Nutrient Management Research Database

Understanding the effect of various agricultural management practices on nitrous oxide (N2O) emissions is crucial to advise farmers and formulate policies for future greenhouse gas (GHG) reductions. In order to estimate present N2O emissions, annual N2O budgets must be thoroughly and precisely quantified from current farms under conventional and alternative management, but subject to practical and economic constraints. In this study, field sites were located on two on-farm processing tomato (Lycopersicon esculentum) fields, under contrasting irrigation managements and their associated fertilizer application strategy: (1) furrow irrigation and sidedress fertilizer injection (conventional system) and (2) drip irrigation, reduced tillage, and fertigation (integrated system). Nitrous oxide emissions were monitored for seven to ten days following major events of cultivation, irrigation, fertilization, harvest, and winter precipitations. Total weighted growing season emissions (15 March–1 November 2010) were 2.01 ± 0.19 kg N2O-N ha-1 and 0.58 ± 0.06 kg N2O-N ha-1 in the conventional and integrated systems, respectively. The highest conventional system N2O emission episodes resulted from fertilization plus irrigation events and the first fall precipitation. In the integrated system, the highest N2O fluxes occurred following harvest and the first fall precipitation. Soil chemical and physical properties of soil moisture, inorganic nitrogen (N), and dissolved organic carbon (DOC) were low and less spatially variable in the integrated system. Used as an index of substrate availability, soil ammonium (NH4 +) and nitrate (NO3 -) exposures were significantly lower in the integrated system. Of greater importance is that the drip irrigation water and fertilizer management of the integrated system also increased crop yield (119 Mg ha-1 vs. 78 Mg ha-1), highlighting the potential for decreasing N2O emissions while simultaneously improving the use of water and fertilizer for plant production.

• The field study was conducted at 2 processing tomato farms in Winters, Yolo County between March 15th, 2010 and April 2011.
• The field management regimes compared were conventional (sidedress fertilizer injection, furrow irrigation (FI) and standard tillage) and integrated (fertigation, sub-surface drip irrigation (SDI), and reduced tillage).
• The conventional field was fertilized six times for a total of 237 kg N ha-1, the bulk of which came from CAN-17.
• The bulk of the fertilizer was applied as a sidedress injection, shanked into each shoulder of the seedbed to a depth of 15cm, one month after transplanting.
• Approximately 64-76 cm of water was delivered during the growing season across ten furrow irrigation events, scheduled using ET from CIMIS stations and soil moisture probes.
• The integrated field was managed under conventional tillage with an alfalfa, processing tomato and sunflower seed rotation before the study period.
• The integrated field was fertilized seven times over the study period for a total of 205 kg N ha-1 with UAN.
• Water was supplied to the crop via SDI, drip tape was buried 23 cm deep. Irrigation was scheduled using ET from CIMIS.
• Each field had 3 plot replicates.
• Fields were sampled for Nitrous oxide emissions (at the center of the seedbed, between rows, on the shoulder of the seedbed, and in the furrow) the day before each management event and once every 12 days in between management events, as well as before and after precipitation events.
• Soils were analyzed for soil moisture and N03, NH4 and DOC concentrations, as well as bulk density and percent soil water filled pores space, total soil C, N and pH.
• Nutrient use efficiency was also calculated as partial factor productivity (PFP).

• Total growing season emissions were 2.01 ± 0.19 kg N2O-N ha-1 and 0.58 ± 0.06 kg N2O-N ha-1 in the conventional and integrated systems, respectively.
• In the conventional system, total weighted annual emissions were 3.06 ± 0.19 kg N20-N ha-1, equaling .76% of N fertilizer applied to tomato and winter wheat. Total weighted annual emissions in the integrated system was 0.95 ± 0.05 kg N20-N ha-1, equaling 0.46% of N fertilizer applied.
• In the conventional system notable N20 fluxes were produced by 2 summer fertilizations, harvest, and the first winter rain event.
• The largest N20 fluxes in the integrated system were observed after harvest and following the first rain event.
• Results show that drip irrigation and fertigation reduces N20 emissions without yield penalties.