INCORPORATION OF TRACERS AND DAZOMET BY ROTARY TILLERS AND A SPADING MACHINE

Soil fumigant efficacy in forest-tree and ornamental nurseries depends on the tillage tool used for incorporation. Maximum depth and uniform ity of incorporation of surface applied materials by three rotary till ers and a spading machine were compared in a loamy sand nursery using ceramic-sphere tracers (1-3 mm diameter) and dazomet ahydro-3,5,dimeth yl-2H-1,3,5-thiadiazone-2-thione) micro-granules. Depth of incorporati on in the top 30 cm of soil was evaluated by (1) recovery of incorpora ted spheres in 2 cm increments, (2) biocidal activity in 6 cm incremen ts, and (3) cone resistance by 1.5 cm increments to 45 cm. Uniformity of incorporation was evaluated by sphere recovery and biocidal activit y, Depths above which more than 95% of the spheres were recovered for the four implements were: 12.5 cm, Kuhn and Fobro rotary tillers; 17 c m, Northwest rotary tiller; 21 cm, Gramegna spading machine. The spadi ng machine produced a distribution of spheres through the soil profile closest to a uniform distribution compared with that produced by the three rotary tillers. Lettuce seed (Lactuca sativa L.) germination was inhibited in the upper 12 cm in low and high dazomet rate treatments, indicating that all four implements effectively incorporated dazomet into that zone, Maximum depth (24 cm) for total inhibition of germinat ion was observed for the spading machine regardless of chemical rate. Cone index values showed the following maximum penetration: 14 cm, Fob ro rotary tiller; 22 cm, Kuhn and Northwest rotary tillers; 27 cm, spa ding machine, All three measures of depth show a distinct superiority of the spading machine when the chemical fumigant must reach depths gr eater than 18 cm, Within transects across the width of the implement, variations of sphere counts among 5 cm(3) volumes were much larger for the rotary tillers than for the spade machine.