1. Use of Slow Release Nitrogen Fertilizer and its effect on soil quality. Soil bacterial population Hernandez, Jorge D., Garcia, Rosalia. and Lightfoot, David A. Southern Illinois University Dept. Plant Soil and Ag. Systems Carbondale, IL 62901-4415 METHODS Corn plants (Zea mays L.) was planted in a silty loam soil (pH= 6.2). Urea and Methylene-urea-triazone (and a control without nitrogen) at a rate 250 mg N kg -1 were incorporated into the soil. Soil samples close to the root zone were collected and DNA extracted. Two weeks and six weeks after N application soil sample were collected; DNA was extracted and 16 S eubacteria RNA locus was amplified using touch-down PCR (primers 341fgc and 534r). The soil community structure was determined measuring migration distance and intensity of the bands within each lane of the DGGE (denaturant gradient gel electrophoresis). The software used to determine the correct analysis of the presence of the bands was Quantity One 4.6.2 from BioRad. DGGE gel was performed with the PCR amplicons. Shannon Wiener Index was determined for colony morphology and DGGE bands. Cs Index was used to determined variation over the time of soil bacterial population INTRODUCTION Slow release nitrogen fertilizers are used to increase nitrogen use efficiency and extend N availability over a plant growing season. One formula of this fertilizer commonly used in turf and horticultural crops is Methylene-urea-triazone (MU), a polymer modified urea base fertilizer. After this compound is applied in the soil it will be subject to slow bacterial degradation, becoming available for plant uptake after hydrolysis occurs.. It is well known the restrictions of the traditional counting plate techniques, where only 1% percent of the microorganisms are cultivable HYPOTHESIS: Every change in the microbial environment leads to a change in the size and structure of soil organism community. In soils the application of the slow release Nitrogen fertilizer will lead to a shift of the microbial community enhancing the growth and establishment of species capable to degrade this type of fertilizer and change overall soil quality. The objectives of this research were to: 1) Compare different techniques of total soil DNA isolation, in the DNA quality and purity, and 2) Study the soil community shift pattern using Shannon indexes and the Dice coefficient after applying urea and methylene urea-triazone. CONCLUSIONS There was a difference between urea and the slow release fertilizer in plant response and bacterial diversity. Although for the first two weeks, DGGE did not show any difference in bacterial diversity, after six weeks differences were observed. The microorganism diversity as measured by Shannon’s index was increased in soil samples treated with MU relative to those without treatment. However, the observed change was not as remarkable as in other communities studies (Ferris and Ward, 1997; Murray et al. 1998; Nübel et al. 1999; van der Gucht et al. 2001). The increased number of bands in MU treatment is in agreement with the increased total counts of soil bacteria MU treated soils. The increment in Shannon index indicated increased numbers of species as well as increased overall diversity between 15 and 42 days. Additionally, comparison of Cs values demonstrated greater similarity of the soil samples from the second week of treatment than in those soil samples from the sixth week of treatment, indicating less variation in a smaller time frame. There is no previous research that involved time series related with N fertilizer application. The work of Koivunen (2004), shows that Agrobacterium tumefaciens is able to grow in MU but at a very slow rate. The N form of this fertilizer is lower in energetic costs compared with urea. The Cs values in these treatments were more sensitive to the presence or absence of individual bands, thus explaining the lower Cs values in MU and Urea soil samples, due to the lower number of bands observed in the control. The greater number of bands observed in MU soil samples compared to the urea and control may be due to the creation of new niches by the mix of different N substrates, allowing increased numbers of bacterial species capable of utilizing these new N sources. DISCUSSION There were no differences between the bands patterns in any treatment at 15 days (Figure 1). However, there were observed differences in the patterns of the bands among all the treatments at 42 days of sampling. The new bands are represented in red (Figure 2). The microorganism diversity as measured by Shannon’s index was increased in soil samples treated with MU relative to those without treatment. A significantly greater biological diversity was observed in the sample group with MU p>F= 0.04 (Figure 3). The increment in Shannon index indicated increased numbers of species as well as increased overall diversity between 15 and 42 days. The analysis of H' index suggested that there was a higher richness and evenness in the bacterial soil community from MU and Urea treatment than the control condition at 42 days. It was hypothesized that bacterial communities living in soils with a history of slow release fertilizer application, change more rapidly than those soils communities that never were exposed to this type of fertilizer (Koivunen and Horwath, 2004). This means that time is important for change in the soil communities, and certainly, Shannon indexes variation in this experiment reflects this theory The Cs index revealed that there were fertilizer treatment-dependent differences in the bands comprising each soil microbial population only at 42 days. Analysis of Cs values showed that the bacterial species comprising each microbial community were significantly altered by MU, p>F = 0.001(Figure 4). Fig 1. PCR DGGE banding pattern of soil samples from 15 days. This banding pattern was obtained utilizing the density trace from BioRad Software. Fig. 2 PCR DGGE banding pattern of soil samples from 42 days. Red line indicates addition of new specie., BioRad Sofware Fig. 3 Shannon Indexes (H) for characterizing soil bacterial diversity in soil treated with different N sources. Fig. 4 Cs Index is all the communities have the same pattern or species distribution. Comparison of soil bacterial diversity. Variation in Soil bacterial populations RESULTS.