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Pore structure is a key determinant of soil functioning, and both root growth and activity of soil fauna are modified by and interact with pore structure in multiple ways. Cover cropping is a rapidly growing popular strategy for improving agricultural sustainability, including improvements in pore structure. However, since cover crop species encompass a variety of contrasting root architectures, they can have disparate effects on formation of soil pores and their characteristics, thus on the pore structure formation. Moreover, utilization of the existing pore systems and its modification by new root growth, in conjunction with soil fauna activity, can also vary by cover crop species, affecting the dynamics of biopores (creation and demolition). The objectives of this study were (i) to quantify the influence of 5 cover crop species on formation and size distribution of soil macropores (>36pm 0); (ii) to explore the changes in the originally developed pore architecture after an additional season of cover crop growth; and (iii) to assess the relative contributions of plant roots and soil fauna to fate and modifications of biopores. Intact soil cores were taken from 5 to 10 cm depth after one season of cover crop growth, followed by X-ray computed micro-tomography (CT) characterization, and then, the cores were reburied for a second root growing period of cover crops to explore subsequent changes in pore characteristics with the second CT scanning. Our data suggest that interactions of soil fauna and roots with pore structure changed over time. While in the first season, large biopores were created at the expense of small pores, in the second year these biopores were reused or destroyed by the creation of new ones through earthworm activities and large root growth. In addition, the creation of large biopores (>0.5mm) increased total macroporosity. During the second root growing period, these large sized macropores, however, are reduced in size again through the action of soil fauna smaller than earthworms, suggesting a highly dynamic equilibrium. Different effects of cover crops on pore structure mainly arise from their differences in root volume, mean diameter as well as their reuse of existing macropores. [ABSTRACT FROM AUTHOR]

Differences in soil nitrous oxide (N2O) fluxes among ecosystems are often difficult to evaluate and predict due to high spatial and temporal variabilities and few direct experimental comparisons. For 20 years, we measured N2O fluxes in 11 ecosystems in southwest Michigan USA: four annual grain crops (corn-soybean-wheat rotations) managed with conventional, no-till, reduced input, or biologically based/organic inputs; three perennial crops (alfalfa, poplar, and conifers); and four unmanaged ecosystems of different successional age including mature forest. Average N2O emissions were higher from annual grain and N-fixing cropping systems than from nonleguminous perennial cropping systems and were low across unmanaged ecosystems. Among annual cropping systems full-rotation fluxes were indistinguishable from one another but rotation phase mattered. For example, those systems with cover crops and reduced fertilizer N emitted more N2O during the corn and soybean phases, but during the wheat phase fluxes were ~40% lower. Likewise, no-till did not differ from conventional tillage over the entire rotation but reduced emissions ~20% in the wheat phase and increased emissions 30-80% in the corn and soybean phases. Greenhouse gas intensity for the annual crops (flux per unit yield) was lowest for soybeans produced under conventional management, while for the 11 other crop × management combinations intensities were similar to one another. Among the fertilized systems, emissions ranged from 0.30 to 1.33 kg N2O-N ha−1 yr−1 and were best predicted by IPCC Tier 1 and Δ EF emission factor approaches. Annual cumulative fluxes from perennial systems were best explained by soil [ABSTRACT FROM AUTHOR]

Supplying adequate amounts of soil N for plant growth during the growing season and across large agricultural fields is a challenge for conservational agricultural systems with cover crops. Knowledge about cover crop effects on N comes mostly from small, flat research plots and performance of cover crops across topographically diverse agricultural land is poorly understood. Our objective was to assess effects of both leguminous (red clover) and non-leguminous (winter rye) cover crops on potentially mineralizable N (PMN) and levels across a topographically diverse landscape. We studied conventional, low-input, and organic managements in corn-soybean-wheat rotation. The rotations of low-input and organic managements included rye and red clover cover crops. The managements were implemented in twenty large undulating fields in Southwest Michigan starting from 2006. The data collection and analysis were conducted during three growing seasons of 2011, 2012 and 2013. Observational micro-plots with and without cover crops were laid within each field on three contrasting topographical positions of depression, slope and summit. Soil samples were collected 4–5 times during each growing season and analyzed for and PMN. The results showed that all three managements were similar in their temporal and spatial distributions of NO3—N. Red clover cover crop increased by 35% on depression, 20% on slope and 32% on summit positions. Rye cover crop had a significant 15% negative effect on in topographical depressions but not in slope and summit positions. The magnitude of the cover crop effects on soil mineral nitrogen across topographically diverse fields was associated with the amount of cover crop growth and residue production. The results emphasize the potential environmental and economic benefits that can be generated by implementing site-specific topography-driven cover crop management in row-crop agricultural systems. [ABSTRACT FROM AUTHOR]

Abstract: Information on spatial variability of different C pools and fractions is important for site-specific monitoring the changes in soil carbon (C) on a farm-scale basis. The objectives of this study were to compare the effects of 16 years of implementation of conventional chisel-plowed management practice (CT) and organic cover crop based practice (CT-cover) on spatial variability of C mineralized in a 210-day incubation; and to study the effects of topography, texture, plant biomass input, and total soil C on mineralizable C. For each management practice we collected more than 350 soil samples at 0–5 cm depth in well-drained Typic Hapludalfs in southwest Michigan. The spatial continuity of CO2 respired C was found to be relatively weak with the variability at distances<1 m constituting more than 65% of the overall variability. In either treatment, only a small portion of variability in CO2 respired C (11–16%) was explained by multiple regression models with topography (WI), soil texture (clay+silt content), main crop biomass, and total C. There was a positive direct effect of total C and a negative direct effect of clay+silt on CO2 respired C. The practical implication of these findings for modeling soil C processes on a farm scale is that in soils similar to those of this study producing site specific maps of labile C inputs using either spatial auto-correlation or auxiliary variables will likely not be feasible. [Copyright &y& Elsevier]

The use of cover crops is a management technique that can potentially increase the amount of carbon (C) sequestered in soil. However, information on cover crop’s role in increasing soil C comes mostly from small experimental plots, while the magnitude of C gains in large agricultural fields may vary spatially in response to topographic and soil variability. Here we assess cover crop effects on soil organic C in 20 large agricultural fields across a topographically diverse landscape under conventional, low-input, and organic managements in corn-soybean-wheat rotation. The low-input and organic managements included rye and red clover cover crops in their rotations. Micro-plots with and without cover crops were laid out within each studied field at three contrasting topographical positions of depression, slope and summit. Soil samples were collected and analyzed for total organic carbon (TOC), particulate organic carbon (POC) and short-term mineralizable carbon (SMC). The magnitude of cover crop effects on SMC and POC varied across topography. The contributions of cover crop’s presence to soil C variables tended to be the highest on topographical slopes and summits. Positive correlations between effects of cover crop presence on SMC with cover crop biomass also were primarily observed on slopes and summits. The results indicate that in the studied agricultural environments preferential placement of cover crops on eroded low fertility elements of the relief can be a particularly effective strategy from both environmental and management standpoints. [ABSTRACT FROM AUTHOR]

Highlights: [•] Topography has a significant effect on red clover and corn performance. [•] The positive effect of red clover biomass on corn yield varies temporally and spatially. [•] Red clover effect was significant in years with lower cumulative precipitation. [•] Red clover effect was higher in summit and slope topographical positions. [ABSTRACT FROM AUTHOR]

Planting cover crops within or following a cash crop may improve soil-based ecosystem services due to increased plant diversity and a longer duration of live vegetation coverage. We examined the effect of three different cover cropping systems on soil properties after one year of a three-year organic transition rotation at four agricultural field sites with contrasting topographical positions, namely depressions, slopes, and summits. The four studied systems were (1) cereal rye (Secale cereal L.) planted after corn (Zea mays L.) harvest (Rye); (2) a mixture of cold susceptible cover crop species, namely, oat (Avena sativa) , winter pea (Pisum sativum), and radish (Raphanus sativus), interseeded into corn (WK); (3) a mixture of cold tolerant cover crop species, namely, annual ryegrass (Lolium multiflorum), Dwarf Essex rapeseed (Brassica napus), and crimson clover (Trifolium incarnatum), interseeded into corn (WH); and (4) a no-cover control (NC). While soil moisture was affected by topography, interseeding cover crops into corn did not influence soil moisture levels at the 0–10 cm depth for the studied year. Soil NO 3 - content was markedly higher in the WK system compared to cereal rye and WH cover crop treatments. The difference was especially pronounced in depressions and summits. Soil N mineralization rates followed the pattern WH>WK>Rye>NC and the effects were most pronounced in slopes. Soil microbial biomass C was the highest in depressions followed by summits and slopes, and in depressions the WH had higher microbial biomass than the other systems. There were no effects of cover crops and topography on soil C mineralization one year after the organic transition was initiated. The WH system increased the fraction of 0.053–2 mm aggregates and decreased > 2 mm aggregates in depressions. The results suggest that the effect of cover cropping can become evident already one year after the organic transition begins. The WH mixture interseeded into the cash crop was an optimal cover crop choice for improving soil characteristics as well as decreasing soil N leaching risks during organic transition in undulating agricultural terrain. However, the magnitude of the benefit provided by WH was mediated by topography. • Cover crops did not affect soil moisture. • Cold tolerant mixtures decreased soil NO 3 - content. • Soil N mineralization rates were highest in response to cold tolerant mixtures. • Cold tolerant mixtures had higher microbial biomass C than the other systems. • Cold tolerant mixtures changed soil aggregate size distribution in depressions. [ABSTRACT FROM AUTHOR]