bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Sunflower Simulation Model: I. Model Development
Authors: Chapman Scott C. , Hammer Graeme L. , Meinke Holger 
Published: July 2010

AbstractIn dryland farming systems, opportunities to improve sunflower (Helianthus annuus L.) yields are mostly associated with management decisions made at planting. Dynamic crop simulation models can assist in making such decisions. This study reports the structure of QSUN, a simple and mechanistic crop model for sunflower, and how it accounts for the dynamic interaction of the crop with the soil and aerial environment. The model incorporates several recent approaches to simulation of crop growth in dryland conditions. QSUN estimates growth, development, and yield of a sunflower crop. Daily inputs of temperature and photoperiod drive a phenology submodel to predict stages of emergence, bud visibility, 50% anthesis, and maturity. Using these stages, the growth submodel, driven by daily inputs of radiation, rainfall, and temperature, estimates leaf area production and senescence and soil water extraction. Biomass production is calculated from the amount of radiation intercepted by leaves or from the amount of water accessible in the root zone, depending on whether radiation or water is limiting crop growth. Seed yield is calculated from the allocation of biomass to the grain following anthesis. Sensitivity testing of the model under several irrigation regimes indicated that QSUN was most sensitive to the rate at which partitioning of biomass to grain increased, the ratio of biomass produced to water transpired, and the rate of soil water extraction in a water limited situation. The model was tested against independent data, with actual phenological data and was able to satisfactorily predict leaf area index (r2 = 0.65), total biomass (r2 = 0.96), and grain yield (r2 = 0.93), thus providing a tool for use in simulations studies and to assist in management decision making.
A Sunflower Simulation Model: II. Simulating Production Risks in a Variable Sub‐Tropical Environment
Authors: Meinke Holger , Hammer Graeme L. , Chapman Scott C. 
Published: July 2010

AbstractIn highly variable environments, farmers require quantitative information on production risk to make well informed farming decisions. In many cases this can only be achieved through simulation studies. Thus, the dynamic sunflower (Helianthus annuus L) model QSUN was used, in conjunction with long‐term climate records, to quantify the impact of climatic variability on production. Simulation results will assist farmers in making important management decisions such as if or when to plant, or which maturity type to choose. Simulations were conducted for three maturity types for planting times throughout the year and for two locations in Queensland, Australia (Dalby and Emerald). For both locations, more than 100 yr of daily temperature and rainfall records were available. Two hypothetical soil profiles were chosen to assess the effect on simulated yield likelihood of (i) maximum plant available soil water holding capacity of the soil (PAWC) and (ii) soil moisture content at sowing. The analysis showed that yields not restricted by water availability were higher at Dalby (370 g m−2) than at Emerald (349 g m−2). At Dalby, simulated median yields for soil profiles either full or half‐full (180 mm PAWC) at sowing were around 100 and 60 g m−2, respectively, with very little seasonal variation. At Emerald, median yields (70–90 and 40–60 g m−2 for the full and half‐full profile, respectively) were generally lower and seasonal variations were apparent: highest simulated median yields were achieved for mid‐summer sowings. Yield variability was assessed by comparing median yields to yields at the 75 and 25% probability level. For both locations, this showed that even at the 25% probability level, yields of more than 100 g m−2 can only be achieved if the soil profile was fully charged at planting. The comparison among maturity types showed no clear advantage of maturity type. These results provide farmers with an objective assessment of production risk in environments, where even one lifetime of experience can be insufficient to sample the climatic variability adequately.
ENWATBAL.BAS: a Mechanistic Evapotranspiration Model Written in Compiled Basic
Authors: Evett S. R. , Lascano R. J. 
Published: July 2010

AbstractENWATBAL, a mechanistic energy, water balance model originally written in the Continuous System Modeling Program (CSMP) simulation language, was largely incompatible with personal computers (PCs). ENWATBAL.BAS was developed to extend the model application to PCs using BASIC, which is widely available. BASIC functions or subprograms were provided to emulate CSMP language commands including integration, implicit root finding, and generation of dependent variable values from tables of dependent‐independent variable data pairs. The BASIC version is highly modular and thus easier to read and maintain. The verification of ENWATBAL.BAS against ENWATBAL, with identical input data, discretization, and time integration steps, indicated no appreciable differences between the two versions. Runtimes for a seasonal simulation (100 d) were nearly the same (about 5 h) for the compiled BASIC version with a 20 MHz, 80386‐based PC and the CSMP version with a MicroVAX II, and four times faster for a 33 MHz, 80486‐based PC. Discretization analysis showed that soil layer thickness should be no larger than 0.002 m for the surface layer although thickness may increase to as much as 0.2 m for subsurface layers. Parameter sensitivity analysis showed that evapotranspiration estimates changed as expected in response to changes in parameter values for surface roughness length, maximum crop water potential, soil albedo, and crop hydraulic resistance. Many model changes were made to the BASIC version subsequent to the speed comparisons resulting in a more advanced and flexible model. ENWATBAL.BAS is a useful tool for investigating the complex mechanisms of evapotranspiration.
Nature and Characterization of Ammonium Effects on Wheat and Tomato
Authors: Gill Maqsood A. , Reisenauer H. M. 
Published: July 2010

AbstractThe very significant yield increases obtained by adding NH4 to NO3‐supplying hydroponic cultures have, for unknown reasons, not been duplicated in soil systems. This research was conducted to consolidate and extend our knowledge of the effects of added NH4 on plant processes, and to define the plant and culture characteristics requisite to optimal utilization of mixed N sources. Wheat (Triticum aestivum L. cv. Anza) and tomato (Lycopersicon esculentum Mill. cv. 6718 VF) were grown in solution cultures providing variables of N source (NO3, NH4, and NH4NO3), culture buffering, and concentration of NH4 and NH3(aq). Treatment effects on plant growth and composition were evaluated. Wheat grew best in NH4NO3 culture, equally well in NO3 or NH4 cultures buffered at pH 6, and poorest in unbuffered NH4 cultures. Growth enhancement with NH4NO3 was accompanied by increased N intake and synthesis of protein. Lowered yields in unbuffered NH4 cultures were associated with H+ injury to the roots and reduced intake of N and nutrient cations. Toxic effects of NH4 per se occurred when culture concentrations exceeded 16 mmol L−1 for roots. Severity of toxicity was associated with abnormally high root and shoot amide concentrations, and tissue levels of unassimilated NH4 exceeding 50 mmol kg−1. In alkaline cultures, NH3(aq) concentrations greater than 0.028 mmol L−1 for tomato and 0.15 mmol L−1 for wheat reduced top growth, and destroyed the structure and functioning of roots. These detrimental effects of NH3(aq) were related to its concentration in the culture, not to tissue NH4.
Cotton and Soybean Root System Growth in Three Soil Temperature Regimes
Authors: Bland William L. 
Published: July 2010

AbstractExploration of the soil by roots has significant implications for both plant growth and soil water dynamics. The important environmental determinants of root growth are identified, but an integrated and quantitative understanding of their relative importance through a range of environments is not yet available. The role of seasonal patterns of soil temperature on root system development throughout a crop’s life was studied in controlled‐environment experiments. Cotton, then soybean, was grown in 1.8‐m deep controlled‐temperature rhizotrons. Three soil temperature regimes were replicated three times for each species. In all treatments of an experiment, the near‐surface (0 to 15 cm) temperatures were equal, to promote similar aboveground growth. This near‐surface temperature was increased during the experiment so as to mimic field conditions typical for each species. One treatment was isothermal with depth, the entire soil column warming the same as the surface. A pattern of subsoil warming similar to that found in regions where the crop is grown was the second treatment, and the third set of columns warmed at roughly one‐half the rate of the second treatment. Rate of downward growth of root systems of both crops increased with the rate at which the soil body warmed. Cotton roots grew downward at 1.7, 1.4, and 0.7 cm d−1 in the treatments used for that study; soybean rooting depth increased at 2.6, 1.2, and 0.9 cm d−1. Results supported the hypothesis that root system growth can be predicted from the local soil temperature of the deepest roots and the temperature‐dependent extension rate of seedling roots.
Energy Exchange and Water Use Efficiency of Field Crops: Validation of a Simulation Model
Authors: Grant R. F. , Rochette P. , Desjardins R. L. 
Published: July 2010

AbstractCrop canopies exercise some control on the exchange of mass and energy with the atmosphere by regulating their stomatal resistance. A hypothesis is proposed in which regulation of stomatal resistance is controlled jointly by the water status of the canopy and photosynthetic capacities of the leaves in the canopy. This hypothesis was incorporated into an ecosystem simulation model, which was tested against data for mass and energy exchange measured over a growing barley crop at different levels of canopy cover and soil water content. Standard differences (square root of the mean square difference) between simulated and measured hourly values for net radiation, latent heat, and sensible heat over the soil‐canopy surface were <50 W m− during each date for which comparisons were made, which is within the range of experimental error. The hypothesis allowed title model to simulate diurnal changes in canopy stomatal resistance under changing atmospheric conditions that were consistent with those estimated from flux measurement techniques. These diurnal changes allowed the model to reproduce changing relationships between latent and sensible heat fluxes measured at different canopy covers and soil water contents. The diurnal changes in simulated canopy stomatal resistance also allowed the model to reproduce diurnal changes in soil‐canopy net CO2 exchange (SD = 3–4 μmol m−2 s−1) and water use efficiency under changing atmospheric conditions and soil water status. The hypothesis for the regulation of canopy stomatal resistance is simple, and yet allows observed canopy behavior to be reproduced over a wide range of conditions.
Oat Companion Crop Management in Alfalfa Establishment
Authors: Curran Bill S. , Kephart Kevin D. , Twidwell Edward K. 
Published: July 2010

AbstractCompanion crops may compete with alfalfa (Medicago saliva L.) seedlings, but establishment with preemergence herbicides and without a companion crop may enhance the potential for soil erosion. Objectives of this study were to (i) compare alfalfa establishment techniques involving clipping or chemical control of weeds and (ii) determine differences in morphological development of alfalfa grown under several establishment techniques. Experiments were conducted at two locations in eastern South Dakota in 1989. Seven treatments included clipping the oat (Avena sativa L.) companion crop at boot stage, not clipping the oat, two treatments with oat sprayed with sethoxydim (2‐[I‐(ethoxyimino) butyl]‐5‐[2‐(ethylthio) propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one) at either S‐(SES) or 15‐cm (SE15) of oat growth, clear seeding (CS), hand weeding (HW), and a control treatment with no weed control. At Aurora, SD, alfalfa yields were greatest in HW and SE5 treatments. Yields were 24 and 36% less for CS and SE15, respectively, than for SES. At Brookings, SD, yield was also greatest for HW; however, CS had the greatest yield among the conventional establishment techniques. Yield for SES was 15% less than CS. At both locations, alfalfa yield was lowest for the two typical companion crop techniques. For typical companion crop and control treatments, mean tap root length, shoot‐to‐root ratio, and shoot length were reduced compared with other treatments. Subsequent alfalfa yields in 1990 were not affected by establishment technique at either location. Chemical control of an oat companion crop provided greater seedingyear alfalfa yields than typical companion cropping and greater protection from soil erosion than clear seeding.
Path Analysis of Heavy Metal Adsorption by Soil
Authors: Basta N. T. , Pantone D. J. , Tabatabai M. A. 
Published: July 2010

AbstractPath analysis, a statistical technique that differentiates between correlation and causation, was used to describe heavy metal adsorption by soil. A path analysis model that evaluates the effect of soil pH, CEC, organic carbon content (OC), and clay content on adsorption of Cd, Cu, Ni, Pb, and Zn by soils from two long‐term cropping experiments in Sutherland and Kanawha, IA, was investigated. In general, direct effects of soil properties on metal adsorption were pH > OC > CEC. Path analysis direct effects of pH on Cd (0.83), Cu (0.93), and Pb (0.96) by Galva (fine‐silty, mixed, mesic Typic Hapludoll) soils from the Sutherland experiment were highly significant (P < 0.01). Significant (P < 0.01) direct effects of pH on Cd (0.93), Cu (0.95), and Pb (0.85) adsorption by Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soils from the Kanawha experiment. Significant (P < 0.01) simple correlation coefficients were found between soil pH and Cd (0.64), Cu (0.89), and Pb (0.84) adsorption by Galva soils and between soil pH and Cd (0.82), Cu (0.74), and Pb (0.62) adsorption by Webster soils. Both path analysis and correlation analysis showed that soil pH was the predominant property affecting Cd, Pb, and Cu adsorption by soil. However, path analysis revealed three additional relationships not found by correlation analysis. They included direct effects of CEC on Ni adsorption (0.72*), OC on Pb adsorption (0.35*) by Galva soils, and OC on Cd adsorption (0.59*) by Webster soils. Partitioning of OC direct and indirect effects suggested that adsorption of Pb and Cd by soil organic matter through complexation reactions was more important than adsorption by organic matter CEC sites.
Accuracy of Sap Flow Measurement Using Heat Balance and Heat Pulse Methods
Authors: Cohen Y. , Takeuchi S. , Nozaka J. , Yano T. 
Published: July 2010

AbstractThe heat balance and the heat pulse methods for measurement of sap flow in plants, were compared under conditions of variable evaporative demands in order to evaluate their accuracy. The study was conducted with potted soybean (Glycine max Merr. cv. tamahomare) and corn (Zea mays cv. kakuteru 901) plants housed in a plastic chamber. The computed sap flow was compared to transpiration rate as measured by weight loss. The calibration coefficient for the heat pulse expresses the ratio of actual transpiration rate, Tr (mg s−1), to measured heat velocity, v (mm s−1), multiplied by the stem area, a (mm2). The ratio Tr/(v × a) was 1.01 ± 0.08 and 1.73 ± 0.1 for soybean and corn, respectively. The coefficient was not affected by plant age, size, or atmospheric evaporative demand. Accuracy of measurements using the heat pulse method was poor at low transpiration rate. The heat balance method does not require calibration (except for the gauge factor for estimating the sheath conductance). Transpiration was estimated accurately by this method in both species at low or moderate rates (0.6 L d−1). As the transpiration rate increased, the computed sap flow deviated from the measured transpiration. In soybean, transpiration was underestimated by 20%, while in corn, it was overestimated by 25%. Results indicated that the basic assumption of the heat balance method (i.e., that the stem surface temperature is considered a reliable measure of the average temperature over the entire cross‐sectional area) may be incorrect either at high or fluctuating flow rates, or whenever the water conducting system is distributed unevenly in the stem cross section.
Grain Yield of Subsurface Microirrigated Corn as Affected by Irrigation Line Spacing
Authors: Powell Norris L. , Wright F. Scott 
Published: July 2010

AbstractWithout irrigation, crop yields are usually water‐limited on the acid soils of the southeastern USA. Economically feasible irrigation systems that require less water are needed. As part of a feasibility study of subsurface microirrigation for corn (Zea mays L.) production, the effects of irrigation line spacing and irrigation water amount were investigated in a 5‐yr study at Suffolk, VA. The soil was a Uchee loamy sand (loamy, siliceous, thermic Arenic Hapludult) with inclusions of Emporia loamy sand (fine‐loamy, siliceous, thermic Typic Hapludult). Treatments were three line spacings (0.91, 1.82, and 2.74 in apart, buried 0.38 m below and parallel to the crop row), low and high water amounts (about 41 and 62% of average pan evaporation, respectively), and a nonirrigated control. Nonirrigated grain yields ranged from 3.12 Mg ha−1 (1987) to 9.73 Mg ha−1 (1989). Irrigated grain yields ranged from 8.27 to 12.02 Mg ha−1. Except for 1987 (the driest year), there was no significant difference between the low and high water application amounts. In 1987, corn irrigated with the higher rate yielded 34% more. Grain yields were highest with irrigation lines placed under each row (narrow spacing) and ranged from a low of 8.55 Mg ha−1 (wide spacing) in 1989 to a high of 12.25 Mg ha−1 (narrow spacing) in 1990. Increased amounts of irrigation water were needed with the wider line spacing to obtain corn grain yields comparable with the other two spacings. It is unlikely that the lowered yield or increased irrigation water required with wide line spacing could offset additional installation costs for the narrow spacing. Irrigation lines spaced in alternate corn row middles (1.83 m) or under the third row (2.74 m) are recommended.
Fall Tillage Method: Effect on Short‐Term Carbon Dioxide Flux from Soil
Authors: Reicosky Donald C. , Lindstrom Michael J. 
Published: July 2010

AbstractThe increasing concern for rising CO2 concentrations from agricultural activities has prompted the need to better understand the flux of greenhouse gases to the atmosphere. This work determines the effect of four fall tillage methods on short‐term CO2 flux from a Hamerly clay loam (fine‐loamy, frigid Aeric Calciaquoll) in the northern Corn Belt. Moldboard plow only, moldboard plow plus disk harrow twice, disk harrow once, and chisel plow once using standard tillage equipment following a wheat (Triticum aestivum L.) crop were compared with no‐tillage. The CO2 flux was measured with a large portable system commonly used to measure canopy gas exchange of field crops. Measurements of CO2 flux were initiated within 5 min after tillage completion for each tillage treatment and continued intermittently for 19 d. Moldboard plow had the roughest soil surface and the highest initial CO2 flux (29 g m−2 h−1) and maintained the highest flux throughout the study. Moldboard plow plus disking twice and chisel plow had similar initial rates (7 and 6 g m−2 h−1, respectively) that were greater than disk harrow and no‐tillage. The high initial CO2 fluxes were more related to depth of soil disturbance that resulted in a rougher surface and larger voids than to residue incorporation. The differences in CO2 flux between tillage treatments were small but consistent 19 d after initial tillage and 64 mm rain. Lower CO2 flux rates caused by tillage were associated with low soil disturbance and/or small voids. Tillage methods affected the initial CO2 flux differently and suggest improved soil management can minimize agriculture's impact on global CO2 increase.
Crop Rotation and Tillage Effects on Soil Water and Cotton Yield
Authors: Bordovsky J. P. , Lyle W. M. , Keeling J. W. 
Published: July 2010

AbstractThe Texas Southern High Plains is a major cotton (Gossypium hirsutum L.) producing area where a monoculture of conventionally tilled continuous cotton is thought to be causing a downward trend in yields. A factorial experiment with split plot design evaluated the main and interactive effects of (i) cotton‐wheat (Triticum aestivum L.)‐fallow rotation vs. continuous cotton, (ii) no tillage vs. conventional tillage, and (iii) furrow diking vs. no diking on cotton yield and soil water. Effects were determined for both dryland and irrigated production. Of the main factors considered, the cotton–wheat rotation had the greatest positive effect on yield and also on soil water variables. Rotation increased dryland and irrigated lint yields 12.6 and 12.8%, respectively. No tillage significantly increased yields (6.9 and 5.5% for dryland and irrigated, respectively) and enhanced seasonal soil water status. Yield increase due to diking was not statistically significant (P > 0.05) under continuous cotton production or when wheat was rotated with cotton. The greatest cotton lint yield and soil water increases were obtained when no tillage was combined with the cotton–wheat rotation (20–25% increases). Percent yield increase was directly associated with improved soil water relations resulting from the cropping and tillage treatments.
Bermudagrass and Cool‐Season Turfgrass Mixtures: Response to Simulated Traffic
Authors: Dunn John H. , Minner David D. , Fresenburg Brad F. , Bughrara Suleiman S. 
Published: July 2010

AbstractAvailability of newer, more competitive cool‐season grasses has renewed interest in persistent, balanced warm‐ and cool‐season species mixtures for sports turf. In this Missouri study, one‐time overseedings of blends and mixtures of Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), Chewings fescue (Festuca rubra L. subsp. commutata Gaud.), hard fescue (Festuca longifolia Thuill.), and creeping red fescue (Festuca rubra L. subsp. rubra Gaud.) were made on established plots of KSU S‐16 and ‘Midiron’ bermudagrass [Cynodon dactylon (L.) Pers.]. One‐half of each plot was subjected to simulated traffic beginning 18 mon after overseeding, using a modified Brinkman traffic simulator. Quality of four mixtures (bermudagrass + Kentucky bluegrass, bermudagrass + perennial ryegrass, bermudagrass + perennial ryegrass + Kentucky bluegrass, and bermudagrass + perennial ryegrass + Kentucky bluegrass + Chewings fescue) remained in an acceptable range at most observation dates after 3 yr of spring‐and‐fall traffic. Bermudagrass control plots were in poor or marginal condition at most observation dates during the same period. Bermudagrass plus fine leaf fescues were severely damaged by simulated traffic. Quality of turf receiving no simulated traffic was generally good and varied seasonally in response to changing environmental conditions. Higher‐impact absorption measurements, based on peak deceleration (maximum g) on turf receiving simulated traffic vs. no traffic, were consistent with decreasing thatch and verdure. Traction (in N·m) decreased on trafficked turf as thatch and aboveground biomass deteriorated. Kentucky bluegrass and perennial ryegrass dominated mixtures with bermudagrass after 3 yr, and showed good tolerance to simulated traffic.