Publications

2022
Menalled UD, Adeux G, Cordeau S, Smith RG, Mirsky SB, Ryan MR. Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no-till planted soybean. Ecosphere [Internet]. 2022;13 (6) :e4147. Publisher's VersionAbstract
Abstract The use of multiple ecological weed management tactics may be an effective solution to weed management challenges associated with reducing tillage. An experiment was conducted to assess how soybean Glycine max (L.) Merr. density and cereal rye Secale cereale L. mulch biomass affected weed suppression and community assembly in no-till production. Soybean was planted at five rates from 0 to 74 seeds m−2, and five cereal rye mulch levels were established from 0 to 2 times the ambient cereal rye biomass within each site–year. We assessed the effects of soybean density and cereal rye mulch biomass on weed suppression, weed community composition, and the functional structure of weed life cycle, emergence timing, seed weight, height, and specific leaf area traits. Weed suppression was influenced by a synergistic interaction between soybean density and cereal rye biomass. The functional dispersion (FDis) of all weed traits, when combined, was reduced by increased soybean density and mulch biomass, suggesting that high treatment intensities induced trait convergence. However, soybean density and cereal rye biomass had differing effects on the FDis and composition of individual traits, suggesting that these management practices represent unique filters during weed community assembly. Mulch biomass had a larger effect on annual weed suppression and weed community composition than soybean density. Farmers who utilize high biomass cover crop mulch for weed management may experience shifts in weed community composition toward an increased proportion of perennials and weeds with later emergence, heavier seeds, and shorter stature. Increasing soybean density may reduce perennial weed biomass, making it a valuable complement to high cereal rye mulch biomass. As such, weed management in no-till soybean is enhanced by combining multiple practices, which can enable synergistic weed suppression and the management of diverse weed functional groups.
Lounsbury NP, Warren ND, Hobbie J, Darby H, Ryan MR, Mortensen DA, Smith RG. Seed size variability has implications for achieving cover cropping goals. Agricultural & Environmental Letters [Internet]. 2022;7 (1) :e20080. Publisher's VersionAbstract
Abstract It is common to use mass-based units (e.g., kg ha–1) to describe cover crop seeding rates. However, this convention obscures important information about seed size and resulting plant density in the field, which may be linked to cover crop performance and ecosystem services. Seed counts of 27 lots of commercially available winter rye (Secale cereale L.) spanned a wide range from 28,000 to 50,000 seeds kg–1. If the lots with the lowest and highest seed counts were seeded at a common mass-based seeding rate of 125 kg ha–1, it would result in a nearly twofold difference in density-based seeding rate, or 3.0 and 5.6 million live seeds ha–1. Including density-based metrics such as live seeds per area and resulting in-field plant density in research will help advance our understanding of cover crop management, and these efforts will make it easier for farmers and policymakers to tailor cover cropping practices for specific goals.
Contosta AR, Asbjornsen H, Orefice J, Perry A, Smith RG. Climate consequences of temperate forest conversion to open pasture or silvopasture. Agriculture, Ecosystems & Environment [Internet]. 2022;333 :107972. Publisher's VersionAbstract
Land use change, particularly the conversion of forest to agriculture, is an important driver of climate change but is rarely considered a major factor in northern temperate regions. This study explored the climate impacts of temperate forest clearing for agriculture in the northeastern United States, hypothesizing that compared to managed cool-season pasture, forest conversion to silvopasture would moderate changes in surface temperature, soil greenhouse fluxes, and soil carbon and nutrient losses. To test this hypothesis, we conducted two land use change experiments, one in New York and the other in New Hampshire, USA. In both locations, forests have regenerated following a period of forest clearing, intensive agricultural management, and farm abandonment, such that secondary forests currently comprise  60–80% of the land base. In both experiments, we measured microclimatic variables of air and soil temperature and soil moisture, soil greenhouse gas emissions of CO2 and N2O, and soil carbon and nitrogen content. Using a mixed-effects modeling framework, we found that near-surface air and soil temperatures were highest in converted pasture plots, lowest in reference secondary forest areas, and intermediate in the converted silvopasture treatment. Soil respiration followed a similar pattern, with elevated soil CO2 fluxes in open pastures as compared to converted silvopasture and reference secondary forest sites. Although we detected few changes in soil C among treatments, we observed higher soil N stocks and soil N2O fluxes in converted pastures but not in the converted silvopasture treatment. Our results suggest that silvopasture may offer a biogeochemical “middle ground” between intact secondary forests and managed open fields, retaining the climate benefits of forests while enabling expansion of the agricultural land base. Understanding the climate impacts of forest conversion to open pasture or silvopasture is critical to better anticipate the climate consequences of potentially re-emerging agricultural land uses, both across the northeastern US and other temperate forest regions globally.
Lounsbury NP, Lounsbury BB, Warren ND, Smith RG. Tarping Cover Crops Facilitates Organic No-till Cabbage Production and Suppresses Weeds. HortScience [Internet]. 2022;57 (4) :508 - 515. Publisher's VersionAbstract
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.
Rowen EK, Pearsons KA, Smith RG, Wickings K, Tooker JF. Early-season plant cover supports more effective pest control than insecticide applications. Ecological Applications [Internet]. 2022 :e2598. Publisher's VersionAbstract
Abstract Growing evidence suggests that conservation agricultural practices, like no-till and cover crops, help protect annual crops from insect pests by supporting populations of resident arthropod predators. While adoption of conservation practices is growing, most field crop producers are also using more insecticides, including neonicotinoid seed coatings, as insurance against early-season insect pests. This tactic may disrupt benefits associated with conservation practices by reducing arthropods that contribute to biological control. We investigated the interaction between preventive pest management (PPM) and the conservation practice of cover cropping. We also investigated an alternative pest management approach, integrated pest management (IPM), which responds to insect pest risk, rather than using insecticides prophylactically. In a 3-year corn (Zea mays mays L.)–soy (Glycine max L.) rotation, we measured the response of invertebrate pests and predators to PPM and IPM with and without a cover crop. Using any insecticide provided some small reduction to plant damage in soy, but no yield benefit. In corn, vegetative cover early in the season was key to reducing pest density and damage, likely by increasing the abundance of arthropod predators. Further, PPM in year 1 decreased predation compared to a no-pest-management control. Contrary to our expectation, the IPM strategy, which required just one insecticide application, was more disruptive to the predator community than PPM, likely because the applied pyrethroid was more acutely toxic to a wider range of arthropods than neonicotinoids. Promoting early-season cover was more effective at reducing pest density and damage than either intervention-based strategy. Our results suggest that the best pest management outcomes may occur when biological control is encouraged by planting cover crops and avoiding broad-spectrum insecticides as much as possible. As part of a conservation-based approach to farming, cover crops can promote natural-enemy populations that can help provide biological effective control of insect pest populations.
Billman ED, de Souza IA, Smith RG, Soder KJ, Warren N, Brito AF. Evaluating warm-season annual forages to fill summer forage gaps in short-season climates. Crop, Forage & Turfgrass Management [Internet]. 2022;8 (1) :e20152. Publisher's VersionAbstract
Abstract Annual warm-season forages have been used to fill productivity and nutritional gaps during summer months throughout the southeastern United States. However, their performance and nutritive value in cooler, short-season temperate climates above 40 °N has been less well studied. This study evaluated the forage mass and nutritive value of four warm-season annual forages brown midrib [BMR] sudangrass [Sorghum bicolor ssp. Drummondii (L.) Moench], buckwheat (Fagopyrum esculentum Moench), Japanese millet [Echniochloa esculenta (A. Braun) H. Scholz], and teff [Eragrostis tef (Zuccagni) Trotter] compared with a cool-season small grain forage, oat (Avena sativa L.), and a cool-season annual forage legume, chickling vetch (Lathyrus sativus L.). Monocultures of the six annual forage species, along with a mixture of all six species, were evaluated over 2 years in southeastern New Hampshire. Forage mass and nutritive value were assessed at weekly intervals over 3 weeks in July–August, approximately 4-to-5 weeks post-germination. Across all three harvests, buckwheat, Japanese millet, and the summer mix produced greater forage mass than oat, while chickling vetch and teff produced the least. Conversely, chickling vetch had greater crude protein (CP), acid detergent fiber, and neutral detergent fiber compared with oat, while buckwheat had the lowest CP, in vitro true dry matter digestibility, and in vitro neutral detergent fiber digestibility of all the species assessed. Japanese millet produced greater forage mass while providing similar nutritive value as oat, making it a good alternative warm-season annual forage for use under cool, short growing seasons.
Cordeau S, Baudron A, Busset H, Vieren E, Smith RG, Munier-Jolain N, Adeux G. Legacy Effects of ContrastingLong-Term Integrated WeedManagement Systems. Frontiers in Agronomy [Internet]. 2022;3:769992. Publisher's VersionAbstract
To reduce reliance on herbicides and maintain crop productivity, integrated weed management (IWM) seeks to optimize synergies between diverse sets of weed management practices combined at the cropping system scale. Nevertheless, data on weed community response to the long-term implementation of IWM practices remain scare. Here, we assessed the effects of four IWM systems with contrasting objectives and practices (S2: transition from superficial tillage to conservation agriculture; S3: no-mechanical weeding; S4: mixed mechanical and chemical weeding; S5: herbicide-free; all with 6 year rotations) compared to a conventional reference (S1: herbicide-based with systematic plowing and a 3 year rotation) on taxonomic and functional weed community composition and structure after 17 years of continuous implementation. We examined the legacy effects of these systems with a uniformity trial consisting of winter wheat managed uniformly across the systems as well as with a novel in situ weed seedbank approach involving tilled strips. We found that resulting weed communities in IWM systems were more species rich (species richness from 1.1 to 2.6 times greater) and more abundant (total density from 3.3 to 25 times greater) than those observed in the reference system, and differed in term of taxonomic and functional composition. In addition, we found that, when systems shared the same weed species, germination patterns of two thirds of the species differed between systems, highlighting the selection pressures some IWM practices exert on weeds. We showed that analyzing the superficial germinable seedbank in situ with tilled strips could provide a comprehensive view of resulting weed communities and be helpful in developing cropping systems that foster agroecological weed management.
2021
Lowry CJ, Brainard DC, Kumar V, Smith RG, Singh M, Kumar P, Kumar A, Kumar V, Joon RK, Jat RK, et al. Weed germinable seedbanks of rice–wheat systems in the Eastern Indo-Gangetic Plains: Do tillage and edaphic factors explain community variation?. Weed Research [Internet]. 2021;61 (6) :475-485. Publisher's VersionAbstract
Abstract Zero tillage (ZT) is widely promoted throughout India's Eastern Indo-Gangetic Plains (IGP) because of its potential to increase wheat productivity and resilience to abiotic stresses. Weeds remain a major barrier to ZT adoption, yet it remains unclear how ZT will influence weed communities in the Eastern-IGP. The primary objective of this study was to characterise the composition of the germinable weed seedbank sampled just prior to the wheat phase of rice–wheat farms in Bihar and Eastern Uttar Pradesh, and examine whether adoption of ZT wheat has shifted weed community composition compared to conventional tillage (CT). Additionally, we examined whether edaphic properties and topography (upland vs. lowland) explain variation in germinable weed seedbank communities. In December 2014, we evaluated the germinable seedbank from 72 fields differing in their historic (>=3 year) tillage practices (ZT vs. CT) in three regions: Samastipur–Vaishali–Muzaffarpur (SVM), Ara–Buxar and Maharajgunj–Kushinagar. Weed community composition and species richness varied by region and topography. ZT adoption was associated with lower relative density of Chenopodium album in the germinable seedbank and lower emergence of Phalaris minor seedlings within farmers’ fields. In upland topographies of the SVM region, ZT adoption was also associated with greater relative abundance of Solanum nigrum in the weed seedbank. However, differences between tillage systems in individual species were not large enough to result in detection of differences at the whole-community level. Variation in edaphic properties, most notably soil texture and pH, explained 51% of the variation in the weed seedbank community. Our work suggests several frequent but poorly understood species (e.g. Mazus pumilus and Grangea maderaspatana) in Eastern IGP for which future research should quantify their effects on crop yields. Finally, future work surveying weed species abundance at harvest could further determine the dominant problematic species in these regions.
Billman ED, de Souza IA, Smith RG, Soder KJ, Warren N, Teixeira FA, Brito AF. Winter annual forage mass–nutritive value trade-offs are affected by harvest timing. Crop, Forage & Turfgrass Management [Internet]. 2021;7 (2) :e20113. Publisher's VersionAbstract
Abstract Annual cool-season forage crops could fill the gaps in spring forage availability that are typical in perennial pastures in the northeastern United States. Despite their potential as supplemental forages, few studies have examined the productivity–quality tradeoffs of annual forages grown as monocultures or mixtures. This study compared five species of winter annual forages grown as monocultures and mixtures for forage mass production and nutritive value across three harvest timepoints. Beginning in fall 2015, plots were planted in monocultures of cereal rye (Secale cereale L.), barley (Hordeum vulgare L.), triticale [×Triticosecale Wittm. ex A. Camus (Secale × Triticum)], wheat (Triticum aestivum L.), and hairy vetch (Vicia villosa Roth), as well as a mix of all five species. Samples were taken on 1, 7, and 14 June 2016, and on 3, 10, and 17 May 2017 to determine forage mass, nutritive value in the second year, and tradeoffs between biomass and nutritive value. The mixture's forage mass always ranked similarly to the best performing monoculture treatments. All monocultures except hairy vetch had increased forage mass at later harvests. In vitro digestibility of neutral detergent fiber was lower in later harvests. Triticale consistently had the greatest forage mass. Barley had greater energy and lower fiber concentrations than the other species. The results of this study suggest that triticale and barley have the most potential for supplementing spring perennial forage production.
Menalled UD, Pethybridge SJ, Pelzer CJ, Smith RG, DiTommaso A, Ryan MR. High Seeding Rates and Low Soil Nitrogen Environments Optimize Weed Suppression and Profitability in Organic No-Till Planted Soybean. Frontiers in Agronomy [Internet]. 2021;3. Publisher's VersionAbstract
No-till planting crops into rolled-crimped cover crops can improve soil health while reducing labor and fuel requirements compared with traditional tillage-based production. However, little information is available to help farmers optimize the management of organic no-till planted crops. Weed suppression, crop yield, and profitability were assessed across soybean [Glycine max (L.) Merr.] seeding rates and soil nitrogen environments in an experiment conducted at two sites in central New York. Soybeans were no-till planted into rolled-crimped cereal rye (Secale cereale L.) at 0, 185,000, 371,000, 556,000, and 741,000 seeds ha−1. Three rates (0, 63, or 125 kg ha−1) of sodium nitrate (15-0-2) were applied across seeding rates to create different soil nitrogen environments. When pooled over sites, the lowest weed biomass occurred at the highest soybean density in the lowest soil nitrogen environment. An interaction was observed between soybean seeding rate and nitrogen treatments on weed communities. Soybean yield increased asymptotically with crop density and was not affected by nitrogen or site treatments. When pooled over nitrogen treatments and sites, partial returns to the soybean seeding rates were maximized at $2,238 ha−1 with 527,800 seeds ha−1. Results suggest that crop density is an important lever for optimizing weed suppression and crop yield in organic no-till soybean, and that managing for low soil nitrogen conditions may further enhance weed suppression while maintaining high yields.
Pearsons KA, Rowen EK, Elkin KR, Wickings K, Smith RG, Tooker JF. Small-Grain Cover Crops Have Limited Effect on Neonicotinoid Contamination from Seed Coatings. Environmental Science and Technology [Internet]. 2021;55 (8) :4679–4687. Publisher's VersionAbstract
Neonicotinoids from insecticidal seed coatings can contaminate soil in treated fields and adjacent areas, posing a potential risk to nontarget organisms and ecological function. To determine if cover crops can mitigate neonicotinoid contamination in treated and adjacent areas, we measured neonicotinoid concentrations for three years in no-till corn-soybean rotations, planted with or without neonicotinoid seed coatings, and with or without small grain cover crops. Although neonicotinoids were detected in cover crops, high early season dissipation provided little opportunity for winter-planted cover crops to absorb significant neonicotinoid residues; small grain cover crops failed to mitigated neonicotinoid contamination in either treated or untreated plots. As the majority of neonicotinoids from seed coatings dissipated shortly after planting, residues did not accumulate in soil, but persisted at concentrations below 5 ppb. Persistent residues could be attributed to historic neonicotinoid use and recent, nearby neonicotinoid use. Tracking neonicotinoid concentrations over time revealed a large amount of local interplot movement of neonicotinoids; in untreated plots, contamination was higher when plots were less isolated from treated plots.
2020
Stewart A, Coble A, Contosta AR, Orefice JN, Smith RG, Asbjornsen H. Forest conversion to silvopasture and open pasture: effects on soil hydraulic properties. Agroforestry Systems. 2020;94 :869-879.Abstract
Growing demand for local products in the northeastern U.S. may incentivize forest conversion to pasture, degrading critical soil hydrologic properties such as surface infiltration (Kh) and subsurface saturated hydraulic conductivity (Ksat). Silvopasture, combining tree cover and grazing, may mitigate these impacts by maintaining the positive effects of trees on soil hydraulic properties. We tested this hypothesis using an experimental field manipulation to compare effects of forest conversion to open pasture versus silvopasture on Kh and Ksat at the Organic Dairy Research Farm (ODRF) and North Branch Farm (NBF). Measurements of surface Kh and Ksat at two soil depths (15 cm and 30 cm) were taken 1 and 4 years after treatment establishment at ODRF and NBF, respectively. Data were analyzed using a mixed effects modeling framework. Results show 15 cm Ksat was significantly lower in pasture compared to forest across both sites. However, in contrast to our hypothesis, soil hydraulic properties in silvopasture did not differ from other treatments at either site. Notwithstanding, silvopasture 15 cm Ksat at ODRF (9.4 cm h−1) was statistically similar to both the forest (22.6 cm h−1) and pasture (3.4 cm h−1) and exhibited a weak positive correlation with proximity to trees (R2 = 0.219, P = 0.042). In conclusion, our study did not find strong evidence that recently established silvopastures mitigate negative hydrologic impacts of forest conversion. Future research should focus on a broader range of northeastern sites and include greater replication over longer time scales to better elucidate opportunities for silvopasture.
Lounsbury NP, Warren ND, Wolfe SD, Smith RG. Investigating tarps to facilitate organic no-till cabbage production with high-residue cover crops. Renewable Agriculture and Food Systems. 2020;35 (3) :227–233.Abstract
High-residue cover crops can facilitate organic no-till vegetable production when cover crop biomass production is sufficient to suppress weeds (>8000 kg ha−1), and cash crop growth is not limited by soil temperature, nutrient availability, or cover crop regrowth. In cool climates, however, both cover crop biomass production and soil temperature can be limiting for organic no-till. In addition, successful termination of cover crops can be a challenge, particularly when cover crops are grown as mixtures. We tested whether reusable plastic tarps, an increasingly popular tool for small-scale vegetable farmers, could be used to augment organic no-till cover crop termination and weed suppression. We no-till transplanted cabbage into a winter rye (Secale cereale L.)-hairy vetch (Vicia villosa Roth) cover crop mulch that was terminated with either a roller-crimper alone or a roller-crimper plus black or clear tarps. Tarps were applied for durations of 2, 4 and 5 weeks. Across tarp durations, black tarps increased the mean cabbage head weight by 58% compared with the no tarp treatment. This was likely due to a combination of improved weed suppression and nutrient availability. Although soil nutrients and biological activity were not directly measured, remaining cover crop mulch in the black tarp treatments was reduced by more than 1100 kg ha−1 when tarps were removed compared with clear and no tarp treatments. We interpret this as an indirect measurement of biological activity perhaps accelerated by lower daily soil temperature fluctuations and more constant volumetric water content under black tarps. The edges of both tarp types were held down, rather than buried, but moisture losses from the clear tarps were greater and this may have affected the efficacy of clear tarps. Plastic tarps effectively killed the vetch cover crop, whereas it readily regrew in the crimped but uncovered plots. However, emergence of large and smooth crabgrass (Digitaria spp.) appeared to be enhanced in the clear tarp treatment. Although this experiment was limited to a single site-year in New Hampshire, it shows that use of black tarps can overcome some of the obstacles to implementing cover crop-based no-till vegetable productions in northern climates.
Smith RG, Warren ND, Cordeau S. Are cover crop mixtures better at suppressing weeds than cover crop monocultures?. Weed Science. 2020;68 (2) :186–194.Abstract
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.
Mortensen DA, Smith RG. Confronting Barriers to Cropping System Diversification. Frontiers in Sustainable Food Systems. 2020;4.Abstract
There is no shortage of data demonstrating that diversified cropping systems can sustain high levels of productivity with fewer external inputs and lower externalities compared to more simplified systems. Similarly, data exist indicating diverse cropping systems have greater capacity to buffer against and adapt to weather extremes associated with climate change. Yet, agriculture in the US Corn Belt and other major crop production regions around the world continues to move toward simplified rotations grown over increasingly large acreages. If our goal is to see more of the agricultural landscape made up of diverse agricultural systems and the ecosystem services they provide, it is critical we understand and creatively address the factors that both give rise to monocultures and reinforce their entrenchment at the exclusion of more diversified alternatives. Using the current state of farming and agriculture policy in the US as a case study, we argue that a pernicious feedback exists in which economic and policy forces incentivize low diversity cropping systems which then become entrenched due, in part, to a lack of research and policy aimed at enabling farming practices that support the diversification of cropping systems at larger spatial scales. We use the recent example of dicamba-resistant crops to illustrate the nature of this pernicious feedback and offer suggestions for creating “virtuous feedbacks” aimed at achieving a more diversified agriculture.
Lowry CJ, Bosworth SC, Goslee SC, Kersbergen RJ, Pollnac FW, Skinner RH, Warren ND, Smith RG. Effects of expanding functional trait diversity on productivity and stability in cultivar mixtures of perennial ryegrass. Agriculture, Ecosystems and Environment. 2020;287 :106691.Abstract
Cultivar mixtures can provide a host of beneficial agroecosystem services in annual grain crops; however, it remains unclear whether these same benefits apply to perennial forage cropping systems, or the degree to which beneficial effects depend on the functional trait diversity of the mixtures. We conducted a field experiment across four locations in the Northeast US in which we grew perennial ryegrass cultivar mixtures varying in cultivar number and range of expression of three functional traits (winter hardiness, heading date, and extended growth) and assessed the effects on dry matter yield and inter-annual yield variability. Trait ratings supplied by the seed company were related to observed variation in perennial ryegrass productivity and/or stability at both the individual cultivar and mixture levels. Winter hardiness was associated with greater perennial ryegrass cumulative biomass, and lower interannual stability. In contrast, extended growth was associated with lower cumulative biomass, and both extended growth and later heading date were associated with greater interannual variability. Overall, cultivar richness was negatively associated with perennial ryegrass biomass and stability; however, the best performing mixtures performed as well as the recommended cultivar for the region. When comparing mixtures with equal cultivar richness, functional trait diversity measured as the additive trait range—the summed range of the three traits associated with the cultivars in that mixture—was positively associated with biomass production and over-yielding, but not interannual variability. Cultivar mixtures of perennial ryegrass can lead to improved forage production when specific functional traits are optimized within mixtures. Our results support the growing understanding that efforts to ecologically intensify agriculture through enhancement of crop diversity are more likely to succeed when they explicitly consider the functional traits of the crops involved rather than solely numbers of cultivars or species.
Coble AP, Contosta AR, Smith RG, Siegert NW, Vadeboncoeur M, Jennings KA, Stewart AJ, Asbjornsen H. Influence of forest-to-silvopasture conversion and drought on components of evapotranspiration. Agriculture, Ecosystems and Environment. 2020;295 :106916.Abstract
The northeastern U.S. is projected to experience more frequent short-term (1−2 month) droughts interspersed among larger precipitation events. Agroforestry practices such as silvopasture may mitigate these impacts of climate change while maintaining economic benefits of both agricultural and forestry practices. This study evaluated the effects of forest-to-silvopasture (i.e., 50 % thinning) conversion on the components of evapotranspiration (transpiration, rainfall interception, and soil evaporation) during the growing season of 2016. The study coincided with a late-summer drought throughout the northeastern U.S., which allowed us to also evaluate the effects of forest-to-silvopasture conversion on drought responses of multiple tree species, including Pinus strobus, Tsuga canadensis, and Quercus rubra. In the reference forest and silvopasture, we observed declining soil moisture and tree water use during the drought for all three tree species. However, the decline in P. strobus water use in response to declining soil moisture in the silvopasture was not as steep as compared with the reference forest, resulting in greater water use in the silvopasture for this species. In contrast, we did not detect different water-use responses between forest and silvopasture in T. canadensis or Q. rubra. This suggests that forest-to-silvopasture conversion via thinning can alleviate drought stress for P. strobus and that this species may be more sensitive to moisture stress when competition for water is high in denser stands. Evapotranspiration was 35 % lower in the silvopasture compared with the reference forest, primarily a result of lower transpiration and rainfall interception. While soil evaporation was greater in the silvopasture, this was not enough to offset the considerably lower transpiration and interception. We observed greater radial tree growth 1–3 years following conversion in the silvopasture as compared with the reference forest for T. canadensis and Q. rubra, but not for P. strobus. Overall, our results suggest that forest conversion to silvopasture (in lieu of clearcutting for new pasture) may mitigate the impacts of agricultural land use intensification and climate change on ecosystem services, especially in terms of sustaining hydrologic regulation functions. Further study is required to determine the generality of these results and whether these benefits extend beyond the first few years post-conversion.
Jilling A, Kane D, Williams A, Yannarell AC, Davis A, Jordan NR, Koide RT, Mortensen DA, Smith RG, Snapp SS, et al. Rapid and distinct responses of particulate and mineral-associated organic nitrogen to conservation tillage and cover crops. Geoderma. 2020;359 :114001.Abstract
Particulate organic matter (POM) is considered an “active” source of nitrogen (N) in cultivated soils, responding readily to management and being more physically accessible to decomposers than mineral-associated forms of organic matter. However, there is increasing evidence that mineral-associated organic matter (MAOM) can also exhibit short-term changes to management that may impact plant and microbial N dynamics. In this study, we investigated how N within soil organic matter fractions responded to three years of tillage and cover crop treatments. We collected soils from a row-crop (maize-soybean rotation) field experiment replicated across three sites in the north central and mid-Atlantic United States: a high-soil organic matter site (3.1% soil organic carbon) in Illinois (IL) and two sites in Michigan (MI) and Pennsylvania (PA) with lower soil organic matter content (1.0% and 1.4% soil organic carbon, respectively). Management treatments included two levels of tillage (chisel plow and ridge tillage) and two levels of cover crop (with and without rye cover crop). Using an optimized sonication method coupled with particle size separation, we isolated and analyzed for N content free POM, occluded POM, a coarse silt fraction, and MAOM. Using partial least squares regression, we also explored broad cross-site relationships between soil organic matter (SOM) fractions, soil N availability, and crop performance. Both particulate and fine fractions responded to tillage and cover crop treatments, but patterns varied by site and fraction. In the low-SOM MI and PA soils, ridge tillage and cover cropping both increased N within POM fractions. The response to ridge tillage was most pronounced, with a 76% and 24% increase in occluded POM N content in MI and PA, respectively. In contrast, at the IL site (high-SOM), the inclusion of cover crops led to higher N, specifically within the fine fractions (coarse silt and MAOM). Cover cropping increased MAOM N content in IL by 24%. When analyzing all sites together, variables associated with fine fractions were more closely associated with N mineralization and crop performance. MAOM can be responsive to short-term management practices and, along with POM, may also be potential sources of N for crops.
Wilhelm JA, Smith RG, Jolejole-Foreman MC, Hurley S. Resident and stakeholder perceptions of ecosystem services associated with agricultural landscapes in New Hampshire. Ecosystem Services. 2020;45.Abstract
Converting non-agricultural land to agricultural uses can result in trade-offs in ecosystem services. As provisioning services increase on new agricultural land, supporting, regulating, and cultural services may decrease. An improved understanding of how stakeholders value different land use types in terms of their perceived ecosystem services, as well as the relative visual appeal of different agricultural landscape features, could assist policymakers and land use planners in decision-making related to agricultural land use in New England, USA. We surveyed two survey samples in New Hampshire, food system stakeholders (e.g., farmers, public health professionals, and technical assistance providers) and the general population, to explore how perception of the visual appeal of specific farmland use types and importance of ecosystem services specifically related to agricultural land might differ between survey samples. Our objectives were to (1) explore how New Hampshire residents perceive the importance of seven ecosystem services, (2) evaluate how two groups of New Hampshire residents—the general public and those who indicated working with or in a food systems sector (food system stakeholders)—perceive these ecosystem services provided by specific agricultural landscapes and determine how those perceptions relate to the visual appeal of each landscape, and (3) assess how eight socio-economic factors may account for the differences between each survey sample in terms of their landscape perception and preference. Roughly 600 New Hampshire residents completed the survey, including 494 individuals from the public and 103 food system stakeholders. From a list of seven ecosystem services, clean water was ranked as the most important across both survey samples, with no significant difference between samples, while food production was ranked significantly higher by the food system stakeholders (p ≤ 0.001). Likewise, on a scale of most (4) to least (1) appealing, food system stakeholders ranked photorealistic visualizations of cropland higher than the public (p ≤ 0.001). Additionally, food system stakeholders ranked the appeal of forestland lower than the public (p = 0.007). Our findings suggest that there are differences in landscape preferences and perception of ecosystem service benefits between the general public and those who work with or in the food system. Future research is needed to determine how these differences in perception might affect land use planning and policymaking related to agricultural expansion and forestland preservation.
Menalled UD, Bybee-Finley KA, Smith RG, DiTommaso A, Pethybridge SJ, Ryan MR. Soil-Mediated Effects on Weed-Crop Competition: Elucidating the Role of Annual and Perennial Intercrop Diversity Legacies. Agronomy 2020, Vol. 10, Page 1373 [Internet]. 2020;10 (9) :1373. Publisher's VersionAbstract
Crop diversity may mediate the intensity of weed-crop competition by altering soil nutrient availability and plant-soil microbe interactions. A greenhouse experiment was conducted to analyze weed-crop competition in soils with varying crop diversity legacies. Soil greenhouse treatments included field soils (i.e., soil nutrient and microbial legacies), a sterile greenhouse potting mix inoculated with microorganisms of the field soils (i.e., microbial legacies), and a sterile greenhouse potting mix. Soils for the greenhouse experiment were sampled and assessed after two-years of conditioning with annual and perennial cropping systems under four levels of intercrop diversity. The greenhouse experiment involved growing one sorghum sudangrass (Sorghum bicolor (L.) Moench × S. sudanese Piper) crop plant and zero to six common lambsquarters (Chenopodium album L.) weed plants in soil from each diversity and cropping system treatment. The weed density treatments created a weed-crop competition gradient, which was used to quantify legacy effects of crop diversity. Weed-crop competition increased with crop diversity in both the field soil and inoculated soil treatments in the annual system. In the perennial system, differences in weed-crop competition intensity were driven by crop yield potential. In the perennial field soil treatment, crop yield potential was greatest in the highest diversity treatment, whereas in the perennial inoculated soil treatment, crop yield potential was greatest in the lowest diversity treatment. Results show potential for negative effects from previous crop diversity on weed-crop competition, and the divergent impact of microbial and nutrient legacies on crop yield potential. Future research should aim to evaluate the consistency of legacy effects and identify principles that can guide soil and crop management, especially in conservation agriculture where soil tillage and its microbial legacy reducing effects are minimized.

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