International Soil Tillage Research Organization

-0 MOLDBOARD PLOW -CHISELA SWEEP -Depth (in)Fig. 4. Depth of incorporated residue as affected by three types ofprimary tillage.two sites; a peak concentration greater than 4 g/kg was observed at sixsites; and a peak concentration less than 2 g/kg was observed at threesites. The peak concentration of COM at both sites (Fig. 1) located ator below 0.1 m was typical of 16 sites. At six sites the peakconcentration of COM occurred at 0.15m or deeper. The three curves ofcumulative relative COM for the moldboard plow (Fig. 4) show the meandistribution with depth, and the shallowest (site 10) or deepestincorporation (site 16).The small peak of dry bulk density (Fig. 1) at 0.25 and 0.31 m atsites 1 and 18, respectively, below the depth of incorporated residueare indicative of the method used to determine maximum penetration ofthe moldboard plow. This depth varied from 0.15 to 0.34 m with a meanof 0.23 m. A peak dry bulk density at 0.19 m in site 18 (Fig. 1) wasproduced by traffic during secondary tillage; generally but not always aseparation of dry bulk density peaks identified maximum penetration ofcompaction during secondary tillage and planting operations. There isanother secondary compaction zone at 0.09 m at site 18.Patterns of incorporated residue in sweep tillage (Fig. 2) were nearlyidentical for sites 21 and 24. A peak concentration of COM occurred inthe shallowest sampled depth of 0 to 0.02 m, and 80% of the residue wasburied above 0.05 m. Yet, after numerous secondary tillages associatedwith pea planting (site 21) and with summerfallow (site 24), theestimated surface cover with wheat residue was less than 10%. The drybulk density curves (Fig. 2) suggest maximum sweep penetration of 0.13 mat site 21 and 0.19 m at site 24, and no distinct separation ofcompaction zones produced by primary versus secondary tillage. Wheatresidue burial with the chisel tillage (Fig. 3) was deeper than withsweep tillage, but yet 60% of the residue was in the upper 0.05 m zone(Fig. 4). There was 3680 kg/ha of wheat residue on the surface, whichis partially explained by less secondary tillage than at site 24 duringsummerfallow. Dry bulk density and COM patterns suggest a maximumchisel tillage depth of 0.2 m.