Methods

Study Area

Westlock, AB

The study was conducted in Westlock, AB, on a farmland with luvisolic soil. This 3-year research involved a crop rotation system, with canola grown in 2022, wheat in 2023, and fava beans in 2024. The farm practices dry farming with no tillage.

Figure 1: Plots set up in the farm, Westlock, AB.

Experimental Design

The experiment followed a randomized block design with 11 treatments, a control with synthetic fertilizer, and a control without any additions. The study included three blocks, each containing 13 plots, where treatments were randomly assigned within each block. Figure 2 illustrates the layout of the randomized block design applied.

Figure 2. Randomized Block Design. B = block numbers, P = plot numbers, and T = treatment numbers. T1: Control, T2: Synthetic fertilizer (SF), T3: Compost, T4: Compost and SF, T5: Compost and biochar, T6: Compost, biochar, and SF, T7: Compost and wood ash, T8: Compost, wood ash, and SF, T9: Compost, wood ash, and biochar, T10: Compost, wood ash, biochar, and SF, T11: Compost, wood ash, and gypsum, T12: Compost, wood ash, gypsum, and biochar, T13: Compost, wood ash, gypsum, biochar, and SF.

The specific materials added in the treatments were compost, biochar, gypsum, wood ash, and synthetic fertilizer. Compost serves as an organic fertilizer and a source of fresh organic matter, while biochar adds recalcitrant carbon to the soil, offering multiple soil health benefits. Wood ash increases soil pH, and gypsum improves soil fertility by reducing sodium in sodic soils by replacing the sodium with calcium. Treatments with and without synthetic fertilizer (SF) were included to evaluate whether SF is essential for agricultural productivity. The image below (Figure 3) is an aerial picture after the organic amendments were applied to the soil, and we can se the randomized block design applied in the field.

Figure 3: Aerial picture of the plots after the addition of organic soils amendments. Source: Gateway Research Organization

Data collection

Greenhouse gas (GHG) measurements were conducted annually from 2022 to 2024, with biweekly sampling during the spring and summer seasons. Using a photoacoustic multi-gas monitor connected to a rectangular greenhouse gas chamber with a tube (Figure 4), each plot was sampled over a 90-minute period, collecting GHG readings every 30 minutes. This setup allowed us to measure both carbon dioxide (CO₂) and nitrous oxide (N₂O) in mg/m³, which were then converted into GHG flux mg/m²/day.

Data preparation for analysis

The formula used for flux calculation is:

Where:

ΔC is the change in concentration in mg/m³,

Δt is the time difference in seconds,

Chamber volume is in m³,

Chamber area is in m²,

Flux is in mg/m²/day.

Figure 4: Scheme of greenhouse gas chamber and the photoacoustic multi-gas monitor. The greenhouse chamber is input in the soil (dimensions 0.635 m x 0.15 m x 0.16 m), and the lid is added on t1=0 and kept until the last measurement. The monitor is connected to a tube (⌀ = 0.004 m and length = 6.5 m) that is then connected to the lid on measurements t1, t2, and t3.

Cumulative Seasonal Flux Calculation

Each year of the study had a different number of observations due to variations in the start and end of the growing season and the spacing between observations (6 in 2022, 8 in 2023, and 5 in 2024). The daily GHG flux in mg/m²/day was converted into cumulative seasonal flux to quantify total GHG emissions during each growing season, providing a comparable and standardized variable for analysis.

The Cumulative Seasonal Flux was calculated using the formula below.

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