Agronomic Practices vs. Climate Factors: A Meta-Analysis of Influences on Nitrous Oxide Emissions from Corn and Soybean Fields

Nitrous oxide (N2O), a potent greenhouse gas (GHG) and major contributor to climate change, is primarily released through agricultural activities. To better understand and quantify how land management practices, local climate conditions, and soil physicochemical properties affect these agricultural N2O emissions, we conducted a review of the peer-reviewed literature on N2O emission from corn [Zea mays L.] and soybean [Glycine max (L.) Merr.] fields. We evaluated the seasonal, cumulative effects of three nitrogen fertilizer rates—no fertilizer (0), low (<188 kg N ha−1), and high (188–400 kg N ha−1)—tillage practices, local climate (precipitation and temperature), soil texture, and soil pH on soil N2O emissions. This meta-analysis included 77 articles for corn and 22 articles for soybean fields. Average N2O emissions during the corn rotation were 2.34 and 2.45 kg N2O-N ha−1 season−1 under low and high N fertilizer rates, respectively, and were both substantially (p < 0.0001) greater than those of non-fertilized corn fields (0.91 kg N2O-N ha−1 season−1). Non-fertilized soybean fields showed seasonal N2O emissions of 0.74 kg N2O-N ha−1, while low fertilizer application triggered a sharp increase (1.87 kg N2O-N ha−1) in N2O emissions by roughly 2.5 times (p < 0.028). Increased temperature did not significantly (p > 0.05) affect the emission of N2O from fertilized or non-fertilized corn fields. Regardless of fertilization and tillage practices, our analysis, including Principal Component Analysis, revealed that in corn fields, precipitation and soil pH are the dominant factors influencing soil N2O emissions. This study uniquely quantifies the influence of climate–soil factors, such as precipitation and soil pH, alongside agronomic practices, on N2O emissions, offering new insights beyond previous reviews focused primarily on fertilizer rates or tillage effects.