Progress report for GNE24-322
Project Information
Many Pennsylvania dairy farmers have adopted double cropping annual forages as a sustainable intensification practice. This system has potential soil health and environmental benefits, but effects on weed management have not been studied. Studies suggest that repeated use of atrazine, an important corn herbicide, can result in enhanced microbial degradation. This would decrease the potential weed control benefits of using atrazine, although it may also reduce the environmental risks of atrazine run-off and non-target effects. In this project, we will test how different crop management practices affect atrazine persistence in soils from dairy cropping systems. We will also quantify microbial activity in these soils to determine the extent to which this effect is microbially mediated. We hope to identify if these sustainable intensification practices are reducing the persistence of an important corn herbicide, and which in-season manure management practices influence persistence. We propose to conduct soil sampling on dairy farms in Pennsylvania and use laboratory assays to assess atrazine persistence. Results will be shared with farmers, Extension agents, and researchers through presentations and publications to inform herbicide stewardship in these systems.
Our overall objective is to understand how crop management legacy and in-season management practices affect the persistence, and thus efficacy, of atrazine and mesotrione in fields with atrazine history.
Specifically, we will:
Objective 1: Quantify the effects of crop management legacy on soil persistence of atrazine and mesotrione in fields with atrazine history.
Hypothesis 1: Soils from annual double cropping (ryelage/corn silage) systems will have lower degradation rates of both herbicides compared to soils from a corn-soy rotation with no cover crops. We expect carbon inputs within annual double cropping systems that result from additional manure inputs and continuous living cover will provide an alternative food source for microorganisms, reducing their degradation of the herbicides. We expect faster degradation rates of atrazine compared to mesotrione, because of the atrazine use history in these soils so we expect enhanced microbial degradation.
Objective 2: Test how the in-season management practice of manure addition affects atrazine degradation in soils from different crop management histories.
Hypothesis 2: Addition of manure prior to the application of atrazine will reduce atrazine degradation rates in both management legacies but will reduce atrazine degradation rates more in the corn/soy rotation. We expect reduced degradation in both types of soils because microbes will use manure as a nitrogen source over atrazine. The effect size will be bigger in corn-soy rotation soils with lower soil organic matter.
Objective 3: Determine the relationship between atrazine degradation rate in different treatments and microbial activity
and diversity.
Hypothesis 3: Microbial activity will be higher in the annual double cropping treatments, and manure addition will further increase microbial activity. In response to atrazine application, there will be a larger increase in microbial activity in the corn-soy plots than in the annual double cropping treatments.
The purpose of this project is to understand how sustainable intensification practices affect herbicide stewardship in dairy cropping systems in Pennsylvania. Growers are adopting sustainable intensification practices to improve nutrient management, increase forage production, and build soil health. However, little is known about how these management practices affect herbicide environmental fate and weed control potential in these systems. Specifically, soil-applied herbicides are increasingly used in no-till production systems. Previous studies suggest that continuous living cover and use of organic amendments may result in diminishing weed control returns due to enhanced microbial degradation of atrazine, a commonly used corn herbicide. Through on-farm sampling and laboratory assays, we hope to better understand how crop management history and in-season manure management practices affect atrazine persistence in soil.
Many dairy farmers in the Northeast region are adopting sustainable intensification practices for forage production by adding a second annual crop. In these annual double cropping systems, farmers plant corn silage which they harvest in late summer, followed by a winter small grain that they harvest the following spring. Annual double cropping increases forage yields by producing a second crop every year, which also increases climate change resilience by reducing reliance on corn silage production which may be threatened by drought or storms during crucial periods of the growing season (Castaño-Sánchez et al. 2022; West et al. 2020). Annual double cropping improves nutrient cycling by providing opportunities for additional manure applications, and removes excess nutrients which reduces nitrogen and phosphorus loss from soil (Glaze-Corcoran et al. 2023; West et al. 2020).
Although annual double cropping systems have economic and environmental benefits, their effect on herbicide stewardship has not been studied. Herbicide stewardship involves system-level management decisions that balance the trade-offs between optimizing weed control potential and minimizing the environmental costs of herbicide use, including off-target movement via surface- or subsurface- runoff, as well as the evolution of herbicide resistance. Recent studies have found that atrazine, a commonly applied soil herbicide, degrades faster than previously expected in agricultural soils with atrazine use history because of enhanced microbial degradation (Mueller et al. 2017). Faster herbicide degradation reduces the length of residual weed control, and therefore benefit to growers, but risk of off-target movement is also likely to decline. Therefore, we hope to understand if soil-applied herbicides are degrading faster than expected in dairy forage systems that utilize double-cropping as a sustainable intensification practice to determine their impact on weed control potential and environmental risks associated with off-target movement.
Enhanced atrazine degradation presents a major weed management challenge in the Northeast region because growers rely on this herbicide as a low-cost option for controlling troublesome large-seeded broadleaf weed species. In soils from across the United States, Mueller et al. (2017) found that atrazine often has a half-life of 2.3 days in fields with an atrazine-use history, in contrast to its expected half-life of up to 60 days. As dairy farmers adopt sustainable intensification practices, are they further reducing the persistence of atrazine in their soils?
Since atrazine is likely less persistent in soils than growers expect, understanding how sustainable intensification practices influence its soil persistence is necessary to characterize its economic value and improve environmental stewardship. In-season manure management decisions affect dairy cropping system sustainability and likely herbicide persistence. In these systems, manure management is a major challenge, and growers apply large quantities of manure multiple times per year. Since manure is often applied before herbicides, it likely affects how herbicides interact with soil. Some dairy farmers have begun using anaerobic digesters for their manure and spread solid digestate instead of liquid dairy manure on their fields. Anaerobic digesters reduce greenhouse gas emissions of manure and generate renewable energy (Holm-Nielson et al. 2009). The solid digestate has different soil nutrient and organic matter levels than liquid dairy manure (Barlóg et al. 2020). Through this study, we will test if the application of manure from different sources (liquid dairy manure vs. digestate solids) affects herbicide persistence in soil.
This project will increase the breadth of my overall PhD research program, where I will investigate various sustainable management practices in dairy cropping systems, including cultural practices to increase crop competitive ability, effects of long-term crop management practices on weed community diversity, and interactions between herbicides and management practices. By helping us better understand possible diminishing returns of herbicides in this system, as well as management practices that can mediate herbicide persistence, this project will support our larger goals of increasing sustainability of weed management within dairy cropping systems.
Cooperators
- (Researcher)
- (Researcher)
Research
We collected soil samples from six dairy farms in Central and Southeastern Pennsylvania that have both annual double cropping fields and nearby corn-soy rotations in Spring 2025. Two complementary laboratory incubation experiments were used to evaluate herbicide degradation differences between management practices, and to test how simulated in-season management practices affect degradation.
Experiment 1: Soil Management Legacy Effects on Two Herbicides
This experiment was a 2 x 2 factorial design with six replications. The main factor was crop management legacy, with two treatment levels: 1) fields that have used annual double cropping of corn and winter grains for at least five years, and 2) fields with history of corn-soy rotations with no cover crop. Both fields will have a history of atrazine use in corn phases of the rotation. The second factor was herbicide applied for the incubation, either atrazine or mesotrione. There were six replicates with collected soil from six cooperating farms.
Experiment 2: Effect of Additional Substrate
This experiment was a 2 x 2 factorial design with six replications. The main factor was crop management legacy, with two treatment levels: 1) fields that have used annual double cropping of corn and winter grains for at least five years, and 2) fields with history of corn-soy rotations with no cover crop. Both fields had a history of atrazine use in corn phases of the rotation. The second factor was manure added which included two treatments: no manure control or liquid dairy manure. Manure was added to soil samples prior to initiation of incubations. There were six replicates with collected soil from six cooperating farms.
Soil collection:
There were six replicates of each treatment combination, where soil from six cooperating farms that have both crop management legacies were sampled. All samples were collected in the early spring prior to application of atrazine or manures that immediately precede corn planting. At each farm, soil samples were collected from two fields with similar soil types, located less than three miles apart, to minimize variation except for the crop management legacy. Soil samples will be collected in the surface 0-10 cm of each field. Soil samples will be collected in a random pattern from 15 sites in each field and mixed thoroughly. From each farm, a management history including previous crop management practices and details about previous atrazine applications will also be collected.
Herbicide and manure incubations
All samples were kept in a cooler after collection until incubations were set up. Laboratory sample incubations will be performed following the protocol described in Mueller et al. (2010). First, soil moisture was ‘normalized’ for each sample since moisture affects microbial activity and atrazine degradation. Soil moisture was normalized following the procedure in Mueller et al. (2017). Soils were placed in a Styrofoam cup with holes in the bottom, fully saturated, then allowed to drain for 12 hours.
For experiment 2, subsamples of each normalized soil were taken to test the simulated in-season manure management practices. From each normalized soil sample, two samples were taken: one for a control with no manure added and one with liquid dairy manure added to simulate an application rate of 8,000 gallons/acre.
Then, treated soil samples were incubated in 20 mL glass vials with plastic caps. A 5 mg soil sub-sample was added to each vial. Incubations were set up for seven timings to test herbicide degradation over time (-1,0,1,2,4,8,16 days after herbicide treatment (DAT)). Three replicates for each timing and treatment combination were set up for each farm.
Aqueous atrazine solutions were prepared by adding 6.6 mg atrazine to 250 mL water and stirring with gentle heat. The concentration was 2800 ppb, or 2 kg ha-1, which is a typical field dose. The mesotrione solution was prepared by adding 2.4 uL Callisto into 125 mL water. Each soil sample had 0.25mL of the herbicide solution added, except the -1 DAT which was frozen with no herbicide added.
The 0 DAT treatment samples was frozen immediately after atrazine is added. All other samples were stored in a dark 22 C environment until their respective incubation is complete, then they were placed in the freezer at -20 C until analysis.
Data Collection and Analysis:
Objectives 1 & 2: Herbicide degradation measurements: Using a protocol based off Mueller et al. (2010), atrazine concentrations will be determined using acetone. In each soil vial, 10 mL of acetone were added. Each sample was then placed on shaker table overnight, for approximately 14 hours. The following morning, 1 mL from each sample was filtered into the LCMS vial. Samples were measured using an HPLC to determine the concentration of atrazine. Then, acetone was evaporated from the tubes in a fume hood and samples were weighed to measure their dry weights.
Extractions of mesotrione will be done using similar methods with acetonitrile to extract mesotrione.
Soil measurements: To characterize differences between soils from fields with different crop management legacies, a one-cup sample of each collected soil sample was separated from the samples when they’re collected. Soil pH, soil texture, organic matter, nitrogen, and carbon were analyzed by the Penn State Agricultural Analytical Services Laboratory (AASL).
Objective 3: Microbial activity measurements: Microbial activity was measured using 72 hour CO2 microbial respiration following the methods of Franzluebbers et al. 2018. Soils from each treatment were dried at 37C. Then, 10g of each soil was added to a 50mL plastic beaker in a pint sized mason jar, rehydrated to 50% moisture, and sealed for 72 hours. After 72 hours, CO2 concentration in each jar was measured using a LICOR CO2 gas analyzer. 3 replicates of each soil treatment from each site were used.
Statistical Analysis
Herbicide half-life was analyzed using a non-linear mixed model in R, where herbicide concentration was modeled as a function of incubation time using log-logistic or Weibull functions, which have a corresponding parameter estimate that calculates days to 50% dissipation. Microbial activity was analyzed using a linear mixed model in R. For both models, crop management and manure addition were fixed effects, and farm was a random effect.
We found partial evidence to support the effects of management practices on atrazine half-life. At 4 of 6 sites, estimated atrazine half-lives from fitted models were between 2.5-6 days. Manure increased atrazine half-life by 1-3 days at 50% of locations.
We also observed effects of management practices on microbial activity. Manure increased microbial respiration at all six sites by 1-4 fold. At 3 of the 6 sites, soils from double cropping systems had higher microbial respiration than those from the standard corn rotation. Overall, these results suggest that atrazine half-life could be altered by management practices, especially by manure application at the pre-plant application timing.
To test if these effects are specific to atrazine or similar for other herbicides, ongoing work is testing how cropping system legacy (double crop vs. standard) affects degradation of mesotrione, another commonly applied corn herbicide.
Research is still in progress, but conclusions will be added when project is complete.
Education & outreach activities and participation summary
Participation summary:
Outreach Activities to Date:
Noelle Connors reported initial results from the project at Northeast Weed Science Society meeting in January 2026 to share results with other researchers and Extension personnel.
Initial Outreach Goals in Progress:
Outreach will be focused on three major areas: 1) outreach to farmers involved directly in the project; 2) extension presentations and publications to other dairy farmers in the Northeast, and 3) outreach to agricultural service providers and professionals. First, results will be shared with participants in the Sustainable Dairy Cropping Systems Project at Penn State at an annual advisory panel meeting. Farmers and other agricultural service providers serving on the advisory board work directly with other farmers in the area to recommend best practices for sustainable management on dairy farms. Second, the results will be published in Penn State’s Field Crop News newsletter article, which has 14,000 subscribers, and an in-person presentation will be given at the Keystone Crops Conference, which targets certified crop advisers and other industry professionals.