| Abstract: | Abstract The Magruder plots are the oldest continuous soil fertility wheat research plots in the Great Plains region, and are one of the oldest continuous soil fertility wheat plots in the world. They were initiated in 1892 by Alexander C. Magruder who was interested in the productivity of native prairie soils when sown continuously to winter wheat. This study reports on a simple estimate of nitrogen (N) balance in the Magruder plots, accounting for N applied, N removed in the grain, plant N loss, denitrification, non‐symbiotic N fixation, nitrate (NO3 ?) leaching, N applied in the rainfall, estimated total soil N (0–30 cm) at the beginning of the experiment and that measured in 2001. In the Manure plots, total soil N decreased from 6890 kg N ha?1 in the surface 0–30 cm in 1892, to 3198 kg N ha?1 in 2002. In the Check plots (no nutrients applied for 109 years) only 2411 kg N ha?1 or 35% of the original total soil organic N remains. Nitrogen removed in the grain averaged 38.4 kg N ha?1 yr?1 and N additions (manure, N in rainfall, N via symbiotic N fixation) averaged 44.5 kg N ha?1 yr?1 in the Manure plots. Following 109 years, unaccounted N ranged from 229 to 1395 kg N ha?1. On a by year basis, this would translate into 2–13 kg N ha?1 yr?1 that were unaccounted for, increasing with increased N application. For the Manure plots, the estimate of nitrogen use efficiency (NUE) (N removed in the grain, minus N removed in the grain of the Check plots, divided by the rate of N applied) was 32.8%, similar to the 33% NUE for world cereal production reported in 1999. |
