bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Sunfleck Theory for Plant Canopies II. Penumbra Effect: Intensity Distributions along Sunfleck Segments1
Authors: Miller E. E. , Norman J. M. 
Published: July 2010

AbstractThe finite (1/2°) angular diameter of the sun causes the fuzziness of the shadow cast onto the ground by a leaf edge to increase in proportion to increase in height of the leaf. When a straight‐line sunfleck segment is terminated by a leaf edge that cuts across it at a slant, the apparent width of the penumbral fringe displayed upon the segment is stretched by the slant.In this paper the intensity distribution along a slanting traverse of a penumbral shadow edge is computed, the statistical distributions of leaf‐edge angles at the ends of segments are analyzed, and these two distributions are combined into a statistically‐averaged intensity distribution along the segment, the distribution being dependent upon the segment length. When this intensity distribution is incorporated into the segment length distribution from the preceding paper of this series, a useful prediction is obtained for the complete distribution of intensity within a plant canopy.
Reflectance and Internal Structure of Leaves from Several Crops During a Growing Season1
Authors: Sinclair T. R. , Hoffer R. M. , Schreiber M. M. 
Published: July 2010

AbstractThe reflectance spectra from 500 to 2600 nm were measured for the leaves of six agronomic crops. Leaf samples were collected at three periods during the growing season; water content was determined and cross sections of the internal leaf structure were observed microscopically. The reflectance spectra of all fresh, green leaves were very similar. However, reflectance at all wavelengths increased as the crop matured and their leaves senesced. Decreased absorption by chlorophyll apparently increased the reflectance of the visible wavelengths (500 to 700 nm). Similarly, water loss accompanying senescence resulted in an increased reflectance in the far infrared wavelengths (1300 to 2600 nm). Changes in the internal structure of leaves caused increases in the near infrared wavelengths (700 to 1300 nm).
Critical Levels of P in Subclover (Trifolium subterraneum L.)1
Authors: Jones M. B. , Ruckman J. E. , Lawler P. W. 
Published: July 2010

AbstractPhosphorus deficiencies are widespread in California annual grasslands and in other areas of the world where subclover (Trifolium subterraneum L.) is an important legume. Therefore, the effects of clipping frequency and stage of growth on critical levels of P in subclover were studied. Critical P level was defined as percent P in the clover part when lack of P limited clover yields to 95% of those obtained with adequate P.In pot experiments subclover was grown in P‐deficient soils fertilized with increasing amounts of P until no additional increase in yield was obtained. When leaves were sampled from plants 48 to 151 days of age, the critical level decreased from 0.61 to 0.11% P, but changes after 120 days were not statistically significant.At day 120, leaves from plants previously defoliated 0, 1, 2, or 3 times had critical values of 0.11, 0.18, 0.23, and 0.28% P, respectively. The last three determinations were for leaves of the same physiological age harvested 13 days after the previous clipping. At 120 days critical P values in stem tissue also increased with increasing frequency of defoliation.
Relationships between Soil Properties, Management Practices, and Corn Yields on South Atlantic Coastal Plain Soils1
Authors: Sopher Charles D. , McCracken Ralph J. 
Published: July 2010

AbstractCorrelations between individual soil properties, management practices, and corn (Zea mays L.) grain yields were observed for 441 corn plots on selected North Carolina Coastal Plain soils. Correlations between different soil properties within soil horizons and correlations between the same properties in adjacent soil horizons show that many of the variables in the crop‐soil ecological system are highly intercorrelated. These intercorrelations limit the usefulness of both simple and multiple regression to characterize cause and effect relationships within the system. However, they can be useful in helping to understand the complex system and to develop soil sampling techniques for future characterizations of the system.Of the 101 independent variables (23 soil properties on each of 4 horizons plus nine management variables) included, 56 variables were significantly correlated with corn grain yields on the well‐drained (Udultic) soils Upper and Middle Coastal Plains (mainly Hapludults and Paleudults). Sixty‐one variables were significantly correlated with yields on the very poorly drained (Aquultic) soils of the Tidewater region (mainly Umbraquults and Ochraquults). The factors most affecting yields on both soil groups were soil moisture holding capacities, certain combinations of clay and sand, extractable P, percent base saturation and properties which control soil acidity, the amount of charge on the cation exchange complex, plant populations, and planting dates. Because of previous high management levels of the fields sampled, applied nutrients were deemed important but not highly limiting on the two soil groups studied.
Nitrogen Utilization by Rice Using 15N‐Depleted Ammonium Sulfate1
Authors: Patrick W. H. , Delaune R. D. , Peterson F. J. 
Published: July 2010

AbstractA field experiment utilizing 15N‐depleted ammonium sulfate was carried out to determine the efficiency with which lowland rice utilized fertilizer nitrogen in large (2.1 ✕15.2 m) plots. Relative uptake of labelled and nonlabelled nitrogen was followed throughout the growing season. At the soft dough stage, small (0.84 m2) subplots were cut and the total aboveground uptake of labelled and non‐labelled nitrogen determined. Labelled and non‐labelled nitrogen contents of the harvested grain was determined.The results showed that nitrogen utilization by lowland rice (Oryza saliva L.) was poor, with 17 and 23% recovery of applied nitrogen in the aboveground portion of the crop at the soft dough stage for 56 and 112 kg/ha rates, respectively. Approximately 12% of the applied nitrogen was recovered in the unmilled grain. The fraction of plant nitrogen coming from fertilizer was relatively high (about three‐fourths) early in the season but decreased to as little as one‐fifth as the season progresssed. Yield response, total nitrogen uptake, and uptake of fertilizer nitrogen were higher for the 112 kg/ha rate than for the 56 kg/ha rate. Even though nitrogen utilization was low, fertilizer nitrogen markedly increased the yield of grain.
Late Summer Irrigation and Establishment of Winter Annual Legumes in a Mediterranean‐type Climate1
Authors: Taggard K. L. , Delmas R. E. , Raguse C. A. 
Published: July 2010

AbstractWinter annual legumes have low fall and early winter forage yields in California's Mediterranean‐type climate. A 2‐year field study was conducted to determine the effects of late summer irrigation on seedling development, forage yield potential, and management problems of subterranean clover (Trifolium subterraneum L.), rose clover (Trifolium hirtum All.), and bur clover (Medicago polymorpha Gaertn). A mixture of three annual grasses, slender wild oats (Avena barbata Pott. ex Link), ‘Blando’ brome (Bromus mollis L.), and annual ryegrass (Lolium multiflorum L.), and a natural stand of indigenous species were included in the study for comparison. By irrigation prior to fall rains, we subjected six successive seedings, 2 weeks apart, to higher temperatures and longer fall‐growth periods than usual.Rates of morphological development of subclover and rose clover were measured until the seven‐leaf stage. In the 1972‐73 season, rose clover showed the largest differences in growth rates between planting dates. Rose clover from the 23 October planting required 90 more days to reach the seven‐leaf stage than when planted 29 September. Early‐flowering subclover from the 23 October planting grew more rapidly than did mid‐flowering subclover and rose clover. In the 1973‐74 season, late‐flowering sub‐clover had the fastest growth rate following 7 August irrigation; there were no differences between clovers following 20 September irrigation.Forage yields for August and September plantings were similar but were greater than those from the October planting. Plants irrigated in August were subjected to daylengths which promoted fall flowering. Summer insect problems, primarily with beet armyworm (Spodoptera exigua Hübner), were associated with August plantings. Subterranean clover produced more dry matter and had fewer problems than did the other legumes tested.
Winter‐Annual Cover Crops for No‐Tillage Corn Production1
Authors: Mitchell W. H. , Teel M. R. 
Published: July 2010

AbstractNo‐tillage corn (Zea mays L.) production minimizes soil moisture and wind erosion losses on sandy soils. Use of leguminous cover crops for no‐tillage mulches would provide these benefits while at the same time supplying a source of biological nitrogen to supplement the N produced with fossil fuel energy. Hairy vetch (Vicia villosa Roth.) and crimson clover (Trifolium incarnatum L.) were grown alone and in combination with non‐leguminous species to determine their value as no‐tillage mulches and sources of biological N. Field tests were conducted on Evesboro loamy sand, a mesic coated Typic Quartzipsamments, involving eight cover crops, three levels of N, and two moisture regimes. Nitrogen was applied, just prior to killing the mulch covers with Paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) (0.28 kg a.i./ha) at rates to deliver 0, 56 and 112 kg N/ha. Hairy vetch and crimson clover mixtures produced grain yields comparable to those obtained by the application of 112 kg N/ha. Approximately one‐third of the total N from mulch covers was released to the corn in a single season, with about 90% of this derived from cover crop top growth. Heavy growth of rye mulch covers was associated with irregular and low corn populations. Mulch covers were less reflective than the bare soil surface, resulting in mulch surface temperatures up to 10 C higher than those with unprotected soil surface. Temperatures immediately below the mulch covers were more than 10 C lower than those at the soil surface.
Soybean Water Extraction, Leaf Water Potential, and Evapotranspiration During Drought1
Authors: Reicosky D. C. , Deaton D. E. 
Published: July 2010

AbstractSoil water is often the most limiting factor in soybean production in the southeastern US. To increase wateruse efficiency in soybean production, it is necessary to characterize the plant's response to the evaporative demand and to soil water stress when the root distribution changes with depth. ‘Davis’ and ‘McNair 800’ soybean cultivars (Glycine max (L.) Merr.) were grown in a field experiment conducted on Norfolk sandy loam (Thermic Typic Paleudults) to evaluate the effect of irrigation on soybean yields and to determine the combined effects of soil matric potential and evaporative demand on evape transpiration (ET) in nonirrigated and irrigated treatments. Water was applied to the irrigated treatment when the matric potential at the 15cm depth was −0.2 bar. Leaf water potential was measured using the pressure chamber technique and ET was measured using a portable chamber during a 34day drought. Only small differences in the midday leaf water potential were found between the two cultivars, whereas ET on the nonirrigated treatments was about two‐thirds of that on the irrigated treatments 25 and 32 days into the drought. Soil matric potential data indicated significant water extraction at the 153‐cm depth in the nonirrigated treatments near the end of the drought. The maximum incanopy air temperature during the drought in the nonirrigated Davis was 6.7 C higher than in the irrigated treatment. Irrigation resulted in a 351‐ and 364‐kg/ha increase in Davis and McNair 800, respectively. Even though the nonirrigated plants exhibited severe wilt symptoms during the drought, the results point out the importance of the root distribution and subsoil water in partially meeting the evaporative demand during drought.
Volunteer Legume Control in Legume Seed Crops with Carbon Bands and Herbicides. II. Red Clover and Alfalfa1
Authors: Rolston M. Philip , Lee W. Orvid , Appleby Arnold P. 
Published: July 2010

AbstractVolunteer legumes from seed in the soil may contaminate seed lots of red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.). No herbicides are available to selectively control these volunteers. Experiments were conducted in western Oregon to determine the potential of using activated carbon applied in 25‐mm bands over the seed row during planting to protect the crop from nonselective herbicides applied to control volunteer legumes. Control of volunteer legumes was estimated visually, and white clover stand and seed yields were measured. Greenhouse and field experiments demonstrated that both red clover and alfalfa can be established with carbon bands and diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea]. Tolerance of red clover to diuron varied with the season of establishment; the greatest injury occurred when diuron was applied in the fall to soils that were wet on the surface. Seed yields for red clover established with carbon bands and 0, 2, and 4 kg/ha diuron averaged 566, 560, and 348 kg/ha, respectively, across all treatments. Seed yield for the two legumes established in 30, 50, and 80‐cm row widths were: alfalfa, 264, 354, and 424 kg/ha, respectively; and red clover, 635, 584, and 376, respectively. In the greenhouse, EPTC (S‐ethyl dipropylthiocarbamate) granules at 10 mg/m of row applied as a mixture with the alfalfa seed, controlled perennial ryegrass (Lolium perenne L.) in the carbon band without reducing the number or weight of the alfalfa seedlings. Atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] or diuron at 1 and 3 kg/ha, respectively, controlled 85 to 99% of red clover volunteers.
Cultivar Response of Festuca rubra Seedlings to Aluminum1
Authors: Nittler L. W. , Kenny T. J. 
Published: July 2010

AbstractEven though several characteristics useful for testing fescue (Chewings fescue Festuca rubra var. commutata Gaud., and red fescue, Festuca rubra L. var rubra) for cultivar purity have been identified, additional methods are needed for distinguishing similar cultivars. The investigation reported here was conducted to determine if cultivar differences not observable on untreated plants would develop in response to a high concentration of aluminum. Seedlings of 20 Chewings fescue and red fescue cultivars were grown in sand nutrient culture with a complete nutrient solution and with continuous light. Twenty‐eight days after seeds were planted a solution of Al2(SO4)3 in water with a concentration of 216 ppm actual Al was applied to the surface of the sand until solution drained from the bottoms of the flats. Thereafter the Al solution was applied 6 days a week and a complete nutrient solution was applied once a week. Plants were evaluated 15 days after the first Al application. Cultivars differed in percentage of plants that developed purplish red leaf blades and also in the percentage of plants that developed necrotic leaf blades. Plants classed as having red leaf blades were 63% and 61% respectively for Kensington and Banner, and, at the other extreme, 16%, 24%, and 24% for ‘Ensylva’, ‘Fortress’ and ‘K4‐21’. Plants classed as having necrotic leaf blades were 57%, 40% and 40% respectively for ‘Ruby’, Ensylva, and Fortress and 0% for ‘Banner’, 1% for ‘Highlight’ and 2% each for ‘Cascade’, ‘Encota’, and ‘Erika’. Cultivar differences were not great enough to place cultivars into discrete categories, but they were great enough to be useful for distinguishing contrasting types.
Root Growth and Morphology, Nutrient Uptake, and Nutrient Status of Soybeans as Affected by Soil K and Bulk Density1
Authors: Hallmark W. B. , Barber S. A. 
Published: July 2010

AbstractDue in part to the difficulty of isolating roots from soil and measuring them, little research has been conducted on root growth and morphology and its relation to shoot growth, nutrient status of shoots, and net nutrient influx. A soil experiment was conducted to measure the effect of increasing soil K and soil bulk density on the above parameters and their interaction. A 2 × 2 × 3 factorial experiment (soil bulk density × K added × date of harvest) was conducted in a greenhouse using soybeans [Glycine max (L.) Merr.] grown in Raub silt loam soil (Aquic Argiudoll). Increasing soil K increased root and shoot growth but had a variable effect on net nutrient influx and plant nutrient content. Increasing soil bulk density reduced root growth, shoot growth, and nutrient composition of shoots but increased net nutrient influx. The detrimental effect of increasing soil bulk density on shoot growth and nutrient status of soybean plants may have been caused by decreased root growth, coarser roots, and lower root surface area/g shoot. Changes in nutrient influx and root surface area/g shoot in some cases counteracted each other in determining plant nutrient status.
An Analysis of Temporal and Regional Variation in Wheat Yields1
Authors: Feyerherm A. M. , Paulsen G. M. 
Published: July 2010

AbstractThe important meteorological and agronomic factors contributing to variation in grain yields over large areas are generally known, but their relative impact on temporal and regional variation has not been generally quantified. In any given year, one or more factors may be given undue credit for high or low yields. This investigation determined the contribution of certain meteorological and agronomic variables to variation in grain yields of fall and spring‐planted wheat (Triticum aestivum L. and T. durum Desf.) on a large‐area basis.We previously developed a winter wheat (WW) and a spring wheat (SW) model to predict grain yields over large areas without the benefit of direct measurement of plant characteristics. The derived relations of meteorological events, applied N, and certain soil characters to yield were considered to be universally applicable temporally and globally. In this study, we applied the models to different years (1955 through 1976) and regions in the U.S. Great Plains and Corn Belt.For WW in semiarid regions of the U.S. Great Plains, soil moisture deficiencies were more important than high temperatures or excessive precipitation as a yield determinant but, for SW, high temperatures were more important than soil moisture‐related variables. During 1955 to 1976 weather conditions for WW yields were poorest during 1956 and best during 1973. Weather conditions for SW yields were poorest during 1961 and best during 1958.Increases in WW yields between 1955 and 1976 attributed to applied N varied from 1.0 quintals/ha in semiarid zones to 2.9 quintals/ha in the more humid Corn Belt. Increases attributed to higher‐yielding cultivars ranged from 7% in the Southern Plains to 25% in the Corn Belt for WW and from 15% in the western portion to 25% in the eastern portion for SW.Yields of WW over the 22‐year period averaged 9.8 quintals/ha higher in the Corn Belt than in the Southern Plains. That difference was attributed to more favorable weather, heavier applications of N, higher‐yielding cultivars, and better soils in the Corn Belt. The difference would have been larger were it not for irrigation in the Southern Plains. Higher yields in the eastern SW region were attributed to more favorable weather, better soils, and higher‐yielding cultivars.
Germination of Great Basin Wildrye Seeds Collected from Native Stands1
Authors: Young James A. , Evans Raymond A. 
Published: July 2010

AbstractGreat Basin wildrye (Elymus cinereus Scribn. & Merr.) is a valuable forage species adapted to saline/alkaline and upland soils on western North American rangelands. Currently, selections are being evaluated for release as cultivators. Germination under high osmotic stress is an important factor in these evaluations. We collected seeds from widely differing habitats and germinated them under osmotic potentials varying from 0 to −16 bars. Osmotic potentials were reduced either with polyethylene glycol (PEG) or NaCl. Under reduced osmotic potentials, germination was strongly negatively correlated with the electrical conductivity (EC) and sodium‐absorption ratios (SAR) of the surface soils where the seeds had been produced. Seedling emergence and growth in a saline/alkaline soil (aquic Durorthidic Torrorthent) were better with seeds produced from plants growing on nonalkaline upland soils than from those growing on saline/alkaline soils. There was no marked correlation between germination with no osmotic stress, seed weight, or percent fill and the characteristics of the soil where the seeds had been produced. It would seem that plants of Great Basin wildrye adapted for growth on saline/alkaline soils produce seeds ill adapted for germination in this environment. Conversely, seeds produced from plants growing under nonalkaline conditions are more adapted to germinate in saline/alkaline soils.
Anthracnose Development on Annual Bluegrass in Response to Nitrogen Carriers and Fungicide Application1
Authors: Danneberger T. K. , Vargas J. M. , Rieke P. E. , Street J. R. 
Published: July 2010

AbstractAnthracnose caused by Colletotrichum graminicola (Ces.) Wils., is a serious disease of annual bluegrass (Poa annua L.) turf. In the northern and pacific‐northwestern United States, annual bluegrass is the predominant golf course turfgrass and in some instances the main turfgrass species of home lawns. In turf, cultural practices are effective ways of controlling many turfgrass diseases. However, no reports are available on cultural practices that may reduce or control anthracnose development on annual bluegrass. The purpose of this study was to look at one cultural practice, N fertilization, along with fungicide treatments for controlling anthracnose. A field study was initiated in November of 1979. Three N carriers (isobutylidene diurea, sulfur‐coated urea, and urea), applied at two rates (1.46 kg N/are/year and 2.92 kg N/are/year) and two timings spring (April initiation) and summer (June initiation), with or without fungicide treatments were evaluated for anthracnose control. Triademefon [1‐(4‐Chlorophenoxy)‐3,3‐dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone] fungicide treatments provided the most effective management of anthracnose. Fungicide treated plots averaged 1.9 and 1.7% infected area for 1980 and 1981 whereas non‐fungicide treated plots were 29.6 and 30.6% infected, respectively. Type of N carrier, whether isobutylidene diurea (IBDU), sulfur‐coated urea (SCU) or urea, had no effect on anthracnose development. Moderate N levels (1.46 kg/are/year) were associated with less disease incidence than the higher level of N (2.92 kg/are/year). Nitrogen applications during the months of June, July, August, September, and November resulted in less disease than N applied in April, May, June, August, and September. Growth chamber inoculation studies showed the number of acervuli formed decreased with increasing N at 22 C. At 32 C, the number of acervuli decreased with increasing N to 0.90 kg/ are but increased at the 1.80 kg/are N rate. In conclusion, N fertilization program of applying moderate levels of N (1.46 kg/are/year) with applications beginning in June followed with applications in July, August, September, and November at 0.24, 0.24, 0.24, 0.24, and 0.48 kg N/are, respectively, resulted in less anthracnose damage than the higher level of N (2.92 kg/are/year) or the alternate application schedule (April, May, June, August, September). If the N program was combined with fungicide applications, anthracnose was effectively controlled.