bluuebunny/crossref_metadata_2025 huggingface dataset:
A Colorimetric Method for Assaying Dissolved Oxygen Loss from Container‐Grown Rice Roots
Authors: Kludze H. K. , DeLaune R. D. , Patrick W. H.
Published: July 2010

Although not easily measured measured, oxygen release from rice (Oryza sativa L.) roots determines the plant's ability to survive reducing conditions. Our main objective was to test titanium‐citrate complex for its potential to quantify dissolved O2 concentrations in solutions bathing the whole root system of container‐grown rice cultivars. Influences of aeration status on root aerenchyma formation and radial oxygen loss from roots were also evaluated. Seven rice cultivars were grown in sand culture fertilized with nutrient solution under well drained and hypoxic conditions. Oxygen concentration was measured colorimetrically 6 h after placing plant roots in the Ti3+ ‐citrate solution. Plants were harvested for root porosity and radial oxygen loss estimates at 14 and 35 d after transplanting. Estimates of radial oxygen loss with the Ti3+‐citrate technique were comparable to those obtained with a polarographic oxygen electrode. Both radial oxygen loss and root porosity were enhanced by hypoxia. Rapid formation of aerenchyma at early growth stages coupled with correspondingly high O2 leakage from roots may explain why some rice cultivars cope with the adverse effects of anaerobiosis better than other cultivars.
Wind Erosion Losses as Related to Plant Silhouette and Soil Cover
Authors: Bilbro J. D. , Fryrear D. W.
Published: July 2010

Wind erosion adversely affects soils, plants, animals, equipment, the environment, and people. Wind erosion can be minimized or prevented by either standing residue or flat residue cover. Our objective was to develop mathematical relationships between these two crop residue properties and soil loss ratio (SLR: soil loss from protected soil/soil loss from flat, bare soil), for more accurate predictions of wind erosion soil losses. Therefore, from a previously reported wind tunnel study (wind tunnel 1.1 m high, 0.51 m wide, and 5 m long) we took data for velocities ranging from 9.4 to 16.1 m s−1 and silhouette areas (S) of upright wood dowels (simulating plant stems) ranging from 31 to 813 cm2 m−2 of soil surface (washed sand <0.42 mm) and developed the following equation for standing residue and SLRs: SLRs = exp(−28.49 × S0.6413/V2.423) (r2 = 0.95), where S = stalk height (cm) × stalk diameter (cm) × stalk density (no. m−2) and V = wind velocity in m s−1 at a height of 0.61 m. We combined data from a second previously reported wind tunnel (0.9 m high, 0.6 m wide, and 7 m long) study in which the soil had been covered from 0.0 to 80.0% with wood dowels, artificial clods, or cotton (Gossypium hirsutum L.) gin trash with data from field studies published by other researchers for various soil types and soil coverages ranging from 8 to 95% with wheat (Triticum aestivum L.) residue or gravel, and developed the following equation for soil cover and SLRc: SLRc = exp(‐0.04380 × psc) (r2 = 0.94), where psc is the percent of the soil that is covered by nonerodible material (e.g., soil aggregates, rocks, plant material). These equations should be useful to researchers developing and evaluating wind erosion models, prediction systems, and wind erosion control practices.
Root Hydraulic Conductivity and Its Components, with Emphasis on Desert Succulents
Authors: Huang Bingru , Nobel Park S.
Published: July 2010

Plant growth and development are often limited by the ability of roots to extract water and nutrients from the soil and to transport them to the shoots. The water absorption and transport ability of roots can be quantified by the hydraulic conductivity, LP. This quantity can be considered in terms of two components, the radial conductivity (LR) for water movement into the root and the axial conductance per unit pressure gradient (Kh) for water movement along the root xylem. The pathways for water movement through roots are discussed, and the hydraulic conductivities are expressed mathematically. The techniques currently used for determining LP, LR, and Kh are presented and conductivities for various plant species are compared. Recent experimental results on structural factors controlling LP and Kh together with the influences of two major environmental factors, temperature and soil water availability, are analyzed for roots of desert succulents. Interpreting the anatomical and physiological controls for LP, LR, and Kh and the variations caused by environmental factors is essential to understand the functioning of root systems for water uptake.
Root‐to‐Shoot Communication in Flooded Plants: Involvement of Abscisic Acid, Ethylene, and 1‐Aminocyclopropane‐1‐carboxylic Acid
Authors: Jackson Michael B.
Published: July 2010

Nonhydraulic communication between roots and shoots of flooded plants is reviewed. Contrary to reports for roots of droughted plants, those of flooded tomato plants (Lycopersicon esculentum L.) did not export increased amounts of abscisic acid (ABA) to the shoots, even though stomata closed in association with increased foliar ABA, and in the absence of marked losses in leaf hydration. Flooded tomato root systems did export more of the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC). Ethylene formed in the leaves by oxidation of the ACC to ethylene and the epinastic leaf curvatures the ethylene induced were found to be inhibited in tomato plants transformed with an antisense gene to the ethylene‐forming enzyme ACC oxidase. Our estimates of the concentration and delivery of ABA and ACC in the xylem sap as it passes into the shoot from the roots avoided artifacts associated with variable sap flow rates and temporary contamination from wounded tissue. Measurements of ethylene production by individual roots of intact seedlings of maize (Zea mays L.) by highly sensitive photoacoustic laser detection confirmed earlier work linking enhanced ethylene evolution with more extensive aerenchyma development in roots that are partially deficient in oxygen. The development of aerenchyma enhances oxygen movement from shoots to roots.
Soybean Pubescence Color Influences Seed Yield in Cool‐Season Climates
Authors: Morrison Malcolm J. , Voldeng Harvey D. , Guillemette Ron J. D.
Published: July 2010

Soybean [Glycine max (L.) Merr.] pubescence color (gray or tawny) may influence the microclimate of the canopy and consequently the seed yield. The objectives of this research were to examine the influence of pubescence color on the seed yield of soybean. Yield data were collected from soybean with either gray or tawny pubescence grown in a regional adaptation trial for three years at three locations. Mean yield, yield stability, and general adaptability were examined to determine if pubescence color interacted with the climate to affect yield. In years or locations receiving >2600 corn heat units (CHU), soybean lines with gray pubescence had either significantly higher yield or the same yield as lines with tawny pubescence. In years or locations receiving <2600 CHU, however, tawny soybean had a significantly higher yield than gray soybean. In cool‐season climates, soybean lines with tawny pubescence had greater seed yield stability and higher general adaptability than those with gray pubescence.
Turgor Potential and Osmotic Constituents of Kentucky Bluegrass Leaves Supplied with Four Levels of Potassium
Authors: Carroll Mark J. , Slaughter Leon H. , Krouse John M.
Published: July 2010

Solute accumulation is one mechanism by which plants are able to sustain positive leaf turgor potentials (ψt). Potassium, the cation most often found in greatest concentration in Kentucky bluegrass (Poa pratensis L.), can influence accumulation of solutes. A 2‐yr glasshouse study was conducted to determine the effect of K availability on accumulation of six osmotically active solutes and ψ1 within leaves of Kentucky bluegrass. Four nutrient solutions containing 0, 10, 100, or 124 mg K L−1 were applied three times weekly to plants grown in silica sand. Small increases in K (0 to 10, or 100 to 124 mg L−1) had no effect on ψt but increasing K from 0 or 10, to 100 or 124 mg L−1 increased leaf ψt 0.19 to 0.35 MPa. Increasing K from 10 to 100 mg L−1 caused leaf osmotic potential (ψЛ) to decline by 0.17 to 0.23 MPa. Potassium was the only measured osmotically active solute that could account for most of the decline in ψЛ. When the supply of K was increased from 10 to 100 mg L−1, the resulting increase in leaf K concentration caused the calculated contribution of K alone to depress leaf ψЛ by 0.29 to 0.31 MPa. Conversely, the combined calculated osmotic contribution of Ca, Mg, glucose, fructose, and sucrose increased leaf ψЛ by 0.12 to 0.13 MPa when K was increased from 10 to 100 mg L−1. The calculated osmotic contribution of all six osmolytes accounted for 46 to 60% of the measured ψЛ. Increasing Kentucky bluegrass K tissue concentration appears to have a small but positive influence in increasing leaf turgor.
Irrigation and Culm Contribution to Yield and Yield Components of Winter Wheat
Authors: McMaster Gregory S. , Wilhelm Wallace W. , Bartling Patricia N. S.
Published: July 2010

Water is generally the limiting factor in U.S. Great Plains wheat (Triticum aestivum L.) production. With increasing demands for limited water, improving the efficacy of irrigation is critical. One technique is to irrigate during responsive stages of crop development, but few studies have examined this approach. This 2‐yr study on a Nunn clay loam soil (fine, montmorillonitic, mesic Aridic Argiustoll) was designed to examine the effects of irrigation, based on stage of crop development, on winter wheat yield, yield components (on a plant basis), and specific culm responses. In the first year, the treatments were control (dryland), and irrigation at late jointing. In the second year, the treatments were dryland, irrigation at late jointing, irrigation at anthesis, and irrigation at both late jointing and anthesis. Irrigation at late jointing or anthesis significantly increased grain yield and the most important yield component (spikes per plant), as well as spikelets per plant, number of kernels per plant, and kernel weight per plant. The increased spikes per plant in the irrigation treatments, particularly with late‐jointing irrigation, was due to reduced tiller abortion. Increased yield was primarily due to the contribution of more secondary tillers (T10, T11, T20, T21, T30, and T31) that produced spikes. The contribution of main stems to the total yield decreased from 92% to at most 86% with irrigation, although the dry weight of main‐stem spikes increased with irrigation. The contribution to total yield of the main yield‐producing tillers, Tl and T2, decreased from 20 to 15% and 19 to 15%, respectively, with irrigation. As with main‐stem spikes, irrigation also increased T1 and T2 spike dry weight. Therefore, the production of secondary spikes due to irrigation treatments was not at the expense of main stem or primary tiller spikes. If only one irrigation can be applied, irrigation at late jointing is recommended for central Great Plains conditions, due to its greater effect on tiller survival. This implies that developmental and physiological processes at late jointing are critical in determining final grain yield, and water stress should be avoided at this growth stage.
A Simple Conductimetric CO2 Analyzer with Automatic Recalibration: I. Design, Implementation, and Functionality
Authors: Acock Basil , Wall Gerard W.
Published: July 2010

Controlled‐environment plant growth cabinets may be used to investigate the long‐term effect of elevated carbon dioxide concentration ([CO2]) on plant growth. Infrared gas analyzers (IRGAs) are normally used to monitor and control [CO2] in plant cabinets. With many cabinets in use, however, it soon becomes impractical to purchase an individual IRGA for each cabinet. A more economical method of monitoring and controlling [CO2] relies on the change in electrical conductivity when CO2 is dissolved in demineralized water. This work describes the design, implementation, and functionality of an inexpensive conductimetric system for controlling [CO2] in plant growth cabinets. Regressing electrical conductivity against [CO2] over the range 0 to 1000 μL L −1 yields a quadratic response. Calibration drift inherent in the conductimetric CO2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosures to within 10 to 15 üL L−1 of the set point. The [CO2] control system is robust enough to maintain this accuracy regardless of the desired [CO2] set point or the mass of plant material within the plant growth cabinet. In this approach, only one IRGA is required to control [CO2] in many plant growth cabinets if each cabinet has a dedicated conductimetric CO2 analyzer.
Alfalfa Establishment with Barley and Oat Companion Crops Differing in Stature
Authors: Simmons Steve R. , Sheaffer Craig C. , Rasmusson Donald C. , Stuthman Deon D. , Nickel S. E.
Published: July 2010

Small‐grain companion crops are commonly used for establishing forage legumes in the north‐central USA. Semidwarf‐stature barley (Hordeum vulgare L.) and oat (Avena sativa L.) show promise as less competitive and more lodging‐resistant companion crops. This study compared forage production and agronomic characteristics of companion‐cropped semidwarf and conventional‐stature genotypes of barley and oat. Alfalfa (Medicago sativa L.) was seeded both with and without companion crops in experiments conducted at St. Paul, MN, from 1987 through 1989 on a Waukegan silt loam soil (fine‐silty over sandy or sandy‐skeletal, mixed, mesic Typic Hapludoll). Both semidwarf and conventional‐stature barley and oat genotypes were evaluated. Small‐grain and alfalfa forage harvests were made at the boot and soft dough stages of the small grain. Subsequent alfalfa harvests also were made later in the establishment season and at first flower in the following spring. Light penetration through the canopies of the various companion crops was monitored in all years. Weed biomass was measured in 1989, to estimate weed suppression by the companion crops. Light intensity at the level of the alfalfa within the semidwarf companion crop canopy was consistently higher than within the conventional‐stature companion crops. Averaged over all small‐grain genotypes, companion crop treatments produced from 202 to 2355 kg ha−1 more forage dry matter than direct‐seeded alfalfa (no companion crop). Alfalfa dry matter production during establishment was suppressed by all companion crops, especially those with conventional stature. Weeds were greatly suppressed by all companion crops. Companion crops increased mortality of alfalfa plants during establishment, but did not lower production of the alfalfa at subsequent harvests in the establishment season or in the following spring. Overall, semidwarf and conventional barley and oat were comparable in performance as companion crops in these studies, but semidwarf genotypes should prove particularly advantageous under conditions where lodging is likely to occur.
Hairy Vetch Kill Date Effects on Soil Water and Corn Production
Authors: Clark Andrew J. , Decker A. Morris , Meisinger John J. , Mulford F. Ronald , McIntosh Marla S.
Published: July 2010

Hairy vetch (Vicia villosa Roth) can fix N2 for subsequent release to a corn (Zea mays L.) crop, but kill date effects on vetch N accumulation, soil water, and subsequent corn production have not been studied. A hairy vetch cover crop can deplete soil water through transpiration, but cover crop mulches can conserve soil water for no‐till corn. In order to determine optimum spring kill date and corn fertilizer N (FN) rates, hairy vetch was killed early April, late April, or mid‐May, followed by three corn planting dates and four FN rates (0, 45, 135, and 202 kg N ha−1). From early April to mid‐May, hairy vetch aerial phytomass and N content increased significantly, from 2800 to 4630 and 96 to 149 kg ha−1, respectively. Corn grain yields ranged from 5.2 to 10.1 Mg ha−1 and were significantly greater following mid or late kill, compared with early kill of vetch, regardless of corn planting date or FN rate. Gravimetric soil water under mid‐ or late‐kill vetch was often significantly greater than after early‐kill vetch. We conclude that soil water conservation by late‐killed vetch mulches had a greater influence on corn production than vetch spring water use. Optimum N production and water conservation occurred when vetch was killed the last week of April. Earlykill vetch sacrificed N production and minimized soil water conservation, resulting in reduced corn grain yield. Late kill did not add significant N benefits, but could deplete soil water or interfere with timely corn planting.
A mobile, Self‐contained, Simulated Rainfall Infilrometer
Authors: Radke Jerry K.
Published: July 2010

Water infiltration rates into soils can provide important insights into the physical properties of the soil and its potential for crop production. Rainfall infiltrometers can make measurements under conditions closer to natural rainfall than ponded or tension infiltrometers. In the past, field measurements of infiltration with rainfall simulators have required the transport and assembly of bulky equipment. A self‐contained rainfall infiltrometer was designed and constructed on a high‐clearance tricycle tractor that can be easily transported over roads on a trailer and then driven in cropped or uncropped field plots. Performance of the unit is the same as the trailer‐based infiltrometer that it replaced.
Wind and Windblown Sand Damage to Pearl Millet
Authors: Michels Karlheinz , Armbrust Dean V. , Allison Bruce E. , Sivakumar Mannava V. K.
Published: July 2010

Pearl millet [Pennisetum glaucum (L.) R. Br.] is grown worldwide in areas affected by wind erosion, but no data on associated damage to millet are available. Laboratory wind tunnel experiments were conducted to determine the kind and extent of damage to millet caused by wind, sandblasting, and burial. In Exp. 1, millet was exposed for 15 min to wind (8, 11, or 14 m s−1) or wind + sand (8.3, 25.0, or 41.7 g m−1 s−1 sand abrader flux) at 8 and/or 16 d after emergence (DAE). Viable leaf area, leaf net photosynthesis, and NO3 content were measured through 21 DAE and dry matter production through 57 DAE. In Exp. 2, millet was seeded as three single seeds or in tufts, exposed to 25 g m−1 s−1 sand flux for 15 min at the 1‐, 2‐, or 3‐leaf stage, and then manually covered by 15 mm sand. Survival was monitored weekly; dry matter was determined 70 DAE. In Exp. 1, survival was uniformly 100%. Wind alone or low sand flux had no effect on viable leaf area. High sand flux decreased viable leaf area by 74% at 2 d after the 8‐DAE exposure and 42% at 5 d after the 16‐DAE exposure. Photosynthesis of the remaining leaf area was reduced up to 88% immediately after exposure compared with the control, and NO3 content of sandblasted millet was increased up to six times. Dry weight was reduced 40% at 21 DAE by the highest sand flux, but 9.7% at 57 DAE. In Exp. 2, burial decreased millet survival and dry weight. Buried tufts had a higher survival rate and 35% more dry weight than buried single plants. Millet buried at the 1‐leaf stage had 28% higher survival than plants treated later. Sandblasting reduced dry matter of buried millet only. Regression analyses between calculated total kinetic effects and growth parameters showed low r2 values. Millet can survive short‐term sandblasting at any growth stage, but growth is reduced by strong sand flux, a sequence of wind erosion events during early growth, or by combinations of abrasion with burial by blown sand.
Evaluation of Excess Soil Phosphorus Supply for Corn by the Ear‐Leaf Test
Authors: Mallarino Antonio P.
Published: July 2010

The P concentrations of ear leaves at silking are often used to assess P status of corn (Zea mays L.). The ear‐leaf test has been evaluated for its ability to detect P deficiencies, but little attention has been given to its ability to quantify excess P supplies. The quantification of high P supplies is important for both economic and environmental reasons and because fertilization has increased P supplies of many soils to levels where additional yield responses are not likely. Grain yields and tissue samples were collected from 41 site‐years corresponding to 2 long‐term and 24 short‐term P‐response trials from 1980 to 1990. The sites included a wide variety of soil types, soil‐test P values, and management practices. Phosphorus fertilization increased corn yields at 13 site‐years and leaf P concentrations at 24 site‐years. Fertilization increased leaf P concentrations at 85% of the soils where fertilization increased yields but at only 46% of the soils where fertilization did not increase yields. The determined critical concentration range for the leaf test, based on various models fit to relationships between yields and leaf P concentrations, was 2.3 to 2.5 g kg−1. This range is below or within the lower range of previously published critical concentrations for this test. Leaf P concentrations increased curvilinearly with increasing soil‐test values, and there were small or no increases at high soil‐test values. This trend, together with the failure of fertilization treatments to increase leaf P concentrations at many high‐testing soils, indicates limited luxury uptake of P in the leaves. The results of this study show that the ear‐leaf test does not evaluate excess soil P supplies appropriately and is not a reliable diagnostic tool for regions having abundant high‐testing soils. The inappropriate evaluation of excess P and the high variability in leaf P concentrations due to growth factors other than P availability limit the value of this test to the diagnosis of severe P deficiency.
Spatial and Temporal Variability of Transplanted Rice at the Field Scale
Authors: Dobermann Achim , Pampolino Mirasol F. , Neue Heinz‐Ulrich
Published: July 2010

Measuring rice (Oryza sativa L.) growth in farmers' fields requires plant sampling techniques that take account of spatial and temporal variability. Our objective was to specify sampling recommendations for transplanted rice at the field scale. Rice was grown in two fields, fertilized and not, at 20‐ by 20‐cm hill spacings. Plant height, tiller number per hill, dry matter yield, and foliage area index were measured during the growth period at 8 locations and harvest samples were taken at 56 locations per field. Variation was low for plant height at all growth stages (CV = 6.1–9.5%); tiller number varied more (CV = 21–33%), especially in the tillering stage. Variation at harvest was intermediate (CV = 12–21%) for most crop variables. Grain yield ranged from 2.41 to 5.88 t ha−1 for the unfertilized field and 4.54 to 8.82 t ha−1 for the fertilized field. Transplanting errors introduced variation among hills. Variation between quadrats within a field was due to varying growth rates between tillering and panicle initiation (PI) and was related to the spatial distribution of inherent soil nutrient availability and fertilizer nutrient supply. Nonhomogeneous topdressed application of N caused location‐specific microvariation in crop stands. At all growth stages, two samples of three randomly selected hills were sufficient to measure plant height in a field. Increasing the number of samples had more effect on the precision of tiller number estimates than did increasing the size of the sampling unit. To measure tiller number between tillering and PI of rice, sampling units of five hills should be used and samples should be collected from 12 to 19 quadrats. At flowering, seven samples are enough. Harvest estimates of agronomic characters should be based on 8 to 12 quadrats when 10‐hill sampling units are used. A stratified random sampling design should be used, and samples should be taken >3 m apart.
Evaluation of the Aphid‐Day Standard as a Predictor of Yield Loss Caused by Cereal Aphids
Authors: Kieckhefer Robert W. , Gellner Jeffrey L. , Riedell Walter E.
Published: July 2010

Accurate prediction of yield loss caused by cereal aphids in small grains involves assessment of the aphid population density on plants, the duration of their feeding, and the growth stage of the crop at the time of feeding. In this research, aphid‐day (one aphid feeding on one plant for 24 h) unitage was used as a standard to compare the effects of feeding by greenbug, Schizaphis graminum (Rondani), Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), and bird cherry‐oat aphid (BCO), Rhopalosiphum padi (L.), on the growth and yield of spring wheat, Triticum aestivum L., to measure the degree of additivity of yield loss caused by aphid feeding on the same plants at several stages of plant growth, and to evaluate the adequacy of the aphid‐day standard as a predictor of yield loss. Results of greenhouse experiments with a scaled series of aphid‐day components (150 aphids ✕ 2 d; 75 ✕ 4 d; 50 ✕ 6 d; 25 ✕ 12 d) of equal total value (300 aphid‐days) showed that the three aphid species were similarly damaging to yield but that for RWA and BCO the 25 ✕ 12 d combination was significantly (P ≤ 0.01) more damaging than the other aphid‐day treatments for those species. The administration of escalating aphid‐day dosages to plants concomitant with advancing plant growth stages (two‐leaf, 300 aphid‐days; four‐leaf, 400 aphid‐days; two‐leaf + four‐leaf, 700 aphid‐days; boot, 1200 aphid‐days; two‐leaf + boot, 1500 aphid‐days; milk, 200 aphid‐days; two‐leaf + milk, 2300 aphid‐days) revealed that yield loss caused by aphid feeding at two plant growth stages was usually significantly (P ≤ 0.01) greater than that at a single stage, but was not fully additive simply as the arithmetic sum of the yield losses at the two stages. Yield losses due to aphid feeding (expressed as milligrams per 100 aphid‐days) declined precipitously with advancing plant growth stage. These results show that the aphid‐day unitage, properly interpreted in relation to the aphid species involved and the growth stage of the crop, is a useful predictor of grain yield loss at harvest. Relating cumulative aphid‐days at successive plant growth stages to ultimate yield loss enables producers to make informed decisions about the need for and timing of rescue chemical treatments.
Carbon Dioxide and Temperature Effects on Pima Cotton Development
Authors: Reddy K. Raja , Hodges Harry F. , McKinion James M.
Published: July 2010

Predicting plant responses to changing atmospheric CO2 and to the possible global warming are important concerns. Effects of CO2 on developmental events are poorly documented, as is the interaction of CO2 and other major climate variables on crop development. The objective of this experiment was to determine the effects of an altered CO2 environment and interactions of CO2 and temperature on pima cotton developmental rates. Pima cotton (Gossypium barbadense L. cv. S‐6) was grown from seed in sun‐lit plant growth chambers. Air temperatures were controlled from 20/12 to 40/32°C (day/night) in 5‐degree increments. Daytime CO2 was maintained at 350 or 700 μL L−1. In a second experiment, the temperature was maintained at 30/22°C day/night and the plants were grown in 350, 450, or 700 μL L−1 CO2. Days required to develop nodes on the mainstem, days from emergence to first square, number of vegetative and fruiting branches, number of fruiting sites produced, number of bolls and squares produced, and number of bolls and squares retained by the plants were determined. Rates of mainstem node formation and the time required to produce the first square and first flower were not sensitive to atmospheric CO2, but were very sensitive to temperature. Prefruiting branch nodal positions required longer to develop than nodes with fruiting branches. Carbon dioxide levels did not affect the time required to produce nodes. Number of branches produced was sensitive to both temperature and CO2. The larger number of bolls set on the lower branches of plants grown at high CO2 provided a larger sink for photosynthate than plants grown at low CO2. This may be the reason for the observed reduction in number of fruit at the upper nodes of high‐CO2‐grown plants. More bolls and squares were produced and retained on plants grown in high‐CO2 environments, except that none were produced in either CO2 environment at 40/32°C. Our results indicate that high‐temperature‐tolerant cotton cultivars would be more productive in the present‐day CO2 world, and they would be essential in the future if global temperature increases.
Defoliation Effects on ‘Mott’ Elephantgrass Productivity and Leaf Percentage
Authors: Chaparro C. J. , Sollenberger Lynn E. , Jones C. S.
Published: July 2010

‘Mott’ elephantgrass (Pennisetum purpureum Schum.) is a high‐quality pasture grass for the tropics and subtropics, but information is needed on growth responses of Mott to clipping management. In 1989, 1990, and 1991, a study was conducted on a hyperthermic, uncoated Aquic Quart‐zipsamment soil to measure Mott herbage dry matter (DM) harvested and plant‐part percentage (1989 and 1990 only) responses to clipping. The study included all 16 treatment combinations of four defoliation heights (10‐, 22‐, 34‐, and 46‐cm stubble) and four defoliation frequencies (3, 6, 9, and 12 wk). Treatments were replicated three times in a randomized block design. Data were analyzed by fitting multiple regression equations starting with a second‐order polynomial model. In 1989, total DM harvested ranged from 8.0 to 16.2 Mg ha−1 and increased (decreasing rate) as defoliation height was lowered and increased linearly as weeks between harvests increased from 3 to 12. The range of total DM harvested was 4.2 to 11.6 Mg ha‐~ in 1990 and 2.6 to 16.1 Mg ha−1 in 1991. Dry matter harvested in 1990 and 1991 increased (decreasing rate) as defoliation height was lowered from 46 to 10 cm and as interval between defoliations increased. Lowest total DM harvested in the third year was observed using a 3‐wk defoliation frequency, 10‐cm defoliation height treatment, a result of reduced plant vigor. Greatest total DM harvested in all years occurred using a 12‐wk frequency, 10‐cm height treatment. Across all treatments, live lamina percentage in total DM harvested ranged from 63 to 100% and was greatest for the 3‐wk frequency, 46‐cm height treatment. Live lamina DM harvested was not affected by treatment in 1989, but in 1990 maximum values were estimated to occur when frequency was 9 to 10 wk and stubble height was 15 to 20 cm. We conclude that Mott elephantgrass is productive and maintains a high leaf lamina percentage over a relatively wide range of defoliation treatments, but close, frequent clipping reduces total DM harvested.
Response of Carbon Metabolism to Night Temperature in Cotton
Authors: Warner Donn A. , Holaday A. Scott , Burke John J.
Published: July 2010

Cotton (Gossypium hirsutum L.) is sensitive to low temperatures during all phases of growth. Throughout the cotton growing season on the High Plains of Texas, days provide optimal sunlight and temperature for metabolism followed by nights with temperatures of 15 to 20°C, well below the optimum. The present growth chamber study compared the response of specific components of C metabolism in vegetative cotton grown with 28°C/28°C and 28°C/20°C day/night regimes. Photosynthesis for cool‐night (20°C) plants measured at 28°C the following day was only 77% of 28°C night plants. Less starch accumulation occurred during the day in the cool‐night plants, yet their predawn starch levels were approximately 2.5‐fold higher than the 28°C plants. Pools of triose phosphate and fructose 1,6‐bisphosphate were lower at night at 20°C than at 28°C. The glucose 6‐phosphate/fructose 6‐phosphate ratio was higher for the cool‐night plants, however, indicative of an apparent limitation in sucrose synthesis subsequent to cytosolic fructose 1,6‐bisphosphatase. The most interesting observation is the maintenance of equal sucrose pools in both treatments, even though the amount of starch catabolized at night was different. This study shows that cool night temperatures alone alter cotton C metabolism throughout each 24‐h period.
Utilization of Allelopathy for Weed Management in Agroecosystems
Authors: Weston Leslie A.
Published: July 2010

Biorational alternatives are gaining increased attention for weed control because of concerns related to pesticide usage and dwindling numbers of labeled products, particularly for minor‐use crops. Allelopathy offers potential for biorational weed control through the production and release of allelochemics from leaves, flowers, seeds, stems, and roots of living or decomposing plant materials. Under appropriate conditions, allelochemics may be released in quantities suppressive to developing weed seedlings. Allelochemics often exhibit selectivity, similar to synthetic herbicides. Two main approaches have been investigated for allelopathic weed suppression. One is use of living rotational crops or mulches that interfere with the growth of surrounding weeds [e.g., tall red fescue, Festuca arundinacea Schreb.; creeping red fescue, F. rubra L. subsp. commutata; asparagus, Asparagus officinalis L. var. altilis); sorghum, Sorghum bicolor (L.) Moench; alfalfa, Medicago sativa L.; black mustard, Brassica nigra (L.) Koch; and oat, Avena sativa L.]. Attempts to select germplasm with enhanced suppressive ability have been limited. The second is use of cover crop residues or living mulches to suppress weed growth for variable lengths of time (e.g., winter rye, Secale cereale L.; winter wheat, Triticum aestivum L.; and sorghum). Cover crop residues may selectively provide weed suppression through their physical presence on the soil surface and by release of allelochemics or microbially altered allelochemics. The ability to understand the physiological basis for allelopathy in a crop plant may allow the weed scientist or ecologist to work closely with molecular biologists or traditional plant breeders to selectively enhance the traits responsible for weed suppression.
Forage Yield and Quality of Six Annual Medicago Species in the North‐Central USA
Authors: Zhu Yanping , Sheaffer Craig C. , Barnes Donald K.
Published: July 2010

Annual medics (Medicago spp.) have been extensively used as winter annual forage and green manure crops in Mediterranean regions, but their potential use in the north‐central USA has not been evaluated. Our objective was to determine the summer and fall forage yield and forage quality of spring‐ and summer‐seeded annual medics. Twelve commercial annual medic cultivars from Australia (representing five species) and ‘George’ black medic (M. lupulina L.), ‘Nitro’ alfalfa (M. sativa L.), and ‘Arlington’ red clover (Trifolium pratense L.) were seeded in spring and summer at Rosemount and Morris, MN, in 1991 and at St. Paul and Becker, MN, in 1992. Forage yields were taken at a single harvest in summer (when most medics were reproductive) from spring‐seeded stands and in the fall first frost (0°C) from summer‐seeded stands. Forage yields of spring and summer‐seeded annual medics ranged from 1.2 to 5.7 and 0.5 to 5.5 Mg ha−1, respectively, depending on location and species. Barrel medic (M. truncatula Gaertn.), snail medic [M. scutellata (L.) Mill.], and burr medic (M. polymorpha L.) cultivars were among the highest yielding, while Nitro alfalfa, George black medic, and Arlington red clover were consistently among the lowest yielding forage species. George black medic, Harbinger strand medic (M. littoralis Rohde ex Loisel.), and Kelson snail medic were among the highest in forage crude protein (CP) concentration for both summer and fall harvests. Forage fiber concentrations of all annual medics except Sava snail medic were equal to or lower than those in Nitro alfalfa. Our results indicate that annual medics have the potential for producing high yields of quality forage in the north‐central USA and might be used as short‐season annual crops for harvest in fall and summer when traditional forage supplies are inadequate.
Fall Harvest Management Effects on ‘Grasslands Matua’ Prairie Grass Quality
Authors: Hall Marvin H. , Jung Gerald A. , Shaffer John A. , Everhart John R.
Published: July 2010

Forage production of ‘Grasslands Matua’ prairie grass [Bromus catharticus M. Vahl; syn. B. unioloides Kunth, B. willdenowii Kunth] (Matua, for short) during the fall months is excellent, but highly management dependent. Unfortunately, fall harvest management effects on the quality of this grass are relatively unknown. Our objectives were to determine the effects of fall harvest management on forage quality of Matua prairie grass during the fall and following spring. Two field experiments were conducted on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalfs). Experiment 1 addressed date of fall harvest and residual stubble height; Experiment 2 addressed frequency of fall harvest and residual stubble height effects on forage quality in the fall and spring. Delaying fall harvest of Matua prairie grass caused forage crude protein (CP) content to decline by about 30%; however, delaying fall harvest had no or little effect on acid‐detergent fiber (ADF), neutral‐detergent fiber (NDF), or in vitro dry matter digestibility (IVDMD). Grasslands Matua quality in the spring was unaffected or inconsistently affected by fall harvest management. Delaying harvest of Matua prairie grass in the spring reduced forage quality but not to the extent reported for other cool‐season forage grasses. Our findings indicate that Matua offers considerable latitude in fall and spring harvest management with regards to obtaining quality forage; however, these finding should be considered along with previous findings that fall harvest management has a large effect on winter survival of Matua.
A Design for a Modular, Generic Soil Simulator to Interface with Plant Models
Authors: Timlin Dennis , Pachepsky Yakov A. , Acock Basil
Published: July 2010

The various linkages in agricultural systems are so complex that research questions are often studied via simulation modeling. The development and upgrading of detailed models requires a large investment of time and resources; therefore, it is necessary to simplify the process of building the model and incorporating modifications as research finds new information to include. The goal of this study was to develop the framework for a generic soil simulator that could easily be modified and incorporated into crop models. Soil and root processes are represented by modules that interact on the spatial—temporal grid covering the soil profile and the simulated time interval. Data were divided into public and private components, to minimize information passing between modules. This modular structure and information hiding simplifies replacement or addition of modules and promotes code reuse. The classes of modules include (i) control modules that oversee interactions between processes, (ii) water, solute, heat, and gas transport modules, (iii) interphase chemical transformation modules, (iv) biochemical transformation modules, and (v) root growth and uptake modules. A representative simulator, 2DSOIL, was assembled according to the proposed design. Examples include the incorporation into a simple crop model and the expansion of 2DSOIL with a management module to simulate chemical application.
Biomass Production and Nitrogen Accumulation in Pea, Oat, and Vetch Green Manure Mixtures
Authors: Jannink Jean‐Luc , Liebman Matt , Merrick Laura C.
Published: July 2010

Interest in the use of green manures has revived because of their role in improving soil quality and their beneficial N and non‐N rotation effects. This study evaluated biomass production, N content, radiation interception (RI), and radiation use efficiency (RUE) of pea (Pisum sativum L.), oat (Avena sativa L.), and hairy vetch (Vicia villosa Roth) mixtures. Treatments were a three‐way factorial of pea genotype (‘Century’ vs. ‘Tipu’), pea planting density (90 vs. 224 kg ha−1), and cropping mixture (solecropped pea vs. pea planted with a mixture of oat and hairy vetch). A mixture of oat and vetch without pea was also planted. Treatments were planted in early June on a Caribou gravelly loam (coarse‐loamy, mixed, frigid Typic Haplorthods) in Presque Isle, ME, in 1993 and 1994. Biomass production and radiation interception were measured by repeated sampling. Mixture biomass was affected by a year × pea density interaction: respective yields for mixtures containing low‐density and high‐density pea were 770 and 880 g m−2 in 1993 vs. 820 and 730 g m−2 in 1994. Mixture N content paralleled biomass production and averaged 20.9 g m−2 across all treatments. While pea sole crops did not consistently produce biomass or N equal to three‐species mixtures, the twospecies mixture of oat and vetch did, yielding 820 g m−2 of biomass and 21.7 g m−2 of N, averaged over the 2 yr. Multiple regression showed that 61% of the variability in mixture biomass production was accounted for by a combination of early‐season pea RI and midseason total mixture RUE. Economic analyses showed that rotations including these green manures may be economically competitive with a conventional rotation of barley (Hordeum vulgare L.) undersown with clover (Trifolium spp.) in a potato (Solanum tuberosum L.) production system.
Nitrogen Placement and Tillage Effects on Dry Matter and Nitrogen Accumulation and Redistribution in Winter Wheat
Authors: Rao Srinivas C. , Dao Thanh H.
Published: July 2010

Nitrogen losses observed with no‐till practices when N fertilizer is surface broadcast prompted the need to reassess N fertilizer management practices for winter wheat (Triticum aestivum L.). Field studies were conducted on Renfrow silt loam (fine‐silty, mixed, thermic Udertic Paleustolls) from 1990 through 1993 near El Reno, OK, to determine the effects of N placement and tillage on dry matter accumulation, N uptake, and N redistribution in winter wheat. Tillage methods were moldboard plowing and no‐till with standing stubble. Fertilizer (60 kg ha−1) treatments were surface broadcast (BR) the same day as seeding, banded (8 to 10 cm below the soil surface) below the seed row (BL), banded between the rows (BT), and no N (control). Fall and spring above‐ground dry matter and N were greater in plowed than in no‐till treatments when precipitation was similar to or above the 24‐yr average. Leaf N content was 8, 12, and 3% greater in BR, BL, and BT treatments, respectively, than in the control. Nitrogen accumulation rates (g m−2 d−1) in heads from anthesis to final harvest were 0.16 for BR, 0.17 for BL, 0.19 for BT, and 0.13 for the control. Final grain yield and grain N content were not affected by N placement in plowed plots. Under no‐till, grain yield was improved by 32% for BL and 15% for BT, and grain N content was increased by 33% for BL and 25% for BT as compared with the BR treatment.
Sensitivity of Phosphorus Uptake to Changes in Root Length and Soil Volume
Authors: Otani Takashi , Ae Noriharu
Published: July 2010

Root length is generally considered important in phosphorus uptake, but it is not known whether a crop with longer roots is always efficient in absorbing P from soils low in available P. Consequently, we investigated the relationships between P uptake and root length, as affected by soil volume, and soil P status. Field‐grown buckwheat (Fagopyrum esculentum Moench), castor (Ricinus communis L.), peanut (Arachis hypogaea L.), pigeonpea [Cajanus cajan (L.) Millsp.], sorghum [Sorghum bicolor (L.) Moench], and soybean [Glycine max (L.) Merr.] were compared in their ability to absorb P from soils with low and high P status. The relationships between root length, soil volume, and P uptake were then examined in pot‐grown buckwheat, peanut, and sorghum using varying pot sizes. Under field conditions, maximum P uptake was by sorghum, which produced the longest roots. A strong correlation (r = 0.85*) between root length and P uptake among crops was observed in high‐P soil, but not in low‐P soil. In pot culture, differences in P uptake were correlated to changes in soil volume rather than root density. Phosphorus uptake per unit soil weight was higher in peanut than in sorghum or buckwheat, especially in low‐P soil. Our results indicate that P uptake by crops is strongly correlated with root length in soils where P availability is high, but not in soils with low P availability, or where volume is limited. Results also suggest that peanut uses additional mechanisms beyond root length to increase P uptake.
OILCROP‐SUN: A Development, Growth, and Yield Model of the Sunflower Crop
Authors: Villalobos Francisco J. , Hall Anthony J. , Ritchie Joe T. , Orgaz Francisco
Published: July 2010

Crop simulation models are important tools for agronomic management strategy evaluation, particularly under rainfed conditions. This paper describes the structure and testing of OILCROP‐SUN, a process‐oriented model of the sunflower (Helianthus annuus L.) crop. The model simulates organ biomass and N content, leaf area index, and soil water and N balances with a daily time step. Daily weather data, soil physical and chemical characteristics, and initial contents of water and N are required inputs. Three cultivar‐specific parameters synthesize crop responses to temperature and photoperiod during development, and two cultivar‐speciflc parameters define potential grain number per capitulum and potential kernel growth rate. Tested against independent data sets, the model generated good predictions of the durations of the sowing‐emergence (range 7 to 32 d; root mean square error [RMSE], observed vs. simulated: 3.7 d) and emergence‐anthesis phases (range 52 to 146 d; RMSE between 2.9 and 4.3 d, depending on the cultivar). The model also simulated seasonal crop biomass and leaf area dynamics for irrigated and rainfed crops sown at two densities satisfactorily, as well as aerial biomass (range 5 to 15 t ha−1; RMSE 1.7 ha−1) and grain yield at maturity (range 1.0 to 6.2 t ha−1; RMSE 0.8 t ha−1) for irrigated and rainfed crops sown at a range of population densities (0.5 to 10 plants m−2). We conclude that OILCROP‐SUN can be used to simulate biomass and grain yields over a wide range of conditions.
Whole‐Plant Physiological and Yield Responses of Maize to Plant Density
Authors: Cox Wiliam J.
Published: July 2010

Modern compared with older maize (Zea mays L.) hybrids tolerate more plant density stress, but more information is required on how modern hybrids interact with plant density. Field experiments were established in 1991 (warm‐dry) and 1992 (cool‐wet) to evaluate whole‐plant physiological, dry matter (DM), and grain yield responses of four commercial hybrids at low (4.5 plants m−2), medium (6.75), and high (9.0) plant densities. As plant density increased, leaf CO2 exchange rates (CER) declined 10 to 20% under mild and 20 to 30% under warm dry conditions. Compared with the high plant density, the low plant density had a 40% lower leaf area index from midvegetative to early grain filling, which offset higher photosynthetic efficiency, resulting in lower crop growth rates during vegetative development and 25% less DM accumulation at silking. When averaged across hybrids, the low plant density averaged 15% lower DM and grain yields than the high plant density. Hybrid ✕ plant density interactions were observed for DM and grain yields. The more prolific hybrid showed mostly linear DM and grain yield responses to plant density, whereas a single‐eared hybrid showed quadratic responses in both years. Another single‐eared hybrid, which did not respond to density, had low leaf CER at all densities, a reduction in kernels per plant at the medium density, and increased barrenness at the high plant density in 1991. Apparently, modern hybrids interact with plant density, regardless of growing conditions, and some modern hybrids do not tolerate density stress in dry years.