Long-Term Effects of Nitrogen Sources on Yields, Nitrogen Use Efficiencies, and Soil

Corn is both the most important and nitrogen (N)-fertilized crop, but N losses from agricultural systems impact the environment. There is a lack of long-term data comparing effects of tilled systems receiving organic N fertilizer (TONF; e.g., manure) versus inorganic N fertilizer (TINF; e.g., urea) on N balance and losses. A long-term study assessing effects of TONF and TINF and comparing them to no till (NT) and strip till (ST) systems receiving inorganic nitrogen fertilizer (INF) was conducted with an irrigated continuous corn (CC) system with minimal erosion in Fort Collins, Colorado, USA. An N balance found a system nitrogen use efficiency (NUESys) for TONF (manure) of 86.3%, which was higher than the NUESys of TINF (enhanced efficiency fertilizer, EEF) of 60.2%. TONF (manure) contributed to higher HGY (2 of 11 yr.), higher C sequestration (P<0.05), and higher soil organic N content (P<0.05) than TINF. Soil phosphorus (P) and nitrate were higher with TONF than TINF (P<0.05). Both TONF and TINF had higher HGY and HGY N content (HGYN) than NT and ST (P<0.05). From 2012 to 2023, the HGY of the TONF did not decrease, while the HGY of TINF decreased with time (P<0.05). TONF is a best management practice to increase yields and N and C sequestration while reducing N losses compared to TINF and achieving higher yields than NT and ST. A combination of manure (30% of N input) with EFF (70% of N input) contributed to a synergistic effect that increased agronomic productivity.