Factors influencing seed setting in several southern grasses

1. The influence of fertilizer mixtures, climate, and ergot upon seed setting (the percentage of florets by weight containing caryopses) in 10 southern grasses was studied for the period of 1937 to 1940, inclusive. 2. Fertilization had no significant effect upon seed setting in the 10 grasses growing on a soil of good initial fertility. 3. Large variations in the quantity and balance of fertilizer materials applied to a poor soil did not influence the percentage of Bahia grass florets to set seed. 4. The application of phosphorus and potassium without nitrogen significantly increased the number of heads in only one grass, common Bermuda. The addition of nitrogen to the basic phosphorus and potash treatment materially increased the production of seed heads in most of the grasses studied. Since seed setting did not vary significantly with treatment, head counts were a good index of the influence of each treatment upon seed yields. 5. Although weekly fluctuations in seed setting occurred in all of grasses, they were generally not great and could not be associated with rainfall, cloudiness, or temperature variations recorded during the course of this study. 6. For the 3-year period, 1938-40, there was a noticeable decline in seed setting with the advance in season in Bahia grass, carpet grass, the Bermuda grasses, and ribbed paspalum. The woollyfinger grass P.I. 111128 set seed equally well throughout the season. 7. This study indicates that Dallis grass, Bahia grass, carpet grass, and common Bermuda grass may be expected to seed well every year and ribbed paspalum most years. The woollyfinger grasses and the two Bermuda grass strains, P.I. 105933 and Tift, were the poorest and least dependable seeders in this group of grasses. 8. Significant seasonal differences in the seed setting behavior of different strains of Bermuda grass were observed. 9. Weekly and annual variations in the percentage of ergot sclerotia in Dallis grass seed exceeded the minimum required for statistical significance. . In most instances increases in the percentage of ergot sclerotia were associated with increases in rainfall at the time of flowering. Likewise decreases in ergot accompanied decreases in rainfall at the time of flowering. . Evidence was presented which indicates that as ergot in Dallis grass increases the percentage of florets setting seed decreases. This indicates that ergot does reduce the percentage of seed set in Dallis grass.