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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />- <br /> <br />, <br /> <br />5 <br /> <br />frequency of irrigation increases, as was observed with tall fescue, Salt accumulation, i.e" Na+, <br />CI', is likely to be greatest during hot weather, when rates of absorption increase for <br />transpiration-dependent ions due to higher evapotranspiration losses. <br /> <br />Despite the essentiality of Cl" as a micronutrient for all higher plants, a tissue concentration <br />exceeding its demand for CI- by the plant species, will lead to toxicity (buring or necrosis of the <br />leaf margin). Tall fescue's high Cl" concentrations indicates a high tissue tolerance to Cl"or a <br />higher requirement for Cl" than birdsfoot trefoil. Under conditions of reduced growth due to <br />excessive salinity, gaseous exchange, Le., CO2, will be limited via stomata and thus reduce <br />photosynthesis and eventually growth. Frequent clipping likely helped tall fescue, as well as <br />birdsfoot trefoil, tolerate the high tissue Cl" concentrations by removing excessive Cl" from the <br />plant. <br /> <br />The potential inhibiting effects on DM caused by salinity may, however, increase with time and <br />with hot weather (soil salt levels temporarily increase with hot weather-evaporation of soil <br />moisture!). Although this study was conducted for over 200 days, soil salinity would likely <br />increase with continued use of poor II water (>10 dS mol). Increased concentrations of salt; <br />especially Na+, will make it more difficult for plants to extract water from the soil. Sodium's <br />ability to strongly hold water in the soil, reduces water availability to the plant and decreases soil <br />permeability to water and air. Thus, water stress will result in reduced plant growth. Sodium is <br />not considered an essential element for most plants. Because its uptake is strongly regulated by <br />Ca2+ in the soil solution, sufficient soil Ca2+ is needed to prevent the accumulation of toxic levels <br />ofNa+ by the plant; soil Ca2+ levels appeared to be high enough at postharvest for all treatments <br />for all plant species in the present study. Thus it is more advantageous to have Ca2+ as a major <br />ion in poor quality water. If it is not present in sufficient concentrations, applications of gypsum <br />to the soil should be considered. <br /> <br />Conclusion <br /> <br />Under our simulated test conditions our results indicate that tall fescue will produce more biomass <br />than birdsfoot trefoil; irrespective of poor quality soil or irrigation with poor quality water. We <br />were not able to quantifY the effect that supplemental lighting and warm temperatures may have <br />exerted on biomass production for all three species grown under greenhouse conditions. Any <br />potential effect would equally affect all three species. It is important to remember, however, that <br />one must carefully extrapolate results observed in a controlled environment (greenhouse <br />conditions) to a highly variable environment (field conditions). Moreover, frequency of clipping <br />(which likely influenced regrowth in all species) would occur less frequent under field conditions. <br /> <br />Tall fescue is known to be a salt tolerant plant, while birdsfoot trefoil is considered moderately <br />salt-tolerant. When planning to use saline water as a source of irrigation water, it is <br />advantageous for any species to receive less saline water at time of planting; plants often are more <br />salt-tolerant as they mature. Using saline water at planting generally retards germination, <br />