Deep Loess Research Articles

The Migration Diary of a Knickpoint in a Channelized Stream With a Cohesive Bed

AbstractThis paper examines the coevolutionary roles of variable flow features and heterogeneous substrates on knickpoint migration. A conceptual model is used to depict distinct migration mechanisms in a channelized headwater system of a representative intensively managed watershed in the Deep Loess Region of the U.S. Midwest. Throughout this region, entrenched streams have eroded into alluvial‐based strata that are horizontally consistent but vertically heterogeneous. Variable flow in these streams switches between vented conditions, where water shoots from the knickpoint face as an aerated plunging jet, and unvented conditions, where water clings close to its face through suction. These switches affect hydrodynamic mechanisms controlling migration but cannot explain fully observed alternating slow‐fast migration rates. It is hypothesized that vertically heterogeneous strata in entrenched streams, specifically strong‐over‐weak layers, facilitate observed changes in knickpoint migration rates. Preferential erosion of weaker sublayers is thought to trigger other erosional mechanisms to accelerate migration even at low flows. Herein, a migration “diary” documents a representative knickpoint's displacement over time with flow measurements and site stratigraphy. Slower migration occurred from 2006 to 2009 through fluvial erosion of a resistant silt loam cap. From 2009 to 2012, migration accelerated as the knickpoint face reached a critical height through scour. A flow back roller formed, which preferentially eroded a weaker sand sublayer. Undercutting/cantilever failure cycles persisted, causing 30 m of retreat within 2 months (i.e., 62.5% of the total migration over 78 months). Comparisons with established fluvial hydraulics‐based and undercutting/cantilever‐based migration models confirm the hypothesis and importance of both stratified substrates and hydrodynamic controls on knickpoint migration.

Channels, terraces, pottery, and sediments – A comparison of past irrigation systems along a climatic transect in northern Jordan

This contribution compares the remains of irrigation systems along a climatic transect in northern Jordan: Gadara (today Umm Qeis) in the north-west, Abila (today Queilbeh) in the north, and Umm el-Jimal (ancient name unknown) in north-east Jordan. While Gadara and Abila were monumental ancient cities of the Decapolis city league, which are located in Mediterranean environments, Umm el-Jimal is a large urban site situated in the steppe. Rainfed agriculture is possible near Gadara/Umm Qeis and Abila/Queilbeh, but not at Umm el-Jimal. Our surveys of the hinterlands revealed evidence for runoff farming at Umm el-Jimal near some wadis, and at Abila/Queilbeh and Gadara/Umm Qeis near both springs and wadis. Contrary to our expectations, the extent of ancient irrigation near Umm el-Jimal appeared more limited and economically less important than at the two other sites. Although the steppe proved covered by an approximately 4 m deep loess cover, these fertile sediments were apparently utilized only to a limited degree for agriculture. This can be deduced from the petty amount of sediments that accumulated behind terrace walls, the small extent of the fields and from low concentrations of nutrients usually associated with manuring. The archaeological surface survey confirms this picture: in the steppe, widely spread pottery scatters were found only within the settlement and the necropolis. The sites to the west revealed larger and more sophisticated remains of irrigation systems, as well as higher concentrations of material culture scatters, which suggest far more intensive land use systems than in the east. The most extensive and sophisticated remains of irrigation canals were found on caliche crusts near Gadara/Umm Qeis. As these rocks are mostly bare of soil cover, they are well-suited to collect runoff and construct rock-cut canals to transport water. We conclude that the available water resources and the geology had the strongest influence on the construction of ancient irrigation systems in northern Jordan.

Soil moisture response to rainfall on the Chinese Loess Plateau after a long‐term vegetation rehabilitation

AbstractThe Chinese Loess Plateau (CLP) is a unique Critical Zone with deep loess deposits, where soil moisture is primarily replenished by seasonal monsoon rainfall. However, the role of vegetation, coupled with complex topography, on rainwater infiltration on the CLP, especially after long‐term revegetation for controlling erosion, is inadequately quantified. Over the growing season of 2016, we monitored soil moisture at the 30‐min interval at 5 depths (10, 20, 40, 60, and 100 cm) in an afforested catchment and a nearby catchment with natural regrowth of grasses. Two monitoring sites were established in each catchment, one in the downhill gully and the other in the uphill slope. We found that vegetation, topography, and rainfall attributes together determined rainwater infiltration and soil moisture replenishment. An accumulated rainfall amount of 9 mm was required to trigger soil moisture response at 10‐cm depth at the 2 grassland sites and the forestland uphill‐slope site whereas 14 mm of rainfall was required for the forestland gully site covered by dense undergrowth and trees. Rainfall events with larger sums and higher peak intensities permitted rainwater infiltration to deeper soil depths. However, no rain recharged soil moisture to 100‐cm depth during the monitoring period. The forestland uphill‐slope site showed the deepest wetting depth (up to 60‐cm depth), fastest wetting‐front velocity (up to 4 cm/hr below 10‐cm depth), and the most significant soil moisture increase (up to 15% cm 3 cm−3 increase at 10‐cm depth) after rainfall in the growing season. The grassland gully site had the highest soil water storage, whereas soil moisture was depleted the most at the forestland gully site. Findings of this study reveal the transient dynamics of soil moisture after rainfall on the CLP, which signifies the role of revegetation on rainwater infiltration in the loess Critical Zone.

Mineral N stock and nitrate accumulation in the 50 to 200 m profile on the Loess Plateau

Nitrogen (N) stored in deep profiles is important in assessing regional and/or global N stocks and nitrate leaching risk to groundwater. The Chinese Loess Plateau, which is characterized by significantly thick loess deposits, potentially stores immense stocks of mineral N, posing future threats to groundwater quality. In order to determine the vertical distributions of nitrate and ammonium content in the region, as well as to characterize the potential accumulation of nitrate in the deep loess profile, we study loess samples collected at five sites (Yangling, Changwu, Fuxian, An'sai and Shenmu) through a 50 to 200m loess profile. The estimated storage of mineral N varied significantly among the five sites, ranging from 0.46 to 2.43×104kgNha−1. Ammonium exhibited fluctuations and dominated mineral N stocks within the whole profile at the sites, except for the upper 20–30m at Yangling and Changwu. Measured nitrate content in the entire profile at Fuxian, An'sai and Shenmu is low, but significant accumulations were observed to 30–50m depth at the other two sites. Analysis of δ15N and δ18O of nitrate indicates different causes for accumulated nitrate at these two sites. Mineralization and nitrification of manure and organic N respectively contribute nitrate to the 0–12 and 12–30m profile at Changwu; while nitrification of NH4+ fertilizer, NO3− fertilizer and nitrification of organic N control the nitrate distribution in the 0–3, 3–7 and 7–10m layer at Yangling, respectively. Furthermore, our analysis illustrates the low denitrification potential in the lower part of the vadose zone. The accumulated nitrate introduced by human activities is thus mainly distributed in the upper vadose zone (above 30m), indicating, currently, a low nitrate leaching risk to groundwater due to a high storage capacity of the thick vadose zone in the region.

How Well Does Noah-MP Simulate the Regional Mean and Spatial Variability of Topsoil Water Content in Two Agricultural Landscapes in Southwest Germany?

Abstract The spatial variability of topsoil water content (SWC) is often expressed through the relationship between its spatial mean 〈θ〉 and standard deviation σθ. The present study tests the concept that a reasonably performing land surface model (LSM) should be able to produce σθ–〈θ〉 data pairs that fall into a polygon, spanned by the cloud of observed data and two anchor points: σθ at the permanent wilting point σθ–〈θwp〉 and σθ at saturation σθ–〈θs〉. A state-of-the-art LSM, Noah-MP, was driven by atmospheric forcing data obtained from eddy covariance field measurements in two regions of southwestern Germany, Kraichgau (KR) and Swabian Alb (SA). KR is characterized with deep loess soils, whereas the soils in SA are shallow, clayey, and stony. The simulations series were compared with SWC data from soil moisture networks operating in the two study regions. The results demonstrate that Noah-MP matches temporal 〈θ〉 dynamics fairly well in KR, but performs poorly in SA. The best match is achieved with the van Genuchten–Mualem representation of soil hydraulic functions and site-specific rainfall, soil texture, green vegetation fraction (GVF) and leaf area index (LAI) input data. Nevertheless, most of the simulated σθ–〈θ〉 pairs are located outside the envelope of measurements and below the lower bound, which shows that the model smooths spatial SWC variability. This can be mainly attributed to missing topography and terrain information and inadequate representation of spatial variability of soil texture and hydraulic parameters, as well as the model assumption of a uniform root distribution.

Soil Drought and Water Carrying Capacity for Vegetation in the Critical Zone of the Loess Plateau: A Review

Core Ideas The progress of research on soil drought in the Loess Plateau was reviewed. Spatiotemporal patterns of dried soil layers were scale dependent. SWCCV was recommended for optimizing water management in the critical zone of the LP. The Loess Plateau (LP) of China is a good representative area for critical zone (CZ) science studies. The LP is famous for its deep loess. In most areas, the thickness of the loess profile is deeper than 100 m, and two‐thirds of the area is arid and semiarid. With the Grain‐for‐Green project, the vegetation of the plateau has recovered gradually. However, with the increase in vegetative coverage, especially the planted vegetation, the water content of the soil profile has decreased and the soil is much drier. In this review, particular emphasis is paid to the dry conditions of deep soil, drought, regional restoration of vegetation, and effective management of soil moisture. We reviewed the progress of research on dried soil layers (DSLs) that resulted from soil drought in the past decades on the Plateau, and then we summarized the development of the concept and models of soil water carrying capacity for vegetation (SWCCV). This review is helpful for understanding the development of DSLs, optimizing soil water management through vegetation mediation, and designing a long‐term sustainable framework for water‐limited ecosystems.

Variations of Soil Organic Carbon Following Land Use Change on Deep‐Loess Hillsopes in China

AbstractLand use change is a key factor driving changes in soil organic carbon (SOC) around the world. However, the changes in SOC following land use changes have not been fully elucidated, especially for deep soils (>100 cm). Thus, we investigated the variations of SOC under different land uses (cropland, jujube orchard, 7‐year‐old grassland and 30‐year‐old grassland) on hillslopes in the Yuanzegou watershed of the Loess Plateau in China based on soil datasets related to soils within the 0–100 cm. Furthermore, we quantified the contribution of deep‐layer SOC (200–1,800 cm) to that of whole soil profiles based on soil datasets within the 0–1,800 cm. The results showed that in shallow profiles (0–100 cm), land uses significantly (p < 0·05) influenced the distribution of SOC contents and stocks in surface layer (0–20 cm) but not subsurface layers (20–100 cm). Pearson correlation analysis indicated that soil texture fractions and totalNwere significantly (p < 0·05 or 0·01) correlated with SOC content, which may have masked effects of land use change on SOC. In deep profiles (0–1,800 cm), SOC stock generally decreased with soil depth. But deep soils showed high SOC sequestration capacity. The SOC accumulated in the 100–1,800 m equalled 90·6%, 91·6%, 87·5% and 88·6% of amounts in the top 100 cm under cropland, 7‐year‐old grassland, 30‐year‐old grassland and jujube orchard, respectively. The results provide insights into SOC dynamics following land use changes and stressed the importance of deep‐layer SOC in estimating SOC inventory in deep loess soils. Copyright © 2017 John Wiley & Sons, Ltd.

Soilscape evolution of aeolian-dominated hillslopes during the Holocene: investigation of sediment transport mechanisms and climatic–anthropogenic drivers

Abstract. Here we study the soilscape (soil-landscape) evolution of a field site in the semiarid zone of Israel. This region, like similar regions around the world, was subject to intensive loess accumulation during the Pleistocene and early Holocene. Today, hillslopes in this region are dominated by exposed bedrock with deep loess depositions in the valleys and floodplains. The drivers and mechanism that led to this soilscape are unclear. Within this context, we use a soilscape evolution model (mARM5D) to study the potential mechanisms that led to this soilscape. We focus on advancing our conceptual understanding of the processes at the core of this soilscape evolution by studying the effects of fluvial and diffusive sediment transport mechanisms, and the potential effects of climatic and anthropogenic drivers. Our results show that, in our field site, dominated by aeolian soil development, hillslope fluvial sediment transport (e.g., surface wash and gullies) led to downslope thinning in soil, while diffusive transport (e.g., soil creep) led to deeper and more localized soil features at the lower sections of the hillslopes. The results suggest that, in this semiarid, aeolian-dominated and soil-depleted landscape, the top section of the hillslopes is dominated by diffusive transport and the bottom by fluvial transport. Temporal variability in environmental drivers had a considerable effect on soilscape evolution. Short but intensive changes during the late Holocene, imitating anthropogenic land use alterations, rapidly changed the site's soil distribution. This leads us to assume that this region's soil-depleted hillslopes are, at least in part, the result of anthropogenic drivers.

Field Performance of <i>Quercus bicolor</i> Established as Repeatedly Air-Root-Pruned Container and Bareroot Planting Stock

Benefits of repeated air-root-pruning of seedlings when stepping up to progressively larger containers include excellent lateral root distribution immediately below the root collar and an exceptionally fibrous root ball. To evaluate long-term field performance of repeatedly air-root-pruned container stock, three plantings of swamp white oak (Quercus bicolor Willd.) 10 to 13 years old were located that also included bareroot planting stock. Initial and final stem diameter and height and above-ground green weights were determined on randomly selected trees at each site. On a site with a sandy, excessively drained, high pH soil, trees (age 10) from container stock were 1.5 times taller, 2.3 times larger in dbh, and 2.8 times greater in green weight than trees from bareroot stock which averaged only 2.9 m tall, 3.9 cm dbh, and 16.3 kg green weight. On a site with high clay, poor internal drainage, and frequent flooding, trees (age 12) from container stock were 1.4 times taller, 1.8 times larger in dbh, and 4.1 times greater in green weight than trees from bareroot stock which averaged 4 m tall, 7.3 cm dbh, and 28 kg green weight. On an upland site with deep loess soils, there was a trend for trees (age 13) from container stock to be only slightly larger than trees from bareroot stock with each stock type averaging 9.6 m tall, 20 cm dbh, and 177 kg green weight. Repeated air-root pruning produced lateral roots immediately below the root collar that resulted in large container stock with large well-balanced root systems that were competitive on harsh or less than ideal oak sites. Although the process is relatively labor intensive, propagation of repeatedly air-root-pruned container stock is readily adaptable internationally to locally available sources of organic matter and open-bottom containers.

Soil and vegetation transformation in abandoned vineyards of the Tokaj Nagy-Hill, Hungary

Two chronosequences, one south (S-sequence) and one southwest (SW-sequence) with differing times since their abandonment (193, 142, 101, 63, 39 and 14years), were studied on Tokaj Nagy-Hill. The sites were investigated in respect of vegetation characteristics, soil physico-chemical characteristics, total organic carbon stocks (TOC stocks), accumulation rates of total organic carbon (TOC accumulation rates), and soil profiles, which were classified according to the World Reference Base (WRB) 2007. The S-sequence was 25–35% sloped and strongly eroded, and the SW-sequence was 17–25% sloped and moderately eroded.Vegetation development at the S-sequence resulted in shrub-grassland mosaics, supplemented by protected herb species and forest development at the earliest abandonment. The SW-sequence was predominantly covered by forest vegetation, and trees were absent at the 63 and 14year old abandonment sites.Soils of the S-sequence show shallow remnants of loess cover with redeposited soil materials containing 15–65% skeletal volcanic rock of weathering products coated by secondary calcium carbonates. The SW-sequence profiles are developed on deep loess or loess derivatives. The calcium-carbonate content was higher in profiles of the S-sequence (18.1±10.4%) than in the SW-sequence (6.7±2.7%); consequently, the pH of the topsoil was higher in the S-sequence, and correlated significantly negatively with the age of abandonment in both sequences (r=−0.893; p=0.01 in S, and r=−0.739; p=0.05 in SW). TOC stocks of the top 6cm soil layers were higher in the S slope (1.82±0.71kgm−2) than in the SW-sequence (0.95±0.49kgm−2), and correlated significantly positively with the duration of abandonment. When calculated for the whole profile, TOC stocks were similar in both S- and SW-sequences (S: 8.21±3.31kgm−2; SW: 8.24±6.01kgm−2). The TOC accumulation rates of the top 6cm soil layers exhibited 18.9±10.0g C m−2y−1 in the S and 7.0±4.2g C m−2y−1 in the SW-sequence.Sites with the same age of abandonment showed different vegetation and soil features in both chronosequences, indicating that time is not the most decisive factor in soil transformation processes after abandonment of viticulture on Tokaj Nagy-Hill. Additional directing factors were slope steepness and exposition.

Long Term Effects of Farming System on Soil Water Content and Dry Soil Layer in Deep Loess Profile of Loess Tableland in China

Soil water is strongly affected by land use/cover in the Loess Plateau in China. Water stored in thick loessal soils is one of the most important resources regulating vegetation growth. However, soil water in the deep loess profile, which is critical for maintaining the function of the “soil water pool” is rarely studied because deep profile soil samples are difficult to collect. In this study, four experimental plots were established in 2005 to represent different farming systems on the Changwu Tableland: fallow land, fertilized cropland, unfertilized cropland, and continuous alfalfa. The soil water content in the 15-m-deep loess profiles was monitored continuously from 2007 to 2012 with the neutron probe technique. The results showed that temporal variations in soil water profiles differed among the four farming systems. Under fallow land, the soil water content increased gradually over time, first in the surface layers and later in the deep soil layers. In contrast, the soil water content decreased gradually under continuous alfalfa. The distributions of soil water in deep soil layers under both fertilized and unfertilized cropland were relatively stable over time. Thus farming system significantly affected soil water content. Seven years after the start of the experiment, the soil water contents in the 15-m-deep profiles averaged 23.4% under fallow land, 20.3% under fertilized cropland, 21.6% under unfertilized cropland, and 16.0% under continuous alfalfa. Compared to measurements at the start of the experiment, both fallow land and unfertilized cropland increased soil water storage in the 15-m loess profiles. In contrast, continuous alfalfa reduced soil water storage. Fertilized cropland has no significant effect on soil water storage. These results suggest that deep soil water can be replenished under the fallow and unfertilized farming systems. Dry soil layers (i.e., those which have soil water content less than the stable field water capacity) in the subsoil of the Changwu Tableland region can be classified as either temporary dry soil layers or persistent dry soil layers. Temporary dry soil layers, which typically form under annual crops, often disappear during wet years. Persistent dry soil layers generally develop under perennial vegetation. Even after removing the vegetation, persistent dry soil layers remain for several decades. This study provides information useful for the conservation and utilization of soil water resources in the Loess Tableland.

Tomography-measured Macropore Parameters to Estimate Hydraulic Properties of Porous Media

A critical hydraulic parameter for geomedia is the saturated hydraulic conductivity. This property is needed in models for predicting water infiltration into soils and water runoff from landscapes. The objective of this study was to use computed tomography (CT)-measured macropore data to predict saturated hydraulic conductivity at four sites from several soil depths and multiple treatments. These core samples were removed from four Midwestern sites. Some study sites included soils developed in loess and glacial till as well as soils developed in deep loess. The four sites included treatments which evaluated different soil management relative to conservation programs with vegetative grasses and agroforestry treatments as well as restored and native prairies. The samples (76mm diam. by 76mm long) were scanned using a computed tomography scanner with 0.19 by 0.19 by 0.5mm resolution. CT-measured pore parameters included macroporosity (> 1000 μm diam.), coarse mesoporosity (200 to 1000 μm diam.), number of pores, circularity of pores, and fractal dimension of macroporosity. The log-transformed saturated hydraulic conductivity was best estimated using the logarithm of number of pores (r2 = 0.69). Results indicate that CT methods can be used as a characterization tool to assess soil pore properties for prediction of saturated hydraulic conductivity.

Experimental Research on Deep Collapsible Loess Foundation Treatment by Dynamic Compaction under Super High Fill

Taking one foundation project as an example, a series of tests are carried out to study the dynamic compaction parameters and its effects on the deep collapsible loess foundation under super high fill in Lvliang region. Analyses are made on the average settlement of each test area before and after dynamic compaction and on the regularity of the main physical and mechanical indexes of soil. At the energy levels of 2000 kN•m, 3000kN•m and 6000kN•m, the main parameters are gained, such as the effective reinforcement depth, the centre distance of tamping points , the standard of stopping ramming, and the optimal ramming number; hence, the empirical formula of the effective reinforcement depth of dynamic compaction. The results of the tests show that the deep collapsible loess foundation in Lvliang region can be effectively reinforced by dynamic compaction, that the stability of foundation is good, and that the loess collapse in the reinforced range is eliminated basically. Moreover, after dynamic compaction above the energy levels of 2000 kN•m, the eigenvalue of the bearing capacity of collapsible loess foundation in Lvliang can reach over 300kPa; the deformation modulus of foundation soil is more than 25MPa. Therefore, the results of the tests can provide a reference for the design and construction of projects of the same kind; it can also provide a reliable basis for relevant norms and standards.

Field Test Research of Pile-Plank Structure on Zhengzhou-Xi'an High-Speed Rail

Pile-plank structure is a new foundation under rail. It has been applied in China, because of its advantages that it can control the foundation settlement effectively and speed up the progress of construction. Zhengzhou-Xi'an high-speed rail is designed to a 350km/h high speed rail. To control the post-construction settlement, speed up construction schedule, this measure is applied in the deep collapsible loess foundation, the first time in the world. To guide the engineering design and to form a theoretical system, field test researches were conducted in appropriate working points, mainly including stress-strain test of bearing sheet and contact stress test between bearing sheet and foundation.

Soil quality in a pecan–kura clover alley cropping system in the Midwestern USA

Intercropping alleys in agroforestry provides an income source until the tree crop produces harvestable yields. However, cultivation of annual crops decreases soil organic matter and increases soil erosion potential, especially on sloping landscapes. Perennial crops maintain a continuous soil cover, increase water infiltration, reduce soil erosion, and improve overall soil quality. The objective of this on-farm study was to assess the effects of a perennial legume, kura clover (Trifolium ambiguum M. Bieb.), on soil quality in a recently established pecan (Carya illinoinensis Wangenh. C. Koch) orchard. The pecan-kura clover agroforestry practice was established on deep loess soils of the Missouri River hills landscape. These silt loams are on 2–20% slopes and can be highly erosive. Kura clover, introduced as the alley crop 5 years after pecan planting, was selected based on its perennial growth habit, nitrogen-fixing ability, winter hardiness, high forage quality, and soil conservation properties. Kura clover was seeded in 2001 and harvested for hay annually beginning 2003. Soil quality indicators of total organic C, total N, water-stable aggregates, and selected soil enzymes were determined on surface soil samples collected annually after kura clover establishment. Soil organic C and activities of soil enzymes increased compared with cultivated and grass pasture control soils by the eighth year of establishment. Water-stable aggregation improved by 50% and surface soil shear strength improved significantly (P < 0.05) in alleys compared with control sites. Results illustrate that kura clover as the alley-cropped component improved soil fertility and biological activity through increased organic matter and improved soil structure, and yielded high quality forage valuable for the cattle-feeding operation. Kura clover maintained or improved soil quality, reduced soil erosion potential, and benefited pecan growth by providing a source of soil nitrogen and improving soil structure for adequate water infiltration and aeration.

Munterville: A New Soil Series in Iowa

Before 2009, the Natural Resources Conservation Service (NRCS) staff noticed plant roots and argillans deep within the B horizon of Gosport polypedons (a fine, illitic, mesic Oxyaquic Dystrudept) while updating Major Land Resource Area (MLRA) 108 (Illinois and Iowa deep loess and drift) and 109 (Iowa and Missouri heavy till plain) in the central United States. In 2009, Gosport soils in MLRAs 108 and 109 were remapped and reclassified. Both map unit transects and the relevé method were used to identify pedons for detailed laboratory analyses. Eight pedons representing Gosport soils were collected from eight counties in southern Iowa, USA (Davis, Jefferson, Keokuk, Lucas, Mahaska, Marion, Monroe, and Van Buren). All of the pedons were described, analyzed, and classified. The results revealed two groups of soils, which are different than that of Gosport: Alfisols, newly named as the Munterville series (fine, mixed, smectitic or kaolinitic, active or superactive, mesic Oxyaquic Hapludalfs), and Ultisols (fine, mixed or kaolinitic, active, mesic Oxyaquic Hapludults) that have not yet been assigned a series name. The aims of this work were to reclassify the Gosport soils and detect the lithologic discontinuities within their sola.

Climatic and environmental changes recorded in loess

∗E-mail: ian.smalley@ntu.ac.uk †E-mail: slobodan.markovic@dgt.uns.ac.rs ‡E-mail: ludwig.zoller@uni-bayreuth.de §E-mail: jones@gamma.ttk.pte.hu of geochemistry, and mineralogy, and sedimentology, and many other disciplines. The Danube basin, a key feature of Central Europe is a beautifully defined loess system, almost a closed system with material being delivered from the surrounding mountains and contributing to major deposits. There is geotechnical interest in Central Europe; all loess deposits present geotechnical problems and Central Europe is no exception. There are problems with landslides in the Danube bluffs and a plan has been drawn up for a nuclear waste repository in the deep loess at Kozloduy, in northern Bulgaria. It might be that the thick loess of Central Europe offers opportunities for solving long-standing and intractable problems of nuclear waste disposal. These are lands where loess snails are studied and human habitations discovered. Here are the Black Earth regions, where chernozemisation was remarkably effective and soil science was invented. These are rich loess regions.

Modeling the impacts of soil management practices on runoff, sediment yield, maize productivity, and soil organic carbon using APEX

Simulation models are increasingly used to analyze the impact of agricultural management at the watershed-scale. In this study, the Agricultural Policy/Environmental eXtender (APEX) model was tested using long-term (1976–1995) data from two watersheds (W2 and W3) at the USDA Deep Loess Research Station near Treynor, Iowa. The two watersheds were cropped with continuous corn ( Zea mays L.) and managed with conventional-tillage at W2 (34.4 ha) and ridge-till at W3 (43.3 ha). The monthly runoff and sediment yield were calibrated for the two watersheds during 1976–1987 by adjusting the curve numbers, curve number index coefficient, RUSLE C factor exponential residue and height coefficients, and erosion control practice factor for grassed waterways. Soil organic carbon values in the top 0.15 m soil layer were calibrated for the two watersheds in 1984 by adjusting the microbial decay rate coefficient. Model validation was conducted from 1988 to 1995. The calibrated model was able to reasonably replicate the monthly and yearly surface runoff and sediment yield for both watersheds for the validation period, with Nash–Sutcliffe efficiencies (EF) larger than 0.62 except for the EF of 0.41 for monthly sediment yield comparison at W3. The errors between the predicted and observed means were all within ±6% for runoff and sediment yield; predicted soil organic carbon in the 0.15 m soils in 1994 were within 10% of the observed values for both watersheds. The percentage error between the predicted and observed average corn grain yields was −5.3% at W2 and −2.7% at W3 during the 20-year simulation period. Scenario analyses were also conducted to assess the benefits of ridge-till over conventional-tillage. Over the 20 years, the predicted benefit of ridge-till versus conventional-tillage on surface runoff reduction was 36% in W2 and 39% in W3, and about 82–86% sediment yield reduction in both watersheds. The cumulative soil organic carbon losses from sediment were reduced about 63–67%. The long-term benefit of ridge-till over conventional-tillage was also quantified as a minimum corn grain yield increase of 3.8%. The results of this study indicate that APEX has the ability to predict differences between the two tillage systems. The modeling approach can be extended to other watersheds to examine the impacts of different tillage systems.

Landscape Correlates Along Mourning Dove Call‐Count Routes in Mississippi

ABSTRACT Mourning dove (Zenaida macroura) call‐count surveys in Mississippi, USA, suggest declining populations. We used available mourning dove call‐count data to evaluate long‐term mourning dove habitat relationships. Dove routes were located in the Mississippi Alluvial Valley, Deep Loess Province, Mid Coastal Plain, and Hilly Coastal Plain physiographic provinces of Mississippi. We also included routes in the Blackbelt Prairie region of Mississippi and Alabama, USA. We characterized landscape structure and composition within 1.64‐km buffers around 10 selected mourning dove call‐count routes during 3 time periods. Habitat classes included agriculture, forest, urban, regeneration stands, wetland, and woodlot. We used Akaike's Information Criterion to select the best candidate model. We selected a model containing percent agriculture and edge density that contained approximately 40% of the total variability in the data set. Percent agriculture was positively correlated with relative dove abundance. Interestingly, we found a negative relationship between edge density and dove abundance. Researchers should conduct future research on dove nesting patterns in Mississippi and threshold levels of edge necessary to maximize dove density. During the last 20 years, Mississippi lost more than 800,000 ha of cropland while forest cover represented largely by pine (Pinus taeda) plantations increased by more than 364,000 ha. Our results suggest observed localized declines in mourning dove abundance in Mississippi may be related to the documented conversion of agricultural lands to pine plantations.

Economically Optimal Nitrogen Rate Reduces Soil Residual Nitrate

Post-harvest residual soil NO(3)-N (RSN) is susceptible to transfer to water resources. Practices that minimize RSN levels can reduce N loss to the environment. Our objectives were (i) to determine if the RSN after corn (Zea mays L.) harvest can be reduced if N fertilizer is applied at the economically optimal N rate (EONR) as compared to current producer practices in the midwestern USA and (ii) to compare RSN levels for N fertilizer rates below, at, and above the EONR. Six experiments were conducted in producer fields in three major soil areas (Mississippi Delta alluvial, deep loess, claypan) in Missouri over 2 yr. Predominant soil great groups were Albaqualfs, Argiudolls, Haplaquolls, and Fluvaquents. At four transects in each field, six treatment N rates from 0 to 280 kg N ha(-1) were applied, the EONR was determined, and the RSN was measured to a 0.9-m depth from five treatment plots. The EONR at sampling sites varied from 49 to 228 kg N ha(-1) depending on site and year. Estimated average RSN at the EONR was 33 kg N ha(-1) in the 0.9-m profile. This was at least 12 kg N ha(-1) lower than RSN at the producers' N rates. The RSN increased with increasing Delta EONR (total N applied - EONR). This relationship was best modeled by a plateau-linear function, with a low RSN plateau at N rates well below the EONR. A linear increase in RSN began anywhere from 65 kg N ha(-1) below the EONR to 20 kg N ha(-1) above the EONR at the three sites with good data resolution near the EONR. Applying N rates in excess of the EONR produced elevated RSN values in all six experiments. Our results suggest that applying the EONR will produce environmental benefits in an economically sound manner, and that continued attempts to develop methods for accurately predicting EONR are justified.