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PR-432

2000 Agronomy Research Report

edited by Michael Barrett

Mention of a trademark or proprietary product is for experimental purposes and does not constitute a guarantee or warranty by the Kentucky Agricultural Experiment Station and does not imply its approval to the exclusion of other products that may also be suitable.


Overview

Agronomy Research 2000: Summaries and Reports of Applied and Field Research

The Department of Agronomy of the University of Kentucky has a tradition of excellence in both basic and applied research. Basic research by faculty in the department, working in areas such as plant biochemistry, physiology, molecular biology, and genetics, has the long-term objective of increasing crop plant productivity and value.

Problem-solving applied research within the department is aimed at near-term benefits to Kentucky agriculture. In addition to research on crop productivity, another major focus of the department is research designed to preserve soil and water quality for agricultural and other uses.

The University of Kentucky recognized this unique combination of excellence in basic and applied research and its contributions to Kentucky's economy when it designated the department as a "distinguished, nationally competitive" research program and one of 20 "targets of opportunity" for the University. As such, the department is looked upon as one of the programs to help lead the way in establishing the University of Kentucky as a top 20 research university by the year 2020.

The Agronomy Research Report is published in even years to inform professional agronomists, crop producers, and crop consultants about recent developments in the University of Kentucky Department of Agronomy. While the department conducts both basic and applied research studies, this report emphasizes recent findings of applied and field experiments with importance to Kentucky agriculture. It contains brief updates on continuing projects and initial reports on recently completed studies.

Research Highlights

Examples of interesting and potentially useful accomplishments during the last year include:

New Crops: Work has been initiated with several types of novel soybean varieties, including high protein, tofu, natto, and high sucrose materials. This project is intended to assess both the comparative yield and quality of such varieties, with an eye to helping Kentucky farmers make reasoned decisions on whether or not to begin growing such novel soybean types.

No-Till Wheat: Studies at the University of Kentucky indicate that no-till wheat is beneficial and economically feasible for many growers in the state. Research is continuing on the long-term effects and Best Management Practices for no-till wheat. Long-term research has shown that both corn and soybeans, when included in a cropping system with wheat, achieve higher yields when planted after no-till wheat as compared to conventionally tilled wheat. Currently, more than 25 percent of the wheat acres in Kentucky is no-till planted.

Working with both primary wheat consulting groups in the state and with the support of the Kentucky Small Grain Growers Association, we have been conducting side-by-side comparisons of tilled and no-tilled wheat. Over the first three years of this study, we have found that no-till yields generally run between 3 and 6 bushels per acre lower than tilled yields. However, when the input costs for both systems were subjected to a partial budget analysis, no-till actually came out slightly ahead ($1.60 per acre). Since we did not factor in a dollar value for reduced topsoil erosion under no-till management, it would seem that growers should give careful consideration to this system.

In response to increased interest in no-till wheat production, no-till variety trials were grown at two locations in the state in conjunction with conventional tests in order to compare varietal performance under the two production methods. Two years of data indicate that, in general, varieties perform equally well in both conventional and no-till systems.

Corn:Recent corn-row width studies conducted in many corn-producing states have shown responses to row widths narrower than 30 inches, but these responses have occurred mostly in areas of the Central and North Central United States. After five years of research on the effect of row width and plant population on corn yields in Kentucky, there does not appear to be any advantage for 20-inch rows over 30-inch rows. The research indicated that in Kentucky, plant population is more important for obtaining high corn yields than narrow rows and that a final population of 26,000 to 30,000 plants per acre is needed for corn with a high-yield potential.

Soybean: Soybean has genes that produce a wide range of pubescence densities. Higher-than-normal pubescence reduces feeding by aphids and thus reduces the spread of soybean mosaic virus (SMV) transmitted by the aphids. However, soybean yield depression is associated with the genetic donors of the pubescence-increasing genes. We developed experimental soybean lines with increased pubescence densities but without the associated yield depression. High-yielding soybean that avoid SMV infection should be possible.

Tobacco: KT 200, a new black shank resistant burley tobacco hybrid, was released by the Kentucky-Tennessee Tobacco Improvement Initiative in April 2000. The new variety was released because of its relatively high resistance to black shank. KT 200 also has high resistance to black root rot, wildfire, tobacco mosaic virus, tobacco vein mottling virus (TVMV), and tobacco etch virus (TEV). The release of KT 200 should provide a burley variety with better resistance to black shank combined with good yield potential and resistance to TVMV and TEV.

Ten years of tobacco research has shown that topping time can affect yield. Topping at 25 to 75 percent bloom produces the best yield, but topping at bud and 100 percent bloom may reduce yield. Quality increases if burley tobacco is topped early (10 to 25 percent bloom). Late-maturing varieties tend to handle bud topping better than early-maturing varieties. Yield may be maximized at approximately 20 to 22 leaves. Leaving more leaves does not necessarily increase yield, but it may reduce weight per leaf.

Harvesting tobacco at the right time is important for maximizing yield and quality. While cutting too early significantly reduces yield, cutting too late severely degrades quality. Combined analysis of data from five locations revealed that yields increase as harvest date is delayed up to four weeks after topping. However, leaving tobacco in the field longer than four weeks does not improve yields. Research in other years has indicated that quality declines rapidly when tobacco is left standing longer than four weeks after topping.

Kura Clover: Two selection cycles were conducted for high seed and forage yields in kura clover at each of two locations: Lexington and Pittston, Kentucky. The objective was to extend the range of kura clover adaptation to more southern locations and to surface mine spoils. Those genotypes that performed well at Lexington also were high performing on the Pittston surface mine spoil. It is anticipated that another cycle of selection will be necessary before release of a new variety.

Red Clover and Ladino Clover: Red clover was more productive and less persistent than ladino clover in two identical trials at Quicksand and Lexington comparing varieties of the two species. Red clover yielded more than ladino clover at both locations, especially in dry conditions. Ladino stands were thicker than red clover at the end of 1999 at both locations.

Fescue: Studies have been ongoing since 1994 to determine the grazing tolerance of new endophyte-free tall fescues compared to endophyte-infected Kentucky 31 (Ky31+). In the first study (grazed two seasons), Cattle Club, Richmond, and Johnstone tall fescue persisted as well as Ky 31+. In the second study (grazed three seasons), Festorina, Dovey, and Barcel were equivalent to Ky31+. The presence of the endophyte did improve grazing tolerance.

Other Research: One of the benefits of no-till may be a positive change in microbial diversity and substrate use. We examined microbial community substrate use in continuous corn plots that had been in no-till or conventional-till soil management for almost 30 years. Microbial communities were distinct in each tillage practice, and no-till plots had significantly greater substrate use than conventional till plots. The data are further evidence that conservation practices benefit soil biological properties.

We determined that the concentration of fecal bacteria in runoff from poultry litter-amended no-till soils exceeded that from soils in which the litter was incorporated. However, the total fecal bacteria loss was reduced in no-till because greater water infiltration occurred in the no-till area. Poultry litter application to no-till soil was, overall, a better management practice to control fecal bacteria runoff than was incorporation by tillage.

The enterohemmorhagic Escherichia coli bacterial pathogen O157:H7 is endemic in livestock and has caused several recent deaths. We observed that O157:H7 was not inherently better at surviving in soil than a nonpathogenic E. coli strain, and both strains were sensitive to soil matric stress. Because most E. coli strains are nonpathogenic, rapid detection methods combined with conservative treatment guidelines should mitigate potential problems with O157:H7 released into the environment.

Homeowner constructed wetlands are increasingly popular on-site wastewater treatment systems. There is little information on the effect of various vegetation types on fecal coliform removal. Wetlands with cattails, fescue, mixed vegetation, or no vegetation were examined for removal efficiency. Regardless of treatment, fecal coliform reduction was greater than 90 percent during the sampling period.

We have engineered plant trichomes to accumulate a compound that increases the mortality of aphids feeding on the leaves and reduces aphid colonization of the leaf itself.

We have developed the techniques necessary to manipulate the genome of tobacco at the single cell level, so that very large numbers of potential genetic changes can be produced before the production of entire plants. As a result of this new approach, we produced several tobacco lines that have altered production of compounds that show pharmacological properties and other lines that show resistance to a herbicide.

Understanding gene regulation during plant embryo and seed development will be essential for designing molecular strategies to increase agricultural productivity. As a first step, we are isolating genes regulated by AGL15, a member of a class of regulatory factors that are often involved in critical developmental decisions.


General Research

Precision Agriculture Opportunities for Kentucky: Agronomic Research at the University of Kentucky

T.G. Mueller, R.I. Barnhisel, and S.A. Shearer

Precision agriculture is about doing the right thing, at the right time, in the right place, in the right way. Technologies employed include global positioning systems (GPS), yield monitors, geographic information systems (GIS), variable rate technologies (VRT), sensors (i.e., soil electrical conductivity), and remote sensing. The goal is to use these technologies to make better decisions about soil use and to optimize crop and soil management. Precision agricultural management is not very different from traditional management approaches. It is still about basing decisions on the best available crop and soil information, which used to be field or farm yield or fertility averages. But today with high-tech tools, yield data are being collected every 15 feet or so, and fertility samples are collected on 1- to 4-acre grids. Precision agriculture technologies are a reality on farms in Kentucky, as many of our producers are already monitoring yields and to a lesser extent conducting variable rate fertilization. Unfortunately, there are few proven methods for using these technologies.

A decision about soil use is the first that a farmer makes for a field or area within a field. Should this land be cropped? If so, with what crop or crop rotation? Certainly, traditional approaches (i.e., soil surveys) can be used successfully for aiding in decision making. These approaches are based on the principle that soil limitations dictate appropriate soil uses, unless these limitations can be overcome through management practices. Precision agriculture approaches are based on the same principle. However, yield monitoring and GIS allow farmers to quantitatively compare the economics of one decision about soil use to another. Digital soil surveys can be overlain on yield maps to explain variability; however, NRCS surveys may or may not be at the scale to explain much of the variability. Agronomy researchers are working on a project to determine whether precision agriculture technologies (i.e., electrical conductivity sensors and elevation models) can be used to make intensive (first-order) surveys more economically and more accurately.

Soil conductivity seems to be an important tool for making soil use decisions because it is related to topsoil depth and depth to bedrock. A study is under way to establish appropriate conductivity measurement protocols for Kentucky soils to explain the causes of soil conductivity variability and ultimately relate it to grain yield variability. The use of precision agriculture tools for soil use decisions has the potential for improving farm profitability. Another research project is designed to develop and evaluate statistical models for predicting soil properties across landscapes (depth of topsoil, soil organic carbon content, and clay content) as an alternative to grid-based sampling or traditional soil survey techniques. The ability to predict these variables accurately would be very useful. For example, regions near the edges of fields or along slopes with little topsoil are often low yielding and unprofitable. If these areas are removed from production, field profitability may improve. Further, if these areas are enrolled in the Conservation Reserve Program (CRP), the whole field economics will improve even more. Researchers in the Department of Agricultural Economics are developing economic decision aids that use yield maps for enrolling unproductive land into CRP. Better soil use decisions not only improve farm profitability, but they also benefit society as well. Removing highly erodible land from production conserves water and soil by reducing erosion and runoff. Adding buffer strips at field borders next to streams (riparian zones) reduces sediment, nutrient, bacterial, and pesticide losses to streams.

Precision agriculture has the potential for improving the efficiency of crop and soil management. If factors that limit productivity and profit can be identified within a field using soil sampling and digitized soils maps or making field observations with GPS, then management steps such as site-specific tillage, variable rate nutrient management, or seeding can be taken. But before soils or crops can be managed, their properties must be assessed. Faculty in the Department of Agronomy are conducting a study to determine if remote sensing can be used to predict forage quality. An investigation is under way to determine how intensively fields must be grid-soil sampled to create accurate maps of soil properties using various interpolation procedures.

There are also studies to determine whether terrain attributes can be used to enhance the predictions of soil properties, thereby improving the accuracy of grid sampling. One study is being conducted to determine the ecological patterns with which perennial weeds are distributed across agricultural fields. Understanding these patterns may help predict the probable location of perennial weeds in the future.

After a particular soil or crop condition is known, there must be some basis for management. Studies are being conducted to determine cause-effect relationships in the landscape. What causes yield variability? Is it landscape position, soil type, or chemical or physical properties? The goal of one research project is to develop an efficient method for creating "management opportunity maps" indicating the factors that likely limit yield across agricultural fields. These maps would be created with historical yield maps and soil sampling for fertility and by making field observations using soil survey techniques. If these causes are understood, then management steps can be taken to improve yields.

Plant available soil water is one of the most important causes of yield variation in Kentucky soils. It is affected by soil type and landscape position. Site-specific irrigation is one way to manage soil water differences in agricultural fields, but unfortunately irrigation is not economical in most areas of Kentucky. Another approach is to alter crop and soil management to match the soil's ability to provide water to plants. In drought-prone areas, it may be a good idea to reduce seeding rates to conserve water. Often, when water limits grain yield, other factors such as nitrogen will not limit plant growth (law of the limiting). Therefore, it may be advantageous to back off nitrogen fertilizer rates on areas that tend to be droughty. Several research projects involving Agronomy, Biosystems and Agricultural Engineering, and Agricultural Economics are evaluating the use of landscape position and soil type as a basis for variable rate seeding and nitrogen fertilization.

There are approaches that could be used for fertilizer recommendations. One approach may be to apply back to the field what has been removed during harvest. A study is being conducted to determine if nutrient removal calculated from yield maps can be used as a basis for fertilization. Another study is being conducted to determine if topographic position can be used to predict the need for starter fertilizer. This relates to soil temperature and the kinetics of phosphorous diffusion in cold soils. Another basis for fertilization is soil sampling either on grids or in zones. An experiment is being conducted to track the changes in soil fertility over time associated with variable rate fertilizer applications based on samples collected at various resolutions.

One expectation is that precision agriculture technologies will improve environmental quality. There is a study to evaluate impact of management practices on soil microbial diversity across Kentucky landscapes. The idea is that some management practices may be more appropriate on some soils or landscape positions than others.

Much of the funding for this work is from two USDA grants that were earmarked for the University of Kentucky. Other supporters include the Kentucky Corn Growers and the Kentucky Soybean Promotion Board. While we have focused on agronomic research in this publication, it is important to recognize that precision agriculture problems are multifaceted and complex and therefore deserve an interdisciplinary research approach. Our colleagues in the departments of Biosystems and Agricultural Engineering and Agricultural Economics are involved with many of our research projects but are also conducting their own precision agriculture research.

Table 1. Researchers at the University of Kentucky who are actively involved in precision agriculture research.
AgronomyAgricultural EngineeringAgricultural Economics
Morris BitzerTom BurksDave Debertin
Richard BarnhiselJohn FultonCarl Dillon
Chad BromerSam McNeillSteve Isaacs
Mark CoyneScott ShearerRon Fleming
John GroveTim StombaughJeremy Stull
Than HartsockJoe Tarraba
Steve HigginsLarry Wells
Tasos Karathanasis
Tom Mueller
Lloyd Murdock
Grant Thomas
Jim Thompson
Mike Collins
Ken Wells


New Crop Opportunities for Specialty Grains

L.J. Grabau

The University of Kentucky College of Agriculture has just received a $556,000 federal grant from the USDA to focus on new crop opportunities in both horticultural and agronomic crops. The emphasis of the horticultural projects will be on specialty peppers, blackberries, nursery plants, and greenhouse plants. Meanwhile, the agronomic emphasis will be on novel types of corn, soybean, and wheat. The overall goal of this "New Crops" project is to enhance the profitability of Kentucky crop enterprises by opening up new, value-added markets for plant products. The agronomic group has chosen to work with the three primary grain crops, reasoning that Kentucky farmers are quite experienced in producing these commodities and will be able to quickly pick up the limited number of new adaptations required to make the specialty grain crops work well for them. Cooperating with agronomy faculty in this sustained effort will be faculty from Biosystems and Agricultural Engineering, Entomology, and Agricultural Economics.

While it is obvious that Kentucky's tobacco producers are under severe pressure, it is also true that the commonwealth's grain producers are under substantial pressure. As their productivity of corn, soybean, and wheat continues to grow, global demand for these commodities has been somewhat soft. In part, this has been due to a weakening of national economies, especially in Asia. Our growers are actively searching for ways to improve the market value of the grain crops they grow. One bright spot has been for soft white winter wheat; some growers have received premiums of up to $0.60 per bushel on that wheat market class. Other examples of potential specialty grain types include high oil corn and triple-null soybean. Some such specialty grains may fit in a relatively narrow market niche (for example, tofu for direct human consumption), while others may fit into a much broader market niche (for example, livestock feed). Many of Kentucky's producers are eager to learn about potential opportunities to enhance their financial situation, and this project is designed to deliver the knowledge they need to assess such opportunities.

Market prices for corn, soybean, and wheat, which together account for nearly all of Kentucky's grain crop production, have been relatively low over the past several growing seasons. While some growers have been able to devise new combinations of inputs to reduce their production costs without incurring yield penalties, most growers are convinced that the best way to improve the profitability of their operations is to secure higher market prices for their products. The concept of "value-added" commodities has been invoked in other Kentucky industries as a means by which more of the additional product value generated through post-production processing can be captured by the state. In the case of specialty grains, the additional value is due to genetic modifications made in the crop variety prior to its planting.

Such modifications have resulted in an impressive array of specialty types of these three major grain crops. For example, soybean specialty types include clear hilum, for tofu markets; sulfonylurea tolerant soybean (STS), sold as non-GMOs to European markets; other non-GMO types, also for European markets; low saturates, high oleic acid, and low linolenic acid types, all with improved vegetable oil quality; high sucrose, low in stachyose and raffinose and good for poultry feed and human food; organically produced, high protein types, mostly for the tofu market; high oil types; natto, small seeded types for Asian markets; and triple-null lipoxygenase types, which have distinct advantages for food products. Corn and wheat have somewhat fewer available specialty types, but both have important newly emerging materials.

With so many specialty grain types being developed, it is somewhat perplexing to producers to determine which may be bona fide opportunities for their operations. They need information on both yields of the specialty types, and the stability of the particular quality factors of interest. Some specialty grains may produce slightly lower yields per unit area, and growers need to have a reliable estimate of just how much that yield penalty might be. In addition, some specialty characteristics may be sensitive to environmental conditions during the growing season. For example, low linolenic acid types may have even lower linolenic acid levels if they are produced under the warm seedfill conditions common in Kentucky. This project will provide accurate information on both the yields and selected quality characteristics of each specialty grain type tested, thus giving producers a solid information base from which to decide the sorts of specialty grain types to investigate under their own unique conditions. Growers will also need to know if they should manage specialty grain crops differently, as well as what modifications in postharvest handling might be necessary. This "New Crops" initiative is expected to provide critical information to and support for Kentucky grain producers looking to take advantage of the emerging specialty grain crops.


Agronomy Research Report 2000 for Plant Cell Biology and Gene Expression Groups

G.B. Collins, R.D. Dinkins, M.S.S. Reddy, C.A. Meurer, C.T. Redmond, and K.P. McAllister

The Plant Cell Biology (PCB) and Plant Gene Expression Laboratories (PGEL) have been active in soybean tissue culture and transformation for more than a decade. Since 1993 we have been a recognized academic leader with the formation of the United Soybean Board-funded Center for Soybean Genetic Engineering and Tissue Culture. In 1995 the PCB/PGEL Laboratories at the University of Kentucky served as the lead institution for the development of the multistate Soybean Center with the inclusion of the soybean research groups of Drs. Wayne Parrott and John Finer at the University of Georgia and the Ohio State University, respectively. This collaborative effort has led to many improvements in soybean transformation and tissue culture that have been published in peer-reviewed journals, presented at scientific meetings, and disseminated to the public via the World Wide Web (<www.ca.uky.edu/PCB> and <www.ca.uky.edu/PGEL>). This collaboration also permitted the University of Kentucky to develop and patent an improved strain of Agrobacterium tumefaciens, named KYRT1, specifically for soybean transformation.

The Center for Soybean Tissue Culture and Genetic Engineering was instrumental in the simultaneous development in 1997 of transgenic soybean carrying the Zein gene from corn for an improved amino acid profile. Initial tests of these transgenic lines under greenhouse conditions demonstrated real gains in the percentage of the sulfur containing amino acids Methionine and Cysteine (Table 1), amino acids for which soybean is deficient. The highest expressing lines of soybean carrying this genetically modified trait will be field tested at both the Lexington and Princeton research stations in 2000 for protein profile under normal production conditions. Seed derived from these field trials will be used for animal feeding trials.

Table 1. Amino acid profile of soybean lines, expressed as percentage of total.
Soybean Line DesignationAmino Acid
CysteineMethionineGlycineProlineLysine
Non-GMO Control1.60%1.88%4.07%5.31%6.93%
GMO Control1.88%2.05%3.94%5.01%6.74%
OSU Zein 41.97%2.14%4.26%5.19%6.85%
OSU Zein 102.16%2.24%3.82%5.20%7.07%
UK Zein 121.98%2.20%3.86%5.08%6.44%
UK Zein 151.84%2.11%3.92%5.00%6.64%
UK Zein 251.91%2.26%3.87%5.15%6.77%
UK Zein 292.04%2.21%4.40%5.07%7.09%

The Center for Soybean Tissue Culture and Genetic Engineering was again expanded in 1999 with the inclusion of the research laboratories of Drs. Lila Vodkin and Jack Widholm at the University of Illinois. Additional progress continues in soybean tissue culture and soybean genomics stemming from this collaborative relationship.

The Plant Cell Biology and Plant Gene Expression Laboratories have also been collaboratively active within the University of Kentucky College of Agriculture. In conjunction with the Plant Pathology research group of Dr. Said Ghabrial, we have engineered multiple lines of soybean with genes for resistance to Bean Pod Mottle Virus, a pathogen that is extremely damaging when combined with Soybean Mosaic Virus. Recent efforts using a leaf assay have demonstrated resistance to this potentially destructive virus (Table 2).

Table 2. Analysis of soybean lines transgenic for Bean Pod Mottle Virus - Coat Protein.
Soybean LineFeature
DNAProteinBPMV Resistance
GUS GeneBPMV GeneNPTII GeneMild StrainSevere Strain
T139-1++-++-
T183-1++-++-
T183-2++-++-
T200-1+-----
T407++++NA+
T477+---NA-
Note: Plant numbers 139-1, 183-1, 183-2, and 200-1 are plants demonstrating stable inheritance of the BPMV transgene. Plants 407 and 477 are still in the initially transformed plant stage and have not yet been evaluated for stable inheritance. NA indicates that the data are not yet available.

The Plant Cell Biology and Plant Gene Expression Laboratories have also been involved with all aspects of tobacco biology, from gene discovery to field trials of plants transgenic for potential agronomic traits. Tobacco has served as both target crop for genetic modification and as an ideal model system for testing transgenes destined for other plant species, such as soybean.

Our demonstrated efficiency using tobacco as a model system has resulted in a positive reputation both within and outside the university. We have provided expertise and training in tobacco transformation as a model system to other University of Kentucky laboratories, research groups from other universities, and private industry groups. This positive reputation has also made both the Plant Cell Biology and Plant Gene Expression Laboratories a highly desirable part of any campus tour for foreign government dignitaries, private company executives and scientists, visiting researchers from other academic institutions, and student (graduate and undergraduate) recruiting tours. This has provided the University of Kentucky with a platform for informing the public at large with a balanced and positive view of plant biotechnology and the benefits that it provides.

The Plant Cell Biology and Plant Gene Expression Laboratories have also made notable progress in the introgression into tobacco of genes for plant development, flowering, metabolite synthesis, pathogen resistance, and herbicide tolerance. Several field trials and greenhouse assays have been conducted with these plant lines, with many more trials ongoing or being planned.

The most recent ongoing field trials with tobacco have involved field evaluation of transgenic lines for resistance to the black shank disease-causing organism under natural conditions. This trial will be taking place in three locations throughout the state in conjunction with the University of Kentucky Tobacco Breeding group and the University of Kentucky Plant Physiology group.


Assessing Soil Fertility Map Quality in Kentucky

T.G. Mueller, S.A. Shearer, K.L. Wells, S. Adams, and A. Kumar

For site-specific soil fertility management to be beneficial to Kentucky farmers, soil properties must be known with some degree of accuracy. A study of map quality for site-specific fertility management is being conducted at several locations (Calloway, Caldwell, Daviess, Hardin, Henderson, Nelson, and Shelby counties) representing important agricultural regions in Kentucky. Soil samples were taken on grids (i.e., 100-ft grid). Additional points were collected with a two-stage sampling approach (stratified-random), and these points will be used to calculate map quality (mean squared error). All samples were analyzed for pH, BpH, P, K, Ca, Mg, Zn, and OM (organic matter) by the Division of Regulatory Services. The grid data (100-, 200-, and 300-ft grids) are being interpreted using inverse distance weighted and kriging. Both procedures are used to make maps in commercial precision agriculture software. Analysis of one location indicates map quality was less than desired at the 100-ft grids (Figure 1). At lower intensities (200- and 300-ft grids), map accuracy diminished further. The industry standard 330-ft (2.5-acre) grid would not have been adequate to accurately map soil fertility in this field. The data from the other seven locations will be analyzed during the summer of 2000. We recommend to farmers and industry that when grid sampling, additional check data points be collected to estimate map quality.

For more information, contact Tom Mueller (mueller@pop.uky.edu; www.uky.edu/~mueller).

Figure 1. Plot of predicted versus measured for interpolated (kriged) soil P (lb P acre-1) using the 100-ft grid. The line represents the 1:1 line. For a good map, the data should be closely clustered along the 1:1 line. A better map was desired at the 100-ft scale.


Soil Electrical Conductivity Variability

N.J. Hartsock, T.G. Mueller, S.A. Shearer, G.W. Thomas, K.L. Wells, and R.I. Barnhisel

Commercial sensors are available that allow rapid field mapping of soil electrical conductivity; however, there has been little research in this area. This study was conducted to determine the nature and causes of soil electrical conductivity variability in Kentucky. Soil conductivity measurements were taken using a Veris® 3100 soil electrical conductivity sensor at various times on several fields representing different agricultural regions of Kentucky. Soil fertility measurements (pH, BpH, P, K, Ca, Mg, and organic matter), soil moisture (12-cm), soil temperature, topsoil thickness, penetrometer with depth, depth to fragipan, depth to clay increase, and depth to bedrock were measured on a number of points in each field. Conductivity varied in both space and time. Many of the spatial patterns that occurred were temporally stable. Conductivity was positively related to cation concentration (e.g., Ca, Mg) and soil moisture (e.g., R2=0.75, Shelby County; R2=0.48, Hardin County; Figure 1), and inversely related to depth to clay increase (e.g., R2 = 0.28, Hardin County; R2 = 0.66 Shelby County; Figure 2) and depth to bedrock (e.g., R2 = 0.33, Shelby County; Figure 3). Electrical conductivity may be useful in production agriculture because conductivity relates to factors that affect soil productivity, use, and management.

Figure 1. Plot of shallow electrical conductivity versus volumetric soil water content.

Figure 2. Plot of deep electrical conductivity versus depth to clay increase.

Figure 3. Plot of deep electrical conductivity versus depth to bedrock.


Topography and Community Substrate Use

G.W. Thomas, T. Mueller, and M.S. Coyne

The speed with which biological soil properties can respond to soil management practices and inputs is a potentially important factor in successfully implementing precision agriculture. It is critical to have quantifiable parameters that will reflect the impact of precision application or management on the biology of soil. However, several factors have prevented biological assessment of soil from playing more of a role in this new technology: biological properties have extreme spatial variability; common measurements such as microbial plate counts are insensitive and imprecise; appropriate biological criteria to map soils consistent with the goals of precision agriculture have been lacking.

Our goal was to investigate biological diversity, as quantified by community substrate use, for its usefulness in revealing mapped sites potentially amenable to change and for its relationship to other chemical and physical properties collected during assessment of sites for precision agriculture.

Community substrate use is a relatively new approach to examining biological diversity. In principle, the type and number of substrates that the microbial population in soil uses will reveal something about the diversity of that population. Low numbers of substrate use will be indicative of constrained microbial populations, while different patterns of substrate use will be indicative of distinct microbial communities.

Preliminary studies elsewhere have suggested that tillage management, soil type, N use, crop rotation, and dominant vegetation will all influence community substrate use. We have also observed that topography influences microbial substrate use. Because topography and soil type will be two of the most readily mapped and most permanent features of a landscape, we determined to examine soil biological diversity using these two features.

An exploratory study was carried out in two farmers' fields using BIOLOG GN microplates to determine the diversity of microbes as affected by soil position in the landscape. The BIOLOG GN plate has 95 separate microbial substrates that give a distinct blue color within 48 hours after inoculation with a soil slurry if the substrate is used.

In one field, located on a karstic plain, the microbes taken from depressions (sinkholes) tended to be more diverse than those taken from ridge and slope positions. In the second study, a transect taken along a drainage gradient showed more diversity in the moderately well-drained soil than in any of the soils that were more limited in drainage.

At present, a principal components analysis is being carried out on these two fields, and preliminary results show very good separation according to landscape position, giving hope that microbial diversity will be a useful tool in characterizing soils beyond chemical and physical criteria.


Vegetation Effects on Fecal Bacteria Removal in Homeowner-Constructed Wetlands

C. Potter, M.S. Coyne, and A. Karathanasis

Homeowner-constructed wetlands for on-site wastewater treatment have created considerable interest over the last several decades. Constructed wetlands duplicate processes occurring in natural wetlands where water, plants, microorganisms, and the wetland substrate purify water through several mechanisms (adsorption, precipitation, biotransformation, uptake). They are used as a secondary treatment for domestic wastewater when other forms of secondary treatment are not feasible. Constructed wetlands have been shown to treat biological oxygen demand (BOD), suspended solids, and nutrients to within required discharge ranges. Although the treatment efficiencies of constructed wetlands have great potential for reducing nutrients and bacteria, the influence that plants have on these systems still needs to be more closely examined.

The primary goal of this research was to investigate planted and unplanted constructed wetlands on the basis of treatment efficiency. Three systems planted with cattails, three systems planted with a variety of flowering plants, three systems planted with fescue, and three systems without vegetation were evaluated. Samples were collected at the inflow and outflow ends of each system and analyzed on a monthly basis for BOD, fecal coliforms, fecal streptococci, ammonium-N, nitrate-N, nitrite-N, soluble-phosphorus, pH, redox potential, and temperature. Total nitrogen, total phosphorus, and dissolved organic carbon were analyzed every other month. Here, the removal of fecal bacteria and BOD by the constructed wetland systems will be discussed.

Fecal bacteria usually do not persist long outside the gut of their host organism. Through several mechanisms, such as natural dieoff, sedimentation, and adsorption, fecal bacteria are removed from constructed wetland systems. For fecal coliforms, all systems showed approximately 90 percent removal during most months (Table 1). However, in some months several systems performed poorly. Reasons for this could include more people in the household (i.e., visitors) or inadequate water supply to the system (i.e., due to vacationing). Cattails appeared to have had the greatest treatment potential for fecal coliforms with 90.2 percent average removal. Fecal streptococci removal was greatest in the constructed wetlands planted with a variety of flowering plants (95.6 percent), followed closely by the systems that remained unplanted (94.9 percent). Cattail and fescue systems still removed almost 90 percent of the fecal streptococci (Table 1).

Table 1. Percent removal of fecal bacteria.
Wetland TypeSystemFecal ColiformsFecal Streptococci
Cattails191.481.5
286.591.5
392.595.2
Avg.90.289.4
Variety195.698.0
290.193.7
383.995.2
Avg.89.995.6
Fescue184.395.1
289.186.9
391.685.4
Avg.88.489.1
No Plants183.992.4
289.195.1
395.997.0
Avg.89.694.9

The BOD analysis began in November 1999 for most of the constructed wetland systems. To date, BOD removal tends to be sporadic among each of the wetland systems as illustrated by the cattail (Figure 1) and unplanted (Figure 2) systems. The systems containing cattails as the dominant vegetation have been the most efficient at treating BOD, with an average treatment efficiency of 71.4 percent. The systems that contain no vegetation averaged about 68.4 percent, and the systems containing a variety of plants and fescue averaged 60.8 percent and 56.2 percent, respectively. The greater removal of BOD from the cattail and no-vegetation systems may be a result of better oxygenation throughout these systems. Cattails are hydrophytes; their ability to bring large amounts of oxygen into their rooting system would result in more oxygen entering the constructed wetland. The systems containing no vegetation may have been slightly warmer and stimulated greater decomposition of dissolved organic matter within the wetland.

Data also indicate that seasonal and temperature differences play a major role in the treatment efficiency of the constructed wetland systems. The collection of data will conclude in September of 2000, by which time we hope to perceive whether any significant differences exist between the wetland types.

Figure 1. Percent biological oxygen demand (BOD) removal in cattail systems. Each bar represents a separate wetland system.

Figure 2. Percent biological oxygen demand (BOD) removal in systems with no plants. Each bar represents a separate wetland system.


Management of Seeded-Bermudagrass during the Establishment Year

G.C. Munshaw, D.W. Williams, and P.B. Burrus

A study of seeding rates and nitrogen fertility regimes was conducted using seeded-bermudagrass managed as golf fairway/athletic field turf. The objectives were to investigate how best to manage seeded-bermudagrass during the establishment year to maximize survival of the first winter. Stolon production and fitness were the response variables of most concern.

`Mirage' bermudagrass was established in the second week of June in 1998 and 1999. Seeding rates were 0.25, 0.50, 0.75, and 1.0 lb pure live seed (PLS) per 1,000 sq ft. Nitrogen was applied at a rate of 1 lb N per 1,000 sq ft either once only at establishment, or every 7, 14, or 30 days following establishment.

The percentage of plot cover was estimated visually during the establishment period. Stolons were harvested three and four months following establishment. Stolon fresh weights and mean diameters were determined. Total nonstructural carbohydrate (TNC) accumulation in stolons was measured in 1999 using stolons harvested just after plots entered dormancy for the winter.

There were no significant interactions between seeding rates and N fertility regimes in either year. The low seeding rate was significantly slower to reach full cover than the higher rates (Table 1). However, there were no differences in coverage among seeding rates at the end of both growing seasons. There were also no differences in overall turf quality among seeding rates by the end of both growing seasons. Increasing N frequencies did not result in faster plot coverage in either year (Table 1).

Table 1. Main effects of four seeding rates and four N frequencies on percent plot coverage in 1998 and 1999.
Observation DatesSeeding Rates (lb 1000 ft-2)N Frequency (days)
0.250.500.751.0Once30147
% Cover% Cover
19986/1850 b72 a65 a75 a72 a66 a63 a62 a
6/2551 b77 a76 a83 a75 a68 a75 a75 a
7/2179 b88 a87 a87 a91 a84 b85 b80 b
19997/2075 c85 b90 ab93 a84 a85 a87 a86 a
8/1388 ab86 b96 a94 ab87 a88 a93 a96 a
Values followed by the same letter within the same observation date are not significantly different (P<0.05).

The lowest seeding rate did produce significantly more stolons than the highest rate in both years of the study (Table 2). Additionally, the lowest seeding rate produced larger stolons (Table 3). There was not a significant response to N treatments in 1998. In 1999, the high N frequency produced more but smaller stolons (Tables 2 and 3).

Table 2. Main effects of four seeding rates and four N frequencies on fresh weights of bermudagrass stolons in 1998 and 1999.
Observation DatesSeeding Rates (lb 1000 ft-2)N Frequency (days)
0.250.500.751.0Once30147
grams stolon 162 cm-2grams stolon 162 cm-2
1998September harvest9.7 a8.1 b8.1 b7.7 b8.9a7.9 a8.1 a8.7 a
October harvest9.8 ab9.2 ab8.0 ab7.4 b9.2 a8.0 a9.0 a8.2 a
1999September harvest8.0 a6.5 b5.6 b5.5 b5.4 b6.8 a6.9 a6.5 ab
October harvest7.7 a6.9 a6.4 ab5.1 b5.4 b6.4 a6.9 ab7.4 b
Values followed by the same letter within the same observation date are not significantly different (P<0.05).

Table 3. Main effects of four seeding rates and four N frequencies on stolon diameter of bermudagrass at four months after seeding in 1998 and 1999.
Observation DatesStolon Diameter (mm)
Seeding Rates (lb 1000 ft -2)N Frequencies (days)
0.250.500.751.0Once30147
October 19981.2 a1.2 ab1.1 ab1.0 b1.2 a1.1 a1.0 a1.1 a
October 19991.4 a1.4 ab1.3 ab1.2 b1.5 a1.4 ab1.2 bc1.0 c
Values followed by the same letter within the same observation date are not significantly different (P<0.05).

TNC concentrations were not different among seeding rates. The intermediate N frequency (14 day) resulted in significantly higher TNC concentrations among N treatments (Table 4).

Table 4. Main effects of four seeding rates and four N frequencies on percent total nonstructural carbohydrates on dry weight of bermudagrass at four months after establishment in 1999.
Observation DatesPercent TNC of Dry Weight
Seeding Rates (lb 1000 ft -2)N Frequencies (days)
0.250.500.751.0Once30147
October harvest13.5 a13.3 a14.3 a13.1 a13.3 ab14.1 a15.2 a11.5 b
Values followed by the same letter within the same observation date are not significantly different (P<0.05).

Previous research has indicated that stolons are important structures for winter survival of bermudagrass. Results from this study indicate that turf managers choosing to use seeded-bermudagrass may improve survival of the first winter following establishment by adjusting seeding rates and N frequencies. Reduced seeding rates and judicial N applications resulted in significantly more and larger stolons and higher TNC concentrations as plants entered the first winter.


Impacts of Typical Cultural Practices on the Severity of Gray Leaf Spot of Perennial Ryegrass

D.W. Williams, P. Vincelli, and P.B. Burrus

Gray leaf spot has become a very important fungal disease of high-maintenance perennial ryegrass. Recent epidemics in central Kentucky have necessitated total renovation of large acreages of turf. Little is known about the effects of common cultural practices on the incidence and severity of this disease.

A study was conducted in 1998 and 1999 to investigate the impacts of mowing height and nitrogen fertility on the severity of gray leaf spot on perennial ryegrass managed as a golf turf. Mowing heights simulated golf fairway (0.75 inch) and golf rough (2.5 inches) systems. Nitrogen (urea) was applied as a split-plot treatment once per month 1 April through 1 September. Rates of N were 0, 0.75 and 1.50 lb N per 1,000 sq ft (M). Plots were inoculated with gray leaf spot in July of both years. The percent of each plot affected by gray leaf spot was estimated visually. Data statistically analyzed was the calculated area under the disease progress curves (AUDPC).

There were no significant interactions between mowing heights and N fertility in either year. Otherwise, the same trends were apparent in both years of the study. Mowing height had no significant effect on the severity of the disease in either year (Table 1). Increasing N rates did significantly increase disease severity in both years (Table 1).

These results indicate that turf managers may expect the disease to occur with equal frequency and severity in both heights of cut. Additionally, applications of water-soluble sources of N should be avoided prior to or during environmental conditions that are conducive to disease development.

Table 1. Area under the disease progress curves (AUDPC) for mowing heights and N fertility treatments in 1998 and 1999. Data collected by visual estimations was percent plot area affected by gray leaf spot.
TreatmentAUDPC (%-days)
Mowing Height (in.)19981999
0.751090.7a340.15a
2.501145.3a277.15a
c.v. (%)17.3038.16
LSD (0.05)833.64413.77
Nitrogen Fertility (lb N/M/month)
0.0794.9b202.87b
0.751163.7ab351.08a
1.501404.4a369.42a
c.v. (%)20.2811.48
LSD (0.05)515.4380.09
Means followed by the same letter are not significantly different (=0.05).


Strategies for the Control of Poa annua in Golf Turf

P.B. Woosley, A.J. Powell Jr., D.W. Williams, and P.B. Burrus

Poa annua continues to be one of the most persistent and hard-to-control weeds in golf turf. There are very few alternatives for selective chemical control, and most cultural practices are either not practical or less effective.

Over the past two years, the University of Kentucky has focused research on the postemergence control and prevention of seedhead formation of annual bluegrass in golf course fairways. Various plant growth regulators (PGRs) and herbicides were evaluated. Our objectives were twofold. First, we wanted to determine what available products showed postemergent control of Poa. Secondly, if a product showed activity against Poa, we wanted to determine the rate, number of applications, and timing that would show greatest Poa control. The PGRs Turf Enhancer®, Primo®, and Embark® and the herbicide Prograss® were evaluated for Poa control in perennial ryegrass and creeping bentgrass fairways.

Fall and winter applications of Prograss have been successful in reducing Poa in perennial ryegrass fairways. In our research, summer applications of Prograss did not provide annual bluegrass control. Volatility of the chemical could explain the observed poor control. However, Prograss did exhibit control of Poa when three applications were applied in late fall and winter (Table 1). Control of Poa was greater in perennial ryegrass compared to creeping bentgrass. Perennial ryegrass is more tolerant to applications of Prograss, and therefore higher rates can be applied to perennial ryegrass fairways. Herbicide injury occurred on creeping bentgrass when Prograss was applied at a high rate (2 lb ai/A or 4 fl oz/1,000 sq ft) during late fall and early winter. Poa control in bentgrass was less at high rates of Prograss compared to lower rates. Creeping bentgrass was severely injured, and Poa recovery was not hindered. It is important to note that turf quality was lower in the winter in plots where Prograss was applied compared to the check. However, by mid-spring, quality of turf where Prograss was applied had surpassed the check. Late fall and winter applications of Prograss showed Poa seedhead suppression in both perennial ryegrass and creeping bentgrass fairways.

Table 1. Mean annual bluegrass control and seedhead suppression.
ProductRateApplicationsSpecies% Poa% Seedheads
Experiment I
Check11/16, 12/18, 2/3Perennial Ryegrass43.3 a23.2 a
Prograss4 fl oz/M1.1 b0 b
Prograss8 fl oz/M0.8 b0 b
Experiment II
Check11/16, 12/18, 2/3Creeping Bentgrass38.5 a21.7 a
Prograss1.5 fl oz/M21.2 c8.6 b
Prograss4 fl oz/M26.7 b3.6 b
Experiment III
Check3/30, 5/3Perennial Ryegrass66.0 a29.0 a
Turf Enhancer0.72 fl oz/M45.8 b29.0 a
Prograss4 fl oz/M34.2 c4.1 b
Experiment IV
Check3/30, 4/20, 5/3, 6/1Creeping Bentgrass27.4 a17.2 a
Prograss1.5 fl oz/M26.5 ab14.1 a
Prograss3 fl oz/M23.4 b4.83 c
Turf Enhancer0.36 fl oz/M16.3 c9.9 b

Spring applications of Prograss did not exhibit as much control of Poa as did late fall and winter applications. Turf Enhancer showed the greatest Poa control in creeping bentgrass fairways in spring. Both Embark and Prograss effectively suppressed seedhead production. Primo and Turf Enhancer did not suppress seedheads, although Turf Enhancer did delay the onset of seedhead formation. Data from these experiments are summarized in Table 1.

Based on our results, for postemergent control of Poa in perennial ryegrass fairways, we would recommend three applications of Prograss at a rate of 1.5 lb ai/A (3 fl oz/1,000 sq ft) starting in November and continuing through February. If areas of turf are heavily infested with annual bluegrass, large areas of bare ground could occur, and therefore slit seeding with perennial ryegrass should be considered.

Since Prograss must be applied at lower rates in creeping bentgrass fairways, the product exhibits characteristics of a PGR rather than a herbicide. As a result, additional applications are likely needed to achieve adequate Poa control. A program of multiple applications at a rate of 0.75 lb ai/A (1.5 fl oz/1,000 sq ft) spaced three to four weeks apart starting in November and continuing through the spring may prove effective for Poa control in creeping bentgrass fairways. This program is currently being researched at the University of Kentucky. Positive results with multiple applications of Turf Enhancer have led us to conduct further research with this product. In addition, the PGR Proxy® is being evaluated for Poa seedhead suppression. In the future we hope to be able to evaluate these products under green height conditions.

Finally, research in characterizing the genetic diversity of annual bluegrass has been initiated. The goal of this research is to identify and characterize different biotypes of Poa. A great deal of variability can be observed in the phenotypes of annual bluegrass plants within one golf course, even within one golf green. Phenotypes range from very dense, fine texture and dark green to less dense, rough, and light-colored plants. We also see differences between time of flowering and seedhead production among plants. Some phenotypes tend to persist as a perennial while others do not. By using molecular techniques, we hope to be able to establish that different biotypes do exist or that these differences in phenotypes are a result of management. If multiple biotypes are present, further work will be conducted to describe where these biotypes are most likely to be found on a golf course. By increasing our understanding of annual bluegrass, we hope to be able to provide better tools to superintendents for controlling annual bluegrass in Kentucky golf courses.


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