Advances in Agronomy, Volume 146 is the latest in a series that continues to be recognized as a leading reference for the latest research in agronomy. Updated chapters in this new release include the Significance and Role of Si in Crop Production, National Comparison of the Total and Sequestered Organic Matter Contents of Conventional and Organic Farm Soils, Purine – N Metabolism in Drought or Salinity Challenged Food Security Crops, Plant Rooting and Cropping Systems Management to Improve N Use Efficiency, and The Important Role of Layered Double Hydroxides in Soil Chemical Processes and Remediation: What We Have Learned Over the Past 20 Years. Each volume in the evolving series contains an eclectic group of reviews by leading scientists throughout the world. As always, the subjects covered are rich, varied and exemplary of the abundant subject matter addressed by this long-running serial.