Jose Guzman, Ph.D.
Education: Bachelor of Science in agronomy (December 2005)
Master of Science and Doctor of Philosophy in agronomy and soil science from Iowa State University
McNair Project: Effects of Long-Term Tillage and Nitrogen Management on Soil Physical and Chemical Properties after 23 Years of Continuous Sorghum (2004)
Mentor: David B. Mengel, Ph.D.
No-till (NT) is a conservation farming approach in terms of long-term sustainability of soil and water resources. A great deal of research evaluating tillage and nitrogen applications on soil chemical properties has been conducted with continuous corn in the Midwest, but not on continuous grain sorghum. The objective of this experiment was to examine the long-term effects of tillage and nitrogen applications on soil chemical properties at different depths after 23 years of continuous sorghum. In 1982, a split-plot experiment was established to evaluate i) two tillage methods (NT and CT), ii) N sources (urea, ammonium nitrate, and polymer coated urea), iii) and various N rates (0, 34, 67, and 134 kg ha-1). A significant tillage and depth interaction for pH, P, K, Ca, Mg, NO3-N, and total carbon was observed. NT had significantly higher concentrations of extractable P, Ca, K, Mg, in the surface 2.5 cm and higher percent total C down to 5 cm when compared to the CT treatments. Percent total carbon increased by 1.1 g kg-1 in NT treatments when compared to the CT treatments. KCl extractable NO3-N was significantly higher in CT at all depths when compared to NT treatments. Bulk density was significant lower in CT. This data illustrates the effect of tillage and nitrogen management on the soil after 23 years of continuous sorghum.