Fig. 2. Influence of N sources on soil CO₂ efflux, Belle Mina, AL, 2003, 2004, and 2006. Treatment means under each year followed by the same uppercase letter are not significantly different from each other at P 0.05. 100 ANN, ammonium nitrate at 100 kg N ha^–1; 100 PLN, poultry litter at 100 kg N ha^–1; 200 PLN, poultry litter at 100 kg N ha^–1.