Proceedings - Soil Science Society of America最新文献

Crambe (Crambe abyssinica Hochst) is an important grain crop for biodiesel production. The objective of this study was to evaluate how spatial distribution of soil properties affects crambe grain yield and oil content. We analyzed six different sampling densities, with a distance between sampling points ranging from 5.5 to 44 m, to identify correlations among soil and crop variables, and the best spatial distribution. Crambe oil content was not correlated to any of the physicochemical properties, whereas crambe grain yield was correlated with total porosity and exchangeable Al and Ca, effective cation exchange capacity, available P, K, Cu, and Zn, and aluminum and base saturation, with highly significant correlation (p < 0.001) for P and K and Cu and Zn. Most soil properties had spatial dependence degrees from weak to strong, and were modeled by spherical or exponential semi-variograms. Spatial data showed that low grain yield is associated with high seed oil content, while crambe grain yield was more correlated with phosphorous availability in soil in the first year (2012) and with Ca, Mg, and soil organic matter in the second year (2013). Spatial variability in soil nutrients is attributed to uneven distribution of fertilizers and surface runoff. The results demonstrate sampling density must be increased to generate more accurate maps for soil chemical properties affecting crambe. The use of a grid of 25 points in a 625 m² of land is suggested, providing more than 60% accuracy for grain yield estimation and more than 40% for most chemical properties’ estimation.

Soil organic matter is assumed to accumulate with conservation management. On-farm surveys using paired-farm and chronosequence approaches could validate assumptions, as well as provide a diversity of soils and management conditions to assess organic matter fractions. The objective of this study was to assess how land use and pasture management affected the gradient of organic matter fractions from active to resistant. Particulate and non-particulate (also called mineral-associated) organic C and N fractions were isolated and soil-test biological activity was measured from 304 profiles at 0- to 10-, 10- to 30-, and 30- to 60-cm depths on 31 private farms in Virginia. Root-zone enrichment contents of these soil properties were calculated following subtraction of a baseline from total stocks of each soil profile. Land use was a key factor affecting root-zone enrichment (0- to 30-cm depth) of particulate organic C (Mg C ha⁻¹) (p ≤ 0.05): conventional-till cropland (6.3) = no-till cropland (9.2) < grassland (14.2) < woodland (16.7). Root-zone enrichments of soil C and N fractions increased with pasture age to a plateau achieved by 25 years and were optimized at cattle stocking rate of 1.0 ± 0.2 Mg live weight ha⁻¹. Feeding hay increased root-zone enrichment of soil-test biological activity (49 kg CO₂-C 3 day⁻¹ [Mg hay]⁻¹). Although non-particulate organic C and N dominated, accumulation with time and steady-state concentration of particulate fractions were vital steps toward greater soil organic matter under conservation management. Root-zone enrichment calculations from on-farm sampling were helpful in distinguishing true effects of management from pedogenesis on soil organic matter formation.

Biological soil crusts (biocrusts) are crucial elements of desert ecosystems, exhibiting patchy distribution patterns across the soil surface and significantly impacting surface soil nutrient dynamics. However, the influence of biocrust patch units, serving as fundamental functional entities, on microbial nutrient restriction remains underexplored. This study conducted measurements on moss crust patches of varying sizes and subcrust soils. Stoichiometric analysis of extracellular enzyme activities (EEAs) related to carbon, nitrogen, and phosphorus was performed, along with vector and redundancy analyses to evaluate microbial nutrient limitation and key influencing factors. The findings reveal that both patch size and soil layer of biocrusts collectively influence soil nutrients and enzyme dynamics, with heightened enzyme activity observed in the crust layer. Vector analysis based on EEA stoichiometry indicates that moss crust patch size insignificantly impacts microbial nutrient restriction within the crust layer. However, microbial nitrogen restriction in the subcrust layer demonstrates a “single-peak” trend, initially increasing before gradually declining. This suggests that microorganisms in medium-sized crust patches exhibit peak activity, intensifying nutrient competition. This research underscores the pivotal role of biocrust patch units as fundamental functional entities, offering comprehensive insights into microbial metabolic constraints under crust cover. The findings underscore the significant implications of enzyme stoichiometric characteristics for desert land management and conservation.

Gelisols (permafrost-affected soils in US Soil Taxonomy) are extensive in Alaska, currently occurring on ∼45% of the land area of the state. Gelisol taxonomic criteria rely on the presence of near-surface (less than 2 m deep) permafrost, but ongoing climatic and environmental change has the potential to affect the presence of near-surface permafrost across much of Alaska throughout the 21st century. In this study, we utilized scenarios of near-surface permafrost loss and active layer deepening through the 21st century under low (SRES B1, RCP 4.5), mid- (SRES A1B), and high (SRES A2, RCP 8.5) emissions scenarios, in conjunction with the statewide STATSGO soil map, to generate spatially explicit predictions of the susceptibility of Gelisols and Gelisol suborders to taxonomic change in Alaska. We find that 15%–53% of Alaskan Gelisols are susceptible to taxonomic change by mid-century and that 41%–69% of Alaskan Gelisols are susceptible to taxonomic change by the end of the century. The extent of potential change varies between suborders and geographic regions, with Gelisols in Northern Alaska being the most resilient to taxonomic change and Western and Interior Alaskan Gelisols most susceptible to taxonomic change. The Orthel suborder is likely to be highly restricted by the late 21st century, while Histels and Tubels are more likely to be of greater extent. These results should be taken into consideration when designing initial survey and re-mapping efforts in Alaska and suggest that Alaskan Gelisol taxa should be considered threatened soil taxa due to the proportional extent of likely loss.

Forests around the world, and in the case of this study, the coastal Pacific Northwest United States, store large amounts of carbon, both above ground in the trees and below ground in soils. Understanding the effects of forest disturbance, including timber harvesting, is important in order to evaluate the role that forestry plays in the global carbon cycle. Soil carbon can be difficult to assess with enough precision to detect the kinds of changes that are expected, yet a series of small changes over time in the same direction could have important cumulative effects. In this study, eight randomly selected Douglas-fir forest stands in Oregon and Washington were sampled at 300 points each using a fixed-depth sampling approach to attempt to detect a 5% or higher change in soil carbon storage to 1 m, longitudinally from pre-harvest to 10 years post-harvest. There was moderate variability in results over time at individual sites, with some sites decreasing slightly and others increasing slightly. Only two sites achieved lower than the 5% minimum detectible difference target. The remaining six sites were able to detect 5.7%–10.7% differences. In one case, an unexpectedly large increase in mineral soil carbon 10 years post-harvest occurred without clear explanation. On average, forest floor carbon stores were 20% larger 10 years post-harvest than pre-harvest. Even with the large increases excluded, both the fixed-depth approach and equivalent soil mass correction showed there was no significant change in mineral soil carbon stores to 1 m at 10 years post-harvest in the region.

Optical methods including laser diffraction have been increasingly used to measure soil texture and particle size distribution. However, they have not been adopted yet as a routine methodology mainly due to the difficulties in comparing their results to more commonly used techniques (i.e., sedimentation methods). Many attempts exist in the literature to find an agreement between methodologies with relative success. In this work, we aim to improve the agreement between methodologies by adjusting parameters of the laser diffraction analysis, including sample treatment (chemical dispersion, carbonate removal, and sand separation), mode of sample addition (subsampling vs. transmittance matching), and analysis parameters (time of sonication and refractive index). Soil texture class determined by laser diffraction agreed with the sieve–hydrometer method in 78% of the runs when the following parameters were used: (1) Refractive index of 1.44 - 0.100i, (2) 180 s of sonication, (3) sand sieving prior to analysis, and (4) sample dispersion by shaking the sample for 1 h with 5% sodium hexametaphosphate. We observed that adding the entire sample to the analyzer (1 g of soil in 100 mL of dispersant) while keeping the appropriate levels of transmittance through dilution (transmittance matching) is a better way of sample addition in comparison to subsampling, especially for coarser soil samples. This work proposes a standard operation procedure that may broaden the adoption of laser diffraction analysis as a routine soil texture methodology.

Field capacity is a dubious soil physical property, but its use continues because of its perceived value for representing a soil's capacity to store water. Appropriate field capacity estimates can be useful for interpreting data from soil moisture sensors, including those in large-scale monitoring networks, but suitable methods for defining field capacity in this context are unclear. Motivated by the desire to determine optimal field capacity values for the Oklahoma Mesonet, our objectives were (1) to develop and apply an automated time series analysis algorithm to estimate volumetric soil water content at field capacity and corresponding matric potential and (2) to compare the resulting water contents to those calculated from traditional matric potential thresholds (−33 and −10 kPa). Across 118 Oklahoma Mesonet sites and three soil depths (5, 25, and 60 cm), a matric potential threshold of −10 kPa underestimated field capacity water content by 0.010–0.014 cm cm⁻³ (3–4%) on average, and a threshold of −33 kPa underestimated it for every site and depth by 0.055–0.078 cm cm⁻³ (16%−22%) on average. Median matric potentials corresponding to field capacity were −7.6 kPa at the 5-cm depth, −7.2 kPa at the 25-cm depth, and −7.3 kPa at the 60-cm depth. The algorithm developed here can be used to estimate field capacity wherever adequate data are available, and for sites where soil water retention properties are known, matric potentials at field capacity can also be estimated. Using a matric potential of −33 kPa as a standard threshold to represent field capacity is not scientifically justified and should be discontinued.

Grazing annual forages in dryland cropping systems has been used to integrate crop and livestock systems, rejuvenate soils, enhance in-field nutrient cycling and soil organic carbon (SOC), and increase net returns by eliminating harvest expenses and feed delivery. However, cattle (Bos taurus) could potentially degrade soil physical properties by increasing compaction and reducing water infiltration in no-tillage (NT) systems. Minimum tillage (MT) may help correct some of these potential soil quality concerns. The objective of this study was to quantify MT effects on soil properties, forage mass, and weeds compared to NT in a grazed winter triticale [×Triticosecale Wittm. ex A. Camus (Secale × Triticum)] annual forage system from 2020 to 2022 near Jetmore, KS. The experiment had two tillage treatments, NT and MT (sweep plow to a depth of 5–13 cm twice during summer fallow), in a grazed continuous winter triticale cropping system. Bulk density was greater in June, pre-till (1.31 g cm⁻³), compared to August, post-till (1.23 g cm⁻³), across tillage treatments. The mean weight diameter of dry aggregates decreased, and wind-erodible fraction increased with MT. Across years, the mean weight diameter of water-stable aggregates was greater with NT compared to MT. The SOC stocks did not differ between tillage practices near the soil surface, but MT increased SOC at the 5- to 15-cm depth. Nitrate (NO₃-N) concentration was 28% higher with MT compared to NT across depths at the August sampling time. Soil pH was slightly lower in NT (5.81) compared to MT (5.94). Penetration resistance was high due to frequently dry soil conditions, but there were no differences between tillage systems. Early-season forage biomass was greater in MT compared to NT in one out of two seasons. Our findings suggest that MT could be used to mitigate adverse effects of grazing on soil bulk density in NT systems but could cause short-term decreases in dry and wet aggregate stability and increased wind-erodible fraction.

A dense concentration of old-growth forest and a wet, cold climate promote mineral weathering and leaching in coastal temperate rainforest soils. Our objective was to assess soil development and soil organic carbon (SOC) distribution across 18 soil profiles in remote, upland terrain of southeast Alaska where pedon data are sparse. We made soil morphological observations, collected samples, and completed laboratory analyses to measure SOC content, pH, and particle size distribution. The survey of upland backslope soils included north- and south-facing hillslopes derived from three lithologies (slate, metavolcanic, and phyllite). The soils across all sites were very gravelly (51.8 ± 20.4% coarse fragments), acidic (mineral soil pH 4.85 ± 0.45), and moderately deep (96.56 ± 37.80 cm); thin, broken E horizons were underlain by thick, carbon-rich spodic horizons. Soil development was relatively consistent as demonstrated by the Profile Development Index with values from 15 to 26 and Podzolization Index values spanning 8 to 14. A mean pedon SOC stock of 198.02 ± 81.42 Mg C ha⁻¹ (n = 18) was calculated using data collected for all upland organic and mineral soils from our work. The accumulation of SOC was similar among soils formed from contrasting lithologies with averages of 182 ± 15.70 Mg C ha⁻¹ for slate, 188 ± 53.80 Mg C ha⁻¹ for metavolcanic, and 218 ± 124 Mg C ha⁻¹ for phyllite. Our work contributes to soil morphological observations, laboratory data, and SOC stock estimates required to better constrain and model pedogenic processes and SOC stock in remote forests where data sets are limited.