An x-ray technique for determining seed placement in direct drilled soils : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University

Abstract

The objectives of this study were to develop and document a reliable workable X-ray technique for identifying seed placement in the soil; to examine those factors which might influence this procedure and to demonstrate the use of the technique in a field experiment. The X-ray technique was based on the principle that seeds coated with a heavy metal powder, when X-rayed within a soil mass, appeared on the X-ray film as white or grey images on a dark background. A coating procedure (based on commercial pelleting) was developed to apply the heavy metal powder to the seed. As the seed images on the X-ray film were to be a shadow representation of the actual seed position in the soil mass, a correction procedure to locate the true positions of the seed was developed. A series of laboratory experiments confirmed that red lead oxide was the most suitable coating material and that higher intensities of coating were required as seed size decreased. Neither soil type nor soil moisture content appeared to have a marked affect on the clarity of the X-ray images. Seed germination was not affected by the amount of red lead oxide coating, the coating procedure, or exposure to moderate levels of radiation. Soil blocks measuring 75 mm by 75 mm by 240 mm long containing the coated seeds should be taken as soon as possible after sowing, as image clarity diminished over time and seed movement occurred in the case of seeds with epigeal germination. Equipment developed to assist in field sampling included a soi1-block-cut ter, re-useable sample bins and a holding jig for X-raying the soil blocks in their bins. Thus the X-ray technique had the ability to determine three dimensional seed placement within a soil mass (sowing depth, in-row width and in-row spacing). The ability of the X-ray technique offers new possibilities for explaining those factors which affect seed placement by direct drilling equipment in field situations.