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Understanding controls on soil organic carbon (SOC) will be crucial to managing soils for climate change mitigation and food security. Climate exerts an overarching influence on SOC, affecting both carbon (C) inputs to soil and soil physicochemical properties participating in C retention. To test our hypothesis that climate, C inputs, and soil properties would differently affect particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), we sampled 16 agricultural sites (n = 124 plots) in the United States, ranging in climate (mean annual precipitation (MAP)—potential evapotranspiration (PET; MAP-PET)), soil pH (5.8–7.9), and soil texture (silt + clay = 13–96%). As MAP-PET increased, soils increased in oxalate-extractable iron (FeO) and aluminum (AlO), decreased in exchangeable calcium (Caex) and magnesium (Mgex), and received greater C inputs. Soil physicochemical properties did not strongly predict POC, confirming the relative independence of this SOC fraction from the soil matrix. In contrast, MAOC was well predicted by combining AlO + [1/2]FeO with Caex + Mgex in a 'matrix capacity index', which performed better than individual soil physicochemical properties across all pH levels (r > 0.79). Structural equation modeling indicated a similar total effect of MAP-PET on MAOC and POC, which was mediated by total C inputs and the matrix capacity index for MAOC but not POC. Our results emphasize the need to separately conceptualize controls on MAOC and POC and justify the use of a unified soil matrix capacity index for predicting soil MAOC storage. [ABSTRACT FROM AUTHOR]

Site selection is key to successful establishment of fruit and nut trees. The upland soils on which pecan [Carya illinoinensis (Wangenh.) K. Koch] trees are commonly planted in the southeastern United States consist of sites that have recently been in row crop cultivation or pine or hardwood timber. Anecdotal observation suggests that orchards planted to land converted from cultivated row crop fields tends to result in better tree growth and survival than those on land recently converted from timber plantations or wooded areas. The objective of this experiment was to compare growth of first- through third-leaf pecan trees planted on sites with varying land-use history [row crop cultivation or pine (Pinus spp.) tree production up to the year before planting] and to determine the effects of supplemental addition of phosphorus (P), potassium (K), and zinc (Zn) at planting on the two sites. These results suggest that the soil conditions of sites recently in pine timber production limit the growth and development of pecan trees planted to those sites. These limitations result from soil acidity and an exhaustion of soil nutrients and loss of organic matter on pine sites, making the uptake of nitrogen (N), P, K, and calcium (Ca) challenging during the establishment phase unless soils are improved before planting. [ABSTRACT FROM AUTHOR]

The fertilizer industry has attempted to increase P mobility and lability after fertilizer application by using nonconventional phosphates or by including additives in the fertilizer formulation. We incubated granular monoammonium phosphate (MAP), sulfur-coated MAP, humic acid-coated MAP, triple superphosphate (TSP), ammonium potassium polyphosphate (AKPP), and ammonium magnesium phosphate (struvite) with soils from the United States and Brazil in Petri dishes for 56 d. We estimated P mobility by measuring P movement away from fertilizer granules and assessed P lability through sequential chemical fractionation of soil collected from the dishes. In addition, we monitored the change in soil pH with distance from fertilizer placed in the Petri dish. Soil pH changed in response to fertilizer additions as a function of initial soil pH. In fertilized soils, the soil pH response followed a quadratic function as the distance from the fertilizer placement site increased. Soil characteristics influenced P mobility, with mobility decreasing from the Hubbard (12% clay; pH 5.3), to Brazil (20% clay; pH 6.5), to Normania (22% clay; pH 5.5), and then Barnes (31% clay; pH 8.0) soil. The use of MAP-based fertilizers resulted in the greatest mobility, while struvite provided the lowest mobility. In contrast, struvite granules dissolved the least resulting in the highest labile P concentrations, due to direct extraction of fertilizer P from undissolved granules (average of 73% of applied P). Comparatively, TSP provided the lowest amount of labile P (average of 52% applied P). Sulfur and humic acid-coated MAP had no effect on P lability or mobility. [ABSTRACT FROM AUTHOR]

Deciduous azaleas are an important element of residential and commercial landscapes in the United States after substantial trait improvements to increase their market appeal. Despite progress in breeding for ornamental characteristics and cold hardiness, intolerance to elevated pH and calcareous soils continues to limit their use in managed landscapes. Therefore, we assessed the utility of in vitro and greenhouse phenotyping approaches to evaluate and select for improved soil pH tolerance to increase the efficiency of breeding for this important trait. The research presented offers an example for implementing image-based phenotyping to expedite cultivar development in woody ornamental crops. [ABSTRACT FROM AUTHOR]

Forages are important throughout the south-east USA for livestock production and wildlife habitat. However, little is known about how forage species commonly grown in this region influence soil-quality indicators. The objectives of this research were to determine short-term response of soil water-stable aggregates (WSA) and density of fungal hyphae (DFH) to: (i) forage species or mixtures grown at identical soil pH levels and (ii) forage species or mixtures grown at field-state versus adjusted soil pH levels. Nine warm-season species (sole crop) and eleven cool-season sole crop or legume-grass mixtures were grown under protected culture in southern coastal plain soil microcosms. Levels of WSA and DFH, and plant shoot and root biomass were evaluated after two 12-week experimental growth periods in both field-state and adjusted-pH soil. Both warm- and cool-season forage species significantly altered short-term responses of WSA and DFH levels; these responses differed when the soil pH was adjusted from the field state with lime addition. The short-term responses of both WSA and DFH to lime addition in coastal plain soil were negative only when certain forage species were grown, and no response was detected for the control. It appeared that differences in plant shoot and root developmental characteristics played a key role in soil WSA and DFH responses to the species studied. Further long-term studies are needed to understand how these relationships are expressed in more variable environments over expanded time frames. [ABSTRACT FROM AUTHOR]

Nitrogen source and rate effects on velvet bent- grass (Agrostis canina L.; VBG) putting greens are not well documented, particularly in the north central United States which has different conditions than areas where VBG is normally grown. Acidic soil pH is perceived as necessary for VBG; in nonacidic soils, acidifying fertilizers may pro- vide better VBG quality than less or nonacidic fertilizers. We wanted to determine the effects of N sources representing a range of acidity and N rates (49, 146, 244 kg ha-1 yr-1) on VBG agronomic and playability characteristics when grown on alkaline soils. Fertilizer treatments were applied at 2-wk intervals to Vesper' VBG putting greens using liquid forms of ammonium sulfate, urea, ammonium nitrate, and calcium nitrate. Separate trials were conducted on two root zones: an 80:20 sand/peat mixture (pH 7.8) and a Troxel silt loam (pH 7.0). Nitrogen source usually had negligible effects on turf characteristics, though occasionally calcium nitrate resulted in poorer quality or shoot density than other sources. Clipping yield, shoot density, and relative chlorophyll index increased, and ball roll distances decreased, as N rate increased. On sand, not even the 244 kg ha-1 yr-1 rate of N guaranteed acceptable turf quality. On silt loam, 146 kg ha-1 N yr-1 usually provided acceptable turf quality, though quality was occasionally improved at 244 kg ha~ N yr1. Velvet bentgrass suffered from mid-summer stress alleviated by higher rather than lower quantities of N fertilizer. [ABSTRACT FROM AUTHOR]

Sugar maple (Acer saccharum Marsh.) decline has occurred throughout its range over the past 50 years, although decline symptoms are minimal where nutritional thresholds of Ca, Mg, and Mn are met. Here, we show that availability of these elements also controls vascular plant species composition in northern hardwood stands and we identify indicator species of these nutrient thresholds. Presence and abundance of vascular plant species and data on 35 environmental variables were collected from 86 stands in New Hampshire and Vermont (NHVT) and Pennsylvania and New York (PANY). Nonmetric multidimensional scaling ordination was used to determine which variables affected presence and abundance of species; both measures gave similar results. A base cation – acid cation nutrient gradient on axis one accounted for 71.9% (NHVT) and 63.0% (PANY) of the variation in the nonmetric multidimensional scaling ordination. Measures of Ca, Mg, and pH formed the base end and Al, Mn, K, soil acidity, and organic matter the acid end in both subregions. In both subregions, sugar maple foliar Mg and Ca had the strongest association with the base end of axis 1; exchangeable Al in NHVT and foliar Mn in PANY were strongly associated with the acid end. McNemar’s exact test and indicator species analysis were used to determine which species were present in stands that met the nutritional thresholds for Ca, Mg, and Mn foliar chemistry. McNemar’s exact test identified 16 species in NHVT and PANY, 16 additional species in NHVT only, and 12 additional species in PANY only. Indicator species analysis identified a subset of these species with the highest frequency of occurrence. Indicator species could provide land managers with a diagnostic tool for determining where on the landscape sugar maple is “at risk” or likely to remain healthy in the face of stresses. Le dépérissement de l’érable à sucre (Acersaccharum Marshall) est survenu partout dans l’aire de répartition de cette essence au cours des 50 dernières années mais il y a très peu de symptômes de dépérissement aux endroits où les seuils nutritionnels pour Ca, Mg et Mn sont atteints. Nous montrons ici que la disponibilité de ces éléments régit également la composition en espèces de plantes vasculaires dans les peuplements de feuillus nordiques et nous identifions des espèces indicatrices des seuils pour ces nutriments. La présence et l’abondance des espèces de plantes vasculaires ainsi que 35 variables environnementales ont été mesurées dans 86 peuplements des tats du New Hampshire et du Vermont (NHVT) ainsi que ceux de la Pennsylvanie et de New York (PANY). L’ordination de mesures multidimensionnelles non paramétriques a été utilisée pour déterminer quelles variables influencent la présence et l’abondance des espèces; les deux mesures ont produit des résultats similaires. Un gradient de nutriments allant des cations basiques à acides sur l’axe un expliquait 71,9% (NHVT) et 63% (PANY) de la variation dans l’ordination. Les mesures de Ca, Mg et de pH formaient la partie basique et Al, Mn, K, l’acidité du sol et la matière organique formaient la partie acide dans les deux sous-régions. Dans les deux sous-régions, le Mg et le Ca foliaire de l’érable à sucre était le plus étroitement associé à la portion basique de l’axe un; l’Al échangeable dans la sous-région NHVT et le Mn foliaire dans la sous-région PANY étaient fortement associés à la portion acide. Le test de McNemar et l’analyse des espèces indicatrices ont été utilisés pour déterminer quelles espèces étaient présentes dans les peuplements où les seuils nutritionnels pour Ca, Mg et Mn étaient atteints dans les feuilles. Le test de McNemar a identifié 16 espèces dans les deux sous-régions, 16 autres dans la sous-région NHVT et seulement 12 autres dans la sous-région PANY. L’analyse des espèces indicatrices a identifié un sous-ensemble des ces espèces dont la fréquence était la plus élevée. Les espèces indicatrices pourraient fournir aux aménagistes du territoire un outil de diagnostique pour déterminer à quel endroit le paysage d’érable à sucre est à risque et où il restera sain face aux stress. Note : l.7 de l’abstract, saccharum Marshall au lieu desaccharum Marsh. [ABSTRACT FROM AUTHOR]

Manganese (Mn) toxicity is common in tropical acid soils, second only to aluminum toxicity. Changes in soil pH and redox potential (Eh) caused by soil moisture conditions and organic amendments certainly affect Mn solubility and toxicity to plants grown in soils with high Mn reserves. Laboratory incubation and greenhouse experiments were conducted to quantify such effects using a high-Mn Oxisol and a moderate-Mn Mollisol from Hawaii, with soybean (Glycine max L. cv. Kahala) being a test crop. The soils were mixed with a green manure (leucaena leaf) at 0, 10, and 20 g kg−1, and were incubated at 24 ± 1°C at 80% of field water holding capacity—equilibrated with air (FC), or N2 gas (N2)—or submerged under 8 cm of water. Soil pH, Eh, and soluble Mn as measured in saturated paste extract, Mehlich-3 and hydroxylamine hydrochloride (NH2OH) solutions were periodically determined over 56 days of incubation. The submergence and N2 treatments increased soil pH towards 7.0 and decreased soil Eh from 600 mV to between 300 and 400 mV, indicating a more reducing environment, which seemed to be controlled by the MnO2-Mn2+ and/or FeOOH-Fe2+ redox couples. Green manure additions had similar effects, but to a lesser extent. Consequently, soluble soil Mn concentrations increased by 100–1000 fold relative to those of the controls (no manure, at FC). There was a marked decrease in soybean growth and a marked increase in leaf Mn concentration in the treatments of submergence and green manure additions. A 10% reduction in dry matter yield was expected when leaf Mn exceeded 200 mg kg−1, leaf Ca/Mn (weight-to-weight) <80, saturated paste Mn >0.50 mg L−1, Mehlich3 Mn >200 mg kg−1, and NH2OH Mn >1100 mg kg−1. The effects were most evident at 14–28 days after incubation. [ABSTRACT FROM AUTHOR]

Soil erosion and the gradual acidification of soils are two major obstacles limiting crop productivity in the Palouse region of eastern Washington and northern Idaho. New tillage practices that replace the traditional moldboard plow are needed to maintain more surface cover to reduce erosion. Two tillage systems and lime were compared at two locations on silt loam soils. Treatment combinations were two levels of tillage (subsoil ridge till (SSRT) and plowing) and two levels of lime (0 and 2.68 Mg ha−1). Crop rotations were barley (Hordeum vulgare L.)–pea (Pisum sativum L.)–wheat (Triticum aestivum L.) at both sites in the US that receive 500–560 mm precipitation annually. Tillage and lime options were implemented after barley stubble and studied for 2 years. Microbial biomass, respiration, and dehydrogenase enzyme activity were enhanced at the Washington site under SSRT because of the initially higher residue levels and because residues were maintained at or near the soil surface compared to plowing. Liming increased soil pH and respiration and maintained microbial biomass at about 100 ug C g−1 higher than for the unlimed plots at the end of 2 years. Soil moisture increased under SSRT at some profile depths. Pea seed yield at the Washington site and wheat yield at the Idaho site were significantly higher for SSRT compared to plowing. Lime significantly increased wheat yield only at the Washington site. Significantly higher surface residue was maintained during the study period from SSRT compared to plowing which contributed to lower rates of soil erosion in winter wheat 30 months after plot establishment. At the Washington site, surface residue levels were 20% in spring of 1992 for SSRT compared to less than 1% for plowing. One year later, soil erosion under winter wheat in spring of 1993 was 1.3 Mg ha−1 for SSRT compared to 8.4 Mg ha−1 for plowing. In general, the higher surface residue maintained under SSRT increased microbial activity, maintained higher surface residue, and reduced erosion in winter wheat, the vulnerable phase in the crop rotation for erosion. [Copyright &y& Elsevier]

Soil acidity and fertility management are critical for crop production on Coastal Plain soils of the southern and southeastern USA. Grasses and legumes are the primary crops grown on these soils. Hybrid bermudagrass (Cynodon dactylon (L.) Pers.) and bahiagrass (Paspalum notatum) are the major warm-season grasses while annual ryegrass (Lolium multiflorum Lam.) is the dominant cool-season grass. Bahiagrass tolerates acidity and low soil fertility. Bermudagrasses tolerate moderate soil acidity levels and readily respond to N, P, and K fertilization. Annual ryegrasses are highly responsive to limestone, N, and P. High rates of ammonium N applied for grass production rapidly increase acidity due to nitrification in these low-buffer-capacity soils. Liming these soils to increase pH improves P use efficiency and forage production. Fertilizer P increased soil test P 38% as soil pH was raised from 4.5 to 6.2 in a Lilbert loamy fine sand (thermic Arenic Plinthic Paleudult). Forage legume crops respond favorably to applied P, K, and B on limed Ultisols. Limestone applied to strongly acid soils increased alfalfa yields greater than 6.2Mgha[SUP-1]. The critical 0- to 15-cm-depth, soil test P level is 20mg kg[SUP-1] for alfalfa (Medicago sativa L.) using the pH 4.2 NH[SUB4]OAc-EDTA extractant on limed Coastal Plain soils. Alfalfa response to applied B was 3.9 Mgha[SUP-1] and was economical to 4.2 kg ha[SUP-1]. Regression analysis predicted that raising the level of hot-water soluble B from 0.3 to 0.7 mgkg[SUP-1] in the 5- to 15-cm depth increased alfalfa dry matter yield 9 Mgha[SUP-1]. The level of hot-water soluble B in the 0- to 5-cm and in the 0- to 15-cm depths did not correlate with yield. [ABSTRACT FROM AUTHOR]

Presents research which showed that rapid changes to ecosystem processes will be superimposed upon and modulated by differences in substrate pH. Studies of trace-gas flux in the Arctic; Factors in land-atmosphere exchange; Soil pH boundary along the Arctic Foothills, Alaska, separating ecosystems; Traits of non-acidic tundra.

The article discusses the debut of the U.S. National Ecological Observatory Network (NEON) prototype. Former director of the U.S. National Science Foundation (NSF), Rita Colwell, proposed the idea during her tenure. Topics include a description of the first prototype site which will be opened on Table Mountain in Colorado and what NEON's objectives will be including environmental monitoring of soil hydrogen-ion (pH) contentration.