The Effect of Improved Agricultural Techniques On N2O Emissions in California Tomato Cropping Systems.

The Effect of Improved Agricultural Techniques on N₂O Emissions in California Tomato Cropping Systems

Taryn Kennedy, Emma Suddick and Johan Six.

The passage of the Global Warming Solutions Act of 2006 (AB32) has spurred widespread efforts to quantify nitrous oxide emissions from major cropping systems in California.  Agricultural activities are the source of approximately 75% of the global N₂O emissions.  Since nitrous oxide is a potent greenhouse gas that also destroys stratospheric ozone, it is important to further understand how various agricultural management practices affect the environmental parameters that influence rates of N₂O emissions.  Research efforts are limited by the spatially and temporally erratic behavior of nitrous oxide and the physical and financial constraints that can prohibit continuous sampling.  As a result, estimates of annual N₂O budgets may not be accurate if measurements do not capture the amplitude and duration of a management induced peak in N₂O flux.  The aim of this project was to quantify annual N₂O emissions via daily measurements following each agricultural event (cultivation, irrigation, fertilization and harvest).  In addition, we examined the spatiotemporal variation of N₂O fluxes across three functional locations in each field.  Field sites were located in tomato cropping systems under two different managements.  The first represented the standard practices in tomato production of conventional tillage and furrow irrigation; the second management utilized reduced tillage, drip irrigation and a grain cover crop.  Gas fluxes were measured in static closed chambers and correlated with environmental parameters (NO₃, NH₄, dissolved organic carbon, soil moisture and temperature).  Nitrous oxide emissions were collected at the center of the seed bed, the shoulder and the furrow, and used to calculate fluxes at the field scale in order to compare conventional and improved agricultural managements.  We anticipated that the integrated system of reduced tillage, drip irrigation and grain cover crop would have lower N₂O emissions than the conventionally tilled and furrow irrigated system.  We expected position-specific variation to correlate with N fertilizer and irrigation placement.  Our preliminary data has shown that seasonal N₂O fluxes are highest under the conventional treatment and lowest in the established reduced till treatment.  In the conventional system, N₂O fluxes were greatest at the shoulder, followed by the furrow position.  Fluxes were highest at the center of the seed bed and the furrow in the integrated system.  The data acquired in this project will be used to calibrate ecosystem models and direct the evolution of agricultural policies and efforts to regulate greenhouse gas emissions.