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 in fields with atrazine history.
Specifically, we will:
Objective 1: Quantify the effects of crop management
legacy on soil persistence of atrazine in fields with atrazine
history.
Hypothesis 1: Soils from annual double cropping
(ryelage/corn silage) systems will have lower degradation rates
of atrazine 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 atrazine.
Objective 2: Test how in-season management practices of
different manure sources affect atrazine degradation in soils
from different crop management histories.
Hypothesis 2a: 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.
Hypothesis 2b: Addition of digestate before atrazine
application will reduce atrazine degradation rate compared to no
manure addition, but increase it compared to adding regular
manure because of a larger microbial population.
Objective 3: Determine the relationship between atrazine
degradation rate in different treatments and microbial activity
and diversity.
Hypothesis 3: Microbial activity and diversity 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.
Research
We will collect soil samples from dairy farms in Central and Southeastern Pennsylvania that have both annual double cropping fields and nearby corn-soy rotations. These samples will be collected in Spring 2025. Laboratory incubations will be used to evaluate herbicide degradation differences between management practices, and to test how simulated in-season management practices affect degradation.
Experimental Design
The main factor will be 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 other factor will be manure source applied with three treatment levels: 1) no manure control, 2) liquid dairy manure, and 3) digestate from anaerobic digestion of cattle manure.
There will be six replicates of each treatment combination, where soil from six cooperating farms that have both crop management legacies will be sampled. All samples will be collected in the early spring prior to application of atrazine or manures that immediately precede corn planting. At each farm, soil samples will be 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.
Atrazine and manure incubations
All samples will be prepared on the day they are collected, less than 24 hours after field collection. Laboratory sample incubations will be performed following the protocol described in Mueller et al. (2010). First, soil moisture will be ‘normalized’ for each sample since moisture affects microbial activity and atrazine degradation. Soil moisture will be normalized following the procedure in Mueller et al. (2017). Soils will be placed in a Styrofoam cup with holes in the bottom, fully saturated, then allowed to drain for 12 hours.
Subsamples of each normalized soil will be taken to test the simulated in-season manure management practices. From each normalized soil sample, three samples will be taken: one for a control with no manure added, one with liquid dairy manure added, and one with anaerobic digestate added.
Then, manure-treated soil samples will be incubated in 20 mL glass vials with plastic caps. A 5 mg soil sub-sample will be added to each vial. A complete factorial analysis will be conducted. Factors include the two crop management history main plots, three manure sources added to each main plot, and seven incubation intervals (-1,0,2,4,6,8,16 days after atrazine treatment (DAT)).
Aqueous atrazine solutions will be prepared by adding 6.6 mg atrazine to 250 mL water and stirring with gentle heat. The concentration will be 200 ppb, or 1 kg ha-1, which is a typical field dose. Each soil sample will have 0.25mL of the atrazine solution added, except the -1 DAT which will be frozen with no atrazine added.
The 0 DAT treatment samples will be frozen immediately after atrazine is added. All other samples will be stored in a dark 22 C environment until their respective incubation is complete, then they will be 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. Approximately 15 g wet soil will be added to a 50 mL falcon tube and weighed as a wet weight. Acetone (40 mL) will be added to each soil sample tube, and placed on shaker table overnight, for approximately 14 hours. The following morning, 1 mL from each sample will be filtered into the LCMS vial. Samples will be measured using an HPLC to determine the concentration of atrazine and three major metabolites: hydroxyatrazine (HA), deethylatrazine (DEA) and deisopropylatrazine (DIA). Then, acetone will be evaporated from the tubes in a fume hood and samples will be weighed to measure their dry weights. Following the methods in Mueller et al. (2017), atrazine concentration from each sample will be regressed against time after treatment using first-order kinetics. This will be used to determine atrazine half-life in different samples, which will be used as the measure of atrazine persistence.
Soil measurements: To characterize differences between soils from fields with different crop management legacies, a one-cup sample of each collected soil sample will be separated from the samples when they’re collected. Soil pH, organic matter, nitrogen, and carbon will be analyzed by the Penn State Agricultural Analytical Services Laboratory (AASL).
Objective 3: Microbial activity measurements: Microbial activity and functional diversity will be measured from each soil sample before atrazine is added (-1 DAT), and at each of the other six incubation intervals (0,2,4,6,8,16 days) to quantify how it changes in the various treatments in response to atrazine. Microbial activity and functional diversity will be measured using Biolog Ecoplates following the protocol from Huang et al. (2020). First, 10 g of soil will be added to a 250 mL flask with 100 mL sterilized water, and shaken for 20 minutes. The mixture will be diluted with sterile water to achieve a 10:3 dilution. This dilution will be used to inoculate the Biolog EcoPlates before the plates are incubated in the dark at 25C. The absorbance will be read using a Biolog Microstation every 24 hours for 168 hours, and data will be collected with Microlog 4.01 software.
Microbial activity will be quantified using average well color development(AWCD), calculated with the equation AWCD= -Σ (C-R)/31 where C is optical density (OD) in each carbon well and R is the OD of the control (Huang et al. 2020; Hackett and Griffiths 1997).
Statistical Analysis
Atrazine half-life will each be analyzed using a non-linear mixed model in R, where atrazine concentration will be 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 will be analyzed using a linear mixed model in R. For both models, crop management and manure addition will both be fixed effects, and farm will be a random effect. Additionally, other soil measures (organic matter, nitrogen, carbon) will be tested in the model as fixed effects to determine if they predict atrazine half-life.
Education & Outreach Activities and Participation Summary
Participation Summary:
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 (November 2025), which targets certified crop advisers and other industry professionals. Finally, Noelle Connors will report the results from the project at Northeast Weed Science Society meeting in 2026 to share results with other researchers and Extension personnel.