Soil C and N: Inputs, Outputs and Current Status in a Long-Term Continuous Corn N-Tillage Trial.

Gains and losses of both C and N are important in agricultural landscapes. A long-term (37 yr) monoculture corn (Zea mays L.) tillage (moldboard plow, no-tillage) by N rate (0, 84, 168, 336 kg N per hectare) trial was sampled to a depth of 100 cm, as was the surrounding native grass sod (age greater than 80 yr), to determine the impact of tillage and N fertilization on soil C and N. Corn yield (C input), in both tillage systems, rose with increasing fertilizer N rate, as did soil C and N, especially in the upper solum. Soil C and N depletion was most associated with land use change (from sod to unfertilized continuous corn, regardless of tillage). Fertilizer N was positively related to soil C and N levels via associated improvements in cropland soil productivity (grain yield). Tillage negated much of the positive impact of N fertilization on soil C and N levels.