Fig. 1. Soil surface CO2 flux measured in continuous maize at three plant populations (P1 = 69200–76600 plants ha–1, P2 = 86400–98800 plants ha–1, and P3 = 108700–116100 plants ha–1) under the M2 (intensive) fertility treatment during the 1999 growing season. Also shown are soil temperature at the 0.1-m depth and water-filled pore space in the top 0.1 m of soil.