bluuebunny/crossref_metadata_2025 huggingface dataset:
Frost‐Seeding Legumes into Established Switchgrass: Forage Yield and Botanical Composition of the Stratified Canopy
Authors: Gettle Randall M. , George J. Ronald , Blanchet Kevin M. , Buxton Dwayne R. , Moore Kenneth J.
Published: July 2010

Grasses need adequate N for optimum herbage yield. Legumes could be grown in mixed swards with switchgrass (Panicum virgatum L.) to provide symbiotic N and replace the need for N fertilization, extend the growing season because C3 species begin growth earlier and continue growth later into the growing season, and increase dry matter (DM) yield. The objective of this field study on a Webster‐Nicollet soil (fine‐loamy, mixed, mesic, Typic Haplaquoll‐Aquic Hapludoll) at Ames, IA, was to compare herbage DM yield and botanical composition for legume‐renovated switchgrass with that of N‐fertilized switchgrass. Five inoculated forage legumes and a legume mixture were frost‐seeded into an excellent stand of established ‘Cave‐in‐Rock’ switchgrass in mid‐March of 1991 and 1992. Grass‐legume DM yield was compared with N fertilization (0, 60, 120, and 240 kg ha−1) in the seeding year (YR 1) and the second year (YR 2). Harvested samples were separated into grass and legume components, and further divided into upper and basal canopy. Nitrogen fertilization provided greatest upper and basal canopy yields in both June and July of YR 1. By June YR 2, legume renovation increased upper‐canopy yields more than for 240 N. Upper‐canopy YR 2 yields of grass‐legume mixtures seeded in 1991 remained greater than for 240 N in July, and were similar to 120 N in August. During a wetter and cooler than normal summer, YR 2 yields of upper‐canopy grass‐legume mixtures seeded in 1992 were similar to 60 and 120 N by July, and similar to both unfertilized and N‐fertilized switchgrass by August. We concluded that yields of legume‐renovated switchgrass were generally greater than for mid to high levels of N fertilization during YR 2. Because of relatively low herbage production during YR 1, producers should consider frost‐seeding legumes into only part of existing switchgrass pastures, while fertilizing the remaining nonrenovated pasture with N to maintain high forage supply and pasture productivity.
Soybean Seedling Emergence Influenced by Days of Soil Water Stress and Soil Temperature
Authors: Helms Theodore C. , Deckard Edward , Goos Robert J. , Enz John W.
Published: July 2010

Soybean [Glycine max (L.) Merr.] producers often plant into a dry seed bed rather than waiting until soil water conditions are optimum for germination and emergence. In some cases, there is sufficient water for imbibition, but not enough for germination. Producers need to know how long seeds can remain viable under this type of stress. Our objective was to evaluate, under controlled conditions, the influence of soil temperature, soil water content, and duration of stress on soybean emergence and seedling development. Our experiment consisted of a factorial combination of (i) three temperatures regimes (low, 17/8°C day/night; medium, 21/12°C, and high, 25/16°C), (ii) four gravimetric soil water contents (0.07, 0.09, 0.11, and 0.13 kg kg−1), and (iii) three stress durations (0, 6, and 12 d). Soil water content influenced seedling development and emergence, and there was a significant temperature ✕ soil water interaction for both traits. Length of stress also influenced seedling development and emergence. In general, emergence was poor after 12 or more days of soil water conditions that allowed seeds to imbibe water, but were too dry to allow the radicle to emerge from the testa. Under these conditions, seedling emergence decreased as soil temperature increased. Producers can use this information regarding the length of stress interval at a given seed stage as indication of when replanting would be necessary.
Allocation and Cycling of Nitrogen in an Alfalfa‐Bromegrass Sward
Authors: Walley Frances L. , Tomm Gilberto O. , Matus Alejandro , Slinkard Alfred E. , van Kessel Chris
Published: July 2010

The N requirements of grasses grown in legume‐grass mixtures can be met in part via transfer of symbiotically fixed N from the legume to the nonlegume. The objectives of this study were to determine above‐ and belowground biomass production and N accumulation of alfalfa (Medicago sativa L.) and meadow bromegrass (Bromus riparius Rhem.) in a mixed stand and to investigate N cycling between these species. Available soil inorganic N was monitored and biomass production and N accumulation were determined over 3 yr. Symbiotic N2 fixation and N transfer were estimated using 15N‐enriched isotope dilution, natural 15N abundance, and N‐difference methods. Both species depleted available soil N to comparable levels (less than 5 mg kg−1 soil). Following the establishment year, the majority of alfalfa N was allocated to aboveground plant production, whereas N‐stressed meadow bromegrass favored belowground allocation. Estimates of the proportion of N derived from fixation in alfalfa using 15N‐enriched isotope dilution and N‐difference methods ranged from 74 to 89%, and 76 to 93%, respectively, after the establishment year. Use of the natural 15N abundance method resulted in consistently lower estimates of N2 fixation as compared with the 15N‐enriched isotope dilution and N‐difference methods. The average potential annual net N input was 86 kg N ha−1 in the mixed sward and 168 kg N ha−1 in monocropped alfalfa. Maximum net transfer of N from alfalfa to meadow bromegrass, estimated using 15N‐enriched isotope dilution, was 55 kg ha−1. Evidence suggests that N transfer largely occurred indirectly via net N mineralization of belowground plant components.
Effect of Phosphorus Soil Test Level on Sorghum‐Sudangrass Response to Phosphorus Fertilizer
Authors: Bauder James W. , Mahmood Shaukat , Schaff Bernard E. , Sieler David J. , Jacobsen Jeffrey S. , Skogley Earl O.
Published: July 2010

Many agricultural soils of the northern Great Plains have excess CaCO3 or CaSO4 and pH levels above 7.8, thereby having high fixation capacity for applied P and resultant poor predictability of crop responses to applied P fertilizer. In addition, initial and residual effects of applied fertilizer P on soil test P values are not well understood. A greenhouse study was conducted with Sordan 79 (sordan), an intraspecific [Sorghum bicolor (L.) Moench] sorghum‐sudangrass hybrid [syn. S. bicolor‐S. sudanense (Piper) Stapf], on three soils with different textures, cation exchange capacities, and CaCO3 contents to determine sordan response to P fertilizer applied to calcareous soils. Soil test P (bicarbonate‐extractable) was adjusted to five initial levels, ranging from 2 to 60 μg P g−1 soil. Fertilizer P was then applied at five levels, ranging from 0 to 40 mg P kg−1 soil. Three successive harvests of the test crop were completed and measurements of dry matter were made. Response surfaces and regression models were developed, describing the relationships among sordan yield, P uptake by the crop, total P applied as fertilizer, and resultant soil test P values. Sordan response to P fertilizer was linear at soil test values of <30 μg P g−1 soil, but the response was curvilinear above soil test values of 30 μg P g−1 soil. However, soils with lower soil test levels did not yield as much, even at the highest P rates, as those soils testing above 30 μg P g−1 soil and with no additional P added. The preplant soil test P concentrations as well as the residual (postexperiment) bicarbonate‐extractable P soil test concentrations increased with increasing rate of fertilizer P. Results of this study suggest advantages of fertilizer strategies that elevate the bicarbonate‐extractable P soil test values of agricultural soils having excess CaCO3 and pH values above 7.8. Only maintenance applications of fertilizer P appear to be necessary when soil test P concentrations are at or above 30 μg P g−1 of soil and these same soils have relatively high CaCO3 or CaSO4 concentrations.
Strip Intercropping and Nitrogen Effects on Seed, Oil, and Protein Yields of Canola and Soybean
Authors: Ayisi Kingsley K. , Putnam Daniel H. , Vance Carroll P. , Russelle Michael P. , Allan Deborah L.
Published: July 2010

Increased world demand for high‐quality edible oil requires agronomic practices that increase oilseed yields with minimal environmental impact. We hypothesized that strip intercrops of canola (Brassica napus L.) and soybean [Glycine max (L.) Merr.] would increase seed, oil, and protein yields compared with sole crops. Canola (cv. Global) was grown in 4.5‐m wide strips adjacent to 4.5‐m strips of later‐planted soybean (cv. Chippewa) at Rosemount, MN, in 1991 and 1992, and at St Paul, MN, in 1992. Zero or 134 kg N ha−1 was applied at planting in the Rosemount studies, and 134 kg N ha−1 was applied at St. Paul. Seed yield, oil, and crude protein (CP) concentrations were determined for individual rows. Land equivalent ratios (LER) were calculated, using inner rows of the strip to represent sole crop yields. Canola border row yields were 225 to 590% of those of sole crop rows. Without N fertilization, soybean border row yields were similar to sole crop rows, but with added N fertilizer were only 50 to 65% of the sole crop yields. Projected LERs (range: 1.02 to 1.65) were significantly greater than 1.0 for strip widths of 1 to 4 m without N, and 1 to 6 m with fertilizer N. Strip intercrops produced edible oil and CP yields up to 170% of the mean of the two sole crops. Intercropping canola and soybean in strips has the potential to reduce fertilizer applications and enhance oil and protein yields compared with sole crops.
Structure and Reflectance of Irrigated Cotton Leaf Canopies
Authors: Maas Stephan J.
Published: July 2010

Assessing the condition of an agricultural crop through remote sensing and crop modeling requires knowledge of crop characteristics related to plant canopy structure and reflectance. A study was conducted to characterize the structure and reflectance of cotton (Gossypium hirsutum L.) leaf canopies over 3 yr using detailed physical and spectroradiometric measurements. Three canopy characteristics (leaf canopy reflectance, width, and height) were measured in several fields in southern Texas and in one field in Arizona. Canopy reflectance in the near‐infrared was independent of canopy density, while canopy reflectance at red wavelengths was only slightly affected by canopy density. Reflectance appeared to involve primarily the top layer of leaves in the cotton canopy. Canopy width, when normalized by leaf area per plant and plant spacing, could be fit with a single relationship for all locations and years. A single relationship was also found to apply to canopy height. The consistency of these characteristics between locations and years suggests that they might be incorporated into physiology‐based cotton models to allow explicit simulation of canopy reflectance.
Tall Fescue Response to Clipping and Competition with No‐Till Seeded Alfalfa as Affected by Fungal Endophyte
Authors: Hoveland Carl S. , Durham Robert G. , Bouton Joseph H.
Published: July 2010

Tall fescue (Festuca arundinacea Schreb.) is generally less productive, persistent, and competitive under stress after removal of its fungal endophyte, Neotyphodium coenophialum (Morgan‐Jones & W. Gams) Glenn, Bacon & Hanlin (syn. Acremonium coenophialum Morgan‐ Jones & W. Gams). Our objectives were to compare endophyteinfected (E + ) and endophyte‐free (E −) tall fescue for (i) forage yield and tiller response at different cutting frequencies and heights and (ii) competition with no‐till seeded alfalfa (Medicago sativa L.). Factorialized combinations of 3‐wk and hay‐stage harvest intervals with clipping heights of 3.8 cm (low) and 7.6 cm (high) were used with E + and E − tall fescue in a 4‐yr study. ‘Alfagraze’ alfalfa was no‐till seeded into E + and E − ‘Kentucky 31’ tall fescue, E − ‘AU Triumph’ tall fescue, orchardgrass (Dactylis glomerata L.), reed canarygrass (Phalaris arundinacea L.), and Kentucky bluegrass (Poa pratensis L.) in each of 3 yr. Forage yield of E + and E − Kentucky 31 was similar (P > 0.05) within a cutting treatment. When cut at 3‐wk intervals, a low as compared with a high clipping height had no effect (P > 0.05) on total forage yield of E + Kentucky 31 tall fescue, but forage yield of E − Kentucky 31 and E − AU Triumph were reduced by 23 and 28%, respectively, in the fourth year. Both E + and E − tall fescue cut every 3 wk during a dry, hot summer at a low clipping height had autumn forage yields only 20 to 25% of that at a high clipping height. Tiller populations declined more on AU Triumph than E − Kentucky 31 in response to cutting. Cutting height had a minor effect on yield with hay‐stage harvest. Endophyte infection had no effect on stands or forage yield of no‐till seeded alfalfa. Alfalfa forage yields were lower with tall fescue than with the other grass species. AU Triumph, a winter‐productive tall fescue, was the grass most competitive with alfalfa.
Maize Shoot and Root Response to Root Zone Saturation during Vegetative Growth
Authors: Lizaso Jon I. , Ritchie Joe T.
Published: July 2010

Excess water adversely affects 12% of the world's soils. In rainfed cropping areas, heavy rainfalls may produce transient soil saturation. Better understanding of plant growth under transient soil water saturation or high water tables is needed for effective simulation models. In particular, improved functions are needed to estimate maize (Zea mays L.) response to root zone saturation of various durations and at different stages of plant growth. This 2‐yr study was conducted in Michigan in a field facility where the water table could be independently managed on several 2.1‐ by 1.5‐m2 plots. Saturated conditions were imposed for 4 or 8 d in early (leaf tip 5–6) or late (leaf tip 10–12) vegetative growth. Shoot growth measurements included leaf extension, biomass, leaf area, leaf senescence, stomatal conductance, and photosynthesis. Roots were observed and counted at several soil depths, using minirhizotron tubes. Root zone saturation had a major impact on almost all aspects of plant growth and yield. Measured yield for the control was 153 g plant−1 in 1991. Plants exposed to root zone saturation yielded about half of the control yield, primarily because of a reduction in kernel number per ear. Biomass growth was reduced through reduced leaf area expansion, increased leaf senescence, and reduced photosynthesis. Root numbers at the 15‐ and 40‐cm depths decreased soon after soil saturation, but root growth increased rapidly about 10 d after the saturated treatments ended and final root numbers were about the same as the control by season's end. Loss of leaf area growth was never recovered, and green leaf area reduction due to senescence further decreased plant growth. Responses to early and late saturation were about the same. Doubling the saturation period reduced final biomass by only an additional 10%, showing the adaptive responses of maize for survival of saturation. Nonetheless, crop yields may be dramatically reduced.
Model Analysis of Sorghum Response to Nitrogen in Subtropical and Tropical Environments
Authors: Sinclair Thomas R. , Muchow Russell C. , Monteith John L.
Published: July 2010

Nitrogen fertilization is important in achieving high sorghum [Sorghum bicolor (L.) Moench yields. Under semiarid conditions, however, the response to N is confounded by seasonal differences in water availability. A simple, mechanistic model was developed to interpret measurements of the growth and yield of sorghum at different levels of N and water supply. The structure of the sorghum‐N model was equivalent to a previously developed maize‐N (Zea mays L.) model, including the N uptake function, which depends on thermal units. The sorghum‐N model was developed considering experimental results obtained in the tropical climate of Katherine, Australia. After adjusting coefficients to describe leaf and grain development for sorghum instead of maize, the model simulated crop N uptake, growth, and grain yield. Without any further changes in the model, sorghum grown in the subtropical climate of Lawes, Australia, with grain yields ranging from 121 to 886 g m−2, was well simulated by the model. A third set of data obtained in an irrigation‐N application experiment at Hyderabad, India, was compared against model results. After adjusting the coefficients that describe the development of the cultivar and the soil organic content at this location, the model produced results comparable to experimental results. Analysis of the model results led to two interesting hypotheses concerning the experiment at Hyderabad: (i) the irrigation level of the well‐watered treatment appeared to be inadequate to avoid drought stress at the end of the cropping season, and (ii) there was seemingly about 4 g N m−2 of soil N unavailable to the crop in each of the irrigation treatments. Overall, the sorghum‐N model proved useful in interpreting and analyzing field measurements of development, growth, and yield of sorghum grown under diverse conditions.
Chicory Productivity, Forage Quality, and Response to Nitrogen Fertilization
Authors: Collins Michael , McCoy Joe E.
Published: July 2010

Chicory (Cichorium intybus L.) shows potential for use in grazing systems. Information is needed regarding the productivity and quality of chicory forage in midlatitude states of the USA. Forage yield and quality of chicory under several levels of N fertilization were determined in a Kentucky field experiment. Plots were established during late spring on a silt loam soil (fine‐silty, mixed, mesic Typic Paleudult) and received 0, 50, 100, 150, or 200 kg ha−1 of fertilizer N annually in two equal portions. Treatments were arranged in a randomized complete block design with four replicates. Herbage was harvested four times each year at 5‐wk intervals. With N fertilization, chicory produced maximum dry matter yields of 7.8 and 5.6 Mg ha−1 in 1992 and 1993, respectively. Increasing N level produced linear increases in first‐harvest yields and linear or quadratic increases at the third harvest, during midsummer, but N effects persisted only during the first growth period after application. Chicory forage was high in moisture: ≥850 g kg−1 in first‐harvest forage, which often increased with increasing N level. Chicory remained almost completely vegetative, and forage quality was consistently high. Nitrogen concentration averaged 22.9 and 22.3 g kg−1 in 1992 and 1993, respectively, and was affected by N fertilization primarily at the first harvest. Chicory forage exceeded 640 g kg−1 in vitro dry matter disappearance and remained below 400 in neutral‐detergent fiber concentration throughout the study. Chicory established rapidly and persisted well. Nitrogen‐fertilized chicory produced high midseason yields of highquality forage, suggesting that this species could supplement cool‐season grasses. The high rate and extent of N recovery found for chicory warrants further research to determine optimum N fertilization regimes.
Energy Balance Simulation for Surface Soil and Residue Temperatures with Incomplete Cover
Authors: Aiken Robert M. , Flerchinger Gerald N. , Farahani Hamid J. , Johnsen Karen E.
Published: July 2010

Knowledge of the effects that crop residue architecture has on exchange processes at the soil surface can extend the applicability of soil and water balance modules. Our objectives were to evaluate the feasibility of using a numerically reduced soil‐residue energy boundary condition module, compatible with the USDA‐ARS Root Zone Water Quality Model, and to compare the accuracy of calculated values against measurements. We developed a Penman‐type energy balance module, PENFLUX, which solves for surface temperatures of a soil slab and a single flat residue layer, adjusting for aerodynamic resistances of standing residue stems. It provides surface boundary conditions for simulations of energy transfer in a one‐dimensional soil profile. PENFLUX simplifies iterative solutions by simplifying radiation, convection, and soil heat algorithms. We collected hourly radiation data; air, soil, and residue temperatures; and wind profile data after wheat harvest on a level Nunn clay loam soil (fine, smectitic, mesic Aridic Argiustoll) (1997 soil series reclassification). Model parameterization avoided fitting model calculations to measurements, as inputs were measured at the site or referenced from literature. PENFLUX calculations exhibited a low degree of random error for dry soil and residue conditions, though systematic bias in surface soil temperature and negative bias in nighttime net irradiance reduced predictive efficiency. Error propagated from surface soil temperature probably contributes to the negative bias in net radiation. The reasonable predictive accuracy of PENFLUX for dry soil conditions demonstrates the feasibility of a numerically simplified model of soil‐residue energy exchanges, and justifies further evaluation against a range of residue architectures and environmental conditions.
Planting Dates for Early‐Maturing Soybean Cultivars
Authors: Steele Colleen C. , Grabau Larry J.
Published: July 2010

Early planting dates may not be required for successful culture of early‐maturing soybean [Glycine max (L.) Merr.] at midlatitudes in the USA. The objectives of this research were to evaluate early‐maturing soybean cultivars in southern environments, to try to identify cultivar characteristics contributing to the fit of these cultivars into this cropping system, and to determine the range of planting dates that best discriminate among northern cultivars. Field trials, involving 12 Maturity Group (MG) II cultivars, were planted in late April to mid‐May, late May to early June, mid‐June, and mid‐July on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) near Lexington, KY, in 1993 and 1994. Yield response to planting date was consistent across years, showing best yields for mid‐June plantings. Pioneer 9273 produced significantly more grain than all other cultivars. Across years and planting dates, the lowest yielding cultivar (IA 2008) produced 19% less than did Pioneer 9273, emphasizing the importance of cultivar selection. Canopy closure ratings at reproductive growth stages R2 or R5 were somewhat better related to yield than were plant mass (at R2 or R5) or plant height. The shortest cultivars had the greatest stubble losses; producers may want to avoid such cultivars. Identification of high‐yielding cultivars was clearest for the first two planting dates. Perhaps cultivars that performed well under cool, moist soil conditions were favored by the earlier planting dates. Selection of early‐maturing cultivars for production south of their traditional full‐season areas appears to be best done from early planting dates in the southerly zone.
Evaluation of a Crop Simulation Model that Incorporates Gene Action
Authors: Hoogenboom Gerrit , White Jeffrey W. , Acosta‐Gallegos Jorge , Gaudiel Refe G. , Myers James R. , Silbernagel Matt J.
Published: July 2010

Crop simulation models are receiving increasing use in agricultural research. However, applications to plant breeding have been limited, in part due to the restricted capabilities of models to represent genetic differences. A gene‐based simulation model, GeneGro, has been developed that integrates action of seven genes into a common bean (Phaseolus vulgaris L.) model. The genes for physiological traits identified in the model include Ppd, Hr, Fin, Fd, Ssz‐1, Ssz‐2, and Ssz‐3. Evaluation of GeneGro was performed by comparison of measured field data vs. simulated data, and through a sensitivity analysis of the model. The experimental data set for model comparison was comprised of 14 field trials conducted in Canada, the USA, Mexico, and Colombia, representing 213 treatment combinations and including 39 cultivars. GeneGro explained 75% of variation in days to flower, 68% in days to maturity, and 39% in seed mass, but only 11% of variation in seed yield. Most of the variation in simulated seed yield was accounted for by the model when mean effects of site and cultivars were removed through regression analysis. This suggests that the poor simulation of seed yield was partially due to errors in simulating differences among sites rather than from simulating the response of genotypes to sites. Seed yield simulations were made for 96 genotypes that represented all expected phenotypic combinations of the seven genes included in the model. Simulations were conducted using historical weather data from Fargo, ND; Madero, Mexico; and Palmira, Colombia. GeneGro predicted that photoperiod sensitivity, conferred by Ppd and Hr, would result in zero seed yields at Fargo, a slight seed yield increase at Madero, and no effect at Palmira. Testing effects of maturity on seed yield, the genotypes fin and Fd resulted in lower seed yields due to shorter growth cycles, in agreement with field trials. The predicted effects of the three genes related to seed size varied among the sites. These results support the use of genetic information to represent cultivar differences in simulation models. They also emphasize the need for a better understanding of the physiological genetics of traits such as phenology, seed size, and growth habit.
Species for Low‐Input Sustainable Turf in the U.S. Upper Midwest
Authors: Diesburg Kenneth L. , Christians Nick E. , Moore Richard , Branham Bruce , Danneberger T. Karl , Reicher Zachary J. , Voigt Thomas , Minner David D. , Newman Robert
Published: July 2010

Low‐input sustainable turf (LIST) management represents a resource‐efficient option in maintaining uniform, persistent turf. What species are best suited to such management needs to be established. To this end, 12 hardy species were evaluated for 3 yr in Illinois, Indiana, Iowa, Michigan, Missouri, Ohio, and Wisconsin: crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. ‘Fairway’, ‘Ephraim’, and ‘Ruff’], streambank wheatgrass [Agropyron riparium Scribn. & Smith ‘Sodar’; syn. Elymus lanceolatus (Scribn. & J.G. Smith) Gould subsp. lanceolatus], Canada bluegrass (Poa compressa L. ‘Reubens’), hard fescue [Festuca ovina var. duriuscula (L.) Koch ‘Durar’; syn. F. lemanii T. Bastard], sheep fescue (F. ovina L. ‘Covar’ and common), tall fescue (F. arundinacea Schreb. ‘Alta’), bulbous bluegrass (P. bulbosa L.), alpine bluegrass (P. alpina L.), redtop (Agrostis alba L. ‘Reton’; Agrostis gigantea Roth), roughstalk bluegrass (P. trivialis L. ‘Colt’), colonial bentgrass (Agrostis tenuis Sibth. ‘Exeter’; syn. Agrostis capillaris L.), and buffalograss [Buchlöe dactyhides (Nutt.) Engelm. ‘Texoka’ and ‘NE‐315’]. AH were field‐established and compared at three mowing heights: 3.8 cm, 7.6 cm, and no mowing. Quality ratings were based on uniform persistence. Tall fescue and common sheep fescue were the best and most broadly adapted to LIST. In Iowa, hard fescue, Canada bluegrass, and crested wheatgrass also did well. Colonial bentgrass was best adapted in Missouri. Redtop and roughstalk bluegrass grew better in a north‐south area from Wisconsin through central Illinois to Missouri. The buffalograsses excelled in Ohio and southern Illinois. Over all species, the 7.6‐cm mowing height allowed the best turf quality. Specifically, tall fescue, colonial bentgrass, redtop, and common sheep fescue performed best at the 7.6‐cm mowing height. Covar sheep fescue, hard fescue, Canada bluegrass, and Fairway crested wheatgrass could not maintain persistent stands under the 3.8‐cm mowing height. No mowing resulted in intermediate levels of quality with all species. A 7.6‐cm mowing height would be appropriate for testing species in LIST within the seven‐state region used in this study.
Root Zone Temperature and Calcium Effects on Phosphorus, Sulfur, and Micronutrients in Winter Wheat Forage
Authors: Miyasaka Susan C. , Grunes David L.
Published: July 2010

An understanding of how environmental factors can alter accumulation of nutrients by plants is needed to anticipate and prevent mineral deficiencies in both plants and grazing animals. To determine the effects of root zone temperature (RZT) and Ca level on mineral concentrations of winter wheat (Triticum aestivum L.), ‘Centurk’ seedlings were grown under three RZT regimes (constant 8°C, constant 16°C, and transferral from 8°C after 23 d to 16°C) and four Ca levels (0.2, 0.6, 2.0, and 5.0 mM) in nutrient solution. Plants grown at 8°C RZT had significantly lower shoot and root concentrations and unit absorption rates of P, S, Cu, Zn, and Mn than did those grown at 16°C. Within 2 wk after transfer from 8°C to 16°C RZT, concentrations of P, S, Cu, Zn, and Mn in shoots and roots increased significantly. Increasing Ca levels in solution significantly increased shoot and root concentrations and unit absorption rates of P and Cu. In contrast, increasing Ca levels significantly decreased concentrations and unit absorption rates of Mn and Zn. Thus, a suboptimal RZT could depress accumulation of P, S, Cu, Zn, and Mn by winter wheat forage, and possibly induce mineral deficiencies in both plants and grazing animals. A high solution Ca level could partially ameliorate this adverse effect on P and Cu accumulation by wheat, but it also could exacerbate the problem of low Mn and Zn concentrations at a cool RZT.
Green Fallow for the Central Great Plains
Authors: Schlegel Alan J. , Havlin John L.
Published: July 2010

Use of fallow to store soil water is a common practice in semiarid regions. In the central Great Plains, the most common dryland cropping system is winter wheat (Triticum aestivum L.)‐fallow. Stubble mulching involving tillage is the predominant weed‐control practice during the 14‐mo fallow period. As a result of tillage, soil organic matter content has declined 40 to 70% since the early 1900s. This decline has called for development of cropping practices that control soil erosion and increase soil organic matter. Green fallow is the practice of growing a legume during the time period not devoted to crop production. Water is a major limiting factor for crop production in the central Plains, and water use by the legume could reduce grain yields. Field studies were conducted near Tribune, KS, from 1990 to 1994 to evaluate green fallow in the central Great Plains. The objectives were to (i) evaluate the production potential of several dryland forage legumes, (ii) quantify the water use of dryland legumes as a function of growth period, and (iii) measure the effects of legume growth on grain yield of subsequent crops. Of 11 legume species evaluated, hairy vetch (Vicia villosa Roth) and yellow sweetclover (Melilotus officinalis Lam.) were the most promising in terms of biomass production and weed control. Hairy vetch was planted in a green fallow system and allowed to grow for selected periods of time. In all cases, green fallow depleted soil water and reduced grain yield of subsequent crops. Allowing hairy vetch growth throughout the fallow period reduced soil water by up to 178 mm and reduced grain yield by 42 to 83%. For every millimeter of soil water depletion by vetch, grain yields decreased by 15 kg ha−1. Although green fallow is too detrimental to subsequent crop yields to be recommended in the central Great Plains, dryland legumes may have potential as forage crops.
Fractal Analysis of Temporal Yield Variability of Crop Sequences: Implications for Site‐Specific Management
Authors: Eghball Bahman , Varvel Gary E.
Published: July 2010

Characterizing spatial and temporal variability is important in site‐specific or long‐term studies to evaluate the effects of different management systems on crop performance. Long‐term experiments offer unique possibilities to study the effects of management practices on crops and soils over time. The objective of this study was to characterize temporal grain yield variability of seven crop sequences using fractal analysis and to determine whether temporal or spatial variability dominated the grain yield variability. Three crops of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and sorghum [Sorghum bicolor (L.) Moench] were studied from 1975 to 1995 in various sequences. Semivariograms were estimated for the standardized crop yield. The slopes of the regression lines of log semivariogram vs. log lag (year) were used to estimate and compare fractal dimensions, which are indications of variability patterns. The intercepts of the log‐log lines, which indicate extent of yield variability, were also compared between crop sequences. A small D‐value indicates dominance of long‐term variation, while a large D‐value (near 2) indicates dominance of short‐term (year‐to‐year) variation. Corn had significantly less temporal yield variability than soybean or sorghum. Continuous corn had less yield variability than corn following soybean. Soybean had the greatest yield variability, regardless of crop sequence. Temporal variability was much more dominant than spatial variability in this study. Temporal variability may greatly influence how spatial variability is expressed in a given field. Yield maps, which are used as an indication of past management in site‐specific cases, may not be useful in making future management decisions when temporal variability is great. In a less productive year, spatial variability of any nutrient may not make much difference in crop yield of a given field.
Zinc and Cadmium Effects on the Early Stages of Nodulation in White Clover
Authors: El‐Kenawy Z. A. , Angle J. Scott , Gewaily E. M. , El‐Wafai N. A. , van Berkum P. , Chaney Rufus L. , Ibekwe M. A.
Published: July 2010

Addition of heavy metals to soils from sources such as biosolid application, smelter emissions, fertilizers, and the like may produce soil solution concentrations of Zn and Cd that can potentially restrict nodulation of legume crops such as white clover. To assess the effects of Zn and Cd on the early stages of nodulation of white clover, a solution culture study was conducted. Rhizobia [Rhizobium leguminosarum bv. trifolii] of a metal‐sensitive strain (USDA 2063) and a metal‐tolerant strain (USDA 2046) were inoculated into nutrient solution with white clover seedlings containing EGTA to buffer Zn2+ and Cd2+ activities. The calculated activities of Zn2+ were p = 8.00, 5.70, 5.25, and 5.00; the calculated activities of Cd2+ were p = 10.50, 9.50, 8.75, and 8.50. Phase‐contrast microscopy was used after staining roots with methylene blue to observe root hair infection at intervals of 1, 12, 24, 72, and 168 h. Few differences were observed between the sensitive and tolerant rhizobial strains. At the lowest Zn concentration, initial attachment of bacteria to root hairs was observed within 1 h. At the highest Zn concentration, attachment was not observed until 12 h. Also, at the highest Zn concentration, a delay was observed for up to 60 h and 4 d, respectively, for the first signs of root hair curling and infection thread formation. Shoot weight decreased with increasing Zn concentration. Few Cd‐induced effects on early stages of nodule development were observed. Cadmium was more toxic to plant growth than Zn. These results show that in addition to direct effects on the macro and microsymbiont, the process of nodulation is susceptible to the toxic effects of heavy metals.
Integrated Weed Management Using Narrow Corn Row Spacing, Herbicides, and Cultivation
Authors: Johnson Gregg A. , Hoverstad Thomas R. , Greenwald Rene E.
Published: July 2010

Potential increases in corn (Zea mays L.) grain yield have led many producers to consider using narrow corn rows. Narrow row spacing is also thought to play a role in reducing weed interference through enhanced light interception by the crop. However, there is little information on how narrow row spacing and cultivation fit into an integrated weed and crop management strategy. The objective of this research was to investigate the potential for reduced herbicide amount (either through below‐label rate and/or banded applications) using narrow corn crop row spacing and timely cultivation. Field studies were conducted in 1995 and 1996 at the University of Minnesota Southern Experiment Station in Waseca. Corn was planted in 51‐ and 76‐cm row spacings. Within each row‐spacing treatment, plots were either cultivated or not cultivated. Eight herbicide treatments were applied to each row space and cultivation plot. Corn row spacing had little impact on giant foxtail (Setaria faberi Herrm.) and common ragweed (Ambrosia artemisiifolia L.) visual control, density, biomass, or height. Cultivation was the single most important variable in reducing the amount of herbicide used. Grain yield was not increased by planting corn in narrow rows. Increased grain yield and weed control reported in previous research studies using narrow row spacing may be due to the choice of hybrid, plant population, and weed spectrum present.
Tiller Demographics and Leaf Area Index of Four Perennial Pasture Grasses
Authors: Mitchell Robert B. , Moser Lowell E. , Moore Kenneth J. , Redfearn Daren D.
Published: July 2010

Developing grazing systems requires basic information on the growth and development of adapted species. The objective of this field study was to determine seasonal tiller demographics and leaf area index (LAI) of intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey], smooth bromegrass (Bromus inermis Leyss.), switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman) tiller populations. This study was conducted in 1992 and 1993 near Mead, NE, on a silty clay loam soil (Typic Argiudoll) as a randomized complete block. Monocultures were harvested six times each year for tiller demographics. Additionally, mean stage count (MSC), a quantified estimate of tiller population maturity, was determined at each harvest. The LAI was indirectly measured using a canopy analyzer at 7‐ to 14‐d intervals. Tiller density for all species generally declined as MSC increased. Tiller demographics were highly variable by year for intermediate wheatgrass and smooth bromegrass, which indicates that grazing management should be based on current tiller populations. Density of vegetative tillers declined most rapidly for smooth bromegrass, followed by intermediate wheatgrass, switchgrass, and big bluestem. Switchgrass and big bluestem tiller demographics were more uniform and predictable across years than intermediate wheatgrass and smooth bromegrass. The LAI for all species increased as MSC increased. Maximum LAI for intermediate wheatgrass, smooth bromegrass, switchgrass, and big bluestem in 1992 was 4.7, 5.1, 4.9, and 5.8, respectively. Integrating tiller demographics and LAI suggests that initial grazing readiness starts with smooth bromegrass in early spring, followed by intermediate wheatgrass in about 2 wk, switchgrass in late spring, and big bluestem in early summer.
Dry Matter Accumulation and Dinitrogen Fixation of Annual Medicago Species
Authors: Zhu Yanping , Sheaffer Craig C. , Russelle Michael P. , Vance Carroll P.
Published: July 2010

Assessment of the N2 fixation potential of annual medics (Medicago spp.) in the upper Midwest is important for predicting the net N contribution to cropping systems. Our objectives were to determine the dry matter (DM) accumulation pattern of herbage, roots, and nodules of several annual medic species used as summer annuals and to measure the percentage and amount of N derived from N2 fixation by annual medics using isotope dilution and difference methods. Experiments were conducted on a Hubbard loamy sand (Udorthentic Haploboroll) at Becker, MN, and a Tallula silt loam (Typic Hapludoll) at Rosemount, MN. The experimental design at both locations was a randomized complete block with six replicates. Medicago truncatula Gaertn., M. polymorpha L., M. scutellata (L.) Mill., and M. rugosa Desr. were inoculated with commercial rhizobial inoculant and were seeded in late May. Herbage, root, and nodule DM of N2‐fixing annual medics continued to increase until about 72 d after planting (DAP). The highest maximum herbage, root, and nodule DM yields were 10 669, 648, and 169 kg ha−1, respectively, from M. polymorpha in 1993. Based on the estimate from the isotope dilution (ID) method, herbage of annual medics at maximum DM accumulation contained 86% N derived from atmosphere (%Ndfa), using ryegrass (Lolium multiflorum Lam.) as a reference crop, or 79% Ndfa, using noninoculated M. rugosa as a reference crop. The amount of Ndfa in annual medic herbage ranged from 100 to 200 kg ha2212;1 based on estimates using either the ID method or the difference method (D‐method), with M. polymorpha producing the highest and M. rugosa producing the lowest amount. Estimates of Ndfa from the ID and D‐methods were strongly correlated. We conclude that annual medics have the potential to contribute a significant amount of N to cropping systems when seeded in the spring and harvested or incorporated into the soil 2 to 3 mo. later.
Soil Carbon Pools under Conventional and No‐Tillage Systems in the Argentine Rolling Pampa
Authors: Alvarez Roberto , Russo Miguel E. , Prystupa Pablo , Scheiner Javier D. , Blotta Luis
Published: July 2010

The Rolling Pampa is the most important cropping region of Argentina, and its soils are subjected to degradation. No‐tillage has been proposed to replace the use of the moldboard plow to reduce soil C losses. The effects of no‐tillage and plow tillage with and without N fertilization (0 or 90 kg N ha−1) on C inputs and outputs of a Typic Argiudoll and on organic C level and density fractions were studied in a field experiment at the end of 15 yr under a corn (Zea mays L.)‐wheat (Triticum aestivum L.)‐soybean [Glycine max (L.) Merr.] rotation. Microbial biomass and the rate of organic C mineralization during laboratory incubations were also determined. Nitrogen fertilization had no significant influence on C emission in the field, soil organic matter level or microbial biomass and activity. The annual C budget was negative under both tillage systems, but no‐tillage lost about 0.7 to 1.5 Mg ha−1 yr−1 more C than did plow tillage. Carbon in the medium‐density fraction (density = 1.6‐2.0 g mL−1) of the 0‐ to 20‐cm soil layer was 30% higher (P ≤ 0.05) under no‐tillage. Light (density < 1.6 g mL−1) and heavy (density > 2.0 g mL−1) organic fractions, total C, and microbial biomass and activity in the 0‐ to 20‐ cm layer were not different in no‐tilled and plowed soils, despite different patterns of distribution with depth. The rates of organic C mineralization during laboratory incubations were the same for both tillage systems. We propose that, after an accumulation phase, soil under no‐tillage loses higher amounts of CO2‐C than under plowing. The use of no‐tillage would not significantly affect soil organic matter pools of the region in situations with low erosion losses.
Optimum Transplanting Dates for Rice in Kerala, India, Determined Using Both CERES v3.0 and ClimProb
Authors: Saseendran Saseendran A. , Hubbard Kenneth G. , Singh Kamalesh K. , Mendiratta Nisha , Rathore Laxman S. , Singh Shyam V.
Published: July 2010

Rice (Oryza sativa L.) is an important food crop for more than half the world's population. It grows best under shallow flooded conditions. For establishing a healthy rice stand in a flooded field, the seedlings of the crop are first grown in nurseries and then transplanted into the field. At a specific location, transplanting dates determine how growing conditions later in the season will affect the rice crop. Dry conditions after ripening, favorable to maintaining the quality of rice through harvest, may be more or less likely to occur, depending on the transplanting date selected. The objective of this study was to determine optimum transplanting dates for rice at five locations in Kerala, a monsoon‐affected state in southern India. Optimal transplanting dates were derived based on two approaches: (i) probabilities of rainfall events using ClimProb, a PC‐based software package, and (ii) target yields simulated by the CERES‐Rice v3.0 crop growth simulation model. Under rainfed conditions, the optimum transplanting dates were from the 23rd to 26th week for multiple cropping in a year, and from the 26th to 32nd week for a rainfed monocrop. The ClimProb approach used here can be adopted for use elsewhere if climate data are available, and the model approach can also be adopted if specific weather, soils, and crop information is available.
Spatial Scale Requirements for Precision Farming: A Case Study in the Southeastern USA
Authors: Sadler E. John , Busscher Warren J. , Bauer Philip J. , Karlen Douglas L.
Published: July 2010

Precision farming has created a critical need for spatial data on crop yield and related soil characteristics. However, because data are not without cost, users need practical guidelines for spatial resolution on which to collect soil and plant data. Our objectives were (i) to describe variation observed in crop response in the southeastern Coastal Plain of the USA, (ii) to compare it with variation in other regions, and (iii) to offer suggestions for precision farming practices in the southeastern Coastal Plain. From 1985 to 1995, corn (Zea mays L.), wheat (Triticum aestivum L.), soybean [Glycine max (L.) Merr.], and grain sorghum [Sorghum bicolor (L.) Moench] yields were mapped at from 10‐ to 20‐m resolution in an 8‐ha field at Florence, SC. Also available were topography (30‐m resolution), depth to clay (15 m), and in 1993, plant height on one date (9 m), canopy temperature on four dates (1.5 m), and detailed crop and soil information at selected sites. Yield of all crops in all years was significantly (P < 0.0007), though not strongly (median r2 = 0.3), correlated with soil map unit. In 1993, infrared thermometer canopy temperature minus air temperature (∆Tc) was correlated with soil map unit, even on the second day after a 46‐mm rain. Spherical semivariograms fitted to yields had ranges from 57 to 252 m (median = 79 m) and nugget/sill ratios from 0.00 to 0.56 (median = 0.32). Semivariograms for canopy temperature and plant height had ranges from 43 to 77 m. If the spatial structure for common soil characteristics matches the spatial structure for crop response, Coastal Plain soils may require study at finer resolution than the >100‐m grid that is commonly used in precision farming.
Annual Medics and Berseem Clover as Emergency Forages
Authors: Shrestha Anil , Hesterman Oran B. , Squire John M. , Fisk John W. , Sheaffer Craig C.
Published: July 2010

Severe winter‐kill of alfalfa (Medicago sativa L.) in some years prompts the need for emergency forages in northern locations. Three annual medic species—barrel medic (M. truncatula Gaertn. cv. Mogul), burr medic (M. polymorpha L. cv. Santiago), and snail medic [M. scutellata (L.) Mill. cv. Sava]—and berseem clover (Trifolium alexandrinum L. cv. Bigbee) and ‘Nitro’ alfalfa were seeded in early spring at East Lansing and the Kellogg Biological Station (KBS) in Michigan in 1994 and 1995. Forage mass was measured at first harvest 60 d after planting and at second harvest 30 d later. Forage mass of annual medics at first harvest ranged from 0.8 to 3.6 Mg ha−1 across locations and years. Berseem clover produced an average forage mass of 2.2 Mg ha−1 at first harvest, which was similar to alfalfa. Crude protein (CP) concentration of annual medics, berseem, and alfalfa ranged from 111 to 210,178 to 233, and 170 to 218 g kg−1, respectively, at first harvest. Regrowth of annual medics (except Mogul) was less than alfalfa or berseem clover; however, the regrowth of Mogul was decumbent and not suitable as hay. Average forage mass and CP concentration of berseem at second harvest was 1.8 Mg ha−1 and 191 g kg−1, respectively, which was similar to alfalfa. Our results indicate that both annual medics and berseem clover can be used as emergency forages in northern locations; however, annual medics have the potential for only one harvest, whereas berseem can be harvested twice during the growing season.