Agricultural & Environmental Letters最新文献

Agriculture faces a dilemma with nitrogen (N)—it is often the most necessary external input to optimize production, several generations of farmers became accustomed to its relatively inexpensive cost, and it contributes to widespread pollution due to numerous loss pathways to the environment. However, standard N fertilizer recommendations have not accounted well enough for a key source via mineralizable soil N. Soil-test biological activity (STBA) is strongly associated with mineralizable soil N, both of which become surface-enriched with conservation agricultural management using soil health principles. A series of field experiments assessed the contribution of mineralizable soil N to the N supply needed to optimize corn (Zea mays L.) grain and fall-stockpiled tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] production. This essay synthesizes how STBA along with cost-to-value threshold can be used to modify the N fertilizer factor to optimize economic return and avoid environmental degradation.

Adjacent fields with contrasting histories present an opportunity to evaluate the legacy of management on soil health (SH) and grain productivity. In 2011, two fields transitioned to no-till grain production. During the previous 25 yr, one was pasture (pasture-to-grain; PTG), whereas the other was annually tilled for grain cropping (long-term grain; LTG). The study objectives were to contrast these two fields relative to SH and productivity. Yield data was collected from 2011 to 2021 and SH sampled in 2021. The PTG out-yielded LTG each year, with an average 46% yield increase. 2021 SH metrics demonstrated similar trends, with PTG 62% higher than LTG. Contrasting across fields (2020–2021), SH metrics were related to yield (r² = .46–.78), but these relationships weakened when assessed within each field. These findings affirm SH indicators are sensitive to the legacy of management and are meaningful indicators of productivity across sites but less informative for within-field variability.

To examine the role of dam impoundment in elevating the levels of soil-associated phosphorus (P) and trace elements in reservoir hydro-fluctuation belts (RHB), soil samples in RHB and adjacent uplands (non-flooded area, NFA) in the Three Gorges Reservoir, China, were collected and analyzed. Concentrations of available P, copper (Cu), chromium (Cr), and zinc (Zn) were found to be higher in RHB than in NFA (p < .05), whereas organic carbon was comparable in RHB and NFA (p > .05). The elevated levels of Cu, Cr, and Zn in RHB were probably associated the repeated drying–rewetting cycles created by the dam impoundment. The 95th percentile of the single-factor pollution index and geo-accumulation index in RHB were 1.29 and −0.21 for Zn, 3.21 and 1.15 for Cu and 3.37 and 1.17 for Cr. Elevated pollution potential of soil-associated Zn, Cu, and Cr existed in RHB of the Three Gorges Reservoir.

Core Ideas

Assessing the success of cover crops (CCs) as a way to promote soil health at the farm scale remains a challenge. At four on-farm CC experiments in Nebraska, we quantified soil health relative to a reference soil. We examined physical, chemical, and biological properties in near-surface soil. Cover crops reduced the soil health gap between bare (no-CC) and reference soil in the short (3-yr) timescale, but the magnitude of responses depended on cropland management history and ecological dynamics of reference site plant communities. Increases in soil health relative to reference soils showed some relationship to increases in soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) yields. Clear discrimination of reference from bare soils was most influenced by organic matter and infiltration measurements conducted under the highest sampling intensity. Framing soil metrics relative to reference soils and ensuring appropriate sampling intensity are important to quantify the effects of CC on farm landscapes.

Tractor guidance (TG) improve environmental gains relative to nonprecision technologies; however, studies evaluating how tractor operator experience for nonguidance comparisons affect gains are nonexistent. This study explores spatial relationships of overlaps and gaps with operator experience level (0–1, 2–3, 6+ yr) during fertilizer and herbicide applications based on terrain attributes. Tractor paths recorded by global navigation satellite systems were used to create overlap polygons. Results illustrate operator experience level is critical for better efficiency gains estimation (for non-TG comparisons). Operators with 6+ yr of experience reduced overlap by 7.7 and 20.6% compared with operators with 2–3 and 0–1 yr of experience, respectively. New operators had consistently higher overlap across all slope (<0.5, 0.5–1, 1–2, 2–5, 5–9, and 9–15%) and roughness classes (<0.1, 0.1–0.2, 0.2–0.3, 0.3–0.5, 0.5–0.7, 0.7–1 and >1). A low interpersonal reliability value of 0.02–0.03 indicates operator experience is crucial to estimate TG efficiency gains and consistent drivers experience levels are needed when evaluating economic and environmental gains from TG.

Pollinator declines have driven research and increased monitoring efforts. Within North Dakota, USA, our research group initiated research in 2015 on pollinator conservation and management. We synthesized results across five projects, producing 12 publications and providing baseline data on pollinator diversity and rangeland management to improve conservation efforts while land-sharing with livestock. We detected 76 species of butterflies and ∼318 bee species. Butterfly diversity and relative abundance were driven by floral resources and less exotic plant invasions, with a positive relationship between flowers and pollinators. Invasive forbs were visited by pollinators, primarily honey bees. We also found management influenced vegetation characteristics within pastures, but landscape context was important for determining the specific outcome. Although pollinator abundance did not distinctly respond to management, diversity was affected by regime and grazer type. Using fire and grazing may benefit flowers to support pollinators. Our research will help guide rangeland management decisions that promote land sharing and benefit pollinator conservation efforts.

Core Ideas

Soil organic carbon (C) and nitrogen (N) accumulation contributes to improved soil health condition, particularly after a history of tillage-intensive land use. Soil-test biological activity (STBA) is an active fraction of organic matter that is responsive to conservation management. This essay summarizes the need, concept, and method of calculating root-zone enrichment of STBA and other organic C and N fractions on private farms. Calculation of root-zone enrichment separates the pedogenic influence on organic matter content from that of contemporary management. This separation is particularly important when attempting to determine STBA or soil organic C stock change in response to management across variable landscapes. Reasonable farm-level estimates of STBA and stocks of soil organic C and N can be obtained from one to two dozen sampling sites on farms with differences in land use, a process that could help propel in-depth assessments of soil health condition and C stock change.

Conservation practices that reduce nutrient and soil loss from agricultural lands to water are fundamental to watershed management programs. Avoiding trade-offs of conservation practices is essential to the successful mitigation of watershed phosphorus (P) losses. We review documented trade-offs associated with conservation practices, particularly those practices that are intended to control and trap P from agricultural sources. A regular theme is the trade-off between controlling P loss linked to sediment while increasing dissolved P losses (no-till, cover crops, vegetated buffers, constructed wetlands, sediment control basins). A variety of factors influence the degree to which these trade-offs occur, complicated by their interaction and uncertainties associated with climate change. However, acknowledging these trade-offs and anticipating their contribution to watershed outcomes are essential to the sustainability of conservation systems.

Urbanization has profound implications for associated ecosystems and organisms. Monitoring pollutants inform risk assessments for human and wildlife health. Honey bees (Apis mellifera) forage widely and collect food from many sources. Thus, they may be a robust integrator of environmental pollutants. Here, we collected honey bees from 10 different locations across the United States to quantify their content of total mercury (THg) and methylmercury (MeHg). Although our limited sample size prevented a meaningful statistical evaluation, we found that bees from urbanized areas had higher THg than those from rural areas, with suburban samples intermediate. The MeHg concentrations in all samples were below the detection limit. Despite its limited scope, this first preliminary dataset on Hg levels in honey bees across the United States suggests that urbanization may play a role in increasing Hg exposure to these pollinators, and that honey bees may be a useful biomonitor of the environmental presence of chemical pollutants.

Matthew Hayek's response to my commentary (Jackson, 2022) is a valuable contribution to an important conversation about how we can provide for our wants and needs while improving our environment. My commentary purposefully simplified a complex topic to encourage interrogation of whether we have the capacity to meet current beef supply (5.9 billion kg yr^–1) by finishing cattle on grassland rather than grain in feedlots. Hayek and I agree that this would require 7.6 million additional finishing cattle because grass-finished cattle take longer to finish and grow less overall (Hayek & Garrett, 2018). My assessment was that we would need ∼16.1 million ha for all 20 million finishing cattle and that we could use the 4.9 million ha currently growing maize for cattle in feedlots, plus ∼12 million ha growing maize for ethanol, which constitutes a net loss of energy coupled with devastating environmental outcomes (Lark, 2020). We seem to agree that there's enough land for the finishing cattle, but Hayek encourages us to consider the upstream supply chain and its ramifications.

Hayek observes that these additional finishing cattle would require more cows, calves, and stocker cattle (∼23.1 million more animals) to reproduce and replace the finishing cattle (Hayek & Garrett, 2018), resulting in ∼18.6 million more grassland ha needed for grazing these feeder cattle. I argue that we desperately need this increased demand for grassland, especially if it replaces cropping systems prone to soil, carbon, and nutrient loss to the atmosphere and waters, where conservation interventions such as no-till, cover crops, and semi-annual forages (e.g., alfalfa) improve, but do not stop, these losses (Lintern et al., 2020; Osterholz et al., 2019; Roland et al., 2022). Inasmuch as most of this feeder-cattle rearing is currently done on rangelands of the West, nearly half of this could occur on the ∼9 million ha of Great Plains land growing corn, soybeans, and alfalfa irrigated with water that is drawing down the Ogallala Aquifer (Carnes & Sanderson, 2022; Evett et al., 2020). Much of these products are fed to livestock, but according to the Iowa Corn website (www.iowacorn.org), much of the corn grain in the United States is exported (11% or ∼4.4 million ha) and much of it is considered “surplus” for “residual use” (9% or ∼3.6 million ha). It is important to note that the exports are sold by aggregator corporations to relatively affluent countries to build corporate wealth and often the surplus corn grain is “dumped” on global markets to suppress prices elsewhere (Hansen-Kuhn & Murphy, 2017).

In more humid regions where feeder cattle are raised on pastures, most of this is done with continuous grazing, which undermines the yield potential of the pastures compared with well-managed rotational grazing t