bluuebunny/crossref_metadata_2025 huggingface dataset:
Lamb Production on Wheatgrasses and Wheatgrass‐Sainfoin Mixtures
Authors: Karnezos T. P. , Matches A. G.
Published: July 2010

Previous research indicates that wheatgrasses (Agropyron and Thinopyron spp.) and sainfoin (Onobrychis spp.) produce high quality forage from early spring to summer on the Southern Great Plains. Little information is available on their potential for lamb (Ovis aries L.) production under grazing. Our objective was to determine levels of spring lamb production from three irrigated wheatgrasses, ‘Hycrest’ [A. cristatum (L.) Gaertner ✕ A. desertorum (Fischer ex Link) Shutters], ‘Luna’ [T. intermedium subsp. barbulatum (Schur) Barkw. and D.R. Dewey], and ‘Jose’ [T. ponticum (Podp.) Barkw. and D.R. Dewey], grown alone and with ‘Renumex’ sainfoin (O. viciifolia Scop.). Replicated pastures grown on a Pullman clay loam (fine, mixed thermic Torrertic Paleustoll) were rotationally grazed (herbage allowance of 6.5% of body wt. d−1) by weaned Rambouillet ✕ Suffolk wether Iambs for an average of 77 d in spring of 1987 and 1988. Seasonal average daily gain (ADG) ranged between 45 and 69 g d−1 for monocultures and between 80 and 104 g d−1 for mixtures. Lamb production per hectare (PROD) for all mixtures was similar (463 kg ha−1), but higher than for monocultures (238 kg ha−1). Mixtures compared to monocultures had greater ADG (63%), feed conversion (55%), and intake (23%). For Jose and Jose‐sainfoin, poor ADG after Week 7 was associated with low herbage crude protein (92‐135 g kg−1) and organic matter digestibility (550‐570 g kg−1). Jose (12.2 Mg ha−1) had the highest herbage accumulation and Hycrest (7.31 Mg ha−1) the lowest. Wheatgrasses, particularly when grown with sainfoin, provide good PROD during spring and early summer.
Grazing Tolerance of Warm‐Season Legumes in Peninsular Florida
Authors: Muir J. P. , Pitman W. D.
Published: July 2010

Despite the potential benefits and frequent favorable results in germplasm evaluations, only limited success has been attained in many areas with tropical pasture legumes. Lack of information regarding both germplasm adaptation and pasture management requirements has been a limitation. Five promising perennial species were evaluated for grazing tolerance and response to fall grazing deferment on an Immokalee fine sand (Sandy, siliceous, hyperthermic Arenic Haplaquod) at Ona, FL. Alysicarpus vaginalis DC; Desmanthus virgatus (L.) Willd.; Galactia elliottii Nuttall; G. volubilis (L.) Britton; Vigna adenantha (G. F. Meyer) Marechal, Mascherpa, and Stainier; and the standard ‘Florida’ carpon desmodium [Desmodium heterocarpon (L.) DC] were subjected to three treatments: (i) continuous grazing through the growing season (late May to mid‐December), (ii) continuous grazing with fall deferment (grazed late May to mid‐September), and (iii) an ungrazed control. Legume main plots, 5 by 15 m in a randomized complete block design, were split in a strip‐plot arrangement to give grazing treatment subplots of 5 by 5 m. Legumes were transplanted in 1986, grazed in 1987 and 1988, and evaluated for persistence through the summer of 1989. By December 1988, the prostrate A. vaginalis had the highest (P < 0.05) survival percentage under both grazed treatments. Survival of D. virgatus, G. elliottii, and V. adenantha was generally highest in the ungrazed control. The Galactia species demonstrated superior adaptation to drought during the spring of 1989. Fall deferment consistently increased survival of only G. volubilis and V. adenantha. Tolerance of continuous grazing was suggested only for A. vaginalis and carpon desmodium. Grazing management strategies involving periods of deferment from grazing during the growing season will apparently be necessary for persistence of stands of D. virgatus and G. elliottii.
Dinitrogen Fixation and Nitrogen Balance in Cool‐Season Food Legumes
Authors: Beck D. P. , Wery J. , Saxena M. C. , Ayadi A.
Published: July 2010

Understanding the magnitude of N2 fixation and export of plant N, particularly in the harvested grain and straw, is necessary to assess the potential for grain legumes to contribute to long‐term agricultural production stability. The proportions of total plant N derived from N2 fixation in four grain legume crops, faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), lentil (Lens culinaris L), and pea (Pisum sativum L.), were estimated in three field experiments conducted for two seasons in Syria (Vertic Chromoxeralf soil) and one season in France (Calcaric Cambisol). Since cultural practices and cultivars affect grain yield, the impact on N2 fixation of sowing date in chickpea and Sitona insect control in lentil, and of cultivar selection of pea and faba bean, was evaluated. By calculating the proportion of total plant N derived from N2 fixation (%Ndfa) using 15N isotope dilution with barley (Hordeum vulgare L.) and non‐nodulating chickpea as reference crops, the effects of removal of N in grain and straw, relative to N fixed and plant uptake of soil mineral N, were estimated. Pea and lentil had similar %Ndfa values across locations, seasons, and cultural practices, with an average 70%Ndfa. In chickpea, winter sowing increased %Ndfa to 72 from 26% in the spring‐sown crop. Dinitrogen fixation in the spring‐sown crop was higher in France (44%Ndfa), while fixation in the winter crop was higher in Syria (80%). Faba bean obtained 9O%Ndfa in France, but only 69% in Syria. The large‐seeded type fixed higher N (74%Ndfa) than the small‐seeded type (64%) in Syria but not in France. The calculated N balance where only grain was removed ranged from 44 kg N ha‐' net gain to 44 kg N ha−1 loss. Where both seed and straw were removed, nearly all calculations were negative, with loss of up to 70 kg N ha−1 from soil.
Phyllochron Change in Winter Wheat with Planting Date and Environmental Changes
Authors: Cao Weixing , Moss Dale N.
Published: July 2010

The phyllochron (degree‐days/leaf) of wheat (Triticum aestivum L.) differs with planting dates and latitudes. An understanding of the causes for these differences is needed to model the development of wheat crop canopies. Stephens and Yamhill winter wheat cultivars were planted on a range of dates in outdoor pots and in field plantings to study the relationship of phyllochron to the daylength and mean air temperature at seedling emergence. Both cultivars had a nearly constant phyllochron for a given planting in both pot and field plantings until 600 cumulated degree‐days (CDD), which was about the time of double ridge formation. Phyllochron values were different, however, for the different planting dates. At about 600 CDD the phyllochron increased in 18 of 20 cultivar‐planting date combinations. Fifty to 60% of the variation in phyllochron prior to double ridge formation could be normalized by either the thermo/photo ratio at seedling emergence (mean temperature to photoperiod) or by the rate of change of photoperiod. These two methods have been suggested previously to normalize phyllochron for differences due to different planting dates. After 600 CDD the phyllochron was not related to thermo/photo ratio, the rate of change of photoperiod, maximum or minimum temperatures, photoperiod or its inverse, or the intensity of solar radiation. Thus, use of a constant value for phyllochron in dynamic crop models of wheat leaf development is not appropriate for all circumstances.
Correction for Slope in Green Speed Measurement of Golf Course Putting Greens
Authors: Brede A. D.
Published: July 2010

Green speed of golf course putting greens (an inverse function of the surface friction) is assessed by use of a stimpmeter, a widely used tool distributed by the United States Golf Association. However, green speed of sloped surfaces cannot be measured satisfactorily due to the distorting effects of downslope gravitational acceleration of the ball. The purpose of this study was (i) to develop a simple equation that could be used to correct for the effects of gravitational acceleration on sloped greens, and (ii) to verify the new equation: Corrected green speed = 2S↑S↓ (S↑S↓)−1, where S↑ = distance of ball roll directly uphill and S↓ = distance of ball roll downhill. A laboratory carpet‐covered runway apparatus and two field putting greens were used for validation. Laboratory green speed readings corrected with the equation were equal, regardless of slope from 0 to 5.6%. By using the equation, a golf course superintendent can check green speed of sloped areas that previously would have been impossible to assess.
Root Response of Tolerant and Intolerant Soybean Cultivars to Soybean Cyst Nematode
Authors: Miltner E. D. , Karnok K. J. , Hussey R.S.
Published: July 2010

Tolerance to soybean cyst nematode (SCN), Heterodera glycines Ichinohe, has been identified in soybean [Glycine max (L.) Merr.] and has potential as a management strategy to limit SCN yield suppression. Little information is available on the growth and morphology of roots of tolerant soybean cultivars parasitized by SCN. This study was conducted to compare root and vegetative responses of a moderately tolerant soybean, ‘Wright’, with an intolerant soybean, ‘Bragg’, to parasitism by SCN. In 1986, Bragg and Wright soybean was grown in the University of Georgia rhizotron in rooting medium infested with SCN Race 3 at initial population densities (Pi) of 0, 1000, or 10 000 eggs/L. Measurements were made of soybean root growth and development, vegetative and reproductive growth stage, leaf number, flower and pod numbers, and nematode activity (development and infection). Number of growing roots on Bragg at Pi 10 000 was suppressed throughout the season, whereas root growth of Wright was stimulated by the presence of SCN. Although not statistically significant, root lengths followed these same trends. Seed yield of Bragg was progressively suppressed as Pi increased, in contrast to that of Wright which was suppressed at Pi 1000, but was not suppressed further at Pi 10 000. Vegetative development of Bragg was suppressed at Pi 10 000 compared to Pi 0 from 18 and 39 d after planting (DAP), respectively, in contrast to Wright which was unaffected. Reproductive development of Bragg at Pi 10 000 was also suppressed between 79 and 133 DAP. The stimulation of root development of Wright in the presence of SCN was probably critical to maintenance of vegetative and reproductive development.
Nitrogen Fertilizer Recovery by Grain Sorghum in Monoculture and Rotation Systems
Authors: Varvel G. E. , Peterson Todd Andrews
Published: July 2010

Grain sorghum [Sorghum bicolor (L.) Moench] has become a major dryland crop for the Great Plains, but information on production in rotations is limited. This study was conducted to determine N fertilizer recovery and use by grain sorghum in monoculture and rotational systems. Grain sorghum was grown under rainfed conditions on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic, Typic Argiudoll) in: (i) continuous grain sorghum monoculture, (ii) a 2‐yr soybean [Glycine max (L.) Merr.]‐grain sorghum rotation, (iii) a 4‐yr rotation of soybean‐corn [Zea mays L.]‐oat [Avena sativa (L.)] + clover [80% Melilotus officinalis (L.) and 20% Trifolium pratense (L.)]‐grain sorghum, and (iv) a 4‐yr rotation of oat+clover‐corn‐soybean‐grain sorghum at Mead, NE. Broadcast applications of 15N‐depleted NH4NO3 were made at 90 and 180 kg N ha−1 in 1985 and 1986 to evaluate N fertilizer recovery. Fertilizer N recovery determined by isotopic methods was significantly higher for grain sorghum in monoculture (64.9%) vs. grain sorghum in rotation (54.9%). Fertilizer N recovery estimated by the difference method ranged from 118.5% in continuous grain sorghum to 9.1% in sorghum following oat+clover. Differences in N‐recovery results by the isotope and difference methods indicated N fertilizer applied to grain sorghum in various cropping systems appeared to be entering different organic soil‐N pools. These results substantiate the importance of the mineralization‐immobilization turnover (MIT) effect in N‐isotope experiments and the necessity for careful interpretation of N‐recovery results, especially between complex cropping systems.
Critical Petiole Nitrate Levels in Potato
Authors: Westcott M. P. , Stewart V. R. , Lund R. E.
Published: July 2010

Critical nutrient concentrations (CNC), below which a yield reduction occurs, for potato (Solanum tuberosum L.) petiole nitrate (PN) have been reported for the Pacific Northwest growing region but differences in method of determination or definition of this parameter have resulted in some discrepancies in values. The objectives of this research were to document seasonal PN levels with varying levels of applied N, to determine CNC at three growth dates [tuber initiation, TI; 21 d after TI(TI + 21); and 42 d after TI (TI + 42)], and to establish the relationship between yield responses to midseason N application and CNC. Experiments were conducted at two sites on a Typic Argiboroll and three sites on a Pachic Haploxeroll in western Montana. Treatments included six or eight N rates between 0 and 336 kg N ha−1 applied as NH4NO3 before hilling and a topdressing of 67 kg N ha−1 broadcast on subplots at TI + 21. Early season PN depended on applied N, with maximum values of 25 to 30 g NO3‐N kg−1 at TI. Values declined with seasonal progression and became increasingly dependent on fertilizer N rates. The N topdressed at TI + 21 increased PN level 6 g kg−1 at TI + 42 compared to non‐topdressed areas. Linear plateau regression of relative yield against PN revealed CNC values of 25 g kg−1 at TI 14 g kg−1 at TI + 21, and 10 g kg−1 at TI + 42. Statistical analysis, could not separate the TI + 21 and TI + 42 regressions, indicating a CNC of 13 g NO3‐N kg−1 throughout the period of tuber bulking. Yield responses to topdressed N, however, were documented only when PN values were below 11 g NO3‐N kg−1 at TI + 21. Conservative interpretation of critical nutrient concentration is justified.
Recovery of Point‐Injected Labeled Nitrogen by Corn as Affected by Timing, Rate, and Tillage
Authors: Timmons D. R. , Baker J. L.
Published: July 2010

Point‐injection technology is being developed to improve fertilizer management, particularly N management. This study was conducted to evaluate the effects of the rate (number) and timing of point‐injections of an ammonium nitrate (NH4NO3) solution on N uptake and corn growth and to measure any differences due to tillage. Nitrogen‐15 depleted NH4NO3 (AN) was hand‐injected beside individual plants at the V1, V5, and/or V9 growth stages at rates of 50, 100, and/or 200 kg N ha−1 with fall moldboard plow (MP), fall chisel plow (CP), and ridge‐till (RT) systems. While MP had the highest grain and total dry matter production (but with the lowest N concentrations in those materials), tillage was not a significant factor in either the percentage of the total plant N derived from labeled AN (NF) or its recovery (NR) for any stage sampled. Generally the year (i.e. different environmental conditions) and application timing or a timing‐by‐year interaction had the greatest influence on NF and NR. Although plants sampled at the V9 stage on the average recovered more N from the V1 application (39%) vs the V5 application (27%), at maturity NR values for grain (35%) and total dry matter (47%) were the same for both V1 or V5 applications (when only two applications were made). However when three applications were made (at the V1, V5, and V9 stages), NR values decreased with time of application for both grain (38, 31, and 26%, respectively) and total dry matter (53, 43, and 33%, respectively). Across application timing, grain NR values were 34 and 31%, respectively, for MP and RT. Compared with preplant knifed‐in labeled N for MP and RT systems in an adjacent simultaneous study, grain NR values for point‐injected N in this study were 16 and 6% greater, respectively, indicating that multiple injections of fertilizer N improved N‐use efficiency.
Rooting Activity and Water Use during Vegatative Development of Crested and Western Wheatgrass
Authors: Frank A. B. , Bauer A.
Published: July 2010

Crested wheatgrass [Agropyron desertorum (Fisch. ex. Link) Schult] and western wheatgrass [Pascopyrum smithii Rybd, (Löve)] are important cool‐season forage species that have contrasting growth patterns. Knowledge of relationships among plant development stage, water use, and rooting activity would aid in understanding the responses of these species to stresses and defoliation. Our objectives were to compare evapotranspiration (ET), rooting activity, and plant water status in relation to Haun development stage of ‘Nordan’ crested wheatgrass and ‘Rodan’ western wheatgrass. These species were grown at three water treatments (50, 100, and 150% of 1 April to 31 October monthly rainfall) and two N fertilizer (11 and 110 kg N ha−1) rates in a rain‐out shelter at Mandan, ND for a 3‐yr period. The soil was a Parshall fine sandy loam (coarse‐loamy, mixed Pachic Haploborolls). Cumulative ET through early boot stage averaged 133 and 170 mm for crested and western wheatgrass, respectively. Maximum ET rate occurred at Haun stage 5 to 6 for both species. Crested wheatgrass rooting activity averaged over three water treatments increased about 4.4 cm d−1 compared to 3.7 cm d−1 for western wheatgrass. Both species exhibited rooting activity to 1.2 m by mid‐May when western wheatgrass had developed to Haun stage 4.9 and crested wheatgrass to 5.7. Water use‐efficiency of crested wheatgrass decreased as water treatment and Haun stage increased, but western wheatgrass did not change with either. Water use‐efficiency of crested wheatgrass, but not of western wheatgrass, was greater at 110 than at 11 kg fertilizer N ha−1. Information on the simultaneous development of plant aerial parts and rooting activity contributes to an understanding of the water‐use relations of these species and has application in development of growth and yield simulation models.
Seed Spacing for Nonthinned Sugarbeet Production
Authors: Eckhoff J. L. A. , Halvorson A. D. , Weiss M. J. , Bergman J .W.
Published: July 2010

Irrigated sugarbeet growers traditionally overseed their crop to assure adequate stands, then hand thin to a final population. The extra seed and hand labor costs may possibly be eliminated. The objective of this study was to determine optimum seed spacing for the greatest sucrose production in nonthinned sugarbeet. ‘AC‐102’ sugarbeet (Beta vulgaris L.) was planted at 10–, 15, 19–, and 23–cm intrarow seed spacings for 4 yr in Sidney, MT, to determine optimum seed spacing for greatest sucrose production of nonthinned sugarbeet. The fall ridging/spring deridging system was used to assure sufficient moisture for emergence. Successful stands were established without supplemental irrigation in 1984, 1985, and 1986, but in 1987, rains after planting and before emergence caused severe crusting of the soil which reduced stands. Seedling and harvest plant densities decreased with wider seed spacing in all years. Sucrose content decreased and impurities increased as seed spacing increased. Yields varied across years, but increased sucrose content and decreased impurities of beets planted with the 10‐ and 15‐cm spacings generally resulted in highest gross sucrose and estimated recovered sucrose yields
Reseeding Potential of Crimson Clover as a Cover Crop for No‐Tillage Corn
Authors: Myers J. L. , Wagger M. G.
Published: July 2010

Leguminous cover crops can provide biologically fixed N to a subsequent corn (Zea mays L.) crop as well as erosion control and moisture conserving mulch, but establishment is costly and often unsuccessful. A field experiment was conducted for 3 yr to determine the self‐reseeding potential of crimson clover (Trifolium incarnatum L.) and its N contribution in a no‐tillage corn production system. Four cover crop management treatments (fallow, annual‐seeded, volunteer‐reseeded, and volunteer strip‐reseeded) were combined factorially with four fertilizer‐N rates (0, 50, 100, or 150 kg ha−1) applied to the subsequent corn crop. The annual‐seeded, volunteer‐reseeded, and volunteer strip‐reseeded clover treatments were desiccated at corn planting. Averaged over 3 yr, crimson clover dry matter was 2.6, 4.2, and 3.5 Mg ha−1 for the annual‐seeded, volunteer‐reseeded, and strip‐reseeded treatments, respectively. In 1988 and 1989, cover crop treatments produced mean corn grain yields of 6.0 and 6.1 Mg ha−1 compared to fallow treatment yields of 3.4 and 4.0 Mg ha−1, respectively. This same pattern was reflected in the silage yields and total corn N uptake. Corn grain yields were unaffected by fertilizer‐N rate in two out of 3 yr due to limited rainfall. Both self‐reseeding treatments successfully reestablished each year and increased corn yields primarily by a mulching effect. Allowing crimson clover to mature before chemical desiccation or leaving strips between corn rows to produce seed appear to be effective methods of reseeding clover in a no‐tillage corn silage production system.
Germination Response of Subterranean, Berseem, and Rose Clovers to Alternating Temperatures
Authors: Evers G. W.
Published: July 2010

Annual clover (Trifolium spp.) stands are sometimes poor because of low and slow germination due to unfavorable temperatures. The study was conducted to identify optimum temperature for germination of relatively new clover species to the U.S. Southeast to improve stand establishment. High temperature germination was also examined to estimate summer germination which usually results in seedling mortality and a decrease of the soil seed‐bank. Seed of 10 cultivars of T. alexandrinum L., T. brachycalycinum Katzn. and Morley, T. hirtum All., T. subterraneum L., and T. yanninicum Katzn. and Morley were subjected to alternating 12 h day/12 h night temperatures of 15/5, 20/10, 25/15, 30/20 and 35/25 °C. Germination counts were made at 3, 6, 9, and 12 d to determine percent germination and germination rate index (GRI). Germination was >80% for all entries at the three lowest temperature treatments except ‘Larisa’ subclover at 25/15 °. At 30/20 °C, germination of ‘Bigbee‘ berseem and T. brachycalycinum subclovers decreased to 54 to 66%, while the other species decreased to <35%. The 35/25 °C treatment suppressed germination to <25%. The optimum temperature for GRI was 25/15 followed by 20/10, 15/5, 30/20, and 35/25 °C. The optimum germination temperature of 25/15 °C occurs in October along the Texas‐Louisiana Gulf Coast. September plantings (30/20 °C) in this area should be limited to T. alexandrinum and T. brachycalycinum species. Cultivars that germinate at summer temperatures of 35/25 °C or higher should be avoided unless they have a high hard‐seed content.
Lowland Rice Apical Development: Stages and Cultivar Differences Detected by Electron Microscopy
Authors: Senanayake N. , De Datta S.K. , Naylor R.E.L. , Thompson W.J.
Published: July 2010

Identification of growth stages and cultivar differences are necessary to develop efficient N fertilizer management for lowland rice (Oryza sativa L.). To help characterize growth stages an electron microscope was used to identify different panicle development stages, cultivar growth differences, and potential yield loss periods. Varieties IR50 (90‐d maturity) and IR42 (120‐d maturity) were grown at the International Rice Research Institute during the 1987 wet season. Thirteen morphologically different development stages up to floral organ development were identified. Between cultivars, duration of each development stage varied. Necknode differentiation was defined as physiological panicle initiation (PI) and observed at growth stage (GS) 1.8 occurring 35 days after seeding (DAS) in IR50 and at GS 1.10 (49 DAS) in IR42. Visual panicle initiation (VPI) was observed at GS 1.9 (42 DAS) in IR50 and at GS 1.11 (64 DAS) in IR42. Panicle development took 15 to 18 d (4–7 d for panicle branches) in IR50 and 24 to 31 d (11‐15 d for panicle branches) in IR42. Therefore the present N management practice of N topdressing 5 to 7 d before VPI coincided with PI for short duration IR50 but not for later maturing IR42. Preflowering and post flowering spikelet abortion reduced the spikelet number in IR50 and more so in IR42 where preflowering spikelet abortion started even before spikelet development was completed. Comprehensive N timing studies based on rice apical development stages are required for improving N efficiency and increasing rice yields.
Mulch Effect on Soil Properties and Tomato Growth Using Micro‐Irrigation
Authors: Tindall James A. , Beverly R. B. , Radcliffe D. E.
Published: July 2010

Although use of micro‐irrigation has risen steadily in Georgia, few studies have been reported describing its effect on yield or rooting distribution of tomato (Licopersicon esculentum). The objective of this experiment was to determine the effects of mulch type (plastic mesh and straw) and micro‐irrigation on soil physical properties and growth of ‘Celebrity’ tomato. In 1986, an experiment was initiated on a Cecil sandy loam (clayey, kaolinitic, thermic, Typic Kanhapludult) at Griffin, GA. Tomato yield and root growth, soil temperature, and water potential in 1987 and 1988 were compared using black plastic mesh and straw mulches and three micro‐irrigation frequencies: control (no irrigation), daily, and twice weekly. Soil properties beneath the two types of mulches were compared in terms of surface evaporation, measured during 24‐h periods several times each year and bulk density, organic C, pH, infiltration rate, and cone index measured at the end of the 1988 growing season. Straw mulch resulted in a significantly greater infiltration rate, and lower pH, bulk density, surface evaporation, cone index, soil temperature and matric potential than the plastic mulch. Yields were higher under the straw mulch compared to the plastic mulch and irrigation increased yield with a straw mulch in 1987 but not 1988. Yields were not increased by irrigation of the plastic mulch treatment. Straw mulches have the potential to improve tomato yields in high‐temperature environments, provided soil pH is controlled.
Stomatal Responses of Field‐Grown Cotton to Radiation and Soil Moisture
Authors: Petersen K. L. , Moreshet S. , Fuchs M.
Published: July 2010

Field research conducted on stomatal responses to water stress has generally focused on sunlit leaves and ignored the role of shaded leaf conductance. This study was carried out on a cotton crop (Gossypium hirsutum, cv. Acala SJ2) to quantify and compare sunlit and shaded stomatal conductance under variable water stress conditions, and to identify the primary environmental parameters regulating the stomatal conductance of sunlit and shaded leaves. Photosynthetically active radiation (PAR), leaf temperature, humidity, and stomatal conductances for both abaxial and adaxial leaf surfaces were measured on cloudless days during two field seasons in 1988 and 1989. Average daytime shaded leaf conductance was approximately 41 and 36% that of sunlit leaves in non‐stress and severe water stress conditions, respectively. The primary environmental parameter affecting sunlit leaf conductance was PAR. Shaded leaf conductance was weakly correlated to PAR and leaf temperature, respectively, under non‐stress conditions. Under water stress, shaded and sunlit leaf conductances were not correlated to leaf temperature. Leaf conductance was not correlated to humidity under any test condition. The derivative of stomatal conductance with respect to PAR decreased as PAR increased, with most of the change occurring in the PAR range typically obtained in the shaded fraction of the canopy. Increasing moisture stress progressively decreased the stomatal response to PAR. When sunlit and shaded leaves were pooled together, a curvilinear regression improved the correlation with PAR. Abaxial conductance comprised a greater percentage of leaf conductance for shaded than for sunlit leaves.
Program for Investigating Genotype‐Environment Interaction
Authors: Lin C.S. , Butler G. , Hall I. , Nault C.
Published: July 2010

This program was written to investigate genotype‐environment (GE) interaction in two‐way classification data. The analysis consists of three parts: (i) stability analysis of genotypes based on a regression or an ANOVA model, (ii) estimation and plotting of residuals, and (iii) cluster analysis for dissecting the data set into homogeneous subsets. These analyses provide diagnostic information to assess genotypic response characteristics and enable a scientist to group the genotypes in such a way that the genotypes within each subset display no GE interactions. It is hoped that by dissecting the data into homogeneous subsets the interaction structure of the data can be revealed. The program can handle five methods depending on whether a regression (linear or quadratic) or an ANOVA model is used, and whether grouping is done with respect to the similarity of GE interaction alone or the genetic effect and GE interaction combined.
Nitrogen Concentration of Young Corn Plants as an Indicator of Nitrogen Availability
Authors: Binford G. D. , Blackmer A. M. , Cerrato M. E.
Published: July 2010

Soil tests for evaluating the N status of cornfields in late spring show promise as a tool for improving N management during corn production. An alternative tool for evaluating N status is tissue testing, which offers the potential advantages of easier sampling and better integration of factors that influence N availability. Here we evaluate total N concentrations of whole corn (Zea mays L.) plants in late spring as an indicator of N availability in cornfields. Studies were conducted at 14 site‐years in Iowa during 1986, 1987, 1988, and 1989. Whole plant samples were taken when corn was 15 to 30 cm tall. Total N concentrations in these plants were determined. Relationships between concentrations of N in young plants and fertilizer N applied were not consistent across the 14 site‐years. The concentrations of N in young plants were poor predictors of soil NO3 concentrations in situations where good relationships between soil NO3 concentrations and grain yields occurred. The tissue test could not detect excessive amounts of NO3 in soils. Concentrations of N in young plants were greatly influenced by factors having relatively little effect on final yields. Overall, the results show that a tissue test based on the concentrations of N in young plants would not be a reliable indicator of the N availability in cornfields.
Morphological Development of Switchgrass and Kleingrass
Authors: Sanderson Matt A.
Published: July 2010

Accurate and precise measurements of plant maturity are essential in research involving perennial warm‐season grasses. The objective of this study was to devise and refine such an index for use with determinate and indeterminate flowering warm‐season perennial grasses. An index of 35 separate stages distributed among three major developmental events (leaf, stem, and reproductive development) was devised and tested on switchgrass (Panicum virgatum L., determinate flowering habit) and kleingrass (Panicum coloratum L., indeterminate flowering habit). Switchgrass and kleingrass were sampled in two growth periods, spring and summer of 1989. Switchgrass only was sampled in spring of 1990. At each sampling, 30 to 50 tillers were classified into stages, counted, dried, and weighed. An additional 30 to 50 tillers were separated also into leaf, stem, sheath, and inflorescence (if exserted) fractions. Kleingrass flowered earlier and developed morphologically nearly three times faster than switchgrass in spring 1989 and twice as fast in summer 1989. In 1990 switchgrass exhibited a sigmoidal development pattern with three distinct phases, each with a different rate of development. The phases were related closely to temperature and rainfall patterns with greater rates of development occurring during relatively cool and wet periods. The experimental index described switchgrass and kleingrass development well. Most stages were rapidly and easily recognized. Reproductive stages were sometimes subjective and may have to be revised.
Model Evaluation for Perennial Grasses in the Southern United States
Authors: Overman A. R. , Wilkinson S. R.
Published: July 2010

Models can be used to estimate yield response of grasses to applied N. This analysis was conducted to show variation of model parameters among grasses at the same location and differences among locations. The logistic equation was used to relate annual dry matter yield to applied N for four locations (Blairsville, GA; Fayetteville, AR; Thorsby, AL; Jay, FL) and five perennial grasses [bermudagrass (Cynodon dactylon L., Pers.), bahiagrass (Paspalum notatum Flugge), tall fescue (Festuca arundinacea Schreb.), dallisgrass (Paspalum dilatatum Poir.), and orchardgrass (Dactylis glomerata L.)]. The model contained three parameters (A, b, c). It was shown by analysis of variance that all grasses exhibited common exponetial coefficients (b, c) for each location, with variation among grasses and with water availability assigned to the linear coefficient (A). Applied N, N1/2, to reach one‐half maximum yield appeared to be inversely related to clay content of the soil. Maximum efficiency of conversion of applied N to dry matter at N = N1/2 was highest for Coastal bermudagrass (approximately 40). The logistic equation provides an excellent model for yield response to applied N.
Radiation Use Efficiency of an Old and a New Maize Hybrid
Authors: Tollenaar M. , Aguilera A.
Published: July 2010

Differences in dry matter accumulation among crop cultivars can be attributed to differences in either the absorptance of incident photosynthetically active radiation (PAR) and/or the conversion of absorbed PAR into dry matter. This study was conducted to quantify the contribution of radiation use efficiency (RUE, g dry matter MJ−1) to the difference in dry matter accumulation between an old and a new maize (Zea mays L.) hybrid. An old (Pride 5) and a new (Pioneer 3902) maize hybrid were grown during 1989 and 1990 at the Elora Research Station, Ontario, on a London loam (Aquic Hapludalf) soil that had been tile drained. Both hybrids were grown at their respective optimum plant density for grain yield (i.e., 7 plants/m2 for Pride 5 and 8 plants/m2 for Pioneer 3902) and, in addition, the new hybrid was grown at 5 plants/m2 which resulted in a leaf area index (LAI) similar to that of the old hybrid grown at its optimum plant density. Starting at silking, 2‐wk crop growth rates (CGR, kg ha−1 d−1) were measured until physiological maturity, and incident PAR and absorptance of PAR by the three treatments were monitored during three 2‐wk periods after silking. From silking to 6 wk postsilking, PAR absorption did not differ among the two hybrids grown at plant densities that resulted in similar LAIs, but crop growth rate was 19% larger for the new hybrid. The difference in crop growth rate between the old and the new hybrid grown at their respective optimum plant density was 33%; approximately 80% of the difference could be attributed to a higher RUE of the new hybrid. The difference in RUE was not associated with a change in the distribution of PAR across the canopy, i.e., extinction coefficients did not differ among treatments. Dry matter accumulation declined for all treatments after 8 wk postsilking, but the decline was steeper for the old hybrid and the decline was associated with rate of leaf senescence. In conclusion, increased dry matter accumulation of new maize hybrids after silking can be attributed, in a large part, to increased radiation use efficiency.
Differential Weed Suppression Ability in Upland Rice Cultivars
Authors: Garrity D. P. , Movillon M. , Moody K.
Published: July 2010

Twenty‐five upland rice (Oryza sativa L.) cultivars were evaluated in 2 yr of field experiments in the Philippines. The research was conducted with low and moderate levels of handweeding to determine the extent of cultivar differences in weed suppression ability. We sought the plant characters that may confer superior competitiveness, and determined their practical significance in contributing to weed management. A large significant variation was observed in the dry weight of weeds (0.84 to 3.89 Mg/ha) associated with the different cultivars. Several cultivars had consistently low weed weights in both weeding treatments across years. Weed weights for the five most competitive cultivars were 75% lower than for those of the five least competitive cultivars. Grain yields were negatively correlated with weed weights, in both weeding treatments in both years (r = −0.48** to −0.59**‐significant at P = 0.01). Plant height, which ranged from 0.73 to 1.35 m, was the character most strongly related to low weed weight, with negative correlations that varied from −0.76** to −0.88** among weeding levels and years. Leaf area index (determined at 60 d after seeding) was also negatively correlated with weed weight, but tiller number was not significantly related to weed weight. The minimum plant height necessary to adequately suppress weeds was approximately 1.00 to 1.15 m. Cultivars with superior yield potential were identified that had a minimum height of 1.0 m, with weed suppression ability similar to the tall traditional cultivars.
Irrigation of Turfgrass with Secondary Sewage Effluent: Soil Quality
Authors: Mancino C. F. , Pepper I. L.
Published: July 2010

Effluent and other secondary waters have become important sources of irrigation water in the U.S. Southwest. Information is inadequate relative to potential long‐term effluent irrigation effects on turfgrass and soil chemical quality. The objective of this field research was to determine the influence of secondarily treated municipal wastewater irrigation on the chemical quality of bermudagrass (Cynodon dactylon L.) turf soil (Sonoita gravelly sandy loam: coarse‐loamy, mixed, thermic Typic Haplargid) when compared to similarly irrigated potable water plots. Research plots were irrigated using a 20% leaching fraction. After 3.2 yr of use, effluent water increased soil electrical conductivity by 0.2 ds m−1, Na by 155 mg kg−1, P by 26 mg kg−1, and K by 50 mg kg−1 in comparison to potable irrigated plots. Soil pH was not significantly affected by effluent irrigation. The concentrations of Fe, Mn, Cu, and Zn were found to be within the range considered normal for agricultural soil. Effluent irrigation increased soil total organic carbon and nitrogen during the first 1.3 yr of irrigation only. Total aerobic bacteria populations were similar in all irrigated plots indicating these microbes were not promoted or inhibited by the use of this wastewater. In summary, the irrigation of this turf soil for 3.3 yr with the secondarily treated wastewater used in this study had no serious detrimental effects on soil quality
Evapotransportation, Crop Coefficients, and Leaching Fractions of Irrigated Desert Turfgrass Systems
Authors: Devitt D. A. , Morris R. L. , Bowman D. C.
Published: July 2010

Reducing irrigation volumes on turfgrass in an arid environment requires close attention to environmental demand. The objective of this research was to quantify the water balances of three turfgrass sites controlled by an evapotranspiration (ET) feedback system and local management. Additional objectives included calculating leaching fractions (LF), crop coefficients (Kc), water savings, and quantifying the variability in potential evapotranspiration (ET0). A 2‐yr study was conducted on three turfgrass sites in southern Nevada growing common bermudagrass [Cynodon dactylon (L.) Pers.] overseeded with perennial ryegrass (Lolium perenne L.). Two vacuum‐drained lysimeters and one automated weather station were placed at each location. One lysimeter was irrigated by input from an ET feedback system while the other was left to local management. The daily Penman combination equation was used to calculate ET0. Hydrologic water balances were maintained on each lysimeter on a weekly basis. A neutron probe was used to measure changes in soil water content in the lysimeters. Actual ET (ET0) varied according to management, with the two golf courses having an average ET0 29% higher than the park site. Differences in ET0 between the park site and golf course sites were attributed to cultural management, in particular fertilizer input. Crop coefficients varied on a monthly basis and between high management vs low management turf. A 4 to 6% error was observed in estimating ET0 among the three sites.
Leaf Emergence and Leaf Duration Related to Thermal Time Calculations in Ceres‐Maize
Authors: Hodges Tom , Evans David W.
Published: July 2010

In the CERES‐Maize model, maize (Zea mays L.) leaf initiation and appearance are modeled using thermal time derived from air temperature. Prior to the elevation of the culm apex, soil temperature, which is calculated by the model from air temperature, is used to calculate thermal time. No provision is made for response differences in leaf appearance rate due to cultivar or daylength. This research compares predicted with actual leaf development for up to 10 hybrids in five experiments for 4 yr. It also compares calculated versus measured soil temperatures in 1 yr. Thermal time requirements for appearance of leaf tips and collars and for duration of leaf expansion were determined using thermal time equations from the CERES‐Maize model. Thermal time values per leaf were stable within experiments, but varied substantially among years and hybrids. Although the CERES‐Maize model predicts leaf tip appearance moderately well, the rate of leaf development appears to differ among hybrids and may be sensitive to daylength and temperature extremes that are not considered by the model. Improvements are also needed in the model prediction of soil temperature.
Portable Soil Coring System that Minimizes Plot Disturbance
Authors: Prior S. A. , Rogers H. H.
Published: July 2010

Reliable sampling of belowground components is an essential aspect of agro‐ecosystems research. Nevertheless, small plot size, limited access, and remote locations can severely restrict such efforts. To overcome these constraints a light weight, field portable soil coring system was designed. The two‐part unit causes virtually no plot disturbance and, in repeated field tests, performed efficiently and reliably. Soil cores greater than 1 m in length and 38 mm in diameter can be taken. The unit uses a pneumatic driver, an electric core extractor, and steel core tubes with clear plastic liners. As many as 24 cores per hour can be collected with this system. The coring system has been found to be ideal for small size plots or where study areas are enclosed.
Estimating Leaf Area of Pearl Millet from Linear Measurements
Authors: Persaud N. , Gandah M. , Ouattara M. , Mokete N.
Published: July 2010

Plant leaf area is a useful observation in physiological and agronomic research. Statistical regression and correlation models have been used to estimate leaf blade area from leaf blade dimensions such as length and width. The objective of this study was to determine if consistent relationships exist among leaf area (A), length (l), and maximum width (m) of pearl millet [ Pennisetum glaucum (L.) R. Br.] leaves from different plant positions and different stages of maturity. Measurements of length, width, and area were made on leaf blades sampled from different positions on pearl millet plants at the 7‐ and 10‐leaf growth stages. Relationships for the model A = klm were derived by least squares regression for these leaves of each position on the plants (where k is an empirical constant). The results of these analyses justified the use of the model A = klm for pearl millet leaves. However, different coefficients may need to be calculated depending on leaf position and growth stage of the plants. This approach could also be applied for other cereal crops whose leaves have similar morphology and anatomy.
Forage and Tuber Yields and Digestibility of Selected Wild and Cultivated Genotypes of Jerusalem Artichoke
Authors: Seiler Gerald J.
Published: July 2010

Jerusalem artichoke (Helianthus tuberosus L.), a perennial forb, has the potential to be utilized as a silage or tuber crop, but little is known about the variability for forage and tuber yields of wild and cultivated genotypes. Four wild and six cultivated genotypes were evaluated for forage and tuber yields, biomass allocation, and in vitro digestible dry matter (IVDDM) concentrations of stems, leaves, tubers, and whole plants (all above‐ground biomass) at different stages of plant development and compared to an annual commercial oilseed sunflower (H. annuus L.) ‘Hybrid 894’. The perennial genotypes were maintained as pure stands while the annual Hybrid 894 was replanted each year. The cultivated Jerusalem artichoke ‘Sunchoke’ had the highest forage yield (6.3 Mg ha−2) which is comparable to some common forage species. The cultivated genotypes also had the highest mean tuber yield (7.19 Mg ha−1). At maturity, the allocation of biomass for Jerusalem artichoke was 68, 23, and 9% for stems, leaves, and heads, respectively. At flowering, the whole‐plant concentration of IVDDM was above the accepted level (598 g kg−1) for adequate animal nutrition for all genotypes except wild ‘Iowa’, wild ‘Texas’, and cultivated Sunchoke. The sunflower Hybrid 894 had higher IVDDM concentrations than the Jerusalem artichoke genotypes. The significant negative correlation between forage yield and IVDDM concentration indicates that these characteristics cannot be simultaneously improved in a breeding program. There appeared to be enough variability to select for increased forage or tuber yields in Jerusalem artichoke.
Nitrogen Effects on Boll Production of Field‐Grown Cotton
Authors: Boquet D. J. , Moser E. B. , Breitenbeck G. A.
Published: July 2010

Nitrogen is an essential nutrient for cotton (Gossypium hirsutum L.) that affects plant growth, fruiting, and yield. This study was conducted to determine N effects on the development of harvestable bolls (HB) at fruiting sites among reproductive branches (sympodia). Field experiments were conducted from 1987 through 1990 on Commerce silt loam (fine‐silty, mixed, thermic, nonacid, aeric Fluvaquent) to evaluate responses to preplant N rates of 0, 28, 56, 84, 112, 140, and 168 kg ha−1, and to split applications of 56 + 56 kg N ha−1. Increasing N decreased HB production at Sympodia 5 through 10, and increased HB at Sympodia 12 through 25. At Sympodia 5 through 10, production of HB at Fruiting Site 1 (first position on sympodial branch) decreased from 49% of fruiting sites at the 0 N rate, to 36% of fruiting sites, with N fertilization of 168 kg ha−1. Harvestable boll production at Sympodia 11 through 16 increased from 58% at 0 N up to a maximum of 69% at 84 kg N ha−1. At Sympodia 17 through 25, fruiting sites developing HB increased from 9% up to a mximum of 28% with application of 140 kg N ha−1. Whole‐plant HB development at Fruiting Sites 1, 2, and 3 was optimized at 42, 23, and 8%, respectively, by N rates between 56 and 84 kg N ha−1. Averaged over all fruiting sites, maximum whole‐plant HB development of 24% was obtained with 84 kg N ha−1. Results demonstrate that increased N increased the total number of HB per plant. Increase in yield potential in response to N was limited, however, by decrease in HB at lower sympodia as N was increased, and by the inability of plants to more effectively develop bolls at Fruiting Site 2 and 3, and those at upper sympodia.