Plant Industry Bulletin 203, Jan. 20, 1911
The Importance and Improvement of the Grain Sorghums
Carleton R. Ball
EARLY CROPS AND EARLY SEASONAL RAINFALL
The effect of earliness in permitting drought evasion is very important. Imagine two plants, one earlier than the other, but otherwise similar in all respects. The earlier plant, having a shorter growing period, not only uses less water, but uses it earlier in the season. This is of especial importance in those parts of the semiarid country where much of the seasonal rainfall occurs in April, May, and June. The earlier plant might be able to mature its crop of seed on the summer rainfall. On the other hand, the later plant might be crippled at a critical stage by the exhaustion of the soil moisture during dry weather in August. It is fairly certain that in much of the Great Plains region the greater part of the soil moisture in a field is not used by the growing crop, but is lost by evaporation, under the average tillage conditions.
Milos are earlier than kafirs, but are not known to be more truly drought resistant. At the experiment farm, Amarillo, Tex., under conditions of extreme drought from the middle of July until October, 1909, the milos yielded on the average 8.3 bushels and the kafirs only 5.5 bushels to the acre. In each crop the figures are the average of between 20 and 30 plats and show that the difference was really in the earliness of the milos as compared with the kafirs, the yields in normal years being about equal.
The writer has produced by selection a dwarf kafir (fig. 6) of the Blackhull variety which is nearly two weeks earlier than the ordinary strains. In 1908, a favorable season, it yielded less by 4.5 bushels than the average of the ordinary Blackhull varieties. In 1909 it yielded 14.4 bushels to the acre, while 20 ordinary strains averaged only 5 bushels, and the best of them yielded only 10.9 bushels. Part of the credit must probably be given to the dwarf stature because another selection, equally early but not dwarf, yielded only 10.7 bushels, as much, however, as any one of the later strains and twice as much as they averaged.
SELECTING FOR EARLINESS
Earliness can be developed only by continuous selection. Such selections can be made either at heading time or at the time of ripening, but are preferably the results of records made at both periods. When the field or seed plat of the variety begins to head, a number of the earliest heads which are otherwise suitable for selection should be marked by means of tags on which is recorded the date of heading. When the heads on these selected stalks begin to show the characteristic colors and texture of the hard dough, or ripening stage, the date of ripening should be added to the tags. Other things being equal, those heads for which the shortest time has elapsed between heading and ripening are to be considered the earliest. These heads should be carefully saved separately and used for continuing the work another season.
In dry regions, where the amount of moisture in the soil is commonly the controlling factor in crop growth, the plants at the ends and sides of a field are often the first to produce heads, especially in dry seasons. This is because the outside plants have a larger area from which to draw moisture, or because run-off water often collects at the edges of fields and provides extra moisture. These early heads will be the first to ripen, but it does not follow that these plants are naturally earlier than the rest of the field.
Fig. 6.— Plat of dwarf and early Blackhull kafir (G. I. No. 310).