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Article

Residual Effect of Imidazolinone Herbicides on Emergence and Early Development of Forage Species in Rice-Livestock Systems

by
Valentina Rodriguez-De-Barbieri
1,
Pablo González-Barrios
2,
Pablo Rovira
3,
Claudia Marchesi
3,
Robin Cuadro
3,
Rodrigo Zarza
3 and
Tiago Edu Kaspary
3,*
1
Faculty of Agronomy, Universidad de la República (UDELAR), Montevideo 12900, Uruguay
2
Department of Biometrics and Statistics, Faculty of Agronomy, Universidad de la República (UDELAR), Montevideo 12900, Uruguay
3
National Institute of Agricultural Research of Uruguay (INIA), Research Station, Treinta y Tres 33000, Uruguay
*
Author to whom correspondence should be addressed.
Int. J. Plant Biol. 2025, 16(3), 110; https://doi.org/10.3390/ijpb16030110
Submission received: 2 August 2025 / Revised: 12 September 2025 / Accepted: 15 September 2025 / Published: 18 September 2025
(This article belongs to the Section Plant Response to Stresses)
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Abstract

The intensification of rice–livestock systems has encouraged the integration of forage species into rice cultivation. However, the use of imidazolinone-tolerant rice cultivars (imazapyr + imazapic, IMIs), essential for weedy rice control, may hinder the establishment of sensitive forages due to herbicide residues. This study evaluated the emergence and early growth of six forage species through bioassays in soils with different IMI use histories. Over three years (2021–2023), soils were collected from three rice-growing regions in Uruguay with contrasting soil properties, at depths of 0–15 and 16–30 cm, under three IMI conditions: Control (no prior use), IMI-1 (applied one season before sampling), and IMI-2 (applied in the season before sampling). Emergence, plant height, and shoot and root biomass were analyzed using linear mixed models and principal component analysis. Shoot biomass was reduced by up to 60% in IMI-2 soils. Poaceae species and T. pratense were the most affected, while T. repens and L. corniculatus exhibited higher tolerance. Multivariate analysis indicated stronger residual effects on sandy loam soils. These findings highlight that imidazolinone persistence varies with forage species and soil properties, underscoring the need for careful planning in rice–pasture rotations to prevent adverse effects on forage establishment and system sustainability.

1. Introduction

The integration of rice (Oryza sativa) cultivation with forage systems represents a strategy aimed at optimizing resource use, enhancing sustainability, and increasing the overall productivity of the system. Following rice harvest, the sowing of grass and legume species in livestock-based systems extends the grazing period and promotes the recovery of the soil’s physical and chemical properties, with positive effects on crop yield in subsequent cycles [1,2,3]. In Uruguay, the main forage species sown in these systems include ryegrass (Lolium multiflorum), tall fescue (Festuca arundinacea), white clover (Trifolium repens), and bird’s-foot trefoil (Lotus corniculatus). However, pasture establishment can be limited by several factors, including the high volume of rice stubble and the presence of herbicide residues from the previous growing season [4].
Approximately 60% of the area devoted to rice cultivation in Uruguay is integrated into rotation systems with pastures. Within this area, around 25% is in soils previously planted with rice tolerant to acetolactate synthase (ALS)-inhibiting herbicides, particularly those belonging to the imidazolinone group (imazapyr + imazapic—IMIs) [5]. In this context, the development and use of IMI-tolerant rice cultivars have enabled effective control of problematic weeds, including weedy rice (Oryza spp.) [6]. These herbicides are characterized by high persistence in soil and prolonged residual activity [7,8,9], which are determined by edaphoclimatic factors, such as soil texture, pH, organic matter, moisture and temperature [10,11,12,13].
Several studies have demonstrated that imidazolinones can remain active in the soil for over 300 days, causing residual effects—known as carryover—on sensitive crops sown in rotation [14,15]. Reductions of up to 94% in dry matter of sorghum (Sorghum bicolor) have been reported 150 days after application [16]. In non-tolerant rice, yield losses close to 55% were observed even 371 days after the last herbicide application. Moreover, a 10% decrease in plant height was recorded when imazapyr + imazapic concentrations reached 4.07 and 5.02 µg kg−1 of soil, respectively [17,18]. In soybean (Glycine max), reductions in both shoot and root biomass were reported up to 359 days post-application [19]. In forage species such as annual ryegrass (Lolium multiflorum) and red clover (Trifolium pratense), significant decreases in forage production were detected up to 180 days after exposure to these herbicides [20,21,22,23].
In this context, bioassays are considered an efficient tool to evaluate the persistence and activity of herbicide residues in the soil [24,25]. They allow for the detection of effects on sensitive species by using soil samples either with direct herbicide applications or with a history of herbicide use.
The aim of this study was to evaluate the carryover effect of IMIs on the establishment and early development of six forage species through bioassays using soils with a history of imazapyr + imazapic application during rice cultivation. The hypothesis was that residues of these herbicides persist in the soil long enough to cause phytotoxic effects, within a magnitude that varies depending on species, soil depth, edaphic properties, and herbicide use history. To our knowledge, this is the first multi-year evaluation of IMIs residues on forage species in rice-pasture rotations in Uruguay. This work provides novel experimental evidence of the carryover effect under controlled conditions and offers practical insights to improve the planning of the forage phase and management decisions in rice-pasture systems.

2. Materials and Methods

2.1. Soil Origin and Sampling

Bioassays were conducted in 2021, 2022 and 2023 using soils collected from agricultural fields located in productive regions of Uruguay, representative of different soil textural classes. For each region and sampling year, approximately 45 days after rice harvest, soils were collected from three contrasting herbicide use conditions: Control, with no history of IMIs application; IMI-1, where imazapyr + imazapic were applied during the cropping season prior to sampling (more than 17 months since the last application); and IMI-2, where imazapyr + imazapic were applied during the season immediately preceding sampling (less than 5 months since the last application) (Table 1).
Composite samples were collected for each condition, consisting of three randomly selected subsamples representative of 30 cm in width × 0 cm in length × 30 cm in depth. Each sample was then divided into two layers: 0–15 cm and 16–30 cm depth. After collection, soils were air-dried at room temperature and partially sieved to facilitate their use for forage species sowing. In addition, a subsample was taken for physicochemical soil analysis. The composite soil sample obtained for each condition was used to fill pots. For each forage species within a given combination, four pots were established from the same composite, thus representing independent biological responses rather than independent soil replicates.

2.2. Soil Characterization

The physicochemical characteristics of the soils used in the bioassays for each sampling region are summarized in Table 2. Detailed data by site, year, and land use are available in the Supplementary Material (Tables S1–S3).

2.3. Experimental Design of the Bioassays

The bioassays were conducted using 0.3 L pots filled with soil corresponding to each combination of site, herbicide use history, and depth. Within each combination, the six forage species were randomized, with four pots per species established. The species evaluated are commonly used in rice-pasture systems: tall fescue (Festuca arundinacea), annual ryegrass (Lolium multiflorum), perennial ryegrass (Lolium perenne), white clover (Trifolium repens), red clover (Trifolium pratense) and bird’s-foot trefoil (Lotus corniculatus). Twelve seeds were sown per pot, and the experiments were maintained under greenhouse conditions (15 ± 5 °C, 12/12 h light/dark cycle, and daily irrigation). A total of 21 days after sowing (DAS), seedlings were thinned to leave two plants per pot. Thus, the four replicates per species represent variability in plant performance under uniform soil conditions, rather than independent soil replicates.
The variables evaluated were:
  • Emergence (%): determined at 21 DAS by counting the number of seedlings emerging per pot. Seedlings were considered to have emerged if they were visible above the soil surface with clearly unfolded cotyledons or first leaves. The value was expressed as a percentage relative to the total number of seeds sown. Although seed physiological quality was not assessed, the seed lots used showed germination and vigor levels above the minimum standards established by the National Seed Institute—Uruguay (INASE) [26].
  • Plant height (cm): measured at 35 and 70 DAS. For grasses, height was determined from the soil surface to the tip of the last fully expanded true leaf. For legumes, it was measured from the base of the plant to the last visible node in the main stem.
  • Shoot and root dry mass: at the end of the bioassay (70 DAS), plants were harvested. Shoots and roots systems were carefully separated, with excess soil gently removed. Both fractions were washed, dried, and then oven-dried at 60 °C until constant weight was reached. Results were expressed as grams of dry matter per plant (g·plant−1).

2.4. Statistical Analysis

Statistical analyses were performed using linear mixed models within a factorial structure that included the fixed effects of IMI herbicide use history, forage species, and sampling depth, as well as their interactions. These three factors were treated as fixed effects, while replication and site nested within year were included as random effects to account for spatial and temporal variability in the experiment. All response variables were analyzed through ANOVA, and when significant effects were detected, multiple comparisons were performed using Tukey’s test at 95% confidence level. Residual diagnostics were also conducted for all variables to verify model assumptions, including normality and homoscedasticity.
Multivariate analyses were performed to complement the results and explore multivariate patterns of association between soil variables—such as texture (sand, silt, and clay), pH, and organic carbon content—and plant response variables. For this purpose, a principal component analysis (PCA) was conducted and graphically evaluated using biplots. All analyses were carried out using R statistical software (version 4.5.0) [27].

3. Results and Discussion

3.1. Plant Response Variables

3.1.1. Emergence

Plant emergence (%) at 21 DAS showed a significant three-way interaction (p < 0.05) among the factors forage species, soil depth, and herbicide use history (Table S4). The different species evaluated in the bioassays exhibited lower emergence values when sown in IMI-1 and IMI-2 soils compared to the Control, with no history of IMI herbicide application (Figure 1).
Among the grasses, F. arundinacea was the most affected species, with an average emergence reduction of 30% in soils with a history of IMI use, regardless of sampling depth (Figure 1). In contrast, L. multiflorum and L. perenne showed lower sensitivity, with emergence reductions close to 20% compared to the Control. Previous studies have reported a lower sensitivity of de Lolium genus to IMI residues, suggesting that phytotoxicity may depend on factors such as application rate, soil properties, and environmental conditions, with no marked effects observed during early development stages [28,29,30,31].
Legume species also showed significant reduction in emergence when sown in soils with a history of IMI herbicide use compared to the Control (Figure 1). This reduction was more pronounced in soils from the upper layer (0–15 cm), with a 35% decrease in T. pratense and 30% in both T. repens and L. corniculatus. In the case of T. repens, similar reductions in emergence have been reported at application rates 280 g a.i. ha−1 of imazapyr. These results highlight both the differential sensitivity among species and the importance of the time interval between herbicide application and sowing [30,32]. However, in the present study, the longer interval between herbicide application and sowing observed in the IMI-1 treatment, compared to IMI-2, did not result in significant differences in emergence. This indicates that the time elapsed alone was not sufficient to reduce the residual (carryover) effect of IMI herbicides in the sampled soils.
On the other hand, although significant interaction was observed among species, depth, and herbicide use history, no consistent effect of sampling depth on emergence was detected. This suggests that there was no clear pattern of IMI residue accumulation in the deeper layers of the soil profile. In fact, the literature reports that these herbicides are often uniformly distributed within the top 15 cm of the soil profile, regardless of whether the system is conventional or no-till and may even be transported upward by mass flow to more superficial soil layers [11,33].

3.1.2. Plant Height

Plant height measurements taken at 35 and 70 DAS showed significant effects (p < 0.05) for two-way interactions among the studies factors (Table S5; Figure 2 and Figure 3). This indicates that the growth response of the forage species was influenced by the different combinations of factors, including herbicide use history, soil depth, and/or the species-specific sensitivity.
In the interaction between herbicide use history and soil depth at 35 DAS (Figure 2a), a general reduction in plant height was observed in IMI-1 treatment compared to the Control. The most pronounced decrease occurred under IMI-2, indicating greater exposure to or residual effect (carryover) of the herbicide in soils with recent IMI applications. At 70 DAS, plants showed good recovery capacity in the deeper soil layer (16–30 cm), which may suggest lower herbicide residue concentrations at this depth (Figure 3a). This pattern is consistent with the results observed for the emergence variable. Additionally, the recovery observed in plant height could also be associated with increased tolerance to herbicide residues in the soil as vegetative development progresses in the different species [34,35].
The interaction between herbicide use history and species revealed greater sensitivity in grasses when grown in IMI-2 soils, particularly at early stages (35 DAS, Figure 2b). At 70 DAS, plant height in F. arundinacea and L. perenne did not differ significantly among soils with a history of IMI use, but remained lower than in the Control. This behavior suggests dynamic species-specific responses at different stages of development (Figure 3b). In contrast, legumes showed less pronounced differences, with similar heights between the Control and IMI-1, or no significant differences at 35 DAS for T. repens. It is important to note that this species exhibited particularly slow development up to 35 DAS, even in the Control treatment, and only at 70 DAS was it possible to distinguish IMI-2 from the other land use conditions (Figure 3b). The occurrence of temperatures below 15 °C may have delayed T. repens development, as several authors indicate that temperatures above this threshold are more favorable for rapid establishment [36].
The interaction between depth and species (Figure 2c and Figure 3c) indicates that, in general, grasses exhibited lower sensitivity to IMI use compared to legumes, showing greater plant height at both soil depths (0–15 cm and 16–30 cm) at both 35 and 70 DAS. This suggests that plant height depends more on species and herbicide use history than on soil depth. In this context, it is important to consider morphological differences in growth patterns, particularly between legumes and grasses, which directly influence plant size.
The plant height response patterns observed in this study are consistent with previous research reporting differential species sensitivity to IMI herbicides residues. Several authors have described height reductions in L. multiflorum ranging from 30% to 50% at application rates of 140 g a.i. ha−1 of imazapyr + imazapic, while for F. arundinacea, T. repens and L. corniculatus, reductions of up to 100% have been reported [37,38,39]. Growth inhibition is considered one of the most characteristic effects of ALS-inhibiting herbicides, as they block the biosynthesis of essential branched-chain amino acids (valine, leucine, and isoleucine) [37,38,40]. The lack of these amino acids disrupts protein synthesis and cell growth, leading to growth inhibition and, lethal doses, plant death [40]. In our bioassays, this effect was expressed phenotypically as visibly shorter plants across sensitive species.

3.1.3. Shoot and Root Dry Mass

Shoot and root dry mass evaluations showed significant effects (p < 0.05) for two-way interactions among the study’s factors (Tables S6 and S7; Figure 4 and Figure 5). In the herbicide use history × depth interaction (Figure 4a and Figure 5a), a significant reduction in both shoot and root biomass accumulation was observed in soils with a history of IMI herbicide use (IMI-1 and IMI-2) compared to the Control, particularly in the upper soil layer (0–15 cm). This reduction was more pronounced under IMI-2, consistent with the patterns observed for emergence and plant height at 70 DAS. In contrast, at the 16–30 cm depth, no differences in shoot and root dry mass accumulation were found between IMI soils, again suggesting that lower herbicide residue concentrations at this depth [34,35].
In the herbicide use history × species interaction (Figure 4b and Figure 5b), L. multiflorum showed the greatest reduction in shoot dry mass (SDM) in soils with the most recent herbicide use, with values of 1.431, 0.642 and 0.418 g·plant−1 for the Control, IMI-1 and IMI-2 respectively. For root dry mass (RDM), F. arundinacea and L. perenne also showed reductions compared to the Control, although no significant differences were found between IMI-1 and IMI-2. In contrast, L. corniculatus and T. repens appeared more tolerant, with no significant differences in RDM accumulation across herbicide use histories compared to the Control (Figure 5b). Phenotypically, this was expressed as visibly smaller plants with less developed root systems in the sensitive species, while tolerant legumes maintained root biomass comparable to the Control.
Similarly, reductions in dry mass accumulation of L. multiflorum and F. arundinacea of approximately 80% and 100%, respectively, have been reported when these forage species were sown after the use of IMI herbicides in rice cultivation [38,39,41,42]. For L. corniculatus and T. repens, similar findings have been reported, showing no reductions in dry mass under different application rates of imazapyr + imazapic [31,32]. In this context, studies conducted in warmer regions of Brazil have proposed L. corniculatus and T. repens as potential phytoremediator species. These studies reported over 90% reductions in IMI residue concentrations in the soil when these legumes were cultivated in rotation [38,43,44].
The greater tolerance of legumes to imidazolinone residues has been attributed to their ability to contribute nitrogen, enhancing the degradation of these compounds in the soil solution. Additionally, the higher lignin content in legume cell walls compared to grasses may promote sorption of IMI herbicides into more soluble fractions [43]. Conversely, other studies have reported reductions of approximately 80% in shoot dry mass in legumes such as L. corniculatus and T. repens under IMIs treatments [38], indicating that legume tolerance may be context dependent.
Regarding the depth x species interaction (Figure 4c and Figure 5c), the dry mass accumulation pattern was similar to that observed for plant height, reinforcing the trend that the observed differences depend more on species-specific morphological traits than on soil depth. This differential tolerance to IMI herbicide residues highlights the varying potential of each species for use in scenarios with a risk of imidazolinone carryover.

3.2. Multivariate Analysis

In the global principal component analysis (PCA) (Figure 6), which included Control, IMI-1, and IMI-2 soils, the first two components explained 57.6% of the total variance (Dim1 = 33.1%; Dim2 = 24.5%). Soil textural variables, particularly sand, silt, and clay, were strongly associated with Dim1, contributing 30.9%, 26.3% and 19.9%, respectively. Sand showed a negative association, whereas silt and clay were positively correlated. In contrast, plant response variables—especially shoot dry mass (SDM) and plant height—were more represented in Dim2, contributing 26.0% and 21.3%, respectively. Soil pH also showed a clear negative association with this dimension (21.4%). Although emergence and organic carbon (OC) are represented in the biplot, their main contribution was expressed in Dim3 (31.0% and 30.1%, respectively) (Table S8). These results indicate that soils with higher silt content tend to favor plant development, while sandier and more acidic soils are associated with lower emergence and shoot biomass.
The PCA conducted by herbicide use history revealed consistent general patterns (Figure 7a–c; Tables S9–S11). In all cases, soil texture variables (sand, silt, and clay) were primarily associated with Dim1, while SDM, pH, and OC were mainly linked to Dim2. Emergence and plant height showed greater representation in Dim3. A positive association between SDM and height with silt and organic carbon was particularly evident in soils with prior IMI use. In these soils, the contribution of favorable edaphic conditions to improved forage species development was more pronounced.
The results of the multivariate analysis were consistent with findings reported in the literature regarding the influence of soil properties on the persistence and bioavailability of IMI herbicides. Soils with higher clay content—such as those from Treinta y Tres or UEPL—tend to promote herbicide adsorption, which reduces immediate bioavailability to plants but prolongs persistence within the soil profile [12,45,46]. In contrast, soils with a low organic matter content and sandy loam texture—such as those from Rio Branco or Tacuarembó—tend to retain imazapyr + imazapic residues in more bioavailable form, thereby increasing their phytotoxic potential [22].
These mechanisms align with the patterns observed in the PCA, where soil texture variables were associated with the dimensions explaining the greatest variance in the dataset and were related to plant response variables. In particular, soils with higher proportions of silt and organic carbon were more closely associated with improved forage performance. Taken together, these results support that the interaction between soil properties and the presence of IMI herbicide residues strongly influences pasture establishment success-even more than 17 months after the last herbicide application [41,42,47].
In summary, the evaluation of emergence, plant height, and shoot and root dry mass revealed consistent differences in forage species responses to imidazolinone residues. The multivariate analysis further integrated these patterns, highlighting the combined influence of soil properties and herbicide use history on pasture establishment. Nevertheless, some methodological considerations must be acknowledged. First, the greenhouse conditions (restricted pot volume, prior drying of soils, and daily irrigation) differ from flooded field conditions and may underestimate IMIs persistence under anaerobic environments. Second, a single composite soil sample was used per condition, which optimized the assessment of species responses under homogeneous conditions but may not fully capture natural soil heterogeneity. Future studies incorporating multiple independent composites per treatment would allow a better representation of soil variability and strengthen inference.

4. Conclusions

This study provides novel experimental evidence of the carryover effects of imazapiyr + imazapic residues by testing six forage species in soils collected from rice cultivated with IMI herbicides. The approach highlights a methodological innovation that allows the evaluation of species-specific responses under real production histories.
The emergence and early growth of six forage species were significantly affected by IMIs residues in soils with a history of application in imidazolinone-tolerant rice. Differences in species sensitivity were evident, as reflected in emergence, growth, and biomass. Phenotypically, sensitive species exhibited visibly shorter plants with reduced biomass accumulation and poorly developed root systems. Among legumes, T. repens and L. corniculatus showed comparatively higher tolerance, whereas T. pratense was strongly affected, highlighting the importance of evaluating species individually rather than by functional group. Grasses were generally the most affected, with F. arundinacea showing higher sensitivity under these conditions.
These results underscore the importance of considering not only the choice of forage species, but also the history of IMI herbicide use and the soil’s physical and chemical properties. The interaction between these factors can strongly influence pasture establishment and productivity, particularly in cropping systems that include IMI-tolerant crops. From a practical perspective, in loamy-sand soils with recent IMI applications (IMI-2), T. repens and L. corniculatus appear as safer options for establishment, while more sensitive species such as F. arundinacea may require greater caution and favorable soil conditions to succeed. Future studies incorporating quantitative analyses of herbicide residues in soil, together with field-based evaluations under varying environmental conditions, will be essential for improving management recommendations and reducing establishment failures.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ijpb16030110/s1, Table S1. Soil Characterization—Year 2021, Table S2. Soil Characterization—Year 2022, Table S3. Soil Characterization—Year 2023, Table S4. Analysis of Deviance Table—Emergence, Table S5. Analysis of Deviance Table—Plant height 35 y 70 DDS, Table S6. Analysis of Deviance Table—Shoot dry mass, Table S7. Analysis of Deviance Table—Root dry mass, Table S8. Global Principal Component Analysis (PCA), Table S9. Control Principal Component Analysis (PCA), Table S10. IMI-1 Principal Component Analysis (PCA), Table S11. IMI-2 Principal Component Analysis (PCA).

Author Contributions

Conceptualization, V.R.-D.-B., R.Z. and T.E.K.; methodology, V.R.-D.-B., R.Z., T.E.K., P.R., C.M., R.C. and P.G.-B.; data curation, V.R.-D.-B., T.E.K. and P.G.-B.; formal analysis, V.R.-D.-B. and T.E.K.; investigation, V.R.-D.-B., R.Z. and T.E.K.; writing—original draft preparation, V.R.-D.-B., R.Z., C.M., R.C., P.R., T.E.K. and P.G.-B.; writing—review and editing, V.R.-D.-B., R.Z. and T.E.K.; supervision, R.Z. and T.E.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Instituto Nacional de Investigación Agropecuaria (INIA), Uruguay (Project Arroz-Ganadería, CL_52).

Acknowledgments

The authors would like to thank the technical staff and farmers from different study areas for their valuable collaboration in the identification, characterization, and sampling of rice fields. Their support was essential for the implementation of the bioassay and the development of this research. We also thank the Instituto Nacional de Investigación Agropecuaria (INIA), Uruguay, for granting us the master’s scholarship, which made this work possible.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Emergence (%) of different forage species as affected by herbicide use history and soil depth, evaluated 21 days after sowing (DAS), INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
Figure 1. Emergence (%) of different forage species as affected by herbicide use history and soil depth, evaluated 21 days after sowing (DAS), INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
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Figure 2. Plant height (cm) of different forage species 35 days after sowing (DAS), as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
Figure 2. Plant height (cm) of different forage species 35 days after sowing (DAS), as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
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Figure 3. Plant height (cm) of different forage species 70 days after sowing (DAS), as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
Figure 3. Plant height (cm) of different forage species 70 days after sowing (DAS), as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
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Figure 4. Shoot dry mass (g·plant−1) as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
Figure 4. Shoot dry mass (g·plant−1) as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
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Figure 5. Root dry mass (g·plant−1) as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
Figure 5. Root dry mass (g·plant−1) as affected by three interactions: (a) herbicide use history × depth, (b) herbicide use history × forage species, and (c) depth × forage species, INIA 2025. Different letters indicate significant differences according to Tukey’s test (p < 0.05).
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Figure 6. Principal component analysis (PCA) of the relationships between early plant development variables (emergence, plant height, and shoot dry mass, SDM) and soil physicochemical properties (sand, clay, silt, pH and organic carbon, OC) according to the herbicide use history: Control (no herbicide use), IMI-1 (application in the previous growing season, ≈17 months before sampling) and IMI-2 (application in the most recent growing season, ≈5 months before sampling). Each point represents a group of samples classified by herbicide use history, with 95% confidence ellipses. Arrows indicate the direction and contribution of each variable to the first two principal components.
Figure 6. Principal component analysis (PCA) of the relationships between early plant development variables (emergence, plant height, and shoot dry mass, SDM) and soil physicochemical properties (sand, clay, silt, pH and organic carbon, OC) according to the herbicide use history: Control (no herbicide use), IMI-1 (application in the previous growing season, ≈17 months before sampling) and IMI-2 (application in the most recent growing season, ≈5 months before sampling). Each point represents a group of samples classified by herbicide use history, with 95% confidence ellipses. Arrows indicate the direction and contribution of each variable to the first two principal components.
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Figure 7. Principal component analysis (PCA) of the relationships between early plant development variables (emergence, plant height, and organic carbon, OC) according to the imidazolinone herbicide use history: (a) Control (no herbicide use), (b) IMI-1 (application in the previous growing season, ≈17 months before sampling), and (c) IMI-2 (application in the most recent growing season, ≈5 months before sampling). Each point represents an individual sample, grouped by sampling site (Rio Branco, Treinta y Tres, UEPL, Tacuarembó), with 95% confidence ellipses. Arrows indicate the direction and contribution of each variable to the first two principal components.
Figure 7. Principal component analysis (PCA) of the relationships between early plant development variables (emergence, plant height, and organic carbon, OC) according to the imidazolinone herbicide use history: (a) Control (no herbicide use), (b) IMI-1 (application in the previous growing season, ≈17 months before sampling), and (c) IMI-2 (application in the most recent growing season, ≈5 months before sampling). Each point represents an individual sample, grouped by sampling site (Rio Branco, Treinta y Tres, UEPL, Tacuarembó), with 95% confidence ellipses. Arrows indicate the direction and contribution of each variable to the first two principal components.
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Table 1. Description of imidazolinone herbicide use for each sampling site in the years 2021, 2022 and 2023.
Table 1. Description of imidazolinone herbicide use for each sampling site in the years 2021, 2022 and 2023.
Sampling AreaYear(s)Herbicide Use HistoryProduct
(Formulation)		Dose
(g a.i. ha−1) 		Number of
Applications		Time Since Last Application
Rio Branco2021, 2022, 2023Control----
IMI-1imazapyr + imazapic52.5 + 17.52≈17 months
IMI-2≈5 months
Treinta y Tres2021, 2022, 2023Control----
IMI-1imazapyr + imazapic52.5 + 17.52≈17 months
IMI-2≈5 months
UEPL 12022Control----
IMI-2imazapyr + imazapic52.5 + 17.51≈5 months
Tacuarembó2023Control----
IMI-1imazapyr + imazapic52.5 + 17.52≈17 months
IMI-2≈5 months
1 UEPL = Paso de la Laguna Experimental Research Station.
Table 2. Mean physicochemical properties of soils used in the bioassays, by site, land use and depth.
Table 2. Mean physicochemical properties of soils used in the bioassays, by site, land use and depth.
Sampling AreaHerbicide Use HistorypH (H2O)Organic Carbon (%)Texture
0–15 cm 216–30 cm0–15 cm16–30 cm
Rio BrancoControl5.46.41.150.64Loam
IMI-15.26.20.850.55
IMI-25.4 6.20.790.59
Treinta y TresControl5.35.91.800.92Silty clay loam
IMI-16.47.61.670.77
IMI-25.36.51.440.79
UEPL 1Control5.46.51.350.75Silty clay loam
IMI-16.27.70.810.52
TacuarembóControl4.85.41.090.49Sandy loam
IMI-15.46.61.300.64
IMI-25.26.50.890.81
1 UEPL = Paso de la Laguna Experimental Research Station; 2 Depth = 0–15 cm and 16–30 cm.
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Rodriguez-De-Barbieri, V.; González-Barrios, P.; Rovira, P.; Marchesi, C.; Cuadro, R.; Zarza, R.; Kaspary, T.E. Residual Effect of Imidazolinone Herbicides on Emergence and Early Development of Forage Species in Rice-Livestock Systems. Int. J. Plant Biol. 2025, 16, 110. https://doi.org/10.3390/ijpb16030110

AMA Style

Rodriguez-De-Barbieri V, González-Barrios P, Rovira P, Marchesi C, Cuadro R, Zarza R, Kaspary TE. Residual Effect of Imidazolinone Herbicides on Emergence and Early Development of Forage Species in Rice-Livestock Systems. International Journal of Plant Biology. 2025; 16(3):110. https://doi.org/10.3390/ijpb16030110

Chicago/Turabian Style

Rodriguez-De-Barbieri, Valentina, Pablo González-Barrios, Pablo Rovira, Claudia Marchesi, Robin Cuadro, Rodrigo Zarza, and Tiago Edu Kaspary. 2025. "Residual Effect of Imidazolinone Herbicides on Emergence and Early Development of Forage Species in Rice-Livestock Systems" International Journal of Plant Biology 16, no. 3: 110. https://doi.org/10.3390/ijpb16030110

APA Style

Rodriguez-De-Barbieri, V., González-Barrios, P., Rovira, P., Marchesi, C., Cuadro, R., Zarza, R., & Kaspary, T. E. (2025). Residual Effect of Imidazolinone Herbicides on Emergence and Early Development of Forage Species in Rice-Livestock Systems. International Journal of Plant Biology, 16(3), 110. https://doi.org/10.3390/ijpb16030110

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