Figure 1

Soil bulk densities at different soil depth under three tillage and crop residue management strategies. Error bars represent standard deviations. Different lower-case letters at the same soil depth indicate significant differences at the 5% level. ns represents no significant differences among the three treatments at the same soil depth. NT: no-tillage with straw removal for winter wheat and summer maize, NTS: no-tillage with straw mulching for winter wheat and summer maize, NPTS: no-tillage with straw mulching for summer maize and plow tillage with straw incorporation for winter wheat.