Advances in Agronomy continues to be recognized as a leading reference and a first-rate source for the latest research in agronomy. As always, the subjects covered are varied and exemplary of the myraid of subject matter dealt with by this long-running serial. This volume 89 contains six comprehensive and timely reviews. Chapter 1 presents a thorough coverage of wet chemistry and state-of-the art molecular scale techniques, such as x-ray absorption fine structure (XAFS) and nuclear magnetic resonance (NMR) spectroscopies, that can be used to characterize phosphorus in organic wastes. Chapter 2 discusses the Wheat Genetics Resource Center that has served the scientific community for 25 years. These resources have been useful to scientists in 45 countries and 39 of the states in the U.S. Chapter 3 covers various aspects of the biology and management of Stevia, a sweet herb of Paraguay. Chapter 4 is a timely review of aspects of soil fertility decline in the tropics as assessed by soil chemical measurements. Chapter 5 covers nematode interactions and assessment of models for their control on crop plants. Chapter 6 presents data and algorithms on ammonia emission form animal operations, a current area of much interest in the area of environmental quality. It contains over 40 figures and 32 tables, and presents a review of the present and future status of soil science. It also offers an analysis of biodiversity in agronomy.