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  • Author or Editor: Chunhua Liu x
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Growth and mineral nutrient content of creeping bentgrass [Agrostis stolonifera (L.) var. palustris (Huds.) Farw.] in response to salinity and humic acid (HA) application were investigated, and the effects of HA application on salinity tolerance was evaluated. Bentgrass plugs were grown hydroponically in one-quarter-strength Hoagland's nutrient solution containing HA at 0 or 400 mg·L-1 with salinity levels of 0, 8.0, or 16.0 dS·m-1. Clipping dry weight (DW), tissue water content, and net photosynthesis (PN) were measured weekly for 1 month. Maximum root length, and root DW from 0 to 10 cm and >10 cm root zones were determined 31 days after treatment (DAT). The turfgrass plugs were mowed three times weekly, with clippings collected and dried for mineral nutrient analysis. Salinity was inversely related to clipping DW, tissue water content, PN, and maximum root length. Salinity had less effect on root growth than top growth. HA treatment did not affect tissue water content, PN, or root growth of salt-stressed turf. Salinity decreased uptake of N, P, K, Ca, and S; increased uptake of Mg, Mn, Mo, B, Cl, and Na; and had no influence on uptake of Fe, Cu, and Zn. Application of HA at 400 mg·L-1 during salinity stress neither increased uptake of the mineral nutrients inhibited by salinity, nor decreased uptake of nutrients which were excessive and toxic in the salinity solution. In general, application of HA did not improve salinity tolerance of creeping bentgrass.

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Humic acids (HA) reportedly enhance the growth of numerous crops; however, little information is available as to their effects on turfgrasses. Experiments were conducted to evaluate the effect of a commercial preparation of HA on the photosynthesis, chlorophyll concentration, rooting, and nutrient content of `Crenshaw' creeping bentgrass (Agrostis stolonifera L.). Bentgrass plugs were grown hydroponically in one-quarter-strength Hoagland's nutrient solution containing HA at 0, 100, 200, or 400 mg·L-1 with measurements made weekly for 1 month. The photosynthetic rates of plants growing in 100 or 200 mg·L-1 rarely differed from that of the control, but 400 mg·L-1 significantly enhanced net photosynthesis on all four observation dates. Chlorophyll content was unaffected by HA rate on all observation dates. Root dehydrogenase (DH) activity and root mass regrowth were significantly increased by HA at 400 mg·L-1 on all dates. The 100 and 200 mg·L-1 rates increased root DH activity on two of four observation dates, but root regrowth was unaffected. At one or more of the rates used, HA increased tissue concentrations of Mg, Mn, and S and decreased those of Ca, Cu, and N, but had no influence on the concentrations of P, K, Fe, Mo, and Zn.

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Rough bluegrass (Poa trivialis L.) is being utilized more frequently to overseed bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] putting greens and rapid seed germination is necessary for successful establishment. Cultivar and seed lot differences in germination rate and sensitivity to cold may exist. Germination of 10 rough bluegrass cultivars/seed lots was examined in growth chambers at 12-hour day/12-hour night temperatures of 25/15, 20/10, 15/5, and 10/0 °C, and on a bermudagrass putting green at three overseeding dates. Differences in germination among cultivars and seed lots were minimal at 25/15 or 20/10 °C, but substantial at lower temperatures. When seeded on the bermudagrass putting green, differences in germination among cultivars/seed lots were greater at the last seeding date (average daily max./min. of 16/2.7 °C), than at the first seeding dates (average daily max./min. of 21/6.1 °C). Use of blends of several cultivars or seed lots is suggested to ensure the successful establishment of rough bluegrass when overseeding at low temperatures.

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