Yield-scaled global warming potential from N2O emissions and CH4 oxidation for almond (Prunus dulcis) irrigated with nitrogen fertilizers on arid land

Abstract

The optimum yield-scaled global warming potential (GWP) of perennial crops on arid land requires effective strategies for irrigation and fertilization. In 2009–2010, N2O emissions and CH4 oxidation were measured from an almond [Prunus dulcis (Mill.) D.A. Webb] production system irrigated with nitrogen (N) fertilizers. Individual plots were selected within a randomized complete block design with fertilizer treatments of urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN). Event-related N2O emissions from irrigation and fertilization were determined for seasonal periods of post-harvest, winter, spring and summer. Peak N2O emissions in summer occurred within 24h after fertilization, and were significantly greater from UAN compared to CAN (p<0.001). Cumulative N2O emissions from UAN were on average higher than CAN though not significantly different. Air temperature, water-filled pore space (WFPS), soil ammonium (NH4+) and soil nitrate (NO3−) showed significant positive correlation with N2O emissions and significant negative correlation was found for the number of days after fertilization (DAF). The percentage of N2O loss from N fertilizer inputs was 0.23% for CAN and 0.35% for UAN while CH4 oxidation offset 6.0–9.3% of N2O emissions. Total kernel yield was not significantly different between fertilizer treatments. Yield-scaled GWP for almond from CAN (60.9kgCO2eqMg−1) and UAN (91.9kgCO2eqMg−1) represent the first report of this metric for a perennial crop. These results outline effective irrigation and fertilization strategies to optimize yield-scaled GWP for almond on arid land.