Abstract: A field experiment was carried out to evaluate effects of conservative tillage on soil enzyme activity following a cropping rotation system of corn and wheat in the Fengqiu National Agro-Ecological Experiment Station, China.The experiment was designed to have 6 treatments or tillage practices, i.e., tillages for both corn and wheat (C_TW_T), no-tillage for corn and tillage for wheat (C_NTW_T), no-tillage for either corn or wheat (C_NTW_NT), tillages for both corn and wheat with straw incorporated (C_TW_TS), no-tillage for corn and tillage for wheat with straw incorporated (C_NTW_TS) and no-tillage for either corn or wheat with straw incorporated (C_NTW_NTS). Results show that Treatment C_NTW_NT was higher than Treatment C_NTW_T, Treatment C_NTW_T was higher than Treatment C_TW_T, and the treatments with straw incorporated were higher than those without in activities of urease, alkaline phosphatase and sucrose  in the soil during the entire wheat growing period. Obviously, Treatment C_NTW_NTS was the highest and Treatment C_TW_T the lowest. Soil dehydrogenase differed from the other 3 soil enzymes in response. Its activity was higher in Treatment C_NTW_T than in Treatment C_NTW_NT in the wheat maturing period, and higher in Treatment C_NTW_NT than in Treatment C_NTW_T and in the treatments with straw incorporated than in those without during the other growth periods.The enzymes differed in response to different treatments at different wheat growth stages. Alkaline phosphatase tended to be low in activity at the seedling stage, peaked at the booting stage and went down at the maturing stage; invertase soared up at the elongation stage and then declined; soil urease tended to be high at the seeding and booting stages; and dehydrogenase increased steadily throughout the whole growth period and peaked at the maturing stage. Correlations between the four soil enzymes all remained at a significant level. Cluster analysis further indicates that the 6 treatments could be sorted into three groups according to the enzyme activity level in the soil as a whole. Treatment C_NTW_NTS is the highest in enzyme activity, demonstrating that the practice can quite well improve soil enzyme activity.

Key words: no-tillage, straw incorporation, wheat-corn rotation, soil enzyme activity