Response of Kyllinga spp. to a Soil Moisture Gradient.

Greenhouse experiments were conducted to determine the effect of soil moisture on the vegetative characteristics of green kyllinga (Kyllinga brevifolia) and false green kyllinga (K. gracillima) when grown alone or in competition with bermudagrass in sand or sandy loam soils. Techniques used to investigate the response of weed species to soil moisture based on frequency or volume of watering are often criticized for problems associated with rooting volume and unnatural soil moisture profile and root distribution. Water table depth gradient tanks allow for natural capillary action (soil water) and surface irrigation to simulate rainfall. When filled with soil and regulated by an outfall, capillary rise keeps the low end of the tank near field capacity and plants growing along higher elevation are subjected to progressively lower soil moisture levels. Six water table depth gradient tanks were constructed. Rhizomes of each Kyllinga spp. were planted perpendicular to the slope (moisture gradient) to allow examination of growth characteristics at several moisture levels. Surface irrigation was used during establishment and periodically throughout the experiment to prevent permanent wilting. Artificial lighting was used during winter months to supplement natural light and approximate summer light intensity and photoperiod. Sand or sandy loam soils were used. Kyllinga spp. were tested individually and in competition with bermudagrass. Soil moisture levels were expressed as centimeters above the water table and ranged from 28 to 144 cm. Growth occurred more rapidly in the sandy loam soil irrespective of species composition. Establishment of both species was slower in the presence of bermudagrass. False green kyllinga exhibited higher biomass accumulation than green kyllinga under high soil moisture when grown in sandy loam soil with or without competition. Both species exhibited higher biomass accumulation under low soil moisture when growth in sand than sandy loam soil.