No abstract

No abstract

No abstract

No abstract

Controlled placement and depth distribution of crop residues are major objectives for tillage management. Appropriate methodology has provided quality information about surface placement, but the distribution of buried crop residue has not been readily measurable. A method was developed to measure dry bulk density (ρb), incorporated coarse organic matter (COM), and organic carbon (C) concentration using one soil sample. Cores, each 0.3‐m long, were taken with a specially constructed sampler (19‐mm diam.); each 0.3‐m core was separated into 20‐mm increments for subsequent analysis. After air‐drying, COM was estimated as that crop residue retained on a 0.5‐mm mesh sieve; C concentration measurements and an associated conservation‐of‐C algorithm were used to estimate COM because the incorporated crop residue could not be completely separated from contaminant soil. These ρb and COM had a CV of 5 and 20%, respectively. A depth function of ρb distinguished primary tillage from secondary tillage and traffic; a tillage pan produced by the moldboard base was usually detected by ρb. Moldboard plowing vs. sweep or chisel tillage consistently produced different depth distributions of COM; at least 85% of the COM was above 0.1 m when tilled with a chisel or sweep and >45% was below 0.1 m when moldboard plowed. Total COM in the profile ranged from 68 to 23% of that measured at harvest, respectively, 28 wk earlier in a wheat‐peas rotation and 82 wk earlier in a wheat‐fallow rotation. Long‐term use of a moldboard plow vs. a chisel or sweep for primary tillage produced consistently different profiles of organic C concentration.