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The raised cosine waveform is a common efficient waveform to control the bandwidth reduction of a communications signal at the cost of controlled Inter Symbol Interference (ISI) with relatively large Peak to Average Power Ratio (PAPR). Reducing the PAPR has been addressed extensively in the literature using methods such as the clipping and coding the data among others. In this paper, we reduce the PAPR by windowing the raised cosine waveform to minimize contributions to PAPR with minimal spectral growth. We simulate the modified raised cosine to determine the reduction in PAPR for various Quadrature Amplitude Modulation (QAM) orders and excess bandwidths.

USA is possible with conservation tillage systems, which minimize soil disturbance and maximize surface residue Improved forage management impacts on soil organic C and S accumulation (Langdale et al., 1992). In the Southern depth distribution and surface residue accumulation could be large, but detailed temporal data are not available. We evaluated the facto- Piedmont region, however, an increasing portion of land rial combination of three levels of N fertilization [inorganic, crimson supports small-farm, cattle-grazing production systems clover (Trifolium incarnatum L.) cover crop plus inorganic, and (Census of Agriculture, 1992). Despite the abundance broiler litter] and four levels of harvest strategy (unharvested, low and importance of managed pastures in the southeastern grazing pressure, high grazing pressure, and hayed monthly) on soil USA, relatively little information is available to describe bulk density, soil organic C, and total S, and surface residue C and rates of soil organic C and N accumulation under pasture S during the first 5 yr of ‘Coastal’ bermudagrass [Cynodon dactylon management systems (Schnabel et al., 2001). (L.) Pers.] management. Soil bulk density of the 0- to 6-cm depth Grazing of a forage crop compared with haying reresponded very little to management, but across treatments it deturns much of the manure directly to the land with a creased 0.06 Mg m 23 yr 21 due to increasing soil organic matter with time. Soil organic C did not respond significantly to fertilization strat- positive impact on soil organic C and N accumulation egy during the 5 yr, but total S of the 0- to 6-cm depth was greater (Franzluebbers et al., 2000), but the impact of stocking under broiler litter than under other fertilization strategies at the end density on plant productivity, soil compaction, and soil of 3, 4, and 5 yr. Low and high grazing pressure were similar in their organic C and S cycling is not well understood. Further, effect on soil organic C accumulation, averaging 140 g m 22 yr 21 . Most the impact of not harvesting forage on soil organic C

Animals influence nutrient cycling within grazed systems, and the effect may be greater with tall fescue (Festuca arundinacea Schreb.) because of endophyte-produced alkaloids that cause fescue toxicosis and alter animal behavior. Twelve grazed tall fescue pastures, established in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) soil near Watkinsville, GA were used to measure fertility (134-15-56 and 336-37-139 kg N-P-K ha -1 yr -1 ) and endophyte (low, 0 to 29% and high, 65 to 94%) effects on P and K distribution. Soil samples were collected in winter 1997 at distances of 1, 10, 30, 50, and 80 m from permanently located shade and water sources at eight depth increments down to 1.5 m. Nutrient accumulation was greatest 1 m from shade and water sources where P, K, and Mg concentrations were 1.7 to 8, 2.5 to 15, and 1.1 to L5 times greater than average concentrations at the remaining distances, depending on depth and fertility level. Accumulation of P, K, and Mg in the area 10 to 80 m from shade and water was limited. When summed for the 0- to 300-mm depth and estimated on a per hectare basis, extractable P was 64% greater in high than in low endophyte-infected tall fescue pastures at 1 m from shade and water sources (703 vs. 428 kg ha -1 , LSD = 93) and averaged 252 kg ha -1 for remaining distances. Endophyte levels did not affect K distribution and only affected Mg distribution under the low-fertility treatment. Endophyte effects accrued over a long time period, which would indicate that altering grazing and pasture management (movement of animals, fertilizer and lime applications, and location of shade and water sources) to reduce these effects would be needed only occasionally to reduce potential environmental risks.

Soil organic matter pools under contrasting long-term management systems provide insight into potentials for sequestering soil C, sustaining soil fertility and functioning of the soil‐atmospheric interface. We compared soil C and N pools (total, particulate and microbial) under pastures (1) varying due to harvest technique (grazing or haying), species composition (cool- or warm-season), stand age and previous land use and (2) in comparison with other land uses. Grazed tall fescue-common bermudagrass pasture (20 yr old) had greater soil organic C (31%), total N (34%), particulate organic C (66%), particulate organic N (2.4 fold) and soil microbial biomass C (28%) at a depth of 0‐200 mm than adjacent land in conservation-tillage cropland (24 yr old). Soil organic C and total N at a depth of 0‐200 mm averaged 3800 and 294 g m ˇ2 , respectively, under grazed bermudagrass and 3112 and 219 g m ˇ2 , respectively, under hayed bermudagrass. A chronosequence of grazed tall fescue suggested soil organic N sequestration rates of 7.3, 4.4 and 0.6 g m ˇ2 yr ˇ1 to a depth of 200 mm during 0‐10, 10‐30 and 30‐50 yr, respectively. Soil C storage under long-term grazed tall fescue was 85 to 88% of that under forest, whereas soil N storage was 77 to 90% greater under grazed tall fescue than under forest. Properly grazed pastures in the Southern Piedmont USA have great potential to restore natural soil fertility, sequester soil organic C and N and increase soil biological activity. Published by Elsevier Science Ltd.

On a watershed scale, geospatial information can be used to identify water resources that are least buffered from contamination. Implementing conservation practices at these locations may accelerate the process of increasing a watershed's ability to support its designated uses. The Upper Oconee Watershed of Georgia contains land areas devoted to poultry, dairy, and beef production. Within these historically agricultural lands, urbanization is proceeding rapidly around existing cities. Agricultural production practices are concentrated in the watershed with poultry in the headwaters area and dairy near a major lake (Lake Oconee). The objective of this research was to relate data sets representing surface water quality at selected sites throughout the watershed to the predominant land use in that portion of the watershed. The location of 550 poultry operations in the headwaters of the Upper Oconee Watershed, away from the city of Athens GA, has minimized conflicts between agricultural and urban interests. Phosphorus, nitrogen, and fecal coliform bacteria were high near the poultry production area, but were reduced within the watershed prior to reaching the intake for the municipal water supply. Athens had a large impact on surface water quality and approximately doubled the amount of phosphorus and nitrogen in the Oconee River. The Oconee River contributed approximately 70% of the water flowing to Lake Oconee. The residents of Lake Oconee have noted the 30 dairies located west of the lake impacting two relatively minor creeks flowing to the lake. These two creeks make up approximately 2.5% of the flow to the lake, but the proximity of the dairies to the lake makes losses of phosphorus, nitrogen, and fecal bacteria apparent in water samples. Fecal coliform numbers were elevated in some creeks with little agricultural or urban development. To test alternative microbial assays, surface water from a grazed watershed was compared to water from a wooded watershed. Assays for enterococci and E. coli may provide a better test for fecal contamination and allow differentiation between natural areas and areas impacted by grazing animals. Analysis of the Upper Oconee Watershed identified agricultural impacts and areas that should be priorities for natural resource management to reduce agricultural non-point source pollution. Focusing conservation efforts at these locations may prevent agricultural-urban conflict. However, the data also indicate that municipal sources of nutrients and fecal bacteria must be reduced to make significant progress in the watershed.

We review our recent experiments on the motion of ultracold sodium atoms in an accelerating one-dimensional standing wave of light. Atoms are trapped in a far-detuned standing wave that is accelerated for a controlled duration. A small oscillatory component is added to the acceleration, and the fraction of trapped atoms is measured as a function of the oscillation frequency. Resonances are observed where the number of trapped atoms drops dramatically. The separation between resonances is found to be proportional to the acceleration, and they are identified as a Wannier–Stark ladder. At higher values of the acceleration, we observe an exponential decay in the number of atoms that remain trapped as a function of the interaction time. This loss is due to quantum tunneling, and we compare the decay rates with Landau– Zener theory. We also observe oscillations in the tunneling rate as a function of the acceleration; these are due to quantum interference effects. PACS: 03.75.-b; 32.80.Pj Quantum transport of particles in spatially tailored potentials has been a topic of active research in recent years, motivated by fundamental interest and by the prospect of controlling electron motion in microfabricated devices. In the regime of quantum transport, motion is dominated by tunneling and interference over macroscopic regions of phase space, and there are many basic questions that remain to be studied. The simplest case of a periodic potential was first studied theoretically in the 1930s by Bloch and Zener as a model of electron conduction in a crystalline lattice [1, 2]. A periodic potential in ∗ Present address: Conley, Rose and Tayon, P.C., 816 Congress Ave., Austin, TX 78701, USA ∗∗ Present address: Intel Corp., 5200 NE Elam Young Pkwy, Hillsboro, OR 97124, USA ∗∗∗ Present address: Hughes Aircraft Co., 2000 E. El Segundo Blvd., El Segundo CA 90245, USA ∗∗∗∗ Present address: Department of Mathematics, CSI-CUNY, Staten Island, NY 10314, USA ∗∗∗∗∗ Correspondence to: raizen@physics.utexas.edu one dimension leads to a quantized energy structure as shown in Fig. 1 for the case of a cosine potential [3]. The levels are broadened into bands due to resonant tunneling between adjacent wells. As the well depth is increased, tunneling in the low-lying bands is suppressed, and particle motion is dominated by single-well dynamics. Near the bottom of the well, the harmonic approximation is valid, further simplifying the analysis. This same band structure can also be displayed in the reciprocal lattice, as shown in Fig. 2. This plot is a dispersion relation between the energy E and the quasi-momentum hk (also referred to in textbooks as the crystal momentum). As a familiar point of reference, free particle motion would be represented in this picture as a parabola, due to the quadratic dependence of energy on quasi-momentum. The parabola is distorted when the periodic potential is turned on, opening band gaps. Note that the quasi-momentum is restricted here to the first Brillouin zone [3]. The natural basis set for this problem is composed of Bloch states that are spatially delocalized. An initial atomic wave packet that is spatially localized will then spread via resonant “Bloch” tunneling. −4π −2π 0 2π 4π φ 0.0 0.5 1.0 1.5 2.0

We observe quantum tunneling of cold sodium atoms from an accelerating one-dimensional standing wave of light. Atoms are trapped in a far-detuned standing wave that is accelerated for a controlled duration. For sufficiently large values of the acceleration, we observe an exponential decay in the number of atoms that remain trapped as a function of the interaction time. We show that this loss is due to quantum tunneling, and compare the decay rates with Landau-Zener theory. We also observe oscillations in the tunneling rate as a function of the acceleration which are due to quantum interference effects.

Recycled paper treated with boric acid (BA) is gaining acceptance as bedding in broiler houses. Applying this litter to Kentucky 31 (K‐31) tall fescue, Festuca Arundinacea Shreb, pastures raises the issue of potential boron (B) toxicity. There is also the question of nitrogen (N) availability from composts made with borated paper and broiler manure. The effect of five N sources at 224, 448, and 896 kg N/ha in a factorial arrangement plus an unfertilized control and high nitrogen‐phosphorus‐potassium (NPK) + additional boron at 45 kg B/ha on growth and NPKB uptake of K‐31 tall fescue was determined in a greenhouse during the spring of 1992. The five N sources were (1) inorganic salts, (2) compost made from hen manure, broiler manure, fescue hay and bark (M1), (3) fresh broiler litter (M2), (4) compost made from broiler manure and borated paper bedding (M3), (5) compost from hen manure, oak leaves, broiler litter (M4). The soil was Cecil sandy clay loam subsoil. Six harvests were made at 4‐cm cutti...

Recycled paper treated with boric acid (BA) is gaining acceptance as bedding in broiler production houses. Applying this litter, or compost made from this litter, to turf raises an issue of boron (B) toxicity. There is also the question of nitrogen (N) availability from composts made from borated paper and broiler manure. The objective of this study was to determine if broiler house litter containing recycled BA‐treated paper poses a toxicity hazard to bermudagrass turf (Cynodon dactylon L. pers x C. Transvaalensis, Burtt‐Davis) when applied at agronomic N rates. The effects of five N sources at rates equivalent to 224, 448, and 896 kg N/ha in a factorial arrangement plus an unfertilized control and a high nitrogen‐phosphorus‐potassium (NPK) treatment with B at 22 kg B/ha on bermudagrass were determined in pot culture during the summer of 1992. The five NPKB sources were (M1) compost made from broiler manure, BA‐treated paper and yard refuse; (M2) fresh broiler manure with BA paper bedding; (M3) ...

We report observation of Wannier-Stark ladders with ultracold sodium atoms in an accelerating one-dimensional standing wave of light. Atoms are trapped in a far-detuned standing wave that is accelerated for a controlled duration. A small oscillatory component is added to the acceleration, and the fraction of trapped atoms is measured as a function of the oscillation frequency. Resonances are observed where the number of trapped atoms drops dramatically. The separation between resonant peaks is found to be proportional to the acceleration. We show that this resonant structure can also be understood as a temporal quantum interference effect. [S0031-9007(96)00369-9]

Time-dependent Hamiltonian dynamics exhibit a wide range of novel effects in both classical and quantum domains [1,2]. Possibly the simplest time-dependent potential is the turning on and off of an interaction, though even here our intuition is clear only for the two extreme cases of fast passage and adiabatic interactions. Since the majority of cases fall between these two limits, it is important to develop a clear understanding and simple physical pictures at intermediate time scales. We show that when the interaction is nonlinear, the mere act of turning on and off a potential in this intermediate regime can lead to classical chaos. Further, we provide a clean experimental demonstration of the classical mechanism of resonance overlap [3 ‐ 5] which leads to classically diffusive growth. This general problem is posed in the context of atom optics with ultracold atoms. The nonlinear interaction is a single pulse of a one-dimensional standing wave of light. This type of time-dependent interaction is ubiquitous and occurs, for example, whenever an atomic beam passes through a standing wave of light. The starting point for this discussion is the model of a two level atom (transition frequency v0) interacting with a standing wave of near-resonant light (frequency vL) which is turned on and off with a time-dependent function fstd. For sufficiently large detuning dL › v0 2v L(relative to the natural linewidth), the excited state amplitude can be adiabatically eliminated [6], leading to a Hamiltonian for the ground state H › p 2 y2M 2 s ¯ hVeffy8df std cos2kLx.

The logistic model has proven very useful in relating dry matter production of forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant ? accumulation through a common response coefficient c. The objective of this analysis was to establish the validity of the extended model for each of the three major nutrients (?, ?, ?), with a common coefficient c between dry matter and each applied nutrient. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant nutrient removal, and plant nutrient concentration to applied nutrient, with overall correlation coefficients of 0.9928, 0.9972, and 0.9975 for applied N, P, and K, respectively. Furthermore, the model closely described the relationship between yield and plant nutrient removal, as well as between plant nutrient concentration and plant nutrient removal, for each nutrient. This work confirmed earlier results for applied ? with various grasses a...

Dry matter yields and plant nutrient uptake of forage grasses are influenced by levels of applied nitrogen (N), phosphorus (P), and potassium (K). Response to one element generally depends on levels of the other two. In this article, a mathematical model is presented which includes the major elements, N, P, and K as inputs. It consists of triple logistic equations with a total of thirteen parameters. The model is evaluated for Kentucky 31 (KY 31) and Kenwell tall fescue (Festuca arundinacea Schreb.) grown at Watkinsville, GA on Cecil sandy loam (clayey, kaolinitic, thermic, Typic Hapludult). Procedures are described for parameter estimation. The model provides high correlation between yields and plant uptake of N, P, and K with applied N, P, and K for both cultivars of tall fescue, as demonstrated in response graphs and scatter diagrams. Intercept and N response coefficients from this study agree closely with those from previous work. Data from this study support the hyperbolic relationship betwe...

The logistic model has proven very useful in relating dry matter production of warm season perennial forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to apply the extended logistic model to cool season Gulf annual ryegrass (Lolium multiflorum Lam.) and to establish a common response coefficient c between accumulation of dry matter and plant N. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and plant N concentration to applied N, with an overall correlation coefficient of 0.9954. Furthermore, the model closely described the relationship between yield and plant N removal, as well as between plant N concentration and plant N removal. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to estimate yields and plant N removal in evaluation of agricultural production and environmental quality.

Models provide a quantitative means to describe response of forage grass to applied nutrients. An extended NPK model of forage grass response to applied nitrogen (N), phosphorus (P), and potassium (K) is presented, which provides estimates of dry matter yield and plant nutrient uptake, as well as plant nutrient concentrations. Yield and plant nutrient uptake are each estimated by logistic equations. Plant nutrient concentration is defined as the ratio of plant nutrient uptake to yield, and thus involves the ratio of two logistic equations. For fixed levels of two of the three nutrients, the equations reduce to the simple case for a single nutrient, developed in previous articles. A rigorous procedure was developed for estimating the model parameters, which was then applied to field data from a complete 4 ¥ 4 ¥ 4 factorial of N ¥ P ¥ K for Coastal bermudagrass on a Cecil sandy loam. It described data from the field study rather well, with scatter diagrams which gave correlation coefficients of 0.98, 0.98, and 0.97 between estimated and observed plant uptake of N, P, and K, respectively. Estimated maximum potential yield of 29.8 Mg/ha was close to the value 30.1 Mg/ha measured at Tifton, Georgia. The model can be used to evaluate interactions among applied N, P, and K, and to estimate nutrient balances and sufficiency levels for the three major elements. Implementation on a pocket calculator is very simple.

We present results of a numerical calculation of gain without inversion in the transient regime. We show that atomic coherence and gain without population inversion can be induced on time scales short compared to atomic radiative lifetimes. We also describe the process in terms of transient dressed states.

A simple model is needed that relates forage grass production (yield and N removal) to management factors (applied N, harvest interval, and water availability). The objective of this analysis was to extend a previous model to include quantitative coupling between yield and N removal in response to applied N for perennial grasses. The extended model was developed from three postulates: (1) annual dry matter yield follows logistic response to applied N, (2) annual plant N removal follows logistic response to applied N, and (3) the N response coefficients are the same for both. Three additional consequences derive from these postulates: (i) plant N concentration response to applied N follows a ratio of logistic functions, (ii) annual dry matter yield and plant N removal are related by a hyperbolic equation, and (iii) plant N concentration and plant N removal follow a linear relationship [...]

Models can be used to describe yield response of grasses to applied N and other management factors. This analysis was performed to show interactions between applied N and overseeded clover on dry matter yield, and to estimate equivalent N supplied by clover. Data from three locations were used. At Watkinsville, GA both Coastal' and common bermudagrass [Cynodon dactylon (L.) Pers.] were overseeded with crimson clover (Trifolium incarnatum L.). At Eagle Lake, TX, both Coastal bermudagrass and Pensacola' bahiagrass (Paspalum notatum Flugge) were overseeded with Yuchi' arrowleaf (Trifolium vesiculosum Savi) and Mt. Barker' subterranean (Trifolium subterranean L.) clovers. At Jat, FL both Coastal bermudagrass and Pensacola bahiagrass were overseeded with crimson clover []

Field studies on response of forage grasses to management factors (such as applied N) are generally conducted over multiple years to insure reliability of treatment responses measured. The increased number of observations enhances statistical analysis and separation of means. The question of system behavior over time naturally occurs. Data from a three year study at Watkinsville, GA with coastal and common bermuda ‐grass [Cynodon dactylon (L) Pers.] were analyzed with the logistic model to estimate approach to steady state. Model parameters (A, b, c) showed an exponential shift with time, approaching 90 % of steady state in the third year. The model provided high correlation ( R > 0.98 ) between dry matter yield and applied N.

Models can be used to estimate yield response of grasses to applied N. This analysis was conducted to show variation of model parameters among grasses at the same location and differences among locations. The logistic equation was used to relate annual dry matter yield to applied N for four locations (Blairsville, GA; Fayetteville, AR; Thorsby, AL; jay, FL) and five perennial grasses [bermudagrass (Cynodon dactylon L., Pers.), bahiagrass (Paspalum notatum Flugge), tall fescue (Festuca arundinacea Schreb.), dallisgrass (Paspalum dilatatum Poir.), and orchardgrass (Dactylis glomerata L.)] (...)

A field study was conducted from 1983 through 1986 to ascertain the effect of endophyte (Acremonium coenophialum), nitrogen fertility and tall fescue (Festuca arundiancea) genotype upon the soluble carbohydrate content of tall fescue from grazed paddocks. Non-grazed paddock exclosures were evaluated for 1984 and 1985. Plant tissues were extracted with 0·1 mol 1−1 H2SO4 to obtain acid-extractable carbohydrate (AEC). The AEC concentration and yield (concentration × dry matter) varied among and within years, generally was not influenced by endophyte, and was influenced by N fertility and cultivar. The AEC concentration from non-grazed exclosures was inversely related to AEC yield. Grazed paddock AEC concentration and yield were not significantly correlated. Grazed paddock AEC concentration remained fairly constant over the growing season, whereas AEC yield was greatest during periods of ample rainfall. The cultivar Johnstone generally had the greatest AEC concentration when compared with AU Triumph and KY-31. Even though endophyte is a carbohydrate sink, sward scale effects on AEC, as influenced by endophyte, were virtually undetected, suggesting that presence of endophyte is not detrimental to the fescue host. Grazed and non-grazed tall fescue AEC concentration and yield patterns differ and indicate the need to interpret non-grazed quality and management data carefully.

A logistic equation was used to relate annual dry matter yield of Coastal bermudagrass [Cynodon dactylon (L.) Pers.] to applied N, P, and K. Yield data from 4 × 4 × 4 (N × P × K) factorial experiment were analyzed. The second order Newton-Raphson procedure for nonlinear regression was used to estimate the seven parameters of the model. A correlation coefficient of 0.9884 was obtained with the model for the 64 data points. A response surface for yield as related to N and K at P = 100 kg ha −1 was drawn from the model. Isoquants (constant yield) were drawn for annual yield of 10Mg ha −1 (...)

Lichens are known to be bioaccumulators of atmospheric pollutants and are abundant in the Canadian arctic. Mining in this region may negatively impact the tundra communities and these impacts may be detected by increased accumulation of heavy metals, greenhouse gas constituents, and organic compounds in lichen tissue. The effect of sampling direction and distance from a diamond mine on bioaccumulation in three lichen species, Flavocetraria nivalis, Flavocetraria cucullata, and Cladina arbuscula, was investigated. Eight sample sites were located immediately adjacent to a diamond mine, one in each cardinal and ordinal direction, and six sample sites each were located 30 and 60 km from the mine (cardinal, NE, and SE). Thirty-three major and trace elements, sulfate (SO(4)), nitrate (NO(3)), ammonium (NH(4)), polycyclic aromatic hydrocarbons (PAH), and phthalates were analyzed in lichen tissue and soil. A significant interaction occurred between distance and direction from the mine. Highest concentrations of Al, Cr, Cu, Fe, Ni, Ti, and V in lichen were at the mine site regardless of direction. Highest concentrations for all other elements were at the mine in at least two directions. Although present in lichen tissue, there was no significant difference among sites for Hg, Mn, S, and three phthalates. PAHs were below detection limits in lichen tissue. The effect of direction was dependent on element and species, although concentrations of most elements were greatest east or southeast of the mine site. At distance from the mine, direction had less of an effect on concentrations. Elevated concentrations in tissue did not negatively impact lichen or plant cover or lichen richness. This research strongly suggests selection of sample sites and species can impact results and interpretation of data from air quality monitoring programs that use lichens as biomonitors.

A logistic equation was used to relate forage yield to applied N for bermudagrass [Cynodon dactylon (L.) Pers.] and bahiagrass [Paspalum notatum Flugge]. It was shown that the equation could be factored into a triple product-one term each for water availability, harvest interval and applied N. The equation provides high correlation (R ≥ 0.98) between yield and applied N for all levels of water availability and harvest interval. Appropriate statistical procedures for nonlinear regression were utilized in the analysis. These results are useful for estimating effects of management factors on forage production

Equations were developed to estimate concentration of nitrogen for bermudagrass forage [Cynodon dactylon, (L.) Pers.] as related to applied nitrogen level and harvest interval. Data from six field studies were used in the analysis. Estimates of N concentration in forage obtained with these equations agreed with data from other studies with fertilizer and waste application to bermudagrass (correlation coefficient of 0.94). Concentration of nitrogen decreased linearly with harvest interval (up to 6 weeks) and increased exponentially with nitrogen level. These equations should provide relevant information for crop production and environmental quality.

Equations were developed to estimate concentrations of phosphorus and potassium for Coastal bermudagrass [Cynodon dactylon, (L.) Pers.] as related to applied nutrient level and harvest interval. Data from several field studies were used in the analysis. Estimates from these agronomic studies agreed with data from fertilizer and waste application for several locations. Concentrations of phosphorus and potassium decreased linearly with harvest interval (up to 6 weeks) and increased exponentially with nutrient level. This information should be relevant to crop production and environmental quality.

A phenomenological simulation model of Coastal bermudagrass was previously developed. In this analysis data from four independent field studies were used to evaluate the model. Yield distributions over time plotted as straight lines on probability paper. Total yield showed a linear correlation with harvest interval. The model predicted both responses. Regression equations were used to relate each of the four model parameters to nitrogen level. Exponential dependence of mean time (T) and time spread (a) upon nitrogen was demonstrated. Dependence of the first order growth parameter (A) upon nitrogen followed the logistic function, while the curvature parameter (C) was described by the ratio of two logistic functions. The model relates dry matter yield to applied nitrogen and harvest interval. It is useful in evaluation of management alternatives for forage production. An example application is included.

An understanding of the long-term cycling of trace elements in soil with broiler litter fertilization under various forage utilization strategies is needed to develop sustainable agricultural production systems. We evaluated differences in Cu, Mn, Zn, and six other trace elements in response to 5 yr of bermudagrass [Cynodon dactylon (L.) Pers.] management varying in fertilization and harvest strategies on a Typic Kanhapludult in Georgia. Chicken (Gallus gallus) broiler litter was a significant source of trace elements that led to 3.4 +/- 0.5 times higher Cu, 2.0 +/- 0.3 times higher Mn, and 2.1 +/- 0.2 times higher Zn in the surface 3 cm of soil than when forage was fertilized inorganically. There were variable effects of broiler litter fertilization on other trace elements, depending upon element, depth of sampling, and forage utilization strategy. Concentrations of all trace elements in soil were below levels considered toxic to plants. Soil at a depth of 0 to 3 cm under grazed paddocks had 33 +/- 5% greater Cd, 18 +/- 1% greater Cr, 53 +/- 24% greater Cu, and 24 +/- 7% greater Zn compared with unharvested and hayed management. Trace elements in soil were unaffected whether forage was unharvested or removed as hay. These results suggest that broiler litter is a significant source of several trace elements and that ruminant processing of forage and subsequent deposition of excreta on the paddock allow these trace elements to accumulate more at the soil surface where they might interact with the high concentration of organic matter.

Soil data were collected from a 30 ha commercial field using a 60 m sampling grid. Monitored yield data were also collected in this field between 1996 and 1999, when it had a wheat–processing tomato–bean–sunflower crop rotation. A comparison between SSURGO–NRCS soil–unit definition and field–measured soil data showed that in this field the former are a good approximation and starting point for precision agriculture studies and management. In a second test, the EPIC model, using the SSURGO database soil type definitions, was found to reproduce the yield variability within this field with reasonable accuracy. The model’s performance was not as good when tested with data from soil samples, apparently due to the way EPIC simulates water holding capacity from texture information and the lack of some key variables (not sampled), such as water content at field–capacity (FC), wilting–point (WP), and soil saturated conductivity. A set of runs was performed to simulate the yield at 13 point–locations in the field using FC, WP, and bulk density. Although the accuracy of the simulation did not improve greatly, the model reproduced the yield trend of two of the crops (wheat and sunflower).

Models can be used to estimate yields and nutrient utilization by forage grasses. The objective of this study was to model response of three cultivars of tall fescue (Festuca arundinacea Schreb.) to applied N over a 3-yr period at Watkinsville, GA. The procedure uses analysis of variance to evaluate linear parameter A and the exponential parameters b and c for the logistic equation. It was shown that yields could be averaged across years and that all differences among cultivars could be assigned to the b (intercept) parameter. 'AU-Triumph' proved to he more efficient at converting soil N to dry matter without applied N than either 'Johnstone' or 'Kentucky 31' cultivars. Endophyte (Acremonium coenophialum Morgan-Jones & Gams) infection did not affect dry matter response relationships of Kentucky 31 [...]

In most eukaryotes, glutathione-dependent peroxidases play a key role in the metabolism of peroxides. Numerous studies have reported that trypanosomatids lack this activity. Here we show that this is not the case, at least for the American trypanosome Trypanosoma cruzi. We have isolated a single-copy gene from T. cruzi with the potential to encode an 18 kDa enzyme, the sequence of which has highest similarity with glutathione peroxidases from plants. A recombinant form of the protein was purified following expression in Escherichia coli. The enzyme was shown to have peroxidase activity in the presence of glutathione/glutathione reductase but not in the presence of trypanothione/trypanothione reductase. It could metabolize a wide range of hydroperoxides (linoleic acid hydroperoxide and phosphatidylcholine hydroperoxide>cumene hydroperoxide>t-butyl hydroperoxide), but no activity towards hydrogen peroxide was detected. Enzyme activity could be saturated by glutathione when both fatty acid and short-chain organic hydroperoxides were used as substrate. For linoleic acid hydroperoxide, the rate-limiting step of this reaction is the reduction of the peroxidase by glutathione. With lower-affinity substrates such as t-butyl hydroperoxide, the rate-limiting step is the reduction of the oxidant. The data presented here identify a new arm of the T. cruzi oxidative defence system.

The NCIMB 8052 strain of Clostridium beijerinckii contains nine copies of a novel insertion sequence, ISCb1, belonging to the IS4 family. The 1764 bp element has 18 bp inverted repeats at its extremities, and generates 11 bp target repeats upon insertion. It contains a 1365 bp ORF whose predicted product (455 amino acids) resembles bacterial transposases. The highly conserved DD(35)E motif is present, as are signatures characteristic of the N3 and C1 domains of bacterial transposases. Codon usage of the ORF is somewhat different from that of other C. beijerinckii genes, suggesting that ISCb1 may have been acquired from another organism by horizontal gene transfer in the evolutionary past. One ISCb1 copy lies close to the site of insertion of Tn 1545 in a mutant strain, C10, which shows a reduced tendency to degenerate (i.e. loss of the potential to form solvents) compared with the wild type. In the C10 strain, the characteristic pattern of DNA fragments detected by an IS-specific probe was altered, but this was due to the Tn1545 insertion itself, rather than an ISCb1-mediated genome re-arrangement. There is currently no evidence that the element is involved in strain degeneration, since 12 independently isolated spontaneous mutants that had lost the ability to form solvents had the same ISCb1 profile as that of the wild type strain. The element is apparently restricted to a series of closely related solvent-forming clostridia.

The objective of this work was to develop a model of the vertical distribution of Coastal bermudagrass at the time of harvest and to relate the distribution to dry matter production over the season. The vertical distribution of Coastal bermudagrass dry matter was shown to follow a gaussian distribution. The model contained two parameters, viz. mass density at ground level (po), and characteristic height (-Z- ')• Both of these followed a gaussian distribution over the season. Since harvest yield (Ay) was estimated from the product of po and -Z-', it followed that Ay exhibited a gaussian distribution over the season, which agreed with earlier analyses by the authors. These results are relevant to agricultural production and environmental quality, and incorporate management factors (applied N, harvest interval, and water availability) into the estimation procedures. Estimates of removal of applied N by crops require an estimate of dry matter production, which in turn varies over the growing season. The present model relates production to plant characteristics (base density and characteristic height). KEYWORDS. Coastal bermudagrass. Harvesting, Forage production. Modeling.

A study was designed to evaluate yield, quality and composition of tall fescue (Festuaa arundinaaea Schreb.) as influenced by water stress under 0, 100, and 400 kg N·ha‐1 during autumn in the southeastern U.S. Four replicates of each treatment were imposed in a completely random design in the field. The experiment was conducted in two successive years with treatments applied to an adjacent area to eliminate residual or carry‐over effects. Water status was verified by gypsum block, tensiometer, and determination of leaf stomatal resistance. Plant tissue was harvested three times during autumn and again in the following spring. Forage yield total was not significantly affected by soil water stress, apparently due to compensatory growth during recovery periods. Soil water appeared to be more rapidly depleted under 400 kg N·ha‐1 than other N treatments. Increasing N fertilizer significantly increased leaf area, leaf number, and was inversely related to the number of senesced leaves. Stomatal resistan...

On a determine les effets de deux niveaux de fertilisation et de l'infection par un champignon endophyte, chez le cultivar «Kentucky-31», sur les distributions laterale et verticale du potassium du sol apres trois ans de pâturage. On a etudie les effets du pâturage, du repos et d'autres comportements des animaux sur les transferts de potassium

ACCUMULATION of dry matter over the growing season of coastal bermudagrass follows a sigmoid distribution described by the error function. The model contains three parameters, viz. total seasonal yield, mean time and time spread. The 2nd order Newton-Raphson method proved very efficient for parameter optimization. Calibration was carried out for data from Watkinsville, GA. Experimental treatments included irrigation status, nitrogen level and harvest interval. The model described the data rather closely. Output includes harvest and seasonal yields and nitrogen accumulation. The empirical model provides a simple tool for analysis of data as related to treatment factors. It should also provide guidance in development of more comprehensive simulation models.

Small plots of Cecil soil established in Kentucky-31 tall fescue were surface applied semi-annually with 0, 22.4, 44.8, 89.6, and 134.4 metric tons/ha of broiler litter for 2 years. Potassium and magnesium were more completely leached from the litter, 99% and 88% respectively, than calcium. At the end of two years at the highest rate, 80% of the calcium remained in the litter. After each year, chemical analysis of depth-incremented soil samples, showed the extent of movement and redistribution of water soluble and exchangeable potassium, calcium, and magnesium. The results indicate that land disposal of broiler litter greatly enhances exchangeable K while reducing the exchangeable Ca and Mg.

The influence of limestone and N:P:K fertilizer rates on elemental composition of Coastal bermudagrass forage was determined to evaluate causes for high yield responses to dolomitic limestone at high N:P:K rates, as well as severe stand loss, and chlorosis of bermudagrass in the unlimed treatments. Increasing N:P:K fertilization resulted in severe Mg deficiency. Maximum yields (when limed with dolomitic limestone) were associated with Mg concentrations of 1.0 g/kg plant tops. Magnesium lost to plant removal, Mg loss to enhanced leaching under N fertilization, and K interference associated with excess K accumulation at high rates of NK inputs all contributed to Mg deficiency. However, the accumulation of excess K, which interfered with Mg uptake when high rates of N and K were applied, was considered to be the primary cause of the observed Mg deficiency.