The effect of uniformity of spacing seed on the development and yield of barley

During the season of 1929, studies were conducted with barley under field conditions to determine the relation between uniformity of spacing seed and development and yield of the crop. Information on this relation under American conditions was specially desired because of the observations of Engledow and his associates that yields of wheat fields in England were greatly influenced by the regularity of spacing seed. Two methods of planting were adopted in this study. In one, seed was planted in such manner that each foot of row received kernels evenly spaced and equivalent in number to a seeding rate of 10 pecks per acre, this being termed the uniform method. In the second, or variable, method, the average rate of seeding was 10 pecks per acre, but consecutive sections of the row were planted at different rates, equivalent to 6, 9, 11, and 14 pecks of seed to the acre, and a random distribution of the four rates was provided. Three rows of each method of seeding alternated throughout the test field, and observations were confined to the center rows to eliminate competition between unlike methods of seeding. A total of 140 foot sections of row were harvested from each of the uniform and variable methods of planting, and a detailed comparison was made of plant development and yield. Yields of grain and straw increased with the seeding rate when the component rates of the variable method were considered. However, the increase in yield was far from proportional to population density, because of the reduced development for individual plants at the closer spacings. The data indicate that the barley plant has considerable ability to modify its development in response to the soil resources available. The average yield of grain from the variable method of seeding was slightly greater than for the uniform method. No reduction in average straw yields resulted from irregularity of stand. Correlation coefficients between yield of grain for each foot section and the average rate of seeding of surrounding sections indicated that thickly populated areas draw on the soil resources of neighboring sparsely populated areas. The balance of the adjustment necessary for normal yields was brought about by increased development of individual plants in thin stands. Root studies indicated that root systems of this crop were not confined to the vertical zone occupied by the aerial portions, and that top growth of individual plants was correlated with root development. The conclusion is drawn that crops, such as oats, wheat, and rye, which are reported to develop more extensive root systems than barley, are probably even more capable of completely utilizing the soil resources in spite of considerable irregularity of stand. The variability of the soil was found to be a far more important factor in determining yields of units of the planted row than population density. Mean values of individual plant characters were not appreciably changed by the irregularity of spacing seed, nor was the reliability of the mean values significantly affected. Because of soil variation, a comparatively large number of samples of the crop will be required to represent fairly conditions in the field being examined. American grain drills, when functioning normally, may be assumed to distribute seed of small grains satisfactorily so far as total yield of crop is concerned. The factor of regularity in spacing seed may be largely ignored in conducting rate-of-seeding tests, even though the variation in seeding rate varies as much as 40% from the mean in consecutive sections of the row.