Nitrous oxide emissions as affected by fertilizer and water table management under a corn-soybean rotation

Nitrous oxide (N2O) emissions from agricultural soils are influenced by several factors, including fertilizer and water management. A 4-year study (2012-15) was conducted to evaluate the impact of different types of fertilizer and water table management systems on N2O emissions under a corn-soybean rotation. The types of fertilizers assessed were inorganic fertilizer (IF) and a combination of inorganic fertilizer and solid cattle manure (SCM) (applied in 2012 and 2014, for corn only), while the water table management systems were regular tile drainage (DR), and controlled drainage with sub-irrigation (CDS). The IF and SCM were combined with DR and CDS in separate plots arranged as a two by two factorial design. The results show that, in 2012, 2013 and 2014, N2O fluxes were significantly (2012, 2013 p < 0.05; 2014 p < 0.1) affected by the fertilizer treatments. In 2012 and 2014, when fertilizer was applied to corn, the emissions were greater from IF than SCM; however, in 2013, under soybean cultivation, the emissions were greater from SCM than IF, indicating slow mineralization of SCM fertilizer compared to IF. In 2014, under corn and 2015 under soybean, the N2O fluxes were significantly higher (P < 0.05) from DR compared to CDS plots indicating a greater reduction of N2O to dinitrogen (N-2) via denitrification. The results also showed that early in the growing season, high N2O fluxes were observed following planting due to fertilizer application, precipitation in excess of 100 mm per month in the early growing season, and spring tillage. The N emission factors of IF-DR, IF-CDS, SCM-DR, and SCM-CDS were 1.2, 0.9, 1.0, and 0.5, respectively. This study concludes that the combination of SCM and CDS is the most efficient at reducing N2O emissions while maintaining sustainable yields in a corn-soybean rotation.