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Efficient termination of cover crops is an important component of cover crop management. Information on termination efficiency can help in devising management plans but estimating herbicide efficacy is a tedious task and potential remote sensing technologies and vegetative indices (VIs) have not been explored for this purpose. This study was designed to evaluate potential herbicide options for the termination of wheat ( Triticum aestivum L.), cereal rye ( Secale cereale L.), hairy vetch ( Vicia villosa Roth.), and rapeseed ( Brassica napus L.), and to correlate different VIs with visible termination efficiency. Nine herbicides and one roller-crimping treatment were applied to each cover crop. Among different herbicides used, glyphosate, glyphosate + glufosinate, paraquat, and paraquat + metribuzin provided more than 95% termination for both wheat and cereal rye 28 days after treatment (DAT). For hairy vetch, 2,4-D + glufosinate and glyphosate + glufosinate, resulted in 99 and 98% termination efficiency, respectively, followed by 2,4-D + glyphosate and paraquat with 92% termination efficiency 28 DAT. No herbicide provided more than 90% termination of rapeseed and highest control was provided by paraquat (86%), 2,4-D + glufosinate (85%), and 2,4-D + glyphosate (85%). Roller-crimping (without herbicide application) did not provide effective termination of any cover crop with 41, 61, 49, and 43% termination for wheat, cereal rye, hairy vetch, and rapeseed, respectively. Among the VIs, Green Leaf Index had the highest Pearson correlation coefficient for wheat (r = -0.786, p = <0.0001) and cereal rye (r = -0.804, p = <0.0001) with visible termination efficiency rating. Whereas for rapeseed, the Normalized Difference Vegetation Index (NDVI) had the highest correlation coefficient (r = -0.655, p = <0.0001). The study highlighted the need for tankmixing 2,4-D or glufosinate with glyphosate for termination instead of blanket application of glyphosate alone for all crops including rapeseed and other broadleaf cover crops.

The magnitude of ecosystem services provided by winter cover crops is linked to their performance (i.e., biomass and associated nitrogen content, forage quality, and fractional ground cover), although few studies quantify these characteristics across the landscape. Remote sensing can produce landscape-level assessments of cover crop performance. However, commonly employed optical vegetation indices (VI) saturate, limiting their ability to measure high-biomass cover crops. Contemporary VIs that employ red-edge bands have been shown to be more robust to saturation issues. Additionally, synthetic aperture radar (SAR) data have been effective at estimating crop biophysical characteristics, although this has not been demonstrated on winter cover crops. We assessed the integration of optical (Sentinel-2) and SAR (Sentinel-1) imagery to estimate winter cover crops biomass across 27 fields over three winter–spring seasons (2018–2021) in Maryland. We used log-linear models to predict cover crop biomass as a function of 27 VIs and eight SAR metrics. Our results suggest that the integration of the normalized difference red-edge vegetation index (NDVI_RE1; employing Sentinel-2 bands 5 and 8A), combined with SAR interferometric (InSAR) coherence, best estimated the biomass of cereal grass cover crops. However, these results were season- and species-specific (R2 = 0.74, 0.81, and 0.34; RMSE = 1227, 793, and 776 kg ha−1, for wheat (Triticum aestivum L.), triticale (Triticale hexaploide L.), and cereal rye (Secale cereale), respectively, in spring (March–May)). Compared to the optical-only model, InSAR coherence improved biomass estimations by 4% in wheat, 5% in triticale, and by 11% in cereal rye. Both optical-only and optical-SAR biomass prediction models exhibited saturation occurring at ~1900 kg ha−1; thus, more work is needed to enable accurate biomass estimations past the point of saturation. To address this continued concern, future work could consider the use of weather and climate variables, machine learning models, the integration of proximal sensing and satellite observations, and/or the integration of process-based crop-soil simulation models and remote sensing observations.

Achieving high corn yields while reducing fertilizer losses seems attainable through nitrogen (N) management decisions that include the use of cover crops (CCs). To determine whether CCs result in a net positive balance between N fertilization and crop utilization, we used US field trial data comparing corn systems with and without CCs, and estimated the amount of N fertilizer that CCs would replace and lead to equivalent grain yields under both systems. Overall, applying lower nitrogen rates to corn without cover crops resulted in similar or higher yields when legumes were used as cover crops (indicating positive nitrogen replacement in the amount of 62 kg ha−1), but lower yields when grasses were used as cover crops (indicating negative nitrogen replacement in the amount of 24 kg ha−1). Our results illustrate the benefits and trade‐offs of integrating single CC species into a corn system, that is, reducing N inputs with legume CCs or supplementing N fertilizer to avoid possible grain yield penalties in the case of grass CCs. Quantifying the N replacement value of CCs would facilitate field‐level recommendations and policy regulations aimed at promoting sustainable corn production in the United States. Core Ideas Managing N fertilizer rates is essential for maximizing the benefits of legume and grass cover crops in corn‐based systems. N fertilizer replacement of grass and legume cover crops was assessed based on data from field experiments in the United States. Legume cover crops were found to positively replace N fertilizer; potentially reducing corn N inputs. Grass cover crops were found to negatively replace N fertilizer; potentially requiring supplementary fertilizer to reduce corn yield penalties. Plain Language Summary Corn needs high amounts of nitrogen (N) fertilizer to grow. However, too much fertilizer can harm the environment. Cover crops (CCs) can improve soil conditions and reduce N fertilizer use. We analyzed data from multiple field experiments to see if legume and grass CCs can replace N fertilizer and still produce yields similar to those without CCs. We found that legumes resulted in similar or higher corn yields but with less fertilizer. In contrast, grasses led to lower corn yields unless more fertilizer was used. These results occurred primarily because legumes add N to the soil while grasses often do not. These findings can help farmers and policy makers to devise better N fertilizer recommendations when CCs are integrated to corn production. NRV is calculated as the N rate application at which the yields of corn with or without cover crops match at two levels of fertilization: 0 kg ha−1 N and N for the highest corn yield attainable. The overall negative NRV for grass CCs indicates the approximate amount of N fertilizer that needs to be supplemented (i.e., not replaced) to corn with cover crops to yield as much as a fertilized corn crop without cover crops. Positive values of NRV for legume CCs indicate the amount of mineral N being saved/replaced while still obtaining corn yields comparable to systems without a cover crop.

This study evaluated the impact of four cover crop species and their termination timings on cover crop biomass, weed control, and corn yield. A field experiment was arranged in a split-plot design in which cover crop species (wheat, cereal rye, hairy vetch, and rapeseed) were the main plot factor, and termination timings [4, 2, 1, and 0 wk before planting corn (WBP)] was the subplot factor. In both years (2021 and 2022), hairy vetch produced the most biomass (5,021 kg ha –1 ) among cover crop species, followed by cereal rye (4,387 kg ha –1 ), wheat (3,876 kg ha –1 ), and rapeseed (2,575 kg ha –1 ). Regression analysis of cover crop biomass with accumulated growing degree days (AGDDs) indicated that for every 100 AGDD increase, the biomass of cereal rye, wheat, hairy vetch, and rapeseed increased by 880, 670, 780, and 620 kg ha –1 , respectively. The density of grass and small-seeded broadleaf (SSB) weeds at 4 wk after preemergence herbicide (WAPR) application varied significantly across termination timings. The grass and SSB weed densities were 56% and 36% less at 0 WBP compared with 2 WBP, and 67% and 61% less compared with 4 WBP. The sole use of a roller-crimper did not affect the termination of rapeseed at 0 WBP and resulted in the least corn yield (3,046 kg ha –1 ), whereas several different combinations of cover crops and termination timings resulted in greater corn yield. In conclusion, allowing cover crops to grow longer in the spring offers more biomass for weed suppression and impacts corn yield.

Farmers are increasingly planting cover crops to improve soil health and provide other ecosystem services. Cover crop incentive programs in Maryland, Pennsylvania, New York, and Vermont were compared and farmers using cover crops were surveyed (n = 328) to characterize program participants and assess the effects of programs on cover crop adoption. Farmers who participated in incentive programs differed from nonparticipants in their perspectives about incentive programs, challenges they faced using cover crops, and reasons for cover crop use. When averaged across farmers, results show that incentive programs doubled average farmer cropland with cover crops from 50.7 ha prior to participation to 101.0 ha during participation. Among participants who no longer were enrolled in a program, cover crop use remained on average 37.2% greater than before enrollment. Results highlight the role of incentive programs in facilitating adoption and provide insights for expanding participation to different farmers and increasing program impact. Core ideas An online survey was conducted to assess cover crop incentive program participants and program impact on adoption. Area planted with cover crops was greater during and after program participation compared to before program enrollment. Differences identified between program participants and nonparticipants may be used to refine programs. Maryland, Pennsylvania, New York, and Vermont were among the states with the greatest adoption of cover crops expressed as a percentage of cropland (excluding alfalfa) in 2017. Frequency of survey respondents across five cover crop area categories (i.e., 0, 0–4, 4–14, 14–40, and 40+ ha) before and during participation in a cover crop incentive program. Map image credit: Steven Wallander (modified from Wallander et al., 2021).

Hairy vetch, (Roth), is a cover crop that does not exhibit a typical domestication syndrome. Pod dehiscence reduces seed yield and creates weed problems for subsequent crops. Breeding efforts aim to reduce pod dehiscence in hairy vetch. To characterize pod dehiscence in the species, we quantified visual dehiscence and force required to cause dehiscence among 606 genotypes grown among seven environments of the United States. To identify potential secondary selection traits, we correlated pod dehiscence with various morphological pod characteristics and field measurements. Genotypes of hairy vetch exhibited wide variation in pod dehiscence, from completely indehiscent to completely dehiscent ratings. Mean force to dehiscence also varied widely, from 0.279 to 8.97 N among genotypes. No morphological traits were consistently correlated with pod dehiscence among environments where plants were grown. Results indicated that visual ratings of dehiscence would efficiently screen against genotypes with high pod dehiscence early in the breeding process. Force to dehiscence may be necessary to identify the indehiscent genotypes during advanced stages of selection.

Cover crop-based, organic rotational no-till (CCORNT) corn and soybean production is becoming a viable strategy for reducing tillage in organic annual grain systems in the mid-Atlantic, United States. This strategy relies on mechanical termination of cover crops with a roller-crimper and no-till planting corn and soybean into cover crop mulches. Here, we report on recent research that focuses on integrated approaches for crop, nutrient and pest management in CCORNT systems that consider system and regional constraints for adoption in the mid-Atlantic. Our research suggests that no-till planting soybean into roller-crimped cereal rye can produce consistent yields. However, constraints to fertility management have produced less consistent no-till corn yields. Our research shows that grass-legume mixtures can improve N-release synchrony with corn demand and also improve weed suppression. Integration of high-residue inter-row cultivation improves weed control consistency and may reduce reliance on optimizing cover crop biomass accumulation for weed suppression. System-specific strategies are needed to address volunteer cover crops in later rotational phases, which result from incomplete cover crop termination with the roller crimper. The paucity of adequate machinery for optimizing establishment of cash crops into thick residue mulch remains a major constraint on CCORNT adoption. Similarly, breeding efforts are needed to improve cover crop germplasm and develop regionally-adapted varieties.

There is relatively low adoption of winter cover crops across the United States, despite the many ecosystem service benefits they provide, and there has been much debate about corn yield penalties following cereal cover crops such as cereal rye (Secale cereale L.). This 12 site‐year, coordinated study across a latitudinal gradient in the northeastern United States sought to determine the interactions between cereal rye biomass and fertilizer nitrogen (N) rate and timing on no‐till corn (Zea mays L.) yield. Total N rates, not the timing of N fertilization, significantly affected corn yields, and higher cereal rye biomass slightly increased corn yields once sufficient N was added. We conclude that if total fertilizer N rates are sufficient, the split between starter N application at planting and sidedress N fertilization does not affect yield in no‐till corn across a range of cereal rye cover crop biomass levels. Plain Language Summary Winter cover crops provide many environmental benefits, but uncertainty in how to manage them and negative effects of cover crops on cash crop yields in conventional agricultural cropping systems hinder their adoption. This study repeated across six sites in the Northeastern United States tested whether the rates of the first fertilizer application at planting (starter nitrogen) needed to be changed at different levels of cover crop biomass. We found that only the total amount of nitrogen from the first and second nitrogen applications had a significant effect on corn yield across a range of different cover crop biomass levels. Corn yield (kg ha−1) by cereal rye biomass level with no nitrogen (N) fertilizer applied (a) versus the high N rate (b) and different levels of cereal rye biomass (kg ha−1) (divided into quintiles). Corn yield penalties were observed in high cereal rye biomass levels with no N added. When sufficient N was applied, corn yield penalties occurred only for mid rye biomass levels but otherwise did not.

The short‐run effects of cover crop use on cash crop yields (e.g., corn [Zea mays L.] and soybeans [Glycine max (L.) Merr.]) have been a topic of debate given that evidence from previous literature has generally been mixed on this issue. Past studies suggest that the observed yield effect varies (i.e., negative, positive, or insignificant), often depending on the applied cover crop species used, weather conditions, and farm management practices implemented (among others). In this study, we examine the short‐run (i.e., 1 year) yield impact of four different cover crop families—grasses (Poaceae), broadleaves (Brassicaceae), legumes (Fabaceae), and others—both as single‐family groups and as mixtures. Data from side‐by‐side on‐farm experimental plots in six Eastern US states were collected from 2017 to 2019 in order to achieve the objective of the study. Statistical analysis of this multi‐year plot‐level data suggests that the majority of the cover crop families and mixtures investigated in this study do not have a statistically significant short‐run effect on subsequent corn yields. In some cases, cover crop treatment even resulted in short‐run yield losses (i.e., a yield penalty). These results imply that cash crop yield benefits from cover crop adoption are likely not going to be observed with just 1 year of use. This lack of immediate economic benefit may explain the relatively low cover crop adoption rate currently observed in the United States and the need for upfront cost‐share subsidy payments to encourage further uptake of this practice. Core Ideas The short‐run yield effect of different cover crop families was examined. Cover crop families and mixtures have mostly no short‐run effect on corn yields. The lack of immediate economic benefit explains the low cover crop adoption rate. Plain Language Summary Cover crops, like grasses, legumes, and broadleaves, are often used in farming to improve soil health and reduce erosion. However, their impact on the following year's crop yields, like corn and soybeans, is debated. This study looked at how four cover crop families — grasses, broadleaves, legumes, and others — affect corn yields in the short term (one year) on farms in six states in the Eastern U.S. The research found that most cover crops did not significantly impact corn yields in the short term. In some cases, using cover crops even led to slight yield losses. This suggests that immediate yield benefits from cover crops may not be seen after just one year. The study shows that cover crops may not provide quick economic benefits, which could explain why many U.S. farmers are hesitant to adopt them. To encourage more farmers to use cover crops, financial support like subsidies may be needed to cover the initial costs.

As plant litter decomposes, its mass exponentially decreases until it reaches a non-zero asymptote. However, decomposition rates vary considerably among litter types as a function of their overall quality (i.e., carbon:nitrogen (C:N) ratio and litter chemistry). We investigated the effects of hairy vetch (HV: Vicia villosa Roth):cereal rye (RYE: Secale cereale L.) biomass proportions with or without broadcasted poultry manure on overall litter quality before and during decomposition. As HV biomass proportions increased from 0 to 100%, the relative susceptibility of HV:RYE mixtures to microbial decomposition increased due to: (i) decrease in the initial C:N ratio (87:1 to 10:1 in 2012 and 67:1 to 9:1 in 2013), (ii) increase in the non-structural labile carbohydrates (33 to 61% across years), and (iii) decrease in the structural holo-cellulose (59 to 33% across years) and lignin (8 to 6% across years) fractions. Broadcasted poultry manure decreased the overall initial quality of HV-dominated litters and increased the overall initial quality of RYE-dominated litters. Across all HV:RYE biomass proportions with or without poultry manure, chemical changes during litter decay were related to proportional mass loss. Therefore, the relative decrease in carbohydrates and the concomitant increase in holo-cellulose and lignin fractions were more pronounced for fast decomposing litter types, i.e., litters dominated by HV rather than RYE. While our results suggest possible convergence of litter C:N ratios, initial differences in litter chemistry neither converged nor diverged. Therefore, we conclude that the initial chemistry of litter before decomposition exerts a strong control on its chemical composition throughout the decay continuum.