Planting rates and spacing for corn under southern conditions

The rate of planting corn is of much practical importance in the South, but a definite rule is needed. Too thick planting is of common occurrence. Different varieties require appreciably different rates of planting. In general the small and short-season varieties require thicker planting than the large, long-season varieties. The experimental results indicative a close relationship between the best rate of planting for grain production and a definite yield of grain per plant. For example, the Hickory King variety was found to yield best when the rate of planting allowed the average plant to produce about 0.45 pound of grain. To approximate the proper stand of corn a simple equation may be used, as follows: N= 56Y/F. In this equation, N stands for the number of stalks per acre, Y for the expectancy, or approximate production in bushels per acre of the field in question under average seasonal conditions, and F is the standard varietal factor, or the average weight of grain per plant at the best rate of planting, as determined experimentally for the variety in question. On land of high productiveness the average weight of grain per plant at the best of planting was found to vary from year to year with the nature of the season, so that the more favorable the season the greater was the weight. The standard varietal factor is practically the result obtained for the average of all seasons. The data as obtained may be interpreted as indicating that a varietal factor is practically a constant between the 36-and 65-bushel limits of productivity. However, the weight of evidence indicates that as the productiveness of the soil changes should be made in the varietal factor. On the average for 15 varieties, this change was calculated to be 0.0014 per bushel change in expected yield. With this in view, the following formulas may be used in connection with the table of standard factors: (1) For land producing on the average more than 64 bushels per acre-- N=56Y/[F+(Y-64).0014]. (2) For land producing on the average less than 64 bushels per acre- N=56Y/[F-(64-Y).0014]. In addition the suggestion is made that no rate of planting should be less than the calculated for a 25-bushel crop. The margin of safety appears to go with a too high rather than a too low rate of planting. The results of three series of experiments agree in showing that the best rate of planting silage corn was little different from that which gave the highest yield of grain. In practice, however, a material increase seems warranted. In the spacing experiments the conclusion was reached that the best results in practice will probably be obtained with a width of row which permits the satisfactory use of tillage implements, but allows the determined number of stalks to be as widely spaced as possible.