DESIGNED EXPERIMENTS IN THE PRESENCE OF SPATIAL CORRELATION

Soil heterogeneity is generally the major cause of variation in plot yield data and the difficulty of its interpretation. If a large degree of variability is present at a test site, some method of controlling it must be found. Controlling experimental variability can be achieved either by good experimental design or by analysis procedures which account for the spatial correlation. Classical designs are only moderately equipped to adjust for spatially correlated data. More complex designs including nearest neighbor designs, Williams designs, and certain restricted Latin square designs are developed for field experimentation when spatial correlation causes classical designs to be less desirable . The designs, both classical and nearest neighbor type designs, are analyzed using the classical statistical analysis approach and a strategy using general linear mixed models which takes into account that there is spatial correlation present. The results indicate that properly designed experiments may be analyzed either by the usual statistical techniques or more complex methods which adjust for spatial correlation. However, if no serious thought is used in constructing the design of the experiment then the usual analysis techniques are no longer valid

ANALYSIS OF SPATIAL VARIABILITY USING PROC MIXED

Many data sets in agricultural research have spatially correlated observations. Examples include field trials conducted on heterogeneous plots for which blocking is inadequate, soil fertility surveys, ground water resource research, etc. Such data sets may be intended for treatment comparisons or for characterization. In either case, linear models with correlated errors are typically used. Geostatistical models such as those used in kriging are often used to estimate the error structure . SAS PROC MIXED allows the estimation of the parameters of mixed linear models with correlated errors. Fixed and random effects are estimated by generalized least squares. Variance and covariance components are estimated by restricted maximum likelihood (REML) . The purpose of this presentation is to show how PROC MIXED can be used to work with spatial data. Several examples will be presented to illustrate how various analyses could be approached and some of the pitfalls users may encounter

Accumulation and Release of Nutrients by Immersed Stalks Collected on Selected Dates Following Harvest

The concentrations of phosphorus (P) and nitrogen (N) in runoff from cropland areas may be influenced by accumulation and release of P and N by stalk residues. A laboratory study was conducted to measure the effects of time since harvest and immersion period on accumulation and release of P and N by corn, soybean, and wheat stalks. Experimental variables included type of stalk material (corn, soybean, and wheat), time since harvest (six residue collection dates over an approximate 1-year period), and stalk immersion period (25 s (0.42 min), 250 s (4.2 min), 2500 s (42 min), 25,000 s (6.9 h), and 86,400 s (24 h)). The initial concentration of each of the P and N constituents in a test solution was 6 μg mL−1. The soybean, wheat, and corn residue released PO4-P at mean rates of 40, 69, and 141 μg g−1 residue, respectively. The amount of PO4-P that was released consistently increased as immersion period became greater. Corn and wheat residue either accumulated or released NO3-N depending on residue collection date. Soybean residue accumulated an average of 20 μg NO3-N g−1 residue. Wheat residue obtained on five of the collection dates accumulated an average of 13 μgNO3-N g−1 residue. Residue collection date also influenced accumulation of NH4-N by soybean and wheat residue. Corn residue released an average of 77 μg NH4-N g−1 residue. The type of crop residue material, the amount of time the residue has remained in the field following harvest, and residue immersion period were found to influence nutrient concentrations of solution

Narrow Grass Hedge Effects on Nutrient Transport Following Compost Application

The placement of stiff‐stemmed grass hedges on the contour along a hillslope has been shown to decrease nutrient transport in runoff. This study was conducted to measure the effectiveness of a narrow grass hedge in reducing runoff nutrient transport from plots with a range of soil nutrient values. Composted beef cattle manure was applied at dry weights of 0, 68, 105, 142, and 178 Mg ha-1 to a silty clay loam soil and then incorporated by disking. Soil samples were collected 243 days later for analysis of water‐soluble phosphorus (WSP), Bray and Kurtz No. 1 phosphorus (Bray‐1 P), NO3-N, and NH4-N. Three 30 min simulated rainfall events, separated by 24 h intervals, were then applied. The transport of dissolved phosphorus (DP), total P (TP), NO3-N, NH4-N, total nitrogen (TN), runoff, and soil erosion were measured from 0.75 m wide × 4.0 m long plots. Compost application rate significantly affected soil measurements of WSP, Bray‐1 P, and NO3-N content. The transport of DP, TP, NO3-N, NH4-N, TN, runoff, and soil erosion was reduced significantly on the plots with a grass hedge. Mean runoff rates on the hedge and no‐hedge treatments were 17 and 29 mm, and erosion rates were 0.12 and 1.46 Mg ha-1, respectively. Compost application rate significantly affected the transport of DP, TP, and NO3-N in runoff. The experimental results indicate that stiff‐stemmed grass hedges, planted at selected downslope intervals, can significantly reduce the transport of nutrients in runoff from areas with a range of soil nutrient values

EMISSION OF VOLATILE ORGANIC COMPOUNDS FROM LAND-APPLIED BEEF CATTLE MANURE AS AFFECTED BY APPLICATION METHOD, DIET, AND SOIL WATER CONDITION

Land application of beef cattle manure may result in the emission of volatile organic compounds (VOC). This study was conducted to evaluate the effects of diet, land application method, soil water condition, and time since manure application on VOC emissions. Manure was collected from feedlot pens where cattle were fed diets containing 0%, 10%, or 30% wet distillers grains with solubles (WDGS). The effects of manure application method (surface-applied or incorporated) and soil water condition (saturated or wet) on VOC emissions were measured over a 48 h period. Heptanoic, hexanoic, isobutyric, and isovaleric acids contributed 23.5%, 17.6%, 9.26%, and 3.39% (0.034, 0.258, 0.030, and 0.014 g m-2 min-1), respectively, to total odor activity values (OAV). The aromatics indole and skatole contributed 14.7% and 8.84%, (0.005 and 0.0004 g m-2 min-1), respectively, to total OAV. Dimethyl disulfide (DMDS) contributed 9.50% (0.013 g m-2 min-1) and dimethyl trisulfide (DMTS) contributed 5.68% (0.030 g m-2 min-1) to total OAV. Emissions of the sulfur compounds (DMDS and DMTS) were substantially greater for the 30% WDGS diet. With the exception of heptanoic acid, flux measurements were greater from the plots where manure was surface-applied than from the plots where manure was incorporated. Emissions of each VOC were greater on the first day following manure application when a saturated soil water condition was present. VOC flux values were found to rapidly decrease following manure application. Effective best management practices for reducing VOC emissions are to incorporate manure soon after application and to delay land application when there is a high probability of rainfall

Tridimensional Regression for Comparing and Mapping 3D Anatomical Structures

Shape analysis is useful for a wide variety of disciplines and has many applications. There are many approaches to shape analysis, one of which focuses on the analysis of shapes that are represented by the coordinates of predefined landmarks on the object. This paper discusses Tridimensional Regression, a technique that can be used for mapping images and shapes that are represented by sets of three-dimensional landmark coordinates, for comparing and mapping 3D anatomical structures. The degree of similarity between shapes can be quantified using the tridimensional coefficient of determination (R2). An experiment was conducted to evaluate the effectiveness of this technique to correctly match the image of a face with another image of the same face. These results were compared to the R2 values obtained when only two dimensions are used and show that using three dimensions increases the ability to correctly match and discriminate between faces

ESTIMATING THE CONTRIBUTION OF SPECIFIC WHEAT VARIETIES TO STATE-LEVEL PRODUCTION

This paper addresses measurement issues involved in estimating the benefits from a university wheat breeding program. The conceptual foundation is to estimate the spatial distribution of farm-level yields for varieties in each year, based on Nebraska winter wheat variety test data from 1972 to 2001, with 9-20 locations per year. We can then estimate the state average yield difference that would occur between the portfolios of varieties that farmers actually grew, and the portfolio of varieties excluding those varieties from the university breeding program. This paper reports estimates of the statewide annual yields of individual varieties using a standard fixed effect model, and with anisotropic power as spatial covariance structure. The results indicates that UNL-developed varieties added significant production increases until the mid 1990\u27s when their portfolio advantage diminished due to the introduction of several high yield private varieties. The lump sum direct producer benefit of the Nebraska varieties is estimated to be about $7 million per year in Nebraska during the 1972-2001 period. Incorporating the spatial structure on variety test data, our estimated producer benefit are about 20% higher than if spatial structure had been ignored

Solar earth‑water distillation for wet sand

Solar earth-water distillation is a means of extracting moisture from an earth medium. Three designs of the hot-box type of solar earth-water still were tested using wet or saturated sand. The designs included: low height with reflective interior siding, tall height with reflective siding and tall height with absorptive siding. The daily volume of distillate from different designs was compared. A twenty-centimeter-tall still with reflective siding produced significantly greater yields than one twice as tall. No significant difference in the yield between tall stills with light-absorptive versus light reflective interior siding was found. A regression equation was developed to predict water production for a low still with reflective siding and a sixteen-degree cover slope. Independent variables included soil moisture, solar radiation and maximum and minimum daily temperature

Influence of Sorghum Wax, Glycerin, and Sorbitol on Physical Properties of Soy Protein Isolate Films

Sorghum wax, sorbitol, glycerin, and soy protein isolate (SPI) composite films were prepared. Effects of sorghum wax, sorbitol, and glycerin concentrations on various films were evaluated using response surface methodology. All independent variables significantly (P \u3c 0.05) affected film water vapor permeability (WVP), tensile strength (TS), elongation at break (E), total color difference, and total soluble matter (TSM). Increasing the sorghum wax concentration decreased WVP and E. As sorbitol content increased in the composite films, WVP and TS increased. Sorbitol had a critical point of 2–5 g/5 g SPI for low values of TSM. The addition of sorbitol contributed more to the properties of the film than did glycerin

Vancomycin minimum inhibitory concentration is not a substitute for clinical judgment: Response to healthcare-associated ventriculitis and meningitis

To the Editor—We read with interest the new clinical practice guideline for healthcare-associated ventriculitis and meningitis published in Clinical Infectious Diseases [1]. The guideline recommends consideration of alternative therapies for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) meningitis and ventriculitis for isolates with a vancomycin minimum in-hibitory concentration (MIC) ≥1μg/mL. We believe this recommendation places inappropriate emphasis on a single determinant of antimicrobial therapy that has uncertain clinical relevance and variable accuracy depending on the antimicrobial susceptibility testing (AST) method used. This may lead clinicians to use less well-evidenced strategies in cases likely to respond to vancomycin