In order to be accurate and effective, fertilizer recommendations must factor in a wide range of considerations, ranging from the site-specific to the climatic. To help guide these decisions, “the 4 R's” have been developed: Right rate, Right place, Right time, and Right form. These 4 R's can be utilized in tandem to maximize a given goal, whether that is maximum yield, maximum profitability, minimize adverse environmental effects, or perhaps a combination of factors. However, the specific recommendations will vary according to farm- or field-specific factors, such as climate, soil mineralogy, crop choice, or labor constraints. As such, it is difficult to make “best management” prescriptions across regions.
Several UC Davis researchers—Hannah Waterhouse, Martin Burger, and Will Horwath—recently investigated the 3 of the 4 R's of corn production over two years (2013-2014) on a farm near Stockton in the San Joaquin Valley. They were particularly interested in how nitrogen fertilizer rate, placement, and timing affected nitrous oxide (N2O) emissions. Additionally, they were comparing emissions and yields between drip and furrow-irrigated corn.