Soil Texture and Planting Depth Effects On Emergence of Large Crabgrass (Digitaria sanguinalis), Virginia Buttonweed (Diodia virginiana), and Cocks-Comb Kyllinga (Kyllinga squamulata).

Soil texture and seed burial depth are potential interactive factors that can affect weed emergence. Greenhouse experiments were conducted to evaluate the influence of soil texture and planting depth on emergence of large crabgrass, Virginia buttonweed, and cocks-comb Kyllinga. Soils were gravimetrically weighed and packed into soil columns to ensure consistent bulk density throughout columns. Columns were placed in a greenhouse with supplemental florescent light and day/night alternating temperature 32/25°C. Twenty-five seeds or fruits from each weed species were planted at each depth.  A three by seven factorial design was utilized with three soil textures and seven planting depths.  Two experimental runs with four replicates were conducted per weed species.  Data included weekly counts of emerged weeds for six weeks. A significant interaction between planting depth and soil texture occurred for each weed species.  Emergence of all weed species was reduced with increasing planting depth.  Cocks-comb kyllinga was reduced with increasing planting depth for all soil types.  Emergence ceased at ≥4 cm and was minimal at 2 cm (2% or less in all soil textures).  Virginia buttonweed planted in Sumter silty clay and Sand/peat mix did not emerge at 6 cm planting depth while the Marvyn loamy sand did not cease Virginia buttonweed emergence until a planting depth of 8 cm.  Large crabgrass emergence was 0% in Sumter silty clay at 8 cm planting depth.  Differences in percent emergence for various soil textures could be due to the differences in the water holding capacity of each soil. Water-holding capacity can vary through the soil profile where weed seed banks are located.  Weed seeds also differ in water imbibing requirements for germination.  Also, soils can physically restrict the shoot of germinated seeds from emerging to soil surface. Planting depth coupled with soil texture can effectively help predict emergence of the evaluated weed species.