Selective placement studies were conducted under greenhouse conditions to determine the relative importance of root vs. foliar absorption of postemergence-applied CGA-362622 by torpedograss. All application methods were equally effective in reducing torpedograss foliage as measured 4 wk after treatment. However, foliar + soil and soil-only were more effective than foliar-only in suppressing regrowth at 10 wk after treatment. Foliar absorption by torpedograss and subsequent translocation was determined with radiotracer techniques. After 72 h, 29% of the applied CGA-362622 had been absorbed, and 2 and 7% of the amount applied had accumulated in developing rhizomes and roots, respectively. CGA-362622 was more readily absorbed and translocated by the root. Hydroponically grown plants were transferred to a hydroponic solution spiked with CGA-362622 at 200 ppb. After 6 h, whole plant concentration was 113.1 ng/plant. Only 56% of amount absorbed remained in the roots, the remainder having been translocated to other tissues. The youngest leaf and the immature rhizomes accumulated 2 and 15%, respectively. CGA-362622 soil adsorption was slightly influenced by CGA-362622 concentration and greatly influenced by soil pH. Average percent recovered in the soil solution (i.e., not absorbed) was 15.3 and 27.4% at pH 5.7 and 6.7, respectively. Soil mobility was also pH dependent. Soil solution and soil mobility data support the observation that soil application followed by root entry is more effective in delivering phytotoxic concentrations to the regenerative tissues of torpedograss than foliar application.

Selective placement studies were conducted under greenhouse conditions to determine the relative importance of root vs. foliar absorption of postemergence-applied quinclorac by torpedograss. Foliar + soil and soil-only applications were more effective than foliar-only in reducing torpedograss foliage at 4 wk after treatment (WAT). However, foliar-only and foliar + soil were more effective than soil-only in suppressing regrowth at 10 WAT. Quinclorac foliar absorption by torpedograss and subsequent translocation, as determined with radiotracer techniques, was minimal. After 72 h, only 26% of the applied quinclorac had been absorbed, and 13.7% of the amount applied remained within the treated leaf. Only 0.3% of applied was recovered in the roots, and none was detected in the developing rhizomes. Quinclorac was readily root absorbed and translocated. After 6 h, a 26.7 μg/plant dose of quinclorac had been absorbed, and 54% of this quantity remained in the roots; the remaining 46% having been translocated throughout the plant. The youngest leaf and the immature rhizomes accumulated 5 and 9% of the amount absorbed, respectively. Quinclorac was not readily soil sorbed as determined by soil solution experiments. Quinclorac was displaced nearly concomitant with the wetting front in soil chromatography. Soil solution concentration and soil mobility were greater at pH 6.7 than at 5.7. Results establish that consistent control of torpedograss with quinclorac is dependent on soil entry and root absorption. Unfortunately, the propensity of quinclorac to be water displaced could negatively affect this control.

Various inorganic soil amendments have been promoted as a means of improving the chemical and physical properties of certain soils. To test this hypothesis, a marginally productive soil was supplemented with 20%, 40%, 60%, and 80% (v/v) of either selected inorganic amendments or sand. Amendments consisted of commercially available diatomaceous earth, calcined clay, zeolite, and crystalline SiO2. The soil material was extracted from the argillic horizon of a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Ability of these soil-amendment mixtures to promote `Tifway' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] growth was evaluated under greenhouse conditions, and contrasted to that obtained in nonamended soil. Selected chemical and physical properties that are pertinent to plant growth were also evaluated. The experiment, which was conducted 3×, began with a §60-day period in which both water and nutrients were optimum. This was followed by a 30-day drought. During optimum water and nutrients, no soil-amendment treatment(s) consistently resulted in superior bermudagrass growth compared to soil alone. However, <2% of the bermudagrass tissue that was produced during the drought became green and succulent with the resumption of irrigation in nonamended soil. This percentage was exceeded by all treatments that contained either ≥60% diatomaceous earth (Axis), or ≥40% calcined clay (Profile); and by 100% zeolite (Clinolite) and 100% silica (Green's Choice). Drought-sustaining ability of soil-amendment mixtures was significantly (P < 0.05) correlated with water-holding ability, soil strength, bulk density, and oxygen diffusion rate, but not correlated with either pH or cation exchange capacity (CEC). While certain inorganic amendments did improve the drought-sustaining ability of soil, the amount required was generally ≥40%.