bluuebunny/crossref_metadata_2025 huggingface dataset:
Rescue of Soybean Flowers Destined to Abscise
Authors: Weibold William J.
Published: July 2010

Many soybean [Glycine max (L.) Merr.] flowers abscise and do not contribute to yield. The objectives of this research were to determine the effectiveness of a proximal pod removal treatment designed to rescue soybean flowers destined to abscise and to determine if the effectiveness of this treatment changes with time after anthesis. ‘Williams 82’ soybean was grown in the field during 1985 and 1986. Racemes were tagged at anthesis of the flower at Position 1 (positions numbered along rachis from proximal to distal ends). Proximal pods (Positions 1 and 2) were removed from one half of the tagged racemes at varying times after anthesis. In 1985, this action resulted in nine treatments (4,6,7,8, 11, 12, 13, 15, and 16 d between anthesis and proximal pod removal). In 1986, five treatments of 3, 5, 7, 9, and 11 d were used. Abscission percentages for the untreated racemes, averaged over the 2 yr, were 5, 12, 30, and 59% for Positions 1, 2, 3, and 4, respectively. Average abscission percentages (all day intervals and both years) for Position 3 were 30% with proximal pods present and 7% with proximal pods removed. For Position 4, average abscission percentages were 59% with proximal pods present and 9% with proximal pods removed. Average seed weights pod−1 (all day intervals and both years) for Position 3 were 0.377 g with proximal pods present and 0.527 g with proximal pods removed. For Position 4, the average seed weights pod−1 were 0.540 g with proximal pods present and 0.610 g with proximal pods removed. In 1986, proximal pod removal increased number of seeds pod−1. Effectiveness of the proximal pod removal treatment in reducing abscission probability and increasing total seed weight pod−1 was not related to length of time between anthesis and proximal pod removal. The fate of pods destined to abscise can be reversed up to at least 11 d after anthesis.
Movement of Rhizobia between Alfalfa Plants
Authors: Chamblee D. S. , Warren R. D.
Published: July 2010

Evidence on the rapidity of movement of rhizobia in the soil is inconclusive. Successful inoculation of most of the legume plants in a field would result in subsequent inoculation of the remaining plants if substantial movement of legume bacteria occurred. The objective of this study was to determine the distance rhizobia move in the soil between inoculated and noninoculated alfalfa (Medicago sativa L.) plants during the seeding year. Three field experiments were conducted in North Carolina. Experiments 1 and 2 were established on a Norfolk sandy loam (fine‐loamy, siliceous thermic Typic Paleudult) and Exp. 3 on an Appling sandy loam (kaolinitic thermic Typic Hapludult). Alternating rows of inoculated and noninoculated alfalfa (subplots) were seeded at spacings of 15,30 and 60 cm (whole plots) in four replications. Periodic measurements of nodulation, color, height of top growth and N concentration of top growth and roots were made. Results indicated that the lateral movement of rhizobia in an 11‐month period was largely limited to a distance of 15 cm. There was evidence that substantial N was obtained by noninoculated alfalfa rows from adjacent inoculated (15‐cm spacing) rows by sloughing and/or excretion.
Management of Long‐Term Field Experiments
Authors: Frye W. W. , Thomas G. W.
Published: July 2010

Long‐term field experiments play an essential role in understanding the complex interactions of plants, soils, pests, climate and management, and their effects on sustainable crop production. This paper outlines the management problems associated with long‐term field studies and highlights design characteristics and management techniques to ameliorate these problems. Management of new long‐term studies includes selecting a suitable site, designing the experiment to facilitate statistical analyses and future expansion, collecting data commensurate with the objectives of the experiment, and incorporating nondestructive changes in the experiment as technology and objectives change. All of the old long‐term experiments that we studied have experienced various changes during their existence. Technological advances in areas such as plant populations, varieties, and fertilizer sources must be incorporated into long‐term experiments to maintain interest and generate useful data. Incidental changes, such as soil erosion, soil and fertility creep between plots, development of soil acidity, build‐up of weeds, and weather effects, are an inevitable feature of long‐term experiments. These are often management problems that must be reckoned with, but they usually do not violate the long‐term integrity or invalidate the results of the experiment. Primary treatments, e.g., tillage method and cropping system, cannot be changed without jeopardizing the long‐term status of the experiment. If properly managed, long‐term experiments generate unique, interesting, and valuable information that provides not only a link to the past but also insights into agronomic practices for sustainable future crop production.
Vernalization and Phyllochron in Winter Wheat
Authors: Cao Weixing , Moss Dale N.
Published: July 2010

Phyllochron (degree‐days/leaf) has been used to describe phasic leaf development in dynamic wheat (Triticum aestivum L.) crop development models. Vernalization controls the rate of crop development in winter wheat. The objective of this experiment was to determine whether vernalization affected the thermal time required for winter wheat to produce leaves. ‘Stephens’ winter wheat plants were grown in a controlled environment chamber and in outdoor pots, using both pre‐vernalized and non‐vernalized germinating seed. In the outdoor pots plants became vernalized naturally and vernalization before sowing had no effect on growth, development, or flowering. In the controlled environment, up to the time of flowering of the vernalized treatment, there were no differences in phyllochron or total leaf number per main stem between the plants seeded using pre‐vernalized and non‐vernalized germinating seed. The non‐vernalized plants continued to produce tillers until the experiment was terminated, however, while tillering ceased at stem elongation in the vernalized plants. These results support the use of a constant value for phyllochron in simulating leaf development in both vernalized and non‐vernalized seedling winter wheat plants. However, they also show the need to adequately model the effect of vernalization on development (i.e., the cessation of leaf production and tillering in conjunction with flowering) in order to simulate the development of the crop leaf canopy.
Nitrogen Balance and Biomass Production of Newly Established No‐Till Dryland Agroecosystems
Authors: Wood C. W. , Peterson G. A. , Westfall D. G. , Cole C. V. , Willis W. O.
Published: July 2010

Soil‐crop management affects the soil‐N balance and, thus, has a direct bearing on soil productivity. This study determined the effects of cropping intensity (crops/time) under no‐till and grassland establishment on aboveground biomass production and the system‐N balance after 4 yr (1985–1989). The effects were examined across toposequences in the West Central Great Plains that had been tilled and frequently fallowed for >50 yr. Production systems included wheat (Triticum aestivum L.)‐fallow (WF), wheat‐corn (Zea mays L.) or sorghum (Sorghum vulgare L.)‐millet (Panicum miliaceum L.)‐fallow (WCMF), and perennial grass (CG). Intense agronomic systems (WCMF) had greater aboveground production, greater N uptake, and greater percent plant residue retention than WF. Continuous grass systems had less aboveground production and N uptake but greater percent plant residue retention than agronomic systems. Soil‐profile NO3–N was lower under WCMF systems than WF systems, but organic N showed the opposite trend implying that more intense systems are at less risk for NO3–N leaching, and have greater potential for replenishment of soil‐organic N via enhanced immobilization. Aboveground biomass production and plant residue production increased downslope, but slope position had little effect on plant‐N uptake, plant residue retention, or soil‐N dynamics. Imposing no‐till and perennial grassland systems created a N‐balance disequilibrium, but more time will be required to ascertain the trajectory of N loss or gain due to establishment of no‐till or grassland management on these soils.
Growth and Physiological Responses of Greenhouse‐Grown Blue Grama to Atrazine
Authors: Morgan J. A. , Knight W. G.
Published: July 2010

Blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Steud.] is an important native forage and the dominant C4 species on the shortgrass prairie. Sublethal concentrations of the herbicide atrazine (6‐chloro‐N‐ethyl‐N1‐[1‐methylethyl]‐1,3,5‐triazine‐2,4‐diamine) have increased range production, tissue N, and drought survival of blue grama. The mechanisms(s) for these responses are not well understood. This experiment was conducted to evaluate C exchange rates, water use, and productivity of blue grama to variable concentrations of atrazine. Plants were grown from seed (Lovington cv.) in soilpacked, column‐lysimeters. Treatment concentrations of 0.0, 0.5, 1.0, and 2.0 mg of atrazine per column were achieved by irrigating columns containing 8‐wk old plants with solution atrazine and/or tap water. Nine days following the initial atrazine application, CO2 exchange rates of plants treated with intermediate and high rates of atrazine averaged 28 μmol plant−1 s−1, 43% lower than rates observed for control and low atrazine treatments. This depression, which persisted for 30 d, was due to inhibition of leaf photosynthetic capacity. As a result, aboveground productivity of the intermediate and high atrazine treatments was inhibited 28% compared to the control. Similar atrazine‐induced reductions in evapotranspiration were noted. By the end of this period, chlorophyll concentrations of all atrazinetreated leaves had increased to an average 0.41 g m−2 compared to 0.33 g m−2 in control leaves. Shoot N concentrations were also affected by atrazine, averaging 23.3 g kg−1 in intermediate and high atrazine leaves and 14.9 g kg−1 in control leaves. Thirty‐seven days after the initial atrazine application, all remaining plants were clipped to 5‐cm height to begin a regrowth cycle. Twenty days after clipping, regrowth of low atrazine‐treated plants was 22% greater than controls. During the initial (2 wk) regrowth period, both increased plant photosynthesis and increased evapotranspiration rates were observed, but only for the intermediate treatment plants. Over the final period studied (2‐4 wk regrowth), no differences, compared to controls, were found for any parameters measured. No evidence for a direct stimulatory effect or hormonal‐type mode of action was found for atrazine.
Peanut Yield as a Result of Fifty Years of Breeding
Authors: Wells Randy , Bi Tin , Anderson William F. , Wynne Johnny C.
Published: July 2010

Breeding for increased yield is known to indirectly alter other plant characteristics in many crop species, including peanut (Arachis hypogaea L.). This 2‐yr, field study examined growth and dry matter allocation to various plant organs of 10 Virginia‐type peanut genotypes bred for increased yield in North Carolina, Genotypes representing the period from 1944 to the present were grown in 1988 and 1989. Growth was measured on five dates in each year. Genotypes expressed as the minimum number of breeding cycles from an indigenous germplasm exhibited a yield increase of 30 g m2 per breeding cycle. Genotypes developed from a greater number of breeding cycles tended to have smaller vegetative mass and shorter main stem lengths. However, concurrent increases in reproductive allocation, measured as pod mass and reproductive‐to‐vegetative ratios (RVR), were evident. Correlation analysis at 133 d after planting (DAP) between the number of breeding cycles and measurements of main stem length, total dry weight (DW), vegetative DW, stem DW, leaf area index (LAI) and RVR resulted in significant correlation coefficients of −0.67,0.38, −0.67, −0.71, −0.42, and 0.74 respectively. At 71 DAP, reproductive growth, measured as peg number, pod number, pod mass, and RVR was correlated with the number of breeding cycles, with significant correlation coefficients of 0.53, 0.52, 0.46, and 0.46, respectively. Reproductive to vegetative ratio continued to be positively related to both breeding cycle number and year of cultivar release throughout reproductive growth. The data indicate greater reproductive dry matter allocation by more recently released genotypes. Further, the allocation in reproductive growth appears related to an earlier transition from vegetative to reproductive development
Path Analysis of Rice Yield and Yield Components as Affected by Seeding Rate
Authors: Gravois K.A. , Helms R.S.
Published: July 2010

Understanding relationships among rice (Oryza sativa L.) yield and yield components (panicle density, filled grain per panicle, unfilled grain per panicle, and grain weight) is critical to utilizing these relationships effectively. Interrelationships among rice yield and yield components for direct‐seeded rice cultural systems using path‐coefficient analysis that describes a priori cause‐and‐effect relationships have not been shown. Our objective was to study direct‐seeded rice yield and yield component relationships as affected by seeding rates using path‐coefficient analysis. ‘Lemont’, a semidwarf rice, was seeded at 43, 85, 128, 170, and 213 kg ha−1 in four environments between 1986 and 1988. The seeding rate by environment interaction was nonsignificant for all traits, indicating stable performance across environments. As seeding rates increased, panicle density increased significantly, and filled grain per panicle decreased significantly, an indication of the compensatory nature between these two traits. Higher panicle densities at the lower seeding rates were due in part to increased tillering of the rice plants. Path‐coefficient analysis revealed that panicle density had the largest positive direct effect on rice yield, even at low seeding rates where filled grain per panicle increased to compensate for decreased panicle density. Direct effects for filled grain per panicle and grain weight were of secondary and/or tertiary importance in determining rice yield. Unfilled grain per panicle had negligible effects on rice yield. To achieve optimum rice yields and grain quality in a direct‐seeded cultural system, adequate panicle density per unit area of uniform maturity must be achieved.
Soybean Biomass Accumulation and Leaf Area Index in Early‐Season Production Environments
Authors: Savoy B. R. , Cothren J. T. , Shumway C. R.
Published: July 2010

Some indeterminate soybean [Glycine max (L.) Merr.] cultivars are adaptable to early plantings in the southern USA (<35°N lat). The purpose of this study was to determine the effects of inter‐row spacing and soil moisture level on dry matter accumulation, leaf area index, and plant height of an early‐planted indeterminate soybean in southcentral Texas. Soybean (‘Williams 82’, Maturity Group III) was planted in mid‐April in 1988 and 1989 near College Station, TX (30° 32'N lat). Harvest maturity occurred in late August. Soil moisture levels were irrigation and no irrigation; inter‐row spacings were 0.36 and 1.02 m. Soil moisture level treatments did not affect any of the measured dry matter or leaf area traits. Reproductive (pod and seed) dry matter production was greater in 0.36‐m rows near physiological maturity in both years. Total dry matter accumulation in 0.36‐m rows was greater than in 1.02‐m rows in 1988, but not in 1989. Leaflet, stem, and petiole dry matter accumulation was similar across soil moisture Levels and inter‐row spacings. Maximum leaf area index was greater in 0.36‐m rows than in 1.02‐m rows in 1988, but not in 1989. Narrow rows had greater radiation use efficiencies (0.48 g MJ−1 in 1988, 0.42 g MJ−1 in 1989) than wide rows (0.35 g MJ−1 in 1988, 0.37 g MJ−1 in 1989). Mean plant height was greater in 1.02‐m rows than in 0.36‐m rows in 1989, but not in 1988. Adequate levels of dry matter accumulation, leaf area production, and plant height were obtained using an adaptable indeterminate soybean in an early‐planted, early‐maturing production environment in south‐central Texas.
Delayed Seeding of Alfalfa Avoids Autotoxicity after Plowing or Glyphosate Treatment of Established Stands
Authors: Tesar Milo B.
Published: July 2010

Re‐establishment of alfalfa (Medicago sativa L.) has often been unsuccessful because of autotoxic effects of the crop on seedlings. This study was conducted at East Lansing, MI on an Udallic Ochraqualfs, fine loamy, mixed, mesic soil. The first objective was to determine the days required to eliminate autotoxic effects for 1‐, 4‐, and 6‐yr old stands of alfalfa with 1.4 Mg ha−1 dry weight of topgrowth after treatments of plowing or glyphosate [N‐(phosphonomethyl)glycine]. The second objective was to determine autotoxic effects of 1.4, 2.7, and 4.0 Mg ha−1 dry weight of topgrowth from year‐old alfalfa plowed prior to seeding the same day. Check treatments were seedings after plowed Kentucky bluegrass (Poa pratensis L.), corn (Zea mays L.), or fallow. Alfalfa was seeded for Objective 1 on 23 June 1982, 12 d after plowing alfalfa and 19 d after glyphosate application on 6‐yr‐old alfalfa; on 5 June 1984 and 29 May 1985, 0, 7, 14, 21, 28, and 195 d (29 May 1985 only) after plowing alfalfa or glyphosate application on year‐old alfalfa; and on 11 June 1986, 7, 14, 21, and 28 d after plowing alfalfa or glyphosate application on 4‐yr‐old alfalfa. Seedings for Objective 2 were made on 5 June 1984. Densities and yields of seedings equaled checks when made at least 14 d after plowing alfalfa or 21 d after glyphosate application on established alfalfa. Seedling densities were similar, but lower than the check, after three levels of alfalfa topgrowth were plowed and seeded the same day. Results indicate alfalfa can be re‐established without significant autotoxicity if seedings are made at least 2 wk after plowing or 3 wk after glyphosate application on established alfalfa or after seeding failure. For maximum killing of old alfalfa and to avoid autotoxicity, plowing of alfalfa and seeding at least 2 wk after plowing, or early‐fall or spring glyphosate application on alfalfa followed by no‐till seeding at least 3 wk after glyphosate application, are recommended.
Cowpea Water Relations and Growth Response on a Toposequence Water Table Gradient
Authors: Timsina J. , Garrity D. P. , Pandey R. K.
Published: July 2010

Cowpea sown after wetland rice in tropical monsoon climates is frequently subjected to soil saturation and a high water table during early growth. We compared the effects of variation in water table regime on the shoot and root growth, and plant water relations of two medium‐maturing (cv. TVX3236‐01G and TVX3410‐02J) and two early maturing (cv. BS6 and IT82D‐889) cowpea [Vigna unquiculata (L.) Walp] cultivars in three water table depth regimes on a Typic Tropudalf toposequence. Our objective was to elucidate the possible mechanisms of differential cultivar adaptation to shallow water table conditions. The shallow water table regime (SWT) significantly reduced the total dry matter accumulation and harvest index for BS6, an early maturing cultivar (reductions in stems, leaves, pods, and total dry matter by 82, 77, 88, and 84% respectively), while the least reductions (reductions by 44, 3, 57 and 55%, respectively) was observed for TVX 3410‐02J, a medium‐maturing cultivar. Roots of the medium cultivars were more concentrated in the top 0.2m in the SWT Site than those of the early‐maturing cultivars. Roots of the medium cultivars later penetrated to 0.8‐m maximum depth compared to 0.6‐m maximum depth for the early cultivars, and extracted soil water from 20 cm deeper in the soil profile than the early maturing cultivars. The medium‐maturity cultivars maintained higher leaf water potentials and lower canopy temperatures throughout the season. This was associated with greater end‐of‐season total soil profile water extraction. The medium‐maturing cultivars showed better adaptation to shallow water table conditions due to superior plant water status, rooting pattern, and biomass production and partitioning.
CARICE: A Rice Model for Scheduling and Evaluating Management Actions
Authors: Miller Baird C. , Foin Theodore C. , Hill James E.
Published: July 2010

Crop growth modeling can be useful in crop management, but previous rice crop models lack the morphologically accurate phenological detail needed for practical application. We designed a rice crop management model, CARICE, for scheduling management actions on the farm and evaluating consequences of alternative management strategies. A simple rice crop productivity model was expanded to include (i) phenology, based on leaf stage; (ii) tiller development, to establish yield components (iii) assimilate partitioning by developmental stage, (iv) assimilate partitioning patterns of California cultivars; and (v) a direct‐seeded cultural system. The key phenological events were accurately simulated: leaf stage development followed the expected pattern; predicted 50% heading was within 6 d of the actual heading dates; and grain filling predictions were within 1 to 11 d of field observations. Cultural management strategies simulated included delayed planting, and managing barnyardgrass (Echinochla spp.; BYG) competition by increasing water depth and seeding tale. Simulated yield results were within the range of field observations, although total aboveground biomass was overestimated. The model simulated a 27% loss in grain yield from a 21‐d delay in planting, which is close to the 21% loss measured in the field. At 11 and 54 BYG plants m−2, the model simulated 20.6 and 54.6% yield reductions relative to the control, as compared with 32.5 and 57.5% reported in the literature. The model predicted the interactive effect of rice seeding rate and water depth management for reducing barnyardgrass competition. The morphologically accurate phenology submodel and the yield‐component approach to calculating yield are keys to using CARICE for scheduling and evaluating management actions and strategies.
Field Response of Alfalfa to Harvest Frequency, Cultivar, Crown Pathogens, and Soil Fertility: II. Crown Rot
Authors: Gossen B. D.
Published: July 2010

Decline in stand density and productivity of alfalfa (Medicago sativa L.) over time in Canada and the USA has been attributed, in part, to crown and root diseases. In 1985, an experiment was initiated at three locations in Saskatchewan to examine the interaction of (i) harvest frequency, (ii) alfalfa cultivar, (iii) inoculation with fungal crown rot pathogens (Coprinus psychromorbidus, Phoma sclerotioides, or Fusarium spp.), and (iv) K nutrition on the etiology, lesion initiation, incidence, and severity of crown rot of alfalfa. Plant samples were collected from the plots in early spring and late fall each year, starting 1 yr after seeding. The pattern of symptom initiation and lesion expansion were similar at all sites. Lesions were observed initially at the base of senescing stems, and spread laterally into the crown and vertically into the tap root. Lesions were observed on plants at all sites on the first sampling date (> 70% of plants affected at Loon Lake and Saskatoon and 32% at Melfort), but severity was low. By the fall of the following year (1987), incidence was near 100% at all sites, and severity had increased markedly. Harvest frequency and K fertility did not affect crown rot at any location. Inoculation with C. psychromorbidus resulted in small increases in crown rot severity at two sites, but inoculation with the other pathogens had no effect. ‘Nordica’ alfalfa was more resistant to crown rot than ‘Beaver’. These results indicate that resistance to crown rot may be advantageous if long‐term persistence is required, but resistance is not required in short‐term rotations. Also, crown rot and crown bud rot, two alfalfa diseases that have previously been described as distinct entities, appear to be a single disease complex, based on similarities in symptom development and the organisms associated with affected plants.
Influence of Plant Growth Regulators and Mowing on Two Bermudagrasses
Authors: Johnson B. Jack
Published: July 2010

‘Tifway‘ hybrid bermudagrass [Cynodon transvaalensis Burtt‐Davy × C. daetylon (L.) Pers.] and common bermudagrass [C. dactylon (L.) Pers.] are popular turfgrasses used throughout the southern USA. When both grasses are managed as a medium‐ to high‐quality turf, frequent mowings are needed to limit vegetative growth and seedhead emergence. Plant growth regulators offer the potential to reduce the number of mowings needed by bermudagrass. Therefore, experiments were conducted on Tifway and common bermudagrasses to determine the effects of plant growth regulators on vegetative growth, seedhead suppression, and mowing requirements. Flurprimidol {α‐(1‐methylethyl)‐α‐[4‐(trifluoro‐methoxy) phenyl]‐5‐pyrimidine‐methanol}, paclobutrazol, {(±)‐(R*R*)β‐[(4‐chlorophenyl) methyl]‐α‐(1,1‐dimethylethyl)‐1H‐1,2,4‐triazole‐1‐ethanol}, and trinexapac‐ethyl [4(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxocyclohexanecarboxylic acid ethyl ester] plant growth regulators were each applied at various rates in three applications at 4‐wk intervals. When Tifway bermudagrass was treated initially with trinexapac‐ethyl at 0.2 kg ha−1, and followed by 0.1 kg ha−1 at 4 and 8 wk, vegetative growth and seedheads were suppressed for 12 wk and the number of mowings were reduced by 70 and 67% during 1992 and 1993, respectively. However, the quality of Tifway bermudagrass as significantly lowered in plots treated with trinexapac‐ethyl at this rate at four rating dates during 1992 and three rating dates during 1993, when compared with turfgrass treated initially at 0.1 kg ha−1, and followed by 0.05 kg ha−1 at 4 and 8 wk. Common bermudagrass was less affected by these treatments. Neither flurprimidol nor paclobutrazol applied in three applications during a 12‐wk period provided consistent vegetative growth and seedhead suppression of common bermudagrass during 1992 and 1993.
Evaluation of a Model to Predict Nutrient Uptake by Field‐Grown Rice
Authors: Teo Yan Hock , Beyrouty Craig A. , Gbur Edward E.
Published: July 2010

The Barber‐Cushman model has not been evaluated under flooded conditions. A field study was conducted on a Crowley silt loam to evaluate the ability of the model to predict NH+4, P, and K uptake by rice (Oryza sativa L.). Total nutrient uptake and root and soil parameters were measured at vegetative (active tillering, maximum tillering, and 1.25‐cm internode elongation) and reproductivec (booting and heading) stages of development of three cultivars (Katy, Mars, and Lemont). The model accurately predicted nutrient uptake during vegetative growth but underpredicted nutrient uptake during reproductive growth. About 90% of the total NH+4 P, and K uptake and root length of the rice cultivars occurred within the surface 20 cm of soil, suggesting that samples collected for routine soil tests should be from the top 20 cm. Ammonium and P uptake in the 0‐ to 20‐cm soil depth were most sensitive to root competition, root radius, nutrient solution concentration, and buffer power. However, K uptake was most sensitive to maximum influx rate, root radius, Michaelis constant, and root growth rate throughout the top 40‐cm soil depth. These findings indicate that NH+4 and P uptake can be enhanced by increasing levels of fertilization in the top 20 cm of soil where these nutrients are found to be limiting. Fertilization should increase the NH+4 and P solution concentrations, thus reducing root competition for these elements. Potassium soil levels were not low enough to limit uptake by the cultivars selected for this study.
Temperature and Soil Water Effects on Dormancy and Mortality of Subterranean Clover Seed
Authors: Fairbrother Timothy E. , Rowe Dennis E.
Published: July 2010

Germination tests were conducted to investigate possible causes for a reestablishment failure of subterranean clover (Trifolium subterraneum L.). ‘Mount Barker’ subterranean clover seeds were germinated on blotters and on the soil surface or at 1 cm depth in nonfumigated and fumigated soil at four constant temperatures for 14 d, followed by constant 15°C for 8 d. Fumigation had no effect on germination. Germination on blotters was reduced to 11.1% at 25 and 30°C, compared with 94.5% at 15°C. Emergence of seedlings was reduced to 37.9% at 30°C, compared with 92.5% at 15°C. Emergence of seedlings at 30°C from soil was greater after 14 d than germination on blotters. In a second experiment, seeds buried 1 cm were germinated at soil water levels ranging from 0.0 to 0.816 kg kg−1. Temperatures were 15 or 30°C for 7 d, then 15°C for 7 d more. Seeds failed to germinate at either temperature in dry or saturated soil. Emergence after 7 d was reduced at 30°C compared with 15°C at soil moisture levels from 0.204 to 0.544 kg kg−1. After 7 more d at 15°C, emergence was similar between temperatures at soil moisture levels from 0.0 to 0.544 kg kg−1. Under saturated soil conditions, 28.5 and 80.8% of the seed rotted at 15 and 30°C, respectively. Our results suggest that subterranean clover seeds can survive in pasture soil for 14 d in an embryo dormant condition during the summer, unless the soil is saturated, in which case soft seeds tend to decay.
Residue Removal Method and Herbicides for Tall Fescue Seed Production: II. Crop Tolerance
Authors: Mueller‐Warrant George W. , Young William C. , Mellbye Mark E.
Published: July 2010

Increased reliance on herbicides for controlling weeds is a significant component of the ongoing transition from open‐field burning (FB) to nonburn systems for grass seed production in the Pacific Northwest. Volunteer crop seedlings are the most abundant weeds present in many certified grass seed fields, but herbicide treatments to control them also have the potential to injure the established crop. Fourteen herbicide treatment sequences plus an untreated check were examined in five residue removal systems at two field sites during two consecutive growing seasons to determine their effect on tall fescue (Festuca arundinacea Schreb.) seed yield and harvest index. Herbicide treatments were applied preemergence (PRE) to seedling grasses in mid‐October, postemergence (POST) in early December, or at both times. Tall fescue seed yield was not affected over a two‐year period by competition from volunteer seedlings. Seed yield was reduced by herbicide injury, particularly in the second year. PRE applications of oxyfluorfen [2‐chloro‐1‐(3‐ethoxy‐4‐nitrophenoxy)‐4‐(trifluoromethyl)benzene] reduced seed yield by 87 and 151 kg ha−1 in 1990 and 1991, respectively, compared with the average for three other PRE herbicides, pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine], metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐l‐methylethyl) acetamide], and trifluralin [2,6‐dinitro‐N,N‐dipropyl‐4‐(trifluoroniethyl)benzenamine]. The untreated check yielded 122 kg ha−1 more seed than the average of all 14 herbicide treatments in 1991. The least injurious herbicide treatment was PRE pendimethalin applied without subsequent POST herbicide. When applied following PRE herbicides, POST applications of 2.7 kg a.i. ha−1 diuron [N'‐(3,4‐dichlorophenyl)‐N,N‐dimethylurea] or 0.14 kg a.i. ha−1 oxyfluorfen plus 1.8 kg ha−1 diuron did not differ in yield or harvest index. An aggressive system for mechanical removal of straw, seed, and postharvest regrowth, vacuum sweeping (VS), reduced tall fescue seed yield and harvest index in 1991 compared with other, less aggressive, mechanical methods, and compared with two methods of burning. Some herbicide treatments applied to control volunteer crop seedlings had a greater effect on tall fescue seed yield than the adoption of nonburn methods of residue removal.
Leaf Area of Strip‐Intercropped Corn in Dry and Normal Growing Seasons
Authors: Fortin M.‐C. , Edwards M.
Published: July 2010

Crop growth models need to be adapted for cropping systems other than monoculture. This study was conducted (i) to determine the effect of row position on leaf area of corn (Zea mays L.) strip‐intercropped with soybean [Glycine max (L.) Merr.] and a small grain crop (oat, Avena sativa L., in 1991; barley, Hordeum vulgare L., in 1992) and (ii) to determine whether an established leaf area model developed from monoculture corn data fits the strip‐intercropping data. Corn, soybean, and small grain were planted in north‐south rows on a mixed, mesic Typic Endoaquoll in Nepean, ON. There was 55.1 rainfall from emergence of Leaf 5 to silking in 1991 and 210.6 mm in 1992. Total green leaf area at grain filling varied with row position each year. The corn row next to the small grain had less leaf area than the middle row in 1991 and more leaf area than the middle row in 1992. These variable results were due to differences in weather in the two years. Dry conditions in 1991 resulted in slow expansion of leaves and in small individual leaf area. As thermal time to full expansion of the largest leaf on the plant was similar in both years, the largest leaf in 1991 occurred at an earlier developmental stage than in 1992 (Leaf 10.5 vs. Leaf 12). An existing leaf area model was found to fit the data, provided that adjustments for row position and for the timing of the development of the largest leaf were included.
Nitrogen‐Sulfur Relationships in Corn as Affected by Landscape Attributes and Tillage
Authors: Cassel D. K. , Kamprath Eugene J. , Simmons F. William
Published: July 2010

Corn (Zea mays L.) root access to the B horizon is needed for adequate sulfur nutrition on sandy, highly leachable Coastal Plain soils with tillage pans. Deep tillage increases rooting depth on these soils, but the interaction of deep tillage with landscape attributes in complex toposequences is not well understood. The effect of chisel plowing 35 cm deep, subsoiling 25 cm deep, and disking 12 cm deep on N and S accumulation by corn on a well‐drained toposequence of Coastal Plain soil was studied in 1984 and 1985. Nitrogen and S concentrations of aboveground biomass were measured at anthesis (Na and Sa,, respectively) and at harvest (Nh and Sh, respectively). Soil surface curvature (CRV) (i.e., its convexity or concavity), and depth to the B horizon (BDEP) were correlated with Sa in both years. Extreme drought in early 1985 resulted in a stronger negative linear response of Sa with BDEP in the chisel plow and disk treatments compared with the subsoil treatment. The Na/Sa ratio was negatively correlated with BDEP for all treatments and with CRV for chisel plow and disk tillage. Deep tillage had the greatest positive effect on S accumulation by corn at the linear slope position, which was the landscape position with the greatest depth to the B horizon.
Runoff, Erosion, and Forage Production from Established Alfalfa and Smooth Bromegrass
Authors: Zemenchik Robert A. , Wollenhaupt Nyle C. , Albrecht Kenneth A. , Bosworth Andrew H.
Published: July 2010

Surface sealing of soils in established alfalfa (Medicago sativa L.) may produce runoff during intensive rainstorms, resulting in soil loss and reduced yield. We hypothesized that smooth bromegrass (Bromus inermus Leyss.) grown in mixture with alfalfa would reduce on‐site runoff and soil loss, and that this should offset any negative effect on forage quality. Alfalfa, smooth bromegrass, and an alfalfa‐smooth bromegrass mixture were established in 1992 on Rozetta silt loam (moderately well drained, fine‐silty, mixed, mesic Typic Hapludalfs) near Lancaster, WI. A 72‐mm h−1 simulated rainfall was applied for 1 h during the growing seasons of 1993 and 1994 to forage regrowth at 4 and 6 wk after first harvest and immediately after second harvest. The addition of smooth bromegrass to alfalfa did not significantly reduce runoff volume, sediment concentration, or total soil loss at any rainfall event at any stage of regrowth in either year. Furthermore, forage yield and concentrations of acid‐detergent fiber and crude protein in the forage were not affected. Averaged over both years and the three sward types, runoff at 6 wk was significantly less than at 0 wk, which was significantly less than at 4 wk. Total soil loss from all sward types summed over six simulated rainstorms was between 0.19 and 0.61 Mg ha−1, much less than the 11.2 Mg ha−1 yr−1 considered tolerable for this soil. Neutraldetergent fiber (NDF) concentration of bromegrass (534 g kg−1) was greater than either the mixture (441 g kg−1) or alfalfa (404 g kg−1). Soil loss and forage quality results do not support adding smooth bromegrass to alfalfa, especially since increased NDF results in lower forage intake by ruminants and reduced milk yield in dairy cattle (Bos taurus); however, livestock operations that could efficiently utilize smooth bromegrass monocultures could reduce soil loss and runoff by doing so.
Ammonia Transport in a Temperate Grassland: I. Seasonal Transport in Relation to Soil Fertility and Crop Management
Authors: Harper Lowry A. , Bussink D. Wim , van der Meer Hugo G. , Corré Wim J.
Published: July 2010

An understanding of N cycling in agricultural systems is necessary to optimize N‐use efficiency and reduce N losses to the environment. The objectives of this research were to evaluate N cycling in a highly fertilized grassland in a humid temperate climate and to observe the effects of N surplus and deficit on NH3 absorption‐desorption by the grass. Soil, plant, and weather measurements were taken concurrently and soil‐plant‐atmosphere N transport were determined. After N application, soil inorganic N decreased rapidly to background levels, due to possible microbial immobilization and plant N demand. Much of the immobilized N was remobilized during the growth period, but at insufficient rates to avoid N stress by the crop, as shown by absorption of NH3. During spring, 45% of the plant N was derived from applied fertilizer, with the balance obtained from mineralized organic N (49%) and absorption of NH3 (6%). During summer, fertilizer N accounted for 60% of accumulated grass N and NH3 absorption accounted for 11% of N not derived from fertilizer (4% of the total N), with the balance coming from mineralized organic N. Soil water content and wind speed were the dominant factors influencing the crop NH3 compensation point (CP). The daily NH3 CP was variable, but the average seasonal NH3 CP was about 14 μg m−3.
Regression Models for Calculating Gas Fluxes Measured with a Closed Chamber
Authors: Wagner Steven W. , Reicosky Donald C. , Alessi R. Samuel
Published: July 2010

Portable closed chambers provide a valuable tool for measuring crop photosynthesis and evapotranspiration. Typically, the rates of change of CO2 and water vapor concentration are assumed to be constant in the short time required to make the closed‐chamber measurement, and a linear regression model is used to estimate the CO2 and H2O fluxes. However, due to the physical and physiological effects the measurement system has on the measured process, assuming a constant rate and using a linear model may underestimate the flux. Our objective was to provide a model that estimates the CO2 and H2O exchange rates at the time of chamber closure. We compared the linear regression model with a quadratic regression model using field measurements from two studies. Generally, 60 to 100% of all chamber measurement data sets were significantly nonlinear, causing the quadratic model to yield fluxes 10 to 40% greater than those calculated with the linear regression model. The frequency and degree of nonlinearity were related to the measured rate and chamber volume. Closedchamber data should be tested for nonlinearity and an appropriate model used to calculate flux. The quadratic model provides users of well‐mixed closed chambers an alternative to a simple linear model for data sets with significant nonlinearity.
Apparent Atmospheric Nitrogen Loss from Hydroponically Grown Corn
Authors: Sharpe Ronald R. , Harper Lowry A.
Published: July 2010

Isotopic 15N tracers have been important tools in the understanding of N cycling in agricultural and natural soil‐plant systems. The objectives of this research were to quantify losses of 15N under controlled conditions, evaluate 15NH3 transport between plants, and assess the potential for error associated with the use of N isotopes. Corn (Zea mays L.) was grown hydroponically in 5‐ to 15‐mm‐diam. gravel in twelve 162‐L barrels. All N was applied as NO3 with enrichment periods of full season, planting through anthesis, anthesis to harvest, or no 15N applied. Plant growth and total N accumulation followed normal growth curves and maximum N content was obtained at anthesis. When 15N treatments stopped at anthesis, plants lost 15N (presumably as 15NH3) equivalent to about 23% of total plant N between anthesis and harvest. In treatments in which 15N applications started at anthesis, total N content in the leaves and stems decreased between anthesis and harvest while 15N content increased indicating a substitution of recently absorbed N for N compounds translocated to the fruit. Volatile losses of N indicate that caution must be exercised when conducting and interpreting 15N experiments. Significant plant‐to‐plant transport of 15NH3 showed that decreases in plant 15N content could not be used to estimate NH3 volatilization for an entire field.
Yield and Green‐Manure Benefits of Interseeded Legumes in a High Desert Environment
Authors: Guldan Steven J. , Martin Charles A. , Lindemann William C. , Cueto‐Wong Jose , Steiner Robert L.
Published: July 2010

Relay intercropping legumes into vegetable crops provides cover and green‐manure benefits to subsequent crops, but has not been adequately researched in high desert regions. This study evaluated the dry matter, N yield, effect on a subsequent forage sorghum [Sorghum bicolor (L.) Moench] crop, and estimated fertilizer‐replacement value (FRV) of several legumes interseeded into sweet corn (Zea mays L.). The study took place under furrow irrigation in north‐central New Mexico (study site elevation, 1737 m) on a Fruitland sandy loam (coarse‐loamy, mixed, calcareous, mesic Typic Torriorthent). Five legumes (hairy vetch, Vicia villosa Roth; barrel medic, Medicago truncatula Gaertn.; alfalfa, Medicago sativa L.; black lentil, Lens culinaris Medik.; and red clover, Trifolium pratense L.) were interseeded into sweet corn at last cultivation or blister stage in 1993 and 1994. Corn ears and stover were harvested in August. The following spring, plots were plowed and seeded to forage sorghum. Estimated FRV for the legumes were calculated from regression equations for sorghum dry matter yield as a function of N fertilizer rate. Herbage N yields in the fall were greatest for hairy vetch and barrel medic and, averaged across interseeding dates, ranged from 55 to 64 kg ha−1 in 1993 and 100 to 108 kg ha−1 in 1994. Whole‐plant N yields (herbage + roots + crowns) in May were greatest for hairy vetch, 205 kg ha−1 in 1994 and 172 kg ha−1 in 1995. Seasonal dry matter yield and N uptake of sorghum were greatest following hairy vetch in 1994, and hairy vetch and alfalfa in 1995. Based on seasonal sorghum yield, hairy vetch and alfalfa had the highest FRV, ranging from 78 to 140 kg ha−1 N.
Swine Lagoon Effluent Disposal by Overland Flow: Effects on Forage Production and Uptake of Nitrogen and Phosphorus
Authors: Liu Fuhan , Mitchell Charles C. , Odom John W. , Hill David T. , Rochester Eugene W.
Published: July 2010

Swine (Sus scrofa) production requires economical and environmentally safe waste management systems. The objective of this study was to determine the effect of swine lagoon effluent on dry matter yield and N and P uptake of a mixture of hybrid bermudagrass [Cynodon dactylon (L.) Pers. cv. Russell] and annual ryegrass (Lolium multiflorum Lam.) grown on a Marvyn loamy sand (fine‐loamy, kaolinitic, thermic Typic Kanhapludult). Treatments included a control with no nutrient additions, NH4NO3 at 560 kg N ha−1 yr−1, and swine lagoon effluent at 560, 1120, and 2240 kg N ha−1 yr−1. Effluent was applied using an overland flow technique. The highest lagoon effluent rate added N at 4 times and P at 11 times the normally recommended rates for these forage grasses. Total dry matter yield was significantly increased by NH4NO3 and swine lagoon effluent additions, compared with the control treatment. Dry matter yield for the lowest effluent rate was not significantly different from that for the NH4NO3 treatment, and dry matter yields were not significantly different among the three rates of lagoon effluent. Increasing the effluent rates generally increased total N and total P concentrations in the forage. Recoveries were about 32% for N and 20% for P at the lowest rate of lagoon effluent, and about 13% for N and 9% for P at the highest rate. The low recoveries of N and P with higher than recommended effluent rates could have environmental implications for the quality of soil, groundwater, and surface runoff.
Ammonia Exchange from Corn Foliage during Reproductive Growth
Authors: Francis Dennis D. , Schepers James S. , Sims Albert L.
Published: July 2010

Developing solutions to atmospheric environmental problems requires a better understanding of chemical processes occurring in each component of the ecosystem. Volatile NH3 loss from plant foliage complicates the assessment of NH3 emissions from agricultural activities. The objective of this study was to use 15N methodology to identify time of occurrence, magnitude, and direction of NH3 exchange between corn (Zea mays L.) fertilized with enriched 15N and the atmosphere during reproductive growth. Ammonia was collected by drawing air over leaves, ear shoots, and whole plants and trapping the NH3 on oxalic acid‐impregnated filter disks. Filter disks were analyzed by ANCA‐MS procedures for total N and atom % 15N. An exchange of NH3 between corn plants and the atmosphere was found to occur during all sampling periods. This suggests that the release and capture of free NH3 is an active component of the metabolic processes taking place in corn plants during reproductive growth. For corn under non‐limiting N fertility, the direction, rate, and magnitude of NH3 exchange from leaves does not appear to be a function of ambient atmospheric NH3 concentrations. Determining the true loss or gain in N between corn plants and the atmosphere during reproductive growth is very difficult as a result of this continuous exchange of NH3. The amount of net N lost from a corn crop will be less than the amount indicated by measurements of isotopic loss, because both interchange between plants and deposition on soil and plants may take place within the field.