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. 2024 Nov 6;54(1):181–190. doi: 10.1002/jeq2.20644

Pennycress reduces potential for nutrient loss in Illinois

Ryan T Meyer 1,✉, Nicholas J Heller 2, Robert L Rhykerd 2, William L Perry 1
PMCID: PMC11718146  PMID: 39505568

Abstract

Nutrient export of nitrogen and phosphorus from row crop agriculture in the Upper US Midwest is a threat to the structure and function of aquatic systems. To meet Environmental Protection Agency (EPA) nutrient reduction goals, the Upper US Midwest needs to implement strategies to reduce nutrient export from agriculture. Studies demonstrate the potential of cover crops to reduce the export of nitrate‐nitrogen from the Upper US Midwest. We investigated the impact of the economically viable winter cash cover crop pennycress (Thlaspi arvense) on soil porewater nutrients and soil nutrients and characteristics. We used nine replicated 0.8 ha plots (n = 3 per treatment) at a production scale research farm over 4 years with pennycress and fertilized pennycress (56 kg ha−1 of urea) treatments compared to a fallow reference. Over the study period, soil porewater nitrate‐nitrogen was reduced by 53% in pennycress plots and 34% in fertilized pennycress plots relative to the fallow reference at a depth of 45 cm. Early season establishment was crucial in providing nutrient reduction potential. In 2021, poor pennycress establishment resulted in porewater nitrate‐nitrogen concentrations 141% higher than in 2022 with excellent pennycress establishment. Following pennycress termination, soil nitrate‐nitrogen was reduced by 24% in pennycress and 26% in fertilized pennycress compared to the fallow reference in the top 30 cm of soil. Following 4 years of pennycress planting, nitrate‐nitrogen concentrations were significantly reduced with no broad effect on soil characteristics. We conclude that the novel pennycress crop has potential to reduce nutrient loss from row crop agriculture in the Upper US Midwest.

Core Ideas

  • We investigated the effect of the cover crop pennycress on ecosystem nutrients.

  • Pennycress cover crops reduced nitrate‐nitrogen and phosphorus but not ammonia.

  • Pennycress usage did not broadly alter soil characteristics.

  • Pennycress may be an effective tool for reducing nutrient loss from agriculture.

Abbreviations

EPA

Environmental Protection Agency

ISURF

Illinois State University Research Farm

PCA

principal component analysis

1. INTRODUCTION

Nutrient contamination of surface waters from subsurface drainage systems is a pervasive and well‐documented concern in the row‐crop agricultural systems of the Upper US Midwest (David et al., 1997; Hanrahan et al., 2021; Robertson & Saad, 2013). Corn and soybean cultivation is the primary source of nitrogen delivery and the second largest source of phosphorus delivery, following pasture and rangelands, to the Gulf of Mexico (Alexander et al., 2008). The majority of the nutrient delivery to the Gulf of Mexico originates from Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Ohio, and Mississippi accounting for 33% of the total drainage area, but 75% of nitrogen and phosphorus delivery (Alexander et al., 2008). To address nutrient loads from these states, the United States Environmental Protection Agency (EPA) has set a goal of a 15% reduction in nitrate nitrogen and a 25% reduction in total phosphorus loads from 1980 to 1996 baseline loads by 2025 (IEPA et al., 2021). In Illinois, nutrient reduction goals are not being met. Nitrate loading from Illinois rivers was 22% (2019) and 28% (2021) above the 2025 nitrate reduction goal, while phosphorus loading was 51% (2019) and 60% (2021) above the 2025 phosphorus reduction goal (IEPA et al., 2019, 2021). Small improvements have been made with nitrate and phosphorus export decreasing from 2016 to 2020 to 2017 to 2021 averages. However, export is still 19.8% (2023) for nitrate and 60% (2023) for phosphorus export above the 2025 goals (IEPA et al., 2023). Modified agricultural practices have the potential to reduce the loss of nutrients from row crop agriculture while also benefiting producers with novel cover crops that can be harvested for biofuel oils.

With much of the row crop agriculture in the Upper US Midwest drained by subsurface (tile) drainage systems, within‐field nutrient reduction strategies such as cover crops are needed rather than edge‐of‐field strategies such as riparian buffer strips (Blann et al., 2009). Subsurface drainage systems are one of the major pathways for the transfer of nutrients from row crop agriculture to aquatic systems (Schott et al., 2017). In the corn‐soybean rotations that are common in the Upper US Midwest, the agricultural fields are typically left barren at least 6 months of the year during which subsurface drainage systems flush nutrients from fields to aquatic systems. Subsurface drainage bypasses traditional edge‐of‐field practices, such as vegetative buffer strips (Lemke et al., 2011). Compared to typical fallow conditions, winter cover crops reduce nutrients held within the soil and soil porewater that could be lost to tile drainage (Christopher et al., 2021; Weyers et al., 2019). Winter cover crops immobilize water soluble nitrate and can reduce nitrate losses from fields up to 90% relative to fallow fields (Hanrahan et al., 2018; Ruffatti et al., 2019). Additionally, winter cover crop residue can act as a cool season nutrient sink by retaining sequestered nitrogen and releasing it to warm‐season cash crops during their growing season (Christopher et al., 2021; Lacey & Armstrong, 2015; Meyer et al., 2023). Winter cover crops are a well understood and effective nutrient reduction strategy for use in tile‐drained agricultural systems.

Producers may incur costs from cover crops (e.g., yield drag) and receive little economic benefit from their usage. As such, cover crops are seldom used in the Upper US Midwest (Zhou et al., 2022). The development of an oilseed‐producing winter cash cover crop may result in a product that provides both environmental benefit and a revenue stream to producers. A promising winter cash cover crop is field pennycress (Thlaspi arvense), a Brassicaceae similar to canola. Pennycress is being developed as a winter cash crop that can fit within corn and soybean cropping systems (Phippen & Phippen, 2012; Zanetti et al., 2019). Breeding and gene‐editing programs are being implemented to produce commercial varieties of pennycress suitable for biofuel production and as animal feed (Chopra et al., 2020; Marks et al., 2021; McGinn et al., 2019; Phippen et al., 2022). As a winter cover crop, pennycress is already demonstrating potential to sequester nutrients, reduce weed pressure, and provide pollinator habitat (Eberle et al., 2015; Johnson et al., 2015; Weyers et al., 2019). In addition to the potential economic benefits of pennycress it may also provide significant environmental benefits similar to other cover crops already in rotation. However, with the intention of using pennycress as a biofuel and animal feed crop it may be fertilized to increase seed yield (Cubins et al., 2019). Rates of fertilization of pennycress range from 112 kg ha−1 N applied in the fall to a split fall spring application of 28 kg ha−1 N. However, high rates of fertilization do not significantly outperform lower rates of fertilization (Cubins et al., 2019). Thus, the effect of fertilization on pennycress requires further investigation, and an intermediate rate of fertilization at 56 kg ha−1 of urea was chosen for this study.

The aim of this study was to assess the viability of the novel winter cover crop pennycress to reduce potential for nutrient loss from agricultural fields in Illinois. We had three primary objectives. First, we aimed to determine how pennycress altered nutrient concentrations in soil porewater. Second, we aimed to determine how pennycress altered nutrient concentrations within the soils themselves. Finally, we examined the potential for pennycress to broadly alter soil physical and chemical characteristics. We predicted that pennycress would reduce porewater nitrate‐nitrogen concentrations relative to the fallow reference, and that the addition of nitrogen fertilizer may result in elevated nitrate‐nitrogen in the porewater after application. Significant changes in ammonia‐nitrogen and dissolved reactive phosphorus concentrations were not expected because of their potential to be bound to soils. Given that soils may respond slowly to winter cover crop rotations, we did not predict changes in overall soil fertility. However, we did expect changes in certain soil chemical characteristics such as nitrate‐nitrogen. The results of this study provide valuable information on the ecosystem benefits of pennycress as a cover crop in central Illinois near the planned commercial launch of this new biofuel crop.

2. MATERIALS AND METHODS

2.1. Study area and experimental design

This study was conducted at the Illinois State University Research Farm (ISURF) located in Lexington, Illinois (40.67N, −88.77 W). Land use at the ISURF is primarily row‐crop agriculture in a corn (Zea mays) and soybean (Glycine max) rotation. The ISURF is in the Turkey Creek watershed and flows into the Mackinaw River, a major tributary of the Illinois River and is part of the Upper Mississippi River Watershed. The study site receives on average 93 cm of annual rainfall with a mean annual temperature of 10.7°C (Northwest Alliance for Computational Science & Engineering, 2022). Data were collected from nine (n = 3 per treatment) replicated, 0.8 ha plots at the study site located within the ISURF. Pennycress, fertilized pennycress, and a fallow reference were utilized in a randomized complete block design. Blocks 1 and 2 composed of plots one through six on the north side of the ISURF are primarily composed of Saybrook silt loam (40.8%) and Drummer and El Paso silty clay loam soils (35.5%). Block 3 composed of plots seven through nine on the south side of the ISURF is primarily Catalin silt loam (34.7%) and Lisbon silt loam (29.4%). Initial nutrient concentrations for each block are shown in Table 1.

TABLE 1.

Initial soil conditions for nitrate‐nitrogen (NO3‐N), phosphorus (P), potassium (K), and percent organic matter (OM) loss on ignition with standard error (SE) for soil blocks following cash crop harvest and cover crop planting in 2019 and 2020.

Year Block NO3‐N (ppm) ± SE P (ppm) ± SE K (ppm) ± SE OM (%) ± SE
Fall 2019 1 11.4 ± 2.1 81.4 ± 24.8 230.8 ± 38.3 6.4 ± 0.5
2 9.6 ± 2.1 69.8 ± 35.3 171.3 ± 30.7 5.6 ± 0.8
3 8.1 ± 2.1 30.6 ± 14.4 221.7 ± 41.5 3.3 ± 0.5
Fall 2020 1 9.2 ± 2.7 50.6 ± 17.8 116.1 ± 7.3 5.6 ± 0.6
2 9.9 ± 2.3 65.4 ± 22.5 119.4 ± 15.5 5.9 ± 0.8
3 4.8 ± 1.6 24.7 ± 16.9 131.5 ± 26.1 3.2 ± 0.5
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Core Ideas

  • We investigated the effect of the cover crop pennycress on ecosystem nutrients.

  • Pennycress cover crops reduced nitrate‐nitrogen and phosphorus but not ammonia.

  • Pennycress usage did not broadly alter soil characteristics.

  • Pennycress may be an effective tool for reducing nutrient loss from agriculture.

2.2. Planting history and crop management

Pennycress was planted as a winter cover crop in‐between alternating corn and soybean cash crops. Prior to pennycress planting, study plots at ISURF farm were tiled in October of 2019 to ensure water from each plot was independent to that plot. The north block was seeded with wild type pennycress at 7.8 kg ha−1 (7 lbs acre−1) of seed in October of 2019, while the south block was seeded at the same rate in January and March of 2020. In April 2020, urea was applied to the fertilized pennycress treatments using a hand spreader at a rate of 56 kg ha−1 as suggested by Cover Cress Inc. Soybeans were planted on all plots in May 2020. In June of 2020, pennycress and weeds were terminated with a combination of glyphosate and 2,4‐D herbicides. Wild pennycress was replanted into standing soybeans in September of 2020 at a rate of 7.8 kg ha−1. Due to low germination, 5.6 kg ha−1 of wild type pennycress seed was added to all plots again in October of 2020. Soybeans were then harvested over the top of the growing pennycress in November of 2020. Reference plots were tilled with a shallow disc in December of 2020. In April 2021, the fertilized treatments received 56 kg ha−1 urea. In May 2021, the fallow reference plots were sprayed with a combination of glyphosate and 2,4‐D to reduce weed pressure. Pennycress was terminated by mowing in June 2021, which was followed by planting of 95‐day corn. In September of 2021, corn was harvested for silage and golden‐seeded pennycress was drilled at a rate of 6.7 kg ha−1. In April of 2022, the fertilized treatments received 56 kg ha−1 of urea. Pennycress was terminated by mowing and soybeans were planted on all plots in June 2022. Soybeans were harvested in October 2022. Following soybean harvest, 6.7 kg ha−1 of golden‐seed pennycress was drilled into all treatment plots. In the fall of 2022 and spring of 2023 pennycress establishment was limited due to late planting and drought conditions.

2.3. Sample collection

To sample soils for chemical analysis, we collected soil cores shortly after pennycress planting in October 2019, November 2020, October 2021, and October 2022 and after pennycress termination in June 2020, June 2021, June 2022, and May 2023. Prior to soil core collection in May 2023, all plots were fertilized with 201 kg ha−1 of nitrogen invalidating 2023 spring data. To sample soil characteristics, we collected three composite samples per plot collocated with soil porewater samplers by homogenizing 20, 1.7‐cm diameter and 30‐cm‐deep soil sores. Soil samples were kept on ice and taken to United Soils Inc. for analysis of pH, buffer pH, colorimetric organic matter, organic matter loss on ignition, cation exchange capacity, nitrogen, ammonia, phosphorus, potassium, calcium, magnesium, sulfur, zinc, iron, manganese, copper, boron, and base saturation. Standardized methods were used to analyze soil samples (North Central Regional Committee on Soil Testing & Plant Analysis, 2015). Pennycress above‐ground biomass was sampled in Spring 2019, 2020, and 2021. Biomass was collected from (n = 3) 1 m2 quadrats in 2019 and 2020 and 0.25 m2 quadrats in 2021 by using scissors to cut all pennycress within the quadrat at the soil level. The biomass was dried at 50°C for 2 weeks and then weighed for dry weight. Aboveground biomass of pennycress was assessed by calculating the arithmetic mean of biomass in each plot.

To sample soil porewater, we used suction cup lysimeters constructed from 2.54‐cm diameter Charlotte Pipe schedule 40 PVC (polyvinyl chloride) pipe cut into 100 cm lengths. A porous ceramic cup (Soil Moisture Equipment Corporation) was placed on the end of the pipe and glued into place with a neoprene stopper secured on the other end. Two tubes were run through the stopper with one tube going to the porous cup and the other just below the stopper. Suction cup lysimeters were installed 45 cm below the soil surface. A vacuum (138 kPa/20 psi) was placed on the lysimeter after a rain event greater than 1.27 cm. The vacuum pulled water though the ceramic cup and was left on for at least 24 h after which a hand pump was used to push the water out of the lysimeter into a 50‐ml plastic vial. To determine nitrate‐nitrogen, ammonia‐nitrogen, and dissolved reactive phosphorus porewater concentrations, samples were analyzed using EPA‐certified methods and a Lachat flow injection analysis system.

2.4. Statistical methods

To determine if there were differences between treatment and reference soil nutrients and characteristics correlations between variables were calculated. Presence of strong correlations made principal component analysis (PCA) an attractive method to summarize and reduce the dimensions of the data. A k‐means cluster analysis of the principal component scores was used to identify patterns between the treatment and reference soil conditions. Nitrate‐nitrogen, ammonia‐nitrogen, percent organic matter, phosphorus, potassium, calcium, pH, magnesium, cation exchange capacity, sulfur, zinc, boron, iron, manganese, and copper were selected for use in the PCA—other variables were not included if they did not bring unique information. We then conducted the k‐means cluster analysis with cluster validation using the within‐cluster sum of square and average silhouette methods. A linear mixed‐effect model analysis of variance was used to test for treatment effects on soil conditions using PCA axis one. The model included the fixed effects of treatment to represent the experimental treatments and block to account for variability between blocks. Date and plot were included in the model as random intercepts to account for the hierarchical structure of the model. The model was fitted with restricted maximum likelihood, and the random terms utilized an unstructured covariance matrix. The model met the assumptions of normal residuals and homogenous variance.

The top 10 variables (boron, calcium, cation exchange capacity, copper, magnesium, organic matter loss on ignition, nitrogen, phosphorus, potassium, and ammonium) that loaded most heavily on PCA axis 1 were included in univariate repeated measures mixed model analyses of variance to assess differences in soil nutrient concentrations between treatment and reference plots. The models included treatment as a fixed effect, block as a random effect, date as a repeated measure, and the interaction between date and treatment. The analyses were conducted using the lme4 package in R (Bates et al., 2015), employing restricted maximum likelihood estimation and an unstructured covariance matrix for the random terms. To ensure reliable model convergence, the Nelder–Mead and bound optimization by quadratic approximation algorithms were utilized where necessary. All models met the assumptions of homogeneity of variance and normality of residuals. Where necessary, mean separation was performed with all pairwise comparisons in the emmeans package in R (Lenth, 2022), with Sidak p‐value adjustments for all pairwise comparisons. All statistical tests utilized an alpha of 0.05, and blocks were considered effective at an alpha of 0.25.

To determine differences in porewater nutrient concentrations between treatment and reference plots, we used a repeated measures mixed model analysis of variance with the same structure as the models used for the soils analysis. The models included treatment as a fixed effect, a block effect, date as the repeated measure, and the treatment by date interaction. The models were fitted with restricted maximum likelihood and utilized an unstructured covariance matrix. Reliable model convergence was achieved with bound optimization by quadratic approximation algorithm. To achieve normality of residuals and homogeneity of variance, a log10+1 transformation was applied to nitrate‐nitrogen and dissolved reactive phosphorus and a square root transformation was applied to ammonia‐nitrogen. Data were back‐transformed for presentation. Mean separation was conducted using all pairwise comparisons with the emmeans package in R (Lenth, 2022). The nitrate‐nitrogen model utilized a Tukey p‐value adjustment for multiple comparisons, while the phosphorus model did not utilize a p‐value adjustment. In the case of phosphorus, the Sidak p‐value adjustment was too conservative and masked significant results indicated by the overall analysis of variance. All statistical tests utilized an alpha of 0.05, and blocks were considered effective at an alpha of 0.25.

3. RESULTS

3.1. Soils

While pennycress altered soil characteristics individually, it did not broadly effect soil characteristics when viewed as a whole (F = 0.831,3.9, p = 0.42). We found blocking was necessary as in‐field conditions differed by block (F = 5.871,3.9, p = 0.07). In the PCA, principal component one explained 53.9% of the variation and was loaded most heavily, all in the same direction, by calcium, magnesium, and boron. Principal component two explained 19.8% of the variation and was loaded most heavily by nitrate‐nitrogen, sulfur, manganese, and phosphorus. Principal component three explained 8.5% of the variation and was loaded most heavily by ammonium, potassium, manganese, and iron. Principal components one and two explaining the most variation in the model were retained. Using the first two axes, the k‐means cluster analysis indicated two distinct clusters with the north plots in one cluster and the south in another (Figure 1).

FIGURE 1.

FIGURE 1

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Results of the soils principal component analysis and k‐means cluster analysis. Red circles indicate clustering from k‐means cluster analysis. Treatments of pennycress, fertilized pennycress (pennycress+N), and the fallow reference did not differ along axis one or two. However, differences in in‐field soil conditions by block drive clustering along axis one, as indicated by the k‐means cluster analysis.

Pennycress altered key soil factors individually. Nitrate‐nitrogen (F = 56.72,47.0, p < 0.0001), phosphorus (F = 4.82,47, p = 0.01) potassium (F = 9.82,47, p = 0.0002), and sulfur (F = 5.42,27, p = 0.007) differed by treatment. Boron (F = 1.62,47, p = 0.2), calcium (F = 1.32,47, p = 0.3), cation exchange capacity (F = 0.72,47, p = 0.5), copper (F = 2.02,47, p = 0.1), magnesium (F = 1.72,47, p = 0.2), organic matter (F = 0.32,47, p = 0.8), and ammonium (F = 0.72,47, p = 0.5) did not differ by treatment. Post F analysis of pairwise comparisons demonstrated that pennycress and fertilized pennycress reduced nitrate‐nitrogen, phosphorus, and potassium relative to the reference while pennycress and fertilized pennycress themselves did not differ (Figure 2). Fertilized pennycress reduced sulfur concentrations relative to the reference, but the unfertilized pennycress and reference did not differ (Figure 2). The blocking effect demonstrated different in‐field conditions between boron (F = 100.21,47, p < 0.0001), calcium (F = 102.511,47, p < 0.0001), cation exchange capacity (F = 113.31,47, p < 0.0001), copper (F = 73.71,47, p < 0.0001), magnesium (F = 104.41,47, p < 0.0001), organic matter (F = 71.81,47, p < 0.0001), potassium (F = 3.81,47, p = 0.06), phosphorus (F = 14.71,47, p = 0.0003), and sulfur (F = 6.51,47, p = 0.01) concentrations, but not for nitrate‐nitrogen (F = 0.11,47, p = 0.7) or ammonium (F = 1.22,47, p = 0.28). The interaction between treatment and date was significant for nitrate‐nitrogen (F = 5.72,47, p = 0.005), but not for boron (F = 0.22,47, p = 0.8), calcium (F = 0.32,47, p = 0.8), cation exchange capacity (F = 0.72,47, p = 0.5), copper (F = 0.82,47, p = 0.4), magnesium (F = 0.22,47, p = 0.8), organic matter (F = 0.12,47, p = 0.9), phosphorus (F = 0.32,47, p = 0.3), potassium (F = 0.72,47, p = 0.5), sulfur (F = 0.72,47, p = 0.5), or ammonium (F = 0.012,47, p = 0.9).

FIGURE 2.

FIGURE 2

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Results from univariate models on selected soil metrics (mean ± SE). Different letters indicate statistically significant differences at p < 0.05. Nitrate‐nitrogen and potassium were reduced in the pennycress and fertilized pennycress (pennycress+N) treatments relative to the fallow reference.

3.2. Porewater

Pennycress had a significant effect on soil porewater nutrient concentrations. Nitrate‐nitrogen (F = 7.62,175.1, p = 0.0006) and phosphorus (F = 3.82,174.6, p = 0.02) differed by treatment while ammonia‐nitrogen (F = 0.202,174.1, p = 0.8) did not (Figures 3, 4, 5; Table S1). The blocking effect indicated different in‐field conditions for dissolved reactive phosphorus (F = 239.41,174.9, p < 0.0001) and nitrate‐nitrogen (F = 3.12,175.6, p = 0.05), but not ammonia‐nitrogen (F = 0.092,174.3, p = 0.9). The treatment by date interaction was significant for nitrate‐nitrogen (F = 8.02,175.1, p = 0.0004) and phosphorus (F = 3.72,174.6, p = 0.03), but not ammonia‐nitrogen (F = 0.192,174.1, p = 0.8). Analysis of all pairwise comparisons demonstrated that nitrate‐nitrogen and phosphorus concentrations across all seasons were significantly lower in the pennycress and fertilized pennycress treatments compared to the fallow reference (Figure 3). Nitrate‐nitrogen and phosphorus concentrations did not differ between pennycress and fertilized pennycress (Figure 3).

FIGURE 3.

FIGURE 3

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Temporal and treatment differences in porewater nitrate‐nitrogen at a depth of 45 cm (mean ± SE). Treatments were pennycress, fertilized pennycress (pennycress+N), and a fallow reference. Pennycress and fertilized pennycress significantly reduced nitrate‐nitrogen relative to the fallow reference, but pennycress and fertilized pennycress did not differ in nitrate‐nitrogen concentrations (p = 0.0006).

FIGURE 4.

FIGURE 4

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Temporal and treatment differences in porewater ammonia‐nitrogen at a depth of 45 cm (mean ± SE). Treatments were pennycress, fertilized pennycress (pennycress+N), and a fallow reference. There were no differences in ammonia‐nitrogen concentrations by treatment (p = 0.8).

FIGURE 5.

FIGURE 5

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Temporal and treatment differences in porewater dissolved reactive phosphorus at a depth of 45 cm (mean ± SE). Treatments were pennycress, fertilized pennycress (pennycress+N), and a fallow reference. Treatments did not differ in dissolved reactive phosphorus concentrations (p = 0.02).

3.3. Biomass

Pennycress above‐ground biomass production was highly variable among all years (Table 2). October planting of pennycress in 2019 produced 52 ± 68 g/m2 in the unfertilized and 42 ± 55 g/m2 in the fertilized treatments. Following a September planting date in 2020 and 2021, the pennycress produced 123 ± 93 g/m2 and 254 ± 148 g/m2 and the fertilized pennycress produced 169 ± 141 g/m2 and 320 ± 113 g/m2 respectively. After another October planting date in 2022, the following spring biomass of pennycress was too low to be sampled in all plots.

TABLE 2.

Mean spring biomass produced by pennycress and fertilized pennycress in relation to fall planting date. NA values for October 2022 planting indicate near zero biomass production as biomass was too low to be sampled and was subsequently terminated early. The near zero biomass production was due to late planting in 2022 and drought conditions in 2023.

Planting date Treatment Mean spring biomass produced (g/m2) Standard deviation
October 2019 Pennycress 52.1 68.6
Pennycress + N 42.3 55.3
September 2020 Pennycress 122.5 93.2
Pennycress + N 169.0 140.7
September 2021 Pennycress 254.4 147.6
Pennycress + N 320.1 112.7
October 2022 Pennycress NA NA
Pennycress + N NA NA
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4. DISCUSSION

Pennycress treatments effectively reduced nitrate‐nitrogen concentrations within the soil (24.1%) and soil porewater (53.3%) relative to the fallow reference averaged over the course of this study. Pennycress shows great potential to reduce nitrate‐nitrogen that would otherwise be lost to aquatic systems. With fertilization, nitrate‐nitrogen reductions in the soil (25.9%) and porewater (33.8%) were significantly less than reference conditions. We concur with other studies that pennycress has the potential to sequester labile nitrogen during the cool season (Weyers et al., 2019). After 4 years of continuous cover cropping with pennycress, we demonstrate that there has been little change in soil fertility due to the presence of pennycress, as shown by the PCA. Trends are starting to appear that pennycress may be improving soil fertility, but more time is required for this to be substantiated. The k‐means cluster analysis demonstrated that block may be driving clustering along principal components one (Figure 1). The difference in blocks was expected as the north and central blocks have more organic matter compared to the south block. With consistent pennycress use, improvements in soil fertility may be expected, but the effects will likely take longer than 4 years to achieve (Sharma et al., 2018).

Pennycress significantly reduced porewater nitrate‐nitrogen in unfertilized and fertilized treatments relative to reference conditions, with no difference between the unfertilized and fertilized treatments (Figure 3). The observed reductions in nitrate‐nitrogen from pennycress in this study are similar to those seen in Weyers et al. (2019) and are comparable to reductions from winter camelina. However, nitrate‐nitrogen concentrations in pennycress were elevated compared to winter rye and radish cover crops (Weyers et al., 2019). No changes in ammonia were observed conferring with other studies (Weyers et al., 2019) (Figures 4 and 5). While pennycress has been investigated in sweet corn and relay cropping systems, its influence on nutrients has yet to be investigated as a conventional cover crop (Moore et al., 2020; Weyers et al., 2019). In this study, we examine pennycress as a conventional cover crop planted within corn and soybean rotations that terminated prior to summer cash crop planting. By doing so, we investigated the nutrient reduction capability of pennycress in a cropping scenario and climate in which it has not yet been evaluated. Given that the nitrate‐nitrogen reductions we observed are similar to pennycress in a cold climate relay cropping system, we strengthen the argument that across usage scenarios and climates, pennycress provides cool‐season nutrient reduction potential.

To achieve crucial spring reductions in nitrate‐nitrogen there must be sufficient fall germination. As with other winter oilseed crops, such as camelina, we found that late September planting was necessary to achieve adequate spring biomass for nutrient reduction (Sindelar et al., 2017) (Table 2). When planted in October, spring pennycress biomass was less than when planted in September (Table 2). Current agronomic practices for pennycress suggest spring fertilization may be needed to increase yields. (Cubins et al., 2019). Our results indicate that fertilization (56 kg urea ha−1) of pennycress may not negatively impact the potential to reduce nutrient loss in tile‐drained systems. Studies on pennycress fertilization are inconclusive as to the effectiveness of fertilization. While unfertilized pennycress may produce adequate seed yields in sweet corn systems, fertilization has been shown to increase total seed yield, and potentially increase profit (Moore et al., 2020; Rukavina et al., 2011). Thus, if fertilization is used on pennycress cover crops, understanding the timing and rates necessary to increase yield while also decreasing leaching requires further experimentation and was beyond the scope of this study.

We demonstrate that in a temperate climate when used as a conventional cover crop planted in‐between cash crops and terminated prior to the following cash crop planting, pennycress has potential to sequester nitrate‐nitrogen. Other cover crops may provide greater nutrient reductions than pennycress, but because they do not provide immediate, direct economic benefit they are seldom used. Winter oilseeds such as pennycress or camelina can provide short‐term economic benefit to producers in addition to the environmental benefits from nutrient reductions (Phippen et al., 2022). While the environmental benefits from oilseed crops may not be as substantial as cereal rye, they are better than leaving fields fallow (Weyers et al., 2019). Solutions are needed for agricultural practices to meet the needs of human society without causing degradation to aquatic systems. While integrating a novel crop into existing cropping systems may be difficult, pennycress has potential to become a part of conventional cropping systems that provides both environmental and economic benefit.

AUTHOR CONTRIBUTIONS

Ryan T. Meyer: Data curation; formal analysis; investigation; validation; visualization; writing—original draft; writing—review and editing. Nicholas J. Heller: Formal analysis; resources; validation; visualization; writing—review and editing. Robert L. Rhykerd: Data curation; formal analysis; investigation; methodology; writing—review and editing. William L. Perry: Conceptualization; data curation; formal analysis; funding acquisition; project administration; supervision; writing—review and editing.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Supporting information

Supporting Information

JEQ2-54-181-s001.docx (14.6KB, docx)

ACKNOWLEDGMENTS

This work was supported by the USDA Agriculture and Food Research Initiative Competitive Grant No. 2019‐69012‐29851. We thank Marley Knowles, Kindyl Ryburn, and Destiny Estes for assistance in sample collection and preparation. Dr. John Sedbrook assisted in reviewing early drafts of the manuscript. Anonymous reviewers provided feedback to substantially improve the manuscript.

Meyer, R. T. , Heller, N. J. , Rhykerd, R. L. , & Perry, W. L. (2025). Pennycress reduces potential for nutrient loss in Illinois. Journal of Environmental Quality, 54, 181–190. 10.1002/jeq2.20644

Assigned to Associate Editor Emily Woodward.

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