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Cover crops are planted during the off-season to protect the soil and improve watershed management. The ability to map cover crop termination dates over agricultural landscapes is essential for quantifying conservation practice implementation, and enabling estimation of biomass accumulation during the active cover period. Remote sensing detection of end-of-season (termination) for cover crops has been limited by the lack of high spatial and temporal resolution observations and methods. In this paper, a new within-season termination (WIST) algorithm was developed to map cover crop termination dates using the Vegetation and Environment monitoring New Micro Satellite (VENµS) imagery (5 m, 2 days revisit). The WIST algorithm first detects the downward trend (senescent period) in the Normalized Difference Vegetation Index (NDVI) time-series and then refines the estimate to the two dates with the most rapid rate of decrease in NDVI during the senescent period. The WIST algorithm was assessed using farm operation records for experimental fields at the Beltsville Agricultural Research Center (BARC). The crop termination dates extracted from VENµS and Sentinel-2 time-series in 2019 and 2020 were compared to the recorded termination operation dates. The results show that the termination dates detected from the VENµS time-series (aggregated to 10 m) agree with the recorded harvest dates with a mean absolute difference of 2 days and uncertainty of 4 days. The operational Sentinel-2 time-series (10 m, 4–5 days revisit) also detected termination dates at BARC but had 7% missing and 10% false detections due to less frequent temporal observations. Near-real-time simulation using the VENµS time-series shows that the average lag times of termination detection are about 4 days for VENµS and 8 days for Sentinel-2, not including satellite data latency. The study demonstrates the potential for operational mapping of cover crop termination using high temporal and spatial resolution remote sensing data.

Summer cover crop utilization by no-till vegetable farms is essential for continuous soil protection, especially in the southern United States where intense storms are likely to occur in hot and humid summer months. A field experiment was conducted at the National Soil Dynamics Laboratory in Auburn, AL, USA, between the summers of 2015 and 2017 to determine the effectiveness of an experimental roller/crimper in mechanically terminating summer cover crops. Iron clay peas (Vigna unguiculata, L.) planted on a sandy loam and pearl millet (Penninsetum glaucum, L.) planted on clay soil were selected to determine termination rate effectiveness in single, double, and triple rolling/crimping over the same area. Overall, termination rates for both cover crops were higher for rolling three times (71%) compared to rolling once (55%) or twice (63%). However, cover crop termination was inhibited due to rainfalls on the experimental area during the three-week evaluation period. In 2016, drought conditions and high temperatures (32.6 °C) caused biomass reduction, especially for pearl millet, of over 31% to 39% compared to 2017 and 2015. Rolling provided higher soil-water conservation compared with the non-rolled control due the cover crop mulch layer blocking sunlight, keeping the soil surface cooler and preventing water evaporation. Recurrent rolling did not cause soil compaction above the 2.0 MPa level that inhibits root growth, but changes in soil strength were dependent on the soil moisture content.

With changes to climate and crop insurance, earlier soybean [Glycine max (L.) Merr.] planting dates need to be investigated. Additionally, the use of a cover crop prior to soybean is promoted as a sustainable practice though little is known about cover crop and ultra‐early soybean planting (prior to April 15). The objective was to evaluate soybean planting date and cereal rye (Secale cereale L.) cover crop termination timing on cover crop biomass, soybean plant population, and yield. The study was conducted in Northeast and West Central Ohio in 2021 and 2022. Treatments included three soybean planting dates (early April, late April, and late May) and three cover crop treatments (termination 1–2 weeks prior to planting or “early,” termination at or after planting or “late,” and no cover crop). Cover crop biomass increased as termination was delayed. Soybean planted in early April resulted in a yield reduction of 1.8 Mg ha−1 when planted into a cover crop compared to the no cover crop control. However, when soybean was planted in late April, grain yield was not different among cover crop treatments. Yield reduction associated with early April planting with a cover crop was likely due to low soybean plant population, especially in Northeast Ohio, where plant population was <55,000 plants ha−1 with a cover crop and >120,000 plants ha−1 without a cover crop. To maximize yield, soybean should be planted by the end of April in Northeast Ohio. In West Central Ohio, soybean can be planted in early April without a cover crop. Core Ideas Soybean planting date and cover crop termination timing on cover crop biomass and grain yield were assessed. Cover crop biomass increased with later termination dates. In West Central Ohio, soybean planted in April yielded greater than soybean planted in May. Planting soybean in early April after a cover crop reduced soybean plant population and grain yield.

No‐till farmers who want more from their cover crops (CCs) are delaying CC termination until the main crop is planted. Delaying termination can help dry wet soils and reduce erosion. This process is referred to as planting green (PG). We hypothesized that PG would (i) dry soil at main crop planting, but conserve soil moisture later in the growing season; (ii) reduce soil temperature; (iii) reduce slug damage on main crops; and (iv) not reduce main crop yield. This experiment was conducted in Pennsylvania between 2015 and 2017 to compare two CC termination dates: preplant killed (PK) and planting green (PG) in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Planting green increased CC biomass an average of 94% and 94 to 181% compared to PK preceding corn and soybean, respectively. Soil was 7 to 24% drier and 0.9°C cooler at corn planting, and 8% drier and 0.7 to 2.4°C cooler at soybean planting in PG compared to PK. Slug damage was not different, lower, or higher in PG corn, and not different or lower in PG soybean compared to PK. Corn yield was reduced and not impacted by PG in higher and lower yielding environments, respectively. Soybean yield was stable across locations, and not affected by cover crop termination date. We concluded that corn was more vulnerable to yield losses from conditions created by PG than soybean; therefore, growers who desire potential benefits and lower risk from PG should first consider soybean. Core Ideas Planting green refers to planting the main crop into a living cover crop. Planting green increased cover crop biomass by 94% in corn and by 94 to 181% in soybean. Planting green dried the soil at main crop planting. Planting green cooled soil 0.7 to 2.4°C at planting. Soybean yield was not influenced by planting green; corn yield was reduced.

Cover crops are increasingly being used for weed management, and planting them as diverse mixtures has become an increasingly popular strategy for their implementation. While ecological theory suggests that cover crop mixtures should be more weed suppressive than cover crop monocultures, few experiments have explicitly tested this for more than a single temporal niche. We assessed the effects of cover crop mixtures (5- or 6-species and 14-species mixtures) and monocultures on weed abundance (weed biomass) and weed suppression at the time of cover crop termination. Separate experiments were conducted in Madbury, NH, from 2014 to 2017 for each of three temporal cover-cropping niches: summer (spring planting–summer termination), fall (summer planting–fall termination), and spring (fall planting–subsequent spring termination). Regardless of temporal niche, mixtures were never more weed suppressive than the most weed-suppressive cover crop grown as a monoculture, and the more diverse mixture (14 species) never outperformed the less diverse mixture. Mean weed-suppression levels of the best-performing monocultures in each temporal niche ranged from 97% to 98% for buckwheat (Fagopyrum esculentum Moench) in the summer niche and forage radish (Raphanus sativus L. var. niger J. Kern.) in the fall niche, and 83% to 100% for triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum]) in the winter–spring niche. In comparison, weed-suppression levels for the mixtures ranged from 66% to 97%, 70% to 90%, and 67% to 99% in the summer, fall, and spring niches, respectively. Stability of weed suppression, measured as the coefficient of variation, was two to six times greater in the best-performing monoculture compared with the most stable mixture, depending on the temporal niche. Results of this study suggest that when weed suppression is the sole objective, farmers are more likely to achieve better results planting the most weed-suppressive cover crop as a monoculture than a mixture.

The Agricultural Production Systems sIMulator (APSIM) was used to evaluate two alternative approaches for extending the cover crop growing window into corn (Zea mays L.) and soybean (Glycine max L.) crop rotations in Nebraska, USA. We evaluated how: (i) shifting corn planting dates (mid‐April to early‐June) and (ii) altering comparative relative maturity (CRM) corn hybrids (80 to 115 days) influence cover crop biomass and corn yields over a 30‐year period. The APSIM model was tested using experimental data and was then used to simulate a range of cover crop planting and termination scenarios. Our results showed no significant yield differences within the same corn relative maturity when planted on April 20 and May 13 but that yield declined when planted in June. During a six week fall cover crop planting window (September 15–October 31), every day before October 31 that the cover crop was planted resulted in additional 62 kg ha−1 of biomass. We also simulated a one month spring termination window (April 1–April 30) and, every day delay in cover crop termination resulted in per day additional 35 kg ha−1 of biomass. Cover crop biomass accrual was highly dependent on weather, where for identical fall planting dates, a warm wet season accrued approximately four times more biomass than a cool dry season. Although we found significant yield differences between early, medium and late season CRMs, earlier fall cover crop planting associated with either earlier spring corn planting or planting an early to medium season variety leads to ten‐fold greater cover biomass. Delayed corn planting by mid‐May had no yield penalty relative to April planting, and could facilitate four‐fold greater cover crop biomass (cover crop terminated April 30 instead of April 1). Our results demonstrate that earlier cover crop planting in fall or later cover crop termination in spring can result in significantly more biomass which can be balanced with yield goals.

Later spring termination of fall‐planted cover crops can result in more biomass production, which has the potential to improve environmental benefits. However, later cover crop termination can also have the potential to harm cash crops, such as through increases in corn seedling disease. With the objective of better understanding such potential competing interactions, we evaluated the impact of early and late termination timing of two cover crops—cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.)—on growth, seedling disease, and grain yield of corn in 2021 and 2022 in Nebraska. The total biomass production varied among treatments. Hairy vetch biomass was lower than cereal rye biomass at both termination times in 2021, but not different from cereal rye terminated early in 2022. Radicle root rot severity, a symptom of corn seedling disease, was not affected by cover crops in 2021. In 2022, however, radicle root rot was most severe in cereal rye terminated late treatments. Hairy vetch did not affect radicle root rot severity, regardless of termination time. Late termination of cereal rye resulted in a reduction in corn yield of 15.3% in 2021 and 76.1% in 2022 compared to no cover crop. Corn (Zea mays L.) grain yield was not affected following hairy vetch at either termination timing. Our results suggest that corn planted following late‐terminated cereal rye can increase the severity of root rot and decrease corn grain yield; however, planting green into hairy vetch can be a successful option to increase biomass without increasing corn seedling disease or decreasing corn yield. Core Ideas Late termination of cereal rye had a negative impact on corn, increasing seedling disease and reducing corn yield. The earlier termination of cereal rye or the addition of N can offset the negative effects of cereal rye on corn. Hairy vetch did not increase seedling disease or reduce corn yield, being a successful “planting green” option.

Cover crops are increasingly used around the world to enhance N cycling and provide a suite of agroecosystem benefits. The N scavenging capacity of cover crops during winter months is well recognized. Our research characterized spring management effects (e.g., early vs. late termination) on cover crop biomass, decomposition and N release rates, inorganic soil N, soil water dynamics, and corn (Zea mays L.) performance. Cereal rye (Secale cereale L.) was established in Beltsville, MD, to evaluate three management scenarios: no cover crop; early termination (∼40 d before corn planting); late termination (∼7 d before corn planting). Cereal rye biomass was quantified before termination, and decomposition was tracked over a 24‐wk period to assess loss. Soil N content to 100 cm, soil volumetric water content, and corn performance were evaluated over the corn growing season. Low spring precipitation in 2016 led to similar amounts of cereal rye biomass for early and late termination; however, late‐terminated cereal rye had lower quality biomass (higher C/N) in both years, leading to slower decomposition and N release rates. Over the corn growing season, late‐terminated cereal rye consistently had smaller soil N pools, suggesting more efficient N cycling (better synchrony of N release from cover crop residues with corn N demand) than early‐terminated cover crops. Corn yields were smallest following late‐terminated cereal rye in 2016, but there was no difference in yields among cover crop treatments in 2017. Overall, we conclude that planting cereal rye cover crops and delaying termination until later in the season will help retain and efficiently cycle N while maintaining high corn yields. Core Ideas We tested the effect of cover crop termination timing on N dynamics before corn. Late‐terminated cereal rye had slower rates of biomass loss and N release. Larger soil N pools in 2017 than 2016 resulted from lower corn yields. Cover crop biomass and corn performance were influenced by precipitation levels. Nitrogen was more efficiently cycled in systems with cover crops than systems without cover crops.

Farmers looking to maximize soil conservation benefits of a rye cover crop (Secale cereale L.) (RCC) may choose to delay termination closer to corn (Zea mays L.) planting. However, delaying RCC termination may reduce corn yield due to nitrogen (N) immobilization and seedling disease. The objective of this trial was to evaluate corn growth and yield in response to in‐furrow (IF) fertilizer and fungicide following a RCC and across different RCC termination timings. A field study was established at three locations in Kentucky in 2019 and 2020 to evaluate corn response to two RCC termination timings (21 d before corn planting [early terminated] and 1 d after corn planting [postplant terminated]) and three IF starter treatments (fertilizer, fungicide, and fertilizer + fungicide). A postplant‐terminated RCC resulted in greater rye shoot biomass, early‐season (Apr–May) soil moisture, and preplant soil inorganic N compared with an early‐terminated RCC. Also, a postplant‐terminated RCC reduced corn stand by an average of 31% at two of three locations and reduced corn yield by an average of 15.7% across locations. The inclusion of IF fertilizer, fungicide, or fertilizer + fungicide did not improve corn yield at any location, and no interaction between RCC termination timing and IF starter was observed. Overall, our results suggest IF fertilizer and/or fungicide does not ameliorate corn stand and yield reductions following a postplant‐terminated RCC. In addition, farmers should look to terminate a RCC earlier (14–21 d before planting) to reduce potential corn stand and yield loss. Core Ideas A postplant‐terminated rye cover crop increased soil moisture and inorganic soil nitrogen. A postplant‐terminated rye cover crop significantly reduced corn stand and yield. In‐furrow starter did not improve corn stand or yield loss following a rye cover crop.

Northeastern U.S. (New York, Pennsylvania, and New England states) dairy farmers are increasingly interested in improving soil health, nutrient sequestration, and dry matter production. Consequently, farmers ask about managing winter cover crops (WCCs) in corn silage (Zea mays L.) rotations. In this literature review we identify WCCs most suitable to the Northeast, and summarize studies on (i) fall and spring N accumulation, (ii) nitrogen fertilizer replacement value (NFRV) for the next corn crop, and (3) environmental and management variables that affect N uptake and NFRV. We also discuss the literature on use of WCCs as forage commodity crops. Overwintering species most suitable for corn silage rotations are wheat (Triticum aestivum L.), cereal rye (Secale cereale L.) and triticale (X Triticosecale Wittm.). Clover (Trifolium spp.) and vetch (Vicia spp.) can add N but require inter‐seeding in the Northeast. The NFRV for vetch typically exceeds that of clover, while the NFRVs of winter cereals tend to be low or negative. A few studies suggest cover crop termination with herbicides compared to tillage incorporation can, when no fertilizer N or manure is added, result in slower decomposition and more gradual N release. Research on the effects of tillage on NFRVs of cover crops is inconclusive. When seeded after corn silage, cereal rye is most effective in N uptake in fall and spring. A corn rotation that includes cereal rye or triticale that can be harvested has the potential to reduce soil erosion, capture residual N, increase annual forage yields, and provide quality forage.