THE LEACHING OF NITRATES FROM AGRICULTURAL SOILS DUE TO FERTILIZER APPLICATION IS CLEARLY A PROBLEM IN MANY PARTS OF THE UNITED STATES. IN CALIFORNIA, NITRATE IN GROUNDWATER IS A HEALTH RISK FOR ABOUT 250,000 PEOPLE IN THE TULARE LAKE BASIN AND SALINAS VALLEY. IN IOWA, THE DES MOINES WATER DISTRICT IS SPENDING MILLIONS OF DOLLARS TO REMOVE NITRATES IN WATER COMING FROM THE RACCOON AND DES MOINES RIVERS. THE EFFECTS OF NITRATES AND ALSO PHOSPHATE MAY BE VISUALIZED IN THE DEAD ZONE THAT FORMS AROUND THE MISSISSIPPI RIVER DELTA IN THE GULF OF MEXICO. TO MAINTAIN PRODUCTIVE AGRICULTURAL SYSTEMS THE APPLICATION OF FERTILIZER IS ESSENTIAL, BUT IT WILL BE IMPORTANT TO FIND MULTIPLE SOLUTIONS TO REDUCE THE NITRATE CONTAMINATION OF GROUND AND SURFACE WATERS. NITRIFICATION INHIBITORS MAY CONTRIBUTE TO REDUCING NITRIFICATION. HOWEVER USING PLANTS THAT EXUDE NATURAL PRODUCTS THAT INHIBIT NITRIFYING BACTERIA IS A MORE ENVIRONMENTALLY FRIENDLY AND IS MORE ECONOMICAL FOR FARMERS AND MAY BE MORE EFFECTIVE THAN THE APPLICATION OF INHIBITORS.THE RHIZOSPHERE IS THE KEY REGION WHERE PLANT ROOTS INTERACT WITH SOILS AND MICROBES TO ACQUIRE ESSENTIAL MINERALS AND WATER. SOIL ECOSYSTEMS CONTAIN ONE OF THE MOST DIVERSE ARRAYS OF MICROBIAL SPECIES THAT ARE FREE LIVING OR LIVE IN ASSOCIATION WITH PLANT ROOTS AND THEIR RHIZOSPHERE. THE CHARACTERIZATION OF THE NITRIFYING MICROBES IN SOILS AND THE OPPORTUNITY FOR BIOLOGICAL NITRIFICATION INHIBITION THROUGH ROOT EXUDATES HAS THE POTENTIAL TO INCREASE THE NITROGEN USE EFFICIENCY OF AGROECOSYSTEMS IN THE UNITED STATES BY EITHER USING SORGHUM IN ROTATIONS OR BY ENGINEERING MAIZE TO PRODUCE EXUDATES THAT INHIBIT NITRIFICATION. THIS BIOLOGICAL SOLUTION HAS THE POTENTIAL TO REDUCE NITRATE LEACHING ON OVER 100 MILLION ACRES OF FARMLAND WHERE MAIZE IS BEING GROWN. THE REDUCTION IN NITRATE LEACHING WILL REDUCE THE NEGATIVE IMPACT THAT FERTILIZERS HAVE ON WATERWAYS AND DRINKING WATER.THE RHIZOSPHERE AND THE SOIL AROUND THE ROOTS ARE THE MAJOR REGIONS FROM WHERE PLANTS ACQUIRE ESSENTIAL MINERALS AND WATER. THE RHIZOSPHERE CONTAINS MANY DIFFERENT ROOT EXUDED METABOLITES INCLUDING CARBON COMPOUNDS, HORMONES, AMINO ACIDS AND OTHER SMALL MOLECULES. RESEARCH ON HOW ROOT EXUDATES INFLUENCE THE SOIL MICROBIOME HAS THE POTENTIAL TO REDUCE THE ENVIRONMENTAL FOOTPRINT OF COMMERCIAL AGRICULTURE AND TO INCREASE THE ECONOMIC EFFICIENCY OF CROP PRODUCTION THROUGH REDUCTIONS IN FERTILIZER. LITTLE IS KNOWN ABOUT HOW PLANT ROOT EXUDATES INFLUENCE THE FUNCTION OF THE SOIL MICROBIOME AND THE EFFECT THIS HAS ON ENVIRONMENTAL PROCESSES SUCH AS NUTRIENT CYCLING. THE GOAL OF THIS PROJECT IS TO ELUCIDATE HOW THE SORGHUM ROOT EXUDATES SORGOLEONE AND STRIGOLACTONE INFLUENCE THE RHIZOSPHERE AND SOIL MICROBIAL COMMUNITIES AND HOW THIS MAY ENHANCE NUTRIENT USE EFFICIENCY AND YIELD.SORGOLEONE IS THE MAJOR ROOT EXUDATE THAT HAS BEEN SHOWN TO BE A BIOLOGICAL NITRIFICATION INHIBITOR, BUT ITS ROLE IN SHAPING THE SOIL MICROBIOME OR IN REDUCING THE LOSS OF NITROGEN FROM FIELD BASED AGROECOSYSTEMS HAS NOT BEEN DETERMINED. STRIGOLACTONE IS AN IMPORTANT ROOT EXUDATE AND PLANT HORMONE INDUCED BY PHOSPHORUS AND NITROGEN DEFICIENCY AND ACTS AS A SIGNAL FOR MYCORRHIZAL FUNGI AND PARASITIC PLANTS, BUT IT'S IMPACT ON THE BACTERIAL, ARCHAEAL AND FUNGAL MICROBIOMES AND ON NUTRIENT USE EFFICIENCY HAS NOT BEEN DETERMINED. THIS PROJECT WILL FOCUS ON HOW ROOT EXUDATES SHAPE MICROBIAL COMMUNITY COMPOSITION AND SOIL FUNCTIONAL PROPERTIES WITH EMPHASIS ON NITRIFICATION AND NITROGEN USE EFFICIENCY.