Nitrous Oxide and Productivity Index for California Almond.

Application of nitrogen (N) fertilizers by agriculture contributes to the increase of the greenhouse gas nitrous oxide (N₂O) in the atmosphere.  In 2009-2010, an index was developed for almond [Prunus dulcis (Mill.) D.A. Webb] by taking a N₂O-N:fruit-N ratio at the tree scale.  Individual trees were selected within a randomized complete block design with fertilizer treatments, urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN).  Event-related N₂O emissions from fertilization and irrigation were determined for post-harvest (PH), bloom (BL), spring (SP) and summer (SU) seasons with significantly greater emissions from UAN compared to CAN in summer (p = <0.001).  Cumulative emissions for the 2009-2010 growing season for CAN were not significantly different than UAN (p = 0.21).  There were no significant differences between almond yield and fruit-N between the fertilizer treatments (p = 0.72).  The results were used to develop an index which, may be used as a metric to score temporal and spatial variability of greenhouse gas emissions and productivity across diverse landscapes of perennial crops.