Residual Effects of Long‐Term Nitrogen Fertilization on Nitrogen Availability to Corn

Long‐term use of N fertilizer in continuous corn ( Zea mays L.) is a common practice in the Corn Belt of the USA, but little information is available on the residual effects of this practice. The objectives of this study were to determine the effects of long‐term N fertilizer use on subsequent N response and the implications of these effects on N availability and management recommendations. Three long‐term N fertilizer treatments (LTN1, LTN2, and LTN3) were applied to a continuous corn study from 1958 to 1983 on a Piano silt loam (fine‐silty, mixed, mesic Typic Argiudoll) in Wisconsin. The long‐term treatments supplied a total of 287, 2775, and 5200 lb N/acre, respectively. In 1984, the LTN treatments were discontinued and a split‐plot treatment arrangement was established with residual LTN treatments as main plots, subplots of 0, 75, 150, and 225 lb N/acre/yr, and four replications. Residual effects of the LTN2 and LTN3 treatments resulted in significantly higher corn grain yields (20 and 46 bu/acre, respectively) compared to the LTN1 treatment in 6 of 7 yr from 1984 to 1990. Preplant soil NO − 3 ‐N concentrations to a depth of 4 ft indicated that corn response in 1984 and 1985 was probably caused by residual inorganic N carryover from previous fertilizer addition, but yield responses in subsequent years were due to greater N mineralization in the LTN2‐ and LTN3‐treated plots. Use of a pre‐sidedress NO − 3 ‐N test did not detect apparent differences between treatments in residual N availability. Corn N response to additional N fertilizer applied from 1984 to 1990 suggests that long‐term N fertilization can affect subsequent N response. This may provide a short‐term buffer against potential yield decreases as a result of any limit on N fertilizer rates.