Are Greenhouse Gas Emissions and Soil Chemical Characteristics Affected by Planting Density, Organic Fertilization, and Saline Water Irrigation in Cactus Pear Cultivation?

Understanding nitrogen dynamics in arid agricultural systems is essential for mitigating greenhouse gas (GHG) emissions in climate-constrained environments. This study evaluated the effects of planting density, organic fertilization, and saline water irrigation on soil chemical properties, carbon and nitrogen stocks, and emissions of CO2, CH4, and nitrous oxide (N2O) in cactus pear cultivation systems. A 2 × 2 × 2 factorial arrangement was used to test two planting densities (30,000 and 75,000 plants ha−1), two organic fertilizer rates (0 and 30 Mg ha−1), and two saline irrigation depths (0 and 25% of ET0). Higher planting density increased soil moisture and carbon content while reducing CO2 and CH4 emissions. Organic fertilization increased the soil C ratio and phosphorus availability and significantly enhanced N2O emissions, whereas unfertilized systems showed negative N2O fluxes. Saline water irrigation reduced N2O emissions, resulting in negative fluxes (−12.50 µg N m−2 h−1), indicating potential suppression of nitrification and denitrification pathways. None of the evaluated factors significantly affected soil nitrogen stocks. Total GHG emissions (CO2-eq) were lower in denser cultivation systems. These results demonstrate that the interaction among high planting density, organic fertilization, and supplementary saline irrigation modulates nitrogen transformations and N2O emissions in semi-arid soils, highlighting management strategies to mitigate nitrogen-derived GHG emissions in cactus-based agroecosystems.