Drip N-Fertigation Strategies To Improve Almond N Uptake, Reduce NO3- Leaching and Reduce N2O Emissions.

Nitrogen fertigation accounts for a growing fraction of agricultural N use, especially in regions where improved water efficiency is sought, such as California. “Strategies” of N fertigation should optimize crop N uptake and reduce mobile N loss through careful selection of N-source, applied N concentration, N application frequency and timing. Various strategies can be modeled using the accessible plant–scale hydrological program HYDRUS 2-D (Hanson, 2006). The work presented was carried out in an almond orchard in Belridge, California (southern San Joaquin Valley). 300 lbs N/acre were applied as UAN through aboveground drip using two schedules: current Standard Practice (4x/year) and High-Frequency Low-N (“HFLN”, 21x/year). In addition, CaNO₃+KNO₃ was applied (as a high-NO₃ alternative) within an HFLN schedule. The comparison of Standard vs. HFLN schedules of UAN application has not shown significant effects on yields and total N₂O emission, but early indications suggest greater NO₃^- leaching under Standard. The comparison of UAN vs. CaNO₃+KNO₃ under HFLN has shown lowered N₂O emissions with high-NO₃^- fertilizers, and no effects so far on NO₃^- leaching. N-applications in this project have been monitored not only with surface chambers and suction lysimeters, but with soil gas probes, temperature probes, tensiometers and a neutron probe for soil moisture. The resulting dataset allows analysis of the depths and magnitude of N₂O production and NO₃^- leaching under different practices. Ultimately the dataset is expected to serve in assessing the feasibility of an N₂O-production module for the hydrological program HYDRUS, which already serves to model crop N uptake and NO₃^- leaching.