Rebecca L. McCulley

Kentucky producers have sought to add industrial hemp ( Cannabis sativa L.) for grain, fiber, and/or floral material to their cropping systems since hemp's legalization in the 2018 Farm Bill. This study sought to quantify hemp's impact on ecosystem services provisioned by the traditional corn ( Zea mays L.)–soybean ( Glycine max (L.) Merr.) rotation. We hypothesized that hemp incorporation would diversify crop rotations and positively impact ecosystem services, such as soil nutrient retention and crop yield. This study was conducted at the University of Kentucky North Farm (Lexington, KY) and consisted of six crop rotation treatments in a randomized complete block design with five replications. Cash crop aboveground biomass and yield were quantified at harvest, and belowground biomass was measured by collecting root cores within 2 weeks of harvest. Cover crop wheat ( Triticum aestivum L.) aboveground and belowground biomass was measured to evaluate impact on the successive crop. Soil samples were collected before and at completion of the 3‐year rotation to quantify soil health impacts. Aboveground and belowground biomass of cash and cover crops were unaffected by hemp's inclusion. Similar results were found for most soil health metrics, including nutrient availability. Grain biomass and fiber hemp root biomass in this study were small (∼4x less than corn) and most comparable to soybean. Overall, this study found that inclusion of industrial hemp does not negatively impact ecosystem services in the short term; however, long‐term effects may arise given differences in root biomass and nutrient return via retting compared to traditional cash crops.

Industrial hemp's return to American agriculture has been accompanied by claims of the crop's carbon neutrality, primarily due to its commercial applications. While carbon can be sequestered within products made with hemp fiber, there is little empirical evidence quantifying greenhouse gas contributions from the crop's production. Here we quantified fiber hemp's soil‐to‐atmosphere greenhouse gas fluxes and root production throughout the 2022 and 2023 growing seasons in central Kentucky and compared them to those of corn cultivated under similar conditions. Daily gas fluxes were measured from the plots throughout the growing season, accompanied by monthly soil sampling (0–10 cm) and root sampling (0–30 cm) at crop harvest. For both years, hemp and corn plots emitted similar cumulative amounts of carbon dioxide warming equivalents (2.1 ± 0.2 Mg ha ⁻¹ ). Nitrous oxide emissions and methane uptake were significantly greater in corn in 2022 but were similar in 2023. Soil permanganate oxidizable carbon for each crop was similar at all time points measured, though there was a seasonal trend, suggesting comparable labile soil organic matter contributions to gas emissions. End of season in‐row root measurements in 2022 and 2023 revealed that corn plots contained up to 3.5 times more root biomass than hemp at both the 0‐ to 10‐ and 10‐ to 30‐cm depth profiles. Under these cultivation conditions, fiber hemp released similar amounts of greenhouse gas equivalents while storing significantly less carbon belowground in roots than corn, calling into question the idea that hemp cultivation is likely to improve the short‐term environmental sustainability of the cropping system.

Red clover ( Trifolium pratense L.) is a widely grown perennial forage legume that supports sustainable livestock production through its high nutritive value and bioactive isoflavones. Future climate change, particularly warming and increased rainfall, may influence forage accumulation and isoflavone concentrations. However, field evidence integrating the combined effects of these climate factors remains limited. To address this gap, we conducted a 2‐year field experiment in central Kentucky manipulating temperature (+3°C, day/night) and precipitation (+30% of the long‐term mean) on red clover (cv. Kenland). Plants were harvested multiple times in a growing season to mimic hay production, and isoflavones were quantified. Warming reduced total isoflavone concentrations by 15% though responses varied by cutting and year, while precipitation alone did not affect total isoflavone concentrations. However, elevated temperature stimulated daidzein concentration in late summer, and the effects of added precipitation on daidzein differed among cuttings. Warming decreased red clover aboveground biomass by 14% across years, whereas added precipitation tended to increase biomass by a similar magnitude but did not significantly offset heat‐related losses. These results suggest that future climatic conditions may reduce red clover productivity and total isoflavone concentrations. Additional rainfall showed limited evidence of mitigating warming‐driven reductions in biomass and isoflavone concentrations, and warming may induce compound‐specific changes in isoflavones (e.g., daidzein). These findings have mixed implications for forage–livestock systems. Decreased isoflavone concentrations (e.g., formononetin) may reduce reproductive risks in livestock, whereas decreases in other isoflavones could diminish benefits related to animal performance and environmental sustainability.

Tall fescue-dominated pastures cover 14 million ha in the eastern US and support 8.5 million beef cattle, making continued productivity and sustainability a high priority. Most tall fescue stands are infected with the symbiotic fungal endophyte Epichloë coenophiala, which improves grass growth and productivity in hot weather and under heavy grazing. Compounds produced by the most common tall fescue cultivar and strain of the fungus (‘KY 31’ common toxic strain) are harmful to grazing animals and lead to economic losses. Alternative fungal strains that do not produce alkaloid compounds toxic to grazing animals were selected and inoculated into grass cultivars to create novel endophyte-grass associations and these have been commercially available to producers for over two decades. Though novel individual tall fescue-endophyte symbioses have been evaluated for forage production and stand longevity, there is little information about the performance of mixed stands that contain multiple tall fescue cultivar endophyte symbiotic combinations. It was hypothesized that increasing fescue symbiotic diversity in stands would increase pasture resilience and sustainability by promoting fescue dominance and productivity and increasing soil carbon pools. Using custom seed mixes, six levels of increasing symbiotic diversity were established with plant and soil parameters compared after five years. Consistent with the hypothesis, more symbiotically diverse stands produced more fescue biomass (+12%) in the fall and limited the invasion of other weedy grass species, while also increasing soil carbon and nutrient pools. The most symbiotically diverse stand emitted more soil carbon dioxide than the least-diverse stand, perhaps due to greater root growth. These results show that increasing symbiotic diversity represents a new, readily adoptable, and effective strategy for increasing soil fertility and tall fescue productivity.

Soil microbes drive ecosystem function and play a critical role in how ecosystems respond to global change. Research surrounding soil microbial communities has rapidly increased in recent decades, and substantial data relating to phospholipid fatty acids (PLFAs) and potential enzyme activity have been collected and analysed. However, studies have mostly been restricted to local and regional scales, and their accuracy and usefulness are limited by the extent of accessible data. Here we aim to improve data availability by collating a global database of soil PLFA and potential enzyme activity measurements from 12,258 georeferenced samples located across all continents, 5.1% of which have not previously been published. The database contains data relating to 113 PLFAs and 26 enzyme activities, and includes metadata such as sampling date, sample depth, and soil pH, total carbon, and total nitrogen. This database will help researchers in conducting both global- and local-scale studies to better understand soil microbial biomass and function.

Hemp (Cannabis sativa L.) cultivation in the United States is reemerging following legalization in the 2018 Farm Bill. Cultivation of hemp for fiber, grain, and flowers has encountered many challenges, including stand establishment and unknowns regarding ecosystem services the crop may provide. Hemp proponents have touted hemp as being carbon neutral or negative, but there is limited research on its root system, the most direct pathway for carbon into soil. Therefore, we sought to measure root system architecture across a subset of commercially available cultivars and to measure aboveground traits to develop allometric relationships that could be used for carbon market estimates. Two monoecious (Fibror 79 and Futura 75/83) and two dioecious cultivars (New West Genetics 2730 and Yuma) were selected from the University of Kentucky's Hemp Trials in 2022 and 2023. Plants (n = 16 total per cultivar; eight per sex for dioecious cultivars) were randomly selected and excavated at early senescence. Plant height, stem basal diameter, aboveground biomass, and root biomass were quantified for development of allometric relationships. Root systems were imaged in PhotoCapture360 and analyzed for root traits, such as total length and average diameter, with GiARoots. Basal diameter was predictive of both aboveground and belowground biomass (r² = 0.69 and 0.77, respectively). Additionally, female and monoecious root systems had smaller diameters but were twice as large as male root systems in mass and surface area. Overall, this study developed predicative equations that may be useful in quantifying hemp's growth and carbon capture potential by flowering behavior.

Global change is associated with variable shifts in the annual production of aboveground plant biomass, suggesting localized sensitivities with unclear causal origins. Combining remotely sensed normalized difference vegetation index data since the 1980s with contemporary field data from 84 grasslands on 6 continents, we show a widening divergence in site-level biomass ranging from +51% to −34% globally. Biomass generally increased in warmer, wetter and species-rich sites with longer growing seasons and declined in species-poor arid areas. Phenological changes were widespread, revealing substantive transitions in grassland seasonal cycling. Grazing, nitrogen deposition and plant invasion were prevalent in some regions but did not predict overall trends. Grasslands are undergoing sizable changes in production, with implications for food security, biodiversity and carbon storage especially in arid regions where declines are accelerating.

Conservation alternatives that include no-tillage (NT) and cover crops (CCs) reduce soil erosion in row-crop agroecosystems. However, little information is available about how these alternatives affect soil textural properties responsible for soil fertility. This study evaluated the soil particle size distribution and volumetric water content after three years of consistent management in a raised bed system. There were four treatment systems in a dryland maize/soybean rotation on a silt loam soil (Oxyaquic Fraglossudalfs) that included: NT + CCs, conventional tillage (CT) + CCs, CT + winter weeds, and CT + bare soil in winter in northwest Mississippi. The NT + CC system retained 62% more coarse sand in the furrow than the other systems (2.1% compared to 1.3%; p = 0.02). Regardless of the location, the NT + CC system (2.5%) retained 39% more fine sand than the CT + CC system (1.8%; p = 0.01), suggesting that coarse and fine sands were being trapped in furrows combining NT + CC systems, minimizing their off-site transport. In furrows, CCs increased soil volumetric water content by 47% compared to other winter covers. In beds, NT + CCs increased bed water contents by 20% compared to CT + CCs (17.1 to 14.3%; p < 0.01). Implementing conservation alternatives may promote the retention of sand fractions in silty loam soils that are important in supporting soil fertility and crop sustainability.