Update 2011: Nitrogen Modeling
It is important to establish spatial patterns of nitrous oxide (N2O) emissions in orchards, and to assess whether the quantity of these emmissions emitted might be substantially influenced by the microirrigation system used.
- Our findings indicated N2O emissions patterns were similar to water distribution patterns for both drip and microjet sprinkler systems. This makes sense as we are finding that soil moisture in perennial crops in Mediterranean climates is a primary variable in driving greenhouse gas emissions. This observation suggests that it might be feasible to model and estimate N2O emissions using water distribution patterns.
- Our findings also indicated that total loss of N as N2O was higher from the drip than from microjet sprinkler irrigation. Water was distributed over a larger area by the microjet sprinklers. Marked increases in N2O emission began at 50% water filled pore space (soil saturation), and it is likely that this level is met for a longer duration in the drip areas.
- A major challenge in accurately estimating of N2O emissions from orchards is the formulation of an approach to scale up chamber-based measurements to the orchard level. We have developed calculations to achieve this, which we continue to refine.
Thus, our preliminary data indicated that the use of microjet sprinklers instead of drip irrigation would reduce the N2O-N loss. It must be kept in mind, however, that we do not know how much of the N is absorbed by trees and other vegetation, or assimilated into microbial biomass and retained in soils.Fig. 1. Distribution of nitrous oxide emissions under a drip emitter following a fertigation event of 30 lbs. N per acre. The distributions of emissions shown were derived from three-dimensional fits of the Gaussian distribution. The data illustrate complexity of constraining emissions from localized fertigation events over time. Fig. 2. Examples of N2O distributions from microjet sprinkler delivered fertigation. The 3-dimensional models illustrate the complexity of constraining emissions from localized fertigation events.