Data from: Long-term compost use and high frequency low concentration fertigation reduce N₂O emissions from a California almond orchard

Using compost as an agricultural amendment offers a means to reduce organic waste, as mandated by California State Bill 1383. Compost application, through the addition of soil organic matter, leads to improvements in soil physical characteristics and soil organic carbon content. Effects of compost application (7-year duration; 38-dry tonnes ha^-1) on soil nitrous oxide (N₂O), inorganic nitrogen pools, soil temperature and water content, bulk density and total carbon and N content were examined. Soils were also measured for soil pH, electrical conductivity, and total C and N. These findings were compared to the control, which had not received compost application.

The research site was located ∼8 km west of Modesto, California (37˚37′38.17“ N 121˚5′21.57”W), on a 10.5-ha almond orchard (Prunus dulcis, 270 m by 395 m). The orchard was replanted in 2012 with Nonpareil cultivars and interplanted with Aldrich and Carmel cultivars, all grafted on Nemaguard peach rootstock [Prunus persica (L.) Bratsch]. Trees were 4.3 m apart along the row, with 6.4 m between rows, and irrigated by surface drip hose with embedded emitters every 3.7 m (0.07 L min⁻¹).

The two treatments, No Compost and Compost (n=3 replicates per treatment), were studied in the growing season (December 2018–August 2019). All other management was consistent between treatments, representing standard practices for the almond industry in this region. The orchard began HFLC nutrient management in 2018, and the total amounts of fertilizer N and irrigation were adjusted in response to anticipated tree demand as determined by the grower. In 2019, orchard received ∼195 kg N ha⁻¹ over 14 fertigation events (March–July, 2019) through a drip irrigation system using HFLC. These 14 fertilization events ranged from 4.5 kg N ha⁻¹ to 28.0 kg ha⁻¹.

Findings were compared graphically against other data from 5 other studies examining the effects of irrigation and fertigation practices on N₂O. Total cumulative emissions were calculated by date and treatment over the growing season. The effects of sampling date, treatment and area spanning the drip zone were analyzed for N₂O, soil temperature and water content, water-filled pore space, ammonium and nitrate.