Nutrient Management Research Database

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 24 h 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 (60.9 kg CO2eq Mg−1) and UAN (91.9 kg CO2eq Mg−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.

The study was conducted in a 'Nonpareil' orchard interplanted with 'Monterey'.

• Trees were planted in 1999 into 40cm high berms at a density of 215 trees ha^-1.
• Each plot had one tree and was irrigated with micro-irrigation using two static sprinklers.  Fertilizers were injected and applied through the micro-irrigation.
• Field measurements were conducted year-round in each seasonal period.
• Two soluble fertilizer N treatments consisting of UAN (32%N) or CAN (17%N) were implemented in a randomized complete block design with 5 replicates for a total of ten sampled plots, with annual total N inputs of 224kg N ha^-1 .
• Irrigation was scheduled to meet evapotranspiration demand, with irrigations scheduled weekly in 24-h sets.  48-h sets were occasionally used to completely recharge soil moisture to 1 meter depth.
• Three chambers per plot were used for collection of N20 and CH4 gas, and more frequent samples were taken after fertilization events.
• Soils were analyzed for total organic carbon, total nitrogen, and soil pH at the end of the experiment, as well as gravimetric water content, water-filled pore space, NH₄⁺-N and NO₃^--N every day that gas was sampled.

• Almond kernel yield was not significantly different between treatments
• Higher soil temperatures led to earlier and greater peak N20 emissions.
• Peak N20 emissions from UAN in 2009 were significantly higher when compared to emissions from CAN treatments in 2009 or 2010.
• Cumulative N20 emissions ranged from .11 to .42% of the total N fertilizer input, and were not different between fertilizer treatments.
• The use of micro-irrigation combined with split N fertilizer applications result in low N losses through N20 emissions and are a potential set of strategies to lower the GWP of perennial agricultural systems.