Nutrient Management Research Database

Greenhouse gas emissions from agriculture and forestry in California are estimated at approximately 8.3% of the total production of 493 million metric CO2-equivalent tons (California Energy Comission (CEC); Research Roadmaps for Greenhouse Gas Inventory Methods; Sacramento, CA, 2005), of which nitrogen (N) fertilizers applied to soils and soil management are estimated to be the major sources of N2O production. Of the approximate 3.89 million hectares (ha) of intensively irrigated cropland in California (California Department of Water Resources (DWR); Agricultural Water Use; Sacramento, CA, URL http://www.water.ca.gov/wateruseefficiency/agricultural/), approximately 1.17 million ha are planted to orchards and vineyards. This acreage is irrigated and fertilized with N using microirrigation systems and liquid N fertilizers (fertigation). Understanding biophysical factors that regulate N2O emissions during fertigation will be necessary for scaling exercises, and for developing sustainable management practices. We present ongoing work showing spatial variation in microbial enzyme activity in the microirrigation wet-up zone related to N2O emissions and indicating that denitrifying microorganisms may be more abundant in the drip zone. Spatiotemporal variation in N2O emissions around conventional aboveground drip and stationary fanjet micro-sprinkler systems in grape, a non-N-intensive perennial crop, and almond, a N-intensive perennial crop were well characterized using 3-dimensional modeling exercises. The quantity of N2O emitted was lower when N was applied through stationary fanjet sprinklers than it was for conventional drip application in an almond orchard on a sandy loam soil.

This book chapter presents a review of the importance of nitrous oxide emissions and the conditions that lead to emissions of N20 in vineyard and orchard soils.  Research conducted to examine spatial variation in nitrification and denitrification enzyme activity and the spatiotemporal variation in N20 emissions at the vineyard/orchard scale in a conventionally managed Napa Valley vineyard is also presented.  N20 emissions were sampled using grids of gas flux chambers in the drip irrigated and fertigated vineyard, using 3 repetitions of 7 chambers.  Measurements from the sampling grids were used to develop 3 dimensional models of N20 emissions.

A similar study was conducted in an almond orchard to determine spatiotemporal variation in N20 emissions. The almond was irrigated with either drip irrigation or microjet sprinkler. In this study transects of gas chambers were used under three trees in each irrigation system.   

Denitrifier enzyme activity was limited to the 0-20cm soil depth, and spatial distribution of nitrifier and denitrifier activity was related to water management with denitrifier activity slightly higher in the drip zone.  In the vineyard study, spatial variation in N20 emissions was large and but a general pattern of a peak in emissions closer to the drip line was observed.  This pattern was less apparent when irrigation water followed the fertigation.   

In the almond study, there was a peak of emissions in near the emitter in the drip irrigation treatment, followed by a rapid decline in emissions moving away from the emitter, similar to what was observed after a fertigation event in the vineyard system.  Under microjet sprinklers, on the other hand, N20 emissions peaked at a distance of around 1 meter from the sprinkler and then decreased rapidly, similar to the water distribution pattern. Total loss of N as N20 was found to be higher from the drip than from the microjet sprinklers.