I. Effect of tillage system and winter burial depth on seedling recruitment (Fig. 3).

1. Hairy nightshade (Solanum sarrachoides) emergence may be suppressed in the spring if soil is not tilled (Peachey et al., 2003). The factors causing this suppression have not been determined but may be due to a restricted emergence zone in untilled soil (Mohler and Galford, 1997), differences in germination rate and dormancy caused by burial depth during the winter, or differences in after-ripening rate of newly produced seed. The objectives of this research were: 1) to compare seedling recruitment and emergence potential in simulated notill and conventional tillage systems; and 2) to determine mechanisms influencing emergence differences in the two tillage systems. I. Effect of tillage system and winter burial depth on seedling recruitment (Fig. 3). Emergence rate of seedlings from buried CT tubes was greatest for seeds buried at 12 cm. Seedlings emerged slower in NT than CT. Less than 4 percent of the hairy nightshade seeds buried at 1 cm in NT seed tubes produced seedlings. 68 and 31 percent of the seeds buried at 12 and 25 cm in CT tubes, respectively, produced seedlings. Hairy Nightshade Emergence in Reduced Tillage Systems: Effects of Burial Depth and SeasonEd Peachey and Carol Mallory-Smith, Senior Research Assistant and ProfessorDepartments of Horticulture and Crop and Soil Science, Oregon State University, Corvallis, OR 97331 Background Results Methods Figure 3. Cumulative emergence of hairy nightshade from soil tubes in field conditions (n = 20 for each depth, +SE). A seed burial system was designed to evaluate hairy nightshade emergence of newly produced seed from a constant depth in two tillage systems while avoiding the direct effects of tillage (such as exposure to light). All seeds germinated and emerged from a constant depth in the spring. Seeds of simulated conventional tillage (CT) were buried at 12 and 25 cm deep in the soil and 1 cm in the spring; all seeds in simulated notill (NT) were buried at 1 cm below the soil surface during both winter and spring. For all experiments, hairy nightshade seeds were extracted from mature berries in the fall by crushing the berries and rinsing seeds. Ten seeds were buried 1 cm deep in 1.6 cm diameter polystyrene test tubes filled with 7 cm of soil. Seed tubes were buried in the soil within 4 hours in the field at 1, 12, and 25 cm. • II. Effect of tillage system, season of emergence, and winter burial depth on emergence potential. • The emergence potential of hairy nightshade was greater in May-June than March-April, but dependent on burial depth in the CT system. • Maximum seedling emergence from seeds buried in CT was at 33.3 C, and was 34 and 37 percent of the seeds buried at 12 and 25 cm, respectively; maximum emergence from seeds buried in NT was at 30.7 C, but only 2 percent of the seeds produced seedlings (Fig. 5). • The germination rate and total emergence of seeds buried in NT were less than for seeds buried in CT at 25 cm (Fig. 6). • A plexiglass cover that protected seed tubes from winter rain increased the germination rate of seeds that were buried in NT tubes (Fig 6.) I. Effect of tillage system and winter burial depth on seedling recruitment. Seed tubes buried at the soil surface in NT during winter were not moved in the spring; tubes buried at 12 and 25 cm during the winter (CT) were exhumed in spring and placed in the soil so that the seeds rested at 1 cm. Sufficient water was applied to encourage germination, and emergence was recorded for approximately 4 weeks or until emergence ceased (Fig. 1). II. Effect of tillage system, season of emergence, and winter burial depth on emergence potential. Soil tubes were exhumed monthly from all depths beginning in March and continuing through June. Seeds were extracted from the soil of 10 % of the seed tubes and germinated at 30 C on blotter paper in Petri dishes to determine burial depth effects on germination rate and dormancy. The remaining tubes were randomly placed in a temperature gradient table and exposed to temperatures of 20 to 36 C at 2.7 C intervals for 14 days (Fig 2). Emergence was counted daily. The fate of seeds was determined for those seeds that did not produce seedlings. The viability of ungerminated seeds was estimated by examining the endosperm. Data were pooled across three years because the effects of year and interactions with other main effects were insignificant compared to other main effects in the model. Data were square root-transformed before analysis; back-transformed means are presented with 95% CI. Variance was analyzed with the general linear model of SAS. A repeated measures analysis was used for depth because this variable could not be randomized in space. Figure 4. Effect of winter burial depth on emergence of hairy nightshade at 14 days averaged over 20 to 36 C constant temperature. Figure 5. Effect of winter burial depth on emergence of hairy nightshade in the temperature gradient table at 14 days. Figure 6. Effect of burial depth and soil coverage on germination at 30 C after seeds were removed from the soil. Discussion • Seedling recruitment in NT was significantly less than in CT, and similar to differences noted in previous field studies. • Seedling recruitment and emergence potential during the optimum period of emergence was greater if seeds were buried in CT at 12 cm than at 25 cm, and comparable to burial depth effects on other species. • The increase in germination rate of seeds from ‘protected’ NT tubes indicates that factors associated with winter rainfall significantly reduced seedling recruitment and emergence potential in NT. • Soil properties influenced by the winter environment (e.g. rainfall) were partially responsible for the reduction of emergence in NT compared to CT. References Mohler, C. L. and A. E. Galford. 1997. Weed seedling emergence and seed survival: separating the effects of seed position and soil modification by tillage. Weed Res. 37(3):147-153. Peachey, R. E., R. D. William, and C. Mallory-Smith. 2003. Effects of notill and conventional planting and cover crops on weed emergence in vegetable row crop. Weed Tech. Accepted for publication Dec., 2003 Figure 1. Seed tubes after they were exhumed from the soil in the spring Figure 2. Seed tubes in the temperature gradient table.