AGRONOMY

This is the environmental decade. Environmental quality, which translates into wise stewardship of natural resources such as soil, water, and crop germplasm, is at the forefront of our clientele's agenda and is the touchstone of the Agronomy Department's programs. Sixty-five percent of the soil surface of Illinois is covered by agronomic crops, so wise and responsible stewardship of Illinois soils and the water that runs over and through them depends upon the development and implementation of cropping-systems strategies for combining crops, soils, water, and human management skills into practices that are sustainable, profitable, and environmentally sound.

We have adhered to our mission of developing such strategies during the past two years, despite financial challenges posed by austere state budgets. Shrinking budgets have led to cancellations of vacant academic staff positions and redirection of others. Despite the financial shrinkage, which is likely to continue for the rest of this decade, there have seen some positive points. We have received program space in the newly renovated National Soybean Research Laboratory that will enlarge our capacity for interdisciplinary research on soybean improvement. Remodeling funds provided by the College of Agriculture allowed the Agronomy Department to relocate its administrative and business offices to be more accessible to relevant accommodations. Within the past 18 months, the Agronomy Department has hired four new faculty to enrich its teaching and research programs in statistics, molecular genetics and biology, weed science, and soil fertility and mineral nutrition. With these investments in new faculty, we've been able to maintain strategic strength despite the overall net loss of faculty position.

In the following sections, we provide results of some of the research our faculty has conducted with funds from the legislature, grants, contracts, and gifts. The unifying theme of this research is the sustainability, profitability, and environmental soundness of Illinois agriculture.

Crop Breeding, Genetics, and Molecular Genetics. This program area contributes fundamental knowledge and new plant varieties necessary for improvement of crop quality, pest resistance, and productivity. Research on the molecular genetics of the soybean is targeting the regulation of the flavonoid pathway, a metabolic chain which produces a host of phenolic compounds important to the functionality of foods and to plant disease resistance. This research is currently focusing on the molecular nature of mutations that control a key regulatory enzyme in the pathway that leads to production of anthocyanin pigments in seed coats. A key challenge is understanding the connection between the regulation of synthesis of anthocyanin pigments and the synthesis of cell-wall proteins that are important for the structural integrity and disease resistance of the soybean seed.

The Bowman-Birk protease inhibitor (BBI) is a major antinutritional factor in soybean seed. Utilizing a monoclonal, antibody-based assay, a total of 12,690 accessions from the soybean, wild annual soybean, and wild perennial Glycine species were tested for the absence of BBI. Seed of all soybean and wild annual soybean accessions from the USDA Soybean Germplasm Collection contained BBI. However, nulls for BBI were found in seed of several wild perennial Glycine species. The nulls identified could potentially be utilized in the production of a soybean cultivar lacking BBI, which would be more digestible to swine and poultry.

Diseases are a major problem to soybean producers. A greenhouse technique to evaluate the response of soybean plants to the causal agent of sudden death syndrome was developed and used to identify a gene for resistance, Rfs, in the soybean cultivar Ripley. New high-yield and pest-resistant cultivars released include Piatt, Spry, and Saline. Piatt has high-yield with semi-determinate growth and is adapted to central Illinois, while Spry has tall-determinate growth and is adapted to drought environments in southern Illinois. Saline is resistant to races three and four of the soybean cyst nematode.

The USDA Soybean Germplasm Collection received five hundred accessions from nine central provinces in China in 1992, which were purelined into seven hundred and thirty new entries for the Collection. This increases the germplasm in the Collection from central China fourfold and represents the largest germplasm acquisition from China in more than fifty years. The entries represent a source of new genes for protein, oil, and pest resistance.

Research on the use of molecular markers in corn breeding was expanded to evaluate clustering procedures and genetic distance measures for determining relationships among corn inbreeds. Use of molecular markers to select for several traits simultaneously was evaluated. Strains resulting from ninety generations of selection with oil contents varying from less than 1 percent to more than 22 percent and in protein content from 4 percent to 32 percent were released on a restricted basis. Markers are also being used to identify plants with high amounts of essential amino acids and families rich with specific fatty acids. By working on kernel composition traits that are associated with economic value, these results will help corn breeders release specialty hybrids with value-added traits for Illinois producers and processors.

Improved procedures for developing corn inbreeds through tissue culture procedures are being sought. Corn anther culture can be used to produce infertile haploid corn plants from developing pollen grains. A chromosome doubling method was devised whereby regenerable callus initiated from the haploid embryos formed during anther culture were treated with antimicotubule chemicals. Large numbers of doubled haploids (instant inbreeds) can be produced within about 6 months. The procedure should provide a means to shorten the normally lengthy period of inbred development.

Corn does not establish or grow well in wet soils or soils flooded after planting. The mechanisms of flooding-intolerance are being investigated. Calcium was found to be a second messenger in signaling flooding-stress in corn seedlings. By using specific antagonists and analyzing intracellular free calcium, it was demonstrated both in suspension-cultured cells and intact seedlings that calcium acts as an essential transducer of low O2 signals. In addition, cDNA and genomic clones representing genes that are selectively expressed during flooding-stress have been isolated and are being characterized.

Research using flow cytometry revealed that the nuclear DNA content of corn plants has a significant relationship with maturity and stress tolerance in this crop. This finding will have application in screening exotic corn germplasm for genomic size. Flow cytometry may provide corn breeders a new tool to use to select those germplasm lines which have the nucleotype best suited for a specific environment.

The small grains breeding program has released a high-yield oat cultivar, Brawn, and two wheat breeding lines for brand-labeling. Both wheat cultivars combine high yield with moderately high-test weight. New procedures are being developed to select for resistance to barley yellow dwarf virus, the major disease of small grains in Illinois.

Crop Physiology, Crop Biochemistry, and Weed Science. This program area provides fundamental and applied knowledge that leads to improved crop productivity, crop management strategies, and weed management. Research on photosynthesis, a key process in plant growth and yield, has revealed the central role of the enzyme rubisco activase. The regulation of this enzyme is being investigated to provide new insights into limitations of the productivity of important Illinois crops such as soybean.

Nitrogen fixation is a process that governs nitrogen accumulation and protein synthesis of soybean. The limitations to the process, which occurs in nodules on roots, are being sought. An evaluation of supernodulating soybean mutants confirmed that nitrogen fixation was greater in mutants than in normal soybean. Two recessive genes controlling nonnodulation of soybean were identified and named as rj5 and rj6. The blockage of nodulation expressed in the nonnodulation mutant was microscopically characterized as being at the stage of root hair curling. This research provides new knowledge of how root nodules form and how nitrogen fixation is regulated.

Efficient transport of mineral materials across plant membranes is important to crop yield and quality. Enzymes called ATPases regulate nutrient transport. Studies were conducted to characterize active site amino acids involved in the mechanism of both the plasma membrane H+-ATPase and +CA2+-ATPase. The plasma membrane H+-ATPase regulates nutrient uptake at the plant cell surface while the plasma membrane Ca2+-ATPase is involved in the maintenance of the low cytoplasmic Ca2+ concentration required for the function of this divalent cation in plant signal transduction. Based on chemical modification studies, it was found that an essential amino acid, tyrosine, was involved in the catalytic mechanism of the plasma membrane H+-ATPase.

Simulation models are potentially powerful tools for managing weeds with nonchemical and chemical approaches. A model was developed that allows the prediction of weed emergence in the field from measurements of temperature and rainfall. Another model, based on electric circuitry principles, was developed to predict water flow through plants. The models will be useful in determining whether chemicals are needed for weed management and if so, how herbicides move through plants to the site of action.

Herbicide-resistant weeds are becoming an increasingly important problem throughout the Corn Belt. Resistance to the popular sulfonylurea and imidozolinone herbicides is of concern to Illinois producers. A new assay to test for acetolactate synthase, the enzyme inhibited by these herbicides, has been developed to provide new knowledge of how herbicide-resistant weeds might be managed.

Soil, Crop, and Water-Management Systems. This program area provides approaches to profitably manage soil and crop systems with sustainable and environmentally sound strategies. Significant corn grain yield increases to applied N fertilizer occurred at only forty-four of seventy-seven locations evaluated over three years. Twenty-one of the thirty-three sites that did not respond to N fertilizer could be explained by factors such as previous crop, manure application, or limited yield due to drought. High P and K levels in the nonresponding sites indicated that heavy past applications of manures or other fertilizer materials may have resulted in an accumulation of organic N that is readily available to crops, but is not measured by currently available soil-testing procedures.

Field tests of contrasting tillage systems were conducted to evaluate ways to maintain or enhance productivity and to determine the extent to which productivity of eroded soils can be restored. Results indicate that productivity in a moldboard plow system may be less sustainable over time than productivity in a no-till system on a sloping and eroded soil in southern Illinois. Analysis of data from long-term tillage experiments show nonsignificant corn and soybean yield response to tillage systems including no-till, moldboard plow, chisel, and disk tillage systems.

Forage studies were conducted to study short-term and long-term autotoxicity and allelopathy using alfalfa, grasses, vetch, and weeds. Autotoxicity of exudates of different alfalfa plant parts decreased in the order of leaf, seed, whole plant, root, flower, and stem. Velvetleaf extracts are very inhibitory, while crabgrass extracts resulted in the least allelopathic effect. Knowledge of the mechanisms of allelopathy may lead to weed-management practices that are less reliant on herbicides. Further, the results clarify why poor stand of alfalfa cannot be rejuvenated by interseeding with alfalfa.

Soil Chemistry, Microbiology, Pedology, Mineralogy, and Physics. This program area provides fundamental and applied knowledge of how soils improve environmental quality by filtering chemicals and nutrients from water and detoxifying materials applied to soils in composts and landfills. Research on the impact of yard waste composting sites on air, soil, and water quality indicates that open-air composting of grass clippings can be accomplished without adverse impact on water quality and without significant odor release. Toxic metal content is very low and does not pose an environmental risk when the compost is soil-applied.

Bioremediation of pesticide-contaminated soils from agrichemical retail sites was achieved by a combination of compost addition and herbicide-tolerant plants. Microbial populations and activity, plant growth, and pesticide degradation were significantly stimulated by addition of compost to contaminated soils.

The variability of soils is a major problem in understanding how they transport water and filter out impurities. Methods for estimating the transport of water and impurities on watershed scales are based on geostatistical and stochastic streamtube concepts, and can serve as valuable tools for estimating in-situ hydraulic properties in the field. At a much smaller scale, variability of soil properties and of flow and transport processes are being investigated in connection with chemical movement into and through soil macropores such as wormholes, decayed-root channels, and shrinkage cracks. Quantifying this variability will reduce uncertainty in determining the fate and transport of agrichemicals.

The organic matter covering soil particles, or peds, may be important in how soils filter impurities out of water. Analysis of soil ped coatings indicated a significantly higher organic-matter content, but no significant increase in clay content compared to ped interiors. Sorption isotherm studies indicated that the organic-matter coatings on peds significantly enhanced sorption of hydrophobically bound pesticides.

Physical and chemical properties of soil clay minerals change significantly when the oxidation state of iron in the clay crystal is reduced. For example, reduction of structural iron in a sodium clay decreases the swelling pressure and increases the hydraulic conductivity twofold. Exchanging the clay with an organic cation decreases the swelling to about 25 percent of that of the sodium clay in the oxidized state. However, reduction of iron in this same clay increases the swelling almost tenfold. This knowledge is important in the design of clay liners to reduce leakage of toxic materials from landfills.

Investigations of the soil nitrogen cycle are important to make most efficient use of nitrogen in plant residues, manures, and applied fertilizers. Laboratory studies to compare the immobilization of ammonium and nitrate in soil showed very little difference during incubations with added glucose, whereas ammonium was immobilized more rapidly than nitrate in the absence of glucose. In a study to compare the mineralization of nitrogen from different types of plant residue, from 13 to 41 percent of the applied nitrogen was mineralized during a 4-week incubation, the proportion decreasing in the order, vetch < corn < soybean in accordance with their total nitrogen content. This knowledge is important in designing nutrient-management practices that maintain soil quality while minimizing the loss of nitrogen and other nutrients to surface and groundwater.

Research Projects

Publications

Doctor's Theses

Master's Theses

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