sustained without fertilizer or residue inputs
(Fig. 4). Linquist and Sengxua (2003) reported
that the AE of applied N to these soils was usually
20–25 kg grain kg–1 N. Good yield responses to
fertilizer N (Experiment 1) and combined fertilizer
application (Experiment 2) support these
findings. Average yields across all sites and years
increased by 1.4 t ha–1 in response to chemical
fertilizer (only N in 1998). The exception to these