Effects of composted swine manure on weed seedbank

Deep-bedded hoop structures where pigs are raised on a thick layer of crop residues represent a promising swine production system that allows recycling of farm waste products. A field study was conducted to evaluate the impact of swine compost on weed seedbank abundance, seed persistence, and seedling emergence. Experiments were conducted from 1998 to 2001 in a chisel plow corn–soybean–winter wheat rotation. In the fall of 1998, and before compost application, weed seedbank abundance, species composition, and viability were characterized. Annual weed seed inputs attributed to compost were assessed between 1998 and 2000 and seedbanks were characterized again in the fall of 2001. Giant foxtail, common lambsquarters, common waterhemp, and Pennsylvania smartweed comprised 99.5 and 80.7% of seeds detected in the seedbank and compost, respectively. Between 1 ± 1 and 169 ± 48 weed seeds m−2 of soil surface (mean ± S.E.M.) were incorporated through compost amendments, the mean number of viable seeds in the compost being less than 8 seeds m−2. Weed seed density in the seedbank ranged from 0 ± 0 to 26,662 ± 8683 seeds m−2 to a depth of 10 cm. Compost did not modify seed abundance, but there was a species-specific response to year of study and crop sequence. Weed seed longevity and seedling emergence were not affected by compost, but more seeds were recovered with a higher viability in 2000 than in 2001. These results indicate that use of composted swine manure represents a small risk to directly increase weed seed abundance in the seedbank.