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Soil texture and organic matter are considered overarching factors controlling a diversity of soil processes and properties. However, a more complete understanding of how these factors quantitatively affect other soil properties has been lacking due to either limited scope of land use and management conditions, confounding climate and environmental conditions with management, or narrow range of soil and management conditions. This study evaluated the strength of associations of sand and total soil N concentrations with soil physical, chemical, and biological properties and processes from 310 surface‐soil (0–10‐cm depth) samples (87% Ultisols, 4% Inceptisols, and ≤3% each of Alfisols, Spodosols, Entisols, and Histosols) collected under conventional‐till and no‐till cropland, grassland, and woodland in four physiographic regions of North Carolina. Sand concentration was most strongly associated with dry‐stable mean‐weight diameter (MWD), MWD product, and sieved soil density (|r| > 0.63, p < 0.001). Total soil N concentration was most strongly associated with particulate organic C and N and soil water content at water‐holding capacity (|r| > 0.74, p < 0.001). Soils under unfertilized woodlands deviated the most from general associations, suggesting that organic matter quality could be unique, and requires further investigation. Overall, sand concentration associated more closely with soil physical properties and total soil N concentration associated closely with both soil physical and biogeochemical properties. Soil chemical properties were only weakly associated with either property. This study suggests that soil texture and organic matter would be complementary, additional properties in holistic soil health assessments that already included routine soil chemical analyses. Core Ideas: Soil texture strongly associated with dry‐stable aggregation but weakly associated with water‐stable aggregation.Total soil N strongly associated with particulate organic C and N and soil water content at water‐holding capacity.Sand and total soil N concentrations were strong combined indicators of bulk density, sieved soil density, and cation‐exchange capacity.Sand and total soil N concentrations were unique soil health indicators in addition to routine soil chemical propertiesSieved soil density could be a relatively rapid and inexpensive indicator that combines the influences of soil texture and organic matter. [ABSTRACT FROM AUTHOR]

Background: Soil organic C and N data from privately managed pastures in the southeastern United States are relatively scant. Methods: A paired‐farm approach was deployed to determine how a variety of soil health parameters related to nutrient and water cycling might be altered under grazed, botanically diverse perennial pastures compared with annual monoculture croplands in three Major Land Resource Areas of the southeastern United States. Results: Soil stability index averaged 0.64 and 0.91 mm mm−1 under cropland and grazed pasture, respectively, suggesting that pastures had a more stable soil surface that was resistant to erosion and allowed rapid water infiltration. Surface‐soil organic C and N fractions (i.e., total, particulate, and mineralizable fractions at 0–10 cm depth) were greater under pasture than under cropland. Across locations, root‐zone enrichments (0–30 cm depth) of organic C and N fractions were greater under pasture than under cropland. Within locations, root‐zone enrichment of total soil N was greater (p < 0.05) under pasture than under cropland in the Blue Ridge (2.87 vs. 1.10 Mg N ha−1, respectively) and the Piedmont (2.80 vs. 2.10 Mg N ha−1), but not in the Blackland Prairie (2.40 vs. 2.12 Mg N ha−1). Conclusions: This study provides evidence that rotationally grazed, perennial grasslands can store more soil organic C and N and improve soil surface stability conditions compared with neighboring croplands producing commodity feed grains for feedlot finishing. [ABSTRACT FROM AUTHOR]

Biologically active and intermediately labile fractions of soil organic matter are important features of conservation agricultural management systems. Depth distribution of soil‐test biological activity (STBA) and particulate organic carbon (C) and nitrogen (N) were characterized under cropland, grassland, and woodland across 25 research stations in North Carolina. Most (87%) of the 310 fields sampled were on Ultisols (udults or aquults). Variation in STBA in the surface 30‐cm of soil was controlled primarily by land use and to a lesser extent by soil texture and physiographic region. Baseline concentrations of STBA and particulate organic C and N at 30‐cm depth were relatively narrowly constrained compared with contents in the 0‐ to 10‐cm depth. Root‐zone enrichment (i.e., total minus baseline contents) of STBA (mean ± standard error; kg CO2–C ha−1 3 d−1) followed the order: conventional‐till cropland (194 ± 17) < no‐till cropland (274 ± 26) < woodland (421 ± 17) < grassland (537 ± 15) across locations. Proportion of root‐zone enrichment of soil organic C as particulate organic C was 43 ± 2%. Root‐zone enrichment of particulate organic C (Mg C ha−1) followed the order: conventional‐till cropland (3.8 ± 0.6) < no‐till cropland (8.7 ± 0.8) < grassland (14.1 ± 0.5) < woodland (16.3 ± 0.6) across locations. The C:N ratio of root‐zone‐enriched particulate organic matter was greater under woodland than under other land uses likely because of N input limitations. Conservation land uses increased root‐zone enrichment of these active and intermediately labile fractions independent of soil types and regions in the state. Core Ideas: Root‐zone enrichment calculations were sensitive to conservation land uses.As a proportion of total root‐zone enrichment of soil‐test biological activity (STBA), 68 ± 7% occurred in the 0‐ to 10‐cm depth.Grasslands and woodlands had greater root‐zone enrichment of particulate organic C and N than croplands.No‐till cropland had greater root‐zone enrichment of STBA and particulate organic C and N than conventional‐till cropland.Greater C:N ratio of root‐zone‐enriched particulate organic matter under woodlands may have been from lack of N input. [ABSTRACT FROM AUTHOR]

Soil aggregation is considered a key indicator of soil health to protect soil against erosion, enhance organic C storage, and offer habitat for soil organisms. Various methods to assess aggregation may change interpretations of management, and therefore should be cross‐calibrated. We assessed the impact of initial sieve opening size (8 or 4.75 mm) prior to determination of dry‐stable and water‐stable mean‐weight diameter (MWD) from two fine‐textured soils—a Rhodic Hapludox from São Paulo, Brazil and a Rhodic Kanhapludult from North Carolina, United States. Both soils were subjected to management expected to alter surface soil conditions. As expected, initial sieving through 8 mm led to greater dry‐stable MWD (3.37 ± 0.60 mm) than initial sieving through 4.75 mm (1.94 ± 0.28 mm). However, soil stability index (water‐stable MWD/dry‐stable MWD) was not affected by initial sieve size opening (0.56 ± 0.13 mm mm−1 under both initial sieve openings). Management interpretations were consistent with both approaches as well, and in particular to detect the strong depth effect on water‐stable MWD (i.e., declining with depth). Water‐stable macroaggregates had 32% ± 25% greater C concentration than microaggregates; similarly under both initial sieving conditions. Soil stability index when initially sieved through 4.75 mm was highly associated with aggregate stability of 1–2‐mm sized dry aggregates, which is a more common procedure. We conclude that passing soil through a screen with 4.75‐mm openings to conduct a diversity of soil analyses can be appropriate for obtaining reasonable estimates of and interpretations about surface soil aggregation. Core Ideas: Soil stability index is water‐stable divided by dry‐stable mean‐weight diameter of whole soil.Soil stability index was similar whether soil was initially sieved through 8 or 4.75 mm.Water‐stable mean‐weight diameter and soil stability index declined with soil depth.Water‐stable macroaggregates had 32% ± 25% greater soil organic C than microaggregates. [ABSTRACT FROM AUTHOR]

Agriculture has undergone dramatic technological and cultural changes over the past century. Many would argue that the changes have been unquestionably positive with huge gains in productivity, reduced labour requirements, and alleviation of food insecurity for most people. However, the adoption of increasingly specialized and separated crop and livestock enterprises has also had widespread negative consequences resulting in (a) decline in biodiversity, (b) degradation of groundwater and surface waters with agrochemical pollutants, (c) poor soil health with monoculture crop production and frequent soil disturbance, (d) intensive greenhouse gas emissions from both specialized cropping systems relying on external inputs and concentrated animal feeding operations that accumulate wastes, and (e) general lack of ecological integrity among components of these specialized systems. Diversified agricultural systems using annual and perennial forages offer opportunities to elevate ecological synergies when crop and livestock operations are integrated. Integrated crop‐livestock systems can internalize nutrient cycling, provide cultural control of weeds, insects and diseases, and share resources in a circular‐based agroecosystem. Cover crops could be transitioned into nutritious annual forages for livestock grazing on currently specialized crop production farms with appropriate local incentives. Perennial forages in ley farming or in pasture‐crop rotations have historical relevance and are a proven practice for conserving nutrients, improving soil health and enhancing biodiversity. Redesigning contemporary agriculture with mixed‐use farming techniques could greatly reduce soil erosion, improve water quality, and invigorate soil health. We suggest that incorporating different types of forages across a diverse landscape can enhance agricultural sustainability and ecological integrity. [ABSTRACT FROM AUTHOR]

Soil erosion is a major constraint to agricultural sustainability. Land management that protects soil from water erosion can be assessed from the fraction of aggregates stable upon water immersion. Conservation management with minimal soil disturbance is known to enhance water‐stable aggregation, but how annual vs. perennial vegetative cover affects soil biological activity and aggregation from soils varying in texture remains relatively unexplored. This study assessed the effects of long‐term conventional‐till and no‐till cropland, grassland, and woodland on dry‐stable and water‐stable mean‐weight diameter (MWD) from 25 research stations across North Carolina. Soil clay concentration varied from 36 to 279 g kg–1 and sand concentration varied from 392 to 904 g kg–1 (5–95% distribution). Across locations, water‐stable MWD followed the order: conventional‐till cropland (0.64 mm) < no‐till cropland (0.87 mm) < woodland (1.12 mm) = grassland (1.15 mm). Soil stability index (i.e., water‐stable MWD/dry‐stable MWD) followed a similar order: conventional‐till cropland (0.59 mm mm–1) < no‐till cropland (0.76 mm mm–1) < grassland (0.92 mm mm–1) = woodland (0.96 mm mm–1). Although water‐stable MWD was positively associated with clay concentration (r =.50, p <.001, n = 310), soil‐test biological activity had the strongest association with water‐stable MWD (r =.80). Soil‐test biological activity reflected biological manipulation of surface‐concentrated organic matter, as mediated by conservation land uses. This study revealed the large impact of surface organic C and N resources on water‐stable aggregation through soil biological manipulations interacting across a textural gradient. Core Ideas: Conservation land uses of no‐till cropland, grassland, and woodland improved soil aggregation characteristics.Soil stability index discerned conservation land use impacts across a soil texture gradient.Soil aggregation characteristics were not different between grasslands and woodlands.Soil‐test biological activity and sand were strongly associated with soil aggregation characteristics. [ABSTRACT FROM AUTHOR]

Estimating soil nitrogen (N) availability is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological properties to predict soil N availability, and plant dry matter and N uptake in two greenhouse trials with sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii) as test crop using soils (0–10 cm) from 57 tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) pastures mostly in North Carolina and Virginia. Soil biological properties, the flush of CO2, cumulative carbon (C) mineralization, soil microbial biomass C, basal soil respiration, and plant available N were positively correlated with net N mineralization, plant dry matter, and N uptake in both the greenhouse trials. The flush of CO2, which is the measure of carbon dioxide released from dried and rewetted soil during the first 3 days of aerobic incubation, explained 77% and 72% of the variation in the plant N uptake in Greenhouse Trial 1 and 2, respectively. Total soil N and residual inorganic N in both trials and manganese in Trial 1 and particulate organic C in Trial 2 added minor contributions to explaining variation in plant N uptake. The flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across diverse pasture soils because (a) it was highly correlated with net N mineralization, plant dry matter, and N uptake, and (b) it was less laborious and more cost-effective than other direct indicators of soil N availability. [ABSTRACT FROM AUTHOR]

Sequestration of organic C in agricultural soils is necessary to improve soil health to meet the challenges of climate change, diminishing biodiversity, water quality deterioration, and rising demands for food and fiber production. New assessment approaches are needed to quantify how conservation agriculture might contribute to soil health improvement and soil organic C (SOC) sequestration. In the southeastern United States, conservation management has been repeatedly shown to stratify SOC concentration with depth. Starting immediately below a zone of tillage influence (i.e., 30‐cm depth), SOC concentration is rarely affected by management due to low C inputs and high decomposition potential, whereas concentration increases toward the surface in a nonlinear manner, presumably with greater inputs of residue and root inputs and changing temperature and moisture conditions. Using these observations as an ecological foundation, SOC sequestration was calculated as the summation of SOC stock greater than the baseline condition at 30‐cm depth. Data from literature sources were mathematically fitted with this new approach as a validation. Two on‐farm surveys with different agricultural management practices (5–40 yr) in the southeastern United States yielded preliminary estimates of SOC sequestration. The interquartile range of calculated SOC sequestration was 4.2–9.4 Mg C ha–1 for conventional‐tillage cropland (n = 45 fields), 13.6–29.7 Mg C ha–1 for no‐tillage cropland (n = 97 fields), and 15.9–26.1 Mg C ha–1 for perennial pasture (n = 29 fields). This new approach will be valuable to estimate SOC sequestration from a greater diversity of conservation agricultural systems practiced on farms within a region and independent of soil type. [ABSTRACT FROM AUTHOR]

Soil‐test biological activity (STBA) is a key indicator describing the functions of soil to catabolize organic amendments, promote soil organic C sequestration, and cycle nutrients. We explored how climatic zone, land use, and physiographic region affected the relationship of STBA with several soil fertility properties and processes. Soils from Georgia, North Carolina, Pennsylvania, and Virginia (wet climate) were Aquults, Fluvents, Udalfs, Udepts, and Udults and soils from Nebraska and Oklahoma (dry climate) were Udolls and Ustolls. Annual cropland and perennial pasture were the land uses. The Prairie region had silt loam and silty clay loams, the Ridge–Valley region had silt loams, and the Piedmont and Coastal Plain regions had fine sandy loam, loam, sandy clay loam, and sandy loams. Across all locations, STBA with the flush of CO2 during 3 d following rewetting of dried soil was most strongly associated with cumulative C mineralization, basal soil respiration, particulate organic C, potential N mineralization during 24 d of aerobic incubation, residual soil ammonium, soil microbial biomass C, and total soil N. Climatic zone modified the association between STBA and net N mineralization, possibly caused by greater N immobilization in drier soils with 2:1 clays. Physiographic region had a small effect on the relationship between STBA and net N mineralization. Land use did not alter this relationship significantly. Soil‐test biological activity was verified as a robust indicator of soil organic N supply, as well as of general soil biological condition to assess the soil's catabolic potential and potential C storage. [ABSTRACT FROM AUTHOR]

Long‐term agricultural experiments in the Coastal Plain of the southeastern United States are needed to understand biogeochemical processes and design better systems to overcome a changing climate and other perturbations. We determined a suite of soil organic C and N fractions after 19 yr of management from a diverse farming system project in Goldsboro, NC. Soil was collected at 0‐ to 6‐, 6‐ to 12‐, and 12‐ to 20‐cm depth increments from 14 treatments that were subsets of five overarching treatments of conventional cropping, integrated crop–livestock systems, organic cropping, plantation forestry, and old‐field successional land use. Surface residue C and N were greater with woody (i.e. plantation forestry and successional) than with cropping systems (7,491 and 2,896 kg C ha−1, respectively; 138 and 60 kg N ha−1, respectively). Soil‐test biological activity was greater with alternative cropping (i.e. integrated crop–livestock and organic systems) than conventional cropping (314 vs. 220 kg CO2–C ha−1 3 d−1, respectively). An integrated crop–livestock system with grazed pasture in long rotations with crops had greater net N mineralization than hayed forage in shorter rotations (111 vs. 92 kg N ha−1 24 d−1, respectively). Total organic C and particulate organic N concentrations were highly stratified with depth, but stocks were not different between conventional and no‐till cropping when summed to 20 cm. We conclude that alternative cropping systems with forage‐based rotations, limited tillage, and organic inputs can create long‐lasting improvements in soil organic C and N fractions than conventional agricultural and more naturalized systems. [ABSTRACT FROM AUTHOR]

Soil-test biological activity is a key indicator for soil health assessment. Methodological details may affect accuracy and precision of this indicator. Accuracy and precision of soil-test biological activity estimates were determined for 10 replications of 10 mass and volume treatments under standard laboratory conditions using an alkali trap technique with acid titration. Five soils varying in texture and organic C and N concentrations were used to assess a gradient of soil mass and volume conditions on C mineralization following rewetting of dried soil during 0–3, 3–10, and 10–24 d of incubation at 50% water-filled pore space and 25◦C. Soil type explained ≥90% of variation in C mineralization, but soil mass and volume treatments also had significant effects on estimates (p < .001). In sets of treatments with the same surface area exposed, increasing soil volume led to lower C mineralization across soil types. Entrapment of CO2 in soil pores may have been the main reason for lower C mineralization, since the effect diminished over time. Treatments with 50 to 100 g of soil were nearest the median estimates of C mineralization for each soil. Precision of C mineralization estimates was greatest when soil mass was ≥50 g of soil. A consistent surface area-to-volume of ∼0.2 cm−1 is suggested with sufficient soil mass to account for potentially enhanced random variation of C-enriched surface soils. [ABSTRACT FROM AUTHOR]

Corn (Zea mays L.) is an important cereal grain in many states and typically receives large N fertilizer inputs, irrespective of historical management. Tailoring N inputs to soil-specific conditions would help to increase efficiency of N use and avoid environmental contamination. A total of 47 trials were conducted on research stations and private farms in four different regions of North Carolina and Virginia from 2014 to 2016 to associate soil N availability with yield response to sidedress N application. Corn grain yield was 10.6 ± 3.4 Mg ha–1 on 36 sites and silage yield was 44.6 ± 8.2 Mg ha–1 on 11 sites. There was positive association between relative yield (i.e., yield without sidedress N application divided by yield with full fertilization) and levels of both plant available N (residual inorganic N + net N mineralization during 24 d) and the flush of CO2 following rewetting of dried soil during 3 d. Economically optimum N fertilizer requirement (EONR) at sidedress declined with increasing level of plant available N and soil-test biological activity (i.e., the flush of CO2). The scalable N factor for production at EONR declined from 20 kg N Mg–1 of grain (i.e., 1.1 lb N bu–1) with no soil biological activity to no N required with soil-test biological activity of 600 mg CO2–C kg–1 in a 3-d period (depth of 0–10 cm). The flush of CO2 when determined in spring at or prior to planting corn was considered an ideal soil-test indicator of soil biological activity due to its simple, rapid, and reliable characteristics related to potential soil N mineralization and corn yield responses to applied N fertilizer [ABSTRACT FROM AUTHOR]

Soil nitrogen (N) mineralization is variably affected by management and edaphic conditions. A routine soil test that reflects both soil biological activity and N mineralization could improve predictions for N fertilizer recommendations to cereal grains on different soil types and landscape settings. We collected soils from 47 corn production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with sorghum-sudangrass [Sorghum bicolor (L.) Moench ssp. Drummondii] dry matter production and N uptake during 6 to 8 wk of growth in the greenhouse. Plant dry matter and N uptake were strongly associated, as expected. Plant available N (sum of net N mineralization during 24 d of aerobic incubation + residual inorganic N) had the strongest association with plant dry matter production (r² = 0.76) and N uptake (r² = 0.85). However, the flush of CO2 during a 0- to 3-d period following rewetting of dried soil was nearly equally effective at r² = 0.74 and r² = 0.76, respectively. Multiple regression models with 4 ± 2 additional variables led to r² = 0.88 ± 0.10 among different separations of data based on depth, region, and soil textural class. We suggest the optimum combination of variables to predict soil N availability would be the flush of CO2, residual inorganic N, and total soil N concentration, as they balance relevant scientific information with limited soil-testing resources (time and labor). We demonstrated that the flush of CO2 was a rapid and reliable indicator of soil N availability. [ABSTRACT FROM AUTHOR]

Nitrogen limits crop production when insufficient and harms the environment when excessive. Tailoring N inputs to cropping systems remains a high priority to achieve production and environmental goals. We collected soils from 47 corn (Zea mays L.) production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with soil N mineralization. Soil organic C at a depth of 0 to 10 cm varied among sites from ~10 to 80 g kg–1, and generally declined with depth because of many sites with no-tillage management. Net N mineralization during 24 d of aerobic incubation (25°C, 50% waterfilled pore space) was 54 to 114 mg N kg–1 (24 d)–1 at 0 to 10 cm, 22 to 41 mg N kg–1 (24 d)–1 at 10 to 20 cm, and 12 to 22 mg N kg–1 (24 d)–1 at 20 to 30 cm (middle 50% of observations at each depth). Total soil N was positively associated with net N mineralization (r² = 0.58), but the flush of CO2 during 3 d was even more closely associated with net N mineralization (r² = 0.77). Association between the flush of CO2 and net N mineralization did not change significantly when data were sorted by different regions or soil textural classes. The flush of CO2 is a rapid, reliable, and robust indicator of soil-test biological activity. The strong association of the flush of CO2 with net N mineralization also corroborated use of the flush of CO2 as a rapid and reliable indicator of soil N availability. [ABSTRACT FROM AUTHOR]

Soil biological activity is an important component of a well-functioning soil. Methodologies for estimating this process vary due to a variety of theoretical, functional, and expediency considerations. We tested the effects of soil processing (sieve size), water delivery method (from top and from capillary), and soil organic matter content (two levels based on depth of sampling) on mineralizable C and N during 0 to 1, 0 to 3, and 0 to 24 d of incubation from soils ranging in texture. Mineralizable C was not affected by sieve size, suggesting that fine grinding should not affect results. Water delivery method did affect mineralizable C estimates at 0 to 1 and 0 to 3 d of incubation, as water delivered by capillary allowed soil to absorb to 70 ± 5% water-filled pore space compared with controlled delivery to 50% water-filled pore space from the top. The extra water only hindered mineralizable C in soils with coarse texture (i.e., sandy loam), whereas mineralizable C in other soil textures was not affected. Net N mineralization during 24 d of incubation was negatively impacted by the higher water content, independent of soil texture, but more so when soils high in organic matter were sieved coarsely than when sieved finely. Despite these variations, close association occurred between mineralizable C (0 to 1 and 0 to 3 d) and net N mineralization (0 to 24 d at 50% water-filled pore space), suggesting that length of incubation and method of water delivery should not restrict the choice of methodological variation from those used here to assess soil biological activity. However, a standard methodology has become increasingly necessary to compare absolute values across management systems, farm types, and regions. [ABSTRACT FROM AUTHOR]

Near-infrared spectroscopy (NIRS) and geostatistics are relatively unexplored tools that could reduce the time, labor and costs of soil analysis. Our objective was to efficiently determine lateral and vertical distributions of soil texture and soil organic C (SOC) fractions in an agroforestry system (a 7-ha field) on a Coastal Plain site in North Carolina. To predict selected properties from a large number of soil samples collected from this field, NIRS was calibrated against laboratory-determined properties. Support vector machines was a multivariate model that performed better than partial least squares to obtain greater precision with NIRS for all soil properties. To predict soil properties with precision across the field, geostatistical modeling with maximum likelihood and ordinary kriging was used. When we combined the two modeling processes, the root mean square error (RMSE) and the RMSE relative to the dataset mean (%RMSE) were 67 g kg-1 for sand (9.3% RMSE), 34 g kg-1 for clay (22.7% RMSE), 1.63 g kg-1 for total organic C (26.7% RMSE), 0.67 g kg-1 for particulate organic C (36.1% RMSE) and 24 mg CO2-C kg-1 3 d-1 for the flush of CO2 (29% RMSE). We conclude that the combination of NIRS and kriging produced acceptable errors and therefore could be used to predict the spatial distribution of soil texture and SOC fractions in this agroforestry system to allow efficient assessment of management changes with time and better predict small-scale input requirements. [ABSTRACT FROM AUTHOR]

Soil texture is known to affect soil organic C (SOC) concentration and microbial activity, but these relationships are not always straightforward. We characterized total, mineral-associated and mineralizable C fractions along a gradient of soil texture within a flood plain field in the Coastal Plain region of North Carolina. Soil was collected from 0- to 5-, 5-to 15- and 15- to 30-cm depth intervals at 204 locations within a 7-ha area. Samples were analyzed for soil particle size distribution, specific surface area (SSA), oxalate-extractable Al and Fe to estimate short-range-ordered (i.e., poorly crystalline) oxyhydroxides and soil C fractions. Overall, relationships among soil C fractions, textural classes and depths were complex. Both SOC (0.4-13.9 g kg-1 soil) and mineral-associated organic C (0-12 g kg-1 soil) increased as soil clay concentration increased (73-430 g kg-1 soil), but having two distinct slopes in each relationship with an inflection point of ∼150 g clay kg-1 soil at 0 to 5 and 5 to 15 cm and an inflection point of ∼250 g clay kg-1 soil at 15 to 30 cm. As clay concentration increased, SSA (12-76 m2 g-1 soil) and oxalateextractable Fe (0.45-5.9 g kg-1 soil) also increased. A weaker relationship was observed between oxalate-extractable Al (0.38-1.5 g kg-1 soil) and either SSA or mineral-associated organic C. Mineralizable C increased with increasing clay concentration up until 143 ± 3, 152 ± 5, and 161 ± 11 g kg-1 (0-5, 5-15 and 15 -30 cm, respectively), but decreased (0-5 and 5-15 cm) or stayed constant (15-30 cm) at higher clay concentrations. On the basis of untested observations, we surmise that binding of C to oxalate-extractable Fe contributed to the accumulation of SOC and suppression of mineralizable C as the clay concentration increased. These results suggest that complex soil texture- physicochemical interactions underlie the inherent fertility of floodplain soils. [ABSTRACT FROM AUTHOR]

The cover image is based on the Original Article Farming with forages can reconnect crop and livestock operations to enhance circularity and foster ecosystem services by Alan J. Franzluebbers et al., https://doi.org/10.1111/gfs.12592. [ABSTRACT FROM AUTHOR]

Perennial lignocellulosic biomass and food crop residues have traditionally been important resources used internally on-farm. However given the growing outlook with advanced biofuel conversion technologies, such biomass sources might be of competing greater value if sold off the farm into the bioenergy feedstock stream. Inputs of carbon embedded in above-ground plant biomass are a key biological energy source for the soil surface — a zone of great importance in the success of food–feed–fiber production and ecological processes essential to environmental quality. This review of literature looks at how above-ground plant biomass contributes to soil properties and processes, water conservation and quality, on-farm forage availability, and as a harvestable biofuel component. Competing needs for this resource could cause serious environmental or economic consequences without sufficient knowledge of their potential impacts. Perennial forages and crop residues are critical for providing surface cover to protect soils against erosion and for providing the organic inputs to support below-ground ecosystem communities, properties, and processes. The amount of biomass required to maintain soil organic matter and various ecosystem services linked to this key soil property may, in many cases, exceed that needed for simple erosion control. Consequences of continuous residue harvest could be detrimental or minor, depending on the climatic and edaphic conditions, as well the type of cropping system and tillage management employed. Achieving a balanced outcome will require scientific evidence of in-field effects, a collective vision for designing landscapes of appropriate functional capacity, and well-designed government policies for crop residue and perennial biomass utilization schemes to contribute to a sustainable agricultural approach. [ABSTRACT FROM AUTHOR]

Highlights: [•] Winter cover cropping with legume-derived N and inorganic fertilizer N were evaluated under conventional and no tillage. [•] Type of cover crop had little influence and grazing of cover crops had minor influence on crop production characteristics. [•] Grazing of winter cover crops by cattle added a stable component to production. [•] No tillage had large positive effects on corn and soybean production, but little effect on winter wheat production. [•] Robust, diversified crop–livestock systems with no tillage can be developed for impoverished soils of the southeastern USA. [ABSTRACT FROM AUTHOR]

Highlights: [•] Integrated crop-livestock systems are effectively implemented in every region of the U.S. [•] New technologies facilitate successful adoption of crop-livestock systems. [•] Adoption of crop-livestock systems in the U.S. occurs primarily among livestock managers. [•] Cash crop managers have few current incentives to incorporate livestock into their crop systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Negative impacts on the environment are a concern with specialized agriculture. [•] Soils rooted with perennial forages have high organic matter content. [•] High soil organic matter content contributes to high soil quality. [•] Improved soil quality with pasture–crop rotations can improve ecosystem services. [•] Review of science of pasture–crop rotations in temperate North and South America. [Copyright &y& Elsevier]

Highlights: [•] Two types of tillage (conventional disk and no tillage) were evaluated for soil nitrate impacts. [•] Two types of winter cover cropping (legume-derived N and inorganic fertilizer N) were evaluated. [•] Type of cover crop had little influence on soil-profile nitrate content. [•] Conventional tillage caused greater profile nitrate change than no tillage. [Copyright &y& Elsevier]

Abstract: Botanical composition and forage productivity of mixed cool- and warm-season perennial pastures are important determinants of agricultural sustainability. Effects of three sources of nutrient (inorganic only, organic+inorganic combination, and organic only) and four utilization regimes (unharvested, low and high grazing pressure, and hayed) were evaluated on botanical composition, residual forage mass, and forage production during seven years of management on tall fescue (Lolium arundinaceum, a cool-season C3 grass) overseeded into existing bermudagrass (Cynodon dactylon, a warm-season C4 grass) sod in Georgia. Nutrient source had few major impacts on responses, except for greater hay yield with organic fertilization (broiler litter) than with organic+inorganic and inorganic only fertilization. Botanical composition of grazed pastures shifted with time from initial dominance with bermudagrass (∼50% basal area) to mixed composition of tall fescue (60%)/bermudagrass (36%) under low grazing pressure and tall fescue (45%)/bermudagrass (48%) under high grazing pressure. To maintain optimum botanical composition and productivity for year-round sustainable grazing, forage mass needs to be balanced within a maximum threshold to avoid deterioration of forage quality and a minimum threshold to avoid environmental degradation. [Copyright &y& Elsevier]

The article discusses the benefits and barriers of well-managed grazing-based farming system and promotes adoption of this conservation tool in the eastern U.S. It informs that this system provides society-wide environment services, productivity and profit to individual producers. It proposes the local, state and federal programs to support grazing system and encourages development of policy options for adoption of pasture-based livestock production as one of several agroecological approaches.

Prediction of soil organic C sequestration with adoption of various conservation agricultural management approaches is needed to meet the emerging market for environmental services provided by agricultural land stewardship. The soil conditioning index (SCI) is a relatively simple model used by the USDA-Natural Resources Conservation Service to predict qualitative changes in soil organic matter. Our objective was to develop a quantitative relationship between soil organic C derived from published field studies in the southeastern USA and SCI scores predicted from matching management conditions. We found that soil organic C sequestration (at 20 ± 5 cm depth) could be reliably related to SCI across a diversity of studies in the region using the regression slope: 1.65 Mg C ha SCI [which translated into a rate of 0.25 ± 0.04 Mg C ha yr SCI (mean±standard error of 31 slope estimates)]. The calibration of soil organic C on SCI scores will allow SCI to become a quantitative tool for natural resource professionals to predict soil organic C sequestration for farmers wanting to adopt conservation practices. [ABSTRACT FROM AUTHOR]

Surface soil characteristics arc of key importance in assessing the sustainability of agricultural management systems. We evaluated the factorial combination of nutrient source (inorganic, mixed organic + inorganic, and organic as broiler litter) and forage utilization (unharvested, low and high cattle grating pressure, and hayed) on soil organic matter during 12 yr of pasture management on a Typic Kanhapludult in Georgia. Nutrient source had very little effect on bulk density, soil organic C (SOC), and total soil N (TSN). Forage utilization greatly affected all soil properties, more so nearest the surface. For example, SOC at a depth of 0 to 3 cm under low grazing pressure was 47.6 g kg-1 and under haying was 28.8 g kg-1 (P < 0.00 1), while at 3 to 6 cm it was 20.1 and 14.9 g kg-1, respectively (P = 0.04), and at 6 to 12 cm it was 12.7 and 11.0 g kg-1, respectively (P = 0.59). Soil bulk density was inversely related to SOC. Total SOC (0-20 cm) plus surface residue C was 3.6 ± 3.6 Mg C ha-1 greater (mean ± standard deviation among six nutrient source it forage utilization comparisons) in the zone nearest shade and water sources than farther away. Sequestration of TSN in the surface 6 cm averaged 8 ± 8 kg N ha-1 yr-1 (mean ± standard deviation among three nutrient source comparisons) when hayed, 31 ± 15 kg N ha-1 yr-1 when left unharvested, and 74 ± 5 kg N ha-1 yr-1 when grazed by cattle with either low or high grazing pressure. These results indicate the large potential of well-managed grazing systems to improve the quality and functioning of soils in the southeastern United States. [ABSTRACT FROM AUTHOR]

Conservation management of degraded land has the potential to build soil fertility, restore soil functions, and mitigate greenhouse gas emissions as a consequence of surface soil organic matter accumulation. Literature from the southeastern United States was reviewed and synthesized to: (i) quantitatively evaluate the magnitude and rate of soil organic C (SOC) sequestration with conservation agricultural management; (ii) evaluate how conservation management affects surface SOC accumulation and its implications on ecosystem services; and (iii) recommend practical soil sampling strategies based on spatial and temporal issues to improve the detection of statistically significant SOC sequestration. Soil organic C sequestration was 0.45 ± 0.04 Mg C ha-1 yr-1 (mean ± standard error, n = 147, 20 ± 1 cm depth, 11 ± 1 yr) with conservation tillage compared with conventional tillage cropland. Establishment of perennial pastures sequestered 0.84 ± 0.11 Mg C ha-1 yr-1 (n = 35, 25 ± 2 cm depth, 17 ± 1 yr). Stratification of SOC with depth was common under conservation agricultural management and appears to be integrally linked to abatement of soil erosion, improvement in water quality, and SOC sequestration. Sampling of conservation management systems should ideally occur repeatedly with time in controlled and replicated experiments, but there is also an urgent need for chronosequence and paired-field surveys of SOC on working farms in the region to validate and expand the scope of inference of experimental results. Landowners in the southeastern United States have great potential to restore soil fertility and mitigate greenhouse gas emissions with the adoption of and improvement in conservation agricultural systems (e.g., continuous no-till, high-residue crop rotations, high organic matter inputs). [ABSTRACT FROM AUTHOR]

Information about several papers discussed at the Farming with Grass conference is presented. It discussed the benefits of using sustainable agriculture in grassland environments particularly to people, profit, production and protection. Gale Buchanan, Department of Agriculture Under Secretary identified four major challenges that agriculture must address during coming decades.

Abstract: Grazing of cover crops in grain cropping systems can increase economic return and diversify agricultural production systems, but the environmental consequences of this intensified management have not been well documented, especially under different tillage systems. We conducted a multiple-year investigation of how cover crop management (grazed and ungrazed) and tillage system [conventional (CT; initial moldboard plowing and thereafter disk tillage) and no tillage (NT)] affected soil physical properties (bulk density, aggregation, infiltration, and penetration resistance) on a Typic Kanhapludult in Georgia. Responses were determined in two cropping systems: summer grain/winter cover crop and winter grain/summer cover crop. Soil bulk density was reduced (P =0.02) with CT compared with NT to a depth of 30cm at the end of 0.5 year, but only to a depth of 12cm at the end of 2, 2.5, and 4.5 years. Grazing of cover crops had little effect on soil bulk density, except eventually with 4.5 years of management. Water-stable macroaggregation was reduced (P ≤0.01) with CT compared with NT to a depth of 12cm at all sampling times during the first 2.5 years of evaluation. Stability of macroaggregates in water was unaffected by grazing of cover crops in both tillage systems. Across 7 sampling events during the first 4 years, there was a tendency (P =0.07) for water infiltration rate to be lower with grazing of cover crops (5.6mmmin−1) than when ungrazed (6.9mmmin−1), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0–10cm (P =0.001) and the difference was greater in ungrazed than in grazed systems (P =0.06). Biannual CT operations may have alleviated any surface degradation with animal traffic, but the initially high level of soil organic matter following long-term pasture and conversion to cropland with NT may have buffered the soil from any detrimental effects of animal traffic. Overall, the introduction of cattle to consume the high-quality cover crop forage did not cause substantial damage to the soil. [Copyright &y& Elsevier]

Tillage, cropping system, and cover cropping are important management variables that control the quantity, quality, and placement of organic matter inputs to soil. How soil organic matter and its different fractions respond to management has not been comprehensively studied in integrated crop-livestock systems. We conducted a 3-yr field experiment on a Typic Kanhapludult in Georgia in which long-term pasture was terminated and converted to annual crops. Tillage systems were conventional (CT, moldboard plowed initially and disked thereafter) and no-till (NT). Cropping systems were summer grain with winter cover crop and winter grain with summer cover crop. Cover crops were either grazed by cattle or left unharvested. Total organic C was highly stratified with depth under NT and relatively uniformly distributed with depth under CT. All soil C and N fractions were greater under NT than under CT at a depth of 0 to 6 cm. Tillage system had the most dominant influence on all soil C and N fractions, and cropping system the least. At the end of 3 yr, total organic C at a depth of 0 to 30 cm was lower under CT than under NT (42.6 vs. 47.4 Mg ha-1 [P < 0.001]). Potential C mineralization was also lower under CT than under NT (1240 vs. 1371 kg ha-1 during 24 d [P = 0.02]). At a depth of 0 to 30 cm, cover crop management had no effect on soil C and N fractions, but within the surface 6 cm some changes occurred with grazing of cover crops by cattle, the most dramatic of which were 1 ± 9% increase in soil microbial biomass C and 3 ± 16% decrease in potential C mineralization. To preserve high surface-soil C and N fractions and total plow-layer contents, NT cropping following termination of perennial pasture is recommended. In addition, since cattle grazing cover crops did not consistently negatively influence soil C and N fractions, integrated crop-livestock systems are recommended as a viable conservation approach while intensifying agricultural land use. [ABSTRACT FROM AUTHOR]

Quantification of the impact of long-term agricultural land use on soil organic C (SOC) is important to farmers and policymakers, but few studies have characterized land use and management effects on Soc across physiographic regions. We measured the distribution and total stock of SOC to a depth of 20 cm under conventional tillage (cvT), conservation tillage (CsT), and pasture in 87 production fields from the Southern Piedmont and Coastal Plain Major Land Resource Areas. Across locations, SOC at a depth of 0 to 20 cm was: pasture (38.9 Mg ha-1) > CsT (27.9 Mg ha-1) > CvT (22.2 Mg ha-1) (P ⩽ 0.02). Variation in soc was explained by management (41.6%), surface horizon clay content (5.2%), and mean annual temperature (1.0%). Higher clay content and cooler temperature contributed to higher SOC. Management affected soc primarily at the soil surface (0-5 cm). All SOC fractions (i.e., total SOC, particulate organic C, soil microbial biomass C, and potential C mineralization) were strongly correlated across a diversity of soils and management systems (r = 0.85-0.96). The stratification ratio (concentration at the soil surface/concentration at a lower depth) of SOC fractions differed among management systems (P < 0.000 1), and was 4.2 to 6.1 under pastures, 2.6 to 4.7 under CsT, and 1.4 to 2.4 under CvT; these results agree with a threshold value of 2 to distinguish historically degraded soils with improved soil conditions from degraded soils. This on-farm survey of SOC complements experimental data and shows that pastures and conservation tillage will lead to significant SOC sequestration throughout the region, resulting in improved soil quality and potential to mitigate CO2 emissions. [ABSTRACT FROM AUTHOR]

Abstract: A 3-year experiment was conducted to determine pasture and cattle responses to tall fescue–endophyte association (free, novel, and wild endophyte associated with ‘Jesup’ cultivar) and fertilization source (inorganic and broiler litter). Fertilization source had only minor or no effects on botanical composition, forage mass, cattle stocking rate, and yearly cattle performance and productivity. However, cattle performance and production were greater with broiler litter than with inorganic fertilization during summer, but lower in autumn and winter, suggesting a difference in timing of nutrient availability to forage due to mineralization of organic nutrients in broiler litter. Pastures with wild endophyte association either had higher forage mass during some periods or were able to carry more cattle than other endophyte associations. Cattle performance was lower with wild than with other endophyte associations at all times of the year, except in summer. Cattle gain in winter was not different among endophyte associations (64kgha−1; p =0.43), was lower in spring with wild endophyte than with other endophyte associations (244kgha−1 versus 302kgha−1; p =0.04), was higher in summer with wild endophyte (147kgha−1 versus 117kgha−1; p <0.001), and was lower in autumn with wild endophyte (97kgha−1 versus 129kgha−1; p =0.10). Seasonal differences in pasture responses to fertilization and endophyte association suggested that management options could be developed to avoid or limit toxic cattle responses to wild endophyte. [Copyright &y& Elsevier]

The article reports on the necessity of management systems to improve soil quality and regenerate ecological processes. It is indicated that conserving and restoring soil can supply soil productivity and sustain environmental quality. The Agricultural Research Service (ARS) of the U.S. Department of Agriculture created the Greenhouse Gas Reduction through Agricultural Carbon Enhancement network (GRACEnet) to study soil C sequestration and greenhouse gas emissions.

Native grasslands in the Great Plains of North America have mostly disappeared in the past century due to agricultural expansion. A grazing study was established on Paleustolls and Argiustolls supporting a remnant, but historically grazed tallgrass prairie in central Oklahoma. Stocking method of beef cattle was differentiated into continuous and rotational treatments (10 sub-paddocks) in 2009 and these treatments continued until present. Soil was sampled in 2009 and 2012 at depths of 0–6, 6–12, 12–20, and 20–30 cm and in 2017 at depths of 0–15 and 15–30 cm. Total, particulate, microbial biomass, and mineralizable C and N fractions were highly stratified with depth, having 2–10 times greater concentration at a depth of 0–6 cm as that at 20–30 cm. Strong associations existed among most of these soil organic C and N fractions, given the large range that resulted from sampling at multiple depths. No discernable differences in soil organic C and N fractions occurred due to stocking method at any sampling time or depth. Evidence for biological nitrification inhibition suggested a mechanism for conservation of available N with less opportunity for loss. In addition, strong association of available N with biologically active C indicated slow, but sustained release of N that was strongly coupled to C cycling. We conclude that stocking method had a neutral effect on conservation of already high antecedent conditions of soil organic C and N fractions during the first 8 years of differentially imposed management. [ABSTRACT FROM AUTHOR]

In this article the author discusses the results of a study conducted by Humberto Blanco-Canqui and Rattan Lal concerning no-tillage and soil-profile carbon sequestration. He views on the remarks of Blanco-Canqui and Lal regarding the difficulties in the interpretation of the results of the approach undertaken in farm survey. The author also indicates concerns on the sampling approach of the study.

Summarizes a report on ecosystem analysis at a watershed level, as presented during a conference sponsored by the Soil and Water Conservation Society in Athens, Georgia in April 1997. Education, research and policy needs; Development of the direction for integrated natural resource systems management; Interagency cooperation and communication.

Lack of forage in the winter dry season is a concern for cattle production in tropical Brazil. Pasture renovation with silage production might solve an immediate concern for forage production and help develop an improved pasture condition after cropping. The present study was focused to compare the production and quality of monocropped sorghum and sorghum intercropped with Marandu grass and/or pigeonpea in two row spacings. The experiment was carried out on a sandy Oxisol in São Paulo state in Brazil with an experimental design of a 2 x 4 factorial arrangement with four replications. Treatments were: monocropped sorghum, sorghum intercropped with Urochloa brizantha, sorghum intercropped with Cajanus cajan (cv. BRS Mandarim), and sorghum intercropped with Urochloa+ pigeonpea with 0.45 and 0.90 m row spacings. Greatest forage production was with 0.45-m spacing for monocropped sorghum and dual-species intercropping. With 0.90-m spacing, greatest production was for Sorghum+Urochloa. Sorghum+Urochloa+Cajanus intercropping provided the highest concentrations of crude protein in silage, regardless of row spacing. An increase in ensiling time reduced quality of the silage due to a decline in crude protein and TDN and an increase in fibers. However, the reduced spacing between lines with the inclusion of legumes resulted in a greater amount of silage with a higher concentration of protein. [ABSTRACT FROM AUTHOR]

In agricultural soils, a large portion of C in crop residues (i.e., non-harvested plant parts left in the field) is annually lost to atmosphere due to the low C use metabolism of soil microorganisms adapting to the environmental stress (moisture stress and substrate C and N imbalance). In this study, we tested the hypothesis that amending soil with biosolids (treated sewage sludge with high stable organic matter and low C:N ratio) can improve the C metabolism of microorganisms in agricultural soils through alleviation of microbial stress, leading to increased sequestration of crop residue-C in agricultural soils. Biosolids were applied at a mean annual rate of 4.2 kg m −2 (dry weight) to eight agricultural fields (biosolids-amended) for 13 years (1972–1984) in western Illinois. Four agricultural fields (unamended) received chemical fertilizer as control. We measured the sequestration rate of crop residue-C in the soils over the span of 34 years (1972–2006) using a 13 C technique. We found dramatically greater sequestration rate of crop residue-C in biosolids-amended soil (32.5 ± 1.7% of total crop residue-C) versus unamended soil (11.8 ± 1.6%). Soil microbial metabolic quotient was significantly lower in biosolids-amended than in unamended fields, indicating that biosolid-amendment reduced soil microbial stress and improved microbial C metabolism. The study concludes use of a soil amendment with high stable C and low C:N is a valid approach to transform agricultural soils from current C-neutral status to a C sink. Biosolids represent a good choice of such soil amendments. [ABSTRACT FROM AUTHOR]

Sustainability research is complex and involves the evaluation of tradeoffs. Environmental, economic, and social aspects should ideally be considered. Even when one only pillar of sustainability is evaluated, results should be assessed within the broader context of overall sustainability. Environmental impacts from forage and livestock systems, as well as confined animal feeding operations, can be positive and negative, depending on the type of operation, environmental setting, weather episodes, and management conditions. These systems also have associated social and economic impacts. As in all agricultural management systems, there are likely to be hotspots of damage due to a particular management style combined with the right soil, landscape, and climatic conditions. Widespread, positive benefits of pasture-based management are possible when forage resources are utilized ideally with best grazing management principles leading to enhanced soil organic carbon storage, high water infiltration, efficient nutrient cycling, and minimal water and nutrient runoff into nearby water bodies. Research to quantify the environmental impacts of livestock management systems can be designed in detail on research stations to understand the direct implications of management differences on plant biomass production that captures atmospheric CO2, on carbon stored in soil organic matter, and on greenhouse gas emissions from ruminant livestock fed controlled diets. On-farm research is also valuable to characterize the impacts of a particular style of management across a diversity of environments using a system-level approach integrated across the farm. Communication strategies engaging major stakeholders from the livestock industry are key to deliver a consistent message to the general public. Perceived benefits, challenges, and opportunities must be science based, seeking opportunities to reduce negative impacts, and enhancing the positive ones. Messaging to the lay audience about environmental impacts can be focused on solutions from positive benefits or problems from negative effects, but should also address economic and social components. [ABSTRACT FROM AUTHOR]

Abstract: The response of soil microbial communities following changes in land-use is governed by multiple factors. The objectives of this study were to investigate (i) whether soil microbial communities track the changes in aboveground vegetation during succession; and (ii) whether microbial communities return to their native state over time. Two successional gradients with different vegetation were studied at the W. K. Kellogg Biological Station, Michigan. The first gradient comprised a conventionally tilled cropland (CT), mid-succession forest (SF) abandoned from cultivation prior to 1951, and native deciduous forest (DF). The second gradient comprised the CT cropland, early-succession grassland (ES) restored in 1989, and long-term mowed grassland (MG). With succession, the total microbial PLFAs and soil microbial biomass C consistently increased in both gradients. While bacterial rRNA gene diversity remained unchanged, the abundance and composition of many bacterial phyla changed significantly. Moreover, microbial communities in the relatively pristine DF and MG soils were very similar despite major differences in soil properties and vegetation. After >50 years of succession, and despite different vegetation, microbial communities in SF were more similar to those in mature DF than in CT. In contrast, even after 17 years of succession, microbial communities in ES were more similar to CT than endpoint MG despite very different vegetation between CT and ES. This result suggested a lasting impact of cultivation history on the soil microbial community. With conversion of deciduous to conifer forest (CF), there was a significant change in multiple soil properties that correlated with changes in microbial biomass, rRNA gene diversity and community composition. In conclusion, history of land-use was a stronger determinant of the composition of microbial communities than vegetation and soil properties. Further, microbial communities in disturbed soils apparently return to their native state with time. [Copyright &y& Elsevier]

Abstract: Soil microbial communities were examined in a chronosequence of four different land-use treatments at the Konza Prairie Biological Station, Kansas. The time series comprised a conventionally tilled cropland (CTC) developed on former prairie soils, two restored grasslands that were initiated on former agricultural soils in 1998 (RG98) and 1978 (RG78), and an annually burned native tallgrass prairie (BNP), all on similar soil types. In addition, an unburned native tallgrass prairie (UNP) and another grassland restored in 2000 (RG00) on a different soil type were studied to examine the effect of long-term fire exclusion vs. annual burning in native prairie and the influence of soil type on soil microbial communities in restored grasslands. Both 16S rRNA gene clone libraries and phospholipid fatty acid analyses indicated that the structure and composition of bacterial communities in the CTC soil were significantly different from those in prairie soils. Within the time series, soil physicochemical characteristics changed monotonically. However, changes in the microbial communities were not monotonic, and a transitional bacterial community formed during restoration that differed from communities in either the highly disturbed cropland or the undisturbed original prairie. The microbial communities of RG98 and RG00 grasslands were also significantly different even though they were restored at approximately the same time and were managed similarly; a result attributable to the differences in soil type and associated soil chemistry such as pH and Ca. Burning and seasonal effects on soil microbial communities were small. Similarly, changing plot size from 300 m2 to 150 m2 in area caused small differences in the estimates of microbial community structure. In conclusion, microbial community structure and biochemical properties of soil from the tallgrass prairie were strongly impacted by cultivation, and the microbial community was not fully restored even after 30 years. [Copyright &y& Elsevier]

Abstract: Soil microbial communities under three agricultural management systems (conventionally tilled cropland, hayed pasture, and grazed pasture) and two fertilizer systems (inorganic fertilizer and poultry litter) were compared to that of a ∼150-y-old forest near Watkinsville, Georgia. Both 16S rRNA gene clone libraries and phospholipid fatty acid (PLFA) analyses indicated that the structure and composition of bacterial communities in the forest soil were significantly different than in the agricultural soils. Within the agricultural soils, the effect of fertilizer amendment on bacterial communities was more dramatic than either land use or season. Fertilizer amendment altered the abundance of more bacterial groups throughout the agricultural soils. In addition, the changes in the composition of bacterial groups were more pronounced in cropland than in pastures. There was much less seasonal variation between the soil libraries. Community-level differences were associated with differences in soil pH, mineralizable carbon and nitrogen, and extractable nutrients. Bacterial community diversity exhibited a complex relationship with the land use intensity in these agro-ecosystems. The pastures had the highest bacterial diversity and could be characterized as having an intermediate degree of intervention compared to low intervention in forest and high intervention in cropland. Changes in bacterial diversity could be attributed to the abundance of a few operational taxonomic units (OTUs). The microdiversity of abundant OTUs in both forest and cropland was consistent with an increase in abundance of many phenotypically similar species rather than a single species for each OTU. Soil microbial communities were significantly altered by long-term agricultural management systems, especially fertilizer amendment, and these results provide a basis for promoting conservation agricultural systems. [Copyright &y& Elsevier]

Aims: Cover crop species selection for soybean (Glycine max) production under no-tillage (NT) management may affect soil organic C sequestration by altering the quantity and quality of C inputs, thereby affecting cropping system sustainability. If so, the underlying mechanisms for such regulation are still unclear. Methods: We assessed changes in soil C and N fractions at 0-0.1 m depth and soil C stock at 0-0.6 m depth during the last three years of dry-season cover cropping in a soybean production system managed with NT for 9 years on a Rhodic Hapludox in Sao Paulo, Brazil. Dry-season management treatments were repeated yearly in a split-plot scheme. Main plots during the fall-winter were (1) ruzigrass (Urochloa ruziziensis), (2) grain sorghum (Sorghum bicolor), and (3) the intercropping of ruzigrass and sorghum. Subplots during spring prior to planting soybean were (a) pearl millet (Pennisetum glaucum), (b) sunn hemp (Crotalaria juncea), and (c) forage sorghum (Sorghum bicolor). Results: Soil C and N fractions were affected according to crop residue characteristics of the rotations. Higher soil C stocks in 2012 and 2015 (7 % an average) were observed at 0.2–0.4 m depth by ruzigrass compared to sorghum. High crop residue input with ruzigrass in the fall-winter sequestered 0.61 Mg C ha− 1 yr− 1 at 0-0.1 m soil depth compared with lower C sequestration using grain sorghum (0.29 Mg C ha− 1 yr− 1). Conclusions: The quantity and quality of crop residues impact its retention on soil surface controlling the dynamics of soil C and N fractions and can be considered relevant for soil C sequestration. These aspects could contribute to the mitigation of atmospheric CO2 in crop production systems. [ABSTRACT FROM AUTHOR]