SPATIAL RELATIONS BETWEEN OAT RESIDUE AND CERAMIC SPHERES WHEN INCORPORATED SEQUENTIALLY BY TILLAGE

Spatial characterization of crop residues and agrichemicals incorporat ed by tillage is needed to interpret biomass-related soil processes. T his study presents such a characterization. We first described oat res idue (Avena sativa L.) and green-sphere distributions produced by chis el plow (CP) and moldboard plow (MP) tillage and then described red-sp here distributions when incorporated during secondary tillage. Finally the co-location of incorporated oat residue and colored spheres was c haracterized. Green and red ceramic spheres were surrogates for shoot residue and incorporated agrichemical, respectively. Characterizations were derived from weights of soil and residue and counts of spheres i n soil cores (1.84 cm diam. by 30 cm long, sectioned into 15 sublength s each 2 cm long). Penetration with MP was 25 cm, CP was 15 cm, and cu ltivator was 17 cm. The MP incorporated 67% of residue in the 10- to 2 0-cm depth, while more that 90% of the incorporated residue in the CP was between 1 and 11 cm deep. Secondary tillage had negligible influen ce on these depth distributions. Green-sphere distributions were relat ed more closely to tool penetration than those of oat residue because root and shoot tissue were not distinguished. Fractional porosity of t he 5.32-cm(3) volumes, adjusted to account for oat residue and sphere volumes, was increased similar or equal to 12% due to these materials. Many 5.32-cm(3) volumes contained no oat residue, whereas only a few volumes had concentrations greater than or equal to 4 times the mean r esidue concentration. Although oat residue was incorporated with prima ry tillage, residue and herbicide surrogates were co-located in 35% of the volumes, many of which contained large concentrations of residue. Exclusive use of either primary tillage with the same secondary tilla ge produces an environment for characteristically different bioactivit y in the upper 10 cm.