Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802
Performing Department
Plant Science
Non Technical Summary
The work proposed herein will address an existing key knowledge gap in our understanding of how climate change will affect cropping systems by investigating how both increasing temperature and variable precipitation will affect weed communities and weed management in Pennsylvania field crops. We will do this with two distinct, yet complementary studies.First, we will investigate the effects that increasing intensity of extreme precipitation events will have on the efficacy of integrated weed management tactics. To do this, we have established a field study investigating the effect of cover crop (with and without cereal rye), herbicide (with and without S-metolachlor), and precipitation intensity (0, 2.5, 5.5, 7.75 cm in a single rain event) on weed emergence and growth within soybean. We will evaluate to what extent extreme rain events decrease the efficacy of S-metolachlor weed control, and whether a cereal rye cover crop can exacerbate or mediate this effect. Our goal is to better inform farmers, crop consultants, and extension educators throughout the state as to how increasing extreme rain events may affect weed management, and the benefits or costs that result from adopting integrated weed management tactics.Second, we will evaluate the role that increasing temperatures will have on weed communities within a perennial forage system. To do this, we will use passive heating structures called open-top chambers (OTCs) to increase ambient temperatures in the field. We will then evaluate how higher temperatures affect the growth and competition, seed production, and weed seed longevity of both winter and summer annual weeds. We will also evaluate how increasing temperatures will affect the persistence of problematic weed species within the soil seedbank. Results of this work will be applied to better inform growers how weed populations may change as a result of climate change by using population models. This question is especially important because perennial forage crops are commonly used within crop rotations to drawdown populations of annual weeds within the soil seedbank.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
0%
Goals / Objectives
The overarching goal of this work is to better understand how a changing climate will affect weed communities and weed management within Pennsylvania field crops.Goal 1 -Quantifying the effects that increasing intensity of extreme precipitation events will have on the efficacy of integrated weed management tactics. We will address this goal by meeting the following research/specific objectives:1. Quantify the effects that increasing intensity of precipitation events have on the relative proportion and timing of emergence of common problematic agricultural weeds;2. Quantify the effects that increasing intensity of precipitation has on residual herbicide efficacy;3. Determine whether cover crops can mediate the effects of extreme precipitation events on residual herbicide efficacy;4. Disseminate results to Pennsylvania growers and extension specialists.Goal 2 -Characterize the effects of increasing temperatures on weed communities within a perennial forage crop. We will address this goal via the following research objectives:1. Quantify the effect that increasing temperatures have on growth and fecundity of common agricultural weeds (both summer and winter annuals);2. Determine to what extent increasing temperatures will affect weed seed longevity in the soil seedbank during a perennial forage phase of a crop rotation.
Project Methods
Goal 1 -Experimental DesignWe have established a field experiment at Rock Springs, PA to examine the effect of extreme precipitation events (0, 2.5, 5.5, 7.75 cm in a single rain event) on weed emergence and growth under management practices that vary in cover crop (with and without a cereal rye cover crop) and use of a residual herbicide (with and without a pre-emergent S-metolachlor application) within a soybean crop. In the fall of 2020, cereal rye was drill seeded (130 kg seed ha-1) using 19-cm row spacing in the designated main plots. In spring of the subsequent year, cereal rye above ground biomass will be measured, and then cereal rye will be terminated with glyphosate and flattened with a roller crimper. A roller-crimper will be used to flatten the standing cereal rye in both cover crop treatments. At soybean planting, the residual herbicide will be applied (S-metolachlor at 1.75 kg ai ha-1) in the designated treatments, and the same volume of water will be applied to the no herbicide split-plots. Soybean (420,000 seeds ha-1) will be planted in 38 cm rows, and standard fertility treatments (NPK) will be applied based on soil tests.To evaluate the effect that varying precipitation has on the efficacy of weed control tactics (S-metolachlor or cover crops) alone or in combination, we will include two weed species that are generally controlled with S-metolachlor (Setaria Faberi and Amaranthus hybridus). 500 viable seeds of each weed species will be sown into separate 0.165 m2 quadrats in the center of the rainout shelter (see Figure 3).Extreme precipitation treatments were selected based on the "heavy"(25.4 to 76.2mm d−1range) and "very heavy"(precip > 76.2mm d−1) classifications described in Groisman et al. (2012). To impose the precipitation treatments, we will use a low-intensity sprinkler according to design of Sporre-Money et al. (2004), which consists of a PVC pipe frame and in the center an inverted cone spray tip, and sprayer nozzle mounted on a PVC sprinkler arm with a water pressure control mechanisms (ball and throttling valve, and pressure gauge).Data Collection and Analysis: Within each cover crop, herbicide, and precipitation treatment we will monitor soil moisture and temperature. We will also quantify weed emergence (total and relative timing) and biomass, as well as soybean biomass and yield. We will first convert emergence to cumulative emergence (%) based on the total seedling emergence per experimental unit per year (each species will be analyzed separately). Cumulative emergence will be modeled using a Weibull function (Weibull 1951). A nonlinear mixed effects model will be used to estimate model parameters using maximum likelihood methods.Goal 2 -Experimental DesignIn Fall 2020, we planted a field at Rock Springs to an alfalfa and orchardgrass mixture, which was separated into three adjacent experiments to examine the effect of increasing temperature effects on: 1. Winter annual weed overwinter survival, fecundity, and competition with alfalfa-orchardgrass (winter annual study); 2. Summer annual weed emergence timing, fecundity, and competition with alfalfa-orchardgrass (summer annual study); and 3. Weed seed longevity in the soil seedbank (seedbank study). The experiment is a randomized complete block design with four replicates.Warming treatments. Immediately after alfalfa planting, we will establish the climate manipulation subplots within each alfalfa main-plot, including: 1. Control; 2. Constant warming (constant warming imposed); 3. Fluctuating warming (warming treatment imposed but then removed whenever weather forecast predicts a drop in temperature from ≥5 degrees C down to 0 degrees C. To simulate warmer temperatures, we will use hexagonal open top chambers ("OTCs,"according to the design of Marion et al. 1997) to passively increase air and soil temperature. OTCs are an effective and relatively inexpensive system to increase air temperature and have been used to simulate warming throughout a wide range of climatic conditions (Bjorkman et al. 2017; Seipel, et al. 2019). Following the design of Marion et al. (1997), the hexagonal open-top chambers will be constructed from 1 mm thick Sun-Lite HP (Solar Components Corporation) attached to a wooden-frame, with a 1.6 m basal diameter, a top opening diameter of 1.0 m, and a height of 0.5 m. OTCs will be anchored into randomly fixed points in the ground.Summer annual study. Within the climate manipulation subplots, we seeded permanent quadrats with seeds of Digitaria sanguinalis and Amaranthus retroflexus to monitor emergence of both summer annual weeds throughout the course of the experiment. Quadrats were divided into two sections (0.5 by 0.1 m), in placed 400 seeds of each weed species selected for the study. We will monitor, count, and then thin emerged weeds within each sub-quadrat weekly throughout the entire spring, summer, and fall. Weed biomass will be collected at each forage harvest, dried, and weighed. We will also collect and quantify any weeds' seeds produced at each harvest timepoint.Winter annual study - Within the climate manipulation subplots, we seeded permanent quadrats with seeds of Setaria media and Capsella bursa-pastoris to monitor emergence of both summer annual weeds throughout the course of the experiment. Quadrats were divided into two sections (0.5 by 0.1 m), in placed 400 seeds of each weed species selected for the study. We will monitor, count, and then thin emerged weeds within each sub-quadrat weekly throughout the entire spring, summer, and fall. Weed biomass will be collected at each forage harvest, dried, and weighed.Weed seedbank study - To examine weed propagule survival within the climate manipulation subplots, we used a modified seeded core method as described in Teo-Sherrell et al. (1996). In September, 2020 approximately 2 weeks after alfalfa planting, we installed 21 cores, grouped into three sets based on extraction year (removed after 1, 2, or 3 years). Seven weed species were selected because they are all common problematic weeds in PA, and vary in their morphological and physiological seed traits.To install seeded cores, we extracted soil cores (5 cm diameter X 15 cm depth) from the soil. The soil from each individual core will be thoroughly homogenized and mixed with 300 seeds from one of the seven weed species (only one species per core), and we then returnedthe soil plus seed mixture back into the same empty core it was removed from. Every week during the study period, cores will be checked for weed germination and any germinated individuals will be counted and removed.To extract the cores, we will use a soil core extractor that is both wider and deeper (7.5 cm width X 20 cm depth) than the original corer to ensure we recover all weed seeds still left in the soil. All extracted cores will be placed in a 0.25 mm mesh screened cylinder and elutriated for 120 min in a continuous flow rotating-drum elutriator. After elutriation, seeds and remaining debris will be air dried, then seeds will be manually separated from soil using a dissecting microscope. A germination test will be performed on seeds from both classes by transferring seeds onto a moist blotter and allowing germination for 10 days at 30 degrees C. Those seeds that do not germinate will be tested for viability via a tetrazolium test.Data analysis -To quantify the effect of microclimate manipulations on weed seed survival and weed seed incorporation into the soil seedbank, we will use repeated measures mixed models with year treated as a repeated measure, microclimate manipulation treated as fixed effects, and block treated as a random effect. We will also use a multivariate approach, partial least squares regression (Carrascal et al. 2009), to examine how variation in specific microclimatic variables influence our weed seed longevity, overwinter survival, and emergence and growth variables.