Search

Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO2) in soil organic carbon (SOC) and emitting non‐CO2 greenhouse gases (GHGs) such as nitrous oxide (N2O) and methane (CH4). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC‐sequestered CO2 and non‐CO2 GHG emissions) and the underlying controls. Herein, we used a model‐data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960–2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N2O and CH4 emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered 13.2±1.16$$ 13.2\pm 1.16 $$ Tg CO2‐C year−1 in SOC (at a depth of 3.5 m) during 1960–2018 and emitted 0.39±0.02$$ 0.39\pm 0.02 $$ Tg N2O‐N year−1 and 0.21±0.01$$ 0.21\pm 0.01 $$ Tg CH4‐C year−1, respectively. Based on the GWP100 metric (global warming potential on a 100‐year time horizon), the estimated national net GHG emission rate from agricultural soils was 122.3±11.46$$ 122.3\pm 11.46 $$ Tg CO2‐eq year−1, with the largest contribution from N2O emissions. The sequestered SOC offset ~28% of the climate‐warming effects resulting from non‐CO2 GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960–2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO2 levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N2O emissions represents the biggest opportunity for achieving net‐zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC‐sequestered CO2 and non‐CO2 GHG emissions for developing effective agricultural climate change mitigation measures. [ABSTRACT FROM AUTHOR]

Repeated application of herbicides has led to herbicide-resistant weed populations. Elevated CO2 often increases weed growth, exacerbating problems including impacts on crop yield and weed control. How rising CO2 affects herbicide-resistant weeds remains largely unknown. Palmer amaranth (Amaranthus palmeri) populations resistant to or susceptible to glyphosate were exposed to ambient or elevated (ambient +200 μmol mol−1) concentrations of CO2 in open-top chambers. Two weeks after CO2 exposure, each population was sprayed with glyphosate at 0, 0.5×, 1.0×, or 1.5× the label rate. Afterwards, CO2 exposure continued for an additional two weeks when visual herbicide injury and leaf gas exchange were assessed. Plants were harvested for determination of treatment effects on growth. Elevated CO2 had little effect on most variables except for decreasing stomatal conductance (~25.5%) and increasing water use efficiency (~49.2%). Glyphosate resistant plants showed decreased height (9.8%) and damage (~56.4%) and increased root dry weight (12.1%), photosynthesis (~41.2%), stomatal conductance (~63.3%), and water use efficiency (~32.0%). In general, increasing rates of glyphosate decreased growth and gas exchange variables, which was frequently only seen in the susceptible ecotype. Data suggest that rising atmospheric CO2 is unlikely to affect Palmer amaranth, including control of glyphosate-resistant populations. [ABSTRACT FROM AUTHOR]

Loblolly pine (Pinus taeda L.) is one of the most planted forest species in the Americas. Since few studies have comprehensively assessed loblolly pine responses to fertilization, the present study performed a meta-analysis of the Americas based on 44 publications (1970-2022) of loblolly pine fertilization under field conditions. In general, fertilization increased root dry matter (+33%), litter (+21%), plant height (+6%), trunk diameter (+9%), wood yield (+30%), and needle concentrations of P (+9%), K (+36%), Ca (+17%), Mg (+14%), and S (+12%). Wood production was higher with residue fertilization, primarily with use of composite residues (cellulosic sludge + ash), compared to mineral fertilization. In regards to mineral applications, wood production was higher when multiple nutrients were added from fertilization and liming operations. Applications at planting (< 1 year) or on established trees (2-8 years), showed similar increases in wood production with higher responses occurring on sandy soils. These factors generally increased needle nutrient concentrations, except for no alteration or slight decreases in N under most conditions. The present study revealed loblolly pine responses to contrasting application strategies, which can help identify efficient fertility management practices for this commercially significant tree species. [ABSTRACT FROM AUTHOR]

This work investigated collateral effects on non-target yerba mate (Ilex paraguariensis A. St.-Hil) plants when using glyphosate for weed control; growth and leaf elemental composition were examined. Special emphasis was placed on examining the heavy metals Cd and Pb due to regulations defining maximum limits in South American infusion products. The experiment was conducted in pots using glyphosate [applied to Congo grass (Brachiaria ruziziensis), soil surface application, and control], two P rates (with and without P), two clonal yerba mate cultivars, and two different soils (basalt- and rhyodacite-derived). When using glyphosate to control Congo grass, total dry matter and basal diameter of yerba mate plants decreased. This effect was enhanced by lack of P. Collateral effects of glyphosate use resulted in increased K, P, and Cu in clone 1 cultivated in basalt-derived soil; with rhyodacite-derived soil, increased levels of Ca, Mg, Mn, Fe, and Zn were observed in clone 1, while clone 2 displayed increases in B, Cd, and Pb. These observations demonstrate that glyphosate use to control undesirable plants can impact initial development and elemental composition of yerba mate, with variations between cultivars and soil type. [ABSTRACT FROM AUTHOR]