Yellow nutsedge (Cyperus esculentus) interference in simulated sweetpotato plant beds

Greenhouse experiments were conducted in 2016 at Pontotoc and Verona, MS. On March 3 (Pontotoc) and March 7 (Verona), landscape fabric was placed in the bottom of polyethylene lugs, each 0.22 m2, then approximately 5 cm of a 1:1 (v/v) blend of soilless potting media and masonry sand was added. ‘Beauregard’ sweetpotato [Ipomoea batatas (L). Lam.] storage roots weighing between 85 and 227 g, and several with emerging sprouts ≤1 cm, were placed longitudinally in a single layer on the substrate, then covered with an additional 3 cm of the substrate. Sprouted yellow nutsedge (Cyperus esculentus L.) tubers were transplanted equidistantly into sweetpotato-containing lugs at six densities: 0, 18, 36, 73, 109, and 145 m−2. Trials were terminated 55 and 60 d after planting at Pontotoc and Verona, respectively. Predicted total sweetpotato stem cuttings (slips) decreased linearly from 399 to 312 m−2 as C. esculentus density increased from 0 to 145 m−2. Predicted total slip dry weight at a C. esculentus density of 145 m−2 was reduced 21% compared with 0 m−2. Predicted rotten sweetpotato storage roots increased from 2.6 to 11.3 m−2 as C. esculentus density increased from 0 to 145 m−2. In response to increasing C. esculentus density, sweetpotato seed roots exhibited increased proximal-end dominance.

Effect of Soil Carbon on Phytotoxicity of Topramezone-treated Irrigation Water to St. Augustinegrass

Topramezone is a 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide that was labeled for aquatic use in Florida in 2013 with a maximum submersed application concentration of 50 µg·L−1. Preliminary greenhouse studies reported that the concentration of herbicide that reduces growth by 10% compared with untreated controls (EC10) of topramezone in irrigation water applied to st. augustinegrass (Stenotaphrum secundatum) grown in 100% sand was 3.5 ppb. The objective of these experiments was to determine whether substrate carbon content influenced the response of ‘Palmetto’ st. augustinegrass to irrigation with topramezone-treated water. The herbicide was applied at concentrations ranging from 0 to 120 ppb to mature plants grown in 7.5-inch-diameter nursery containers. Pots were filled with washed masonry sand amended with one of five carbon contents: 0%, 0.3%, 0.6%, 1.5%, and 4.0%. Plants were irrigated twice weekly for 4 weeks with topramezone-containing water and grown out for 12 weeks after the final topramezone treatment to evaluate possible recovery from any herbicide damage. Plant material was clipped as needed for a total of eight harvests and each harvest was dried and weighed. EC10 values for ‘Palmetto’ st. augustinegrass grown in substrates with 0%, 0.3%, 0.6%, 1.5%, and 4.0% carbon were 3.7, 7.3, 10.1, 28.1, and 25.7 ppb, respectively. These experiments revealed that substrate carbon content has a noteworthy effect on the susceptibility of ‘Palmetto’ st. augustinegrass to topramezone in irrigation water. However, regular irrigation with water containing high concentrations of topramezone is likely to cause damage to ‘Palmetto’ st. augustinegrass in Florida's sandy soils.

Effect of aging on the penetration resistance of sands

The main objective of this study was to understand the effect of aging on the penetration resistance of freshly deposited sands. Two types of sand, locally available river sand used as masonry sand and Beaufort Sea sand, were selected for the study. The sands were allowed to age under a constant stress of 100 kPa in a specially designed apparatus in a dry state, as well as submerged in distilled water and in simulated sea water. Penetration resistance of the sand beds was measured periodically by pushing 4 probes into the sand bed. Mineralogical and fabric studies on freshly deposited and aged sand samples were conducted to detect the effect of aging, if any, on sand grains. The results indicate that aging significantly increases the penetration resistance of sands. The rate of increase in penetration resistance was higher for the submerged sand as compared with the dry sand. The increase in penetration resistance of the sand in a dry state was attributed to rearrangement of sand grains. In the submerged state, besides the rearrangement of sand particles, partial cementation caused by precipitation of salts and probably also silica on the sand grains and in the pores resulted in the larger increase in the penetration resistance. Key words : sand, aging, penetration resistance, freezing and thawing, sea water, distilled water.