Fig. 4. Mean predicted corn leaf N concentrations as functions of cumulative growing degree days (GDD) after corn planting in 2000 and 2001 near Boone, IA. The P(N) symbols represent the probabilities of significant differences between corn response to composted swine hoop manure and fresh swine hoop manure from similar origins. , *, and ** represent significance at the 0.1, 0.05, and 0.01 probability levels, respectively. The black arrow in each figure represents the time of 50% silk emergence, Plant Growth Stage R1.