Soil texture involvement in germination and emergence of buried weed seeds

Laboratory trials were performed to test germination and emergence characteristics of jimsonweed (Datura stramonium L.) seeds buried in 10 different soil types (with or without the control of soil external gas environment) with pronounced sandy or clay texture. The aim of the experiments was to investigate if the physical characteristics of the soils were involved in both buried-seed ecology and emergence dynamics. Germination inhibition due to burial depth was found to be directly proportional to clay content and inversely proportional to sand content. Measurement of soil air permeability showed a close relation between gas exchange potential and depth-mediated germination inhibition. Comparative analysis of the germination response in nonsoil and soil hypoxia suggested that inhibition is caused not so much by hypoxia per se as by the presence of fermenting metabolites that could not easily be eliminated due to decreased respiratory activity. In situ inspection of buried seeds also revealed that the increased time required for emergence in clay soils is primarily due to increased mean germination time rather than greater difficulty in seedling penetration upwards through the soil before emergence. Partial removal of germination inhibition of buried seeds was facilitated by elevated air oxygen availability but only with sandy soils, showing that inhibition is closely linked-to soil ability to induce gas exchange with external air. At excessive burial depth (12 cm), seeds exhibited induction of secondary dormancy independent of soil texture. In conclusion, these experiments demonstrated that soil physical properties have a strong effect on buried-seed ecology and consequently on seedbank dynamics in the agroecosystem.