Minimizing N-losses at the orchard scale

Reduction of reactive nitrogen losses from commercial orchards as nitrate in leachates and nitrous oxide (N2O) gas is one of the most significant challenges which intensive agriculture faces in the 21st century. In this study, we aimed to quantify at the field scale nitrate losses below the root zone (>250 cm) and N2O emissions and the way it is affected by the N application rate (i.e., 3 vs. 20 applications). With the aid of static chambers and solution samplers, N2O emissions and porewater nitrate concentrations were monitored at 12 locations around a 15-year-old almond orchard in Madera county, California. Results indicated that most of the N losses occur early in the growing season (February-May) when fertilizer is applied to wet soil or during postharvest and preseason flooding events. Within the fertigation cycle, fertilizer injection at the end of an irrigation event generally resulted in lower nitrate losses below the root zone compared with fertilizer injection mid-way through the irrigation. Reduction of the applied N load by accounting for irrigation water nitrate as 1:1 equivalent to fertilizer N ensued N losses through deep leaching. Split N application (20 events) significantly lowered N2O emissions and showed a reduction in N leaching, suggesting that this method could be used to mitigate N losses from almond orchards.