Contamination of white clover seed crops by buried seed

Abstract

The first study examined white clover seed loss in the offal trail of a header harvester. Seed counts in offal trails were 83 800/m* compared to intermediate areas at 22 500/m*. 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/m* 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 after4 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. Keywords Trijblium repens L., buried seed, offal trail, direct drill, conventional cultivation, burial depth