Proceedings - Soil Science Society of America最新文献

Potassium fertilizer recommendations for optimal crop production may be improved by considering the ratio between expanding 2:1 layer silicates (smectite) with non-expanding 2:1 layer silicates (illite). However, the interactive effects between clay mineralogy and various soil tests are not well understood. This study evaluated the relationships among soil test K (STK), water-soluble K, HNO₃-extractable K, pH, apparent cation exchange capacity (CEC_a), soil organic matter, clay content, and smectite:illite ratios. Soil samples (0–15 cm) were collected from 41 locations in central and eastern South Dakota, with textures ranging from sandy loam to clay. Data were partitioned into soils with smectite:illite ratios < 1 (illitic), ≥1 but ≤4.5 (smectitic), and > 4.5 (highly smectitic). Mean pH and CEC_a were lowest in illitic soils, higher in smectitic soils, and highest in highly smectitic soils, whereas STK and water-soluble K were lowest in highly smectitic soils relative to illitic and smectitic. Correlation analysis also showed that STK decreased with increasing smectite:illite ratio. These results suggest that exchangeable and water-soluble K forms are reduced when the proportion of smectite increases. There was a strong, positive relationship between STK and HNO₃-extractable K across all three smectite:illite ratio groups. For soil pH, however, the relationship with STK was positive for illitic and smectitic soil groups, but negative for highly smectitic soils. Overall, these results suggest that the smectite:illite ratio influences the relationship among soil parameters and STK. This improves our understanding of the influence of clay mineralogy on plant-available K and the implications for K fertilizer recommendations.

Long-term agricultural experiments are uniquely positioned to capture the spatiotemporal dynamics of farming system effects on soil profile properties, which typically require decades for measurable changes to become apparent. Soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks were determined at a depth of 0–30 cm in the 34th year of the Rodale Institute Farming Systems Trial (FST), Kutztown, Pennsylvania, USA. Only the organic agriculture (OA) with manure (OA-MNR) system plots had higher SOC concentrations and stocks than the plots of the other systems but only at depths of 0–10 and 10–20 cm, and not on equivalent soil mass (ESM) basis to 30-cm depth. The ESM SOC stocks to 30-cm depth at the tilled plots were 53.3, 56.2, and 61.9 Mg C ha⁻¹ for conventional (CONV), OA-legume (OA-LEG), and OA-MNR systems, respectively. The concentrations and stocks of TN, as well as ESM TN stocks to 30-cm depth at the tilled plots, were higher for both OA systems compared to CONV. However, observations at the recently established reduced tillage (RT) subplots were inconsistent, as at least 10 years may be needed to ensure that differences in tillage treatment effects on SOC can be detected. The results are consistent with many other long-term field experiments that have reported differences in SOC and TN concentrations and stocks only in the topsoil. Overall, the OA-MNR system was advantageous in 2015 in increasing SOC and TN compared to the CONV and OA-LEG systems. Thus, OA practices when combined with composted manure addition can result in increases in the SOC stock in the long term. However, subsequent studies should assess the implications for input of manure sourced from outside the OA-MNR system. Further, soil samples should be taken several times over multiple years to more comprehensively assess management-induced changes in soil properties.

If soil samples are collected using the traditional linear depth methods, comparisons of soil constituents are most often confounded with differences in soil bulk density. Recent interest in quantifying soil C stocks will therefore require improved soil sampling protocols. The dry mass per unit area method eliminates soil bulk density as a measurement factor and therefore allows unbiased comparisons between sampling dates, soil conditions, soil types, sampling techniques, and treatments that affect soil bulk density. This note explains how this simple change in quantifying soil depth eliminates soil bulk density as a factor and improves the quantification of soil C stocks.

Around 30% of peatland in Nordic and Baltic countries has been drained for forestry. Drained peatlands are major sources of dissolved organic carbon (DOC) and nutrients to surface waters, contributing to global warming, eutrophication, and brownification. However, the effects of forest clearcutting and changes in the water table on the biodegradation of DOC to CO₂ are poorly known. We collected peat columns from drained, uncut, and clearcut forests for a common garden experiment and exposed them to high and low water tables to study the effects of clearcutting and water table levels on DOC production and biodegradation. ¹³C-labeled glucose was added to half of the columns to study the effects of labile carbon (C) addition on DOC dynamics. We measured the concentration, quality, and biodegradation rate of DOC monthly by incubating the column porewater at 15°C. Nitrogen (N) limitation of DOC biodegradation was studied by adding ¹⁵N-labeled glycine to half of the incubated water samples. DOC concentrations decreased in the columns with both low water table and glucose addition, while clearcutting had no clear effects. The biodegradation rate of recalcitrant DOC in the later stages of the incubation increased with glycine addition but was not affected by glucose or water table. The results suggest that the biodegradation of recalcitrant DOC in these drained peatland forests is N-limited and dependent on the quality of DOC, which can be seasonally variable.

Arid regions in Northwest China were characterized by water scarcity and soil salinization problems. Understanding water evaporation behavior in salinized soils is crucial to quantify land water loss and control soil secondary salinization. This study aims to explore how specific components in irrigation water influence soil evaporation, focusing on soil pore-water composition, sodium adsorption ratio (SAR) in particular, and their concentrations. Soil columns saturated with different levels of salt concentration (C1, C2, and C3), SAR (S1, S2, and S3), and salt type (NaCl and CaCl₂) were placed in a Climate-Controlled Chamber and underwent evaporation for 20 days. The salt areal ratio, salt crust thickness, crust composition, and their mutual interactions with soil evaporation were investigated. Results show that CaCl₂ tends to precipitate as subflorescence, while NaCl as efflorescence. Subflorescence for the CaCl₂ treatment (1.192 mmol L⁻¹) inhibits evaporation, but takes no effect on evaporation for a C3 treatment (0.392 mmol L⁻¹), indicating that the evaporation rate will not be reduced if a lower salt concentration prevents internal precipitation from reaching the threshold for soil pore clogging. Under varying salt concentrations, SAR affects salt areal ratio ($�r_{\mathrm{salt}}$) differently, while increased salt concentration consistently accelerates $�r_{\mathrm{salt}}$ regardless of SAR levels. Initially, the salt crust enhances evaporation (days 1–3), then suppresses it (days 3–10), and finally evaporation is primarily influenced by soil moisture content (after day 10).

Acid forest soils in the Monongahela National Forest (MNF), West Virginia, were limed at 10 Mg ha⁻¹ by helicopter. Effects of liming were evaluated 1 and 5 years after liming by measuring pH, acidity, and aluminum (Al) and calcium (Ca) concentrations in limed and unlimed soils. First-year results were reported by Fowler et al. Unlimed soils had soil pH of 4.2, while limed soils had pH of 5.6 in O horizons 5 years after liming. Ca concentrations averaged 6.4 cmol_c kg⁻¹ without liming compared to 31 cmol_c kg⁻¹ 5 years after liming. Soil acidity and Al concentrations in O horizons were five times lower in limed soils compared to unlimed soils after 5 years. The beneficial effects of liming these acid forest soils have persisted through 5 years.

Digestion of animal manures with crop residues to produce methane (CH₄) gas is a promising technique to generate “green” energy from agricultural wastes while producing biofertilizers. This study was conducted to understand nitrogen (N) release by biofertilizers from the products of solid-state anaerobic digestion of untreated corn stover and stover treated with aqueous ammonia (NH₄OH), calcium hydroxide (Ca(OH)₂), or Ca(OH)₂ plus Fe₃O₄ nanoparticles blended with dairy manure. Eight biofertilizer materials (feedstocks and digestates) from anaerobic digestion were incubated in the lab for 28 days and the NH₄–N and NO₃–N data obtained were used to predict N release for seasonal plant availability. Of the untreated and alkaline pretreated biofertilizer materials examined, only calcium hydroxide-pretreated digestate (CaD) had greater N release (220 mg kg⁻¹) than the untreated soil control (155 mg kg⁻¹) after 28 days of incubation time. In addition, CaD had the most rapid N release rate (0.16 mg kg⁻¹ day⁻¹) and shortest lag phase time (41 days) with a predicted mineral N release of 777 mg kg⁻¹ at 120 days. However, including Fe₃O₄ nanoparticles slightly suppressed N release. Thus, applying calcium hydroxide-pretreated digestate to soil could complement N supply for crop cultivation as facilitated by the initial carbon to nitrogen (C/N) ratio, despite slight N immobilization when iron nanoparticles were added.

Soil organic matter concentrations are associated with soil texture in some but not in all studies. Why there are variable responses to soil texture can have logical reasons, the most obvious of which are inconsistent historical land uses, interactions with climatic and landscape settings, and management variations within a land use. In an evaluation of surface soils (0- to 10-cm depth) under consistently undisturbed land use from 648 sites across relatively narrow climatic variations in North Carolina, large soil texture variations were assembled into structured populations (n = 27) of sand and clay categories (n = 24). Sand concentration varied from 220 to 881 g kg⁻¹, silt concentration varied from 67 to 517 g kg⁻¹, and clay concentration varied from 47 to 360 g kg⁻¹ (5%–95% limits). Overwhelmingly, total, particulate, and non-particulate organic C and N fractions were more statistically associated with sand concentration than with clay concentration alone. Sand concentration is the inverse of clay + silt summation and is a necessary feature when determining particulate organic C and N. Soil bulk density and sieved soil density were also more closely associated with sand concentration than with clay concentration alone. This study confirmed there was no saturation limit for the accumulation of non-particulate organic C and N (sometimes labeled mineral-associated organic matter). Therefore, sand concentration should be considered the best indicator of soil textural influence on soil organic matter properties and a key contextual feature necessary for soil health assessments.

Soil organic matter (SOM) influences a wide range of ecosystem processes, including nutrient cycling, water movement, plant productivity, and biodiversity. In agricultural landscapes, adjacent land uses often differ in SOM contents and related soil properties, such as soil organic carbon (SOC) stocks, but the direction and magnitude of these effects are inconsistent across studies. We assessed how land uses differed in SOM and related properties in a representative US Midwest agricultural–forest landscape to support land-use and management decisions by local landowners and producers. We measured SOM, bulk density (Db), root biomass, and pH, and estimated SOC stocks, in a Typic Hapludalf under four adjacent land uses (permanent forest, pasture, restored prairie on former pasture, and spruce plantation on former pasture). Surface SOM concentrations and stocks were higher under permanent forest (89 g kg⁻¹ and 85 Mg ha⁻¹, respectively) and pasture (63 g kg⁻¹ and 81 Mg ha⁻¹, respectively) than under restored prairie (49 g kg⁻¹ and 58 Mg ha⁻¹, respectively) and spruce plantation (46 g kg⁻¹ and 46 Mg ha⁻¹, respectively). Land uses also differed in Db, root biomass, and pH, with permanent forest and spruce plantation soils having generally lower Db, more root biomass, and more acidic pH than pasture and restored prairie soils. Specific statistically significant differences depended upon depth in the soil profile. Overall, our results suggest that each land use differentially impacts a unique set of soil properties, precluding any single explanation or management recommendation aimed at improving soil health as a whole.

To mitigate water shortages, mulched drip irrigation disrupts soil-air gas exchange, disturbing the balance between gas production and diffusion in the soil. This study explored the effects of nitrogen (N) application and aerated irrigation on the soil microenvironment, greenhouse gas emissions in the root zone, and processing tomato yields. The objective was to offer a theoretical framework and scientific evidence to guide fertilization practices, improve the soil microenvironment, and enhance crop productivity, especially under aerated irrigation. Two irrigation methods (non-aerated [A0] and aerated [A1]) and two N rates (150 kg·hm⁻² [N1] and 270 kg·hm⁻² [N2]) were tested. Results showed that aerated irrigation increased soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), and ammonium nitrogen (NH₄⁺-N), while N application enriched soil nitrogen content. Both aeration and N application elevated N₂O and CH₄ emissions. Path analysis revealed that fertilization-coupled drip irrigation indirectly influences carbon-nitrogen cycling genes by altering soil nutrient levels, affecting greenhouse gas emissions. Soil nutrients and functional gene abundance directly impacted yield, with nitrate nitrogen (NO₃⁻-N) showing the most substantial direct effect on processing tomato yield (direct path coefficient = −1.047***). Under A1N2 (aerated irrigation with 270 kg hm⁻² N), soil nutrient levels improved (total carbon: 25.19 g·kg⁻¹, SOC: 18.25 g·kg⁻¹, DOC: 93.65 mg·kg⁻¹, TN: 0.97 g·kg⁻¹, NH₄⁺-N: 2.64 mg·kg⁻¹, and NO₃⁻-N: 1.18 mg·kg⁻¹), resulting in a yield of 32.05 t hm⁻², a 23.69% increase over increase over A0N1. Aerated irrigation combined with moderate nitrogen application is recommended for sustainable production to enhance soil fertility and crop yields. However, mitigation strategies such as nitrification inhibitors or optimized irrigation schedules should be employed to minimize greenhouse gas emissions.