bluuebunny/crossref_metadata_2025 huggingface dataset:
Soybean Yield Responses and Intraspecific Competition from Simulated Seedcorn Maggot Injury
Authors: Higley Leon G. , Pedigo Larry P.
Published: July 2010

The reproductive and competitive responses of plants to early season stresses are not well known. In field experiments from 1983 to 1986 we examined these effects for one system; simulated seedcorn maggot (SCM), Delia platura (Diptera: Anthomyiidae) injury to soybean, Glycine max (L.) Merr. Injury included different plant densities (simulating stand reductions) and different ratios of plumule‐injured to uninjured plants (simulating different levels of plumule destruction). Our objectives were to describe (i) how simulated SCM injury affected total yield, yield components, and intraspecific competition between injured and uninjured plants, and (ii) to determine the value of the replacement series experimental design for examining intraspecific competition from injury. Plant density did not influence plot yields but did affect yield components of injured and uninjured plants. The proportion of injured to uninjured plants influenced plot yields in 1983 and 1984 but not in 1985 or 1986. Uninjured soybean were much stronger competitors than injured soybean. Yield reductions of injured plants were attributable to competition from uninjured plants. Specifically, competition seemed to increase shading and reduce assimilate availability of injured plants. The replacement series design was a powerful technique for describing intraspecific competition arising from insect injury.
Germination of Twenty Forage Legumes as Influenced by Temperature
Authors: Brar G. S. , Gomez J. F. , McMichael B. L. , Matches A. G. , Taylor H. M.
Published: July 2010

Many studies have shown that water potential at planting will affect germination rate and final germination. Much less is known, however, about the effects of different temperatures at planting on seed germination. Our objectives were to compare the influence of different temperatures on the germination percentage and germination rate index of 20 forage legumes. Legume seedlings were grown for 10 d in polyethylene growth pouches placed in germination chambers and held in the dark at constant temperatures of 10, 15, 20, 25, or 30 °C. There were major effects of temperature on germination rate and germination percentage for all 20 legume entries. If we define satisfactory germination as 80% germination at 10 d after planting, 18 of the 20 entries had satisfactory germination at some temperature between 10 and 30 °C. There were no significant effects of temperatures between 10 and 30 °C on germination percentage at 10 d for ‘Arlington’ red clover (Trifolium pratense L.) and ‘Maxidor’ alfalfa (Medicago sativa L.) entries. Since temperature had a strong influence on germination, seeding time for some legumes should be selected to match expected temperatures for particular locations.
Organic Matter, Nutrient, and pH Distribution in No‐ and Conventional‐Tillage Semiarid Soils
Authors: Unger Paul W.
Published: July 2010

There is widespread interest concerning whether the influence of conservation tillage systems on soil conditions is beneficial or detrimental to crop production. Objectives of this study were to evaluate the distribution with depth of organic matter (OM), total N, NO3‐ N, P, K, Ca, and pH on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). The crop rotation used was dryland winter wheat (Triticum aestivum L.)‐grain sorghum [Sorghum bicolor (I,.) Moench]‐fallow (WSF) involving stubble mulch (SM) tillage arid no‐tillage (NT). The SM field and an adjacent NT field had been used for the WSF rotation since 1956. No‐tillage was started on the adjacent field in 1981 (NT‐81), continuing the same rotation. On another field, the NT‐WSF rotation was started in 1979 (NT‐79) on land previously used for irrigated crops. Sampling was in August 1988 at depths of 0 to 1, 1 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, 10 to 15, and 15 to 20 cm. On the SM field, there were few differences, except for pH, throughout the tillage zone (0‐8 cm). There were differences at depths below 8 cm in some cases relative to those above 8 cm. The NT fields tended to have higher mean OM, N, NO3−N, P, and K values at the surface than the SM field, but all differences were not significant. In general, more differences with depth were significant on NT fields than on the SM field. Although NT is changing the distribution of OM and some plant nutrients in the soil, the changes are relatively small and NT appears to be a viable cropping practice for conserving soil and water and maintaining crop productivity on dryland in the southern Great Plains.
Effects of Furrow Diking and Tillage on Corn Grain Yield and Nitrogen Accumulation
Authors: McFarland M. L. , Hons F. M. , Saladino V. A.
Published: July 2010

Cultural practices that conserve soil and water while maintaining or improving crop yield and quality are needed. Furrow diking and reduced tillage may constitute two such practices. The effects of furrow diking in combination with reduced (ridge tillage) or conventional disk tillage on soil‐water content, grain yield, and N accumulation of corn (Zea mays L.) were evaluated on a Weswood silt loam/Ships clay intergrade (fine‐silty, mixed thermic Fluventic Ustochrept/ very‐fine mixed thermic Udic Chromustert) near College Station, TX in 1987 and 1988. Five N rates (0, 75, 150, 225, and 300 kg N ha−1) as NH4NO3 were preplant subsurface banded into plots representing all combinations of tillage (reduced or conventional) and diking (all furrows diked or all furrows open). Neither diking nor tillage significantly increased soil‐water content in the above average rainfall year of 1987. In contrast, furrow diking with conventional tillage, and reduced tillage, with or without diking, significantly increased soil‐water content in the surface 150 cm compared to nondiked, conventional tillage treatments in the below average rainfall year of 1988. Diking significantly decreased or tended to reduce grain yields in 1987 at most fertilizer‐N rates, but had no effect on grain yield in 1988. Diking significantly increased grain‐N accumulation at the 150 kg N ha−1 rate in 1987, but had no effect at higher or lower N rates. Leaf‐N concentration was not affected by diking in 1987, and diking had no significant effects on grain‐N uptake or leaf‐N concentration in 1988. Effects of N fertilization on grain yield, grain‐N accumulation, and leaf‐N concentration were generally similar for reduced and conventional tillage treatments.
Heteroscedasticity in Whole Plant Growth Curves Developed from Nonreplicated Data
Authors: Meek D. W. , Hutmacher R. B. , Mackey B. E. , Davis K. R.
Published: July 2010

Agronomic researchers usually neglect heteroscedasticity in crop growth formulae and analysis. When they consider it they are not consistent in the methods they use. This study was conducted to: (i) find a method of testing for heteroscedasticity in nonreplicated whole plant growth data and (ii) determine the best weighting for such crop growth data. We developed seven different crop growth models with yield data collected during the growing season of five different crops (14 sets total, six with replicates). Next we performed tests for heteroscedasticity on model residuals and heterogeneity of variance tests on replicated data. Finally we conducted simulations to assess the confidence interval coverage of various weighted predictions based on one model fit to two of the replicated crop sets. Five of the models usually exhibited realistic growth responses throughout the growing season. All heterogeneity of variance tests were significant (P < 0.05) and most suggested a logarithmic weighting. In contrast, tests devised from groups of sequential residuals usually indicated a square root weighting but were generally not significant (P ≥ 0.05). Simulations revealed that weighting was needed but that none of the variance models always adequately characterized the true variance. While not a good variance model, a linear trend in a model's squared residuals (P < 0.10) proved to be a sound test for heteroscedasticity in growth curves developed from nonreplicated data. Crop growth curves need to be weighted with an exact Box‐Cox variance model when replicates are available and one intermediate between the logarithmic and square root model when replicates are unavailable.
Seasonal Forage Production and Regrowth of Hard and Soft Red Winter Wheat
Authors: Carver Brett F. , Krenzer Eugene G. , Whitmore Wayne E.
Published: July 2010

The dual use of winter wheat (Triticum aestivum L.) for forage and grain throughout the southern Great Plains of the USA demands that breeding programs consider forage characteristics during cultivar development. This study was conducted to determine if the present pool of adapted cultivars provides enough variability in seasonal forage production and regrowth to allow future genetic improvement. Eighteen cultivars from two market classes, soft (SRW) and hard red winter (HRW), were evaluated in three environments. Long‐term (seasonal) and short‐term forage harvests (weekly regrowth following the long‐term harvest) were scheduled in the fall and late winter to correspond to maximum forage growth. Soft and hard wheat classes did not differ in average long‐term or short‐term production in the fall. The SRW cultivars produced 30% more winter forage, but the HRW cultivars produced 26% more late winter regrowth than the SRW cultivars. Within‐class differences were detected in both seasons, except for fall regrowth. Long‐term winter production was not correlated with long‐term fall production. Short‐term forage regrowth was a linear function of accumulated growing degree‐days. No significant relationship was found between long‐term production and regrowth rate in the fall. In contrast, an inverse rank‐order relationship (r = −0.53, df = 16, P ≤ 0.05) was found in the winter, where differences in regrowth rate were likely influenced by ontogeny. Soft and hard red winter cultivars appear equally suited as germplasm sources for genetic improvement of wheat forage capacity.
Silage Characteristics of Elephantgrass as Affected by Harvest Frequency and Genotype
Authors: Woodard K. R. , Prine G. M. , Bates D. B.
Published: July 2010

Elephantgrass (Pennisetum purpureum Schum.) was evaluated in the colder subtropics of Florida as a potential forage source for ruminants. Our objective was to determine if this thick‐stemmed bunchgrass could be stored as silage. A dwarf (‘Mott’) and two tall (PI 300086 and ‘Merkeron’) elephantgrasses were harvested one, two, and three times per season and ensiled (direct‐cut) during 1986 and 1987. Dry matter (DM) recoveries for all silages ranged from 861 to 984 g kg−1 of DM ensiled. Mean pH values ranged from 3.8 to 4.0 for tall elephantgrass silages made from plants harvested at the different frequencies. Highest pH values were obtained from silages made from immature dwarf elephantgrass plants harvested three times per year (2‐yr mean was 4.3). Lactic acid was the major end‐product of fermentation in most silages with the exception of those made from immature dwarf elephantgrass where lactic and acetic acids were both major fermentation components. Butyric acid levels were negligible in all silages. In vitro digestible organic matter (IVDOM) concentration of silage was mainly dependent on that of initial forage at the time of harvest. Water soluble carbohydrate concentrations in fresh herbage (range: 26.2–83.7 g kg−1 DM) increased with more frequent harvesting. Buffering capacities of fresh PI 300086 herbage were exceptionally low and increased with more frequent harvesting. The ease with which elephantgrass was preserved as silage was attributed to adequate levels of water soluble carbohydrate concentrations and inherently low buffering capacities in standing forages.
Yield and Quality of Forage Maize as Influenced by Hybrid, Planting Date, and Plant Density
Authors: Graybill J. S. , Cox W. J. , Otis D. J.
Published: July 2010

Although forage maize (Zea mays L.) is grown extensively on livestock operations, most management studies in the USA focus on grain production. Field studies were conducted in New York to evaluate dry matter (DM) yield and forage quality responses of commercial hybrids to planting dates and densities. Six hybrids were planted on 25 April, 9 May, and 23 May and thinned to 5.0, 6.5, and 8.0 plants m−2 in 1988 and 1989. A significant year ✕ planting date interaction was observed for DM yield because dry early‐season conditions in 1988 negated the advantage of early planting in northern latitudes (13.4, 13.9, and 14.6 Mg ha−1 for planting dates 25 April, 9 May, and 23 May, respectively). When averaged across years, high plant densities increased DM yields (15.7, 16.5, and 17.5 Mg ha−1 at 5.0, 6.5, and 8.0 plants m−2, respectively) with no significant effect on harvest index (524, 523, and 526 g kg−1 at 5.0, 6.5, and 8.0 plants m−2, respectively). A hybrid ✕ density interaction was observed for DM yield that suggests that some hybrids in this study performed better at higher densities. Plant density had little effect on acid detergent fiber (ADF) and neutral detergent fiber (NDF) concentrations indicating that forage quality can be maintained at high densities. Hybrids showed distinct variation for ADF (186‐217 g kg−1), NDF (414‐434 g kg−1), and crude protein (CP) (72‐77 g kg−1) concentrations. The forage quality differences among hybrids may be of sufficient magnitude to be of value to the forage producer.
Growth and Nutrient Composition of Maize Genotypes in Acid Nutrient Solutions
Authors: Jariel D. M. , Wallace S. U. , Jones U. S. , Samonte H. P.
Published: July 2010

Crop production in acid soils may be limited by several factors, including low pH. Development of acid‐tolerant cultivars requires information about differences in tolerance to low pH among crop genotypes. To determine whether differential responses to nutrient solution pH occurred among seven maize (Zea mays L.) genotypes, seedlings were grown in a growth chamber in flowing solutions at pH levels ranging from 3.3 to 6.7. Top weights, root lengths and weights, and concentrations of Ca, Mg, Fe, Zn, and Mn in plant tops were determined after 12 d. All genotypes grew well with pH of 4.0 to 5.5, with maximum dry weights of plant tops at pH 4.6 for most of the genotypes. However, all genotypes had necrotic root tips and decreased root lengths at pH 3.3, with relative root lengths (length at pH 3.3/maximum length) ranging from 0.26 to 0.55. Root weights were relatively unaffected by solution pH, but top weights decreased markedly at both pH extremes. Iron concentrations of all genotypes were decreased at pH 6.7, and interveinal chlorosis, resembling Fe deficiency, appeared in the younger leaves. Relative top weights (weight at pH 3.3/maximum weight) averaged 0.79 for Trinidad Grpl&2 and ‘PDMR Comp 1’ and 0.58 for ‘UPCA Varl’, ‘PDMR3’, Kalimpos, and Dikit at pH 3.3, and relative top weights among genotypes were positively correlated (r = 0.85) with Mn concentrations in tops. Based on relative top weight at pH 3.3, the former two genotypes were relatively more tolerant of extremely low pH than those in the latter group.
Analysis of Factors Related to Wheat Yield on Farm Fields in the Buberuka Highlands of Rwanda
Authors: Burleigh J. R. , Yamoah C. F. , Regas J. L. , Eylands Val J.
Published: July 2010

The wheat (Triticum aestivum L.) improvement program in Rwanda has focused on disease resistance, but other factors, including site characteristics, may impact on cultivar performance. The objectives of this study were to identify on farm fields those factors related to wheat yield that may enhance the wheat improvement strategy. Soil samples from 25 fields in 1988 and 30 in 1989, were analyzed for chemical properties. Fields were characterized by slope, azimuth, irradiance, and disease severity. Grain yield and yield components were regressed on soil and site characteristics, and disease development. Nitrogen and Al explained 35% of the variability in tiller and spike numbers for 1988; whereas, slope and stripe rust severity comprised the best model for 1989. For combined seasons, N and Al, powdery mildew and stripe rust severities, and field slope explained 55% of the variability in tiller and spike numbers. Tillers and spikes per square meter also were correlated as a second degree polynomial with irradiance and maximum numbers occurred at 28 MJ m−2 d−1. Aluminum and N were significant variables for grains per spike in 1989, and their regression coefficients usually were not significantly different among seasons. Among most yield components their standard partial regression coefficients usually were greater than for other independent variables. Azimuth and slope were model components for grains per spike, kernel weight, and grain yield. Responsiveness to N and tolerance to Al, therefore, are important selection criteria and the continued search for resistance to Puccinia striiformis West, and Erysiphe graminis DC. f. sp. tritici E. Marchal is warranted. Yields could be improved by selecting lines that tiller well under high solar flux and testing early generations on sites representative of the region.
Pickup Attachment for Small‐Plot Combine
Authors: Ehrensing D. T. , Crane J. M. , Bolton F. E.
Published: July 2010

Research scale combines currently available are not designed to harvest windrowed seed crops. A pickup attachment was constructed from a commercially available unit that allows mechanized harvest of windrows with plot‐scale combines. This piece of equipment was used successfully during the 1989 season to harvest a variety of seed crops.
Productivity and Quality of Annual and Perennial Clover‐Tall Fescue Mixtures
Authors: Pederson G. A. , Brink G. E.
Published: July 2010

Winter annual legumes seeded in perennial clover‐tall fescue pastures could increase early spring herbage production without N fertilizer. This study determined the productivity and forage quality of ‘Regal’ white (Trifolium repens L.) and ‘Kenland’ red clover (T. pratense L.)/tall fescue (Festuca arundinacea Schreb.) mixtures grown with and without ‘Yuchi’ arrowleaf (T. vesiculosum Savi.), ‘Tibbee’ crimson (T. incarnatum L.), and ‘Meteora’ subterranean clover (T. subterraneum L. var. yanninicum [Katzn. & Morley] Zoh.). The experimental design was a split plot with four replicates. Whole plots were red, white, red + white, and no perennial clover. Subplots were arrowleaf, crimson, subterranean, and no annual clover. All species were broadcast seeded on a Catalpa silty clay (fine, montmorillonitic, thermic Fluvaquentic Hapludoll) at Mississippi State, MS, in October 1984. The annual clovers were reseeded in September 1985 and 1986. Arrowleaf and crimson clover competition resulted in 11% less total dry matter and 16% less clover yield compared to no annual clover in perennial clover plots during the first 2 yr of the study. The only yield advantage for perennial clover/tall fescue mixtures with arrowleaf or crimson clovers was in the third year when perennial clover stands declined (mainly due to dry weather conditions) and annual clover overseeding gave 114% greater clover yields. Subterranean clover had little effect on yield or forage quality when grown with perennial clovers. Crude protein and in vitro digestible dry matter concentrations were increased in early spring 1985 and 1987 by the addition of arrrowleaf or crimson clovers to perennial clover plots.
Soil and Canopy Energy Balances of a Row Crop at Partial Cover
Authors: Ham J. M. , Heilman J. L. , Lascano R. J.
Published: July 2010

When crops are grown in a row configuration, heat and mass transfer within the soil‐canopy system influence the energy and water balance of the crop. Field experiments were conducted near Lubbock, TX, to examine the energy balance of the soil and canopy separately, in cotton (Gossypium hirsutum L.) under a variety of aerial and soil moisture conditions. Bowen ratio techniques were used to obtain the field energy balance, including total latent heat flux (LE). Latent heat flux from the crop canopy (LEc was determined from sap flow measurements of transpiration. Latent heat flux from the soil (LEs) was computed as the daerence between LE and LEc. These measurements were coupled with radiation measurements at the soil surface to partition the energy balance into soil and canopy components every 12 min throughout the day. Results indicate that detailed measurements of energy exchange within the soil‐canopy‐atmosphere system can be obtained without making simplifying assumptions about energy transfer. Daily energy balances were strongly influenced by sensible heat transport, and the radiation balance alone did not account for the magnitude or diurnal pattern of LES and LEC. When the soil surface was dry, the canopy simultaneously absorbed sensible heat originating from the soil and above‐canopy air, accounting for more than 21 and 12% of LEC respectively. After an irrigation, LES accounted for more than 50% of LES even when the leaf area index was greater than two, and 11 to 21% of daily LEC occurred at night. The soil surface absorbed sensible heat from the canopy after irrigation, which increased LE1 while decreasing LEC. Analysis indicates that within‐canopy radiative and convective energy transfer must be considered to accurately characterize LES and LEC in row crops during periods of partial cover.
Soybean Stem Growth under High‐Pressure Sodium with Supplemental Blue Lighting
Authors: Wheeler R. M. , Mackowiak C. L. , Sager J. C.
Published: July 2010

High‐pressure sodium (HPS) lamps are popular for plant lighting because of their high energy conversion efficiencies. Yet their spectrum has very little blue light (BL), which may cause undesirable morphological responses. To study this, ‘McCall’ soybean [Glycine max (L.) Merr.] plants were grown for 28 d in growth chambers using HPS lamps, with or without supplemental light from blue phosphor fluorescent lamps. Total photosynthetic photon flux (PPF) levels (including blue fluorescent) were kept near 300 or 500 µmol m−2 s−1. Blue fluorescent levels ranged from 7 to 20 µmol m−2 s−1, providing from 6 to 18 µmol m−2 s−1 of supplemental BL (400‐500 nm). Stem and internode lengths were longest under 300 µmol m−2 s−1 HPS lighting and became progressively shorter with increasing supplemental BL until a total of approximately 30 µmol m−2 s−1 of BL (from HPS and BL supplement) was present in the spectrum. Beyond this, extra BL had no effect. Two other lamps rich in BL, metal halide (Optimarc) and fluorescent (Vita‐Lite), also produced plants with short stems, as did HPS lighting maintained at 500 µmol m−2 s−1. Results suggest that use of high‐pressure sodium or other blue‐deficient sources for lighting at low to moderate photosynthetic photon flux levels may cause abnormal stem elongation, but this can be prevented by adding a small amount of supplemental blue light.
Bite Dimensions and Herbage Intake by Cattle Grazing Short Hand‐Constructed Swards
Authors: Ungar E. D. , Genizi A. , Demment M. W.
Published: July 2010

The objectives of this study were to contribute to the understanding and quantification of the effect of sward structure on the ingestive behavior and intake of livestock. Hand‐constructed swards of approximately 0.43 m2 were used to determine the bite dimensions, bite weight, and short‐term intake rate of steers (Bos taurus L.) grazing short swards. Swards were constructed of leaf blades of Paspalum dilatatum Poir. at homogeneous heights of 0.04, 0.06, 0.08, and 0.10 m and heterogeneous heights with means of 0.06 and 0.10 m at two leaf densities. Treatments were replicated using three 4‐yr‐old steers. Bite depth (B) was defined as the initial sward height (H) minus the mean residual height of grazed leaves. Bite area (A) was defined as the surface area represented by the mean number of leaves grazed per bite. Leaf density had no effect on bite dimensions. Linear regression of B on H and linear regression of A on H explained 99% and 89% of the variance, respectively. Mean bite weight ranged from 0.053 to 0.807 g. Correlation of measured bite weight with the product of the measured B, A, and bulk density yielded a coefficient of determination of 0.97. Mean intake rate ranged from 131 to 1473 g h−1. Bite weight accounted for 93% of the variance of intake rate. Bite dimensions on heterogeneous swards were similar to those on homogeneous swards, though by different mechanisms. The importance of biting overlap, leaf insertion in the mouth, and tongue sweeping are discussed in relation to mean bite dimensions and weight.
Water Deficit Effects on Maize Yields Modeled under Current and “Greenhouse” Climates
Authors: Muchow R. C. , Sinclair T. R.
Published: July 2010

The availability of water imposes one of the major limits on rainfed maize (Zea mays L.) productivity. This analysis was undertaken in an attempt to quantify the effects of limited water on maize growth and yield by extending a simple, mechanistic model in which temperature regulates crop development and intercepted solar radiation is used to calculate crop biomass accumulation. A soil water budget was incorporated into the model by accounting for inputs from rainfall and irrigation, and water use by soil evaporation and crop transpiration. The response functions of leaf area development and crop gas exchange to the soil water budget were developed from experimental studies. The model was used to interpret a range of field experiments using observed daily values of temperature, solar radiation, and rainfall or irrigation, where water deficits of varying durations developed at different stages of growth. The relative simplicity of the model and its robustness in simulating maize yields under a range of water‐availability conditions allows the model to be readily used for studies of crop performance under alternate conditions. One such study, presented here, was a yield assessment for rainfed maize under possible “greenhouse” climates where temperature and atmospheric CO2 concentration were increased. An increase in temperature combined with decreased rainfall lowered grain yield, although the increase in crop water use efficiency associated with elevated CO2 concentration, ameliorated the response to the greenhouse climate. Grain yields for the greenhouse climates as compared to current conditions increased, or decreased only slightly, except when the greenhouse climate was assumed to result in severely decreased rainfall.
Canopy Structure and Nutritive Value of Limpograss Pastures during Mid‐Summer to Early Autumn
Authors: Holderbaum J.F. , Sollenberger L.E. , Quesenberry K.H. , Moore J.E. , Jones C.S.
Published: July 2010

Cattle (Bos spp.) grazing warm‐season, perennial grasses in the lower Southeast USA often gain at a slower rate during mid‐summer to early autumn than they do before or after this season. This has been observed with ‘Floralta’ limpograss [Hemarthria altissima (Poir.) Stapf et C.E. Hubb.], and speculation is that low average daily gains (ADG) may result from changes in canopy structure or herbage nutritive value. During four consecutive 21‐d periods beginning in July 1987 and 1988, a study was conducted on Pomona sands (sandy, siliceous, hyperthermic Ultic Haplaquods) to detect periods of low ADG on rotationally grazed limpograss, and to determine if changes in canopy structure or herbage nutritive value occurred concurrently. Canopies were stratified into two layers of equal depth during each period to characterize herbage bulk density, plant part composition, herbage crude protein (CP), and in vitro digestible organic matter (IVDOM). Additionally, the potential of limited protein supplementation [none, 0.63 kg d−1 (LO) of a 21% CP corn (Zea mays L.)‐urea mixture, or 0.73 kg d−1 (HI) of a 50% CP corn‐urea mixture] to prevent the decline in ADG of steers grazing limpograss was evaluated. Daily gains of steers receiving the 50 and 21% CP supplement treatments (0.59 and 0.53 kg, respectively) were greater than those of nonsupplemented steers (0.29 kg) during the 84‐d trial. Regardless of supplement treatment, steer ADG was lowest during the second period in 1987 (30 July‐20 August) and third period in 1988 (25 August–15 September). Upper (UL) compared with lower canopy layer (LL) had three to six times greater leaf blade to stem plus sheath ratio, 30 to 50% as great a bulk density, 5 to 10% greater IVDOM, and 25 to 100% greater CP. Canopy factors associated with low gain were not identified conclusively, but during periods of low steer ADG, LL stem plus sheath mass was greater than for other periods, whole canopy CP concentration was lower or tended to be lower, and pregraze canopies were tall (57–60 cm), possibly indicating greater physiological maturity of herbage.
Influence of Soil pH and Fertility Programs on Centipedegrass
Authors: Johnson B.J. , Carrow R.N.
Published: July 2010

Improper Centipedegrass [Eremochloa ophiuroides (Munro) Hack] fertilization often results in a lower quality turf and progressive decline. Since the grass is best adapted to low fertility and the optimum pH range is uncertain, an experiment was initiated at Griffin, GA, to determine the influence of soil pH and fertility programs on centipedegrass. Soil pH did not influence the growth of Centipedegrass during the first 2 yr after sprigging (1986 and 1987) when the annual fertility program (N‐P‐K, kg ha−1) was ≥100‐44‐83. When N‐P‐K was reduced ≤50‐22‐42 kg ha−1, centipedegrass growth in soil with pH of 6.2 or 6.7 was better than at 5.1. Soil pH did not influence turf quality or density from 1988 through 1990 when fertilized with 100‐44‐83 kg N‐P‐K ha−1. However, soil pH influenced the quality and density of centipedegrass when fertilized at rates greater than 100‐44‐83 kg NP‐K ha−1. Decline of centipedegrass occurred during spring 1988 when the grass was treated with 200‐88‐166 kg N‐P‐K ha− and grown in soil with pH ≥ 6.2 compared with no decline when grown in soil with pH 5.1. Turf quality and density in 1990 was higher in late April when the grass was grown in soil with pH of 6.2 than 5.1, but soil pH differences were not observed by late May. Therefore, soil pH level was not an important factor when fertilized annually at 100‐44‐83 kg N‐P‐K ha−1, but at lower fertilizer rates, the growth was best during the first 2 yr after sprigging when pH was ≥6.2
Leaflet and Canopy Photosynthesis of Peanut Affected by Late Leaf Spot
Authors: Bourgeois G. , Boote K.J.
Published: July 2010

Late leaf spot, induced by Cercosporidium personatum (Berk. & Curt.) Deighton, is the most important foliar disease affecting peanut (Arachis hypogaea L.) in Florida and neighboring states. The disease first occurs as necrotic lesions on peanut leaflets and subsequently induces leaflet abscission. Field experiments were conducted to study the effects of late leaf spot on leaflet and canopy photosynthesis. Fully expanded leaflets at the tip of the main stem were tagged and leaflet photosynthesis was measured during the subsequent weeks with a portable photosynthesis system. Leaflet photosynthesis was reduced linearly with the increase in the percentage of necrotic leaf area. Reduction in light utilization due only to necrotic leaf area did not explain completely the reduction in leaflet photosynthesis. Regression analysis suggested that 15% necrotic leaf area contributed to a 65% reduction in the photosynthesis of infected leaflets. It appears that there was an effect on leaflet photosynthesis due to host cells invaded or affected by the pathogen. A chamber made of aluminum frame covered with mylar film was used to estimate canopy photosynthesis over a land area of 0.56 m2. At the canopy level, the effect of reduction in leaflet photosynthesis was negligible compared to the effect of disease‐induced defoliation. The decrease in leaf area index was the major component involved in the reduction of canopy photosynthesis because of the effect of late leaf spot. Canopy photosynthesis was inversely proportional to total disease severity, which is an expression of both defoliation and necrotic area.
Response of Three Quackgrass Biotypes to Nitrogen Fertilization
Authors: Tardif Francois J. , Leroux Gilles D.
Published: July 2010

Variability in the response of quackgrass [Elytrigia repens (L.) Nevski] biotypes to N is worth considering if quackgrass is to be used as a forage crop. This study was conducted to determine whether the growth response of quackgrass to different N rates varies among biotypes. The effect of 0, 150, 250 kg N ha−1 on the number of tillers and rhizome buds, total biomass, shoot and rhizome biomass, and shoot to rhizome biomass ratio of three biotypes grown on a St‐Nicolas gravelly loam (loamy, mixed mesic, Typic Dystrochrept) was measured at Ste‐Foy, Québec, Canada, in 1985 and 1986. The response of biotypes to N differed for all variables. At Harvest 1 of 1985 and at Harvests 1 and 2 of 1986, dry matter production of Biotype 3 was at least two times more important at 250 kg N ha−1 than at 0 kg N ha−1. Biotype 1 response to N was comparable to that of Biotype 3 in 1986, but not in 1985. Biotype 2 response to N was inferior to that of the other biotypes and was significant only at the first harvest of 1986. Variations found between years are attributed to differences in rainfall regime. The response of a quackgrass biotype to N is to be considered if it is to be used as a forage crop or in a breeding program.
Agronomic and Economic Response of Spring Wheat Cultivars to Ethephon
Authors: Khan A. , Spilde L.
Published: July 2010

Efforts to optimize grain yields in wheat (Triticum aestivum L.) are often hindered by excessive lodging associated with intensive cereal management systems. The plant growth regulator ethephon [(2‐chloroethyl) phosphonic acid] has been used as an essential component of intensive cereal management systems in Europe to control lodging and maintain high yield potential. The objective of this study was to determine the effect of ethephon on four hard red spring wheat cultivars in North Dakota environments. A randomized complete block design in a split plot arrangement with four replicates was used at each of four locations in 1987 and 1988. Main plot treatments consisted of the cultivars Era, Stoa, Len, and Nordic, and split plots were assigned to ethephon and control (no ethephon). Application of ethephon (280 g a.i. ha−1) increased grain yield 5.4% when averaged across environments and cultivars. Generally, ethephon application tended to increase spikes per square meter but had no effect on kernel weight and kernels per spike. Ethephon treatment reduced lodging in 1987. Lodging was absent in 1988. Application of ethephon had a significant positive effect on test weight, but did not influence grain protein concentration and maturity. Economic parameters, net benefit, and marginal rate of return, indicated ethephon could be recommended for cultivars Era, Len, and Stoa, but not for Nordic under environmental conditions similar to those in this study.
Rubber and Resin Yield Performance of New Guayule Selections
Authors: Estilai A. , Ehdaie B. , Naqvi H. H. , Dierig D. A. , Ray D. T. , Thompson A. E.
Published: July 2010

Guayule (Parthenium argentatum Gray) is a promising alternative to the rubber tree (Hevea brasiliensis Muell. Arg.) for domestic production of natural rubber in semiarid regions. Guayule is not yet a crop and its commercialization will depend on the development of high rubber‐yielding cultivars. The objectives of this study were to determine if individual plant selection has been effective in improving rubber yield; to determine the suitability of California selections for rubber and resin production in Arizona; and to examine the extent of genotype‐by‐environment (G ✕ E) interactions in improved guayule selections. Plant height, width, dry weight, rubber content, resin content, rubber plus resin content, rubber yield, resin yield, and rubber‐plus–resin yield were measured for 24 guayule genotypes planted at Riverside and Palmdale, CA, and Maricopa, AZ, from 1986 to 1989. Genotypes were significantly different for all traits except for plant width and dry weight at Maricopa. The highest rubber yields were 743 kg ha−1 yr−1 at Riverside, 172 at Palmdale, and 564 at Maricopa. Genotype A9 at Riverside and Genotype A22 at Maricopa exceeded the mean rubber yield of two standard varieties by 163 and 66%, respectively, indicating that selection for increased rubber yield within heterogeneous germplasm has been successful. The highest resin yield was 1405 kg ha−1 yr−1 at Riverside, 668 at Palmdale, and 1006 at Maricopa. With rubber plus resin yields of 2085 and 1579 kg ha−1 yr−1, Genotypes A4 and A22 appear acceptable for large‐scale production at Riverside and Maricopa, provided economic markets are found for guayule resin. The G ✕ E interaction effects were significant for all traits. Analyses of data suggested that both quantitative and qualitative differences in performance of genotypes in different locations were responsible for the observed G ✕ E interactions.
Iron Fertilization Effects on Shoot/Root Growth, Water Use, and Drought Stress of Creeping Bentgrass
Authors: Glinski D. S. , Carrow R. N. , Karnok K. J.
Published: July 2010

Creeping bentgrass (Agrostis palustris Huds.) golf greens in the U.S. Southeast are subjected to summer drought and heat stresses. This study was initiated to determine the effects of foliar Fe on FC‐sufficient bentgrass shoot responses, root growth, and respones to drought stress. Ferrous sulfate (FS), Lawn‐Plex (LP), and Sequestrene 330 (Seq. 330) (FeSO4‐7H2O; Fe phosphate‐citrate; and sodium ferric diethlenetriamine‐pentaacetate, respectively) were applied to a golf green at 1.12 kg Fe ha−1 per month for a 17‐mo period. All Fe sources improved color and visual quality throughout the year; summer color improved 5.9% compared to 8.6 to 9.5% for all other seasons. Total extractable tissue Fe was not well correlated with color (r < 0.54). Iron carriers had different effects on growth, especially between late summer and winter. Lawn‐Plex increased cool‐season clipping yields while Seq. 330 reduced verdure in the summer by 18% compared to the control. Root growth (weight and length) was equal to, or less than the control for all Fe treatments. In August, FS‐treated plants exhibited a 31% decrease in root length density (RLD) in the 0 to 10 cm zone. In October, 10‐ to 20‐cm depth RLDs were reduced relative to the control by 31% for FS and 28% LP for treatments. While LP tended to reduce rooting, it was the only Fe carrier to exhibit consistently better (15– 40%) soil moisture extraction than the control. Iron had no apparent effect on canopy temperature as a stress indicator. Since shoot growth, root growth, and water extraction responses often varied with Fe carrier, many reported Fe effects are probably due to the carrier rather than Fe. Exceptions would be the color and visual quality improvements observed for all Fe carriers.
Soil Thermal Regime Influence on Water Use and Yield under Variable Irrigation
Authors: Wraith J.M. , Hanks R.J.
Published: July 2010

Soil temperature has been shown to influence the early growth and development of many plants. It is not clear, however, how these findings are related to seasonal field soil water and crop growth dynamics. We conducted a study to investigate the seasonal influence of the field soil thermal regime on soil water depletion and growth of winter wheat and corn under variable irrigation levels, at Logan, UT, during 1987 and 1988. Soil surface mulches and buried heat cables were used to modify soil temperature, and a line‐source sprinkler system provided a range of water application levels. Soil water depletion increased with soil temperature, and depth of maximum soil water depletion was 0.2 to 0.4 m deeper for warm than cool soil treatments during most of the growing season for both crops. This was true even where early‐season temperature differences were minor or nonexistent. Earlier maturation of plants grown in the warmer soil caused reduced water uptake later in the season, resulting in similar cumulative soil water depletion for all temperature treatments. The depth of plant roots under low irrigation during 1988 increased with soil temperature, but this relationship was not consistent under the higher irrigation level. In 1987, soil temperature did not significantly affect final crop yields. Larger, and earlier, treatment differences in the soil thermal regime in 1988 caused significant plant growth responses to persist throughout the growing season. There were no interactive responses of plant growth and yield parameters to soil temperature and irrigation levels. Seasonal influences of the soil thermal regime on crop water use should be considered in applications where the seasonal status of soil water in the root zone is of fundamental importance.
Feruloyl‐ and Para‐Coumaroyl‐Carbohydrate Esters from Grass and Cellulose Degradation by Ruminal Microorganisms
Authors: Akin D.E. , Hartley R.D. , Borneman W.S.
Published: July 2010

Phenolic compounds are a primary limitation to forage digestibility, but the specific mechanism that limits microbial activity requires elucidation. The objective of this research was to determine the influence of phenolic acid‐carbohydrate esters isolated from ‘Coastal’ bermudagrass (Cynodon dactylon L. Pers.) on cellulolysis by rumen microorganisms. One or 5mM concentrations of 0‐[5‐0‐(trans‐feruloyl)‐α‐L‐arabinofuranosyl]‐ (1→3)]‐0‐β‐D‐xylopyranosyl‐ (1→4)‐D‐xylopyranose (FAXX), 1 mM 0‐[5‐0‐(trans‐p‐coumaroyl)‐α‐L‐arabinofuranosyl]‐(1→3)‐0‐β‐D‐xylopyranosyl‐(1→4)‐D‐xylopyranoses(PAXX), equivalent concentrations of free phenolic acids and equivalent concentrations of L‐arabinose plus D‐xylose were added to anaerobic incubation vials containing MN 300 cellulose. Inhibition of cellulolysis by about 24% in the 5 mM study appeared to be due to the sugars and not the phenolic moiety. These studies suggest that these free phenolic‐carbohydrate esters have minimal effect on fiber‐digesting microorganisms in the rumen.
Soil Nitrogen Status as Affected by Tillage, Crops, and Crop Sequences
Authors: Eck H. V. , Jones O. R.
Published: July 2010

Conservation tillage practices, including no‐till (NT), reduce soil erosion and increase precipitation storage efficiency, but may decrease available soil N. We conducted studies at two sites to determine the comparative effects of NT and stubble mulch (SM) on the N supplying capacity of Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls) cropped to continuous wheat (Triticum aestivum L.) (CW), continuous grain sorghum [Sorghum bicolor (L.) Moench] (CS), wheatsorghum‐fallow (WSF), and wheat‐fallow (WF) sequences. AT one site, accumulation of NO3‐N in the surface 1.2 m (in kg ha−1) was CW NT ‐ 20, CW SM ‐ 37, CS NT ‐ 28; CS SM ‐ 24, WSF NT ‐ 34, WSF SM ‐ 52, WF NT ‐ 57, and WF SM ‐ 60. Tillage significantly affected N accumulation only on the WSF sequence. Nitrate ‐N moved deeper into the profile under NT than under SM, indicating that differences in the root zone may have resulted from differential leaching rather than from differential nitrification. Yields under no‐till and stubble mulch were similar except on continuous grain sorghum where nitrogen deficiency was encountered and stubble mulch outyielded no‐till.
Fertilizer‐Nitrogen Use Efficiency of Irrigated Wheat: I. Uptake Efficiency of Preplant versus Late‐Season Application
Authors: Wuest S. B. , Cassman K. G.
Published: July 2010

The addition of N fertilizer late in the growing season to improve grain quality is a potential management option for production of irrigated hard red spring wheat (Triticum aestivum L.). This study compared the recovery of fertilizer N applied at planting with that of fertilizer N applied at anthesis, and evaluated the effects on soil N uptake. In a 2‐yr field study, N fertilizer rates of 120, 180, or 240 kg N ha−1 at planting and 0, 30, or 60 kg N ha−1 at anthesis were applied to ‘Yecora Rojo’ wheat. The experiment utilized a duplicate plot design such that for every N‐rate treatment there were two plots, one plot received 15N labeled fertilizer at planting, and the other received I5N labeled fertilizer at anthesis. The recovery of N applied at planting ranged from 30 to 55%, while that of N applied at anthesis ranged from 55 to 80%. The contribution of soil N (non‐fertilizer N) to total plant N was not affected by the N rate or timing of application. In another field study 120, 180, or 240 kg N ha−1 was applied at planting and 0 or 45 kg N ha−1 at anthesis the first year, and 85, 140, 195, and 250 kg N ha−1 applied at planting and 0, 25, 45, and 65 kg N ha−1 at anthesis the second year. A small dose (< 1 kg ha−1) of NH4‐15N was iqjected 5 cm below the soil surface to follow the effect of N application at anthesis on uptake of existing inorganic soil N. Fertilizer N at anthesis increased the amount of iqjected 15N taken up by the plants from 38 to 48% the first year, and from 49 to 61% the second year. In both studies, the amount of fertilizer N applied at anthesis had the greatest influence on postanthesis N uptake, which ranged from 17 to 77 kg N ha−1. Without supplemental N applied at anthesis, postanthesis N uptake only provided from 12 to 18% of the total grain N demand, and postanthesis N uptake was not increased by greater preplant N input levels. Likewise, extractable and mineralizable soil N at anthesis were not affected by preplant N treatments. These results indicate that a late N application can be efficiently taken up by plants, and does not decrease soil N uptake. To achieve acceptable grain protein levels for bread wheat in this. imgated cropping system, N should be supplied late in the season to improve N uptake during grain fill.
Closed‐Chamber Effects on Leaf Temperature, Canopy Photosynthesis, and Evapotranspiration
Authors: Wagner S.W. , Reicosky D.C.
Published: July 2010

The portable, closed‐chamber technique permits simultaneous measurement of crop canopy photosynthesis (carbon dioxide exchange rate, CER) and evapotranspiration rate (ET) under field conditions and is a valuable tool for evaluating new management practices to increase water‐use efficiency. Because plants react quickly to environmental changes, and the technique may affect the plant environment during the brief (1 min) measurement period, further exploration of the technique was required. The objective was to measure the effect of a portable closed chamber (8.15‐m3 volume, covering 2.67 m2 of soil surface area) on leaf and air temperatures and to determine any subsequent effects on calculated CO2 and water vapor exchange rates. Measurements of CER and ET were made on field plots of irrigated and non‐irrigated maize (Zea mays L.) shortly after anthesis. Leaf and air temperatures were measured at 2‐s intervals inside and outside the chamber for 1 min prior, 1 min during, and 1 min after chamber closure. Leaf and air temperatures in the closed chamber increased 2 to 4 °C in 1 minute. Changes in canopy CER and ET were not strongly correlated with mean leaf temperatures. The calculated CER and ET rates underestimated the rates extrapolated to time 0 by approximately 10%, partially attributed to the increase in leaf temperature. Therefore, chamber measurements should be made rapidly to minimize possible effects of temperature increases and other plant environment changes. While there are limitations, the chamber technique provides a practical method for measurements of field canopies.