Soil has been proposed as a driver explaining the development of monodominant forests in the tropics, for example, Gilbertiodendron dewevrei forests (GDF) in central Africa. The aim of this study was to compare the physical and chemical properties of soils under GDF with those under an adjacent mixed forest (AMF), while controlling for topography. To this end, we set up sixteen 0.25-ha plots according to forest type and topography (plateau vs. bottomland), in the Yoko forest reserve, Democratic Republic of Congo. In each plot, we measured litter thickness and collected a total of 80 soil samples at depths of 0–5, 5–10, 10–20, 20–40 and 120–150 cm, for standard physical and chemical analyses. When controlling for topography and soil texture, we found that most of the chemical properties of soils under GDF did not differ from those of soils under AMF, particularly acidity, cation concentration, total N and the C:N ratio. The litter layer was 2.3 times thicker under GDF than under AMF stands, and, for a given texture, soils under GDF had a slightly higher organic C concentration in the 0–5 cm soil layer. This study suggests that G. dewevrei stands modify organic matter dynamics, which may be important in maintaining its monodominance.

This paper evaluates the possible contribution of aeolian silt to soils of Mt. Ślęża (southwest Poland). Silt loam textures are common across Lower Silesia and are often confused with silt clay loam, especially at the outer boundaries with thin loess deposits. Eight study sites with different thicknesses of silt loam mantles that are covered and/or mixed with underlying sediments were examined in the field. To test our hypothesis, we analyzed the particle size and geochemistry of representative horizons. Concentrations of major and trace elements as well as their cross ratios confirmed the aeolian origin of silt loam materials and clearly distinguished them from basal sediments. There is a clear relationship between the presence and depth of aeolian mantles and mixing zones with the type of underlying material. Furthermore, the incorporation of aeolian silt to regoliths/soils was a main agent initiating and stimulating clay translocation leading to the formation of an argic horizon below the silt mantles. Mixing aeolian silt with acid granite regoliths and further illuviation resulted in the formation of alisols, while silt contributions to serpentine sediments resulted in development of skeletic luvisols. Soils receiving very weak input of aeolian silts remain as leptosols/cambisols.

Laboratory studies were conducted to evaluate flumetsulam adsorption and mobility in seven Mississippi soils of different organic matter content, pH, and texture. Adsorption isotherms were determined for all soils using a 1:1 (soil: water) technique. In six of seven soils, Freundlich n constants were close to unity, suggesting a partitioning-like adsorption mechanism for flumetsulam. Mobility was examined using packed soil columns. 14C-flumetsulam recoveries in leachate ranged from 1 to 70% and were influenced by both organic matter content and soil pH. However, the effects of organic matter content and soil pH were not independent. Consequently, clear relationships between flumetsulam mobility and either organic matter content or soil pH were not established across all soils. However, among soils of similar pH (7.5 ± 0.3), mobility decreased linearly (R 2 = 0.75) as organic matter content increased from 0.7 to 3.6%. Across soils with similar organic matter content (3.9 ± 0.3%), mobility increased linearly (R 2 = 0.98) as soil pH increased from 5.3 to 7.2. Net adsorption constants (K d ) provided a more accurate assessment of flumetsulam mobility across all soils than K oc .

‘Tracy′, ‘Tracy-M′, and ‘Centennial′, soybean [Glycine max (L.) Merr.] cultivars were evaluated under greenhouse and field conditions for their tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one]. The I50 (50% injury) concentration of metribuzin, as determined in nutrient culture, for Tracy-M was more than three times the I50 for Tracy, but was equivalent to the I50 for Centennial. Data from greenhouse and field studies on Sharkey clay and Dundee silt loam soils indicated that Tracy-M was more tolerant to metribuzin than its parent selection, Tracy, but no more tolerant than Centennial when metribuzin was applied preplant soil incorporated or surface preemergence alone or in combination with several dinitroaniline herbicides.

Response of flax, canola, field pea, sunflower, field corn, lentils, and common buckwheat to soil residues of CGA-131036 and chlorsulfuron applied at 22 g ai ha–1 was determined on two soil types at Morden, Manitoba. on a fine sandy loam with a pH of 7.4 and 4.5% organic matter, the length of time required before crops showed no phytotoxicity from CGA-131036 residues was: sunflower 4 yr; canola and common buckwheat 3 yr; flax 2 yr; field pea and field corn 1 yr. on a clay loam with a pH of 6.5 and 5.3% organic matter, the corresponding duration was: lentil, canola, and sunflower 3 yr; flax and field pea 1 yr. Chlorsulfuron residues persisted somewhat longer than CGA-131036 residues on the sandy loam but not on the clay loam.

Research was conducted to determine the suitability of the Fermi-Dirac distribution function for modeling the seedling emergence of downy brome, johnsongrass, and round-leaved mallow, as influenced by burial depth. Six sets of previously published emergence data were used to formulate the model and test its adequacy. Two independent johnsongrass emergence data sets were used to validate the model. Constant temperature growth chamber studies were conducted to evaluate the effects of temperature and moisture on the model parameters. The Fermi-Dirac distribution function was found to adequately describe the seedling emergence of downy brome, johnsongrass, and round-leaved mallow as indicated by a good visual data fit, narrow confidence intervals for the model parameters, and regression analysis of observed vs. modeled data. Although this function is a model used in physical science, its parameters can be related to abiotic factors such as soil texture, temperature, and moisture.

The photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated. Ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr, and 87 and 8% degradation of imazamethabenz and atrazine in aqueous solutions, respectively, after 48 h. The order of susceptibility to photolysis in decreasing order was imazaquin = imazethapyr > imazapyr > imazamethabenz > atrazine. In soil Studies, 45% of imazaquin and 52% of imazethapyr dissipated from moist sand after 48 h of exposure. Herbicide dissipation on air-dry sand and on field capacity and air-dry silty clay loam was less than 10% in most instances. Atrazine photolysis was not detected. This research indicates that photolysis of imidazolinone herbicides in solution is rapid. Photolysis on soil occurs readily on coarse-textured wet soils probably due to greater availability of the herbicide for photochemical alteration.

Broadcast applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] pellets and foliar sprays were tested at four rates for hardwood control and safety to loblolly pine (Pinus taeda L.) at each of eight study locations differing in soil characteristics. Reduction in the number of hardwoods in the stand (hardwood density reduction) was greater with the pellet on soils with more than 60% sand, while the liquid formulation was most efficacious for finely textured soils. Hardwood density reduction with the pellet was negatively correlated with percent silt, clay, soil organic matter, and cation exchange capacity, and positively correlated with percent sand. With foliar sprays, hardwood density reduction was positively correlated with hexazinone rate and negatively correlated with soil pH. Pine mortality was positively correlated to percent sand with the pellet and negatively correlated to soil pH with broadcast sprays. Regression models incorporating pine height, herbicide rate, soil texture, cation exchange capacity, soil organic matter, and acidity could explain up to 78% of the variation in hardwood density change and 77% of the variation in pine mortality. Selective control of hardwoods in young loblolly pine stands is a function of hexazinone rate, formulation, and various soil factors.

Bulk apparent soil electrical conductivity (ECa) sensors respond to multiple soil properties, including clay content, water content, and salt content (i.e. salinity). They provide a single sensor value for an entire soil profile down to a sensor-dependent measurement depth, weighted by a nonlinear response function. Because of this, it is generally difficult to elucidate strong relationships between ECa and the measured properties of individual soil layers. This research investigated inversion of the equations that govern the ECa-depth response relationship to reconstruct the soil conductivity in profile layers using data collected in multiple fields in the Midwest US. Layer conductivities obtained by inversion were first validated by comparison with true conductivities measured as a function of depth with an ECa-sensing penetrometer. Then, the validated layer conductivities were related to laboratory- measured soil properties. Inversion worked well but sometimes required iterative adjustment of initial conditions and other input parameters to obtain best results. Strong linear relationships (r2≥0.76) were obtained between inversion-estimated and measured layer conductivity data in all cases, sometimes with a truncated depth range. Layer conductivity data was successfully used to estimate soil texture fractions in the two alluvial fields examined. This was not the case for a claypan soil field, where there appeared to be parameters other than texture strongly affecting the EC response. Further examination of this approach is warranted to potentially provide improved ways to estimate depth-variable soil properties using ECa.

Methiozolin is a new isoxazoline herbicide being investigated for selective POST annual bluegrass control in creeping bentgrass putting greens. Glasshouse and field research was conducted from 2010 to 2012 in Tennessee and Texas to evaluate annual bluegrass control efficacy with methiozolin. Application placement experiments in the glasshouse illustrated that root absorption was required for POST annual bluegrass control with methiozolin at 1,000 g ai ha−1. Soil-plus-foliar and soil-only applications of methiozolin reduced annual bluegrass biomass greater than treatments applied foliar-only. Field experiments evaluated annual bluegrass control efficacy with two application rates (500 and 1,000 g ha−1) and six application regimes (October, November, December, October followed by [fb] November, November fb December, and October fb November fb December) on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1,000 g ha−1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha−1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Most sequential methiozolin application regimes controlled annual bluegrass more than single applications. On sand-based greens, sequential application programs controlled annual bluegrass 70 to 79% compared to 85 to 92% on soil-based greens. Responses indicate that methiozolin is a root-absorbed herbicide with efficacy for selective control of annual bluegrass in both sand- and soil-based creeping bentgrass putting greens.

Scotch broom is a large, leguminous shrub that has invaded 27 U.S. states. The species produces seeds with a hard coat that remain viable in the soil for years. Growth-chamber studies were conducted to determine effects of temperature regime and cold-stratification period on seed germination. Seedling emergence, mortality, and biomass also were studied in response to sulfometuron and metsulfuron herbicides and variation in soil texture and watering regime. Germination was greatest for a dark/light temperature regime of 15/20 C. Initial rates of germination increased as stratification period was varied from 0 to 60 d, but final germination after 90 d did not differ significantly among periods. Applied alone or in combination, sulfometuron and metsulfuron decreased biomass and increased mortality of seedlings. Mortality from simulated soil drought was greater in the presence versus absence of sulfometuron (20 and 6% mortality, respectively) probably because the herbicide reduced root biomass by 58 to 95%. Invasiveness of Scotch broom is facilitated by a prolonged period of germination across a broad temperature range. Increased control of Scotch broom seedlings with sulfometuron is likely if application is timed to expose recently emerged seedlings to developing conditions of soil drought.

Common ragweed is a troublesome allergenic invader and noxious weed of several crops. Despite extensive research to understand the factors affecting its invasion, the role of environmental stresses and soil types on survival and growth is poorly understood. The objective of this study was to determine the effects of drought, salinity, and soil types on survival, growth, and nutrient uptake of ragweed in greenhouse experiments to predict its invasiveness in Turkey. Three separate experiments, with five drought intensities (100, 75, 50, 25, and 12.5% of field capacity [FC]), four levels of salinity (0, 3, 6, and 12 dS m−1), and five soil types varying in sand, silt, and clay content were performed. Severe drought and salinity levels reduced seedling survival, while soil type had no effect. Increasing drought and salinity negatively affected growth and nutrient uptake; the poorest growth was observed under severe drought intensity. Ragweed exhibited intensive tolerance to drought, even severe levels, while it tolerated salinity up to 6 dS m−1 for seedling survival. Growth was negatively affected above 3 dS m−1. The highest and lowest nutrient accumulations were recorded under moderate and extreme drought intensities, respectively. Similarly, the highest Na accumulation was observed under extreme saline conditions, whereas the highest P uptake and K/Na ratio were achieved under nonsaline conditions (0 dS m−1). Variation of soil texture had no effect on growth and nutrient uptake. The highest Ca, Mg, and Na accumulations were recorded on clay soil, while higher P accrued on sandy-loam soil. Increased tolerance of ragweed to severe drought and moderate salinity and its nonselective nature for soil type indicate that semiarid and partially arid regions in Turkey have plenty of vacant niches for ragweed invasion.

Despite the important functional role of deep roots in withdrawing water during drought, direct measurements of root distribution are very rare in tropical rain forests. The aim of this study was to investigate the root distribution of Entandrophragma cylindricum, a common tree species in the Central African semi-deciduous rain forest, in Ferralsols and Arenosols. We dug two pits to a depth of 6 m in Ferralsols and two pits to a depth of 3 m in Arenosols, close to E. cylindricum trees. The vertical soil profiles were divided into 10 × 10-cm grid cells and the roots counted were distributed in three diameter classes. We fitted a root distribution model to our dataset. We found that vertical root distribution was shallower in Arenosols than in Ferralsols. Root penetration was not stopped even by a Ferralsol with high gravel content in its subsoil. Overall, our measurements showed that 95% of all roots were distributed to depths of between 258 and 564 cm from the soil surface, which is much deeper than the 95 cm depth previously reported in the literature for tropical rain forests. As sampling depth could explain this discrepancy, we recommend a sampling depth of at least 3–5 m to accurately estimate root distribution. The drier the dry season, the deeper the sampling depth should be. Our results are consistent with global models of root distribution in forest ecosystems, which are driven by climate variables. We thus suggest that deep rooting could be common in rain forests with a marked dry season.

The availability of spatial data sourced from either field-derived or satellite-based systems has created new opportunities to estimate and/or monitor changes in carbon sequestration rates, climate change impacts or the potential habitat alterations occurring across large landscapes. However, an effort to create models is not standardized, in part, due to different needs and data sources available for the models. For example, data may have different spatial resolutions with varying degrees of complexity in regards to inputs and statistical methods. This study determines effects of 20, 15, 10, five and one km sampling resolutions on detection of changes in net primary productivity (NPP), occupancy selection criteria for areas to be included in the sample and identification of significant variables impacting NPP in Indonesia forests. Production forest designated for selective harvest was used to define the sampling areas. Variances explained by predictive models were similar across cell sizes although relative importance of variables was different. Partial dependence plots were used to search for potential thresholds or tipping points of NPP change as affected by an independent variable such as minimum daytime temperature. Applying different cell occupancy selection rules significantly changed the overall distribution of NPP values. The magnitude of those changes within a cell size varied with changes in cell size. The mean estimated NPP for production forests across Indonesia differed significantly at every sampling resolution and occupancy selection criteria. Lows ranged from 1.107 to 1.121 kg C m−2 yr−1 for the 1-km cell size for the three occupancy selection criteria with highs ranging from 1.245 to 1.189 kg C m−2 yr−1 for the 20-km cell size. The difference in NPP values between these two cell sizes for the three occupancy selection criteria extrapolates to a range in annual biomass of 132 × 106 to 66 × 106 t for the total area of production forests in Indonesia.

Variation in understorey irradiance is both a cause and consequence of the structure and dynamics of closed-canopy forests, which are also influenced by soil nutrients and water availability. We tested the hypothesis that understorey light regimes differ among four mixed dipterocarp forest types that share the same rainfall, but grow on different soils along an edaphic gradient at one site in Borneo. Based on data from photosynthetically active radiation sensors deployed at 1-m height at 36 locations for 351 sensor-days, we found significant soil-related variation in irradiance. The more productive forest types on clay and fine loam had lower daily photosynthetic photon flux density (PPFD) than those on the more nutrient-depleted and better-drained sandy loam and loam. They also had fewer moderate to high-intensity sunflecks, and a greater proportion of their daily PPFD came from low-intensity light. Understorey irradiance did not, however, monotonically decline with increasing soil resources. Forests on intermediate soils had greater irradiance than those with more and less soil resources, due to steeper slopes. Plant communities arrayed on resource gradients are commonly used to test hypotheses of environmental factors driving their assembly. Our results indicate that consideration of multiple resource dimensions in such tests is critical.

Equations were developed to predict soil matric potential as a function of soil water content, texture and bulk density in sandy soils. The equations were based on the additivity hypothesis - that water-retention of a whole soil depends on the proportions of several particle size fractions, each with fixed water-retention characteristics. The new model is an advancement over previously published models in that it embodies three basic properties of water-retention curves: a) matric potential is zero at saturation water content, b) matric potential approaches -∞ as water content approaches zero, and c) volumetric water content in dry soil is proportional to bulk density. Values of model parameters were taken from the literature, or estimated by fitting model predictions to data for sandy soils with low organic matter content. Most of the variation in water-release curves in the calibration data was explained by texture, with negligible effects of bulk density and sand particle size. The model predicted that variation in clay content among soils within the sand and loamy sand textural classes had substantial effects on water-retention curves. An understanding of how variation in texture among sandy soils contributes to matric potential is necessary for interpreting biological activity in arid environments.

Plant productivity, distribution and diversity in tropical rain forests correlate with water availability. Water availability is determined by rainfall and also by the available water capacity of the soil. However, while rainfall is recognized as important, linkages between plant distribution and differences among soils in available water capacity have not been demonstrated. One reason for this may be that measurements of soil moisture, such as gravimetric water content, may be overly simplistic. To investigate this, we compared two sites in Panama, Allee and Rio Paja, which have similar rainfall but different plant communities. Soil water release curves were obtained from about −0.1 MPa to −9 MPa, permitting us to calculate available water capacity. The Rio Paja site had 17% greater available water capacity (between −0.1 MPa to −3 MPa), whereas the gravimetric water content at Rio Paja was lower by 16% in rainy season and by 41% at the end of the dry season. Hence soil gravimetric water content and soil available water capacity did not correspond. The results suggest that available water capacity may better predict plant distributions. Hence, whenever possible, available water capacity should be determined in addition to gravimetric water content.