The first study examined white clover seed loss in the offal trail of a header harvester. Seed counts in offal trails were 83 800/m² compared to intermediate areas at 22 500/m². Consequent problems in sampling for buried seed are discussed. The second trial measured buried seed two years after a white clover seed crop. In the top 25 cm of soil 66 200 seeds/m² remained following conventional cultivation but only 26 000 occurred under direct drilling. With conventional cultivation 80% of seed was buried below 10 cm depth, but 63% of the buried seed was in the O-5 cm layer with direct drilling. In a third study the rate of hard seed breakdown was examined. Breakdown was rapid on the surface but after 4 years 36% of seed survived at 10 cm depth and 65% at 20 cm buried. The practical implications on cultivation practices required to permit change of cultivars without contamination problems are discussed.