Reducing seed bank viability using soil solarization in dredged sediment applied to agricultural fields 

Abstract

<p>Many intensively cultivated agricultural areas suffer from soil losses, due to accelerated soil erosion processes, which eventually deposit in adjacent stream channel. To prevent flood risks, the deposited sediments are routinely dredged from the streambed, and due to the lack of a cost-effective solution, piled upon the stream bank. Dredged sediments (DS) piles threat the ecological balance in the riparian habitat because they serve as a reservoir for weed seeds and enable the further establishment of invasive species. As an alternative to DS piling practice, DS might be return to the cultivation cycle as amendments to agricultural fields. However, our previous work confirmed that the DS seedbank (in the Nahalal-stream basin), contained high amount of weed species. We found that applying dredged sediments with no pre-treatment might contribute 29 new weed species to the adjacent agricultural field. The objective of the current study was to examine the efficiency of soil solarization treatment in reducing seed viability in DS returned to the agricultural field. The efficacy of soil solarization was tested during the months of July-September 2022 under a field experiment in which DS were applied upon a commercial agricultural field in a layer 10 cm thick. The treatments in the experiment included, DS soil with and without solarization treatment, and with comparison to the original soil of the field. The soil temperatures and water contents were monitored throughout the experiment. Seeds of <em>Ricinus comunnis</em> and rhizomes of<em> Phragmites australis </em>and<em> Cynanchum acutum </em>(three dominant weeds previously found in DS soil) were buried at two depth (5 and 10 cm) in the different experimental plots. In addition, after the solarization treatment soil samples were collected from the different experimental plots and germination assays were conducted in order to evaluate the seedbank viability. Vegetation surveys were conducted during the winter growing season in order to assess weed infestation rates for each plot. The maximum soil temperature measured at a depth of 5 cm during the solar treatment was 58.4˚C. The results indicated on high efficiency of the solarization treatment in reducing seed viability. Out of 200 <em>R. comunnis</em> seeds buried at two depth in the solarization treatment, not a single seed germinated after the treatment (compared to 60% germination in plots without solarization treatment). For both <em>P. australis </em>and<em> C. acutum, </em>with fresh rhizomes viability of 60% and 36%, respectively, no viability was detected in emergence assays for the buried rhizomes in all treatments. The first vegetation survey (October 2022) revealed that solarization treatment on DS soil, drastically reduced weed seedling density. In comparison, the average weed seedling density in DS soil without solarization and in the field original soil were 127 and 22 (no. weeds m<sup>-2</sup>), respectively. In addition, solarization treatment completely reduced seedling emergence in the seedbank viability germination assays. According to our findings, we suggests soil solarization as an effective, non-chemical tool, for reducing seedbank viability for safely reusing DS in agricultural fields.    </p> <p> </p>