exposure to atrazine, acetochlor, and alachlor through ingestion, dermal, and inhalation routes were notably greater than those for children. This disparity primarily reflects differences in body weight and exposure frequency between the two groups.

According to USEPA guidelines, an HQ or hazard index (HI) value of 1 serves as the threshold for acceptable risk. An HQ or HI exceeding 1 indicates a potential for adverse non-carcinogenic health effects, whereas values below 1 suggest that the risk is minimal under current exposure conditions [73,74]. In this study, the computed HQ and HI values for all evaluated herbicides were substantially lower than the threshold, indicating that the non-carcinogenic health risks posed by soil contamination are currently negligible for both adults and children within the study area.

Nonetheless, it is important to recognize that children may be more vulnerable to pesticide exposure due to their ongoing physiological development, increased hand-to-mouth behavior, and generally lower body weight, which can amplify internal doses relative to adults. These factors contribute to a relatively higher exposure risk for children, despite overall low HQ values [75]. Therefore, while the present findings suggest that the general population faces minimal non-cancer health risks from current soil contamination levels, special attention should still be given to protecting sensitive subpopulations.

From a broader perspective, the co-occurrence of multiple herbicides in agricultural soils may alter their environmental fate and persistence, potentially leading to cumulative or synergistic effects that are not captured by individual risk assessments. Several environmental variables—including soil texture, pH, organic matter content, and microbial community structure—can influence herbicide degradation kinetics and thus modify exposure scenarios over time.

To address these complexities, this study further examined the natural degradation dynamics of the five target herbicides under different tillage practices. This investigation aims to provide a scientific basis for optimizing agricultural management strategies and promoting sustainable pesticide use practices that minimize long-term environmental and health risks.

4.5. Influence of Tillage Practices on Herbicide Degradation

The observed variations in degradation rates highlight the combined effects of pesticide molecular properties and soil environmental conditions. Even under identical tillage treatments, significant variations were observed in the dissipation rates among the selected herbicides. Conversely, individual pesticides exhibited differing persistence levels when exposed to distinct soil management systems. These findings underscore the complex interplay between pesticide physicochemical properties and soil environmental conditions in governing degradation behavior.

The observed differences in degradation rates can be primarily attributed to the inherent molecular characteristics of each pesticide, including solubility, volatility, adsorption capacity, and susceptibility to microbial transformation. Additionally, tillage-induced modifications in soil structure, moisture content, organic matter availability, and microbial community composition further modulate the biotic and abiotic processes responsible for pesticide dissipation.

The findings underscore the importance of integrating soil management strategies into pesticide risk assessment frameworks. Appropriate tillage methods can help reduce environmental contamination by enhancing herbicide degradation without compromising crop productivity.

4.5.1. Comparative Degradation of Pesticides Under the Same Tillage Treatment

Differences in pesticide degradation rates are primarily governed by inherent chemical properties such as molecular structure, water solubility, adsorption behavior, and susceptibility to microbial or chemical degradation processes.

Nicosulfuron’s high lability under typical soil conditions is due to its susceptibility to chemical hydrolysis. In contrast, acetochlor and alachlor, both chloroacetamide herbicides, possess stable molecular structures and exhibit high hydrophobicity, which promotes strong sorption to soil organic matter. This reduces their bioavailability and slows down microbial degradation, leading to prolonged persistence in the soil environment [76,77]. Atrazine and mesotrione displayed intermediate degradation rates, likely due to a combination of moderate sorption and variable susceptibility to biotic and abiotic degradation mechanisms. Microbial degradation plays a key role in the dissipation of many pesticides, particularly those with moderate to low sorption properties. Microbial degradation plays a key role in the dissipation of many pesticides, particularly those with moderate to low sorption properties. Several bacterial genera—including Bacillus, Micrococcus, Arthrobacter, Corynebacterium, Flavobacterium, Pseudomonas, and Rhodococcus—are well known for their high pesticide-degrading capabilities [78].

The introduction of SS treatment led to enhanced degradation of mesotrione, which can be attributed to the addition of crop straw, which serves as a carbon and energy source for soil microorganisms, thereby promoting the proliferation of specific microbial communities capable of metabolizing mesotrione [79]. However, the same treatment slowed the degradation of other herbicides, which suggests that straw application may have temporarily immobilized these compounds through increased organic matter content or altered microbial community dynamics, thereby delaying their breakdown. Studies have shown that straw incorporation can shift microbial community structure, favoring copiotrophic bacteria that enhance nutrient cycling and pesticide mineralization under certain conditions [80].

ST treatment demonstrated complex impacts on different herbicides. Atrazine showed accelerated degradation, while alachlor experienced inhibited degradation. For nicosulfuron and acetochlor, degradation rates under ST fell between those observed under CK and SS, indicating a moderate influence of this tillage method on their dissipation. Mesotrione degraded slightly faster under ST than under CK but slower than under SS, reflecting a combined effect of soil physical disturbance and microbial stimulation induced by subsoiling.

In summary, these findings illustrate that even under the same tillage regime, herbicides exhibit distinct degradation behaviors, largely dictated by their physicochemical properties and interactions with the soil matrix. Furthermore, different tillage practices—by altering soil structure, microbial habitat, and organic matter dynamics—can either enhance or suppress pesticide degradation, highlighting the importance of integrating soil management strategies into pesticide risk assessment frameworks.

4.5.2. Degradation Responses of Individual Pesticides to Different Tillage Treatments

The interaction between tillage practices and straw management strategies exerted highly differentiated effects on the degradation dynamics of individual herbicides, reflecting both pesticide-specific physicochemical properties and tillage-induced alterations in soil environmental conditions.

For atrazine, significant differences were observed across the three tillage regimes. The SS treatment notably delayed degradation, whereas the ST treatment maintained or slightly accelerated it. These findings suggest that ridge-based straw mulching may reduce atrazine bioavailability through enhanced adsorption or altered microbial activity, while rotary tillage under ST likely promotes degradation via improved soil aeration and mixing [81]. Degradation kinetics revealed distinct temporal patterns under different tillage treatments. Under ST, atrazine degradation began more rapidly compared to CK and SS, indicating enhanced early-stage dissipation. A marked increase in degradation rate was also observed during the mid-to-late incubation phase, resulting in high final degradation efficiency. In contrast, CK showed slower initial degradation but still achieved near-complete breakdown by the end of the observation period, highlighting the resilience of atrazine biodegradation under conventional management practices.

Both acetochlor and alachlor, classified as chloroacetamide herbicides, exhibited similar responses to the tested tillage treatments. Straw incorporation prolonged their degradation times under both SS and ST regimes, indicating increased persistence in the soil environment. Degradation patterns revealed that acetochlor was relatively stable over time, with minimal variation across treatments, suggesting that tillage had limited impact on its overall dissipation. In contrast, alachlor showed distinct differences in early-stage degradation, with the ST treatment promoting faster initial breakdown. However, degradation rates tended to converge in later stages, resulting in generally low final degradation efficiencies. These observations suggest that while certain tillage practices may temporarily enhance alachlor degradation, long-term suppression occurs, potentially due to straw-induced adsorption or microbial inhibition.

For nicosulfuron, the SS treatment significantly delayed degradation, while the ST treatment resulted in an intermediate effect. Kinetic analysis revealed a consistent and gradual increase in degradation over time across all treatments, with no statistically significant differences among them. By the end of the observation period, degradation exceeded 95% in all cases, indicating that although straw incorporation, particularly under SS, may initially slow down degradation through adsorption or microenvironmental changes, nicosulfuron’s high susceptibility to hydrolysis and microbial degradation [82] ensures near-complete dissipation regardless of the tillage method.

Mesotrione exhibited the most distinctive response to tillage practices among the five herbicides. Degradation was markedly accelerated under SS, while ST also promoted a faster degradation rate compared to CK. Degradation kinetics demonstrated rapid breakdown under both CK and SS during the early stage, whereas degradation started more slowly under ST. This trend persisted throughout the incubation period. The slower initial degradation under ST could be attributed to mechanical disturbance affecting microbial community structure or altering the spatial distribution of straw, which might have temporarily hindered microbial access to mesotrione [83,84]. Nonetheless, high final degradation efficiency was eventually achieved, underscoring the adaptability of microbial populations to changing soil conditions induced by subsoiling.

In summary, the degradation behavior of each herbicide responded uniquely to the applied tillage and straw management strategies. These differential responses highlight the interplay between pesticide molecular characteristics, soil physical–chemical properties, and microbial activity modulated by agricultural practices. Understanding such interactions is crucial for optimizing soil management systems that balance pesticide efficacy with environmental safety.

4.5.3. Cross-Pesticide Comparison of Degradation Efficiency at the Mid-Incubation Period

The mid-incubation phase serves as a critical time point for evaluating relative differences in degradation rates among various pesticides under uniform tillage conditions. This study reveals that mesotrione consistently exhibited the highest degradation efficiency across all tillage treatments at this stage, highlighting its intrinsic rapid dissipation characteristics and distinct responsiveness to soil management practices.

Under CK conditions, mesotrione showed superior degradation efficiency compared to atrazine, acetochlor, and alachlor. Nicosulfuron also demonstrated high degradability, though its rate at this stage was not significantly different from that of mesotrione under CK.

Under SS conditions, however, mesotrione’s degradation advantage became even more evident, surpassing all other herbicides, including nicosulfuron. This observation suggests a potential synergistic interaction between mesotrione and straw incorporation. Crop straw incorporation can alter soil microbial community composition by introducing abundant labile organic carbon. This change may promote the growth of specific microbial populations capable of degrading mesotrione, potentially accelerating its breakdown [85].

Under ST conditions, mesotrione maintained significantly higher degradation efficiency compared to the strongly adsorbed and slowly degrading chloroacetamide herbicides—acetochlor and alachlor. However, its performance did not differ significantly from that of atrazine or nicosulfuron at this stage. This outcome reflects the complex interactions induced by mechanical soil disturbance. On one hand, ST may have improved soil structure, aeration, and the spatial distribution of straw, which could favor aerobic microbial activity and enhance pesticide degradation. On the other hand, the initial physical disruption caused by rotary tillage might have transiently suppressed or dispersed certain microbial populations, delaying the onset of active degradation. The observed reduction in degradation efficiency differences between mesotrione and some herbicides under ST may be attributed to treatment-specific changes in soil–pesticide–microbe interactions. Similarly, nicosulfuron’s consistent degradation pattern suggests a high degree of stability in its dissipation process, even under altered soil conditions imposed by tillage practices.

This study demonstrates that the combined effects of tillage regimes and straw management strategies exert profound and differential influences on pesticide degradation dynamics in agricultural soils. These effects are highly dependent on the physicochemical properties of each compound and its dominant degradation pathways. Straw incorporation generally retarded the degradation of hydrophobic compounds such as acetochlor and alachlor, likely due to increased soil organic matter content, enhanced sorption capacity, and reduced bioavailability. In contrast, for compounds that are readily metabolized by soil microorganisms—such as mesotrione—straw acted as a valuable carbon and energy source, promoting the growth of specialized or co-metabolizing microbial communities and thereby accelerating degradation. These findings highlight how different tillage methods can substantially alter the environmental fate of herbicides, influencing their persistence and potential ecological risks [86]. Different tillage methods can substantially impact the degradation of herbicides in soil, affecting their persistence and potential environmental risks [31].

To effectively mitigate pesticide residues in agroecosystems, this study recommends integrating straw incorporation with either ST or SS for atrazine and mesotrione, given their positive responses to these practices. For persistent herbicides like acetochlor and alachlor, alternative compounds or enhanced degradation strategies should be considered to reduce residual contamination risks.

The results also provide actionable insights for sustainable agricultural management and policy development. Our findings suggest that conservation tillage systems—particularly those involving moderate soil disturbance and straw retention—can be strategically implemented to enhance herbicide degradation and reduce environmental risks, especially in regions where atrazine and mesotrione are commonly used. However, for more persistent herbicides such as acetochlor and alachlor, careful regulation and monitoring of application rates and timing are necessary to avoid long-term soil contamination. These outcomes support the development of site-specific pesticide use guidelines and soil conservation policies that align with local agronomic and environmental conditions.

Future research should focus on characterizing the dynamics of soil microbial communities and key functional genes involved in pesticide degradation under different tillage-straw systems. Additionally, efforts should explore strategies to optimize tillage intensity, timing, and residue management to support sustainable pesticide use while minimizing environmental impacts.

5. Conclusions

This study provides a comprehensive assessment of herbicide residues in agricultural soils under different tillage regimes, revealing distinct patterns of persistence and environmental behavior among the tested compounds. Atrazine residues ranged from ND to 21.10 μg/kg (mean: 5.28 μg/kg), while acetochlor showed the highest variability, ranging from 2.29 to 120.61 μg/kg (mean: 25.26 μg/kg). Alachlor was detected at much lower levels (ND–5.71 μg/kg; mean: 0.34 μg/kg). Nicosulfuron and mesotrione were not detected, indicating rapid dissipation or limited application frequency.

Soil properties, such as organic matter and pH, were positively correlated with available potassium and acetochlor concentrations, highlighting their role in modulating pesticide behavior.

Health risk assessments indicated negligible non-cancer risks for both adults and children through ingestion, dermal contact, and inhalation. However, long-term monitoring is still recommended to ensure environmental and public health safety.

Crucially, this study demonstrates that tillage methods significantly influence herbicide degradation kinetics in soil, thereby affecting their environmental persistence and associated ecological risks. For instance, ST and SS treatment enhanced the degradation of atrazine and mesotrione, indicating that these management practices may be effectively integrated into residue mitigation strategies for such compounds. In contrast, acetochlor and alachlor exhibited longer half-lives, especially under straw incorporation, likely due to increased adsorption and reduced bioavailability.

In conclusion, this study emphasizes the pivotal role of agricultural management practices in shaping the environmental fate of herbicides. By integrating tillage and residue management strategies tailored to specific pesticides, it is possible to enhance degradation, reduce persistence, and mitigate ecological and health risks, thereby supporting the long-term sustainability of agroecosystems.