Coarse Silty Research Articles

Impact of soil organic matter on Pu migration in five Lithuanian surface soils

Pu distribution coefficient Kd variation was experimentally determined and examined in natural soil samples considering the type of soil, particle size, pH, the concentration of macroelements and organic matter content. This research was carried out with sand, silty sand, peat, clayey sand and clayey loam samples by applying 236Pu tracer in flow-through column tests. Due to relatively short contact time of 0.5–40 h the tests are considered as have not reached equilibrium state and represent the fast-moving contaminants retardation processes closer to field conditions. Every soil sample was fractionated into two particle size fractions: ≤0.25 mm and 0.25 ÷ 0.5 mm. Analysis revealed that Kd of Pu is higher for the smaller soil particle fraction (≤0.25 mm). The experimental study with 1.6, 4, 6 and 9 pH tracer solution revealed a tendency of elevated Kd when 4 pH and 6 pH solutions were applied, but obtained Kd values were not correlated with initial soil pH due to high buffering capacity of soils. This study shows a very significant influence (r = 0.98) of organic matter content on the Pu distribution coefficient. The Kd of Pu for the fine fraction of peat soil with high organic matter content (67%) reached maximum values of 6597 L/kg and 6200 L/kg when tracer solution was applied of pH = 4 and pH = 6, respectively. In comparison, the minimum Kd value of 3.9 L/kg was obtained for the coarse silty sand fraction with the lowest organic matter content of 1.3% at tracer pH = 1.6. A statistically reliable high correlations of r = 0.95 and 0.94 were also observed between Kd and specific soil elements Mg and Pb content in soils, respectively. The content of Fe in soils was significantly correlated (r = 0.67) with the Kd values of plutonium as well. However, the organic matter content in soils appeared to be the governing factor determining good correlations and causing the highest Kd of Pu values.

Silt-sized sediments and gypsum on surface formations in the Ebro valley. A disambiguation of the term gypsiferous silts

Since the 60’s, many authors have reported the presence of common silt-sized materials in the Ebro valley, on surface formations and positions that have given rise to several interpretations, sometimes contradictory. According to the references, three main terms are used (gypsiferous silts, loess and flour-like gypsum) applied to silts and fine sands with gypsum accumulations. The two first terms are applied to materials with carbonate contents up to 40-50%, coarse silty to fine sandy textures, and located in different positions. Loess normally appears as thick outcrops on slopes leeward from the main wind direction, with a limited pedogenesis consisting of a partial carbonate mobilisation and gypsum contents between 0 and 30%. The third (gypsum-rich) type has a variable spatial distribution, appearing between limestone layers, along footslopes, outcropping as metric surface formations, or as generalized karstified subsurface accumulations. Their composition is almost 100% silt- to fine sand size lenticular gypsum. While some authors claim for an aeolian origin to all these materials, only part of them (loess) has a clear aeolian origin, while flour-like gypsum derives from on-site weathering of gyprock or by precipitation of calcium- and sulfate saturated watertables as it is reported to occur in many other arid regions; and the rest (gypsiferous silts sensu stricto) are mainly colluvial-alluvial. This distinction is necessary since they differ in their geotechnical behaviour and properties relevant for agricultural land uses, therefore they should be taken into account when carrying out geological mappings or soil surveys in this and similar arid regions.

Silt-sized sediments and gypsum on surface formations in the Ebro valley. A disambiguation of the term gypsiferous silts

Since the 60’s, many authors have reported the presence of common silt-sized materials in the Ebro valley, on surface formations and positions that have given rise to several interpretations, sometimes contradictory. According to the references, three main terms are used (gypsiferous silts, loess and flour-like gypsum) applied to silts and fine sands with gypsum accumulations. The two first terms are applied to materials with carbonate contents up to 40-50%, coarse silty to fine sandy textures, and located in different positions. Loess normally appears as thick outcrops on slopes leeward from the main wind direction, with a limited pedogenesis consisting of a partial carbonate mobilisation and gypsum contents between 0 and 30%. The third (gypsum-rich) type has a variable spatial distribution, appearing between limestone layers, along footslopes, outcropping as metric surface formations, or as generalized karstified subsurface accumulations. Their composition is almost 100% silt- to fine sand size lenticular gypsum. While some authors claim for an aeolian origin to all these materials, only part of them (loess) has a clear aeolian origin, while flour-like gypsum derives from on-site weathering of gyprock or by precipitation of calcium- and sulfate saturated watertables as it is reported to occur in many other arid regions; and the rest (gypsiferous silts sensu stricto) are mainly colluvial-alluvial. This distinction is necessary since they differ in their geotechnical behaviour and properties relevant for agricultural land uses, therefore they should be taken into account when carrying out geological mappings or soil surveys in this and similar arid regions.

In situ Measurements of the Characteristics of Suspended Particles in the Barents Sea by the LISST-Deep Laser Diffractometer

The key indicators of marine sediment genesis are the particle size distribution (PSD) and volume concentration of suspended particulate matter (SPM). However, their study is not widespread in ship oceanology research. This paper reviews experience in using the LISST-Deep laser particle size analyzer for the study of marine SPM in situ. We present the first data on the volume concentration and PSD of SPM in the Barents Sea obtained during the 75th cruise of the RV Akademik Mstislav Keldysh in June 2019. We carried out an assessment of the adequacy of information display on the polydisperse system composition of the Barents Sea water body, which contains particles of a wide particle size spectrum of differing genesis and shape. This paper gives a regression and correlation analysis of LISST-Deep data with a Wet Labs turbidity meter and Multisizer 3 Coulter Counter, as well as the SPM mass concentration measured by the membrane filtration technique. All of them demonstrated reliable correlations between characteristics of SPM of the Barents Sea. Their correlation and determination coefficients varied from 0.6 to 0.8. The laser diffractometer produces more detailed vertical distributions of marine SPM parameters than does a turbidity meter, especially for euphotic zones. We found a significant correlation of LISST-Deep data with the concentration of dissolved oxygen, which increases for coarse–silty and sandy fractions (47.7–92.6 and 92.6–250 µm, respectively). Also, there is a correlation with SPM composition between parameters as organic carbon concentration and phytoplankton pigments. These correlations give some indirect indications of SPM composition from laser diffractometer measurements.

Effects of wind velocity and soil characteristics on dust storm generation in Hawr-al-Azim Wetland, Southwest Iran

Nowadays, dust storms are an important environmental problem in Iran (especially in Khuzestan Province). The Hawr-al-Azim Wetland is a source for generation of dust storms. One-third area of this wetland is located in Iran. In this study, dust discharge is calculated using wind velocity, mean soil grain size (D50) and soil dry density. Soil characteristics were determined by data collected from 16 boreholes drilled in this wetland. Distributions of D50 and soil dry density in the wetland were determined using ordinary kriging method. Then critical wind speed was calculated in different regions of the wetland. The wetland soil is composed of medium and coarse silty soil. The dust mass discharge has reduced from 2003. The maximum monthly dust discharge mass occurs in June and July (along with a mean monthly wind velocity of 4.42 m s-1 and 4.27 m s-1, respectively). Because of the little amount of clay particles and the high wind velocity, increased soil moisture content cannot help in neither raise inthe critical shear velocity nor decreased dust mass discharge. Also, the produced dust is transported towards Northwest Iran because the dominant direction of wind is 270° to 300° relative to the north.

SOIL-WASHING AND THERMAL PLASMA TREATMENT FOR DECONTAMINATION OF DREDGED MARINE SEDIMENTS FROM THE MIDIA PORT - ROMANIA

The aim of this paper is to show the results of two methodological approaches applied for decontamination of the Midia Port dredged sediment to assess their potential reusability. Firstly, the sediment samples were defined in physical, chemical, microbiological and ecotoxicological terms. The results were compared to the limit values established by environmental regulations for dredged sediment management. Some sediment samples exposed a very high concentration of hydrocarbons; the sediments were classified in three categories on the basis of their level of organic/inorganic pollutants. The polluted sediment samples were subjected to the soil-washing treatment. The post treatment analysis revealed that the coarse silty and sandy fractions resulted unpolluted. The soil-washing induced the physical concentration of pollutants (i.e. C>12) in the silty-clay fraction. The wastewater from the treatment plant, once treated, showed no critical issues. After soil-washing treatment, the sediment samples were exposed to a laboratory scale 30kW RF thermal plasma source. Two types of plasma assisted treatments have been performed: the carbothermal process (to evaluate the technical feasibility of silicon extraction during material inertization) and the vitrification process (only for material inertization). Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) withal X-ray fluorescence (XRF) and leaching tests were used to investigate the obtained material. The acquired results revealed a decontamination of the collected sediments with leaching test results below legal limits. EDS analysis showed the increment of silica (SiO2) content by about 5-7 % after the plasma treatment and that the localized extraction of silicon by the carbothermal reduction process has been obtained.

Effect of Zeolite Application on Growth and Yield of Chinese Cabbage and Chemical Properties of Soil Under Greenhouse Cultivation

Zeolite may help crop growth, yield increase, and salt removal. Field experiment under greenhouse cultivation was conducted to study the effect of zeolite application on growth and yield of Chinese cabbage (Brassica campestris L.) and soil. Soil was classified as Gyuam series (coarse silty, mixed, nonacid, mesic family of Aquic Fluvaquentic Eutrudepts). Six zeolite rates were 0, 3, 5, 10, 20 and <TEX>$40Mg\;ha^{-1}$</TEX>. Experimental design was a completely randomized design. Chinese cabbage was grown three times consecutively. Established plant number of plant and yield as fresh weight (F.W.) were measured and soil samples were taken before and after harvesting. Chinese cabbage yield was <TEX>$76.9Mg\;ha^{-1}$</TEX> at a rate of <TEX>$20Mg\;zeolite\;ha^{-1}$</TEX>, <TEX>$54.3Mg\;ha^{-1}$</TEX> at a rate of <TEX>$5Mg\;zeolite\;ha^{-1}$</TEX>, and <TEX>$51.3Mg\;ha^{-1}$</TEX> at control (no zeolite), respectively. Second order regression analysis using zeolite rate and yield showed that optimum zeolite application rate was between 24 and <TEX>$26Mg\;ha^{-1}$</TEX>. The regression equation explained about 88% of the yield variability. The electrical conductivity (EC) decreased from 3.2 to <TEX>$1.0dS\;m^{-1}$</TEX> for all treatments so that salt accumulation was not a concern. Based on the results, we recommend that optimum zeolite application rate is between 20 and <TEX>$24Mg\;ha^{-1}$</TEX> for Chinese cabbage under greenhouse cultivation.

Rare earth element compositions of core sediments from the shelf of the South Sea, Korea: Their controls and origins

Rare earth elements (REEs) of bulk sediments and heavy mineral samples of core sediments from the South Sea shelf, Korea, were analyzed to determine the constraints on REE concentrations and distribution patterns as well as to investigate their potential applicability for discriminating sediment provenance. Bulk sediment REEs showed large variation in concentrations and distribution patterns primarily due to grain size and carbonate dilution effects, as well as due to an abundance of heavy minerals. In the fine sandy sediments (cores EZ02-15 and 19), in particular, heavy minerals (primarily monazite and titanite/sphene) largely influenced REE compositions. Upper continental crust-normalized REE patterns of these sand-dominated sediments are characterized by enriched light REEs (LREEs), because of inclusion of heavy minerals with very high concentrations in LREEs. Notably, such a strong LREE enrichment is also observed in Korean river sediments. So, a great care must be taken when using the REE concentrations and distribution patterns of sandy and coarse silty shelf sediments as a proxy for discriminating sediment provenance. In the fine-grained muddy sediments with low heavy mineral abundance, in contrast, REE fractionation ratios and their UCC-normalized patterns seem to be reliable proxies for assessing sediment provenance. The resultant sediment origin suggested a long lateral transportation of some fine-grained Chinese river sediments (probably the Changjiang River) to the South Sea of Korea across the shelf of the northern East China Sea.

Effects of Planting Configuration and In-Row Plant Spacing on Photosynthetically Active Radiation Interception for Three Irrigated Potato Cultivars

Research studies have evaluated the production of potatoes (Solanum tuberosum L.) grown in conventional and bed planting configurations. However, intercepted photosynthetically active radiation (PAR) from these planting configurations has not been quantified. A study conducted in 2008 and 2009 quantified and compared the intercepted PAR from three planting configurations (four row conventional ridged-row [4RC], five row bed [5RB], and seven row bed [7RB]), and from different plant spacings of cvs Russet Burbank, Russet Norkotah, and Ranger Russet potatoes under sprinkler irrigation. A second study was conducted in 2007 to evaluate the relationship between PAR and leaf area of Russet Norkotah and Russet Burbank for the three planting configurations. These studies were conducted at the USDA-ARS Northwest Irrigation & Soils Research Lab in Kimberly, ID, on a Portneuf silt loam (coarse–silty mixed mesic Durixerollic Calciorthid). The canopy of Russet Norkotah and Ranger Russet potatoes grown in 5RB and 7RB planting configurations intercepted more PAR during the early vegetative and tuber initiation growth stages compared to the 4RC planting configuration at equal populations in 2008 and 2009 at all measurement dates. The canopy of Russet Burbank intercepted more PAR during the early growth stage in 2008 when planted in the bed planting configurations compared to the 4RC planting configuration, but not on the July 17, 2008 and July 9, 2009 dates. The canopy cover of Russet Burbank potatoes planted in the 4RC planting configuration tended to catch up with the bed planting configurations quicker than the other two cultivars. In general, the quantity of PAR intercepted as affected by planting configuration did not influence total tuber yield and other measured production variables. Cumulative PAR interception 0–72 days after planting (DAP) was increased 35%, 38%, and 32% for the 5RB and 65%, 69%, 23% for the 7RB relative to the 4RC planting configuration for Ranger Russet, Ranger Norkotah, and Russet Burbank, respectively. Cumulative PAR interception for the season was increased 15%, 16%, and 4% for the 5RB and 23%, 23%, 5% for the 7RB relative to the 4RC planting configuration for Ranger Russet, Ranger Norkotah, and Russet Burbank, respectively. The relationship between intercepted PAR and leaf area for Russet Norkotah during the early vegetative and tuber initiation growth stages was significantly different between the three planting configurations, with intercepted PAR at a given leaf area in the order of 7RB>5RB>4RC. For Russet Burbank, the relationship was significantly different for the 5RB and 7RB compared to 4RC planting configuration only, with intercepted PAR at a given leaf area in the order of 7RB=5RB>4RC.

Assessment of Properties of a Harkey Soil under Organic and Conventional Farming Systems

Farming practices involving less intense chemical use are becoming popular in the United States primarily because of environmental concerns related to the use of chemicals in conventional farming systems. Physical and chemical soil properties were assessed on four farms, one conventional farm and three organic farms 3 (OF3), 6 (OF6), and 9 (OF9) years after certification. All farms were located in Doña Ana County of southern New Mexico, sited on Harkey soil (coarse silty, mixed, calcareous, thermic typic Torrifluvents). OF3, OF6, and OF9 were planted to cotton (Gossypium arboreum L.), chile (Capsicum annuum), and alfalfa (Medicago sativa) in 2006, respectively, and the conventional farm was planted to cotton. Core and bulk soil samples were collected from each farm at three different locations and three depths during September 2005, June 2006, and November 2006. Clay content was positively correlated with field capacity, wilting point, and available water capacity (AWC) and negatively correlated with transmission pore volume (VTP) and sand content at most depths. The one-way analysis of means of soil physical and chemical properties separately by depth showed that bulk density (ρb) was greater in November 2006 samples than in September 2005 and June 2006 samples in OF9 and was lowest in the conventional farm. In general, saturated hydraulic conductivity (Ks), volume of storage pores, effective porosity, AWC, and VTP showed little variation and were not related to the amount of time under organic farming. Soil pH and electrical conductivity (EC) were greater in the organic farms, and EC values mostly increased with increasing amount of time under organic farming. The greatest EC (2.6 dS m−1) in OF9 indicated that 9 years of manure application has raised soil salinity only slightly. Although no evidence on significant improvement of soil quality due to organic farming was observed, with regard to soil storage and transport properties and soil salinity, the organic farming system is sustainable for this region.

Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last glacial-interglacial cycle

Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last glacial-interglacial cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2–4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period.

Compost and Manure Effects on Fertilized Corn Silage Yield and Nitrogen Uptake under Irrigation

Dairy manure increases the yields of dry bean (Phaseolus vulgaris L.) and spring wheat (Triticum aestivum L.) from eroded, furrow‐irrigated soils and may increase corn (Zea mays L.) silage yield from steeper eroded areas under sprinkler irrigation. In a 2‐year field study in southern Idaho on Portneuf silt loam (coarse silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid), the effects of a one‐time, fall application of 29 or 72 Mg ha−1 of dry manure or 22 or 47 Mg ha−1 of dry compost on subsequent silage yield and nitrogen (N) uptake from previously eroded, sprinkler‐irrigated hill slopes were evaluated. In October 1999, stockpiled or composted dairy manure was disked to a depth of 0.15 m into plots with slopes from 0.8 to 4.4%. After planting field corn in 2000 and 2001, a low‐pressure, six‐span traveling lateral sprinkler system was utilized to apply water at 28 mm h−1 in amounts sufficient to satisfy evapotranspiration to 6.4‐×36.6‐m field plots. Yields in 2000 were 27.5 Mg ha−1, similar among all rates of all amendments and a fertilized control. In 2001, compost applied at oven‐dry rates up to 47 Mg ha−1 increased yield compared to controls. Silage yield in 2001 increased initially then decreased with increasing manure applications. Where compost or manure was applied, regardless of rate, 2‐year average N uptake was 15% greater than controls. Regardless of treatment or year, yields decreased linearly as soil slope increased.

Surface and subsurface losses of N and P from salt-affected rice paddy fields of Saemangeum reclaimed land in South Korea

The present study was carried out to evaluate nutrient losses that occur during the course of agricultural activity from rice paddy fields of reclaimed tidal flat. For this study, we chose a salt-affected rice paddy field located in the Saemangeum reclaimed tidal area, which is located on the western South Korean coasts. The plot size was 1,000 m2 (40 m × 25 m) with three replicates. The soil belonged to the Gwanghwal series, i.e., it was of the coarse silty, mixed, mesic type of Typic Haplaquents (saline alluvial soil). The input quantities of nitrogen and phosphorus (as chemical fertilizer) into the experimental rice paddy field were 200 kg N ha−1 and 51 kg P2O5 ha−1 per annum, and the respective input quantities of each due to precipitation were 9.3–12.9 kg N ha−1 and 0.4–0.7 kg P ha−1 per annum. In terms of irrigation water, these input quantities were 4.5–8.2 kg N ha−1 and 0.3–0.9 kg P ha−1 per annum, respectively. Losses of these nutrients due to surface runoff were 22.5–38.1 kg N ha−1 and 0.7–2.2 kg P ha−1 for the year 2003, and 26.8–29.6 kg N ha−1 and 1.6–1.9 kg P ha−1 for the year 2004, respectively. Losses of these nutrients due to subsurface infiltration during the irrigation period were 0.44–0.67 kg N ha−1 and 0.03–0.04 kg P ha−1 for the year 2003, and 0.15–0.16 kg N ha−1 and 0.05–0.06 kg P ha−1 for 2004. When losses of nitrogen and phosphorus were compared to the amount of nutrients supplied by chemical fertilizers, it was found that 11.3–19.1% of nitrogen and 0.5–1.7% of phosphorus were lost via surface runoff, whereas subsurface losses accounted to 0.2–0.8% for nitrogen and only 0.02–0.04% for phosphorus during the 2-year study period.

Calibration of modelled mixing patterns in loess grain‐size distributions: an example from the north‐eastern margin of the Tibetan Plateau, China

AbstractGenetically meaningful decomposition (unmixing) of sediment grain‐size distributions is accomplished with the end‐member modelling algorithm. Unmixing of the loess grain‐size distributions of a Late Quaternary loess–palaeosol succession from the north‐eastern Tibetan Plateau indicates that the loess is a mixture of three end‐members representing very fine sandy, coarse silty and medium silty loess. The unmixing approach potentially enables the unravelling of sediment fluxes from multiple dust sources, opening the way to significant advances in palaeoclimatic reconstructions from loess grain‐size distribution data. However, as laser‐diffraction size analysis is a volume‐based technique, the proportional contributions of the modelled end‐members might deviate (significantly) from weight proportions. Hence, calibration of the end‐member volume proportions to weight proportions must be established before one can calculate the source‐specific dust fluxes. This paper reports the findings of a sediment‐mixing experiment which enables calibration of the modelled mixing patterns established for the Tibetan loess–palaeosol succession.

Using Repeated-Load Triaxial Tests to Evaluate Plastic Strain Potentials in Subgrade Soils

The design and the analysis of flexible pavement systems depend on soil layer characterization, traffic loads, and number of passes. The current AASHTO design method for flexible pavements uses resilient characteristics of subsoils to characterize and determine the structural support of each layer and to design the thickness of the layers. This moduli property, however, does not fully account for the plastic strain or rutting potentials of subsoils, as in the cases in which silt and mixed soils undergo high plastic deformations but possess high resilient properties. A study was initiated to establish a test procedure to use a repeated load triaxial device to measure plastic strain potentials of subgrade soils. Laboratory-compacted soil specimens were subjected to a repeated deviatoric load, determined as a percentage of static deviatoric load at failure under unconsolidated undrained conditions. The plastic strains were monitored during 10,000 repeated load cycles, and the accumulated plastic deformations were determined. The test procedure and test results conducted on two types of soils, a coarse sand and silty sand, are presented. Effects of soil type, compaction moisture content, dry unit weight, confining pressure, and deviatoric stresses on the plastic strains were addressed.

Milankovitch-scale multi-proxy records from fluvial sediments of the last 2.6 Ma, Pannonian Basin, Hungary

The continuous cores of two nearly 500 m deep boreholes, cutting Pleistocene fluvial sequences in the eastern part of the Pannonian Basin, Hungary have been studied. Magnetostratigraphy indicates that the sediment sequences span the last 2.6 Ma without significant hiatuses. Comparison of systematic variations in magnetic susceptibility with changes in grain size distribution revealed Milankovitch-scale cyclicity in sedimentation of 40 and 100 kyr cyclicity, which also shows a correspondence with the δ 18O variations of the ODP 677 site. Comparison of pollen and gastropod paleoecological data with the magnetic susceptibility proxies suggests that climate was a major allogenic control on the cyclicity. Zones of high magnetic susceptibility correspond closely with sandy and coarse silty parts of the borehole successions which largely coincide with pollen and molluscs indicating a warm climate. On the contrary zones with low magnetic susceptibility correspond to silts and clays, and in most cases coincide with cold climate indicator pollen and molluscs. Heavy mineral and XRD studies revealed that magnetic susceptibility reflects the absolute amount of detrital Fe-oxide minerals, mostly magnetite. Variations in the amount of magnetite are related to changes in heavy mineral content, which arise primarily from changes in sediment supply to the basin by rivers. The depositional model for the Pleistocene fluvial sediments suggests that sediment flux increased towards the basin during interglacials, due to the increased discharge and transport capacity of the rivers, while a decreased sediment supply to the distal parts of the basin occurred during glacials. A delay between erosion and storage of weathering products near to the source area and subsequent transportation and re-deposition of sediments in the basin interior setting is an important cause of this effect.

POTASSIUM MANAGEMENT EFFECTS ON COTTON YIELD, NUTRITION, AND SOIL POTASSIUM LEVEL*

ABSTRACT A three-year field experiment was conducted on an alluvial Morganfield silt soil (coarse silty, mixed, non-acid, thermic, Typic Udifluvent) to determine potassium (K) fertilizer rate and placement effects on cotton lint yield and soil K levels. The experiment was arranged in a randomized complete block design with four replications. An incomplete factorial arrangement of treatments (including 0, 68, 136, and 204 kg K ha−1 broadcast, 0, 34, and 68 kg K ha−1 banded in factorial combination with 0, 68, and 136 kg K ha−1 broadcast, and 204 kg K ha−1 broadcast with zero banded and 102 kg K ha−1 banded with 0 kg K ha−1 broadcast) was used. Cotton lint yield increased linearly with band application of K only in a relatively dry growing season possibly due to enhanced K uptake especially early in the season. Combination of band and broadcast application of K fertilizer was more effective in increasing cotton lint yield than either method alone. Maximum lint yield was obtained with the application of 34 kg K ha−1 banded plus 136 kg K ha−1 broadcast. This combined treatment resulted in greater leaf K concentration and total K uptake than either broadcast or band application alone. A linear increase in petiole and leaf K at early flowering resulted from broadcast incorporated K rates. Extractable soil K increased linearly in the 0 to 15 cm depth with increasing broadcast application of K fertilizer. Maximum lint yield was predicted at a soil K level near 160 mg kg−1. The Morganfield (CEC=11.1 cmolc kg−1) soil required approximately 2.2 to 2.3 kg fertilizer K ha−1 to increase soil K by 1 kg ha−1 in the 0 to 15 cm depth.

CHANGES IN SOIL PHYSICAL CHARACTERISTICS DURING TRANSITION FROM INTENSIVE TILLAGE TO DIRECT SEEDING

Converting from intensive tillage to no–till systems often increases soil strength, but the long–term impact of no–till on soil strength is not fully understood. Soil strength (evaluated with a hand–held cone penetrometer) and soil water content were evaluated in the top 30 cm of a replicated wheat/fallow rotation in a Pacific Northwest silt loam (coarse–silty, mixed, mesic, typic Haploxeroll). Soil water content was significantly lower in the no–till plots than in intensive tillage plots, which required a correction to remove the impact of soil water on penetrometer resistance. A regression equation was developed to adjust cone index values for soil water content. Comparisons of cone penetration resistance, adjusted for soil water, were made among intensive tillage, first–year no–till, and 17–year no–till. First–year no–till soil was resistant to penetration, but after 17 years of no–till the soil strength was lower and approached tilled conditions. Cone index values just below the plow layer (18 cm) increased from 2 to 3 fold the first year of no–till, but after 17 years of no–till the cone index values were not statistically different between no–till and intensive tillage below the tillage layer. This research demonstrated that silt loam soil structure improved with time during transition from intensive tillage to no–till.

FURROW IRR IGATION AND N MANAGEMENT STRATEGIES TO PROTECT WATER QUALITY

N management under furrow irrigation is difficult because nitratenitrogen (NO3-N) is frequently leached to groundwater. Banding and sidedressing N fertilizer on a non-irrigated side of a row of corn (Zea mays L.) might increase N uptake and minimize nitrate leaching potential by reducing the NO3-N in soil profiles at harvest, thereby protecting water quality. For two years in the field, we evaluated two N placements (broadcast vs. banded), two row spacings (0.76-m vs. a modified 0.56-m), and two ways of positioning irrigation water (applying water to the same side or alternating sides of the row with successive irrigations) for their effects on N uptake in corn silage and soil profile NO3-N (to the 0.9-m depth). In southern Idaho, we grew field corn in Portneuf silt loam (coarse silty, mixed superactive, mesic Durinodic Xeric Haplocalcid) by irrigating every second furrow nine times in 1988 and seven times in 1989. We measured N uptake by harvesting whole plants at physiological maturity and NO3-N in soil samples taken at two in-row locations in selected plots after each irrigation. Where irrigating alternating sides of the row, two-year average N uptake from 0.76-m rows was 131 kg ha 1, 15% greater (P < 0.001) than from 0.56-m rows. Where irrigating the same furrow all season, N uptake from banding equaled that from broadcasting the first year but was 21% greater (P < 0.001) the second. Applying water to the same furrow decreased profile N by about 170 kg ha 1 under 0.76-m rows by season's end in 1988. In 1989, irrigating the same furrow and banding N into an adjacent, never-irrigated furrow produced season-average profile N of a) 303 kg ha 1, the least under all fertilized 0.76-m rows, and b) 152 kg ha 1 under 0.56-m rows, half that under similarly treated 0.76-m rows. Our findings suggest that corn in 0.76-m rows should be fertilized by banding N into every second furrow and irrigated season-long using the remaining, non-fertilized furrows because those practices maintained or increased N uptake in silage and minimized residual NO3-N in 0.9-m soil profiles at season's end.

Nitrogen Placement, Row Spacing, and Furrow Irrigation Water Positioning Effects on Corn Yield

Furrow irrigation often leaches NO3–N. We hypothesized that banding and sidedressing N fertilizer on a nonirrigated side of a corn (Zea mays L.) row would maintain yield and decrease NO3–N leaching. In a 2‐yr field study in southern Idaho on a Portneuf silt loam (coarse silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid), we evaluated the effects of (i) N placement (broadcast vs. banded), (ii) row spacing (0.76 m vs. a modified 0.56 m), and (iii) irrigation water positioning (applying water to the same side or alternating sides of a row with successive irrigations) on field corn yield and N uptake. We irrigated every second furrow nine times in 1988 and seven times in 1989. Compared with broadcasting, banding maintained grain yield in 1988 and increased it by 11% in 1989. Where N was banded in 0.56‐m rows in 1989, silage yield when only the nonfertilized furrow was irrigated was 22.9 Mg ha−1, which was 22% greater than when alternating furrows were irrigated. Compared with 0.56‐m rows, the 0.76‐m rows had no effect on 2‐yr average grain yield but tended to increase 2‐yr average silage N. Banding N on one side of a row, rather than broadcasting, and applying water all season to the furrow on the other side of the row maintained or increased grain yield, increased silage yield by up to 26%, and increased N uptake in silage by up to 21%, particularly from N‐depleted profiles. Applying water to the same furrow, rather than alternating furrows, did not reduce yield or N uptake.