Nitrous oxide (N2O) is potent greenhouse gas produced by microorganisms in soil, and it is responsible for one third of net agricultural greenhouse gas emissions in California. Research over decades has investigated the biophysical mechanisms of soil N2O production, and identified a general suite of management practices that influence the magnitude and duration of emissions, such as fertilizer and irrigation rate, type, timing, and placement. Despite these advances, current process models that estimate soil N2O losses (e.g. DNDC) are not yet parameterized for the range of crop types, environmental conditions, or nutrient and irrigation management regimes used by growers in the desert vegetable producing regions of southern California and Arizona. Studies in other agricultural systems have shown that fertilizer efficiency enhancers such as controlled-release fertilizers (CRF) and nitrification inhibitors (NI) can reduce environmental N losses and improve yield. Both of these technologies aim to reduce microbial rates of nitrification, which is often the rate-limiting process in the production of N2O from soil. These studies suggest that CRN and NI can increase N availability to plants, leading to increased crop N use efficiency and production. To date, however, few studies have quantified the effects of CRN and NI on yield and N2O emissions in vegetable crops under the semi-arid/arid growing conditions of the US Southwest. Given the current regulatory mandate in California to reduce agricultural N losses, field evaluations are needed to test these promising technologies across a range of crop types throughout the California/Arizona desert vegetable growing region, as well as integrate these findings into current models.
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