This volume in Advances in Agronomy contains seven outstanding reviews that discuss cutting edge developments in the crop and soil sciences. Chapter 1 addresses desertification and its relation to climate change. Chapter 2 discusses fate and transport of viruses in porous media. Chapter 3 is a comprehensive treatment of the future needs of root water and nutrient uptake modeling. Chapter 4 is a review on micronutrients in crop production, including a discussion on improving the supply and acquisition. Chapter 5 provides information on soils in tropical and temperate regions. Chapter 6 desribes free-air CO2 enrichment in agriculture. Lastly, chapter 7 discusses break crops and their application in organic agriculture. Advances in Agronomy continues to be recognized as a leading reference and a first-rate source of the latest and best research in agronomy. Major reviews deal with cutting edge issues of interest to agronomists, as well as crop and soil scientists. As always, the topics covered are varied and exemplary of the panoply of subject matter dealt with by this long-running serial. Donald Sparks is the editor and has been a president of the Soil Science Society of America. Advances in Agronomy has the highest impact factor among serial publications in Agriculture. The Science Citation Index, 1986, reports an impact factor over 2,459 and a cited half-life over 10 years.