bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tillage Effects on Grain Sorghum and Wheat Yields in the Texas Rolling Plains
Authors: Bordovsky David G. , Choudhary Manilal , Gerard Cleveland J. 
Published: July 2010

AbstractSoils of the Texas Rolling Plains have poor structure, low soil organic matter contents, and low water holding capacity. Alternative farming practices must be explored to conserve and improve this natural resource. An 11‐yr (1979‐1989) field experiment was conducted at the Texas A&M University Research Station at Munday to determine the effects of tillage (reduced vs. conventional) and residue management (with vs. without residue) on grain yields of continuous grain sorghum [Sorghum bicolor (L.) Moench] and continuous wheat (Triticum aestivum L.) under dryland and irrigated conditions. A grain sorghum—wheat rotation (double‐crop) under reduced tillage was included in the irrigated study. Yields of reduced‐tillage grain sorghum in dryland and irrigated studies were as high or higher than yields of conventional‐tillage grain sorghum. Removal of surface residues in irrigated grain sorghum caused a significant decrease in yields. In contrast, reduced‐tillage systems and surface residues caused reductions in yields for dryland and irrigated wheat, which may be the result of decreased plant populations caused by poor seed‐to‐soil contact when planting through surface residues and N deficiency caused by immobilization. The average yield of irrigated wheat or grain sorghum using reduced‐tillage double‐cropping (2 and 3 Mg ha−1, respectively) was lower relative to wheat (3.5 Mg ha−1) and grain sorghum (4.6 Mg ha−1) grown continuously under conventional tillage.
Evaluation of Switchgrass Rhizosphere Microflora for Enhancing Seedling Yield and Nutrient Uptake
Authors: Brejda John J. , Moser Lowell E. , Vogel Kenneth P. 
Published: July 2010

AbstractMany rhizosphere microorganisms enhance nutrient uptake and plant growth, but their effectiveness can vary with host species and with genotype within species. This study evaluated the effectiveness of rhizosphere microflora indigenous to the rhizosphere of switchgrass (Panicum virgatum L.) for enhancing seedling yield and nutrient uptake. Switchgrass roots and rhizosphere soil were collected from native prairies and seeded stands in Nebraska, Kansas, Iowa, Missouri, Virginia, and North Carolina. Seedlings of four switchgrass cultivars were inoculated with root fragments and rhizosphere soil from each collection, fertilized with a nutrient solution, and grown in steamed sand for 12 wk in a greenhouse. Seedlings inoculated with rhizosphere microflora produced up to 15‐fold greater shoot and root yields, and recovered up to 6‐fold more N and 36‐fold more P than seedlings inoculated with rhizosphere bacteria only. These responses were consistent for all four switchgrass cultivars and were probably due to arbuscular mycorrhizal fungi. Switchgrass rhizosphere populations were highly variable in their ability to recover N and P and stimulate seedling shoot and root yields. Seedlings inoculated with rhizosphere populations from seeded switchgrass stands averaged 1.5‐fold greater shoot and root yields than seedlings inoculated with rhizosphere populations from native prairies. Rhizosphere populations that stimulated the greatest N uptake differed from populations that resulted in the greatest P uptake. Highly effective microbial populations appear to develop in the rhizosphere of seeded switchgrass stands.
Conservation Tillage Corn Production for a Semiarid, Subtropical Environment
Authors: Smart James R. , Bradford Joe M. 
Published: July 2010

AbstractBecause of the extreme climatic differences between their regions, farmers in southern Texas and northern Mexico have been reluctant to adopt conservation tillage systems developed in the north‐central or midwestern United States. With greater knowledge of the benefits and risks of conservation tillage practices under a semiarid, subtropical environment, producers can make better decisions regarding tillage practices. The objectives of this study were to compare the effects of conventional and conservation tillage on corn (Zea mays L.) yields and production costs during the transition from conventional to reduced tillage and provide farmers with guidelines for implementing conservation tillage in a subtropical, semiarid environment through evaluation of grain yield and production economics as affected by tillage. Conventional tillage (CT), reduced tillage with wide V‐sweeps (RT), and preplant no‐tillage (PPNT) were compared for both spring and fall corn production over three years. Grain yields for PPNT were lower than CT in the spring (−9%) and fall (−20%) of the first cropping year. Yields in PPNT were equivalent or up to 12% greater than CT yields in Years 2 and 3. Production costs were lower in the PPNT than in the CT, because of the reduced number of tillage trips over the field. A three‐year average of net returns for corn grown in the PPNT spring treatment was $47 ha−1 greater than RT, and $104 ha−1 more than the CT systems. Average fall corn net returns over three years for the PPNT were $5 ha−1 more than RT and $104 ha−1 more than CT systems. Average net returns from PPNT for spring and fall cropping seasons over three years was $23 ha−1 greater than the RT and $104 ha−1 greater than CT. Greater economic returns and lower production costs of PPNT compared with CT systems for all seasons and years were the result of reduced energy and operator time requirements. The conservation tillage systems (RT and PPNT) resulted in greater economic returns, compared with a CT tillage system, due to both greater yields in dry years and lower production costs in all years.
Comparison of Three Methods for Estimating Defoliation in Soybean Breeding Programs
Authors: Bowers Glenn R. , Kenty Michael M. , Way Michael O. , Funderburk Joseph E. , Strayer John R. 
Published: July 2010

AbstractThe proper assessment of defoliation by phytophagous insects in soybean [Glycine max (L.) Merr.] is required when screening germplasm for insect resistance. The objective of this study was to evaluate the effectiveness and relative efficiency of the widely used visual or relative assessment of insect defoliation compared with a more quantitative assessment for use in soybean breeding programs. In 1985 and 1991, visual assessments (whole plot, 1985; whole plant and average of partitioned plant, 1991) were compared with an established quantitative assessment. Twenty leaflets were randomly removed from each of the upper, middle, and lower thirds of the canopy of each plot. These leaflets were compared with a template of known defoliation in 1985. In 1991, a leaf area meter was used to determine the actual amount of defoliation of each plant. In 1990 and 1991, two types of visual estimates (whole plant and average of partitioned plant) were also compared with each other. Sampling time was estimated for each method. Estimates between visual and quantitative assessments were highly correlated each year. Precision was similar for each method. Sampling time for the visual assessment was at least 30 times faster than the quantitative assessment. The results of these studies show that relative estimates can be used to assess insect defoliation accurately and quickly.
Crop Sequence and Surface Residue Effects on the Performance of No‐Till Corn Grown on a Poorly Drained Soil
Authors: Wolfe Alice M. , Eckert Donald J. 
Published: July 2010

AbstractOn noncrusting, poorly drained soils, yield differences between corn (Zea mays L.) grown following corn and following soybean [Glycine max (L.) Merr.] can be much greater when no‐till rather than moldboard plowing practices are used. We conducted this experiment to determine whether differences in previous crop, surface residue cover, or a combination of both contribute to yield differences when no‐till corn follows corn or soybean. Corn was grown without tillage in 1991 and 1992 on a tile‐drained Kokomo silty clay loam (fine, mixed, mesic Typic Argiaquolls), following either corn or soybean. On half of the plots, residues were switched, so that the previous crop was corn but surface residue was soybean, and vice versa. On other plots, residue was left undisturbed. Plots with corn residue cover showed slightly lower spring soil temperatures in both years, and in 1992 showed slower early development of corn plants, than did plots covered with soybean residue. In both years, however, final plant height, grain yield, and stalk mass were greater where corn followed soybean, regardless of residue cover (P < 0.05). These differences appeared greater in 1991, a dry year, than in 1992, a more favorable year for corn production. Corn following corn showed more barren stalks and fewer kernels per ear than corn following soybean in the dry year, 1991 (P < 0.05). Nutrient concentrations in ear leaves of corn plants were all above sufficiency levels, were unaffected by surface residue, and were inconsistently affected by previous crop. Results indicate that lower yields of no‐till corn following corn rather than soybean are due more to previous crop than surface residue influences.
Improved Pasture Establishment and Production on Water‐Repellent Soils
Authors: Crabtree William L. , Gilkes Robert J. 
Published: July 2010

AbstractPasture establishment and production is reduced by water‐repellent soils. Ameliorative techniques are explored with this study. Two field experiments were conducted on water‐repellent soils to investigate (i) the improvement in emergence of pasture species with furrow sowing and the use of a press wheel and banded wetting agent and (ii) the residual effectiveness (applied 2 years previously) of a wetting agent on pasture growth and composition. In the first experiment, conventional level sowing (flat planting) was compared with furrow sowing using press wheels. Five pasture species were included, and the furrow‐sown treatments involved a banded wetting agent applied at four rates. Furrow sowing with a planter having press wheels increased the average emergence at 14 days after sowing by 133% relative to the conventional treatment and emergence was further increased 44% by banding 4 L ha−1 of wetting agent in the furrows. There was a large (up to sixfold) increase in early pasture production (330 to 2010 kg ha−1) and a large effect on pasture composition due to the residual effect of a wetting agent applied 2 years previously. The proportion of subterranean clover (Trifolium subterraneum L.) in the pasture increased from 6 to 33% due to the use of a wetting agent. This study shows that the effect of water repellency on pasture emergence and productivity is severe and that these ameliorative techniques are useful tools for improving pasture emergence.
Relation of Available Potassium to Soil Moisture
Authors: Luebs R. E. , Stanford G. , Scott A. D. 
Published: July 2010

AbstractPreliminary studies revealed that exchangeable K levels in Iowa soils fluctuated in response to vapor pressure changes and air drying. This phenomenon was investigated in relation to (1) K nutrition of plants in the greenhouse and (2) the problem of predicting the relative K‐fertility status in a wide range of Iowa soils. The thirteen soils employed in the greenhouse study showed variable increases in exchangeable K content upon air drying. Accompanying increases occurred in K uptake by the corn plants. Effects on K absorption by plants associated with drying of the soils often were equivalent to applying 60 to 120 lbs. K per 2 million lbs. of soil.Relative ability of the soils to supply K to plants under green‐house conditions was better correlated with exchangeable K content of undried than of air dried soils. This was true whether or not soils were air dried for cropping.Under field conditions, fluctuations in soil moisture levels in the surface one‐inch layer were accompanied by marked changes in content of exchangeable K over an 11‐week period. Below this layer, exchangeable K remained nearly constant since moisture content did not drop so low as in the surface. Results obtained in both field and laboratory showed that not much increase in exchangeable K occurred until soil moisture level had dropped to near 5 per cent or below. On the basis of overall results obtained it is concluded that for Iowa soils exchangeable K values determined after air drying may not be as reliable as those determined on moist soils, in predicting K supplying abilities of soils. Additional field studies are needed, however, to evaluate effects of alternate drying and wetting of soil on K nutrition of the crop.
A Field‐Calibrated Portable Neutron Rate Meter for Measuring Soil Moisture in Citrus Orchards
Authors: Stolzy L. H. , Cahoon G. A. 
Published: July 2010

AbstractSelected features of investigations previously described in the literature have been incorporated with new ideas in the construction of a dependable portable neutron‐scattering device for measuring soil moisture. The equipment and method of calibration have given very satisfactory results.The detector tube consists of a proportional counter tube filled with an enriched BF3 gas and a fast neutron source attached in an annular container at the mid‐plane of the counter tube. Thermal neutron densities in the soil are measured by inserting the detector tube into lined access holes in the field. When removed from the access hole, the detector tube is drawn into a shield composed of lead, paraffin, and cadmium. The paraffin acts as a shield for the fast neutrons and also serves as a standardization material for adjusting the meter.A rate meter was chosen to indicate the slow neutron flux returning to the detector tube. The counter tube voltage was at first supplied by a vibrator type power supply, which was later replaced by a transistorized power pack.The total weight of the equipment and shield was too much for one operator to carry conveniently; the entire unit was therefore mounted on a modified golf cart.A definite curvilinear relationship was shown between the percent volume of water in the soil and the meter reading. The regression equation of soil moisture on meter reading was Ŷ = 0.2462 + 0.4337X + 0.0101X2. The correlation between Y and Ŷ was R = 0.9833. The standard error of estimate from the mean Y (18.34) was 1.42. This study further confirmed other investigations, in that a single calibration curve served for many soil types.
Inorganic Nitrogen Oxidations in Relation to Associated Changes in Free Energy
Authors: Chao Tyng‐Tsair , Kroontje Wybe 
Published: July 2010

AbstractFree energy changes of inorganic nitrogen oxidations in acid and basic media are calculated, interrelated, and used to interpret some research data reported in the literature. The data obtained indicate that hyponitrous acid and nitrous oxide may be considered intermediates in nitrification, however, the existence of hydroxylamine as an intermediate between ammonia and/or ammonium ion and nitrite is not supported by the calculations obtained. It is shown that in acid solutions nitrite may undergo three reactions: it may decompose to nitric oxide and nitrite, oxidize to nitrate, or be reduced to nitrous oxide; in alkaline solutions nitrate seems to be the only product. Nitrous oxide may evolve under aerobic conditions from the decomposition of hyponitrous acid and under anaerobic conditions from the interaction of intermediate products, hydroxylamine, and nitrite.
Age Relationship of Wavy‐Gilgaied and Nongilgaied Soils in Western South Dakota
Authors: White E. M. 
Published: July 2010

AbstractThe incidence of wavy‐gilgaied, nongilgaied‐Chestnut, and lithosolic soils formed from Pierre shale was estimated at intervals in a creek valley by a transect method to test the concept that the three soils form a chronosequence. Recent geologic erosion was found to decrease progressively up the valley. The distribution of both the wavy‐gilgaied soil and the lithosolic soil in the valley was significantly related to the extent of the recent geologic erosion. The distribution of nongilgaied‐Chestnut soils was not significantly related to the amount of erosion along the valley. Wavy‐gilgaied soils were most abundant where erosion was least and thus the soil age was greatest, whereas Lithosols were most abundant where erosion was greatest and thus the soil age was least. Chestnut soils occurred in both locations, presumably where the soil age was intermediate.
Particle Size Sorting of Proglacial Eolian Materials
Authors: Franzmeier D. P. 
Published: July 2010

AbstractBagnold proposed that there is a critical size separating particles moved by saltation from those carried in suspension. This theory was tested in proglacial deposits near the Wabash and White Rivers in Indiana. Here the westerly winds of glacial times piled the sand by saltation into a band of dunes and carried the silt in suspension and deposited it as loess east of the dunes. Soil C horizons were sampled in transects across the dune and loess belts of both areas and were analyzed for particle size using narrow size intervals. In both areas a zone between 40µ and 80µ diameter separates dune sand from loess. Between these limits the dune sands and loess are more than 94% exclusive of each other. Glacial till that is representative of the source of outwash, which, in turn, is the source of the eolian deposits, contains much 40 to 80µ material. This size fraction, however, is practically missing from both the dunes and the loess. Apparently this fraction was selectively removed by wind or by water and deposited elsewhere.
Mass Transfer Studies in Sorbing Porous Media I. Analytical Solutions
Authors: van Genuchten M. Th. , Wierenga P. J. 
Published: July 2010

AbstractAn analytical solution is presented for the movement of chemicals through a sorbing porous medium with lateral or intra‐aggregate diffusion. The liquid phase in the porous medium is divided into mobile and immobile regions. Diffusional transfer between the two liquid regions is assumed to be proportional to the concentration difference between the mobile and immobile liquids. Sorption processes in both the dynamic and stagnant regions of the medium are assumed to be instantaneous and the adsorption isotherm is assumed to be linear. The analytical model derived here describes the extensive tailing observed during flow through an unsaturated, aggregated sorbing medium and explains the often observed early breakthrough of chemicals in the effluent.
Experimental Evidence on the Origin of Vermiculite in Soils on Lower Palaeozoic Sediments
Authors: Adams W. A. 
Published: July 2010

AbstractVermiculite occurs as a pedogenetic product in soils on Lower Palaeozoic sediments in mid‐Wales. Iron‐rich chlorite and dioctahedral illite, both of which are present in these sediments, are possible precursors. Field evidence on the occurrence of vermiculite indicates an increase in vermiculite coincident with chlorite weathering and a maximum vermiculite content in moderately weathered horizons. The vermiculite content of highly weathered eluvial and organic horizons of podzols is low. Using an oxidation procedure involving Na2Cr2O7 it was possible to transform chlorite to a vermiculite having similar X‐ray diffraction properties to soil vermiculite. The transformation was demonstrated on intact clay‐sized fractions of a Silurian mudstone and on chlorite separated electromagnetically from a soil derived from Lower Palaeozoic sediments.
The Effect of Discharge Rate and Intermittent Water Application by Point‐source Irrigation on the Soil Moisture Distribution Pattern
Authors: Levin I. , van Rooyen P. C. , van Rooyen F. C. 
Published: July 2010

AbstractA comparison was made between the results of laboratory and field experiments regarding predictions of soil moisture distribution from a point source on the one hand, and those theoretically calculated by a computer simulation model (Bresler, 1975) on the other hand. A good agreement was found between computed and experimental data. When the verified model was used for predictions regarding soil water distribution under point‐source irrigation, it was found that when the same total amount of water (12 liters) was added to the soil with a 2, 4, or 8 liters/hour continuously applied trickle source, a loss of 26% of the total amount applied was affected below the 60 cm depth after 12 hours. The initial water content of the soil was adjusted to the field capacity value. Under identical conditions I liter/hour continuously applied and 2 liters/hour pulsed (intermittent) irrigation resulted in only a 12% loss. The lateral distribution of the water showed that in the first group of treatments 80% of the water in the wetted soil volume was distributed 45 and 43 cm horizontally from the point source after 12 and 24 hours respectively. In the second group of treatments the distribution was to 29 and 40 cm. Thus the second group of treatments showed a clear advantage in reducing water loss under the root zone while still not significantly affecting the horizontal distribution. The pulse treatment can therefore replace the advantageous low (1 liter/hour) discharge rate while to a large extent avoiding the difficulties of blocking of outlets by maintaining a higher (2 liter/hour) discharge rate.
Calculation of Internodal Conductances for Unsaturated Flow Simulations: A Comparison
Authors: Schnabel R. R. , Richie E. B. 
Published: July 2010

AbstractFive techniques for calculating internodal conductance were compared during a finite‐difference solution of the Richards equation. Arithmetic, geometric, and harmonic means as well as integrated and upstream weighted conductances were used to calculate steady‐state water content distributions and infiltration into three soils. The water content distributions simulated using the integrated conductance resulted in distributions equivalent to those calculated analytically. Simulation results of infiltration most closely matched literature data when the integrated or geometric mean conductances were used. The harmonic mean conductance gave unacceptable results for all situations simulated.
Flocculation Series Test Yielding Time‐Invariant Critical Coagulation Concentrations of Sodium Illite
Authors: Hesterberg Dean , Page A. L. 
Published: July 2010

AbstractCritical coagulation concentrations (CCCs) of Na illite were measured using flocculation series tests. Results consistent with kinetic theories of coagulation showed the effect of coagulation/settling time on the CCC at various pH levels. A general flocculation series test procedure for reference and soil minerals is proposed. This test controls particle‐interaction dynamics and uses a long coagulation time to minimize the effects of variations in particle diffusion rates and solids concentrations, and to yield time‐invariant CCCs. After combining Na illite dispersions with a series of pH‐adjusted, concentrated NaClO4 solutions, the mineral particles coagulated primarily by Brownian diffusion. To control the release of interlayer K from Na illite, an equilibrium K concentration of 0.1 mol m−3 was added to all suspensions. The CCCs were detected from turbidity measurements taken after various coagulation time intervals. Between 2 and 17 h, CCCs generally decreased with increasing particle‐interaction time; however, CCCs measured after 17 and 36 h were equivalent and time invariant.