Influences of Tillage Systems and Cover Crop Management on Weed Density and Yield for Organic Vegetables.

Cover crops can be a part of wide strategy of integrated weed management in vegetable cropping systems. Implementation of conservational tillage practices may maintain optimum crop yields while providing numerical environmental benefits for agricultural land. To identify effective weed management options for use in conservational tillage systems, studies have been conducted to investigate the influences of tillage systems in conjunction with a mixture of three cover crop species on weed density and yield of organic vegetables in Maryland, USA. Tillage treatments were conventional tillage without (bare ground, BG) and with black plastic mulch (BP), strip-till (ST) and no-till (NT). Three cover crop species were forage radish (FR, Raphanus sativus), crimson clover (CC, Trifolium incarnatum L.), crimson clover and rye (Secale cereal). Cover crops were no till drilled at seeding rates of 4.5 and 12.3 kg ha^-1 for FR and CC, and 0.0 (except volunteer growth), 67.3, and 44.8 kg ha^-1 for rye  on 19, 05 and 11 September in 2011, 2012 and 2013. Cover crops were flail-mowed in BG and BP plots early May and ST and NT plots in mid-May. One week after flail-mowing in the BG and BP plots, the field was chisel plowed, followed by shallow disking, and plastic mulch was laid in BP plots. Eggplant seedlings were transplanted while sweet corn no-till drilled in mid-May. Weed density was assessed during early to middle growing season and followed by hand weeding. Eggplants were hand harvested twice or three times a week while sweet corn ears picked up when mature.  In all three years, weed density followed the same pattern: higher in BG and ST than in NT and BP treatments in the plant rows and higher in BG and BP than NT and ST in the inter rows. However, Overall weed density was relatively lower in summer of 2013 than in the other two summers, which may be linked to the greater C:N ratio of cover crop biomass in spring of 2013. Sweet corn yield was not different among ST, NT and BG treatments and less in BP treatment because of greater insect damage in the BP plots. Eggplant yield in 2012 was less in NT than in any other treatment plot because of slow plant growth and delayed fruit mature in NT plots. However, there was no treatment effect on eggplant yield in 2014. Though NT showed promising in reducing weed pressure consistently, slow plant growth was observed especially for eggplant probably because of the cool soil temperature. If integrating other management tactics such as stable seed bed to control early weed pressure, strip-till would be the best choice among the four practices in reducing weed pressure while maintaining optimum crop yield.