Cover Crop Biomass Research Articles

Water productivity of forage sorghum in response to winter cover crops in semi-arid irrigated conditions

Forage sorghum (Sorghum bicolor (L.) Moench) is a suitable alternative for corn silage in water-limited environments due to its similar yield potential as corn but with less water input. Cover cropping could further improve forage sorghum yield and water productivity, making it the best alternative forage crop for arid and semi-arid regions. This two-year study evaluated the effect of fallow and cover crops on soil volumetric water content (VWC), soil water extraction, changes in soil water storage (∆S), seasonal crop evapotranspiration (ETseasonal), cropping system evapotranspiration (ETsystem), seasonal crop water productivity (CWPseasonal), cropping system water productivity (CWPsystem) and forage sorghum yield under a no-till semi-arid irrigated condition. Treatments included three winter cover crop mixtures: grasses + brassicas + legumes (GBL), grasses + brassicas (GB), grasses + legumes (GL), and a no-cover crop control (fallow), arranged in a randomized complete block design with four replications. Cover crops significantly reduced soil VWC at the beginning and up to 30 days after sorghum planting (DAP). However, at 60 DAP, the VWC was mostly similar among all treatments, and at 90 DAP, it was 17–21% higher under the cover crop treatments than fallow. The ETseasonal was 22–26% higher under cover crops than fallow during cover crop growth, but it was 12–13% greater under fallow than the cover crops during forage sorghum growth. Total soil water extraction at sorghum harvest was 8–89% higher under fallow than cover crops treatments. Averaged across years, cover crop biomass yield was 11% greater with the GBL mixture than the GB and GL mixtures. Forage sorghum yield was 23%, 32%, and 18% higher under GBL, GB, and GL cover crop mixtures, respectively, than fallow. Compared to fallow, cover crop mixtures improved sorghum CWP by 38–43%. Results indicated that forage sorghum yield and CWP under semi-arid irrigated systems could be substantially improved with winter cover cropping than leaving the land fallow.

Mixed planting reduces the shaping ability of legume cover crop on soil microbial community structure

Cover crop species and management are the key factors for reaping maximum benefits. Current studies lack a comprehensive assessment of the effects of cover crop species and planting patterns on soil properties, plant properties, and rhizosphere microbial communities at the full-blooming stage. A field experiment was conducted for 8 years (2011–2018) in Tianjin (fluvo-aquic soil) in China to compare various cover crops (hairy vetch, February orchid and rye) under different planting patterns (monoculture or mixed culture) in terms of cover crop biomass, soil physicochemical and biological properties, and rhizosphere microbial communities through high-throughput sequencing. The following groups were established: CK (winter fallow; the control), FO (February orchid monoculture), RY (rye monoculture), HV (hairy vetch monoculture), FOHV (February orchid–hairy vetch mixed culture), and RYHV (rye–hairy vetch mixed culture). RY had the highest biomass and nitrogen (N) uptake, and HV had the lowest biomass and highest N content. Mixed culture produced biomass higher in amount than the average biomass of monocultures of each individual species. RYHV showed a higher amount of biomass and uptake of nutrients, especially N. Cover crop planting significantly increased soil organic matter content (22.45 %–33.22 %), N levels (78.28 %–412.04 %), and available phosphate (9.70 %–45.03 %) and potassium (20.71 %–56.62 %) levels, but no significant differences in soil pH and total phosphorus content were found among the treatments. FO and HV treatments showed higher increments in soil biological properties: soil microbial biomass C (Cmic) and soil microbial biomass N (Nmic) and nematode density than the RY treatment. Mixed planting further promoted these properties, and FOHV treatment showed the highest values, which indicated improved soil properties. HV treatment significantly reduced bacterial and fungal diversity and the number of operational taxonomic units. These effects can be alleviated by mixed planting with FO and RY. Principal component analysis showed that the bacterial and fungal communities in the control were distinct from those in the cover crop treatments, and the difference was the greatest in the HV treatment. However, mixed planting with FO and RY reduced this difference between HV and CK. Structural equation model integration and analysis confirmed that the bacterial community was primarily regulated by soil physicochemical properties, whereas the fungal community was primarily regulated by plant properties. Soil biological properties affected bacterial and fungal communities, and mixed planting alleviated the impact of hairy vetch on soil microbial communities.

Aboveground Carbon Fixation and Nutrient Retention in Temporary Spontaneous Cover Crops in Olive Groves of Andalusia

In Southern Spain, olive trees have traditionally been cultivated in marginal areas with relatively shallow and bare soils under rainfed conditions, resulting in heavy soil losses and soil degradation. The implementation of temporary spontaneous cover crops in the inter-rows of olive groves, has proven to be a suitable diversification strategy to reduce soil erosion but it can also contribute to climate change mitigation and the boosting of internal nutrient recycling. However, information on the contribution of cover crops to atmospheric CO2 fixation and on nutrient retention in olive groves is scarce, which is a major drawback when it comes to modelling on larger spatial scales. In this study, we aimed to assess the potential effects of temporary spontaneous cover crops in olive groves on CO2 fixation and nutrient retention. The aerial biomass of cover crops (0.25m2 frames) and contents of carbon and nitrogen (CNHS analyser), phosphorus and potassium (IPC-MS) were analyzed in 46 commercial olive groves with different tree densities and cover crop layouts; the whole farm (WCC), the whole farm except the area below the tree canopy (CCC) or in bands of a given width in the inter-row area (BCC). Cover crops of 56% of the olive groves were under BCC whereas only 17% were under WCC. The annual net primary production of cover crops under WCC (1,707.4 kg DM ha−1 y−1) was significantly higher than that of CCC (769.5 kg DM ha−1 y−1) and with intermediate values for BCC (1,186.4 kg DM ha−1 y−1). Similarly, the annual rate of C-CO2 fixation in the annual net primary production of olive groves with WCC (642.1 kg C ha−1 y−1) was 1.35 and 2.1 times higher than the olive groves with BCC and CCC, respectively. On average, 19.5 kg N ha−1 y−1, 2.48 kg P ha−1 y−1 and 24.30 kg K ha−1 y−1 was accumulated in the biomass of the cover crops. This study demonstrates that cover crops contribute significantly to CO2 reduction and the retention of significant amounts of tree-unused nutrients. In addition, the higher the area covered by cover crops, the higher the contribution to these ecosystem services.

The importance of species selection in cover crop mixture design

AbstractCover crops are increasingly being included in crop rotations as a mechanism to promote diversity and provide agroecosystem services, including weed suppression. Recently, cover crop mixtures have increased in popularity in an attempt to provide a greater diversity in ecological services as compared with monocultures. Several recent studies, however, have failed to detect a positive effect of cover crop diversity on biomass production or weed suppression. Here we assessed biomass productivity and weed suppression in 19 cover crops seeded as monocultures and 19 mixtures of varying species composition and functional richness (two- and three-species mixtures) of full-season cover crops in Atlantic Canada. Cover crop biomass production and weed suppression varied by species identity, functional diversity, and species richness. As cover crop biomass increased regardless of diversity, weed biomass declined. Highly productive forbs and grasses provided the greatest weed suppression in monoculture. In line with previous observations, mixtures were not more productive or weed suppressive on average than the most productive monocultures. We observed that the inclusion of the highly productive species buckwheat (Fagopyrum esculentum Moench) and sorghum–sudangrass [Sorghum × drummondi (Nees ex Steud.) Millsp. & Chase] in a mixture increased stand evenness, productivity, weed suppression, and spatiotemporal stability. Taken together, our results suggest that effects of diversity on mixture productivity and weed suppression are species specific. This further demonstrates the importance of species selection in cover crop mixture design.

Comparing satellites and vegetation indices for cover crop biomass estimation

• Adequate biomass is required for cover crops to provide significant ecological benefits. • Satellite imagery predicted field level cover crop biomass accurately. • Satellite imagery more accurately estimated biomass than handheld sensors. • At least one vegetation index for each satellite system accurately predicted biomass. • NDVI was not the best predictor of cover crop biomass for any satellite. Cost-share programs based on measures of participation rather than performance are available to farmers who plant cover crops. However, cover crops only provide significant ecological benefits like reduced nutrient loss when adequate biomass is established. The purpose of this study was to determine whether satellite imagery can effectively estimate cover crop biomass in fields with diverse species composition, and whether increased spatial resolution and satellite imaging frequency can increase biomass estimation accuracy. Aboveground biomass samples of 1 m 2 were collected for 86 sites within 26 agricultural fields containing unique cover crop species composition to assess biomass production. In-field sensors were used to measure normalized difference vegetation index (NDVI) and groundcover percentage. Three satellites (Landsat-8 [30 m resolution], Sentinel-2 [10 m resolution], and PlanetScope [3 m resolution]) were used to calculate eight vegetation indices (VIs) for comparison with cover crop biomass. Multiple linear regression, correlation coefficients, and root mean square error (RMSE) were used to perform hierarchical clustering to rank VIs calculated from each satellite for biomass estimation accuracy. Satellites predicted cover crop biomass at the field level very accurately (r 2 up to 0.79), demonstrating the potential of large-scale biomass estimation at relatively low cost compared to in-field sampling. All satellite-VI pairs estimated biomass more accurately than the in-field sensors. Performance of VIs varied by satellite, but each satellite had at least one VI that performed very well for both site-level and field-averaged data. When using PlanetScope or Landsat-8 imagery, the perpendicular vegetation index provided the most accurate cover crop biomass estimation on a per-site basis and ratio vegetation index performed best using Sentinel-2 imagery. PlanetScope was the only satellite to provide useable imagery for every site due to increased revisit period; however, its increased spatial resolution did not increase estimation accuracy overall compared to Landsat-8 or Sentinel-2.

Integration of Satellite-Based Optical and Synthetic Aperture Radar Imagery to Estimate Winter Cover Crop Performance in Cereal Grasses

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.

The potential of cover crops to increase soil organic carbon storage in German croplands

AimsSoil organic carbon (SOC) stocks of croplands can be enhanced by targeted management, which boosts soil fertility and contributes to climate change mitigation. One SOC sequestration option is adopting cover crops. The aim of this study was to quantify the SOC sequestration potential of cover crops in Germany.MethodsWe simulated SOC scenarios on 1,267 cropland sites with site-specific management data using an SOC model ensemble consisting of RothC and C-TOOL. A new method was developed to estimate carbon input from cover crops that included the effects of climate, sowing date and species on cover crop biomass production.ResultsThe recent cover crop area could be tripled to 30% of arable land in Germany. This would enhance total carbon input by 12% and increase SOC stocks by 35 Tg within 50 years, corresponding to an annual increase of 0.06 Mg C ha-1, 2.5 Tg CO2 or 0.8 per mill of current SOC stocks in 0–30 cm depth. On sites with cover crops, 0.28–0.33 Mg C ha-1 a-1 would be accumulated within 50 years. Our simulations predicted that even if the full potential for cover crop growth were realised, there would still be a decline in SOC stocks in German croplands within 50 years due to the underlining negative SOC trend.ConclusionsCover crops alone cannot turn croplands from carbon sources to sinks. However, growing them reduces bare fallow periods and SOC losses and thus is an effective climate change mitigation strategy in agriculture.

Legume Cover Crop Contributions to Ecological Nutrient Management in Upper Midwest Vegetable Systems

Cover cropping, especially with legumes, is a critical approach to ecological soil nutrient management as a means to meet Sustainable Development Goal (SDG) 2, addressing food security issues via sustainable agriculture approaches. However, cover cropping in some of the most intensified food production regions of the northern U.S. is challenged by short growing seasons and harsh winters with variable temperatures and increasingly erratic snowfall. In this study, we explore the potential of winter annual legume cover crops to augment soil organic carbon (C) and nitrogen (N) stocks within a horticultural cropping system under climate conditions that allow only modest cover crop biomass production. We compared hairy vetch, cereal rye, red clover, and a hairy vetch/rye biculture in a randomized complete block design at two sites (North Central and Southwest Research and Outreach Centers in Minnesota) over 2 years. Cover crops were established in fall and terminated in spring prior to sweet corn planting, and soils sampled both at pre-cover crop termination and 2 weeks post-termination. We determined several indicators of C and N dynamics, including microbial biomass C (MBC), permanganate-oxidizable C (POXC), particulate organic matter C and N (POMC and POMN, respectively), extractable soil N (EXTN), and potentially mineralizable N (PMN). Out of all treatments evaluated, vetch production increased soil EXTN the greatest after 2 weeks, contributing two to 11 times more EXTN to soils compared to non-vetch treatments, meeting N requirements for sweet corn in three out of four site-years. Overall, time of sampling, either pre-or post-termination, consistently impacted soil measurements, with p < 0.05 in 20 out of 24 soil parameter × site-year combinations. Study results suggest that cover crops planted in colder northern climates during winter fallow periods can supply valuable N following spring termination, but termination effects on labile C and N pools are mixed. Our findings advance understanding of how cover cropping can support SDG 2 outcomes by assessing cover crop legume systems under biophysical conditions that challenge cover crop integration in agroecosystems.

Fall cover crop nitrogen uptake drives reductions in winter-spring leaching.

Cover crops can reduce nitrate leaching after cash crop harvest. Despite widespread cover crop implementation, there has been a limited effect on water quality in the Chesapeake Bay watershed. We hypothesize that typical timing for Maryland cover crop planting after cash crop harvest is too late to allow roots to take up substantial nitrate from the soil profile before it is leached by winter drainage water. Across four site-years (including sandy and silty soils), we compared various planting dates for a radish (Raphanus sativus L.)-crimson clover (Trifolium incarnatum L.)-triticale (Triticosecale) cover crop mixture. Also, across two site-years we compared early-planted pure rye, radish, and a three-species mixture with no cover. We measured cover crop biomass and N content and used tension lysimeters to measure deep soil porewater nitrate concentrations. Cumulative nitrate leaching was calculated from these concentrations and weather-based drainage estimates. Cover crops were planted on four dates over a 6-wk period. Overall, cover crops planted first, second, third, fourth, and no cover crop (just weeds) resulted in 3,340, 3,160, 1,600, 303, and 164kg ha-1 of biomass; biomass N accumulation of 65.5, 68.6, 44.0, 9.88, and 4.79kg N ha-1 ; and mean porewater concentrations of 2.71, 2.57, 4.72, 10.0, 17.1mg L-1 of nitrate-N, respectively. Over two site-years, the three-species mix performed as well or better than pure rye or radish. Early planting altered cover crop species proportions, increased cover crop productivity, and reduced nitrate leaching from agricultural fields.

Tarping Cover Crops Facilitates Organic No-till Cabbage Production and Suppresses Weeds

Small-scale vegetable farmers are interested in cover crops and reduced tillage, but scale-appropriate technology and equipment are necessary to expand these practices to the growing segment of small farms. We sought to determine the efficacy of tarps, an increasingly popular tool on small farms, to end overwintering cover crops and provide weed suppression for subsequent no-till cabbage production. In three fields over two seasons in Maine, we grew a winter rye (Secale cereale L.) and hairy vetch (Vicia villosa L.) cover crop, which we managed by a factorial combination of tillage (no-till, till) and tarping (tarp, no-tarp) in June, followed by a transplanted cabbage crop (Brassica oleracea L. var. Capitata) in July. Within each treatment, subplots were either weeded by hand or left unweeded. Cover crop biomass ranged from 2.8 to 4.5 Mg⋅ha−1. Mean cabbage weights in the novel no-till system (no-till/tarp) were greater than (year 1) or equal to (year 2) those in tillage-based systems (till/no-tarp and till/tarp). In year 1, the mean cabbage weight in weeded subplots was 48% greater in no-till/tarp than in till/no-tarp systems. In unweeded subplots, this difference was 270%, highlighting the efficacy of the no-till/tarp system to reduce the impact of weeds. In year 2, weed biomass was higher with all treatments than it was in year 1, and unweeded subplots failed to produce marketable heads (i.e., >300 g). The mean cabbage weight in weeded subplots was equal among no-till/tarp, till/tarp, and till/no-tarp systems. Tarping had a strong effect on weed biomass and weed community composition measured at the time of cabbage harvest in unweeded subplots. In year 1, weed biomass at the time of cabbage harvest with tarp treatments was less than half that with no-tarp treatments. Tarps effectively facilitated the cover crop mulch-based no-till system. We propose that this system is an adaptive strategy for farmers affected by climate change. However, both cover crop production and tarping shorten the growing season. We discuss tradeoffs and opportunity costs using the metric of growing degree days.

Cover crops and carbon sequestration: Lessons from U.S. studies

AbstractSequestering soil organic carbon (SOC) with cover crops (CCs) to mitigate climate change and enhance other soil ecosystem services is generating much enthusiasm. However, the potential of CCs to sequester large amounts of SOC appears to be debatable, which warrants further discussion on regional and national scales. This paper discusses both CC effects on SOC based on studies in the United States up to 30 May 2021 and practices that could enhance CC ability to sequester SOC. Cover crops accumulated SOC only in 22 (29%) of 77 comparison (CC vs. no CC) counts. Cover crops accumulated 0.2–0.92 Mg C ha−1 yr−1 (0.41 Mg C ha−1 yr−1 average) across the 22 comparisons where CCs increased SOC and 0–0.92 Mg C ha−1 yr−1 (0.12 Mg C ha−1 yr−1 average) across the 77 comparisons in the upper 30‐cm soil depth. Cover crops increased SOC most in low‐C soils (<1% C) and after 5 yr but not when CCs produced <2 Mg biomass ha−1. Because SOC accumulation was primarily correlated (r = .38; p = .006) with CC biomass and years under CCs (r = .37; p = .009), current CC management practices need modification to enhance SOC accumulation. Planting after crop harvest in summer and terminating late to increase CC biomass production along with long‐term (>5 yr) use can be potential strategies. Overall, CCs can accumulate SOC only in one‐third of cases based on U.S. studies, which urges the modification of current CC management practices to boost SOC sequestration.

Weed suppression in cover crop mixtures under contrasted levels of resource availability

Cover crop (CC) mixtures appear as a promising agroecological tool for weed management. Although CC supress weed growth by competing for resources, their suppressive effect under contrasting levels of soil resource availability remains poorly documented. A two field:year experiment was conducted to investigate the weed suppressive effect of four CC mixtures. They were composed of 2 or 8 species including or not legume species and compared to a bare soil control. The experiment included two levels of irrigation and nitrogen fertilisation at CC sowing. The objectives were to assess (i) weed and CC aboveground biomass response to CC mixtures and resource availability, (ii) the weed suppressive effect of CC mixtures across a gradient of CC biomass and (iii) weed community response to CC mixtures and resource availability. CC and weed biomass were mainly influenced by interactions between CC mixtures and fertilisation and between CC mixtures and irrigation, with contrasted effects between field:years. Nitrogen fertilisation increased biomass of non-legume based CC mixtures but this only resulted into a further reduction of weed biomass of little biological relevance. Legume-based CC mixtures suppressed weeds to a greater extent without nitrogen fertilisation in year 2 but not in year 1, possibly due to contrasted initial soil nitrogen availability (lower in year 2). Weed biomass generally benefited more from irrigation than CC mixtures. Among the 33 weed species recorded, weed communities in each plot were dominated by wheat volunteers, Geranium dissectum, Veronica persica and Echinochloa crus-galli, whose biomass varied depending on the interaction between year, CC mixture and resource availability. Our results revealed that competitive outcomes between CC mixtures and weed species were driven by a complex interaction between resource availability and species traits. Further experiments focusing on plant traits should improve our understanding of weed:CC competitive outcomes under various levels of resource availability.

The role of microbes in the increase of organic phosphorus availability in the rhizosheath of cover crops

Background and aimsThe characterisation of plant-available phosphorus (P) pools and the assessment of the microbial community in the rhizosheath of cover crops can improve our understanding of plant–microbe interactions and P availability.MethodsMustard (Sinapis alba), phacelia (Phacelia tanacetifolia) and buckwheat (Fagopyrum esculentum) were grown as cover crops before soybean (Glycine max) in an on-farm experiment on a soil low in available P in southwest Germany. The cycling of P through the cover crop biomass and the enzyme-availability of organic P (Porg) pools in the cover crop rhizosheath were characterised. The soil microbial community (PLFA), activity (acid and alkaline phosphomonoesterase, as well as phosphodiesterase), and microbial P were assessed. The abundance of 16S-rRNA and phoD, coding for alkaline phosphomonoesterase in bacteria, were quantified using real-time qPCR.ResultsMustard contained the greatest amount of P in its large biomass. In the rhizosheath of all cover crops, the concentration of enzyme-labile Porg was higher than that in the control bulk soil, along with substantial increases of microbial abundance and activity. There were little differences among cover crop species, few changes in the bulk soil and only a limited carryover effect to soybean, except for fungi.ConclusionsTurnover of microbial biomass, especially saprotrophic fungi, increased by rhizodeposition of cover crop roots; this was likely responsible for the observed increases in enzyme-available Porg. Microbial function was correlated linearly with microbial biomass, and the data of enzyme activity and phoD did not suggest a difference of their specific activity between bulk and rhizosheath soil.

Soil water storage, winter wheat yield, and water‐use efficiency with cover crops and nitrogen fertilization

AbstractSummer cover crops extract soil water and may affect succeeding winter wheat (Triticum aestivum L.) yield and water‐use efficiency (WUE). We examined the effect of summer cover crops and N fertilization rates on soil water storage at wheat planting (SWP) and harvest (SWH), winter wheat yield, evapotranspiration (ET), and WUE from 2017–2018 to 2019–2020 at Changwu and Chang'an in the Loess Plateau of China. Cover crops were soybean [Glycine max (L.) Merr., SB], sudangrass [Sorghum sudanense (Piper) Stapf, SG], soybean and sudangrass mixture (SS), and no cover crop (CK) and N fertilization rates were 0, 60, and 120 kg N ha–1 applied to winter wheat. Soil water was measured to a depth of 2 m at wheat planting and harvest, and grain yield, ET, and WUE of wheat were evaluated. Cover crop biomass was greater for SS than SB at both sites. The SWP and ET were greater for CK than other cover crops at all N fertilization rates, but SWH varied for cover crops, N fertilization rates, years, and sites. Winter wheat grain yield and WUE were greater for SS than other cover crops and increased with increased N fertilization rates in all years and sites. Although SS and 120 kg N ha–1 reduced SWP and ET, wheat yield and WUE were greater than other cover crops and N fertilization rates in the semiarid climatic condition of the Loess Plateau of China where annual precipitation is adequate to reduce the detrimental effect of water stress.

Exploring Overwintered Cover Crops as a Soil Management Tool in Upper-midwest High Tunnels

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.

Benefits of Cover Cropping Systems in Walnut Orchards as Sustainable Agricultural Practice

In recent years walnut orchards implemented cover crops in between rows to improve soil’s quality, lessen soil’s erosion, increase organic matter, manage nutrient movement and availability, enhance water retention, and expand microbe, insect, and flora diversity. Commonly selected cover crops in California are from families Poaceae, Brassicaceae, and Fabaceae. Considerations should be made when choosing a particular cover crop mixture to enhance multiple benefits and improve sustainable practices in orchard settings. An experiment was conducted in a walnut orchard to compare functionality and benefits of three systems multi-crop, monocrop, and no vegetation cover crop system. The following components were evaluated: cover crop and weed biomass, cover crop species field distribution, and ability to provide better coverage and weed suppression properties. Brassica mixture, clover and grasses showed highest presence in field conditions and excellent weed competition attributes, while peas and faba beans had low presence and did not compete well growing in a mixture with other cover crops. Multi-crop treatment demonstrated the highest dry and wet biomass as well as the greatest weed suppression. Recommendations are to carefully consider current practices in walnut orchards, to seasonally include vegetation cover rather than bare soil, and to choose multi-crop cover rather than monocrop. Implementation of multi-crop species as a sustainable practice would increase soil’s quality, improve biological management through rise of natural beneficial predators and enhance integrated pest management methods.

Short‐term impacts of cover crops in maritime potato (Solanum tuberosum) systems

AbstractCover cropping is a soil conservation practice widely investigated in agronomic crops, but less is known about cover crop implications in specialty cropping systems, particularly in a high disturbance system like potato (Solanum tuberosum L.). Brassica cover crops are popular in eastern Washington potato production, but brassica seed crop production in western Washington presents issues with use of brassica cover crops in the region's fresh‐market potato systems. To identify winter cover crops compatible with regional restrictions and climatic challenges in western Washington potato systems, trials including a no‐cover control, eight single species (including brassicas, grasses, and legumes), and a grass–legume mixture were conducted in Mount Vernon, WA, in 2018–2019 and 2019–2020. We examined cover crop and weed biomass production, potato yield and quality, and short‐term soil health impacts by measuring permanganate oxidizable carbon (POXC) and inorganic nitrogen before cover crop incorporation and at midseason. Cover crop biomass and weed suppression varied by year, with annual ryegrass (Lolium multiflorum Lam.) producing the most biomass in both years despite poorer weather conditions and reduced cover crop biomass in other treatments in 2020, making it a good cover crop candidate for western Washington. Both POXC and inorganic nitrogen were greater at midseason but did not vary among cover crop treatments, suggesting that temporal variation influences POXC and inorganic nitrogen more than a single winter of cover crops. Potato yield and tuber wireworm damage varied by year, but not across cover crop treatments, and tuber symptoms resembling black scurf did not vary by year nor treatment.

Cereal rye cover crop terminated at crop planting reduces early‐season weed density and biomass in Wisconsin corn–soybean production

AbstractA fall‐established cereal rye (Secale cereale L.) cover crop has potential to provide weed suppression in fields that will be planted with corn (Zea mays L.) and/or soybean [Glycine max (L.) Merr.], reducing the selection pressure for herbicide resistance as part of an integrated weed management approach. However, biomass from an overwintering cover crop can be limited in areas with prolonged cool‐spring growing conditions, like in the Upper Midwest region of the United States. This study was conducted to determine if a cereal rye cover crop grown in Wisconsin and terminated at the time of crop planting could provide effective levels of early‐season weed suppression in corn–soybean systems practicing no‐till soil management. Cover crop biomass, weed biomass, and weed density were assessed at two Wisconsin locations (eight site‐crop‐years total; four site‐years of each corn and soybean) in 2019 and 2020. Cereal rye biomass production at the time of crop planting ranged from 290–1,480 kg ha–1. Overall, no‐till management with a cover crop reduced weed density by 31% and reduced weed biomass by 61% compared with no‐till without a cover crop. These results indicate that the use of a cereal rye cover crop in the Upper Midwest has potential to reduce the exclusive reliance on spring burndown herbicides in no‐till, but limited spring cover crop biomass in this region may diminish the weed‐suppressive effects from this management practice compared with other parts of the United States where higher amounts of cover crop biomass can be achieved at crop planting time.

Evaluation of conservation tillage practices in the production of organic flue‐cured tobacco

AbstractIntensive tillage in flue‐cured tobacco (Nicotiana tabacum L.) contributes to soil erosion and reduced water‐holding capacity of soils. Conservation tillage minimizes soil disturbance by planting a crop directly into the residue of overwintered cover crop. Reducing tillage has been shown to improve soil health (increased rainwater infiltration, improved water‐holding capacity, reduced erosion) and to reduce production costs (fuel and labor). The objective of this study was to compare the effects of conservation and conventional tillage on weed management in organically grown flue‐cured tobacco. Field studies were conducted in Kinston, NC, in 2019 and 2020 and in Rocky Mount, NC, in 2020, comparing the impacts of conventional tillage and conservation tillage on weed emergence and tobacco production. An overwintered cereal rye (Secale cereal L.) cover crop was conventionally tilled or terminated via roller‐crimper and left in place as a mulch prior to transplant of flue‐cured tobacco. Cover crop biomass, weed emergence and biomass, soil resistance, crop yield and quality, and cured leaf chemistry were evaluated. In all environments, conservation tillage with cover crop residue reduced weed density and biomass when compared with conventional tillage treatments. In 2019, cured leaf yield was higher under conservation tillage practices than under conventional tillage. In 2020, environmental conditions in both locations resulted in crop loss. These results indicate that conservation tillage practices may be an effective weed management strategy while improving yields in an organic production system. However, organic flue‐cured tobacco grown under conservation tillage is vulnerable to extreme rain events due to the exclusion of in‐season cultivation.

Short‐term corn yield response associated with nitrogen dynamics from fall‐seeded cover crops under no‐till dryland conditions

AbstractThe availability of in‐season N to corn (Zea mays L.) following fall‐seeded cover crops depends on seasonal patterns of nitrogen (N) transformations that are site‐ and year‐dependent and resist prediction. Our objectives were to evaluate N dynamics following different cover crops (legume, nonlegume, none) and their relationship with subsequent corn yields within an established no‐till winter wheat (Triticum aestivum L.)–cover crop/corn–soybean (Glycine max) rotation over two site‐years in the U.S. Northern Plains. Spring cover crop biomass and N uptake, in‐situ soil N mineralization following cover crop termination, and corn grain yield and N uptake were measured. Legume cover crops were associated with higher corn yields, whereas rye (Secale cereale) did not significantly decrease corn yields despite N immobilization by a large rye cover crop in one year. Legume cover crops produced the highest rates of N mineralization during periods of high N demand by corn (V6–R3) and the highest seasonal amounts of mineralized N compared with rye or no cover crops. In‐situ N mineralization measurements better predicted yields across all treatments compared with approaches using cover crop biomass and N content. In situ N mineralization rates during corn growth stages V6–R3 provided a superior prediction (r = .83) of corn yields compared with all seasonal estimates of N provided by cover crops. Lower apparent N use efficiency calculated with contributions of in‐season N mineralization indicated that less fertilizer N can be applied in the growing season following legume cover crops.