To compare these systems, researchers buried seeds of two types of weeds, smooth pigweed and common lambsquarters, in mesh bags. Tests were conducted at agricultural research locations in Maryland and Pennsylvania. Seed viability was determined by retrieving seeds every six months over the two-year period.
Depth of seeds in the soil, environmental conditions, and soil management are among the factors that affect seed persistence. Under conventional soil management, tillage is an important practice that manipulates the depth of seeds and environmental conditions that can influence weed seed persistence. Organic soils have enhanced biological activity, with more carbon, moisture, and microbial activity that could lead to greater seed decomposition.
The organic soils in this study were higher in total soil microbial biomass than the soils of the conventional farming tests. This was measured by phospholipid fatty acid content. But the results of the tests did not lead researchers to conclude that this microbial biomass has a dominating role in seed mortality.
Pigweed seeds showed a shorter life span under the organic system in two of four experiments. Organic system lambsquarters seeds had a shorter life span in just one of the four experiments, while the conventional methods had the shorter life span in two of four experiments. These results leave an ambiguous answer to the question of which farming system can better eliminate seeds deep in the soil to control weeds from their source.
Silke D Ullrich, Jeffrey S Buyer, Michel A Cavigelli, Rita Seidel, John R Teasdale. Weed Seed Persistence and Microbial Abundance in Long-Term Organic and Conventional Cropping Systems. Weed Science, 2011; 59 (2): 202 DOI: 10.1614/WS-D-10-00142.1