UC Davis

Abstract

The sustainability of agricultural practices is of paramount importance in mitigating climate change. Chapter 1 of this body of work investigates the impact of alternative fertilization practices on the yield-scaled global warming potential (YS-GWP) in almond orchards. Almond production is a contributor to greenhouse gas emissions, primarily due to nitrogen-based fertilizers. By exploring alternative fertilization methods, this research aims to identify strategies that reduce the environmental footprint of almond cultivation while maintaining or enhancing yield. Field experiments were conducted in an almond orchard using three alternative fertigation practices: Advance Grower Practice (AGP), Pump and Fertilize (P&F), and High Frequency Low Concentration (HFLC). AGP followed the current practice producers generally use to meet annual N demand for almond tree growth; P&F is a reduction in applied N rate in response to measured N concentrations in the groundwater so that the added N and groundwater N reach the same total N applied; HFLC is a practice of applying smaller N rates in an individual event, with a greater number of fertigation events to reach similar total N load applied annually as other treatments. The results revealed that both P&F and HFLC reduced the YS-GWP compared to the AGP. The HFLC fertigation demonstrated 52% to 78% decrease in GWP per unit of almond yield compared to AGP, while P&F showed 48% to 58% decrease over AGP. These reductions were attributed to the improved nitrogen use efficiency and reduced nitrous oxide emissions associated with the alternative practices. The findings of this chapter demonstrate that adopting alternative fertilization practices can effectively mitigate the environmental footprint of almond orchards while maintaining or even improving crop yields. These practices offer viable options for almond growers to reduce greenhouse gas emissions, enhance sustainability, and contribute to climate change mitigation efforts. Future research should focus on long-term monitoring of these practices and their economic viability to support their widespread adoption in almond production systems and other similar agricultural systems.Nitrogen management in agricultural systems plays a crucial role in optimizing crop growth and yield while minimizing environmental impact. The second chapter of this body of work aimed to investigate the dynamics of applied nitrogen during high frequency-low concentration fertigation in a California almond orchard. The experiment was conducted over three growing seasons in a commercial almond orchard located in California's Central Valley. Fertigation was applied as high frequency-low concentration fertigation (HFLC). I analyzed HFLC at an orchard scale, and how the variability of the soil and irrigation distribution might translate into flux estimations. Nitrogen was applied through either drip irrigation or fanjet micro sprinklers across four orchard blocks. I analyzed HFLC at an orchard scale, and how the variability of the soil and irrigation distribution might translate into flux estimations. Several parameters were monitored throughout the study, including GHG emissions, soil nitrogen content, various soil physicochemical factors and almond yield. This work provided some insight into the dynamics of N loss through soil N2O production during the application of HFLC fertigation on an almond orchard. While HFLC fertigation strategy has demonstrated a reduced potential for nitrogen losses, minimizing the environmental impact and promoting sustainable almond production, the influence of irrigation type and soil physicochemical factors needs further elucidation. No significant correlations were revealed in the data collected for this chapter. This chapter presents a comprehensive analysis of the dynamics of applied nitrogen during high frequency-low concentration fertigation in a California almond orchard. The findings highlight the need for further examination of the potential for this innovative approach in improving nitrogen use efficiency and reducing nitrogen losses to the environment. These insights can contribute to the development of sustainable nitrogen management practices in almond orchards and other similar agricultural systems, thereby ensuring the long-term viability of crop production while safeguarding environmental resources. Compost’s use as an agricultural amendment offers an opportunity to reduce organic waste, as mandated in the State of California (USA) (SB 1383). Organic soil amendments, such as compost, can improve soil physical characteristics, nutrient cycling and soil carbon through the increase in soil organic matter. Fertilizer application through micro irrigation systems (i.e. fertigation) is increasingly common in almonds in California’s Central Valley, as it is an effective method to manage water availability and nutrient loss. In the third chapter of this body of work I examined the effect of compost application (7-year duration) on soil nitrous oxide emissions, inorganic N pools, soil temperature and water content, soil bulk density, and total C and N content. The almond orchard (Nonpareil cultivars interplanted with Aldrich and Carmel cultivars, all grafted on ‘Nemaguard’ peach rootstock [Prunus persica (L.) Bratsch]) was on an Oakdale sandy loam soil type. It was fertigated 14 times with urea ammonium nitrate or calcium ammonium nitrate, using high frequency and low concentration (HF-LC) applications, for a total of 195 kg N ha-1. Soil without added compost ('no compost') tended to have higher fluxes (up to 2.75-fold) than soil with compost ('compost'). Emissions from 'no-compost' ranged from 0.29 to 5.5 g N2O-N ha-1 day-1 while 'compost' ranged from 0.34 to 3.7 g N2O-N ha-1 day-1. Additionally, I observed a substantial reduction in annual cumulative N2O emissions from 'compost', 11.5 g N-N20 ha-1 compared to 20.1 g N-N20 ha-1 in ‘no compost’. Soil pH, EC, total C and N tended to be greater in 'compost', and bulk density tended to lower in 'compost' than 'no-compost'. No relationships between N2O emissions and soil temperature, volumetric water content, water-filled pore space, and inorganic N pools were observed in either treatment. The findings in this chapter indicate that long-term applications of compost in perennial crops, in combination with a HF-LC nutrient management program, could reduce losses of N as N2O to the atmosphere.