Effects of Temperature, Calcium and Arsenous Acid on Seedlings of Poa pratensis

Abstract

1. Germination of seeds in the pots having a high calcium carbonate content (pH 8.0) began about a week after that in the pots having no calcium carbonate (pH 5.6). 2. Thirty-five days after planting, the secondary roots formed at the time of germination continued to live in the minus calcium carbonate series, while there were few or none when calcium carbonate was present. 3. The average length of roots was almost twice as great when calcium carbonate was present as when absent. 4. Ninety days after planting, top growth of grass grown on a substrate having a high calcium carbonate content was, on the basis of dry weight, approximately 33 per cent greater than when calcium carbonate was absent. 5. When the effects of temperature and calcium carbonate are considered, it is found that at 15⚬ C. the presence of calcium carbonate is associated with an increase of 77.3 per cent in dry weight, and at 25⚬ C. with 135.6 per cent, calculations being based on the dry weight of 100 seedlings. 6. Data indicate that calcium carbonate content of the soil is not of as great importance in producing extensive root growth in seedlings as is temperature. During the period of this experiment root growth was definitely greater at 15⚬ than at 25⚬ C. 7. The presence of calcium carbonate in the substrate was correlated with an evenly increased metabolic activity and growth regardless of temperature. This is especially reflected in the top/root ratios. 8. Under conditions of high temperature (22⚬-23⚬ C.) liming of the soil shortly after germination has taken place may be most favorable for the establishment of a good stand. 9. Time of germination was not delayed by the arsenic when applied as a 0.01 per cent solution, but with increasing concentration there was increasing retardation. With the lowest concentrations germination and growth were greater than in the control pots. 10. In Kentucky bluegrass an upper tolerance was found for arsenous acid (0.05 per cent), a single application of 0.1 per cent solution being sufficient to kill seeds and seedlings. 11. Harmful effects of arsenous acid were progressively less with decreasing concentration from 0.1 to 0.01 per cent. 12. Bluegrass treated with a 0.01 per cent arsenous acid solution showed greater germination than did untreated seeds. A thicker and taller stand was produced in a shorter time and this advance was maintained throughout the experiment. 13. Considerably higher concentrations of arsenous acid are required to kill the growing point of the stem than to kill the leaves. 14. Arsenous acid has a greater toxicity to Kentucky bluegrass seeds than to the seeds of some other grasses.