Tillage and Cover Crop Effects on Weed Seed Persistence: Do Light Exposure and Fungal Pathogens Play a Role?

Abstract

In a series of seed burial studies, we tested the hypothesis that reduced tillage and cereal rye (Secale cerealeL.) cover cropping influence seed persistence and that these effects are mediated by differences in fungal pathogens and exposure to light. Seeds of Powell amaranth (Amaranthus powelliiS. Watson) and large crabgrass [Digitaria sanguinalis(L). Scop.] were buried in mesh bags in a long-term experiment with two levels of tillage (full-width tillage [FWT] or strip tillage [ST]) and two levels of cover cropping (none or cereal rye). In Experiment 1, seeds were exhumed each spring for 3 yr and tested for viability. In Experiment 2, untreated and fungicide-treated seeds were buried, exhumed at shorter intervals, and tested for viability. In addition, a subset of seeds in FWT treatments were exhumed and stored in either light or darkness during tillage operations and evaluated for persistence at 8.5 mo after burial (MAB). In Experiment 1, the persistence ofD. sanguinalisseeds declined by 80% at 7 MAB regardless of cover crop or tillage treatment. The persistence ofA. powelliiseeds at 19 MAB declined by 95% in FWT compared with only 50% in ST. In Experiment 2, seed persistence of both species was greater in ST compared with FWT treatments, for seeds that had been exposed to light, but not for those that were maintained in darkness. Rye cover cropping resulted in a 2-fold increase in overwinter persistence of seeds ofD. sanguinalisregardless of fungicide treatment. These results demonstrate that increased persistence under ST was primarily due to reductions in light-induced fatal germination and that increased overwinter persistence ofD. sanguinalisin rye cover crop treatments could not be explained by differences in decay due to fungal pathogens controlled by the seed treatment.

Weed communities after decades of mineral fertilization and tillage treatments in a corn–soybean rotation

“…densities (>250 m −2 ) were observed in no-till compared to moldboard tillage in soybean and attributed to lower herbicidal efficacy (Buhler and Oplinger 1990). Higher large crabgrass seed persistence was observed in undisturbed soil under strip tillage compared to moldboard-plowed soil and was related to light exposure followed by fatal germination during spring tillage (Frost et al 2019).…”

Weed emergence and seedbank after three years of repetitive shallow cultivation in a muck soil field

“…Shallow inter-row rotary cultivation generated both decreases and increases in the emergence of the most abundant species during the season but, except for barnyardgrass, emergence was generally higher in cultivated plots, especially later during the season. Tillage is known to increase emergence in mineral soil by exposing buried seeds to light and oxygen (Frost et al 2019). Although some weeds do not require light for germination, hairy galinsoga and barnyardgrass are photoblastic (Maun and Barrett 1986;Warwick and Sweet 1983), as are Canadian populations of common purslane (El-Keblawy and Al-Ansari 2000).…”

“…However, few studies have quantified the effect of repetitive shallow cultivation (less than 10 cm deep) on weed emergence and especially viable seed banks in muck soil. Previous studies done in mineral soil indicate cultivation or other soil perturbations such as secondary tillage increase weed seed germination and emergence (Roberts and Dawkins 1967;Roberts and Feats 1972;Mulugeta and Stoltenberg 1997;Boyd et al 2006), notably by increasing seed exposure to light and oxygen (Frost et al 2019). As for the persistence through dormancy or quiescence (non-dormant seeds that do not germinate due to unfavorable conditions) of seeds not subject to germination or seed predation, studies in mineral soil suggest it is generally increased by cultivation or tillage compared to undisturbed soil as seeds remain deeper in the soil profile.…”

“…The underlying mechanism for this persistence would be generated by seed burial at depths where biological activity from bacteria and fungi that can decay them is lower, but empirical in situ evidence is scarce and the effect can be species specific (Davis et al 2006;Wagner and Mitschunas. 2008;Ulrich et al 2011;Frost et al 2019). Shallow cultivation would therefore be less likely to increase persistence, but again information specific to muck soil is lacking.…”

Cover crops as a weed seed bank management tool: A soil down review

“…Potentially, this use of tillage to stimulate germination and increased pathogen activity via green residues could be useful. However, in a seed burial experiment comparing fungicide treated Digitaria sanguinalis seed versus nontreated, differences in decay could not be attributed to fungal pathogens in a cereal rye cover crop (Frost et al, 2019). More research is needed in this area.…”