MATERIAL AND METHODS
study sites and soil properties. two field experiments were conducted during 2010-2011 at hebi (35 67'N,114 98'E) and Luohe (33 57'N,113 98'E)in the central china. the data on solar radiation and temperature during the study period were collected from an adjacent weather station and are presented in figure 1. there are winter wheat-summer maize rotation at hebi and luohe. for several decades,soil tillage is conducted after the harvest of maize and before the winter wheat sowing.soil tillage (20 cm depth)with moldboard plough,followed by a disk harrow for seedbed preparation.summer maize is sowed under no tillage condition. the two year experiments were conducted on the same site with the same plots. soil basal samples were collected at the beginning of experiment. the main physical and chemical properties of soil in the two study sites are presented in table 1.