Data from: Alternative fertilization practices lead to improvements in yield-scaled global warming potential in almond orchards

This study investigates the impact of alternative fertilization practices on the yield-scaled global warming potential in almond orchards. Almond production contributes to greenhouse gas emissions due to fertilizer nitrogen (N) use. Field experiments were conducted in an almond orchard using three fertigation practices: Advance Grower Practice (AGP), Pump and Fertilizer (P&F) and High Frequency-Low Concentration (HFLC).

The study was conducted in a commercial almond orchard (16 ha, 2015 and 2016 growing seasons) in the San Joaquin Valley (Madera, California; 36◦ 49’ 15.85” N 120◦ 12’1.20 W, elevation 60 m). The trees (ca. 16 years, 73 trees per row) were spaced 5.5 m tree to tree within row and approximately 14.6 m between alternating rows of Nonpareil and Carmel cultivars. The soil type was the Cajon soil series (Mixed, thermic Typic Torripsamments), characterized by loose fine sand with low organic carbon content and low water holding capacity (Web Soil Survey, 2021). The orchard exists in a semiarid, Mediterranean-like climate. All samples were collected in the second and third year after fertigation treatments were initiated.

Urea Ammonium Nitrate [UAN; 32% nitrogen (N), composed of 50% urea-N, 25% NH₄⁺-N, and 25% NO₃ ^--N) was delivered through the irrigation system to all three irrigation treatments (i.e. fertigation). Generally, the fertilizer N content was similar across all Pump and Fertigate treatments but the frequency of application varied. Two treatments (, P&F; HFLC, High Frequency-Low Concentration) provided a similar total, annual N targeted to meet the demands for high yielding commercial almond production based on above- and below-ground growth. The third, AGP, applied approximately 30% more N fertilizer than P&F and HFLC because it represented the standard growing practice with respect to timing and quantity of fertilizer application for the local industry. P&F and HFLC reduced the amount of applied N fertilizer by accounting for groundwater N concentrations. Each fertigation treatment was composed of four tree rows, with each of the four replicates placed along one of the two center tree rows.

Greenhouse gas emissions from fertigation were sampled using an array of static chambers that were placed to cover the drip zone and within the tree row and alley. At the same time, soil water content, temperature and inorganic N pools were collected. During harvest, almond yields were measured to allow for calculation of yield-scaled global warming potential.