Compost application and reduced synthetic nitrogen fertilization promote sustainable olive production in super-high-density orchards

As a high-value crop, olives are widely cultivated in Mediterranean-climate regions, including California. However, appropriate nitrogen (N) fertilization and nutrient management are required for the sustainable cultivation of olives, particularly in the rapidly adopted super-high-density systems. Identifying the N requirements for super-high-density olive orchards is essential for maximizing yield, improving olive quality, and enhancing soil health to achieve sustainability goals. Despite the importance of such information, there is a lack of recent research in this area. To address this gap, we conducted a two-year study at two super-high-density olive orchards in California’s Central Valley, using an isotopic approach not previously applied in field-grown olives, to understand how N fertilization strategies and soil health management practices, such as compost utilization, affect N uptake, olive yield, and oil quality. The findings were then used to elucidate the N requirements of super-high-density olives in order to revise N application guidelines tailored to growers adopting super-high-density systems. Our results showed no consistent effect of reduced N application rate on yield or oil quality, while compost amendments increased the uptake of fertilizer-derived N by olive trees in the first year. These findings suggest that, depending on the ability of the soil to provide sufficient nutrients, synthetic N fertilizer use in super-high-density orchards could be reduced without compromising yield or oil quality. Furthermore, compost amendments show promise as a sustainability strategy, potentially improving fertilizer N retention and reducing losses.