Formation of new aggregates and weed seed behaviour in a coarse- and in a fine-textured loam soil. A laboratory experiment

Abstract

Investigation of the influence of soil texture on the formation of new aggregates in the field in correspondence with weed seed behaviour was simulated in the laboratory. Therefore, mixtures of six aggregate sizes of a sandy loam and a silty clay loam soil all smaller than 12.5 mm, tagged with coloured glass beads of approximately 2 mm diameter and containing a known amount of Papaver rhoeas seeds, were subjected to simulated field treatments, using cylinders of 8-cm diameter and 10-cm height. Compaction was applied to half of the samples of each soil before and after growing of a crop. In a first period of 10 weeks grass was grown and in a successive second period of 2 weeks freezing+thawing were applied. Results of both periods were intensified in a successive third and fourth period. Weed seeds in the aggregate fractions were allowed to germinate before and after crop growth and also after the first freezing+thawing period. Redistribution of the tracers within the aggregate fractions was used to characterize aggregate reshaping, and the numbers of emerged weed seedlings served as an indication of weed seed behaviour. After the first crop period on the compacted sandy loam as well as on the compacted silty clay loam only about 20% of the original aggregates were probably “undisturbed”. When there was no soil compaction, the percentage on the sandy loam soil was also about 20% whereas that on the silty clay loam soil was 30% higher. The fine-textured loam soil had a better physical potential for good yields than the coarse-textured one. More weeds were observed on the sandy loam than on the silty clay loam.