Agricultural & Environmental Letters最新文献

This study evaluates cover crop (CC) effects on microbial community structure in a winter wheat–sorghum–fallow rotation with pea, oat, and canola; mixtures of pea and oat; pea and canola; pea, oat, and canola; and six species mixture (SSM) of pea, oat, canola, hairy vetch, forage radish, and barley as CCs, and fallow as treatments. Soil microbial community structure was analyzed at CC termination (phase I), 36 days (phase II), and a year (phase III) after termination using an ester-linked fatty acid methyl ester analysis. Total microbial biomass (TMB) under oats was significantly greater than under canola (by 47%) in phase I (p ≤ 0.05). The TMB was >48% under pea, pea + canola, and SSM, and arbuscular mycorrhizal fungi was 70%–93% more under pea, canola, and their mixtures than fallow in phase II. While microbial abundance varied with CCs at and after 36 days post-termination, these effects did not persist for a year. Long fallow period after cropping or cover cropping appears detrimental to microbial community proliferation.

Soil respiration is one of the main soil health indicators and is influenced by several factors in agricultural fields. Identifying key factors that control soil respiration is desirable for informed soil management decisions and for promoting and scaling up soil health. This study aimed to (i) quantify the relationships between potential soil respiration and selected soil properties, crops, and slope positions, and (ii) identify key factors controlling these relationships using a neural network model. Ninety soil samples from 0- to 5- and 5- to 20-cm soil depth were collected from footslope, backslope, and summit in three fields planted with soybean (Glycine max L. Merr.), alfalfa (Medicago sativa L.), and corn (Zea mays L.). The model provided great accuracy (coefficient of determination: 0.96; root-mean square error: 7.8; and mean absolute deviation: 3.8) and explained nearly 96% of variations in soil respiration across soil depth, crop, and slope positions. Soil depth, ammoniacal nitrogen (NH₄-N), crop types, slope position, and silt content were identified as the top five factors influencing potential soil respiration at the field level. Potential soil respiration was more sensitive to potassium, phosphorus, pH, cation exchange capacity, and mean weight diameter and less sensitive to NH₄-N, nitrate nitrogen, soil organic matter, and clay content. It increased with pH, electrical conductivity, mean weight diameter, potential nitrogen mineralization, and potassium, and it decreased with increasing silt content. Soil from 0 to 5 cm under soybean or at the summit slope position exhibited a higher respiration. Using a small dataset, this pilot study accurately predicted potential soil respiration in agricultural fields and identified key drivers controlling it. The results from this study highlight the complexity of using potential soil respiration as a standalone test for evaluating soil health. This does not diminish the usefulness of potential soil respiration as a soil health indicator to support agricultural management decisions and as a reference in future soil health studies. However, it emphasizes the importance of considering multiple factors when interpreting the significance of soil biological indicators for soil health assessments.

Ammonium phosphate fertilizers are a common phosphorus (P) source for crops, namely monoammonium phosphate, diammonium phosphate, and ammonium polyphosphate. Despite containing appreciable nitrogen (N), ammonium phosphate fertilizers are generally considered P fertilizers. However, the approximately 8.5 million Mg N co-applied with P annually as ammonium phosphate fertilizers represents 8% of global N fertilizer input flux to agroecosystems. Despite this, a systematic review of the literature revealed only one direct assessment of N losses from ammonium phosphate fertilizers. An additional five studies reported NO₃-N leaching and N₂O-N emissions from soils fertilized with ammonium phosphates, but inadvertently as observations from failed or control treatments that are confounded (e.g., not accounting for non-fertilizer contributions to N losses). The magnitude and fate of N co-applied with P in ammonium phosphate fertilizers is a blind spot in agroecosystem N budgets and environmental footprints that necessitates quantification.

Although communicating research is a key part of public science, current graduate curricula in the agricultural sciences usually have a narrow focus on communication appropriate for presenting to scientific and academic audiences, such as in the form of the dreaded “seminar.” Yet the importance and impact of agriculture extends well beyond research communities, and communicating with other potential audiences is essential for realizing the full impact of research. Because public speaking is among the greatest fears for many people, it is critical to provide students with the tools needed to communicate effectively with diverse audiences, particularly as only a fraction of them will go on to give regular research seminars once they enter the professional world. Better communication can lead to more constructive engagement with the public as well as with policy-makers, toward improved understanding of the science they are funding and from which they are benefiting. Purposeful instruction in public speaking should help alleviate the common anxieties that student presenters often experience. Here, we summarize general communication strategies that can be incorporated into any graduate agricultural science course to help address this need.

Farmers are increasingly planting cover crops to improve soil health and provide other ecosystem services. Cover crop incentive programs in Maryland, Pennsylvania, New York, and Vermont were compared and farmers using cover crops were surveyed (n = 328) to characterize program participants and assess the effects of programs on cover crop adoption. Farmers who participated in incentive programs differed from nonparticipants in their perspectives about incentive programs, challenges they faced using cover crops, and reasons for cover crop use. When averaged across farmers, results show that incentive programs doubled average farmer cropland with cover crops from 50.7 ha prior to participation to 101.0 ha during participation. Among participants who no longer were enrolled in a program, cover crop use remained on average 37.2% greater than before enrollment. Results highlight the role of incentive programs in facilitating adoption and provide insights for expanding participation to different farmers and increasing program impact.

Robust assessment of crop water availability requires effective integration of soil moisture data within the range of field capacity (θ_FC) to permanent wilting point (θ_PWP). Emerging needs for spatiotemporally dynamic θ_FC and θ_PWP are difficult to achieve with lab determinations. Therefore, we used long-term data from 182 sites across the United States to evaluate whether soil moisture extremes defined by 95th and 5th percentiles represent θ_FC and θ_PWP, respectively. Soil moisture extremes and lab-measured θ_FC and θ_PWP were well correlated (R² = 0.71−0.92), however, both 95th and 5th percentiles overestimated θ_FC and θ_PWP at most depths (RMSE = 6%–16% vwc). Percentiles of soil moisture distribution that corresponded to lab-determined θ_FC and θ_PWP varied widely and were a function of precipitation received at the site and site- and soil-depth specific clay content. These findings imply that while θ_FC and θ_PWP may not be broadly represented by soil moisture extremes (95th and 5th percentiles), there may be potential to statistically infer the positioning of θ_FC and θ_PWP within long-term soil moisture distributions using biophysical determinants such as aridity and soil characteristics.

Many peatlands have been drained for anthropogenic purposes, and there is high interest in restoring them for their carbon storage ability and critical habitat. Peatlands hold a disproportionate amount of global soil carbon, making peatland restoration a promising approach for mitigating carbon emissions. In this study, site factors were investigated that affect peat carbon dioxide flux at Cold Spring fen in Minnesota, which is undergoing restoration. Peat carbon dioxide flux and water table depth were monitored throughout the growing season at two locations previously disturbed to different degrees by row-crop agriculture. Flux ranged from 0.55 to 12.71 µmol m⁻² s⁻¹ and was highest during peak growing season. Lower flux corresponded to elevated water table conditions. The more disturbed location often had lower flux, indicating success in hydrological restoration. The water table is an important factor in peatland restoration, and water table management should be considered to maximize carbon sequestration.

Permanganate oxidizable carbon (POXC) is a popular soil health test developed to measure “labile” C via the reduction of permanganate, dependent on several stoichiometric reduction oxidation assumptions. As a proof-of-concept experiment to evaluate the interpretation of POXC as “labile” C, we tested 17 compounds ranging in biological lability under standard POXC assay conditions at a fixed C mass (25 mg) in a quartz (2–0.053 mm diameter) matrix. POXC was high for lignin, whereas carbohydrates did not differ from the quartz control. Functional group-based reactivity partly explained permanganate reduction. These findings indicate that (i) POXC is not a labile C fraction and (ii) corroborate previous concerns that the stoichiometric oxidation–reduction assumptions in the calculation of C oxidation from permanganate reduced are not sound. POXC interpretation should regard POXC as a chemically defined fraction, report in units of moles permanganate reduced per kg soil, and avoid terms such as “labile” and “active.”

Living mulch (LM) is used in agricultural fields to suppress weeds, control diseases, and mitigate erosion. It also enhances soil nutrient supply at the root death and decay stage during the growing season. However, benefits of LM to soil hydraulic properties related to soil pore structure have not been elaborated here. We focus on temporal changes in soil hydraulic conductivity (K) in a field where sweet potato was grown with and without LM (barley, Hordeum vulgare L.). K was measured in the field using a mini-disk infiltrometer at three different pressure heads. In the plots with LM, K decreased significantly in August and then increased in October compared to plots without LM (at –0.5 cm pressure head). Changes in soil pore structure due to root growth or death and decay may alter soil hydraulic conductivity.