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In California’s water-seeded rice systems, both high yields and nitrogen (N) use efficiency are achieved when the pre-plant N fertilizer (usually aqueous-ammonia; aqua-N) is injected into a dry seedbed before flooding and planting. However, there are situations where applying N fertilizer in this manner is not possible. The objective of this study was to evaluate N management practices by testing different N sources and application times. Over two growing seasons (three site-years) we evaluated different N sources including aqua-N, granular urea, ammonium sulfate, and three enhanced efficiency nitrogen fertilizers (EENFs). Application times for the EENFs, urea, and ammonium sulfate were one day after flooding and 2 weeks after flooding. Urea and ammonium sulfate were also applied in a 4-way split (ratio of 20:30:30:20 applied every two weeks). In 2021, additional treatments were added with aqua-N, ammonium sulfate, and urea applied before flooding; and urea applications at 3, 4, and 5 weeks after flooding. Grain yield and agronomic nitrogen use efficiency (ANUE) were measured and used to make comparisons. All fertilizer N treatments increased grain yields and ANUE relative to the zero-N control. The EENF treatments performed similarly to or worse than urea applied alone. Splitting urea applications was the best option for applying N fertilizer after the field was flooded. Only one split N treatment was evaluated in this study; this warrants further research on fine-tuning the best N splits for these systems.

Improving nitrogen (N) management is critical to maximizing the productivity and sustainability of our agroecosystems. Improving N management requires an understanding of crop N status and yield potential early enough in the growing season when changes to N management can influence yields. However, given the lack of tools currently available to accurately assess crop N status, farmers continuously face the challenge of determining whether their crops require additional N fertilizer. The recent emergence of remote sensing technology has provided a promising alternative that can provide farmers the information they need in an accurate and timely manner. Several studies have demonstrated the potential of remote sensing technology to accurately assess the health and vigor of vegetation at the landscape scale, however few have explored how this technology can be utilized to inform sustainable crop management at the farm scale. This knowledge gap is what inspired this research and led us to investigate how remote sensing technology can be utilized to improve in-season N management in California rice systems.In California, where more than 200,000 ha of flooded rice (Oryza sativa) is cultivated annually, the recommended N management strategy is for farmers to apply the average seasonal N fertilizer requirement prior to flooding and planting as aqua-ammonia injected into the soil. On-farm studies have reported that N fertilizer applied in this manner is efficiently utilized by the crop as it remains protected from denitrification and ammonia volatilization losses until the crop needs it. At panicle initiation (PI), it is recommended to assess crop N status to determine if additional N fertilizer inputs are required as top-dress. The current tools available to assess rice N status include the SPAD chlorophyll meter and Leaf Color Chart, but these tools are not often used as they are time consuming and subjective. Thus, most top-dress N applications take place without evaluati

Improving nitrogen (N) management is critical to maximizing the productivity and sustainability of our agroecosystems. Improving N management requires an understanding of crop N status and yield potential early enough in the growing season when changes to N management can influence yields. However, given the lack of tools currently available to accurately assess crop N status, farmers continuously face the challenge of determining whether their crops require additional N fertilizer. The recent emergence of remote sensing technology has provided a promising alternative that can provide farmers the information they need in an accurate and timely manner. Several studies have demonstrated the potential of remote sensing technology to accurately assess the health and vigor of vegetation at the landscape scale, however few have explored how this technology can be utilized to inform sustainable crop management at the farm scale. This knowledge gap is what inspired this research and led us to investigate how remote sensing technology can be utilized to improve in-season N management in California rice systems.In California, where more than 200,000 ha of flooded rice (Oryza sativa) is cultivated annually, the recommended N management strategy is for farmers to apply the average seasonal N fertilizer requirement prior to flooding and planting as aqua-ammonia injected into the soil. On-farm studies have reported that N fertilizer applied in this manner is efficiently utilized by the crop as it remains protected from denitrification and ammonia volatilization losses until the crop needs it. At panicle initiation (PI), it is recommended to assess crop N status to determine if additional N fertilizer inputs are required as top-dress. The current tools available to assess rice N status include the SPAD chlorophyll meter and Leaf Color Chart, but these tools are not often used as they are time consuming and subjective. Thus, most top-dress N applications take place without evaluati

Flooded rice systems are critical for global food security but contribute significantly to anthropogenic greenhouse gas (GHG) emissions due to high methane (CH4) production in anerobic soils. Herbicide use in conventional rice systems has also created selection pressure for herbicide resistant aquatic weed species that threaten yields. Dry seeding (DS) rice, which in California includes early season drainage events, has been shown to reduce CH4 emissions and shift weed species emergence for improved control compared to continuously flooded water-seeded systems (WS). The effect of these drainage events on nitrogen (N) fertilizer losses and nitrous oxide (N2O) emissions, however, are not well understood. In a two-year study we quantified the effects of early season drainage events utilized in DS rice on global warming potential (GWP) (CH4 + N2O in CO2 eq.), nitrate (NO3-) accumulation, and N fertilizer losses as measured by the difference in crop N-uptake compared to a WS control. Despite 1.06 kg ha-1 more N2O emissions in the DS system the GWP was 4,610 CO2 eq. kg ha-1, a 42% reduction compared to 7,983 CO2 eq. kg ha-1 in the WS system. This was due to a 46% reduction in CH4 in the DS (126 CH4 kg ha-1) relative to the WS (235 CH4 kg ha-1) system. Nitrate accumulation in the DS system amounted to 25.9 kg N ha-1, and subsequent N losses via denitrification likely contributed to the 22.4 kg N ha-1 less crop N-uptake in the DS system. These results suggest that DS rice has potential for improved environmental impact via GWP reductions. Future research should consider the effects of increased pre-plant N application rates and timing for improved N management, a quantification of annual GWP including CO2 emissions, and changes in soil organic carbon stocks in DS rice.