Till Sites Research Articles

Predicting productivity of trembling aspen in the Boreal Shield ecozone of Quebec using different sources of soil and site information

Site quality index (SQI) of trembling aspen ( Populus tremuloides Michx) in the Boreal Shield of Quebec was predicted using two sources of information: (1) mappable permanent site variables derived from permanent sampling plots and other sources and (2) measured soil and site properties including both biological and permanent site variables. General mappable information did not produce reasonable relationships ( R 2 < 0.25) with SQI while measured variables were able to explain much of trembling aspen SQI variability. For the two parent material types found in our study, i.e. fluvial and till, there was no difference between median SQI values between groups. However, different soil and site variables were better at predicting trembling aspen productivity for the individual parent material types. As much as 60% of the variability in trembling aspen productivity was explained when both biological and permanent site variables were considered in stepwise regression models. When treated individually, models developed for fluvial sites better explained trembling aspen productivity compared to models developed for till sites. Moreover, the ability of the model to predict trembling aspen productivity on till sites when using permanent site variables alone, e.g. soil texture, elemental chemistry and elevation was decreased ( R 2 < 0.3). This indicates that the inclusion of biological site variables such as overstory species composition and forest floor properties provide a major contribution to SQI prediction and are necessary to yield high R 2. Overall, the data indicate that the traditional mapping of landscape attributes such as drainage and deposit as well as inferred soil geochemistry do not contribute much to explaining SQI. At present, field measurements are needed to predict SQI with a reasonable degree of precision within a forest management unit.

Carbon sequestration, vegetation dynamics and soil development in the Boreal Transition ecoregion of Saskatchewan during the Holocene

Boreal forest soils have the potential to sequester large amounts of carbon by accumulating charcoal from fire. Some suggest that sequestration rates could be large enough to account for some of the missing sink in the global CO 2 budget, but further data on soil charcoal pools are necessary to adequately develop boreal carbon budgets under a changing climate and fire regime. The primary objective of this study was to determine the amount of charred wood in surface mineral soil horizons (Ah) of the Boreal Transition of Saskatchewan, a fire-prone grassland forest ecotone region of western Canada. A second objective was to use the charcoal data to infer vegetation dynamics and the development of these Ah horizons as a function of parent material type, i.e. glacio-fluvial, glacio-lacustrine and glacial till. The latter objective served to provide information in regards to future vegetation shifts and ecosystem C budgets of Boreal Plain ecosystems under climatic warming. The carbon fraction measured as charcoal is an important component of organic matter in Ah horizons of Chernozemic soils in Saskatchewan and differs from the classical model of humus fractions in Chernozems which suggests that it is a system created from microbial degradation of root litter only. The carbon sequestered as charcoal within the whole ecoregion was estimated at 36.1 Tg, which is the lower limit of the global annual rate of charcoal accumulation in terrestrial environments estimated from experimental fires. Charcoal pools were consistently lower in the fluvial soils relative to the lacustrine and till soils. We suggest a model where dry conditions and low water availability prevailing under the coarser fluvial soils during the Holocene favoured the dominance of low productivity herbaceous vegetation that led to a high ash to charcoal production ratio from fire and to the development of relatively thick Ah horizons through below ground additions of organic matter from root decay. We propose that the more available water in lacustrine and till soils favoured the growth of trembling aspen which, through less frequent/intense fires relative to grasslands and incomplete burning of the woody material, led to high charcoal accumulation rates in soil. The development of thick Ah horizons in lacustrine soils likely occurred during a warm and dry period of the early Holocene (i.e. the hypsithermal) when herbaceous vegetation invaded forested land or during dry spells in the mid to late Holocene (e.g. the Medieval Warm Period) when opening of forest canopies occurred, thus augmenting light transmission to the forest floor and favouring the growth of herbaceous vegetation in the understory. Such events did not create deep Ah horizons in the tills soils as a consistent rock impediment near the surface limited the penetration of understory roots at greater depth. These results suggest that fluvial sites my be the first shifting to herbaceous vegetation in the future due to climatic warming, followed by till sites and then lacustrine sites.

Characterization and Quantification of Pneumatic Fracturing Effects at a Clay Till Site

Environmental fracturing offers assistance to remediation efforts at contaminated, low-permeability sites via creation of active fracture networks, and hence, reduction of mass transport limitations set by diffusion in low-permeability matrices. A pilot study of pneumatic fracturing, focusing on direct documentation of fracture propagation patterns and spacing, was performed at a typical basal clay till site. The study applied a novel package of documentation methods, including injection of five tracers with different characteristics (bromide, uvitex, fluorescein, rhodamine WT, and brilliant blue), subsequent tracer-filled fracture documentation via direct and indirect methods, and geological characterization of the fractured site. The direct documentation methods consisted of Geoprobe coring, augering, and excavation. A mass balance and conceptual model have been established for the distribution of the injected tracers in the subsurface. They reveal that tracer was distributed within 2 m of the fracturing well, mainly in existing fractures above the redox boundary (2 to 4 m.b.s.; 5 to 10 cm spacing). Spacing of observed tracer-filled fractures was large (>1 m) at greater depths. The number of fractures induced/activated could possibly be increased via adjustments to the fracturing equipment design.

Gaseous mercury emissions from natural sources in Canadian landscapes

Field measurements of mercury air‐surface exchange from natural settings were made in various Canadian landscapes. Soil and water samples were analyzed for mercury concentrations, and air‐surface exchange fluxes from these substrates were determined using dynamic chamber, micrometeorological, or modeling methods. Environmental variables, including air and soil/water temperature, solar radiation, humidity, and wind speed, were monitored concurrently with the air‐surface exchange to better understand the processes affecting the environmental cycling of mercury. Average mercury fluxes from aquatic landscapes ranged from 0.0 to 5.0 ng m−2 h−1 with total mercury concentration in water ranging from 0.3 to 6.5 ng L−1. A significant correlation (R2 = 0.47) was found between gaseous Hg fluxes and total Hg concentration in water. Mean gaseous Hg fluxes from forest soils varied from −0.4 to 2.2 ng m−2 h−1, while those from agricultural fields ranged from 1.1 to 2.9 ng m−2 h−1. Non‐mineralized bedrock, sand, and till sites yielded fluxes ranging from −0.03 to 5.9 ng m−2 h−1. Mean fluxes from mercuriferous geological substrates at various locations were large compared to non‐mercuriferous sites, ranging from 9.1 to 1760 ng m−2 h−1, and represent natural emissions. The corresponding total mercury substrate concentrations ranged from 0.360 to 180 ppm. A significant correlation (R2 = 0.66) was found between Hg fluxes and total Hg concentrations in mineralized and non‐mineralized substrates. These gaseous Hg flux measurements represent a significant contribution to understanding natural mercury cycling, but there are still insufficient data and knowledge of processes to properly scale up fluxes from natural sources in Canada.

Multi-site assessment of cultivation-induced soil change using revised landform segmentation procedures

The range of soil properties associated with soil taxonomic class results from natural soil formation and soil-changing effects of human activity. My goal was to assess cultivation effects on soil formation and soil organic carbon (SOC) at four cultivated and two native hummocky till sites from the same climatic region of Saskatchewan. A revised landform segmentation procedure was used for comparisons across sites. Neither A horizon thickness nor SOC was related to topographical attributes at the native sites, but both had significant relationships (P = 0.001) with profile curvature (Pearson r= −0.53 and −0.57 for A horizon thickness and SOC, respectively), specific dispersal area (r = −0.40 and −0.54) and plan curvature (r = −0.24 and −0.34) at the cultivated sites. The greatest decreases in A horizon thickness (16 cm) and SOC (56 Mg ha-1) at the cultivated sites occurred in divergent shoulder elements, which have high rates of tillage-induced soil loss. Increases in soil thickness (including depth to calcium carbonate) occurred in concave footslope and depressional elements, but in situ losses of SOC outweighed the effects of SOC deposition. Soil thinning caused increases in the proportion of Orthic Regosols and decreases in the proportion of Calcareous Chernozems, but horizonation changes in the dominant Orthic Chernozems were minor. The self-terminating nature of the horizonation changes and improved conservation measures suggest that the future rate of soil change in these landscapes may be lower than in the past. Key words: organic carbon, topography, landscape-scale, erosion, tillage redistribution, digital elevation model, cesium

Near-surface soil characteristics and understory plants as predictors of Pinus contorta site index in southwestern Alberta, Canada

The physical and chemical properties of forest floor humus (inclusive of L–F–H horizons) and the uppermost 10 cm of the mineral soil zone (i.e. the primary nutrient absorption zone), and understory plant species abundance were compiled for 42 native Pinus contorta Doug. ex Loud. var. latifolia Engelm. ex S. Watson (lodgepole pine) stands located on mesic till sites in the Lower Boreal–Cordilleran ecoregion of southwestern Alberta. Stand ages ranged from 78 to 146 years. These fire-origin stands were stratified into three site index (SI 50) classes, which represented a productivity gradient in terms of height growth. Extractable Ca and bulk density of humus, extractable Ca in the mineral soil and pH, Bm horizon thickness, and sand content were positively associated with increasing SI 50; while humus and Ae horizon thickness, silt, Fe and Al content of the mineral soil were negatively related. Differences occurred in nutrient regime classes and humus form frequencies among the SI 50 classes. About 60 regression equations ( P<0.05) based on one or two independent variables were developed to predict P. contorta SI 50. The amount of explained variance among these equations differed by the type of variable: soil physical (maximum r 2 of 22%) < soil chemical (29%) < plant species (45%) < plant growth-forms (63%) ≈ humus form (67%) variables. Standard errors of the estimate for the 12 best regression equations ranged from 1.6 to 2.4 m, with coefficients of variation ranging from 7 to 10%. Most of the better regression models were based on understory plant growth-forms. Greater abundances of deciduous shrubs, forbs, and pteridophytes were associated with sites that had better tree height growth, while ericaceous species, bryophytes, and lichens were common on poorer sites.

THE INFLUENCE OF SUBSTRATE ON VEGETATION HISTORY AND ECOSYSTEM DEVELOPMENT

Comparison of vegetation, soil, and climatic history at two sites differing in soil texture and thus soil water-holding capacity reveals long-term differences in terrestrial ecosystem development. Vegetation history reconstructed using pollen analysis and modern surface samples reveals that the site on till has hosted species with higher moisture requirements than those at the outwash site since the early Holocene. The outwash site had incomplete forest cover for much of the Holocene in contrast to the till site, which likely had a closed-canopy forest for most of its history. Comparison of vegetation and soil records reveals a correspondence between the timing of changes in vegetation and soil at both sites for most of the Holocene and provides evidence for greater weathering rates under coniferous than deciduous forest or savanna. Soil and vegetation changes are synchronous within, but not across, sites 13 000–3000 yr BP, suggesting that local interactions between soil and vegetation may have been important in determining the timing of ecosystem change. In contrast, there was synchronous change in soil and vegetation across sites ∼3000 yr BP, when hemlock became established at the till site and weathering intensified at both sites. This synchrony suggests a regional driver of ecosystem change, most likely the climatic change to higher moisture availability that occurred in the late Holocene. Thus, both climate and interactions between soil and vegetation have influenced the timing of ecosystem change, and the relative importance of their influence has varied over time.

Identifying riparian sinks for watershed nitrate using soil surveys.

The capacity of riparian zones to serve as critical control locations for watershed nitrogen flux varies with site characteristics. Without a means to stratify riparian zones into different levels of ground water nitrate removal capacity, this variability will confound spatially explicit source-sink models of watershed nitrate flux and limit efforts to target riparian restoration and management. We examined the capability of SSURGO (1:15 840 Soil Survey Geographic database) map classifications (slope class, geomorphology, and/or hydric soil designation) to identify riparian sites with high capacity for ground water nitrate removal. The study focused on 100 randomly selected riparian locations in a variety of forested and glaciated settings within Rhode Island. Geomorphic settings included till, outwash, and organic/alluvial deposits. We defined riparian zones with "high ground water nitrate removal capacity" as field sites possessing both >10 m of hydric soil width and an absence of ground water surface seeps. SSURGO classification based on a combination of geomorphology and hydric soil status created two functionally distinct sets of riparian sites. More than 75% of riparian sites classified by SSURGO as organic/alluviumhydric or as outwash-hydric had field attributes that suggest a high capacity for ground water nitrate removal. In contrast, >85% of all till sites and nonhydric outwash sites had field characteristics that minimize the capacity for ground water nitrate removal. Comparing the STATSGO and SSURGO databases for a 64000-ha watershed, STATSGO grossly under-represented critical riparian features. We conclude that the SSURGO database can provide modelers and managers with important insights into riparian zone nitrogen removal potential.

Quaternary geology of the Babine porphyry copper district: implications for geochemical exploration

The Quaternary stratigraphy of the Babine Lake region is characterized by a Late Wisconsinan succession of advance-phase glaciolacustrine sediments, glaciofluvial deposits, and till. Pollen data from a rare new interglacial site suggest a colder than present Middle Wisconsinan climate. Ice flow during the last glaciation was dominantly southeasterly, but in the Babine Range a regional, westerly ice-flow event occurred. Evidence for westerly flow diminishes eastward of Babine Lake, suggesting that the valley was near the eastward limit of an interior ice divide. Deglacial sediments include ice-marginal debris-flow, glaciofluvial, and glaciolacustrine sediments. Raised-delta elevations indicate that Glacial Lake Babine extended nearly 150 m above present lake level to 850 m asl, and higher, earlier phases may have existed locally. A variety of Holocene deposits cap the Quaternary succession. Glaciation has important implications for exploration in this copper-producing area. Southeasterly glacial dispersal patterns dominate, despite a regionally complex ice-flow history. Highly anomalous concentrations of copper occur in tills down-ice of most known bedrock copper occurrences, and a number of similarly anomalous till sites with no known copper sources have been identified in drift-covered areas. Exploration problems due to the thick and complex surficial cover can be overcome by selective sampling of basal tills, the composition of which clearly reflects the presence of buried mineral deposits. The effectiveness of till geochemistry as a method for locating buried mineralization in the region will be enhanced by careful selection of sample media and by a clear understanding of the glacial history.

Variability of Site Response in Seattle, Washington

Ground motion from local earthquakes and the SHIPS (Seismic Hazards Investigation in Puget Sound) experiment is used to estimate site amplification factors in Seattle. Earthquake and SHIPS records are analyzed by two methods: (1) spectral ratios relative to a nearby site on Tertiary sandstone, and (2) a source/site spectral inversion technique. Our results show site amplifications between 3 and 4 below 5 Hz for West Seattle relative to Tertiary rock. These values are approximately 30% lower than amplification in the Duwamish Valley on artificial fill, but significantly higher than the calculated range of 2 to 2.5 below 5 Hz for the till-covered hills east of downtown Seattle. Although spectral amplitudes are only 30% higher in the Duwamish Valley compared to West Seattle, the duration of long-period ground motion is significantly greater on the artificial fill sites. Using a three-dimensional displacement response spectrum measure that includes the effects of ground-motion duration, values in the Duwamish Valley are 2 to 3 times greater than West Seattle. These calculations and estimates of site response as a function of receiver azimuth point out the importance of trapped surface-wave energy within the shallow, low-velocity, sedimentary layers of the Duwamish Valley. One-dimensional velocity models yield spectral amplification factors close to the observations for till sites east of downtown Seattle and the Duwamish Valley, but underpredict amplifications by a factor of 2 in West Seattle. A two-dimensional finite-difference model does equally well for the till sites and the Duwamish Valley and also yields duration estimates consistent with the observations for the Duwamish Valley. The two-dimensional model, however, still underpredicts amplification in West Seattle by up to a factor of 2. This discrepancy is attributed to 3D effects, including basin-edge–induced surface waves and basin-geometry–focusing effects, caused by the proximity of the Seattle thrust fault and the sediment-filled Seattle basin.

Comparison of compaction induced by conventional and zero tillage in two soils of the Rolling Pampa of Argentina

Zero tillage is often perceived as causing shallow soil compaction in the Rolling Pampa of Argentina. Adjacent conventionally tilled and 4-year zero tilled sites of a sandy loam (Bragado Series, Typic Hapludoll) and a silty clay loam (Peyrano Series, Typic Argiudoll) were compared in terms of their organic carbon content, bulk density, relative compaction, penetration resistance and pore size distribution. A permanent sod was also included as a reference for the silty clay loam. Zero tillage did not affect significantly soil organic carbon content (8.8 to 10.7 g kg −1 in the sandy loam, and 13.5 to 14.8 g kg −1 in the silty clay loam), bulk density (1.0 to 1.2 Mg m −3, and about 1.3 Mg m −3, respectively), relative compaction (0.70 to 0.80, and 0.70 to 0.85, respectively) and pore size distribution of the topsoil, but a significant increase of penetration resistance from 0.8 to 5.0 MPa was observed in the sandy loam, and from 1.9 to 3.2 MPa in the silty clay loam. These penetration resistance increases could not be attributed to shallow compaction but to soil hardening. Compaction was only found in the subsoil of the conventionally tilled sandy loam, which had 0.10–0.17 Mg m −3 higher bulk density and 2.4–2.5 MPa higher penetration resistance than the zero tilled site. Under permanent sod the silty clay loam had only slightly higher pore volume >50 μm (7–12%v) than under cropping (2–7%v). The low macroporosity of the silty clay loam must then be attributed to genetic causes and not to soil management. This soil should be either periodically loosened by ploughing or maintained moistened through irrigation, in order to prevent the development of mechanical constraints to crops.

Diuron and Simazine Losses to Runoff Water in Mediterranean Vineyards

AbstractThe Mediterranean climate is characterized by a hot and dry summer where occasional storm events induce erosion and runoff. The high leaching potential of pesticides to surface waters under such climate conditions are not in relation to the main body of data that originated from summer‐rain row‐crop scenarios. In this 2‐yr study we monitored runoff discharge and concentrations of the two soil applied herbicides diuron [3‐(3,4‐dichlorphenyl)‐1,1‐dimethylurea] and simazine [6‐chloro‐N2,N4‐diethyl‐1,3,5‐triazine‐2,4‐diamine] from two field sites—one tilled and one no‐till—cropped with grapevine (Vitis vinifera L.; Cinsault and Aramon, respectively). Despite a time lag of 140 d in 1994 between chemical application and first runoff event, diuron concentrations in overland flow exceeded 200 µg L−1 at the no‐till site. In 1995 the first strong rainfall‐runoff event following application carried &gt;87 and 60% of the respective seasonal simazine and diuron loss at both sites, although it accounted for &lt;17 and 7% of the total runoff volume at the no‐till and tilled site, respectively. At the no‐till site, seasonal diuron loss during 1995 was 1.71% of applied; the corresponding value for simazine was 1.25%. Only 0.68 and 0.79% of the respective applied diuron and simazine mass were washed from the tilled field, reflecting differences in runoff volume between sites. Pesticide losses depended primarily on runoff volume and intensity. Event average herbicide concentrations in surface runoff followed an exponential decay over time. Estimated first order rate coefficients were at least twice as large as those derived from soil samples using the alcoholic solvent extraction technique. The decreasing water availability with time compared with the herbicide content at the soil surface indicated an increasing adsorption with time.

Seasonal variations in infiltration rate under no-till and conventional (disk) tillage systems as affected by Lumbricus terrestris activity

Lumbricus terrestris activity can improve water flow into soils, but the effects of L. terrestris (nightcrawlers) on infiltration and runoff rates throughout the growing season have not been quantified. Our objective was to quantify and describe the effects of L. terrestris on infiltration rates under an established no-till and a disk tillage system on a silt loam Alfisol (fine-loamy, mixed, mesic Aquollic Hapludalf) in west central Indiana. Under each tillage practice there were areas within the field that had L. terrestris activity and other areas that had no activity, as indicated by the presence or absence, respectively, of middens. Infiltration was measured using a portable sprinkling infiltrometer which delivered 7 cm of water h −1 to a 1.4 m 2 area. Infiltration was measured five times during the growing season, for the disk tillage treatment: (1) before any spring field work began; (2) immediately after tillage but before planting; (3) immediately after planting; (4) 3 weeks after planting; and (5) after harvest. For no-till treatments, the measurement times were the same as times 1, 3, 4, and 5 of the tilled site. Results showed that in early spring before any tillage was performed, the tilled treatment without middens had the highest infiltration rate and the tilled treatment with middens had the lowest. Immediately after planting and 3 weeks after planting, no-till with middens had the highest infiltration rates, but disk tillage treatments had the lowest infiltration rates. Measurements after harvest showed that no-till with middens again had the highest infiltration rates. The presence of L. terrestris, as indicated by the presence of middens, appears to have increased infiltration rates in a no-till system on this soil. In the disk system, however, the activity of L. terrestris and the presence of their middens apparently was not persistent enough to affect infiltration rates, and the amount of surface residue cover may be a more important factor in this system.

Early postharvest succession in relation to site type in the southern boreal forest of Quebec

Early vegetation development following harvest was evaluated for nine common site types in the southern clay belt of northwestern Quebec. Stocking of broadleaf tree and high shrub stems less than 1 m tall was either stable or declined on all sites over a period of 8 years following harvest, whereas stocking of stems over 1 m displayed increases on all but mesic clay sites. These latter sites had the lowest broadleaf and high shrub stocking but a high cover of raspberry (Rubusidaeus L.), low shrubs, and herbs. Mesic to hydric clays and hydric organic site types had considerably higher cover of ruderal and introduced species than sand and till sites, TWINSPAN indicator species analysis was used to explore phytosociological associations of postharvest vegetation. The distribution of 11 phytosociological groups among the nine site types was analysed using contingency analysis to test the specificity of species groups to site types and the floristic amplitude of the latter. With the exception of one phytosociological group that displayed a broad spectrum of site type occupation, these groups tended to be associated with sites of similar soil moisture regimes and (or) parent material types. While site type may be improved upon as a stratifier by integrating other environmental, biotic, and operational variables, it does appear to provide a good initial basis for stratification in studies of postdisturbance vegetation dynamics.

Rill Erodibility Parameters Influenced by Long-term Management Practices

A field study was conducted to estimate rill erodibility parameters on two paired north central Illinois soils with differing long-term management practices (conventional and no-till) in an effort to support on-going erosion and sediment transport modeling. Simulated rainfall and a sequence of inflows were applied to six treatments: aged tilled conventional, fresh tilled conventional, aged tilled no-till, fresh tilled no-till, undisturbed no-till with residue removed, and undisturbed no-till. Two models (shear stress and stream power) were used to analyze rill detachment rates. Baseline rill erodibilities for fresh tilled conventional (0.00879 g s1 N1) and fresh tilled no-till (0.00541 g s1 N1) were significantly different using the shear stress model. Consolidation also produced significant differences in erodibilities for the conventional tilled site (0.0122 g s1 N1 and 0.00879 g s1 N1 for aged and fresh tilled treatments, respectively). When stream power was used to model the response of rill detachment, no significant differences were detected in erodibility and critical stream power for baseline conditions. However, the stream power model accounted for most of the variability in detachment rates within each treatment. Long-term no-till significantly reduced sediment concentrations in the runoff from all other treatments (0.0045 g/g and 0.0067 g/g for undisturbed and undisturbed residue removed, respectively). Sediment concentration was a function of residue and consolidation.

The spatial variability of soil resources following long-term disturbance.

The spatial distributions of selected soil properties in two adjacent sites in southwest Michigan were examined to evaluate the potential effects of chronic disturbance on resource heterogeneity. One site was a cultivated field that had been cleared, plowed, and cropped annually for decades prior to sampling while the other, uncultivated field was cleared of original forest in 1960 after which it was mown annually but never plowed or cropped. We took replicate samples from a 330-point unaligned grid across the sites for soil pH, gravimetric moisture, inorganic phosphorus, total carbon, and net nitrification and nitrogen mineralization potentials. Soils in the cultivated site contained less than half as much carbon as in the uncultivated site, but had higher levels of inorganic phosphorus and moisture, and higher soil pH. Potential net nitrogen mineralization and nitrification rates did not differ between sites. Geostatistical analysis showed that almost all properties examined were strongly autocorelated within each site; structural variance as a proportion of sample variance ranged from 30-95% for all properties, and for any given property differed little between sites. The distance over which this dependence was expressed, however, was for all properties but pH substantially less in the uncultivated site (7-26 m) as compared to the tilled site (48-108m), especially for total C and net nitrification and N mineralization. These results suggest that the spatial pattern and scale of soil variability can differ markedly among edaphically identical sites and that these differences can be related to disturbance history.

Internal Drainage Under Irrigation of Two Slowly Permeable Subsoils of the Northern Great Plains

Lack of water limits crop yield in the semiarid northern Great Plains but many soils of the northern Great Plains have been thought to be nonirrigable because of their slowly permeable subsoils. We measured the internal drainage in response to two levels of nitrogen fertility and three levels of irrigation or overirrigation — one, two, or three times the calculated evapotranspiration — of corn (Zea mays L.) at two sites for five and six years. Both of our sites had subsoils classified as slowly permeable; one site had alluvial subsoil, the other had glacial till subsoil. For sufficient nitrogen fertility (200 kg N/ha) at the glacial till site, drainage between 1 July and harvest from the 2ET treatment was 109 mm greater than from the 1ET treatment; drainage from the 3ET treatment was 197 mm greater than from the 2ET treatment. Insufficient nitrogen fertility (100 kg N/ha) reduced crop water use and resulted in greater drainage. At the glacial till site, the average internal drainage between 1 July and harvest from all three irrigation treatments at 100 kg N/ha was 100 mm greater than at 200 kg N/ha. The maximum five-year average drainage amount between 1 July and harvest at the till site was 471 mm, more water than the average applied to the 1ET treatments during the same period. Tensiometer measurements occasionally indicated saturation at the 2.0-m depth at the alluvial site, but not at 0.9 or 1.35 m; saturation was never encountered at the till site at 0.9, 1.35, or 2.0 m. Based on the measured drainage rates and lack of perched water table development, the soils tested in this study can drain enough water to permit successful well-managed irrigation.

Secondary forest succession in New Hampshire, USA

Secondary forest succession in the northern hardwood and spruce-hemlock forests of central New Hampshire, USA, was examined by regressing percentage composition of the major species over stand age, using both temporary and remeasured plots in essentially uncut stands ranging in age from 3 to over 190 years. Plots were classified by site: fine till, sandy till, and softwood sites. Successional change varied by site, and five ecological species roles were detected: dominating climax, stable climax, minor climax, persistent successional, and temporary successional species. After heavy cutting, stands on fine till sites move through an abundance of successional species such as pin cherry ( Prunus pensylvanica L.), aspen ( Populus spp), paper birch ( Betula papyrifera Marsh.), and yellow birch ( B. alleghaniensis Britton) toward a predominence of sugar maple ( Acer saccharum Marsh.) and American beech ( Fagus grandifolia Ehrh.). A similar trend occurs on sandy till, although red maple ( A. rubrum L.) — a low nutrient-demanding species — is a more common successional species and American beech is much more aggressive than sugar maple. On softwood sites (shallow, dry, wet, or poorly aerated soils), the successional species, including high proportions of red maple, are succeeded by a predominance of eastern hemlock ( Tsuga canadensis (L.) Carr.) and, especially at higher elevations, red spruce ( Picea rubens Sarg.). On these softwood sites, a persistent representation of successional species is maintained by frequent stand disturbances. On fine and sandy till, exogenous disturbance has a minimal influence on the composition of the climax forest. Minimum time-to-climax was estimated at 170 years and 250 years on fine till and softwood sites, respectively, using the species composition of old-growth forests in the region as standards.

Addition of organic matter and elements to the forest floor of an old-growth Acersaccharum forest in the annual litter fall

Litter fall and its content of N, P, K, Ca, Mg, S, Fe, Mn, Zn, and Cu were measured monthly over a 5-year period in an old-growth Acersaccharum Marsh, stand on a till site in central northern Ontario. Determined were the following: the amount, and the temporal and spatial distributions, of organic matter and elements deposited annually in the different litter fractions; the proportion of elements conserved within the tree phytomass through retranslocation versus that shed in the annual litter fall; and the residence time of litter-transported elements in the forest floor. Element transfer through the annual litter fall was also compared with that by other vectors of transport to the forest floor. Over the study period, total litter fall averaged 3730 kg•ha−1•year−1 (dry weight), with 78% consisting of leaves, 8% of flowers and fruits, and the remaining 14% mainly of twigs, branches, and bark slough. Annual element depositions (kg•ha−1) averaged as follows: N, 40.6; P, 1.8; K, 9.1; Ca, 37.6; Mg, 3.9; S, 3.0; Fe, 0.57; Mn, 2.67; Zn, 0.28; and Cu, 0.03. Turnover time of the forest floor was calculated as 7.4 years. Residence times (years) of elements in the forest floor were as follows: N, 18.3; P, 18.3; K, 1.5; Ca, 6.1; Mg, 6.8; S, 5.1; Fe, 257.2; Mn, 4.8; Zn, 18.1; and Cu, 5.8. Although the turnover time of forest-floor organic matter did not differ appreciably from values reported for A. saccharum forests elsewhere, residence times for elements suggested somewhat slower cycling, probably as a result of reduced uptake related to the advanced age of the stand. Potassium, followed by S, P, and N, were all conserved to a high degree by A. saccharum trees through retranslocation to the tree's perennial parts prior to leaf fall; Cu, Mn, and Mg were conserved to a lesser degree; Zn, Ca, and Fe were conserved very little. In comparing the leaching loss of elements from foliage with quantities conserved through retranslocation and quantities shed in the annual litter fall, the relative orders of magnitude do not give cause for concern that A. saccharum trees risk appreciable leaching losses of base cations, including K, from foliage as a result of acidified precipitation, at least at levels experienced in central northern Ontario during the early 1980s.

An investigation of the bevameter soil physical measurements in the prediction of soil tool draft

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.