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Abstract Harvesting corn (Zea mays L.) stover for use as bioenergy feedstock may provide short‐term economic benefits and perhaps improve grain yield in continuous corn systems, but excessive stover removal may lead to long‐term depletion of soil C stocks. To better quantify the impacts of stover harvest on the soil C balance, we investigated CO2 fluxes under three harvest treatments (none, moderate, and high) in three continuous corn systems: (a) no tillage and no biochar applications, (b) chisel plowing with biochar amendments, and (c) chisel plowing without biochar amendments were quantified. We sampled static chambers 14, 13, and 15 times in 2010, 2011, and 2012, respectively, and the measurements were used to calibrate the Agricultural Production Systems sIMulator model. Although CO2‐C emissions did not differ among the three systems, both moderate (approximately 30%) and high (approximately 60%) stover removal rates reduced simulated CO2‐C emissions by nearly 10% and more than 22%, respectively. Despite these reductions in CO2 flux, the sum of CO2‐C and stover C exceeded CO2‐C losses in those plots without stover removal. This finding suggested soil C depletion was occurring for the soil and crop management practices used, even though depletion was not evident after 3 years. Application of biochar increased soil C levels, suggesting it may be able to offset some C losses. We conclude that for sustainable, highly productive agroecosystems that include stover harvest, all agronomic practices must be optimized to minimize C losses and maintain soil quality.

There is a need to quantify agriculture’s potential to sequester carbon (C) to inform global approaches aimed at mitigating climate change effects. Many factors including climate, crop, soil management practices, and soil type can influence the contribution of agriculture to the global carbon cycle. The objective of this study was to investigate the C sequestration potential of conservation agriculture (CA) (defined by minimal soil disturbance, maintaining permanent soil cover, and crop rotations). This study used micrometeorological methods to measure carbon dioxide (CO2) flux from several alternative CA practices in Harare, central Zimbabwe. Micrometeorological methods can detect differences in total CO2 emissions of agricultural management practices; our results show that CA practices produce less CO2 emissions. Over three years of measurement, the mean and standard error (SE) of CO2 emissions for the plot with the most consistent CA practices was 0.564 ± 0.0122 g CO2 m−2 h−1, significantly less than 0.928 ± 0.00859 g CO2 m−2 h−1 for the conventional tillage practice. Overall CA practices of no-till with the use of cover crops produced fewer CO2 emissions than conventional tillage and fallow.

Core Ideas Industrial biotechnology waste as a soil amendment approximates farmer practice yields. Applying waste amendments significantly increased soil organic C compared with farmer practice. Using waste nutrients for agriculture and soil organic matter improves sustainability. Reuse of industrial biotechnology by‐products has become an important component of circular bio‐economies whereby nutrient‐rich wastes are returned to agricultural land to improve soil fertility and crop productivity. Heat‐inactivated spent microbial biomass (SMB) from the production of 1,3‐propanediol is an industrial fermentation by‐product with nutrients that could replace or supplement conventional fertilizers. Our objectives were to determine if SMB utilization as a soil amendment in agriculture could generate environmental benefits while meeting farmer yield expectations and assess the impact of SMB application on CO2 emissions. This study examined the replacement of typical farmer fertilizer practices with the application of SMB. In addition to yellow dent maize (Zea mays L. var. indentata) grain yield and aboveground biomass, soil organic carbon (SOC) was measured. The eddy covariance (EC) micrometeorological method was used to measure CO2 flux. Overall maize yields were positively correlated with increasing application rates of SMB. After two SMB applications, SOC increased by 45% on the SMB plot as compared with an increase of 11% on the farmer practice plot. The SMB‐treated plot also emitted more CO2 (794 g CO2 m−2 yr−1) compared with the farmer practice treatment (274 g CO2 m−2 yr−1). Results from this study provide information on the efficacy of waste product nutrient cycling in the soil–plant ecosystem that could improve productivity and sustainability.

Core Ideas Aerodynamic methods can be used to gap‐fill Bowen ratio energy balance micrometeorological measurements. Eddy covariance and Bowen ratio energy balance methods agree during turbulent daytime conditions. Measuring nighttime net ecosystem exchange is challenging using turbulence‐based micrometeorology. There is a need to understand the potential benefits of using the biotechnology waste by‐product from manufacturing as a fertilizer replacement in agriculture, by quantifying the economic value for the farmer and measuring the environmental impact. Measuring CO2 emissions can be used to assess environmental impact, including three widely used micrometeorological methodologies: (i) the Bowen Ratio Energy Balance (BREB), (ii) aerodynamic flux‐gradient theory, and (iii) eddy covariance (EC). As a first step in quantifying benefits of applying biotechnology waste in agriculture, a detailed examination of these three methods was conducted to understand their effectiveness in quantifying CO2 emissions for this specific circumstance. The study measured micrometeorological properties over a field planted to maize (Zea mays L. var. indentata), one plot treated with biotechnology waste applied as a nutrient amendment, and one plot treated with a typical farmer fertilizer practice. Carbon dioxide flux measurements took place over 1 yr, using both BREB and EC systems. The aerodynamic method was used to gap‐fill BREB system measurements, and those flux estimates were compared with estimates produced separately by the aerodynamic and EC methods. All methods found greater emissions over the biotechnology waste application. The aerodynamic method CO2 flux estimates were considerably greater than both the EC and a combined BREB‐aerodynamic approach. During the day, the EC and BREB methods agree. At night, the aerodynamic approach detects and accounts for buildup of CO2 at the surface during stable periods. The BREB systems combined with aerodynamic approaches provide alternate methods to EC in examining micrometeorological properties near the surface.

Tree species and fertilization sources may affect the soil organic carbon (SOC) and fertility in agroforestry (AF) systems in temperate regions, but this remains unexplored. This study assesses the longitudinal trends in the SOC and major nutrients in a 17-year AF site established on an Ultisol in Fayetteville, AR. We evaluated how management and fertilization (mineral vs. organic) affect the soil’s physical and chemical properties using the tree species: red oak (Quercus rubra L.) and pecan Carya illinoinensis (Wangenh.) K. Koch. Long-term applications of poultry litter increased the soil pH, whereas the Mg and S concentrations decreased compared to the baseline levels (1999). Poultry litter increased the soil P concentration in 53% compared to the baseline levels and reduced the soil C:N ratio. After 17 years, increased Ca, SOC, and N concentrations were observed in the soils under the pecan stands that received poultry litter. Positive correlations occurred between the SOC and N (r = 0.96) as well as the Ca (r = 0.71) and P (r = 0.61) at a soil depth of 0–15 cm. Our findings demonstrated that the changes in SOC and fertility in the AF soils vary according to tree species and fertilization, mostly due to distinctive leaf litter and nutrient inputs. Organic matter accumulation increased the SOC retention and nutrient availability in the temperate AF systems.

Silvopasture systems combine tree and livestock production to minimize market risk and enhance ecological services. Our objective was to explore and develop a method for identifying driving factors linked to productivity in a silvopastoral system using machine learning. A multi-variable approach was used to detect factors that affect system-level output (i.e., plant production (tree and forage), soil factors, and animal response based on grazing preference). Variables from a three-year (2017–2019) grazing study, including forage, tree, soil, and terrain attribute parameters, were analyzed. Hierarchical variable clustering and random forest model selected 10 important variables for each of four major clusters. A stepwise multiple linear regression and regression tree approach was used to predict cattle grazing hours per animal unit (h ha−1 AU−1) using 40 variables (10 per cluster) selected from 130 total variables. Overall, the variable ranking method selected more weighted variables for systems-level analysis. The regression tree performed better than stepwise linear regression for interpreting factor-level effects on animal grazing preference. Cattle were more likely to graze forage on soils with Cd levels −1 (126% greater grazing hours per AU), soil Cr −1 (108%), and a SAGA wetness index of Dactylis glomerata L.). The result shows water flow within the landscape position (wetness index), and associated metals distribution may be used as an indicator of animal grazing preference. Overall, soil nutrient distribution patterns drove grazing response, although animal grazing preference was also influenced by aboveground (forage and tree), soil, and landscape attributes. Machine learning approaches helped explain pasture use and overall drivers of grazing preference in a multifunctional system.

Forage management and environmental conditions affect water soluble carbohydrate (WSC) storage, and, in turn, influence ruminant forage utilization in silvopastoral systems. The objective was to determine effects of four dependent variables: forage species [(non-native, C3 (orchardgrass (Dactylis glomerata L.)) and native C4 mix (8:1:1 big bluestem (Andropogon gerardii Vitman), little bluestem (Schizachyrium scoparium Michx. Nash) and indiangrass (Sorghastrum nutans L.))]; fertility (poultry litter and an unfertilized control); forage sampling date (mid-May, late-May, early-June, mid-June, and late-June); and hour of day (0800, 1100, 1400, and 1700 h) on WSC accumulation in a silvopasture. Concentrations of WSC (g kg DM−1) were greater (p ≤ 0.05) for C3 forages, with poultry litter not impacting WSC accumulation. Overall, WSC was greatest in mid-June, with the lowest WSC concentration observed at 0800 compared to 1100, 1400, and 1700 h (p ≤ 0.05). Therefore, harvesting forages later in the day resulted in greater WSC. A stepwise regression model indicated acid detergent fiber, ash, and forage P concentration were the best predictors (R2 = 0.85, p ≤ 0.05) of forage WSC. These results may be useful in future studies aimed at explaining diurnal cattle grazing preference and optimum forage harvest timing in silvopastoral systems.

Crop canopy CO exchange rate (CER) includes crop photosynthesis and soil/plant respiration. A portable canopy chamber is effective in determining crop CER values at a relatively small spatial (m) scale. The objectives of this study were to use a canopy chamber to measure CO fluxes in corn ( L.) and soybean [ (L.) Merr.]. Chamber measurements were performed for 18 and 15 d in 2013 and 2014, respectively. The canopy chamber measures instantaneous CER fluxes, and daily and daytime cumulative CO values were calculated from the instantaneous CER. The chamber CER results were compared with nearby eddy covariance (EC) flux tower measurements at a variety of time scales, i.e., instantaneous, daily, and daytime cumulative (multiple months). The daily and daytime cumulative chamber CER values were within 5% of the EC results, providing evidence for the effectiveness of the portable canopy chamber method. In conclusion, the portable canopy chamber provides reliable CO flux measurements despite the small size of field plots.