Update 2012: Fertigation System Comparison

Objectives

Maria Mar Alsina and Anna Clara Fanton sampling for spatial patterns of N-oxide emissions at an experimental orchard site. Colusa Co., 2012.

To define N2O spatially emissions in two irrigation systems and use them, besides seasonal changes, to accurately calculate the annual budget in an almond orchard depending on the irrigation system.
To evaluate temporal variability of N2O emissions with respect to environmental factors such as water-filled pore space and temperature.

Summary of the Experiment

In order to better understand production and consumption of greenhouse gases (GHGs) in agriculture and have more quantitative estimates of carbon sequestration that includes offsets from GHG production, it is important to have quantitatively accurate estimates of net GHG fluxes. Nitrogen fertilizers applied to soils and soil management are estimated to be the major sources of the GHG nitrous oxide (N2O), and N2O is believed to be the most important GHG in agriculture. Liquid fertilizers applied through microirrigation systems (fertigation) is the predominant method of N application for woody perennial crops in California, where most of North American tree fruit and nut crops are grown.

The microirrigation water/fluid fertilizer emitters generate a different water distribution pattern in wetting soil around it, and, therefore, a different distribution of N in soil if the fertilizer is applied via fertigation. Soil water and mineral-N distribution should affect the generation of N2O and CH4 as well as the spatial and temporal distribution of the emissions of these gases through the soil to the atmosphere during fertigation.

The net N2O-N flux over a season (2009-2010) depended on emitter type with the conventional drip fertigated orchard emitting more than twice of N2O. The spatial pattern of N2O fluxes was similar to the soil water distribution pattern and strongly differed depending on the microirrigation emitter used. The seasonal emissions per hectare of nitrous oxide N2O were lessened by using microsprinkler irrigation as the fertilizer delivery system, compared to drip irrigation (Fig. 1). This result provides growers with a tool for lowering almond orchard carbon footprint.

Fig. 1. N2O emissions (nmol N2O-N m-2 min-1) spatially scaled to the orchard level for sprinkler irrigation (filled symbols) and drip irrigation (open symbols) Total moles of N2O emitted was estimated as the integral of the surface defined by the N2O flux distribution around the emitters and scaled up using the number of emitters per hectare, plus the N2O flux observed outside the wet-up area. Arrows represent dates when fertigations occurred.

For more information see the presentations and publications under Outreach